Higher aperture values vs focus stacking?

8 years 6 months ago #115249 by Todd Knight
So if you have the flash power and using higher aperture values what is the need of focus stacking? When would you use focus stacking over a higher aperture while photographing macro?


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8 years 6 months ago #115270 by steveheap
I'm investigating Macro at the minute, so here is my explanation of why you may want to do this. A high aperture value - eg f22, causes a softening of the image in its own right. Because the physical size of the aperture is so small, the light around the edges gets bent, and so creates slightly blurred edges in the image. I think most lenses have their sharpest performance between f8 and f16. A second reason may be (and I'm not sure) that with a small aperture size you probably get a slightly less out of focus background which may be distracting.

With focus stacking, you are getting each part of the image in focus on its own, and combining those different areas in one image. The lens is performing at its best range, each piece is in focus (instead of being not visibly out of focus which is what depth of field means, I think) and the background has the blur associated with the wider aperture.

Steve

My Stock Photo Blog
www.backyardsilver.com

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8 years 6 months ago #115275 by Baydream

steveheap wrote: I'm investigating Macro at the minute, so here is my explanation of why you may want to do this. A high aperture value - eg f22, causes a softening of the image in its own right. Because the physical size of the aperture is so small, the light around the edges gets bent, and so creates slightly blurred edges in the image. I think most lenses have their sharpest performance between f8 and f16. A second reason may be (and I'm not sure) that with a small aperture size you probably get a slightly less out of focus background which may be distracting.

With focus stacking, you are getting each part of the image in focus on its own, and combining those different areas in one image. The lens is performing at its best range, each piece is in focus (instead of being not visibly out of focus which is what depth of field means, I think) and the background has the blur associated with the wider aperture.

Steve

:goodpost:

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8 years 6 months ago #115281 by chasrich
I have had that same question in my head now for the past few weeks. Thanks for posting this. I was going to find the answer on my own and most likely will anyway. Thanks Steve for a very good answer. I know a little more about what I might expect. :goodpost: :thumbsup:

“Amateurs worry about equipment, professionals worry about money, masters worry about light, I just make pictures… ” ~ Vernon Trent

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8 years 6 months ago #115347 by Henry Peach
I would think avoiding aperture diffraction would be the main reason.

Stacking images might also reduce noise.

The common anecdotes I hear on lens sharpness is the sweet spot is usually a couple of stops closed down or in the middle of the range. Having used plenty of lenses that go against this I've learned it's best to assess lenses individually.

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8 years 6 months ago #115392 by Screamin Scott
Focus stacking involes using many images with minute changes in focus point & is fine for studio work, but is a bit impractical in the field. Using smaller apertures does have the effect of losing some sharpness due to diffraction, however, unless you are pixel peeping or making huge enlargements, you won't readily notice it .

Scott Ditzel Photography

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8 years 6 months ago #115468 by Shadowfixer1
You can't get the depth of field to match focus stacking. If the subject is fairly flat then you could, but if the depth of the subject is too great, focus stacking is the only way to achieve focus all the way through. Diffraction is way overblown in my opinion. I've never seen it ruin an image. if you need the depth, use the aperture to get it.

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8 years 6 months ago #115523 by steveheap
You will wish you hadn't asked the question after this reply!

I was reading a very detailed magazine about macro photography this afternoon and it went into great detail about many of these questions.

The starting point is that a lens only really focuses an object in the "object plane" onto the sensor with minimal blur (I'll come back to that word later). Objects in front of, or behind the object plane are focused into areas in front of and behind the sensor and so a point will appear as a circle on the sensor - this is called the circle of confusion. Because a smaller aperture restricts the light to the central part of the lens, the circle of confusion gets smaller as the aperture is stopped down and things appear to be in focus.

The reason we see things with a small circle of confusion as being in focus is that the eye can only resolve detail down to a certain level (apparently a circle of confusion less than 0.029mm on a full frame camera) is thought to be a point as far as the eye is concerned, and so appears to be completely sharp.

All that would suggest that continuing to stop down the lens would make these circles of confusion smaller and hence more objects are in focus. But, there is a second factor. Even a theoretically perfect lens will always render a point as a circle due to the quantum nature of light. This is the Airy disc and I think it is caused by interference of the edges of the aperture on the light waves. So the smaller the aperture, the more interference and the larger this Airy disc becomes. At a certain aperture size, the Airy disc is a big as the circle of confusion and any further reduction in the aperture size only makes the background look sharper, but the subject itself will become less sharp.

This is reached at f22 on a APS-C or f32 on a full frame (although this is the effective aperture which is different to what is engraved on the lens). That whole topic is beyond me at the minute. It appears that practically speaking, the "engraved" aperture at which the deterioration is around f16 or so.

Fascinating (or is it the inner geek in me...)

I'm just getting into stacked focus, but it appears that to do it properly, you need to move the camera closer to the subject in very small increments rather than touch the focus ring. Why? Because the focal length and perspective of a fixed lens changes as the focus point is changed and so simply altering the focus ring alters the whole view of the subject.

OK - enough already!

Steve

My Stock Photo Blog
www.backyardsilver.com

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8 years 6 months ago #115825 by Dragonflies

Screamin Scott wrote: Focus stacking involes using many images with minute changes in focus point & is fine for studio work, but is a bit impractical in the field. Using smaller apertures does have the effect of losing some sharpness due to diffraction, however, unless you are pixel peeping or making huge enlargements, you won't readily notice it .


Agree, in the field you sometimes just don't have the benefit of focus stacking. However there have been good points made by a number of you in this thread. :goodpost:


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