Diffraction Question

[Jack Lusted]

I've just got around to printing up a macro shot and I'm a little disappointed as it is not as sharp as it ought to be.

Equipment - Mamiya C330 with 80mm lens
Magnification ~75%
Exposure 2s @ f:22
film Ilford delta 400, dev in X-tol 1:1

Naturally the set up was properly supported on a good tripod.

My question is - by using the small f:22 stop to increase depth of field did I inadvertently introduce a noticeable diffraction effect sufficient to to take the edge of the sharpness? Would the image have been sharper had I used f:8?

Thanks for any feedback.

Jack

[keithwms]

At what enlargement are you printing the image? If you are only enlarging a factor of say 3-5 or so and seeing softness then I doubt diffraction is your issue. Yes you will have some at f/22 but it really shouldn't be a shot killer in medium format. Can you post an example?

A couple basic questions (which I hope are not insulting!): is the neg itself sharp under loupe? Is it held flat in the enlarger? Is the enlarger well aligned? Are you stopping down the enlarging lens excessively?

P.S. One clue about diffraction softness is that it will affect the whole image pretty much equally, whereas many other sources of fuzz won't... that might help you diagnose the problem.

[Jack Lusted]

Keith,
Thank you for replying.
I'm enlarging the neg about 5-6 times.
I don't have a strong lupe, so the neg looks okayish - it's a bit too soft for my liking and it could have done with a stop more exposure.
The enlarger is fine optically, properly aligned and pretty solid.
Lens stopped down to f;11 for exposure.

I hope that I've managed to attach a scan of the print.

Jack

[keithwms]

Jack, you did manage to attach a scan! And I don't see any softness issues on my monitor. It'd be pretty hard to diagnose a problem, if there is one, unless you zoom in much more on the scan. But what I see looks fine.

A couple stray thoughts...

*Perhaps you might run the neg through KRST- it might give you a bit more tonal contrast; my assessment of the deltas is that they do tend to produce slightly soft-n-dreamy edge contrast, compared to the traditional b&ws. In my experience, if you go from a trad. grain film to a delta you might at first feel like sharpness is lacking. In my opinion, it isn't that the film is inherently less sharp, it's that it has less edge 'bite' so to speak.... If you want the appearance of more edge sharpness then you might consider fp4+ or hp5+.

*I'm not familiar with your lens and can't say offhand whether it is sufficiently optimized for close focus. This might be an issue but I would think it'd give you disappointing sharpness toward the edges, not across the whole image.

Again, I can't make out any issues in your attachment, really. I think it works well as is.

[Q.G.]

Stopping down as far as possible in pursuit of DOF is indeed not a very good idea.
It will indeed reduce sharpness visibly.
But not increase DOF by enough to be useful.

[ic-racer]

Originally Posted by Jack Lusted

I've just got around to printing up a macro shot and I'm a little disappointed as it is not as sharp as it ought to be.

Equipment - Mamiya C330 with 80mm lens
Magnification ~75%
Exposure 2s @ f:22
film Ilford delta 400, dev in X-tol 1:1

Naturally the set up was properly supported on a good tripod.

My question is - by using the small f:22 stop to increase depth of field did I inadvertently introduce a noticeable diffraction effect sufficient to to take the edge of the sharpness? Would the image have been sharper had I used f:8?

Thanks for any feedback.

Jack

Simple answer = YES

The amount of diffraction will be related to your calculated relative aperture from your 'bellows extension', so your f22 was really much smaller.

[Jack Lusted]

Keith,
Again, thank you for your comments.
Somehow the scan does seem to have sharpened things up a bit.
I'll give the negs a go in selenium toner - that certainly seems a good idea.
Previously I've tended to use HP5+ so your point about the deltas is well taken - it might be that and slight under exposure that may be the issue.

Jack

[Jim Noel]

I suspect you neglected to take into account that lenses used at this magnification have a bellows factor to be considered. Most people only think of this for large format cameras,but it does come into play on the Mamiya twin lens cameras when the bellows is racked out for close ups.
Using this factor your effective aperture is somewhere around f32-f45 (I'm not in the mood to do the math work before breakfast). This would cause not only the under exposure to which you refer, but also is more likely to get you into the realm of diffraction.
There is a scale on the side of the Mamiya to help you compensate for the bellows.

[ic-racer]

Just another note on the diffraction/DOF problem. As you increase you film format size (for the same size 'macro' subject mater) you are in a LOOSE-LOOSE situation with diffraction and DOF!

This (macro and micro photography) may be one field where the eventual development of small sensor technology will favor the 'Dark Side'

[Q.G.]

Originally Posted by ic-racer

Just another note on the diffraction/DOF problem. As you increase you film format size (for the same size 'macro' subject mater) you are in a LOOSE-LOOSE situation with diffraction and DOF!

This (macro and micro photography) may be one field where the eventual development of small sensor technology will favor the 'Dark Side'

Well...
There are two ways to aproach photomacrography.

One is the 'frame-drive' approach, thinking of a frame as something to fill as its first goal.
Then you do indeed need higher magnification (= less DOF, but not necessarily more diffraction - depends on how much you stop down, of course) when switching to larger formats.

The other is the 'magnification-driven' approach, having a certain scale, and with it a certain level of detail, as its goal.
In this approach, larger formats mean more 'real estate' to fit the subject in.
Since DOF depends on magnification, not on format size, you do get the same DOF (assuming same f-stop). Diffraction then too does not change.