Re: lens brightness
Hi all. As I am reading threads with two days lag (the web version is _that_ slow), it all might have been answered already. I address the issue of bellows factor and its difference in tele or wideangle slr lenses, as well as T stop. 1) f/stop can't be just focal length/front diameter, because front diameter is much larger in retrofocus wideangles (my 2.8/20 has ~65mm dia, but it isn't f/0.3 lens g). Also, to even more complicate it, f/stop isn't just physical diaphragm/aperture opening dividing focal length... I can't find the exact calculation at the moment, but I remember that it included such values like entrance pupil diameter and exit pupil diameter, and that the diaphragm diameter wasn't included directly! 2) T/stop (true transmission, in practice, than only computed, theoretical, geometrical transmission). It is measured not computed. e.g. one 4/400mm movie lens was stated as T/4.5 transmission stop. It is slower because of light losess at each air-glass surface (due to reflectance of uncoated glass, even SMC glass reflects some light). With formula on Boz's KMP, we get at least 5% loss of light in complex 2.8 pro zoom (usually 12 groups or more), with SMC. With advances in SMC this might be less. That's T/2.94 instantly. Add to it manufacturers tolerances (about 5% too), and 2.8 lens might test actually as 3 (like some 300mm are tested to be less, ~280mm). 3) with retrofocus and tele designs, the usuall formula for close up loss of light changes too (or rather we should use formula with this in mind). Normally, lens losess 2 stops at 1:1 magnification AFAIK. With tele designs, lens loses up to 1.5x more! (this is often cured by using some IF design, which sometimes lessens the focal length). OTOH, retrofocus (wide) lenses loose less light at 1:1 ! Maybe just 1 stop compared to normal 2 stops. That's because again, the entrance and exit pupils come into it. Entrance pupil of telephoto lens is large, but exit pupil is small. Vice versa in retrofocus wideangle lens. The entrance divided by exit (or vice versa?) pupil diameter is in the proper equation for loss of light with closer focus than infinity. So a plain tele lens without any fancy IF or REAR design might loss even almost stop at very close portrait distance. Example would be old 4/300 (not *) SMC K, or K 5.6/400 lenses. If I find the proper formulas, I will post them, but I guess they must be in any good photo encyclopaedia or on web (my focal press encycl. is now packed away in crates, as is majority of my library :( Frantisek - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
On Mon 2001-09-24 (09:19), Shel Belinkoff wrote: Martin Trautmann wrote: Real numbers are not required: If it's not enough light, the exposure meter will double your time, whether the selected aperture is called 2.8 or 3.5, whether it is a faked or real number, as long as you do need double times. Well, Martin, there's a fly in your intellectual ointment: What happens to exposure calculations when one is not using a camera with TTL metering? Hi Shel, concerning the discussions that I had seen here, I expected that almost every user here used equipment with TTL metering. Yes, I simplified things in my reply, and thus I've seen interesting replies, not only concerning hand-held meters (which would have major trouble with incorrect aperture declarations), but e.g. flash as well. Since I use rangefinder cameras, hand-held meters, and even cameras with non-ttl metering, and the exposures are correct regardless of how I meter, and regardless of which lenses I use, how might that be explained? I'd say: by the tolerance of the exposed material :-) Martin - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
William Robb [EMAIL PROTECTED] quotes: The f number of the lens equals the focal length divided by the diameter of the entrance pupil of the aperture. ...and it's important to note, that the entrance pupil is _not_ the physical front element of the lens (although with long focal lengths (and in the extreme case of a single element lens) it will be equal to it). It is, rather, the apparent optical diameter of the lens, which you can observe by holding the lens, /sans camera/, aperture blades wide open, with a light surface behind it, and looking at it from the front side, from a distance. Notice that in the case of a wide angle lens, the apparent optical diameter is smaller than the front element. Basically, a real, composite lens is the optical equivalent (modulo imperfections) of an imagined single element lens of the specified focal length, and of a diameter equal to the focal length divided by the specified max aperture number. This non-existent lens is what you see in the above experiment. -tih -- Puritanism -- the haunting fear that someone, somewhere, may be happy. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Theatrical motion pictures are shot on negative film. For other uses transparency film was often used, but today is pretty much replaced by video tape. The point I was making was that with two rapidly changing slide images one can see a 1/10 stop difference in exposure. My point is valid! Your observation is of little consiquence to the subject. --graywolf - Original Message - From: PAUL STENQUIST [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Tuesday, September 25, 2001 5:46 AM Subject: Re: lens brightness Motion pictures are shot on negative film. A positive print is made from the negative. