Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
On Thu, 27 Feb 2003 00:21:28 -0600, you wrote: So, yes, the 50mm lens on an APS sized sensor would have the same angle of view, d.o.f. at same aperture, perspective, and flattening effect as a piece of 35mm film cropped. But so would a 75mm lens on a full-sized piece of 35mm film. Hope this is clear. This is one of those perennial questions in photography--it just always comes up again and again and again. --Mike I support Mike's observation. The DSLR's smaller sensor acts like a 1.5x teleconverter. Your lenses just get longer with the smaller sensor, no matter what. My 300/f4mm lens becomes a 450/f4mm lens, and my formerly wide angle 24-135mm zoom becomes a very different animal of 36-202mm. So break out those good old long Pentax and K-mount lenses, those who have been yearning for Big Glass. I personally am jumping with glee - my Tokina AT-X 300/2.8 and Pentax 1.7x AF Adapter will make a very fine 765mm/f5 lens. Even the little K 200/2.5 is looking pretty good at 300/2.5. And the 600/4 with 1.4XL teleconverter becomes an amazing 1260mm/f4 lens. Drool city for this telephoto aficionado. -- John Mustarde www.photolin.com
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
On February 27, 2003 07:34 am, John Mustarde wrote: On Thu, 27 Feb 2003 00:21:28 -0600, you wrote: So, yes, the 50mm lens on an APS sized sensor would have the same angle of view, d.o.f. at same aperture, perspective, and flattening effect as a piece of 35mm film cropped. But so would a 75mm lens on a full-sized piece of 35mm film. Hope this is clear. This is one of those perennial questions in photography--it just always comes up again and again and again. --Mike I support Mike's observation. The DSLR's smaller sensor acts like a 1.5x teleconverter. Your lenses just get longer with the smaller sensor, no matter what. The way it makes the most sense to me is to think in terms of the film moving. You've got a cone coming out of the back. The further back the film plane the wider the lens. x x x x x xx x x x x x x Your piece of film needs to fiit inside that cone. So if you only change the film size the same lens can go from very long to wide. Nick
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
Not really. The fact that the 50 has a field of view more like a 75 is created by cropping, not optical zooming. In effect, the less-than-24x36 image sensor size means that there's a permanently enabled digital zoom feature on the camera. All you're doing is cropping. The perspective-flattening effects of longer optics aren't going to come into play (or will they? maybe I'm the confused one). This is explained in one of Ansel's books (The Camera?). A lens of a given focal length projects an image of the same size regardless of film format. For example, if a 300mm lens on a 4x5 camera projects a subject 1 inch high on the film, then a 300mm lens on a 35mm camera will project the same subject 1 inch high. The difference being that of course on the 4x5 it would take up only about 1/4 of the film, while on 35mm it would be nearly full frame. Bill
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
John wrote: And the 600/4 with 1.4XL teleconverter becomes an amazing 1260mm/f4 lens. Drool city for this telephoto aficionado. ...and with 50% reduction in resolution for the lens alone + the reduction of the converter. I'm sorry, but the FA* 600/4 isn't that good. Pål
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
The way it makes the most sense to me is to think in terms of the film moving. You've got a cone coming out of the back. The further back the film plane the wider the lens. x x x x x xx x x x x x x Your piece of film needs to fiit inside that cone. So if you only change the film size the same lens can go from very long to wide. Nick, That's a good way to put it. --Mike
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
On Thu, 27 Feb 2003 15:26:30 +0100, you wrote: John wrote: And the 600/4 with 1.4XL teleconverter becomes an amazing 1260mm/f4 lens. Drool city for this telephoto aficionado. ...and with 50% reduction in resolution for the lens alone + the reduction of the converter. I'm sorry, but the FA* 600/4 isn't that good. Pål You must really have a dud of a FA* 600/4 lens. We call them lemons where I come from. Have you had the optics checked? My 600/4 is plenty good wide open with the 1.4x TC, and not so good with the 2-XL TC. I'd be interested to see some of the poor resolution photos from your 600/4 and 1.4 XL. Even web photos would probably show the deficiencies of such a poor lens. Could you post some? -- John Mustarde www.photolin.com
Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
I really don't know what you're talking about. I'm not saying the 600/4 is a lemon. What I'm saying is that if you reduce its resolution by 50% and then add a teleconverter, then it suck as all lenses will. - Original Message - From: John Mustarde [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Friday, February 28, 2003 1:01 AM Subject: Re: Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8 On Thu, 27 Feb 2003 15:26:30 +0100, you wrote: John wrote: And the 600/4 with 1.4XL teleconverter becomes an amazing 1260mm/f4 lens. Drool city for this telephoto aficionado. ...and with 50% reduction in resolution for the lens alone + the reduction of the converter. I'm sorry, but the FA* 600/4 isn't that good. Pål You must really have a dud of a FA* 600/4 lens. We call them lemons where I come from. Have you had the optics checked? My 600/4 is plenty good wide open with the 1.4x TC, and not so good with the 2-XL TC. I'd be interested to see some of the poor resolution photos from your 600/4 and 1.4 XL. Even web photos would probably show the deficiencies of such a poor lens. Could you post some? -- John Mustarde www.photolin.com
