M8 Expectations

[j. borger]

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With landscapes in general you want as much in focus as possible (front to back).

If that is the goal and you shoot at f8 ....... set infinity marker at f 5,6 ......

Because if you set the infinity marker at f 8 .... you do not have enough dof in the far distance (due to cropfactor ,,). On the other hand: if you focus at infinity with the focus pad ... you loose unnecessary dof in the foreground (which might or might not be a problem depending upon the lens and how far you shoot into the scene).

Just experiment from here as Rob states ....!

[jlm]

so why aren't we seeing diffraction in the large format images of the f64 school: Weston and Adams, for example, where f16 was considered wide open; is it a matter of final enlargement? an Adams 16x20 print from 4x5 is a 4x enlargement; that 4x would be a pretty tiny print from the M8, eh?

[jaapv]

Because those lenses were a whole lot longer for a considerably larger format.

That means the aperture opening was magnitudes larger than with our teeny weeny lenses, so they were not small enough to "bend "the light.

[jlm]

jaapv:

I found this, which says something different:

Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

at the very bottom:

 

Technical Note:

 

Since the physical size of the lens aperture is larger for telephoto lenses (f/22 is a larger aperture at 20 mm than at 100 mm), why doesn't the size of the airy disk vary with focal length? This is because the distance to the focal plane also increases with focal length, and so the airy disk diverges more over this greater distance. As a result, the two effects of physical aperture size and focal length cancel out. Therefore the size of the airy disk only depends on the f-stop, which describes both focal length and aperture size. The term used to universally describe the lens opening is the "numerical aperture" (inverse of twice the f-stop). There is some variation between lenses though, but this is mostly due more to the different design and distance between the focal plane and "entrance pupil."

[jaapv]

That is about telelenses and an unchanging format. The long lenses used on view cameras are of long focal length, but in relation to the film size, normal lenses. A different situation than what this quote refers to.

[jlm]

so it really is about the ratio of enlargement, as f22 on any size lens and any size format will produce the same size Airy disc and the diffraction limt is defined as when the Airy diameter exceeds the circle of confusion. the coc is all about enlargement to the final viewing size.

[jaapv]

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The ratio of enlargement on a 8x10 negative is a lot less than on a 36x24 one, having huge impact on the coc, if one postulates the same size of print. I'm too tired after a hard days work to plough through all the maths, but I'm sure that explains the abilty of large format lenses to have their diffraction limit at smaller apertures.