Diffraction limited pixels... Really?

[Stoshowicz]

Shame on you for bringing the practical realities of real world photography to a theoretical discussion of DOF . You are of course correct, there are many more variables than DOF & aperture. Your previous post is also correct about the difficulties of making this calculation for a real lens without the manufacturers data. However, in that case, you have a much easier option - namely testing. All you need is a good tripod, good technique, and a convenient brick wall. Put the lens on you interested in. Set up you camera on the tripod, making sure the sensor plane is exactly parallel to the wall, and make test shots at various F-stop values. ( don't forget to use your mirror lockup and electronic first curtain if available to remove camera shake. )

You can vary the distance to the wall, but I think that usually, with the exception of special lenses like macro lenses, the optimum f-stop will not change much with distance to the subject. On the other hand, if you have a zoom lens, you will need to test at a variety of focal lengths as the optimum f-stop does tend to change with focal length on a zoom lens.

For anyone who's interested, this site lets you see how the airy disk of a perfect lens compares to pixel size for a number of cameras.

Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

Yes , I do want to know the mathematically calculated ideal. Thats exactly it. You could take lots and lots of shots of a brick wall , the number of permutations -possible outcomes is huge.
If one was going to fire cannon balls then statistically find an experimental center of impact , all the work could have been biased by crosswind. Thats why one calculates the trajectory first , then compares results against the ideal.
If you fire with no calculation , you are just guessing.

 

[Stoshowicz]

You probably should do some careful validation before you do too much computational work. Assuming the DOF formula is accurate at macro distances is suspect. For one thing, as the lens is racked far out for close focus, the focal nodes (design points in the lens) shift substantially. This doesn't much matter at landscape distances, but becomes a significant factor at macro. And, just assuming the DOF formula's assumed criteria is same as your criteria is also suspect.

I still think the viewfinder and rear LCD are the best tools. Look at the view you get, and the results you get, and then simply do what you need to do to get what you want. This may involve a little skill to know what to do, but experience is the best teacher. Keeping everything in the one focal plane is a biggie. One three inch dragon fly is surely much like the previous one. We can see what happens. We just need main ideas - we don't need to know the hairy physics (theory and practice can be different in practice ). Mostly, we just have to realize that trying a few things can help substantially. It really is not rocket science.

I agree again , its not rocket science , its just a big huge long calculation that should have a very simple useable result ,, the answer should look something like ,, making some basic assumptions about standard lighting outdoors ,barometric pressure , ambient temperture etc , the sharpest resolution of a three inch deep object is managed by this lens and camera at f/X , Y mm , and at a distance of Z feet.

Yes we all chimp shots to a degree, but Id just like to be able to set those two parameters on the lens and then approach to the correct distance, knowing that -to the degree I waver from that known standard -is the degree to which I am not optimizing for sharpness.

And anyone else using that basic combo , and wants to optimize for sharpness when they can actually approach the object, maybe a flower , some food product , perhaps even faces etc , can roughly use this same standard.

 

[WayneF]

I was just suggesting that some simple trial and error experiment will likely give an easier and better (more dependable) answer.

Just do it, as they say.

 

[dslater]

Yes , I do want to know the mathematically calculated ideal. Thats exactly it. You could take lots and lots of shots of a brick wall , the number of permutations -possible outcomes is huge.
If one was going to fire cannon balls then statistically find an experimental center of impact , all the work could have been biased by crosswind. Thats why one calculates the trajectory first , then compares results against the ideal.
If you fire with no calculation , you are just guessing.

You may find this article useful:

Large format photography: how to select the f-stop

It calculates the optimum f-stop by finding the point where the de-focus circle of confusion = diffraction.

 

[Stoshowicz]

I was just suggesting that some simple trial and error experiment will likely give an easier and better (more dependable) answer.

Just do it, as they say.

I was just hoping some one could actually answer the question. I didn't think I was going to have to battle to justify the reason why I want to know the parameters.
Ill post to Nikon themselves. Thanks , have a nice weekend guys.

 

[dslater]

I was just hoping some one could actually answer the question. I didn't think I was going to have to battle to justify the reason why I want to know the parameters.
Ill post to Nikon themselves. Thanks , have a nice weekend guys.

