Since I am new to Large Format photography I have been reading and studying day and night. Of course one of the factors that I paid attention to while putting together my gear was the size of the Image Circle of the Lenses I was choosing. Color,Contrast, and Sharpness were also a concern.
I have been wondering on how the F stop selected affected the size of the Image Circle projected on the Film Plane. So I started looking for information on how to Calculate the Image Circle Size. Since I noticed when looking at lens specs that the manufacturers all seem to spec their lenses Image Circles at F 16 or F 22 I started to wonder what size are the Image Circles at F 4.5, 5.6, 8, 32, 45, or even F 64? Do image circles get progressively larger as you stop down and progressively smaller as you open up the lens? This might seem like a very simple question for some but also its a complicated one for someone like me who is new and might not understand yet how everything works. I certainly did not want to ruin an image because I did not stop down my lens enough to get a large enough Image Circle for coverage, and at the same time, I did not want to limit the F Stops that were usable with particular lens on my camera.
After a little searching, I found that Schneider Optics posted in one their FAQs that the Image Circle size does not really change. They claim that what happens is that the distribution of light changes as the F stop is changed on the lens. For example if I take my 75mm 4.5 Nikon SW Lens, and open it all the way up to 4.5 the brightest part of the lens is the center and the light hitting the edges of the projected Image Circle is diminished in intensity compared to the center. Of course my conclusion from this is that the wider the lens the bigger problem this would be based on the curvature of the glass and design of the lens.
So based on my long winded post, I am wondering how important it would be to know the size of your Image Circle for each F Stop of your lens?
I also understand that as you stop down your sharpness is also affected, so I am wondering how you know at what point, F stop, Image Circle Size, that the sharpness degrades for any particular lens?
All answers would be appreciated.
Thanks
Jason
I have been wondering on how the F stop selected affected the size of the Image Circle projected on the Film Plane. So I started looking for information on how to Calculate the Image Circle Size. Since I noticed when looking at lens specs that the manufacturers all seem to spec their lenses Image Circles at F 16 or F 22 I started to wonder what size are the Image Circles at F 4.5, 5.6, 8, 32, 45, or even F 64? Do image circles get progressively larger as you stop down and progressively smaller as you open up the lens? This might seem like a very simple question for some but also its a complicated one for someone like me who is new and might not understand yet how everything works. I certainly did not want to ruin an image because I did not stop down my lens enough to get a large enough Image Circle for coverage, and at the same time, I did not want to limit the F Stops that were usable with particular lens on my camera.
After a little searching, I found that Schneider Optics posted in one their FAQs that the Image Circle size does not really change. They claim that what happens is that the distribution of light changes as the F stop is changed on the lens. For example if I take my 75mm 4.5 Nikon SW Lens, and open it all the way up to 4.5 the brightest part of the lens is the center and the light hitting the edges of the projected Image Circle is diminished in intensity compared to the center. Of course my conclusion from this is that the wider the lens the bigger problem this would be based on the curvature of the glass and design of the lens.
So based on my long winded post, I am wondering how important it would be to know the size of your Image Circle for each F Stop of your lens?
I also understand that as you stop down your sharpness is also affected, so I am wondering how you know at what point, F stop, Image Circle Size, that the sharpness degrades for any particular lens?
All answers would be appreciated.
Thanks
Jason
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