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Kinda slams the door in the face of anyone not using ~your~ preferred method, eh? Regards, Anthony Farr - Original Message - From: Rob Brigham [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, 24 September 2001 11:04 PM Subject: RE: lens brightness Unless you set the aperture from the body - then you will know the aperture! -Original Message- From: Aaron Reynolds [mailto:[EMAIL PROTECTED]] Sent: 24 September 2001 13:43 To: [EMAIL PROTECTED] Subject: Re: lens brightness Martin Trautmann wrote: In fact I don't know why this should be done. 28-70/3.5-4.0 should be superior to 28-70/4.0!? ...unless you use a hand-held meter, in which case you won't be able to set your exposure exactly because you don't know what aperture your lens is at. -Aaron - - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. I believe 2.8 should be effective aperture, i.e. it should reflect lens construction, light loss in glass, etc. IOW, 2.8 should be the same be it prime or zoom. It can't be (as people sometimes say on this list) as simple as lens diameter divided by focal length; otherwise my FA28-70/4 could not be constant aperture zoom :-) (But it is possible some manufacturers cheat and their lenses can have significantly different max. aperture than stated) Ivan - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. Thanks for any help. I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly, should deliver the same amount of light at the film plane when set to 2.8. No ifs, ands, or buts! Otherwise photography doesn't work with interchangeable lenses. Most zooms these days will change maximum aperture over their zoom range. It is cheaper to build a lens this way. But some of the old Pentax A series lenses held a constant aperture over their zoom range...A35-105/3.5 and A28-135/4 come to mind. Regards, Bob S. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
On Mon 2001-09-24 (07:39), [EMAIL PROTECTED] wrote: I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. Thanks for any help. I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly, should deliver the same amount of light at the film plane when set to 2.8. No ifs, ands, or buts! Otherwise photography doesn't work with interchangeable lenses. 2.8 is NOT 2.8 - this number does not depend on real measurements, but on physical calculations only. Aperture is give mainly by diameters ond focal length. Real numbers are not required: If it's not enough light, the exposure meter will double your time, whether the selected aperture is called 2.8 or 3.5, whether it is a faked or real number, as long as you do need double times. Sad to say that any fake is possible. Maybe you can compare real numbers when you take two different lenses of identical focal length and compare the data they suggest. Which Pentax would show continous integer numbers for times, instead of 36/60/125/... only? Regards Martin - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
On Mon 2001-09-24 (13:32), Ivan Prenosil wrote: It can't be (as people sometimes say on this list) as simple as lens diameter divided by focal length; otherwise my FA28-70/4 could not be constant aperture zoom :-) Constant aperture is done by adjustment 'tricks' of the efficient aperture - the diaphragm blades can be closed for shorter focal lengths. In fact I don't know why this should be done. 28-70/3.5-4.0 should be superior to 28-70/4.0!? Regards Martin - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Hi, On 2001.09.24, at 20:39, [EMAIL PROTECTED] wrote: I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly, should deliver the same amount of light at the film plane when set to 2.8. No ifs, ands, or buts! The aperture value simply depends on geometry as William and Nenad wrote before. I should add that not only surface light- loss but also vignetting reflects the amounts of light coming through the lens. There is T-value which depends on the amount of light through the lens. When you set the two different lenses at the same T-value, they deliver the same amount of light at the film plane. I do not consider it too much to say that two different lenses with different constructions deliver the different amounts of light at the film plane when set to the same aperture value. BTW, the differences between the amounts of light through the lenses do not seem very big. Hope this helps. -- Yoshihiko Takinami Osaka, Japan [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Martin Trautmann wrote: In fact I don't know why this should be done. 28-70/3.5-4.0 should be superior to 28-70/4.0!? ...unless you use a hand-held meter, in which case you won't be able to set your exposure exactly because you don't know what aperture your lens is at. -Aaron - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: lens brightness
