Diffraction limited IQ with D300 + 105mm VR macro lens

Bruce Williams · Post by **Bruce Williams** » Sat Feb 07, 2009 4:24 pm

Following on from my last posting (see: http://www.photomacrography.net/forum/v ... php?t=6677) where the question of diffraction limitation and image detail was touched on. I thought it would be interesting to run some qualitative tests using my Nikon D300 with the Nikon 105mm VR macro lens. My objective was not so much to assess changes in dof but more to help give me a “real world” feel for IQ at the various aperture settings.

I tried out a number of different subjects and eventually settled on an old sock as having sufficient textural detail to give me a reasonable feel for the changes in IQ.

Approach:

Sock was pinned vertically against a box.
Subject was lit by 2 x Nikon SB-R200 wireless speedlights, remotely controlled by the D300's on-board flash.
Lens was set to closest focus (magnification ~1:1) and VR was off.
Focus was manual.
White balance was AUTO as I was shooting NEF and using a WhiBal card.
Mirror was locked-up and shutter triggered on 30sec time-out.
Apertures used: f/5.6, f/8, f/11, f/16, f/22, f/32 and f/45
Images were cropped in CS3 (no sharpening or other enhancements).
I used the “Save for Web” option in CS3 to produce a file size of <200Kb (note: I could see no discernable difference between the pre and post “reduction” images in CS3).

I felt that the diffraction limit effect on IQ was noticeable from f/22 and unacceptable from f/32.

Out of interest, I subsequently processed the f/32+f/45 image through Focus Magic which gave significantly improved IQ, sufficient perhaps to suggest that f/32 might (on occasions) offer a worthwhile trade-off to achieve added dof where stacking was not a possibility. I would have posted the result but have used up my allocation for the day.

Here's the results:

Tip: If you're finding it difficult comparing (say) the f/8 result with the f/32 result, bring this thread up in two copies of your web browser and run them side by side.

I'd be interested in any comments or suggestions.
Bruce

rjlittlefield · Post by **rjlittlefield** » Sat Feb 07, 2009 5:16 pm

Bruce, a couple of comments...

1. We changed the posting rules a while back. The new rules say

The posting limit is three (3) images in each Image Gallery every calendar day. There is no limit for image postings in the technical discussion forums, as long as the images are specifically referenced in the discussions.

If you'd like to post more images to more fully discuss this topic, then have at it!

2. I believe your data confirm that this camera+lens combination does set aperture in terms of working or effective f-number, and not in terms of nominal f-number. According to the review HERE, the nominal settings for this lens range from f/2.8 to f/32. But your series goes from f/5.6 to f/45.

Can you do another simple check, please -- what is the widest aperture you can set the lens, when it is focused at 1:1 and when it is focused at infinity?

--Rik

mgoodm3 · Post by **mgoodm3** » Sat Feb 07, 2009 6:34 pm

The D300 (my D200 does) will give an effective aperture in the viewfinder with newer lenses.

Bruce Williams · Post by **Bruce Williams** » Sat Feb 07, 2009 7:09 pm

mgoodm3 - Thanks for pointing that out - I hadn't realised that I was reading effective aperture in the viewfinder.

Rik - Thanks for clarifying the position - I'll post a few more pics tomorrow (it's almost 2am here - so off to bed). Btw, although I did shoot at f/5.6 I didn't include it in this thread (just f/8 - f/45 effective) as I felt I would be unlikely to shoot macro (even when stacking) below f/8.

I have just checked the aperture settings with the 105mm VR lens as you asked:

At closest focus aperture can be set between f/4.8 and f/57.
At infinity aperture can be set between f/2.8 and f/32.

Bruce

rjlittlefield · Post by **rjlittlefield** » Sat Feb 07, 2009 8:25 pm

Bruce Williams wrote:At closest focus aperture can be set between f/4.8 and f/57.
At infinity aperture can be set between f/2.8 and f/32.

That nails it down. These are definitely effective apertures. If the lens were focusing purely by extension, it would be limited to f/5.6 to f/64 at closest focus. But while focusing closer, it also shortens its focal length a bit, and that slightly offsets the drop in effective aperture.

Thanks for the further info.

--Rik

Bruce Williams · Post by **Bruce Williams** » Sun Feb 08, 2009 4:53 pm

Thanks Rik, I feel a lot clearer on the subject now.

Earlier in this thread I mentioned using Focus Magic on some of these test images. I thought some of you might be interested in the results, so here's some before and after examples using the f/16 and f/32 images.

This first pic shows the before and after on the f/32 image:

This next pic compares the Focus Magic enhanced f/32 with the out-of-camera f/16

This pic shows the before and after on the f/16 image.

This last pic compares the f/16 with the f/32 after both have been through Focus Magic.

I of course appreciate that other forms of post processing may well bring out more detail on both images.

Bruce