Macro-Aperture vs diffraction

[Thegreatroberto]

OK, so as per the title.
Camera Nikon D700 on a tripod with a Nikkor 105D macro lens.

What is the point at which the diffraction becomes noticeable. You may think I'm best place to answer this, but it sort of assumes my focussing is spot on. Light this afternoon is fading fast and the lens is hunting..............

But I'm guessing around F/13, but the lens goes to F/45, so why would you ever use that if the diffraction just makes the image soft?

 

[HoppyUK]

Too many variables to calculate with any reliability, the biggest one being 'becomes noticeable'.

Diffraction will be measureable at quite low f/numbers, but the point at which this becomes 'unacceptable for my own personal use' is another question altogether. Generally speaking, with macro the priority is getting sufficient depth-of-field. It's no good having one area of the subject pin sharp when everything else is just a blur.

 

[Thegreatroberto]

Too many variables to calculate with any reliability, the biggest one being 'becomes noticeable'.

Diffraction will be measureable at quite low f/numbers, but the point at which this becomes 'unacceptable for my own personal use' is another question altogether. Generally speaking, with macro the priority is getting sufficient depth-of-field. It's no good having one area of the subject pin sharp when everything else is just a blur.

Just had a play albeit using flash as a main source of light.
At close to 1:1 type "distances" DOF is next to nothing anyway, let along anything bigger than F/13. I did try F/54 ( yes it does go that small), and some softness is visible. As to whether this is diffraction, or some other quality of the lens, I duno. But at aperatures like F/22 and even F/32 the image appeared fine. So, I'll keep these as my smallest apertures.
Long time since I played with macro. Everything is against you limited DOF, hence the need for small apertures, hence the must for a tripod, the must for the subject NOT to move...................
Maybe I'll try some stacking. Any recommendations for stacking software ?

 

[sk66]

I would say it depends on how critical the work is. If it's not terribly critical stop down as far as necessary to get the DOF you need. As Hoppy said, diffraction is the lesser concern.
If it is critical work then use the best aperture and focus stack for DOF.

 

[GardenersHelper]

Too many variables to calculate with any reliability, the biggest one being 'becomes noticeable'.

Diffraction will be measureable at quite low f/numbers, but the point at which this becomes 'unacceptable for my own personal use' is another question altogether. Generally speaking, with macro the priority is getting sufficient depth-of-field. It's no good having one area of the subject pin sharp when everything else is just a blur.

Spot on.

Some other aspects of the equation are that it depends what size sensor you are using, it depends how much depth-of-field is enough for your purposes and it depends on how much you crop.

These days I have reverted to using a bridge camera with a 6mm wide sensor for my close-ups/macros (which is most of what I do, using achromats). f/8 is the smallest aperture on my bridge cameras, and it gives depth-of-field and loss of detail/sharpness similar to those you get from using f/22 on a micro-four thirds or APS-C camera. I believe the equivalent in terms of depth-of-field and loss of detail/sharpness for a full frame camera is around f/45.

Here are some examples of apertures several fine macro photographers use. Kurt (Hock Ping GUEK) orionmystery often uses f/11 with an APS-C camera. Brian Valentine (LordV) often uses f/8 with a full frame camera; he goes far beyond 1:1 by the way using an MPE-65. John Kimbler (Dalantech) often uses f/11 with a full frame camera for macros, including high magnification use of the MPE-65, and around f/5.6 to f/8 for what he terms close-ups (1/4 to 3/4 full size). Mark Berkery uses f/11 with a small sensor (in his case 7mm wide sensor) bridge camera (using achromats), and I suspect this might be nearer to f/32 than f/22 in terms of its equivalence to APS-C depth-of-field and detail/sharpness loss.

For my purposes (mainly screen display 1100 pixels high, and occasional prints of A4 and very occasionally 16x12) I find minimum aperture is fine. That is for invertebrates. For flowers, berries, buds etc, including some rather small ones, I tend to use larger apertures, but that is for depth-of-field purposes not sharpness/detail issues. FWIW here is a set of invertebrate images containing two images from each of four cameras (using achromats), three bridge cameras and a micro-four thirds camera. All were captured using the smallest aperture available: f/8 in the case of the bridge cameras ans f/22 for the micro-four thirds camera. (For some reason Flickr refuses to show these at the intended viewing size of 1100 pixels high unless you specifically ask to see the "Original" version for images individually. )

If you use less magnification and crop you gain in depth-of-field but lose detail compared to capturing the same scene using the whole sensor. How that trade-off works out in practice is, like apertures (and for that matter shutter speed, ISO, the use of flash and/or tripod and stacking) a matter of experimentation and may vary with subject matter and motion, ambient conditions, camera and personal preferences as to working methods, post processing and the look and style of the finished product.