Unless you set the aperture from the body - then you will know the aperture! -Original Message- From: Aaron Reynolds [mailto:[EMAIL PROTECTED]] Sent: 24 September 2001 13:43 To: [EMAIL PROTECTED] Subject: Re: lens brightness Martin Trautmann wrote: In fact I don't know why this should be done. 28-70/3.5-4.0 should be superior to 28-70/4.0!? ...unless you use a hand-held meter, in which case you won't be able to set your exposure exactly because you don't know what aperture your lens is at. -Aaron - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Martin Trautmann wrote: Constant aperture is done by adjustment 'tricks' of the efficient aperture - the diaphragm blades can be closed for shorter focal lengths. In fact I don't know why this should be done. 28-70/3.5-4.0 should be superior to 28-70/4.0!? I suppose one point is, that it's from the age of manual and often in manual mode used cameras (MX,LX,...). With those it's much easier to work, as one doesn't need to look continuous at the meter. Nowadays with automatic cameras constant aperture zooms got rare. The other reason may be at wide open at the short end the vignetting and the uneveness of the sharpness. If the aperture is closed at bit, these and other optical faults may be reduce to acceptabel values. regards - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
On Mon 2001-09-24 (15:33), HUDERER Bernd wrote: Nowadays with automatic cameras constant aperture zooms got rare. True: only some Pentax AF lenses have constant aperture values: FA 20-35/4 F 24-50/4 FA 28-70/4 FA* 28-70/2,8 FA* 80-200/2,8 F* 250-600/5,6 FA* 250-600/5,6 That's only 7 out of 29 zoom lenses Some others are Sigma EX 24-70/2,8 DF DG Sigma EX 28-70/2,8 DF Sigma35-70/2,8 Sigma EX 70-200/2,8 Sigma70-210/2,8 Sigma EX 100-300/4 Tamron SP AF 28-105/2,8 Tamron SP AF 35-105/2,8 Tamron SP AF70-210/2,8 LD Tamron AF200-400/5,6 LD Tokina AT-X 235AF PRO 20-35/2,8 Tokina AT-X 24-40/2,8 Tokina AT-X 270AF 28-70/2,8 Tokina AT-X 280AF PRO 28-80/2,8 Tokina AT-X 828AF 80-200/2,8 Tokina AT-X 828AF PRO 80-200/2,8 Tokina AT-X 340AF 100-300/4 Tokina AT-X 340AF II 100-300/4 Regards Martin - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
- Original Message - From: Subject: Re: lens brightness I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. Thanks for any help. I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly, should deliver the same amount of light at the film plane when set to 2.8. No ifs, ands, or buts! Otherwise photography doesn't work with interchangeable lenses. It would be nice, but unfortunately, it just doesn't work this way. A 200mm f/4 lens will have a maximum aperture of 50mm diameter, as will an 80-200mm f/4 lens, if both are calibrated correctly. This does not mean they will both deliver the same amount of light to the film, only that the maximum apertures are the same. The T-stop may be quite different, depending on the efficiency of the lens. Constant aperture zooms are very nice for fill flash, even with auto everything cameras, as the background will tend to stay at the same density, no matter what focal length you are shooting at. William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Yes. Note: The lenses of almost all motion picture cameras use T-stops (measure of light transmission). At one time in the industry, before the excellent coatings of today and when the lenses of these cameras were mounted on turrets, there could be a significant difference between an f/stop and a T-stop and between one lens and another. Even with the advent of zoom lenses, the problem continued when shooting scenes with several cameras using different lenses. You might detect the difference on the silver screen because you would be seeing the results side by side and in time and overlapped. I've read that the human eye can detect a difference of about 1/3 stop and some films exaggerate this (high contrast films). Photographs are not usually viewed as same scene side-by-side, and even when they are, the change doesn't take place overlapped in 1/30th of a second. In a print, or adjustment of a slide for the printed page, it may be nearly impossible to detect small differences that might be obvious on the silver screen. Some camera lens makers publish the maximum T-stop of their lenses. The f/stop and T-stop of a pinhole camera are the same. T-stop determines light transmission accurately and DOF and diffraction closely. F/stop determines DOF and diffraction accurately and light transmission closely. Mirror tele's throw everybody off. When they say they're f/8, what do they really mean? Regards, Bob... --- In the carboniferous epoch we were promised perpetual peace. They swore if we gave up our weapons that the wars of the tribes would cease. But when we disarmed they sold us, and delivered us, bound, to our foe. And the gods of the copybook headings said, 'Stick to the devil you know.' --Rudyard Kipling From: Yoshihiko Takinami [EMAIL PROTECTED] Hi, On 2001.09.24, at 20:39, [EMAIL PROTECTED] wrote: I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. I'm with you 2.8 is 2.8. Two different lenses, if calibrated properly, should