Re: Advantage of small f/number!
Hallo Bill! The front element of a 50 mm f/1.4 lens has bigger diameter than a 50 mm f/4 lens. (Am I correct?) Therefore the preliminary amount of light energy reaching an imaginary plane or film behind the lens per unit time per unit area is more than a 50 mm f/4 lens as it has a smaller front element. When it is stopped down to f/4, the amount of light reaching the film plane is more than 50 mm f/4 lens. The above explanation depends only on one point that the front element of a 50 mm f/1.4 lens has bigger diameter than 50 mm f/4 lens, if it is at all correct. However, you are absolutely right that f/4 is still f/4 or in other words, the diameter of the aperture at f/4 is identical in both the cases and therefore, the light has to pass through the holes of identical diameters but what I mean to say is that the intensity of light in 50 mm f/1.4 lens is more than a 50 mm f/4 lens. Please correct me, if I am wrong anywhere. Many thanks for your comments. With best regards, Ayash Kanto. On Mon, 1 Jul 2002, Bill D. Casselberry wrote: Ayash Kanto Mukherjee wrote: I have some doubts regarding lenses with small f-numbers. Suppose you have two lenses, one is 50 mm f/4 and the other is 50 mm f/1.4. If, I stop down the second lens to f/4, which one will give faster shutter speed for correct exposure? I feel that second lens has more light gathering power therefore it will give high shutter speed. Am I correct? No - they'd be the same since f4 is f4 no matter the lens, etc. It is possible that one may have some indistinguishable difference due to light transmission efficieny, but it is doubtful that it would be significant enough to register except using extremely small latitude emulsions. I suspect no auto exposure camera system would be sensitive enough to detect this and change the shutter speed. Bill - Bill D. Casselberry ; Photography on the Oregon Coast http://www.orednet.org/~bcasselb [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 . - 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: Advantage of small f/number!
Hallo Yves! Just a few minutes ago, I replied to Bill. You are absolutely right in your point. I know that quite well. The f-number is defined as the ratio of focal length to the diameter of the aperture (Am I correct?). But I am talking about the preliminary intensity of light reaching the film plane because of the wider diameter of the front element in the case of 50 mm f/1.4. Your reply is of course comprehensible. Many thanks for your reply. With best regards, Ayash On Mon, 1 Jul 2002, Yves Caudano wrote: At 20:56 1/7/02 +0530, you wrote: I have some doubts regarding lenses with small f-numbers. Suppose you have two lenses, one is 50 mm f/4 and the other is 50 mm f/1.4. If, I stop down the second lens to f/4, which one will give faster shutter speed for correct exposure? The correct exposure will be obtained with the same shutter speed for both lenses. Actually, that same shutter speed should even give the correct exposure for any lens [*]. This is because f-stops are defined so that this property holds. As a result, for identical f-stops, the actual diameter of the diaphragm will depend on the focal length and the lens design. To go back to your comparison between the two 50 mm lenses, I expect the optical quality of the F1.4 lens to be better at f4 than the F4 lens, though (since you are not pushing your lens to its limits, especially regarding vignetting). [*] assuming infinity focus and (as mentioned earlier by Bill Casselberry) negligible transmission losses. Hope this helps (and is comprehensible), Yves - Dr. Yves Caudano Laboratoire LASMOS Département de Physique Facultés Universitaires Notre-Dame de la Paix 61 Rue de Bruxelles B-5000 Namur Belgium [EMAIL PROTECTED] tel : + 32 (0)81 72 5487 fax : 4707 URL : http://www.scf.fundp.ac.be/~ycaudano/ Lasmos laboratory URL : http://www.fundp.ac.be/sciences/physique/lasmos/ - 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: Advantage of small f/number!
