Macro and diffraction with 1.6 crop, causing soft/OOF shots?

[Laramie]

So I'm playing around with some macro. I'm using my 40D since it has liveview and should produce the greatest depth of field out of my 3 bodies. I'm using a 100mm macro and Tamron 1.4x. In the range from f22-f32 I'm getting really soft shots even though it really looks like I'm in focus on the screen/in viewfinding.

Does the 100mm on a crop cam have a aperture sweet spot?

[sandpiper]

Diffraction will certainly be starting to kick in at such small apertures. TCs also cause a little softening, so you're getting a double whammy.

[Laramie]

Here's a 100% crop, 100mm with 50mm 1.4 reversed, no TC. Still seems soft. Maybe I need tubes for the 100 instead of the reversed 50?

http://i49.photobucket.com/albums/f282/tylerpebley/IMG_7428.jpg

[LordV]

Diffraction starts to get really noticeable around F11 at 1:1 and gets exponentially worse smaller than that. It also gets worse with higher mags and as commented above you will lose some IQ with the TC. Other things like camera movement obviously can contribute to lack of image sharpness. Suggest you try some comparison shots at F8,F11, F16 and F22 and draw your own conclusions. I'm assuming you are using full flash for the shots to negate camera shake ?

AFAIK the diffraction issues are the same no matter how you achieve the magnification and are linked to the apparent aperture = actual aperture * (1+M) where M is the magnification. So even at 1:1 the apparent aperture is double that set on the lens.
Brian V.

[DQE]

Lord V,

Based on a very quick review of its contents, I believe the web page below provides a table of the effective f/stops that are consistent with your comments. Perhaps seeing the effective f/stops in a table format would be easier for some people to grasp.

I assume that diffraction induced image blur would track with the calculated or tabulated exposure loss and the associated effective f/stop. Focus stacking provides a solution to this problem without so much compromise of image blur, as described in your tutorials and many of your photos, of course.

One should certainly expect a lot of diffraction from the physically smaller (numerically larger) f/stops at higher magnification. For example, f/16 at 1x effectively becomes f/96 at 5x magnification and will produce a great deal of diffraction-induced image blur. Even f/5.6 is effectively f/33.6 at 5x magnification.

The relative importance of image blur depends on one's style, one's artistic intent, the subject, and trade-offs with other parameters, as you've often discussed.

http://www.dangphoto.net/mpe65.htm

.

[Laramie]

Diffraction starts to get really noticeable around F11 at 1:1 and gets exponentially worse smaller than that.

Suggest you try some comparison shots at F8,F11, F16 and F22 and draw your own conclusions.

I'm assuming you are using full flash for the shots to negate camera shake ?

Thanks LordV. Yes, I am using flash. I just did some tests and f11 really seems like the sweet spot. Yes, depth of field is shallower, but on my 100mm macro+40D, f11 is SHARP and anything smaller get much more noticeably softer.

[LordV]

Thanks LordV. Yes, I am using flash. I just did some tests and f11 really seems like the sweet spot. Yes, depth of field is shallower, but on my 100mm macro+40D, f11 is SHARP and anything smaller get much more noticeably softer.

Glad you did the tests - one of the wonderful balances you have to do in macro- DOF vs sharpness via aperture :)

Brian v.