deliver the same amount of light at the film plane when set to 2.8. No ifs, ands, or buts! The aperture value simply depends on geometry as William and Nenad wrote before. I should add that not only surface light- loss but also vignetting reflects the amounts of light coming through the lens. There is T-value which depends on the amount of light through the lens. When you set the two different lenses at the same T-value, they deliver the same amount of light at the film plane. I do not consider it too much to say that two different lenses with different constructions deliver the different amounts of light at the film plane when set to the same aperture value. BTW, the differences between the amounts of light through the lenses do not seem very big. Hope this helps. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Rob Brigham wrote: Unless you set the aperture from the body - then you will know the aperture! ...except I can't do that with my LX, ME Super or 67. And yes, there are zooms for the 67 (two of 'em!). :) -Aaron - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Ivan Prenosil wrote, re effective lens aperture: It can't be (as people sometimes say on this list) as simple as lens diameter divided by focal length; otherwise my FA28-70/4 could not be constant aperture zoom :-) Hi ... Like you, I don't believe it's as simple as diameter/focal length, and somewhere i have the details of that. I've noticed, for example, that my Leica lenses are often quite a bit smaller in diameter than the same focal length/aperture combination in Pentax and other SLR lenses. However, zooms can be a constant aperture. I have two Pentax zooms w/constant aperture. There is a mechanical means by which the aperture diameter is adjusted as one moves through the focal range. This is apart from the aperture ring on the lens. -- Shel Belinkoff mailto:[EMAIL PROTECTED] Why should I use a meter? What if the darn thing broke on me when I was out making a photograph? Then what would I do? - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Hi, I noticed the same thing today. Few days ago I bought M42 Kmount adapter to enable the recently acquired screw mount SMC Takumar 3,5/28. Just today I met with a friend who owns Carl Zeiss Jena 135/3.5 lens (which was made for Practica cameras and has M42 mount) with intention to compare his CZJ 135/3.5 with M135/3.5. To make a long story short, when I was metering with the ME Super the same scene with both lenses, I noticed that at the same aperture, the shutter speed chosen by the camera was different with each lens. For example, at F3,5, it was metered at 1/125 with M135, however with Carl Zeiss Jena it was about 1/2 stop lower, between 1/60 and 1/125. I see two explanations: first, because of better SMC coating on the Pentax there was less light loss or, second, that true wide open F stop of the CZJ is slower than wide open F stop of M 135/3,5. Unfortunately, I didn't test them at other apertures. Matjaz Shel wrote: I can't really respond that except to share an example of some interesting metering behavior, which, in a convoluted fashion, may provide some insight if not an actual answer. As you know, I have a few Pentax lenses and when I meter with some k-mount lenses, using the meter in ~all~ my LX bodies, I find that the meter readings are different than with other lenses at the same aperture. I've made the readings from the same patch of open sky, so things like a different FOV, or factors such as colors, shouldn't enter the picture. The k-mount lenses in question all seem to be off by about one stop as reported by the LX meter readout. However, shooting at the metered setting results in properly exposed negatives. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Right. And closely related to the info from Wheatfield Willie given earlier, f-stops are computations of DOF. On many medium format cameras, esp. those with bellows focusing, you'll see a scale on the side which instructs the user regarding exposure and focus distance. Look at a photo of the Mamiya RB and C220/C330. These cameras, among others, have this scale on the side. As a consequence, exposure can change based on focus distance, though DOF remains the same. Aperture setting DOES NOT equal identical exposure at differing focus distances. my 2c Collin ---ORIGINAL MESSAGE--- Subject: Re: lens brightness A factor affecting light transmission will be lens extension. Set to any given aperture, charts typically show that a 50/1.4 lens will need about 1/3 stop more exposure when focused at 18 than it needs at infinity. This may be due to the size of the image circle being cast over the negative at varying extensions. Mark Rofini - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Shel Belinkoff wrote: [snip] ...I've noticed that newer lenses transmit more light than some older lenses, due in part, I'm sure, to the coatings used. F2.8 seems to be the same for all my newer lenses, but F2.8 is a little underexposed with some earlier lenses. One of the American magazines I once read regularly, it may have been Modern Photography, used to publish t-stops as well as f-stops in lens reviews. I recall there being differences although I do not recall how large they were. At any event, no reviews present such info any more, I am sure because the differences have gotten minuscule with just about modern coated lenses, as you note. Bob Harris - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: lens brightness
