P�l Jensen wrote:
>
> Isaac wrote:
>
> > It's easy, you can't change a lens' illumination angle. Coverage of a
> > lens is defined by its illumination angle, not the size of the circle of
> > illumination. If what you say above is true, I should be able to shoot
> > 8x10 film with my SMC 50mm f1.4, and I can't... The angle of
> > illumination is set by the design of the lens, along with its
> > resolution, distortion, etc... The resolution of a given area inside of
> > the circle of illumination, at a given size (i.e. at a given focusing
> > distance) will remain constant no matter what size of film you project
> > that image onto. If you change the focusing distance (increasing the
> > size of the image circle), the resolution can indeed go down, but for
> > other reasons involving the reproduction ratio...
> > As you point out, the larger formats rarely need to have as high a
> > resolution, so the designers do not put the extra expense into the
> > lenses typically, but it is theoretically possible to design a lens for
> > 8X10 that will have as good a "resolution" inside of 24x36 as a good
> > 35mm lens.
>
> I certainly agree but was not exactly what I meant with my admittedly rather bad
>example. When designating equal lenses (MF and 35mm) I was thinking of overall
>performance. Eg the two lenses projects the same information content (total number of
>lines for instance) but on circles with different size. These lenses will then have
>the same resolution and be equally sharp on the finished product; eg a 8X10 print.
>This what I mean with the same quality. An MF lens with the same l/mm as a 35mm
>system lens can resolve a hell of lot more information in total than the 35mm system
>lens simply due to the larger area of the MF lens. Or in another way, a MF lens
>doesn't need the same resolving power as a 35mm lens to appear equally sharp on a
>reproduction of a certain size.
Right, but that's not what the thread is about... I think... We were
talking about the lenses, not how much the film can resolve. If you take
in the same angle of view in both 35mm and medium format, odds are that
the medium format image will contain more information just because of
the density of info on the bigger neg. I thought that we were talking
about putting a medium format lens on a 35mm body. In that case the
medium format lens will resolve the same as it ever did, just over a
smaller area.
> If a lens have a certain l/mm it will be constant regardless of format. But I won't
>say that l/mm are equal comparable issues when comparing 35mm and MF lenses. For the
>same angle of view a MF lens and a 35mm lens with the same l/mm the MF lens resolves
>a hell of a lot more in finished photograph because theres a hell of a lot of more
>mm's on a MF negative/positive. Hence, whats constitutes a good MF lens is something
>different than whats a good 35mm lens.
But not if they're both on a 35mm body... Once again, you are right
about there being fewer resolution demands put onto a medium format lens
(for the same amount of enlargement) when taking medium format pictures,
but a lens' performance does not decrease just because you switch
cameras. A lens will always perform the same weather its on a 35mm
camera or medium format camera. Theoretically, if you wanted to see how
your MF lens performs on 35mm, just crop out a 24x36 area from the
center of your image...
This is probably the core of the issue. As you say it is possible to
design a LF lens to be equally good as a 35mm but I wonder if it is
common or even viable on a consistent basis.
No on both counts I'm afraid... I only jumped in because it sounded
like you were saying that a lens' performance would somehow decrease
just by switching cameras. I think we both agree that in practical terms
MF optics just aren't as good over a 24x36 area...
Isaac
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