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View Full Version : Macro, aperture & sharpness question


ScubaRoy
20th June 2011, 06:59 PM
Having read Ian's article on diffraction softening at smaller apertures I have been trying to keep to f8 or wider. The problem obviously comes when trying to get decent DOF for macro subjects where smaller apertures are required.

Say I take a picture using an 50mm lens so the subject fills the frame. If I then attach an EC14 and frame the subject the same then am I correct in thinking that, because I am further from the subject, the DOF will be greater?

Are there any other suggestions on this?

JohnF
20th June 2011, 07:16 PM
Hi -

The only "real" way to handle the conundrum between needing better DOF and avoiding diffraction softening is to cheat. :-)

Seriously: there is a way to stack photos such that taking a series of photos where the focus varies slightly between pictures to get a nice, overall sharp photo while retaining optimum sharpness. If you simply google "macro photo stacking" you'll find quite a bit of info out there.

If you want to do this a lot, there are hardware solutions out there as well that take it to an extreme, stepping, say, 0.05mm per exposure for several hundred photos. Not inexpensive kit (expect to pay north of 400 quid at the end of the day for hardware and software), but it's pretty much the cat's meow.

Of course, you can do it the proper way as well: move up to a medium format digital back and attach that to a view camera so that you can manipulate the in-focus area to meet your exact needs.

Personally, I find diffraction to first rear its ugly little nebulous head after f11. Sometimes even f16 for longer focal-length legacy equipment (I use an ancient 100mm f4 Leica lens on a bellows, diffraction there is first detectable around f16...and even then is moderate. F22 and beyond, yech.

JohnF

Graham_of_Rainham
20th June 2011, 07:23 PM
The EC14 will make the 50mm into a 70mm. So @ f/8 with the focus point at say 10 ft
the DoF will go from 2.94ft for a 50mm lens down to 1.47ft for the 70mm lens. In otherwords half

http://www.dofmaster.com/dofjs.html


The E-500 has automatic focus shifting (BKT focus) that works reasonably well, which can then be used to form a stack in PS.

Alan Clogwyn
20th June 2011, 07:37 PM
As I understand it for Macro, to frame a given object, lets say an ant, to fill the frame would give the same DOF no matter what lens or focal length is used, you always need the same F number to get it all in focus.

I may well be wrong but that's how I understand it.

ScubaRoy
20th June 2011, 08:21 PM
Thanks for the replies.

I know about the principles of focus stacking but, if I understand it correctly, it requires a number of frames all focussed at slightly different parts of the subject. Unfortuantly, as my main interest is underwater photography, this isn't something that is unlikely to be practical. Just getting the focus in the right place can be challenge enough. Similarly changing the camera isn't something that is an option having just spent a small mortgage on getting the E520 underwater.

Alan - It looks like you are correct. Using the DOF calculator in Grahams link:

50mm focal length @ f8 100cm from subject gives 9.14cm DoF
70mm focal length @ f8 140cm from subject gives 9.13cm DoF

As I rarely print bigger than A4 I guess my only other option is to frame the subject smaller and then crop.

Any other ideas?