On Mon, 24 Sep 2001, Chris Brogden wrote: That might have something to do with lens-to-film distance. Maybe the smaller mount doesn't need as large an opening because it's closer to the film plane than the K-mount? (Total guess) That being said, it happens [...] No guess at all. Did everybody forgot their high school physics at the same time? The illumination from a light source fall by the inverse square root of the distance to that source. An object twice as far as another one will receive only a fourth the amount of light the first object is receiving. That is why you must adjust exposure when using bellows. In typical use (no bellows) the built-in meters of cameras compensate for the difference in lens to film distance between infinity and closest focusing. The effect would be more pronounced on tele than on ultrawide (the 15mm hardly moves at all, compared to a 135). I will speculate that the measuring point for the formula will likely show the distance is calculated from the center of a lens to the film plane for a simple one element lens, and from the rear nodal point for a compound lens. Michel - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Bob wrote: Now, tell me how interchangeable lenses are used along with those fancy hand held light meters. When you take out your Pentax Spot Meter, do you adjust it every time you put a different lens on the camera? Oh, the T-value for that lens is 1/2 stop better than this one? (I'm serious here, not pulling your leg!) I'm not pulling your leg either when I say that if you want accuracy less than 1/2 stop then you cannot use a separate meter, and that has nothing to do with the meter itself but due to the fact that theres no way you can transfer this exact meter reading to a camera with less than 1/2 stop accuracy. The best Pentax ever for exact metering and exposure is the Z-1p because it has spot metering. a dead precise meter, a dead precise shutter (as oppose to all early Pentaxes), exposure setting in 1/3stops increments, and most importantly, exposure readouts in 1/3 stop increments. Pål - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Shel wrote: Since I use rangefinder cameras, hand-held meters, and even cameras with non-ttl metering, and the exposures are correct regardless of how I meter, and regardless of which lenses I use, how might that be explained? It can only be explained with that you're not very critical when it comes to exposure : -) Mechanical cameras shutters are all of them at least half a stop off on the higher speeds - often in a random manner. Aperture setting on lenses are usually 1/3 to 1/2 stop off. Light transmission of lenses might vary from lens to lens and focusing distance due to extension . Non professional film has 1/3 stop error margins. Processing error margin is 1/3 stop if lucky. Then theres meter calibration. Without a precise built in spot meter accurate metering with user control within 1/3stop Precision is basically impossible. And how do you set that exposure on a mechanical camera where the shutter speed is in one stop increments? The error margin here is 1/2 stop. Fortunately, in most cases all these errors cancel each other. Pål - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
The difference among f/stops on modern lenses with excellent coatings is (supposedly) exceptionally small. Some zoom lenses may show differences when used with slides and compared side to side with primes by someone with an exceptionally critical eye, I suppose. I'll bet that even this us usually too small to be of any concern. Your Dad's old Speed Graphic may not have been multi coated, but it was coated and probably has only 4 elements. The difference is marginal, and it doesn't matter. It mattered even less in the day of the old Speed Graphic. The film of the day was BW print, wide latitude and often the printing sucked by today's standards anyway... Thank you for failing to properly attribute quotes. - and this from a group that is probably zealous about copyrights and proper tribulation of their photo work! Sheesh! Regards, Bob... --- In the carboniferous epoch we were promised perpetual peace. They swore if we gave up our weapons that the wars of the tribes would cease. But when we disarmed they sold us, and delivered us, bound, to our foe. And the gods of the copybook headings said, 'Stick to the devil you know.' --Rudyard Kipling From: [EMAIL PROTECTED] OK folks, I hear what you are saying. Now, tell me how interchangeable lenses are used along with those fancy hand held light meters. When you take out your Pentax Spot Meter, do you adjust it every time you put a different lens on the camera? Oh, the T-value for that lens is 1/2 stop better than this one? (I'm serious here, not pulling your leg!) If I take out my Dad's old 2x3 Speed Graphic