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Macro, apertures, sharpness and diffraction questions in Medium Format

Overread 9 4.1k 19 England
4 Oct 2011 5:28PM
So I've got a Mamiya RB67 Pro-S somewhere in the post on its way to me and I'm keen to experiment with its use within macro areas. However I'd like to see if I can save myself a roll of film and pick some peoples minds with regard to how the optics behave with this camera with regard to the limitations on sharpness with regard to diffraction.

In short if anyone has any ideas as to how far I can stop the lenses down before softening starts to affect the final image, both with and without extension tubes, I'd be very grateful.

For reference these are the lenses in the post on their way to me:
Lenses 90mm f/3.8, 50mm f/4.5, 180mm f/4.5,
tubes: Mamiya No.1 and No.2

With some light reading and research it seems that the 90mm and 180mm will be the better choices since the 50mm might well show distortion/blurring/softening of the corners with the extension tubes added.

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User_Removed 8 4.6k 1 Scotland
4 Oct 2011 6:51PM

I'd suggest starting to experiment with the 180mm lens.

But bear in mind that, with a 6x7 negative, sharpness (or lack of it) is much less of a problem than with 35mm (or digital) - basically because you are going to be "enlarging" the image less to arrive at your desired size of print. It is one of the huge advantages of medium format.
User_Removed 8 4.6k 1 Scotland
4 Oct 2011 6:56PM
....also remember that you can experiment quite freely with both lenses and film types.

You have three lenses and three film holders. You can change the lenses in a single roll of film and you can change the films without having to finish one roll before trying another.

One word of caution - if you are not going to be doing your own film developing, try to find a reliable film processor. Some are much better than others. (Unfortunately it seems to relate to cost). Loxley Colour are good. Also, if you are going to use a commercial scanning service, the same applies. Once more Loxley are p[ossibly the best (but pricey).
Overread 9 4.1k 19 England
5 Oct 2011 12:00AM
Oh aye I'll expect a lot of my early shots are going to be little more than experiments, just the whole film process itself will be new to me so its certainly got a lot of scope for messing around with it to get comfortable.

On the developing front from what I've been glancing at its not too hard to have negative developing done at home, though chances are I won't go down that rout until I can afford a good scanner to also do home scanning. Probably be a fairly largish investment (espon V-700 is talked about) but certainly worth it in the long run at keeping costs down at least on the day to day type processing.
LenShepherd 10 3.6k United Kingdom
6 Oct 2011 3:38AM
ephotozine do regular reviews that show with 24x36 format f16 optical performance is often no worse than f4 and f22 often still rates good - diffraction can be a much overrated "bogey".
At medium and longer focus distances with medium format 6x7 you gain an 2-3 stops before diffraction starts to be a resolution limiting problem. On the other hand, depending on lens construction and the method of achieving close up, 1:1 image size can cause diffraction to become an issue 1-2 stops faster.
Another issue is dealing with camera shake. Going closer is the same as using longer lens in that the effect of camera shake increases - by as much as 3-4 shutter speeds by 1:1 on 6x7. Mirror's on 6x7 can have a fair bit of vibration too. How you shoot to control camera shake and mirror vibration is perhaps a bigger issue than whether you can safely go to f16 or f22 at 1:1 and still get very good resolution.

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