Re: pentax-discuss-d Digest V03 #8
On Wednesday, Feb 26, 2003, at 18:54 US/Pacific, [EMAIL PROTECTED] wrote: already have the perfect portrait lens--the 75mm effective (a.k.a. 50mm) f/1.4 lens. Now just give me a good fast moderate wide-angle for the *ist D and I'm home free. Not really. The fact that the 50 has a field of view more like a 75 is created by cropping, not optical zooming. In effect, the less-than-24x36 image sensor size means that there's a permanently enabled digital zoom feature on the camera. All you're doing is cropping. The perspective-flattening effects of longer optics aren't going to come into play (or will they? maybe I'm the confused one). -- David Barts Portland, OR
Is perspective cropping? WAS: pentax-discuss-d Digest V03 #8
Not really. The fact that the 50 has a field of view more like a 75 is created by cropping, not optical zooming. In effect, the less-than-24x36 image sensor size means that there's a permanently enabled digital zoom feature on the camera. All you're doing is cropping. The perspective-flattening effects of longer optics aren't going to come into play (or will they? maybe I'm the confused one). Well, perhaps. The fact is, you could say the same thing about any smaller format. You could say that all you're doing with rollfilm is cropping the field of view of 4x5 film, and all you're doing with 35mm film is cropping the field of view of the rollfilm. A 300mm is normal on an 8x10 camera, moderately telephoto on a 4x5, long portrait length on a 6x7, and long telephoto on 35mm. As far as PERSPECTIVE is concerned, it doesn't change with focal length anyway. If you took a picture on 8x10 film with a 300mm lens, then cut out a tiny 36mm x 24mm piece from the middle of it, that little piece would have exactly the same perspective as would a piece of 35mm film aimed at the same target with a 300mm 35mm lens. No, the pictures wouldn't look exactly the same, because the smaller camera would resolve better. But in terms of flattening they'd be the same. So, yes, the 50mm lens on an APS sized sensor would have the same angle of view, d.o.f. at same aperture, perspective, and flattening effect as a piece of 35mm film cropped. But so would a 75mm lens on a full-sized piece of 35mm film. Hope this is clear. This is one of those perennial questions in photography--it just always comes up again and again and again. --Mike
Re: pentax-discuss-d Digest V03 #8
J. C. O'Connell said: I saw a Pentax 500mm screw mount lens on eBay, I can buy it for $100, but it's not a Takumar. On the other hand, it's not a mirror lens, and it has an adjustable aperture. How is the non-Takumar 500mm? All of the PENTAX brand 500mm screw lenses were Takumars. It probably was a third party lens. The good 500mm Pentax screw lens is the 500mm F4.5 But weren't there different lines of Takumars, some with multi-coated optics and some without? Is there any way to tell? Because I'm not just trying to get a 500mm lens, I have a 500mm reflex. I'm trying to find something in the neighborhood of profesional quality optics at prices I can actually pay, and that's what the SMC screw mount Takumars are, if I can believe the legends. (Can I believe the legends?) But I wouldn't limit myself to Takumar if there are comparable alternatives (Carl Zeiss?).
Re: pentax-discuss-d Digest V03 #8
How bizarre. A lens I have had in stock for at least a year, also on the website for a year, instantly met reserve last night the bidder is a UK customer whom I regularly see at camera shows. The wonders of eBay I suppose. (It's the uncommon 28mm F2.8 M version 2). Kind regards from sunny Brighton Peter -- CAMERA DIRECT 8 DORSET STREET BRIGHTON EAST SUSSEX BN2 1WA UK TEL 44 1273 681129 FAX 44 1273 681135 http://www.camera-direct.com
Re: pentax-discuss-d Digest V03 #8
If the information is there you can get it out. It may be poor in quality. And one wouldn't use the kind of image processing I mention on bacterial cells. Perhaps on some of their ultrastructural components. The calls are not ordered enough and they are far far too big. The purple membrane of photosynthetic bacteria has been studied by electron microscopy and image analysis. And who wouldn't like perfect images and clean spectra? Don Don Williams ___ Dr E D F Williams http://personal.inet.fi/cool/don.williams Author's Web Site and Photo Gallery Updated: March 30, 2002 - Original Message - From: Gregory L. Hansen [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Wednesday, January 08, 2003 9:31 PM Subject: Re: pentax-discuss-d Digest V03 #8 Dr E D F Williams said: It does not matter how noisy a signal is, if the information is there it can be retrieved. In Electron Microscopy the images are often terribly noisy. For ordered structures Fourier transforms, rotational symmetry, or a combination of methods is useful. I have programs to do things like that and if I can find a decent electron micrograph of a virus I'll try to prepare some images that illustrate the cleaning of an image. Image processing can be done in real time on an optical bench, but its more difficult. It matters, but it depends on the application. Pictures of virii are usually shown in black and white, for instance, and bacteria stained to present false colors. What's important there is to see structure. In my case, I've been trying to extract signal that's a factor of 100 smaller than the noise, and it's not easy and I don't really trust the results I'm getting. There's nothing to do but keep taking data until the statistics favor me. In terms of photography, if you have too much noise you might be able to clean up a picture and clearly see the features of a dog, but lose much of the texture of fur and other small details. It's always better when your raw data is as clean as possible.
