cbtsam Loc: Monkton, MD

1) On my AF MICRO Nikkor 105mm 1:2.8 D lens, the smallest aperture is marked 32. However, when I focus close, say about 1:5 or closer, the smallest aperture reads out in the viewfinder as 40 on my Nikon DSLRs (D70, D300, or D810).

How am I to understand this? Is it just the exposure that's changed as I focus closer, so the aperture blades don't move, but the effective exposure changes as if it were f/40? Is the depth of field increased, as if it were f/40? Or do the blades actually move to f/40?

2) When I select an aperture of f/32, I know I can expect a decrease in sharpness due to diffraction. However, if I select, say, f/10, I may not get much or any diffraction, but the reduced DOF may put an important part of the image (call it area X) out of focus, and thus certainly leaving area X appearing not sharp. So, if I select a tiny aperture, say f/32, and my DOF increases enough to include that important part of the image (area X), won't that make area X appear sharper than when it was out of focus? And, if it does appear sharper than when it was out of focus, isn't it sometimes useful to stop the aperture down as far as possible to get enough DOF to keep area X in focus?

3) When I use a tiny aperture and encounter diffraction effects that undermine sharpness, to what extent can that be countered by using sharpening tools in post processing software like Photoshop?

4) I understand I can avoid needing tiny apertures by using focus stacking, so please don't avoid my questions by reminding me of focus stacking, or some other technique I'm not asking about.

ejones0310 Loc: Tulsa, OK

I can't answer your defraction question, but according to Ken Rockwell's web page on this lens:

Macro lenses focus close enough that the effective aperture changes as you get closer. The TTL meter for available light and flash exposure compensates for this. The F100, unless you change this in a custom function, will read and set the true effective f/stop regardless of distance. That means that at infinity the f/stop range is from f/2.8 through f/32, but at 1:1 the effective range is f/5 through f/57.

cameraf4 Loc: Delaware

Not really sure just how much DOF you need when you are racked-out for a Macro shot, but I would open-up a stop. F32 may be a problem but I have the same lens and, so far, f22 hasn't given me any "side effects."

ejones0310 Loc: Tulsa, OK

Check this link for more information on diffraction.

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

imagemeister Loc: mid east Florida

1.As you focus closer, the lens/elements move further away from the sensor. Your lens acts as a light source inside the camera. As a light source, it is governed by the inverse square law - this is why the exposure is affected. I am not going into the DOF part of this - it gets really complicated fast !

One thing you can do in close up photography to increase apparent DOF is to tilt the lens. This does not actually increase DOF, just moves it to a more advantageous position in relation to the subject. That is why Canon has released 3 new macro tilt/shift lenses !

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amfoto1 Loc: San Jose, Calif. USA

It depends upon the particular lens.... but, yes, the "effective" aperture can change depending upon focus distance. It's particularly noticeable in macro lenses that focus extremely close. It's also most dramatic in lenses that AREN'T internal focusing (IF).

For example, my Canon MP-E 65mm's smallest selectable aperture is f/16 (and is non-IF). However, at the highest magnification possible with that lens (5X life size or 5:1) the effective aperture is f/96! This lens extends considerably when focused closer.

The freshly hatched snail shown below is about 5 or 6mm long and was photograped using the MP-E 65mm focused to around 4X and with aperture set to f/16. I'd have to check the chart, but it's probably in the range of f/70 to f/85 effective aperture. I needed a very small aperture because Depth of Field is extremely shallow at such a high magnification... the plane of sharpness is only a fraction of a millimeter deep. There's A LOT of diffraction occurring in this image, though it's not very obvious at Internet resolutions and sizes. (For more sense of scale, the green/tan banded line running across the lower portion of the image is actually the edge of a leaf the snail was crawling upon. A ring light was used to illuminate the shot.)



Depending upon how they actually achieve focus, Internal Focusing (IS) lenses may not see the same change in aperture. It depends upon where the lens focusing group is in relation to the aperture, where or not th effective aperture will change.

Their effective aperture may change less... however, IF macro lenses effective focal length changes significantly. For example, my Canon 100mm f/2.8 at it's closest focus (1:1) actually has roughly a 70mm effective focal length.

Add'l info: https://www.cambridgeincolour.com/tutorials/macro-lenses.htm

imagemeister Loc: mid east Florida

First time I have heard this concept ! - It does sound plausible. ...

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cbtsam Loc: Monkton, MD

Thanks, Alan. So, the effective aperture for exposure and for DOF changes as you focus closer. My 105mm f/2.8 macro is not internal focusing either, and it's effective focal length changes as well, sometimes making framing a bit dicey, as every change in focus point changes effective focal length, changing the size of the subject in the viewfinder. And I take it that (1) you choose the tiny aperture (around f/70) for greater DOF, and (2) that you find you can achieve adequate sharpness somehow, despite the diffraction that comes with such a tiny aperture; are these suppositions of mine correct? And, if I am correct, what if anything do you do to offset the diffraction that comes with f/70?

Thanks again for your input.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

1) If I remember correctly, the AF MICRO Nikkor 105mm 1:2.8 D is not an internal focus design, so the lens elements are moved further away as you focus closer, and that diminishes the light hitting the sensor. Internal focus lenses remain the same size as you get closer, and the closest focusing distance is arrived at by shortening the focal length by moving around the internal elements. Internal focus lenses can suffer from focus breathing, like the Nikkor 28-300 which is around 135mm when zoomed to 300 and focused at the minimum focusing distance.

2) Without getting into a discussion about circle of confusion and pixel sizes and airy disks, suffice it to say that yes, you will get a softer image, but the fine details at 1:1 magnification are bigger than the airy disk and will be rendered with decent contrast and sharpness. But if you were to shoot a landscape at F32, it would lack detail and be soft.

3) They can be recovered to a modest degree. It depends on the subject, magnification and aperture.

cbtsam Loc: Monkton, MD

Thanks Gene; very helpful as usual.

One detail: yes, the AF MICRO Nikkor 105mm 1:2.8 D is not an internal focus design. However, you do get some focus breathing, as I noted; according to Rorslett, at 1:1 it's about 60mm [http://www.naturfotograf.com/lens_spec.html]. I guess Nikon is using two tricks to get to 1:1.

Your item 2) explains how I'm getting pretty good sharpness at f/40, not at all at 1:1, but still pretty close up - about 2-3 feet from the focus point according to the lens markings, which also indicate that 1:1 is at 1 ft. I compensate with a lot of sharpening in Photoshop, and the results are as your analysis seems to predict.

Thanks again. Between you and Alan, I think I've got the answers I was seeking.

speters Loc: Grangeville/Idaho

I have used apertures as small as f/48 several time to increase DOF and it does work, more nicely with some lenses than others, but stacking in my mind gives the best results as well as giving one way more flexibility. One can make stacks using the lenses sweet spot, or stack wide open to still have a nice bokeh in the image, etc. etc.!