At 23:11 1/7/02 +0530, you wrote: Hi again! You probably sent this mail before receiving my previous answer: I hope this will clarify it anyway. The front element of a 50 mm f/1.4 lens has bigger diameter than a 50 mm f/4 lens. (Am I correct?) Yes Therefore the preliminary amount of light energy reaching an imaginary plane or film behind the lens per unit time per unit area is more than a 50 mm f/4 lens as it has a smaller front element. If the diaphragm is wide open, yes. No, if both lenses are set to the same f-stop. When it is stopped down to f/4, the amount of light reaching the film plane is more than 50 mm f/4 lens. No, because you will close down the diaphragm of the F1.4 lens so that the same amount of ligth will arrive on the film than with the F4 lens with its diaphragm wide open. The additional, outer rays, allowed by the larger front elements of the F1.4 lens are blocked by the diaphragm, so that, eventually, the same amount of light reaches the film. The above explanation depends only on one point that the front element of a 50 mm f/1.4 lens has bigger diameter than 50 mm f/4 lens, if it is at all correct. It depends also on the size of the diaphragm. However, you are absolutely right that f/4 is still f/4 or in other words, the diameter of the aperture at f/4 is identical in both the cases and As a said in my previous mail, the diameter of the aperture at f4 may vary between lenses (especially of different focal length). However, the amount of light reaching the film at f4 is identical from lens to lens (by definition of f-stops, and this is why they are useful!). therefore, the light has to pass through the holes of identical diameters but what I mean to say is that the intensity of light in 50 mm f/1.4 lens is more than a 50 mm f/4 lens. I am writing the following quickly, so take it with a pinch of salt: if the F1.4 has the same design than the f4 lens and just has larger front elements, I indeed would guess that the diaphragm opening of the F1.4 lens at F4 should be the same than the size of the diaphragm of the F4 lens wide open. In other words, I expect that, in that *particular* case, the diaphragm of both lens would have the same diameter when the same amount of light reaches the film. I may be wrong though. However, this would be definitely true for a very simple lens consisting of a single element: in that case, the amount of light reaching the film depends only on the diaphragm size and not on the (larger) lens diameter, since the diaphragm blocks all the outer rays and lets only the rays coming from the lens center in. Closing the diaphragm behind a large lens is then equivalent to take a lens with a smaller diameter. Many thanks for your comments. You are welcome. Yves - Dr. Yves Caudano Laboratoire LASMOS Département de Physique Facultés Universitaires Notre-Dame de la Paix 61 Rue de Bruxelles B-5000 Namur Belgium [EMAIL PROTECTED] tel : + 32 (0)81 72 5487 fax : 4707 URL : http://www.scf.fundp.ac.be/~ycaudano/ Lasmos laboratory URL : http://www.fundp.ac.be/sciences/physique/lasmos/ - 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: Advantage of small f/number!
Hi Yves! Your explanation is absolutely clear to me. So, it is the diaphragm which blocks of the extra amount of light collected by lenses with bigger front element. Yeah! I liked the pinch of salt. I am very much thankful to you and Bill. Now, I am in a position to arrive at the second stage of the drama. I was watching world cup football on TV and there I saw that all the photographers are equipped with small f-number lenses, seemed to be 300 mm f/2.8 kind. They must be shooting at shutter speed of 1/125 th of second in order to stop the action. Now the light in an artificially illuminated stadium is too low. The solution to the problem is to use a fast film and a steady tripod since the focal length is too large to hand hold the set-up. I shall like to know what aperture do they use with what film speed? Do they use those big lenses to take an advantage of f/2.8 or do they always shoot at wide open apertures? (I don't think so as the photographs appear quite sharp with good depth of field (3 m) in the sports magazine) I can put the question in another manner. Suppose I have a 300 mm f/5.6 lens. What film speed should I use in order to stop the action as well as attaining good depth of focus (say, 4 m) in an artificially illuminated stadium? I apologize for this kind of complicated question. I am just inquisitive, that's all. Many thanks for explanation. It cleared a lot of doubts. With best regards, Ayash. On Mon, 1 Jul 2002, Yves Caudano wrote: At 23:11 1/7/02 +0530, you wrote: Hi again! You probably sent this mail before receiving my previous answer: I hope this will clarify it anyway. The front element of a 50 mm f/1.4 lens has bigger diameter than a 50 mm f/4 lens. (Am I correct?) Yes Therefore the preliminary amount of light energy reaching an imaginary plane