Image circle too large?

[Jac@stafford.net]

You guys! Water, pipeline as analogies? Come on.

CoC is not inherent in the medium, lens or anything else. It is what a person chooses to use as a metric to determine how much fidelity is determined by degrees of enlargement.

[Theodoros]

If they are the same and one is spread over a greater area then the exposures will be different. Are they? Simple to test with a digital back.

Yes it will be the same... the supply depends on the pipe diameter and the time the pipe is active... The surface size doesn't change either as to alter reception of supply per area... only the distance of the surface from the pipe's mount changes... if you collect the liquid is of the same amount... and since the reception surface is of constant size in both cases, you'll have the same amount of liquid on it if you evenly distribute it on the surface (which is the lens design job)... It's the distance from the entrance pupil that will alter the DOF though... It's then back in physics (from engineering) distances change, so magnitudes change in proportion too... Think of vignetting, the more the image circle the less of it... isn't it?

[Theodoros]

You guys! Water, pipeline as analogies? Come on.

CoC is not inherent in the medium, lens or anything else. It is what a person chooses to use as a metric to determine how much fidelity is determined by degrees of enlargement.

Only if you use an enlarger... which then reverses the process of capturing and thus reverses the image circle projected from the capturing process (the larger IC is projected as smaller and the smaller IC as larger for the same size print)... It's not the same if you print from an image sensor (or a per area scanned film).... Then the mounting distance difference is the only truth you are left with...

EDIT: ...and the lens resolution of course...

[Argentum]

so you're saying the image circle is the same for both lenses but the DoField is different?

[Theodoros]

so you're saying the image circle is the same for both lenses but the DoField is different?

It's not what I'm saying, but it can be also true if the position of the entrance differs... Don't expect dramatic differences though... it is a proportional change... but it is there.

[Jac@stafford.net]

Only if you use an enlarger... which then reverses the process of capturing and thus reverses the image circle projected from the capturing process [...]

Oi! Your mental gymnastics could drive a man to drink! Thank you for that. Carry on. I'll shut down and have a bourbon.

[Argentum]

I still want to know about the difference between your Fuji GX680 210/5.6 which if I'm not mistaken is designed with a larger image circle to cope with anticipated tilts and shifts which your Zeiss Contax 210/4 isn't. So my question still stands, has your fuji lens had its aperture modified to maintain expsoure across different lenses or is its aperture a true ratio of the focal length.

[Theodoros]

I still want to know about the difference between your Fuji GX680 210/5.6 which if I'm not mistaken is designed with a larger image circle to cope with anticipated tilts and shifts which your Zeiss Contax 210/4 isn't. So my question still stands, has your fuji lens had its aperture modified to maintain expsoure across different lenses or is its aperture a true ratio of the focal length.

I don't understand the question... my Fuji 210 never had any modification... why should it? Distribution of light is (supposed to be) even across image areas no matter the size of them... for equal image areas you get the same amount of light distributed despite the lens image circle, the rest is (supposed to be) lost or absorbed! (although it "passes" through the lens) So why modify it? ...The entrance pupil of the lens is positioned at a significantly larger distance from the image area and this causes DOF to be shallower...

[Argentum]

I'm telling you that if your lens is spreading the image across a wider area it affects the exposure. The inverse square law states this. It is a physical law which you can't ignore. The lens designer can do one of two things. They can ignore it which means if you do a side by side test, your fuji lens will require a longer exposure than your contax lens or they can tweak the lens aperture so that although it actually says F8 its actually giving somewhere between 5.6 and f8. And that would result in your fuji lens and your contax lens giving the same exposure at f8 even though your fuji lens is actaully using a slightly wider aperture. I want to know which is the case for your fuji lens. If its the latter then you are not comparing f8 with f8 when you are talking about different DoField. You can easily test this by framing and focusing same area on your digital back with both lenses and seeing if required exposures are the same of if the fuji requires a longer exposure or not. If it requires longer exposure then apertures are probably very close. But if it requires same expsoure then i am saying its aperture will actually be wider than f8. The physics says so. Do the test.
A lens of any focal length has a fixed field of view so one lens can not capture more light than another of the same focal length at the same aperture (excepting glass absorption but we'll ignore that for now).

[Theodoros]

I'm telling you that if your lens is spreading the image across a wider area it affects the exposure. The inverse square law states this. It is a physical law which you can't ignore. The lens designer can do one of two things. They can ignore it which means if you do a side by test your fuji lens will require a longer exposure than your contax lens or they can tweak the lens aperture so that although it actually says F8 its actually giving somewhere between 5.6 and f8. And that would result in your fuji lens and your contax lens giving the same exposure at f8 even though your fuji lens is actaully using a slightly wider aperture. I want to know which is the case for your fuji lens. If its the latter then you are not comparing f8 with f8 when you are talking about different DoField. You will can easily test this by framing and focusing same area on your digital back with both lenses and seeing if required exposures are the same of if the fuji requires a longer exposure or not. If it requires longer exposure then apertures are probably very close. But if it requires same expsoure then i am saying it aperture will actually be wider than f8. The physics says so. Do the test.

Aaaah... I now see what you are getting at... Well no... it doesn't work like this, you see when focal length is constant and aperture the same, your pipe's mouth is the same but the liquid entering has more pressure as to supply more liquid for the larger image circle... (sucks more, spits more ) It's only that the rest than what concerns the image area is lost... (thrown to garbage)... What you are left with is with a pipe that supplies the same pressure (in proportion) for only the image area but is positioned further apart....