 

[GardenersHelper]

Long time since I played with macro. Everything is against you limited DOF, hence the need for small apertures, hence the must for a tripod, the must for the subject NOT to move...................

There are some fine macro photographers (who often work beyond 1:1) who don't use a tripod, for example the four mentioned in the previous post: none uses a tripod; two of them use a pole (LordV) or stick (Mark Berkery) to provide some stability. Only one of the four uses very small apertures. (Just to add to the variety a bit, I usually use a tripod, but I very often keep my hands on the camera, so I'm not using it in the "normal" way, but more like the pole/stick option.)

Maybe I'll try some stacking. Any recommendations for stacking software ?

Zerene Stacker. They do a 30-day full function trial.

 

[GardenersHelper]

I would say it depends on how critical the work is. If it's not terribly critical stop down as far as necessary to get the DOF you need. As Hoppy said, diffraction is the lesser concern.
If it is critical work then use the best aperture and focus stack for DOF.

I read you to mean "If it is critical work then use the sharpest aperture and focus stack for DOF". Have I got the sense of it right?

I wouldn't equate sharpest with best. If the aperture that gives the dof you need provides sufficient sharpness for your purposes (including for any critical work, however defined) then I don't think it matters whether it is the sharpest aperture. And stacking may often be impractical out in the field, which is where most close-up and macro photographers work. (That isn't to say that stacking isn't a good thing - I use it myself. It is a very good thing, and I intend to try using it more often this year. But it is often impractical.)

 

[pingu666]

its possible that the high f numbers aren't real f stop in terms of dof, but a mix of t stop,
the iris might close down to f22 say, but at closer focus it loses light due to how it works.

t stop is light transmittance, but we rarely use that term in still photography.

 

[sk66]

I read you to mean "If it is critical work then use the sharpest aperture and focus stack for DOF". Have I got the sense of it right?

Not quite. By "best" I mean the widest aperture that is sharp enough. It's completely the opposite direction from aperture for DOF.

I think when we start discussing handheld macro work (1:1+) at small apertures for DOF then it really starts getting to where specialty speed light lighting needs to be involved.

I know focus stacking is more often impractical than not.... I've never figured out how to reliably get an insect to hold still for one shot, much less 50.

 

[sk66]

its possible that the high f numbers aren't real f stop in terms of dof, but a mix of t stop,
the iris might close down to f22 say, but at closer focus it loses light due to how it works.

t stop is light transmittance, but we rarely use that term in still photography.

??
An f-stop is an f-stop...
The only thing is it doesn't have to be the physical size of the aperture opening, but rather the "apparent size" (which can change on lenses with moving elements after the diaphragm).

 

[HoppyUK]

its possible that the high f numbers aren't real f stop in terms of dof, but a mix of t stop,
the iris might close down to f22 say, but at closer focus it loses light due to how it works.

t stop is light transmittance, but we rarely use that term in still photography.

Yes. When you're at 1:1, you lose two stops of light compared to normal distance shooting. Just a fact of physics. Nikon chooses to report that, which is why the OP's Nikon 105 macro shows f/45. Technically, that's the T-stop, not the f/number. The same lens on a Canon would show f/22, so they're both equally wrong/right depending how you look at it, but either way TTL metering compensates for difference automatically.

Serious macro photography at high magnifications is a specialist skill, and technically challenging on a number of levels. A bit of diffraction is mostly the least of your worries.

 

[pingu666]

i think using teleconverters, extension tubes (some macro lenses follow that basic principle of moving lens forward to focus closer) can effect the "fstop", but not the depth of field or the other way around. some/most? macro lenses go from transmitting f2.8 ish to about f5.6 at closest focus, not to sure how that effects the depth of field...

 

[HoppyUK]

i think using teleconverters, extension tubes (some macro lenses follow that basic principle of moving lens forward to focus closer) can effect the "fstop", but not the depth of field or the other way around. some/most? macro lenses go from transmitting f2.8 ish to about f5.6 at closest focus, not to sure how that effects the depth of field...

