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Old Oct 23, 2010, 4:26 AM   #1
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Default Focus Stacking vs Higher Aperture

I just shot some artistic macro photos of roses and I couldn't decide which looks better - focus stacking or a higher aperture. It took 4 photos @ f/4.5/0"5 vs 1 photo @ f/32/8", and there were defects with the stacked result.

I mean, even if I'm outside, it would be easier to use a higher aperture with a dedicated ring flash.

So, what do you think stacked focus is better for?

Thanks, guys.
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Old Oct 23, 2010, 2:42 PM   #2
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first of all, what camera and lens do you use? because most (if not all) p&s with small sensor don't go beyond F/8, with APS-C sensor the diffraction starts to kick in at F/16 and goes worse from there.
there is no right or wrong answer, especially with artistic macro, it's more the effect you are after and the dof limitations, which depend on the size of your subject and your working distance. when you don't have enough dof you either shoot a focus stack, or go for a selective focus.
this is a 9 shot focus stack made in a free CombineZP prog:



a 19 shots stack:



and a single frame of that stack (shot at F/11):



partial focus stack (4 frames):



with static objects focus stacking is simple and works well, with animated objects it's a bit more challenging.
focus stack of 4 frames, slightly cropped frame, 60mm macro with 25mm extension tube (about 1.5x magnification), there are some stacking artefacts I haven't cloned out:



the same as above, but cropped a lot more:


3 images stack, this was a tiny gecko, the eye is 2mm in diameter, head and body - about 2cm (without a tail):



btw, the ring flash will give you flat unattractive shadowless light if you don't play with ratios and/or additional diffusion.
best regards,
Alex

Last edited by algold; Oct 23, 2010 at 2:47 PM.
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Old Oct 23, 2010, 3:55 PM   #3
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The sensor size has nothing to do with diffraction. It is a characteristic of the lens, based on the physical aperture. The f/number can be used as a guide, but since it is based on the focal length of the lens, the focal length must be known. The physical aperture of a 100mm lens is larger, for the same f/number than that of a 50mm lens. The reason diffraction is seen at lower f/numbers on P&S cameras is simply that they have (usually) shorter focal lengths.

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Old Oct 23, 2010, 4:59 PM   #4
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Brian, you are right, of course. The logic behind sensor size -> diffraction in layman's terms: smaller sensor -> physically smaller lens with physically smaller aperture -> diffraction starts to affect IQ at lower F-numbers. Let's not start adding the effective aperture at MFD at 1:1 magnification and up to the equation .
btw, what's your take on focus stacking?
regards,
Alex
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Old Oct 23, 2010, 6:59 PM   #5
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I haven't used focus stacking at all, not being heavily into macrophotography. When I do floral closeups and such, I tend to use the OOF areas that shallow DOF gives me, rather than eliminate them.
For some of the super macros I have seen, focus stacking seems about the only way to go, as even very small apertures don't seem to give much DOF.

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Old Oct 24, 2010, 10:42 PM   #6
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Thanks AlGold, you obviously put a lot of time and effort into your response.

I'm currently using a Canon T2i. I found the stock 18-55mm lens to be the best for Macro photography, short of the Canon 65mm macro lens, which I haven't tested yet.
With three magnification swatches (4x, 2x and 1x put together), I can photograph an image at 55mm at less than an inch away. True, it doesn't have 5:1, but I'll look into the Canon 65mm soon.
If it's important, I could get a 5D Mark II with a full-frame sensor, but the only thing I really lack with T2i is burst. I could do a great deal with 10 FPS.

The bullet example you added was helpful, indeed. But, I was talking about f/32, and I'm not sure what 'diffraction' is, in this context.
I SUPPOSE that even at f/32, the background wasn't in focus, which means that it would be inferior to a stack of at least two images, even if they are both f/32.

But the majority of example photos I see of focus stacking, such as yours, are on a white background where that doesn't matter. And in my tests, at f/32 (again, f/32 because that is the maximum my 55mm lens is capable of), both the rounds and the cartridge would be in complete focus.