I don't think anyone is trying to make you justify the question. The problem is that we can't answer it for a real lens because not all the relevant data is available. The calculation of a theoretical ideal lens is relatively simple, but your lens, like almost every other lens out there is not perfect. Performing the calculation you want requires detailed knowledge of the optical characteristics and aberrations of your lens. This information is not published. Further, there's variation among individual copies of a given lens, so even if this information were published, it would be average values, not the specific values for your particular copy.

 

[Stoshowicz]

You may find this article useful:

Large format photography: how to select the f-stop

It calculates the optimum f-stop by finding the point where the de-focus circle of confusion = diffraction.

Actually this article is pretty good , but its fairly difficultly presented , does this say the best Fstop is always f11 at this point ?
To summarize, if D is the focus spread expressed in millimeters, then the optimal f-stop which yields the sharpest possible image at the depth of field limits is N = sqrt(375 D). This works regardless of focal lengths, formats, and movements. The resulting resolution at the limits of depth of field (ie for your far and near points) cannot be improved in anyway and determine the maximum possible enlargment. Here are some tabulated values by whole fstops:
Table of optimal fstops (1)

 

[dslater]

Actually this article is pretty good , but its fairly difficultly presented , does this say the best Fstop is always f11 at this point ?
To summarize, if D is the focus spread expressed in millimeters, then the optimal f-stop which yields the sharpest possible image at the depth of field limits is N = sqrt(375 D). This works regardless of focal lengths, formats, and movements. The resulting resolution at the limits of depth of field (ie for your far and near points) cannot be improved in anyway and determine the maximum possible enlargment. Here are some tabulated values by whole fstops:
Table of optimal fstops (1)

No, not really. The parameter D is the focus spread of everything you want to bring into focus - i.e. how much depth of field you need. Once you have determined the DOF you need, this calculation tells you the f-stop to use that will give you the best possible result. This is different from the hyperfocal marks on your lens in that those marks represent the f-stop that gives you the minimal acceptable result, not the sharpest possible result.

 

[aroy]

Theory is fine, calculations even better, but ultimately we are basing these on data which may not be upto mark. Lens data is generally based on theoretical calculations by lense designers, and has very little to do with the actual lense manufactured. The one in your hand may be even off the theory due to to manufacturing tolerances. That is why I am firm believer in testing what I have and using empirical data gathered. So if I have to find DOF, I would consult the DOF tables, but then test the DOF in field, and effects of high F stops on sharpness.

I again reiterate my view that a bit of IQ loss due to diffraction ;at F32/F40; is much better than loss of focus of half or more of the image at F8. After all when I am photographing a fly or a flower I do not want half of it out of focus. One must not forget that the aim is to capture the image diffraction effects be damned.:fat:

 

[J-see]

After all when I am photographing a fly or a flower I do not want half of it out of focus. One must not forget that the aim is to capture the image diffraction effects be damned.:fat:

Yet that's an inescapable problem in macro. You'll never get all the flower or all the fly in focus the more you close in at 1:1. There are only two solutions: step back and crop down or stack. Both will provide perfect focus but at a cost. If not desiring that, you have to pick the part you want in focus.


To add; not with that much pleasure I bought an SB-700 today to solve some macro issues. The idea I had using LEDs turned out to be a failure. I discovered that when it comes to additional light, even a thousand Lumen is but the equivalent of attempting to make a difference by farting during a hurricane. I had the R1C1 in mind but its functionality is somewhat compromised by the length of my lens which is why I settled for the SB-700.

Now I got to do some reading up on flash and get over my dislike.

 

[aroy]

Large format photography: how to select the f-stop

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I think this summarizes succinctly

However, if the subject is very "three-dimensional" you might have to stopping down a lot to have enough depth of field. In this case, do not worry about point 1, since the effect of not having enough depth of field will be more detracting than the loss of resolution due to diffraction, which is not that significant with large format.

 

[J-see]

Large format photography: how to select the f-stop

​

I think this summarizes succinctly

However, if the subject is very "three-dimensional" you might have to stopping down a lot to have enough depth of field. In this case, do not worry about point 1, since the effect of not having enough depth of field will be more detracting than the loss of resolution due to diffraction, which is not that significant with large format.

I'm going to disagree here because without context, this is a nonsense argument. It presupposes that DOF trumps everything and that less DOF would therefor automatically imply a worse image.