This is going a bit beyond the Basics forum, but from memory I think the Nikon 105 macro at f/2.8 focused on infinity actually shows f/4.8 when focused at 1:1. It should read f/5.6, but because it uses internal focusing to get close, one of the side effects of that is a reduction in focal length. In other words, at 1:1 it's more like a 90mm f/2.4, with a T/stop of T/4.8 (if you follow ).

 

[GardenersHelper]

Not quite. By "best" I mean the widest aperture that is sharp enough. It's completely the opposite direction from aperture for DOF.

Ah, I understand. I don't think we're so far apart as the sharpest aperture is going to be much closer to the widest than the narrowest aperture.

I think when we start discussing handheld macro work (1:1+) at small apertures for DOF then it really starts getting to where specialty speed light lighting needs to be involved.

Indeed so.

I know focus stacking is more often impractical than not.... I've never figured out how to reliably get an insect to hold still for one shot, much less 50.

Ah, my stacks have thus far been mainly two or three images, and usually images that turn out to be stackable rather than having been captured with stacking in mind. The 50, 100, 150 or whatever stacking is studio/workbench stuff. I like looking at the results but doing it doesn't appeal to me.

As to getting insects to hold still, it's odd, but I quite often find invertebrates that stay still long enough for me to capture a number of images, from different directions/with different framing/magnification and/or differing aperture/shutter speed/ISO/exposure and flash compensation. Unsurprisingly this is especially true early in the morning, in the hour or two after dawn, but is also the case often enough at other times of day.

 

[sk66]

The aperture change is due to the lens design... It's a change in the "effective aperture." With a macro lens the aperture diaphragm moves forward with the front elements in order to allow close focus. The effect of front elements (may be internal) moving forward is a doubling of the lens' focal length at 1:1. The effective aperture is actually 2 stops smaller.

The basic idea is the same reason less expensive zooms have a variable aperture and TC's change the aperture. In all of these cases the lens is a longer FL with a smaller aperture. (i.e. a 2x TC on a 200mm f/2.8 *IS* now a 400mm f/5.6. And a 150mm f/2.8 at 1:1 macro *IS* a 300mm f/5.6, and they will act exactly like one. Not reporting the "effective aperture" is more of an "error" than otherwise IMO.
A lens 2x longer w/ 2 stops smaller aperture will have ~ 1/2 the DOF from a given distance.

None of these are actually T-stops. A T-stop is essentially a "corrected (effective) f-stop" that accounts for inefficiency of transmission due to the lens design (elements).

 

[LCPete]

Very interesting thread

I've been doing macro and close up for a while now and just learnt by trial and error
Without really understanding the reasons why for example it's a lot more difficult the closer you get to 1:1 to get enough depth of field and harder to get sharp shots

 

[HoppyUK]

The aperture change is due to the lens design... It's a change in the "effective aperture." With a macro lens the aperture diaphragm moves forward with the front elements in order to allow close focus. The effect of front elements (may be internal) moving forward is a doubling of the lens' focal length at 1:1. The effective aperture is actually 2 stops smaller.

The basic idea is the same reason less expensive zooms have a variable aperture and TC's change the aperture. In all of these cases the lens is a longer FL with a smaller aperture. (i.e. a 2x TC on a 200mm f/2.8 *IS* now a 400mm f/5.6. And a 150mm f/2.8 at 1:1 macro *IS* a 300mm f/5.6, and they will act exactly like one. Not reporting the "effective aperture" is more of an "error" than otherwise IMO.
A lens 2x longer w/ 2 stops smaller aperture will have ~ 1/2 the DOF from a given distance.

None of these are actually T-stops. A T-stop is essentially a "corrected (effective) f-stop" that accounts for inefficiency of transmission due to the lens design (elements).

Off-topic - apologies to the OP.

Or... to put it another way, it's an Inverse Square Law effect. Double the focal length = one quarter the brightness (two stops reduction).

I think you're right about T/stops. Technically the aperture change with macro at 1:1 is a true f/number change, not an 'effective' change. So the T/stop might actually be higher!

 

[sk66]

I think you're right about T/stops. Technically the aperture change with macro at 1:1 is a true f/number change, not an 'effective' change. So the T/stop might actually be higher!

Absolutely....