Hello,

I am moving from 4x5 and 8x10 film to using a Leaf Aptus 65 on a Arca Swiss 6x9 and will be purchasing a 45mm lens and something around a 90mm to 100mm and have some questions.

1. Why are digital lens optimized for f/8 - f/11 apetures, and how will stopping down a digital lens to
f/16 - f/22 effect image quality on a digital back? Does this change result from a change in lens quality or something to do with how a digital back records an image? Would the effect be the same on a 100mm lens as a 45mm lens? If I will be using a lens predominantly in the f/16 - f/22 range, should I buy a film lens instead of a digital lens?

2. If I want to stitch exposures together by shifting the camera back, would a film lens with a much wider image circle be preferable (say a Rodenstock 100mm Sinar-S compared to their 105mm digital lens) or would a digital lens still have advantages?

Thanks for any information or links to information anyone can provide.

Drew Harty

The anwer to all of these questions is TRY before you BUY !

Small apertures.

A small chip has more depth of field than a 54 film so f8/11 may give you the DOF you are after if you are used to 22 at 54 film

There is a phenomenon called diffration which mean lenses can soften at small apertures where the size of the hole is close to the length of the wavelength of light or some such techno gabble so f22 may not be very sharp

In terms of the image circle/digital lens question here is my experience

At 47 the digitar is required as non digitars go a bit funny at the edges (I was trying for postbox shaped - two landscapes stitch)

At 100 'film' lenses seem fine

SO I have a 47 Digitar and a 100 vintage schneider - I sent the 45 non digitar back

SMM

There are several web sites which provide calculators for determining diffraction. Here is one which also explains the whole concept.

http://www.cambridgeincolour.com/tutorials...photography.htm

With a MFDB, printing to moderate sizes, the lenses are diffraction limited at around F11.

If you print smaller, you can stop down more (because the diffraction will be less apparent).
If you use larger film, the same holds true.

The lenses designed for 645 are optimized at F11 or F16 because, beyond that, they are diffraction limited.

The lenses designed for 4x5 can be optimized for F22 or F32 because, beyond that, they are diffraction limited.

The real upside to this, is that the strobe equipment weighs half as much to get the same focus.

The cambridge color site was very interesting and answered all my questions.

Contrary to what I would have thought, it appears that working with a 45 mm lens on a MFDB will have less DOF at the lens defraction limits than working with the equivalent 125mm lens at its defraction limits on 4x5.

Thanks for the info,

Drew