or film behind the lens per unit time per unit area is more than a 50 mm f/4 lens as it has a smaller front element. If the diaphragm is wide open, yes. No, if both lenses are set to the same f-stop. When it is stopped down to f/4, the amount of light reaching the film plane is more than 50 mm f/4 lens. No, because you will close down the diaphragm of the F1.4 lens so that the same amount of ligth will arrive on the film than with the F4 lens with its diaphragm wide open. The additional, outer rays, allowed by the larger front elements of the F1.4 lens are blocked by the diaphragm, so that, eventually, the same amount of light reaches the film. The above explanation depends only on one point that the front element of a 50 mm f/1.4 lens has bigger diameter than 50 mm f/4 lens, if it is at all correct. It depends also on the size of the diaphragm. However, you are absolutely right that f/4 is still f/4 or in other words, the diameter of the aperture at f/4 is identical in both the cases and As a said in my previous mail, the diameter of the aperture at f4 may vary between lenses (especially of different focal length). However, the amount of light reaching the film at f4 is identical from lens to lens (by definition of f-stops, and this is why they are useful!). therefore, the light has to pass through the holes of identical diameters but what I mean to say is that the intensity of light in 50 mm f/1.4 lens is more than a 50 mm f/4 lens. I am writing the following quickly, so take it with a pinch of salt: if the F1.4 has the same design than the f4 lens and just has larger front elements, I indeed would guess that the diaphragm opening of the F1.4 lens at F4 should be the same than the size of the diaphragm of the F4 lens wide open. In other words, I expect that, in that *particular* case, the diaphragm of both lens would have the same diameter when the same amount of light reaches the film. I may be wrong though. However, this would be definitely true for a very simple lens consisting of a single element: in that case, the amount of light reaching the film depends only on the diaphragm size and not on the (larger) lens diameter, since the diaphragm blocks all the outer rays and lets only the rays coming from the lens center in. Closing the diaphragm behind a large lens is then equivalent to take a lens with a smaller diameter. Many thanks for your comments. You are welcome. Yves - Dr. Yves Caudano Laboratoire LASMOS Département de Physique Facultés Universitaires Notre-Dame de la Paix 61 Rue de Bruxelles B-5000 Namur Belgium [EMAIL PROTECTED] tel : + 32 (0)81 72 5487 fax : 4707 URL : http://www.scf.fundp.ac.be/~ycaudano/ Lasmos laboratory URL : http://www.fundp.ac.be/sciences/physique/lasmos/ - 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
Re: Advantage of small f/number!
Ayash Kanto Mukherjee wrote: You are absolutely right in your point. I know that quite well. The f-number is defined as the ratio of focal length to the diameter of the aperture (Am I correct?). Yep - so the light-gathering of the bigger front element will get funneled down to the same as the f4 when stopped down to f4 But I am talking about the preliminary intensity of light reaching the film plane because of the wider diameter of the front element in the case of 50 mm f/1.4. The intensity of the source doesn't enter into things. Unless it differs between the time you use the f1.4 and the time you use the f4, an autometering system will give the same shutter speed at any given f-stop. Things do look brighter in the viewfinder w/ the f1.4, but when stopped down this disappears. Bill - Bill D. Casselberry ; Photography on the Oregon Coast http://www.orednet.org/~bcasselb [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[2]: Advantage of small f/number!
Hi, Suppose I have a 300 mm f/5.6 lens. What film speed should I use in order to stop the action as well as attaining good depth of focus (say, 4 m) in an artificially illuminated stadium? If your subject is 2m in height then to fill the frame using a 300mm lens you must be 17m away. To achieve a depth of field of about 4m your aperture must be at f/16. On a bright day you can do this with ISO 400 film at 1/500 second. According to Michael Freeman in his book Light all stadiums that have TV coverage use multi-vapour lamps, because these produce a colour quality close to normal daylight. He suggests that for ISO 400 film at 1/60 or 1/125 you will need an aperture of f/2.8. So to achieve a depth of field of 4m your film needs to be rated at 12,800. However, most of the photographers are probably using digital cameras, so these calculations may not apply. For example, a nominal 300mm lens is effectively longer than that, and the f-stop ratio is changed, so there may be more depth-of-field than I've indicated. These numbers are for 35mm. --- Bob mailto:[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: Advantage of small f/number!
