treslek Loc: London

not sure how it all works but i believe from this shot people like n72 can give me some info, nikond90,tamron f2.8 macro lens, f22 , 1/180 sec .

Nikonian72 Loc: Chico CA

Your Nikon D90 APS-C sensor is 23.6-mm x 15.8-mm. Your captured image at Minimum Focusing Distance (above), is about 24.5-mm wide, very close to 1:1 magnification (life-size).

You will discover that your DoF at this Minimum Working Distance is quite narrow, even at f/22.

treslek Loc: London

cheers n72 i,m assuming due to the narrow dof this is why people photo stack ,i find it very hard to keep my focus i only have to breath out and the focus point move,s any help on that please.

LoneRangeFinder Loc: Left field

I've done a little stacking. With focus stacking you can also use your lens at it's optimal aperture to minimize diffraction. For most lenses, this means f/5.6 to f/8. http://www.slrgear.com does an excellent job on the "science side" of lens testing. They haven't, however, tested all of the lenses out there.... My avatar is a stacked image.

treslek Loc: London

thank you for that loneranger they have reviewed my tamron lens and rate it highly mmm must be me lol.

Macromad Loc: New Zealand

Try a macorail and a tripod.

GPappy Loc: Finally decided to plop down, Clover, S.C.

I guess I'm not understanding what advantage stacking photos of a flat object would accomplish. Am I missing something?

LoneRangeFinder Loc: Left field

No advantage for a flat object. I can't speak for Treslek, but I believe it was a general comment in response to Nikonian72's mention of the shallow depth of field. Not to hijack, but here's my avatar with is a stack of 11 raw files. 200 asa @ f/8 & 1/30 sec.

magnetoman Loc: Purbeck, Dorset, UK

You need to explain the technique of stacking various areas of focus to achieve a single image all in focus, I think?

LoneRangeFinder Loc: Left field

I capture the files using a tripod-mounted focusing rail with camera and lens. I use a cable release to minimize contact with the camera. The plane of focus is moved incrementally for each capture using the focusing rail. I then download the files and combine using Helicon Focus (there are other options-- Zerene was not available for Macs @ purchase time). I then continue with some post-processing. The first requirement is to crop the portions of the composition that did not include information from all files. It's important to plan for this step. There are many tutorials that explain this much better than I just did.

rhadams824 Loc: Arkansas

I have some understanding of DOF in relation to f-stop and also stacking to achieve greater DOF but if you do an f22 or even f32 photo and post it along with the stacked photo it would aid in seeing the benefits of stacking over a single high f-stop photo.

I do have a question about diffraction. Is there any difference between diffraction effects on a FF vs a DS camera since some of the light waves entering the DS camera do not strike the sensor. My understanding is that on a FF camera all the light waves entering a lens strike the sensor. Just thinking that wave diffraction would be worst at the outer edges of the light entering the camera lens than toward the middle. Since the DS sensor uses more of the center light rays is diffraction less noticeable than on a full frame at the same f-stop.

At the same distance the FF would have to be cropped to give a photo of the same dimensions as the DX which would remove the edges where greater diffraction might occur. If the FF is moved closer to cover the same area as the DX the DOF would decrease and diffraction would be greater so I guess this is may be a moot point and my question is not relative to achieving a better photo with a DX over a FF when diffraction effects enters the picture.
Sometimes I think too much but wanted input from someone who can answer my question. I have read about diffraction effects relative to f-stop but didn't find anything on FF vs DX cameras.

Nikonian72 Loc: Chico CA

Nikonian72 Loc: Chico CA

Your premise is not quite correct. ALL lenses longer than 55-mm project an image wider than a Full Frame sensor, meaning some light strikes outside of the 24-mm x 36-mm sensor. On a DX format camera, all lenses longer than about 38-mm project an image wider than APS-C sensor.

Circular Aperture Diffraction is explained here:
FAQ: Why are my Digital Images Sharper at f/11 than f/22?
http://www.uglyhedgehog.com/t-59819-1.html

Nikonian72 Loc: Chico CA

I concur.

LoneRangeFinder Loc: Left field

I will do such a demonstration the next time I prepare files for stacking: single frame f/32 vs stacked image.

I generally chose subjects that front to back fall outside of the DOF for macro. (Orchids are an example)

Otherwise, it becomes more about minimizing diffraction. Every lens has a "sweet spot"-- from my experience using my 105g-- it's around f/5.6-f/8-- with f/8 being my starting point.

Nikonian72 has answered the FF v. DX question....