and the GE meter hand held lightmeter, it says shoot at this f stop/speed. It doesn't say much about T-values for the lens. Is the difference that marginal that it doesn't matter? Regards, Bob S. Note: The lenses of almost all motion picture cameras use T-stops (measure of light transmission). At one time in the industry, before the excellent coatings of today and when the lenses of these cameras were mounted on turrets, there could be a significant difference between an f/stop and a T-stop and between one lens and another. Even with the advent of zoom lenses, the problem continued when shooting scenes with several cameras using different lenses. You might detect the difference on the silver screen because you would be seeing the results side by side and in time and overlapped. I've read that the human eye can detect a difference of about 1/3 stop and some films exaggerate this (high contrast films). Photographs are not usually viewed as same scene side-by-side, and even when they are, the change doesn't take place overlapped in 1/30th of a second. In a print, or adjustment of a slide for the printed page, it may be nearly impossible to detect small differences that might be obvious on the silver screen. Some camera lens makers publish the maximum T-stop of their lenses. The f/stop and T-stop of a pinhole camera are the same. T-stop determines light transmission accurately and DOF and diffraction closely. F/stop determines DOF and diffraction accurately and light transmission closely. Mirror tele's throw everybody off. When they say they're f/8, what do they really mean? - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Bob Blakely wrote: Thank you for failing to properly attribute quotes. - and this from a group that is probably zealous about copyrights and proper tribulation of their photo work! Sheesh! Sorry Bob, from work thru AOL Anywhere Mail, quoting is a miserable task - PITA. I appreciate your note and discussion of T values in the movie industry. It gave a lot of insight and credibility to your comments. Regards, Bob S. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
I'm just having a hard day an' I'm constipated. Regards, Bob... --- In the carboniferous epoch we were promised perpetual peace. They swore if we gave up our weapons that the wars of the tribes would cease. But when we disarmed they sold us, and delivered us, bound, to our foe. And the gods of the copybook headings said, 'Stick to the devil you know.' --Rudyard Kipling From: [EMAIL PROTECTED] Bob Blakely wrote: Thank you for failing to properly attribute quotes. - and this from a group that is probably zealous about copyrights and proper tribulation of their photo work! Sheesh! Sorry Bob, from work thru AOL Anywhere Mail, quoting is a miserable task - PITA. I appreciate your note and discussion of T values in the movie industry. It gave a lot of insight and credibility to your comments. Regards, Bob S. - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
- Original Message - From: Shel Belinkoff Subject: Re: lens brightness Ivan Prenosil wrote, re effective lens aperture: It can't be (as people sometimes say on this list) as simple as lens diameter divided by focal length; otherwise my FA28-70/4 could not be constant aperture zoom :-) Hi ... Like you, I don't believe it's as simple as diameter/focal length, and somewhere i have the details of that. I've noticed, for example, that my Leica lenses are often quite a bit smaller in diameter than the same focal length/aperture combination in Pentax and other SLR lenses. Let me clarify, it is not quite as simple as focal length/aperture diameter, as I first stated. My encyclopedia of photography says: The f number of the lens equals the focal length divided by the diameter of the entrance pupil of the aperture. I don't know if this makes a huge difference in terms of this discussion, though it is important when measuring to measure at the front of the lens rather than the back of the lens, as exit pupil diameters are different from entrance pupil diameter on non symmetrical lenses (thats what we use on reflex cameras) William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
- Original Message - From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, September 24, 2001 11:35 AM Subject: Re: lens brightness OK folks, I hear what you are saying. Now, tell me how interchangeable lenses are used along with those fancy hand held light meters. When you take out your Pentax Spot Meter, do you adjust it every time you put a different lens on the camera? Oh, the T-value for that lens is 1/2 stop better than this one? (I'm serious here, not pulling your leg!) I almost never worry about it. I just presume that f/5.6 (example only) is f/5.6 no matter what lens I am using. Of course, I only use the hand held meter with the large format camera and a few lenses (non of which are zooms) in the studio. For macro work with non ttl flash, I calculate the light loss directly with the built in meter, then adjust the output of the strobe accordingly. My exception is with my old (uncoated) 90mm f/6.8 Schneider Angulon. It definitely needs a half stop more exposure because of light loss. It's negatives also require 2/3 zone more development to get the negatives to the same contrast as my modern lenses. If I take out my Dad's old 2x3 Speed Graphic and the GE meter hand held lightmeter, it says shoot at this f stop/speed. It doesn't say much about T-values for the lens. Is the difference that marginal that it doesn't matter? It might be, but it also might not be. In my situation, it isn't. I think it could well be a problem with zoom lenses with lots of glass, but these tend to be used with TTL metering, or with uncoated lenses that have lots of veiling flare (thats where the light goes when it bounces off the glass rather than going through it). William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
