Hi, I’m adapting 35mm format lenses for use on a view camera. I’m interested in capturing the full image circle of the lens. From my tests I find most lenses in the 28-50mm range produce a circle somewhere between 52 and 60mm at infinity. The image circle calculator here generally comes up with a figure of around 43mm. For instance my 35mm 3.5 Pentax has a stated angle of view of 63 degrees, this gives 43.27 on the calculator, however I measure 54mm on the negative, is there a reason for the discrepancy? I’m not expert and it’s quite possible I’ve misunderstood something. I’m looking for lenses that will fit 120 film, most are okay at infinity but close focus is more of a problem. Thanks. M.
Hello, lenses are normally designed to go beyond the frame they are intended for in their data sheet. It is not an sharp image drop down at the frame’s corner. So it is normal to find a “surplus of image” when you install it on a camera that has a larger frame, compared to the camera that lens maker originally specified the lens to be fitted on. In every lens, as you go from center to the image’s borders, there is an image degradation. Then, image size has to do also with how much degradation one is ready to accept. Some lens makers more strict in this respect and although the lens actually produces an image beyond the minimum that is needed to cover a specific full frame, around 43mm in the case of 35mm film, they do not consider that extra border acceptable and do not advertise, for instance, that it would also do medium format or something alike. Beyond image degradation, at a certain distance from center, there won’t be any kind of image, good or bad, because that is simply out of reach for light passing through the lens and hence it is completely black.
The calculator in this page addresses more the opposite situation, that is when you know the image circle (maybe through the more readily available info that is the angle of view) and then you check here whether it will cover or not a certain format you have in mind for that lens by calculating the diagonal of that format.
Hi, Thanks for your reply. What you say makes perfect sense. I was hoping the angle of view given by manufactures would be for the full cone of light because that is what I was looking for, however the angle given is that which matches the intended format hence the formula gives, in almost all cases, 43mm as the image circle for a 35mm format lens, I wonder in what situation this information be of use? Of course it does make sense to know the image circle for shift lenses or large format using movements.
I would love to use 5×4 which would allow more options but it’s just to expensive for colour film and processing.
The lens makers want to say something like “up to this format, or image circle, I guarantee an evenly illuminated and sharp image”. The cone of light is larger than that, but in that region is up to the user to access whether the image quality is good enough or not. Normally it becomes blurred and dimmer. But for sure, for certain aesthetic purposes, it can be explored as something interesting.
Yes, and it’s indeed the ‘something interesting’ that I’m enjoying exploring. If I may I have technical question. I’ve tried lenses made for the Pentax Auto 110 these as expected have a smaller image circle than lenses for 35mm. As you will know these lenses have no aperture – it’s fixed at f2.8. I believe the camera’s shutter was programmed to also act as the aperture. Can you give some insight into the effect of putting the diaphragm behind the lens? Obviously this strategy can work as it was used by Pentax and it’s something on my list of things to experiment with – I would mount the Pentax lens in front of a Copal shutter.
The position of the diaphragm is something important. It not only reduces the general amount of light, but it is planned to do so discarding, in priority, the worst part of light, the one that introduces more aberrations. Some landscape lenses, at the beginning of photography, had it in front of the lens. Most of modern lenses have it somewhere between the glasses. The Pentax 110 has it working as a shutter (as you mentioned) and being in the camera body, it is behind the lens. But I don’t know if that feature called for any special lens design. What I know is that this is quite unusual. But considering that this is the “official” diaphragm placement for those lenses, at this particular aspect, you are good to go with your experiment.
Thanks for your reply, the outcome of such experiments is to ask myself; have I made a compelling image? Or, if not; is the direction of travel promising? I found reading the essays elsewhere on the site time well spent, there are many interesting insights into the nature and history of the photographic image.
Very useful calculator. Thank you, Wagner.
Hi, I’m adapting 35mm format lenses for use on a view camera. I’m interested in capturing the full image circle of the lens. From my tests I find most lenses in the 28-50mm range produce a circle somewhere between 52 and 60mm at infinity. The image circle calculator here generally comes up with a figure of around 43mm. For instance my 35mm 3.5 Pentax has a stated angle of view of 63 degrees, this gives 43.27 on the calculator, however I measure 54mm on the negative, is there a reason for the discrepancy? I’m not expert and it’s quite possible I’ve misunderstood something. I’m looking for lenses that will fit 120 film, most are okay at infinity but close focus is more of a problem. Thanks. M.
Hello, lenses are normally designed to go beyond the frame they are intended for in their data sheet. It is not an sharp image drop down at the frame’s corner. So it is normal to find a “surplus of image” when you install it on a camera that has a larger frame, compared to the camera that lens maker originally specified the lens to be fitted on. In every lens, as you go from center to the image’s borders, there is an image degradation. Then, image size has to do also with how much degradation one is ready to accept. Some lens makers more strict in this respect and although the lens actually produces an image beyond the minimum that is needed to cover a specific full frame, around 43mm in the case of 35mm film, they do not consider that extra border acceptable and do not advertise, for instance, that it would also do medium format or something alike. Beyond image degradation, at a certain distance from center, there won’t be any kind of image, good or bad, because that is simply out of reach for light passing through the lens and hence it is completely black.
The calculator in this page addresses more the opposite situation, that is when you know the image circle (maybe through the more readily available info that is the angle of view) and then you check here whether it will cover or not a certain format you have in mind for that lens by calculating the diagonal of that format.
Hi, Thanks for your reply. What you say makes perfect sense. I was hoping the angle of view given by manufactures would be for the full cone of light because that is what I was looking for, however the angle given is that which matches the intended format hence the formula gives, in almost all cases, 43mm as the image circle for a 35mm format lens, I wonder in what situation this information be of use? Of course it does make sense to know the image circle for shift lenses or large format using movements.
I would love to use 5×4 which would allow more options but it’s just to expensive for colour film and processing.
The lens makers want to say something like “up to this format, or image circle, I guarantee an evenly illuminated and sharp image”. The cone of light is larger than that, but in that region is up to the user to access whether the image quality is good enough or not. Normally it becomes blurred and dimmer. But for sure, for certain aesthetic purposes, it can be explored as something interesting.
Yes, and it’s indeed the ‘something interesting’ that I’m enjoying exploring. If I may I have technical question. I’ve tried lenses made for the Pentax Auto 110 these as expected have a smaller image circle than lenses for 35mm. As you will know these lenses have no aperture – it’s fixed at f2.8. I believe the camera’s shutter was programmed to also act as the aperture. Can you give some insight into the effect of putting the diaphragm behind the lens? Obviously this strategy can work as it was used by Pentax and it’s something on my list of things to experiment with – I would mount the Pentax lens in front of a Copal shutter.
The position of the diaphragm is something important. It not only reduces the general amount of light, but it is planned to do so discarding, in priority, the worst part of light, the one that introduces more aberrations. Some landscape lenses, at the beginning of photography, had it in front of the lens. Most of modern lenses have it somewhere between the glasses. The Pentax 110 has it working as a shutter (as you mentioned) and being in the camera body, it is behind the lens. But I don’t know if that feature called for any special lens design. What I know is that this is quite unusual. But considering that this is the “official” diaphragm placement for those lenses, at this particular aspect, you are good to go with your experiment.
Thanks for your reply, the outcome of such experiments is to ask myself; have I made a compelling image? Or, if not; is the direction of travel promising? I found reading the essays elsewhere on the site time well spent, there are many interesting insights into the nature and history of the photographic image.
I am glad to hear that!! Good luck with your projects!!