Hi! I understand your point quite well now. I liked the term funneled down that you used in your explanation. Many thanks, Bill. With best regards, Ayash. On Mon, 1 Jul 2002, Bill D. Casselberry wrote: Ayash Kanto Mukherjee wrote: You are absolutely right in your point. I know that quite well. The f-number is defined as the ratio of focal length to the diameter of the aperture (Am I correct?). Yep - so the light-gathering of the bigger front element will get funneled down to the same as the f4 when stopped down to f4 But I am talking about the preliminary intensity of light reaching the film plane because of the wider diameter of the front element in the case of 50 mm f/1.4. The intensity of the source doesn't enter into things. Unless it differs between the time you use the f1.4 and the time you use the f4, an autometering system will give the same shutter speed at any given f-stop. Things do look brighter in the viewfinder w/ the f1.4, but when stopped down this disappears. Bill - Bill D. Casselberry ; Photography on the Oregon Coast http://www.orednet.org/~bcasselb [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 . - 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[2]: Advantage of small f/number!
Hi! It is quite an informative email. I never knew the details of the lighting in a stadium until I recieved your mail. On Mon, 1 Jul 2002, Bob Walkden wrote: Hi, According to Michael Freeman in his book Light all stadiums that have TV coverage use multi-vapour lamps, because these produce a colour quality close to normal daylight. He suggests that for ISO 400 film at 1/60 or 1/125 you will need an aperture of f/2.8. So, it means that 400 ISO film is not enough. One has to use atleast 1600 ISO film provided that the lens in use is 300 mm f/5.6. So to achieve a depth of field of 4m your film needs to be rated at 12,800. I am shattered. However, most of the photographers are probably using digital cameras, so these calculations may not apply. For example, a nominal 300mm lens is effectively longer than that, and the f-stop ratio is changed, so there may be more depth-of-field than I've indicated. These numbers are for 35mm. Aah! those DIGI-guys are always at an advantage but I don't want to go DIGI. Many thanks for your comment. With best regards, Ayash. - 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: Advantage of small f/number!
Hi Joe! So, you mean that professional photographer are shooting all the time at f/2.8 and hence they possess those lenses becuase they really need that aperture only. Yes, you are right that a monopod will make the life much easier under such situation. Many thanks for your helpful comments. With best regards, Ayash. On Mon, 1 Jul 2002, Joseph Tainter wrote: In regard to shooting a teletphoto lens in a stadium. I would recommend investing in a monopod to steady your shots. With a monopod you can gain 1 or 2 EV over hand-held. For example, a 300 mm. lens should be shot at 1/350. With the monopod, you might go to 1/180 or even 1/90. If the professional photographer with an f2.8 lens shoots 1/350 at f2.8, you could shoot 1/90 at f5.6 and save a great deal of money (that is, by buying an f5.6 lens rather than one that opens to f2.8). Joe - 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: Advantage of small f/number!
Hi Giafranco! I visited the websites that you have mentioned and can understand the position from where you took the shot. I was suspecting from the beginning that it should be some sort of hilltop because the skycrappers in your photograph look small but I never knew that there is castle with rich history. A great view as if you are on the top of the world and can see rest of the world. I can feel the sensation when somebody goes at such a place. As far as the 50 mm lens problem is concerned, I have understood well now. So, I won't feel much sorry, if I don't have a small f-number lens. Or should I feel sorry? Am I missing something? Thank you so much for such a nice and informative reply. With best regards, Ayash. On Mon, 1 Jul 2002, Gianfranco Irlanda wrote: Hi Ayash, I took the picture from one of the windows of Castel Sant'Elmo, which is one of the four castles of Naples, the only one built on the hill. Built during the 16th Century on the site of a former, smaller, castle, Castel Sant'Elmo became a prison in the 18th Century until the 1952. It is now a museum and there is kept the photographic archive of the Cultural Superintendence of Naples. You can see many pictures of the castle at: http://progetti.webscuola.it/progetti2000/790/CastelSantElmo.html Too bad the page is in Italian only, but you can clearly see the vault windows I took the picture from. There's a nice but small picture at: http://www.medcruise.com/napo/f01_napo.html The castle is the higher building on the background. The view I took is from the right side (facing NE). I have some doubts regarding lenses with small f-numbers. Suppose you have two lenses, one is 50 mm f/4 and the other is 50 mm f/1.4. If, I stop down the second lens to f/4, which one will give faster shutter speed for correct exposure? The speed will be the same, if you don't change anything: if you compare f/4 of both lenses you'll see that the area enclosed into the diaphragm of the stopped down f/1.4 lens is the same of the aperture of the f/4 lens wide open. Ciao, Gianfranco = Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com - 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 .