- Original Message - From: Pål Jensen Subject: Re: lens brightness Bob wrote: Now, tell me how interchangeable lenses are used along with those fancy hand held light meters. When you take out your Pentax Spot Meter, do you adjust it every time you put a different lens on the camera? Oh, the T-value for that lens is 1/2 stop better than this one? (I'm serious here, not pulling your leg!) I'm not pulling your leg either when I say that if you want accuracy less than 1/2 stop then you cannot use a separate meter, and that has nothing to do with the meter itself but due to the fact that theres no way you can transfer this exact meter reading to a camera with less than 1/2 stop accuracy. The best Pentax ever for exact metering and exposure is the Z-1p because it has spot metering. a dead precise meter, a dead precise shutter (as oppose to all early Pentaxes), exposure setting in 1/3stops increments, and most importantly, exposure readouts in 1/3 stop increments. I respectfully disagree. On my view camera lenses, I admittedly have to work in whole stops with shutter speed, but I can work with 1/6 stops very accurately with the aperture. With the Zone VI modified Pentax spot meter, I can measure the exposure range of the scene quickly, and decide exactly where I want the highlights to fall on the film slope. I can do this through coloured filters without having to worry about non linear response of the meter (unlike ANY built in camera meter from any company), and transfer the reading to the lens with great precision. Whether I think all this precision is needed is another story completely (I don't). William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
In critical work such as with motion picture transparency film, the eye can detect as little as 1/10 a stop difference between scenes. With negative films you can adjust in the printing stage so they are not so critical. And, if you are not showing them side by side no one will notice. --graywolf - Original Message - From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, September 24, 2001 1:35 PM Subject: Re: lens brightness OK folks, I hear what you are saying. Now, tell me how interchangeable lenses are used along with those fancy hand held light meters. When you take out your Pentax Spot Meter, do you adjust it every time you put a different lens on the camera? Oh, the T-value for that lens is 1/2 stop better than this one? (I'm serious here, not pulling your leg!) - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
From: Nicholas Wright Subject: lens brightness I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. Thanks for any help. The maximum aperture is derived by dividing the diameter of the aperture wide open into the focal length. In theory, it will tell you something about how much light hits the film. However, a lens with a lot of glass (a zoom lens with a dozen or more lens elements) is bound to transmit less light than a lens with less glass (a prime lens may have as little as 4 elements, depending on design and focal length) because of light loss caused by glass surface reflections. This was the thing that lens coatings, and especially multi coating is supposed to cure. If the zoom lens is multicoated throughout, the light loss due to internal reflections may be so insignificant as to be unmeasurable. I have seen cheapo junk lenses that transmitted a full stop less light than what they should have, probably due to a combination of the lens being slower than marked, and internal reflections. William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: lens brightness
Hi Nick, I think that a prime does transmit more light than a zoom as it has a simpler lens construction with less glass elements to reflect light. Having said that, the coatings on the glass are designed to minimise reflection (and maximise transmission) so the difference should be minimal. In any case TTL metering would compensate automatically. Regards Nenad - Original Message - From: Nicholas Wright [EMAIL PROTECTED] To: PDML [EMAIL PROTECTED] Sent: Monday, September 24, 2001 1:00 PM Subject: lens brightness I have heard remarks that a 200/2.8 prime will transmit more light than an 80-200/2.8 zoom. Is this true? I thought a 200/2.8 was a 200/2.8 whether it be a prime or part of a zoom. Thanks for any help. Nick - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