Where as, and this is why I dislike focus stacking, with FS, you'd have to take dozens of photos to literally have EVERYTHING in focus. On my Rose (examples of which I can give upon request), the numerous flaps are all at different distances, so while two photos, one of the closest part and one of the farthest part are adequate, when you zoom in, not ALL of the rose is in focus. Where as, at f/32, it was truly amazing to be able to zoom in to every part of it and see it in focus.

That's what I gather so far.
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Old Oct 24, 2010, 11:52 PM   #7
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You can get a much better technical explanation of diffraction than I could provide, on Wikipedia. In non-technical terms, it is the slightly blurred halo you get when you look at an object which is backlighted. When the lens aperture gets small enough, these haloes overlap, causing the whole image to lose sharpness. So, while the DOF is increased, the overall focus suffers.

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Old Oct 25, 2010, 10:29 AM   #8
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Track, you can always use dof calculator to check how much dof you get with your particular settings: focal length, aperture and distance to your subject. Then just take a few test shots and decide for yourself when the loss of sharpness due to diffraction is more than the gain of more dof with smaller apertures. If you don't have enough dof, use focus stacking or artistic selective focus - whatever works better for you.
Here is the link to the dof calculator:
http://www.dofmaster.com/dofjs.html

On a side note, Canon's kit zoom is a nice and compact lens, but it's nowhere near a true macro lens. It's great for close-up photography, but 28cm minimum focus distance is just not enough to fill the frame with your subject. It is possible to use it with extension tubes or a close-up lens, or you can reverse it, but that's another story.
regards,
Alex

Last edited by algold; Oct 25, 2010 at 11:20 AM.
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Old Oct 25, 2010, 1:57 PM   #9
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Quote:
Originally Posted by VTphotog View Post
The sensor size has nothing to do with diffraction. It is a characteristic of the lens, based on the physical aperture. The f/number can be used as a guide, but since it is based on the focal length of the lens, the focal length must be known. The physical aperture of a 100mm lens is larger, for the same f/number than that of a 50mm lens. The reason diffraction is seen at lower f/numbers on P&S cameras is simply that they have (usually) shorter focal lengths.

brian
I have some problems with this explanation. The relevant point is made in this article: http://www.cambridgeincolour.com/tut...hotography.htm which I am quoting below.

"Technical Note:
Since the physical size of the lens aperture is larger for telephoto lenses (f/22 is a larger aperture at 200 mm than at 50 mm), why doesn't the size of the airy disk vary with focal length? This is because the distance to the focal plane also increases with focal length, and so the airy disk diverges more over this greater distance. As a result, the two effects of physical aperture size and focal length cancel out. Therefore the size of the airy disk only depends on the f-stop, which describes both focal length and aperture size. The term used to universally describe the lens opening is the "numerical aperture" (inverse of twice the f-stop). There is some variation between lenses though, but this is mostly due more to the different design and distance between the focal plane and "entrance pupil.""

It is a worthwhile to read the entire article as it does discuss differing sensor sizes.

One might also note the diffraction discussion in DPRs review of the new Sony-Zeiss 24mm f/2 when used on an APS-C body vs. an FF body. Review here: http://www.dpreview.com/lensreviews/sony_24_2_m15/ .

Bottom line: Diffraction is sensor dependent but not focal length dependent.

A. C.
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Old Oct 25, 2010, 2:26 PM   #10
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Focus stacking is particularly relevant to to technical photography where the minimum resolvable detail is critical to the purpose of the photograph. Kodak's '70s era booklet on close-up and macrophotography devoted an entire chapter to the subject. Specific examples were shown in which diffraction rendered the photo unusable because of loss of resolution even when the DoF is adequate and then the results were resolution is retain by use larger aperture and focus stacking. Note, this booklet obviously predates digital photography so focus stacking involved actually making prints with several focus planes, physically cutting the several prints, pasting them together and rephotographing the resultant print. Artifacts were dealt with by a physical paint brush. Kodak also provided a practical guide/method for determining the number of photos required.

Focus stacking can be as relevant now as then but made easier by digital photos and the appropriate software. I think the clip and cartridge photo is both well done and an excellent example.

A. C.

Last edited by ac.smith; Oct 25, 2010 at 2:40 PM.
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