An image requires to be sharp where it needs to be sharp for it to work and such can be possible using any DOF. It purely depends upon the context of that specific shot. Just pumping up the DOF because more must be better ignores the fact more DOF comes at the expense of more than some possible diffraction.

 

[aroy]

I'm going to disagree here because without context, this is a nonsense argument. It presupposes that DOF trumps everything and that less DOF would therefor automatically imply a worse image.

An image requires to be sharp where it needs to be sharp for it to work and such can be possible using any DOF. It purely depends upon the context of that specific shot. Just pumping up the DOF because more must be better ignores the fact more DOF comes at the expense of more than some possible diffraction.

Sorry, the context was macro, where the DOF at normal apertures is razor thin. In those cases I would prefer slightly degraded (due to diffraction), to part of the image out of focus.

 

[Woodyg3]

LOL. In my opinion, you guys are overthinking the whole thing. If you need greater depth of field, use a small aperture. If you want shallow depth of field, use a large aperture. Worrying about just exactly how sharp the image will be is seldom as important as the depth of field for a given shot.

 

[WayneF]

I'm going to disagree here because without context, this is a nonsense argument. It presupposes that DOF trumps everything and that less DOF would therefor automatically imply a worse image.

Yes, the context (about a formula) was closeup. The need for more DOF is obviously true of macro specifically, and close up in general. Landscapes or portraits (where DOF actually exists), we might debate it.

However, if the subject is very "three-dimensional" you might have to stopping down a lot to have enough depth of field. In this case, do not worry about point 1, since the effect of not having enough depth of field will be more detracting than the loss of resolution due to diffraction, which is not that significant with large format.

I might point out that this was exactly the original thread context. When stopped down DOF helps more than diffraction hurts, we are dumb not to go with it. It is part of "knowing how". Longer lenses (50mm and more) can handle it rather well (this author is discussing 4x5 large format, a "normal" lens is around 160mm). Macro however is a different subject, about reproduction ratio instead of focal length.

​

 

[Eyelight]

I was just hoping some one could actually answer the question. I didn't think I was going to have to battle to justify the reason why I want to know the parameters.
Ill post to Nikon themselves. Thanks , have a nice weekend guys.

I could answer the question but would need your camera and lens to do so.

Here is what I would do:

Take a series of shots of the same flat subject at each aperture. I would use a tripod and flash to mitigate camera movement. A good subject would be a window screen as it is easy to focus precisely and do not refocus between shots. Viewing the images will give an idea of the acceptable range of aperture.

Using the aperture at the center of the range from above, calculate the combination of distance and focal length to yield a DOF of 4+ inches. Take a series of photos using these combinations. The results should yield the acceptable focal length(s) for the lens.

Doing these two test will give aperture, focal length and distance. So, maybe an hour and 20 photos will answer the question. The likely range will be f/11-f/16 and 150-200mm, but your lens might be special.

Confirm the results by snapping a photo of a mock dragonfly.

 

[J-see]

Sorry, the context was macro, where the DOF at normal apertures is razor thin. In those cases I would prefer slightly degraded (due to diffraction), to part of the image out of focus.

I fear macro is even too broad a context. As I mentioned, a part of the image out of focus is an inevitable part of macro. It's technically impossible to have everything in focus in one shot unless you "cheat".
At 1:1, DOF isn't the size of a football field even at f/45.

You'll have to live with fuzz and decide what you want sharp and what not. Full sharpness is not possible and more DOF not by definition better. It's the context of every specific photo that defines that.

 

[J-see]

I might point out that this was exactly the original thread context. When stopped down DOF helps more than diffraction hurts, we are dumb not to go with it.

I fully agree with that. When the current DOF isn't working for that shot, it would be plain silly to not stop down out of fear for diffraction. If you don't, you'll end up with a lousy shot anyways.

To add; DOF in macro or DOF in landscapes or portraits are not different in my opinion. Relative to their medium, they're identical. It's just that in macro DOF is a tad bit harder to control and any adjustment results into a more severe change.

 

[Stoshowicz]

I fully agree with that. When the current DOF isn't working for that shot, it would be plain silly to not stop down out of fear for diffraction. If you don't, you'll end up with a lousy shot anyways.

To add; DOF in macro or DOF in landscapes or portraits are not different in my opinion. Relative to their medium, they're identical. It's just that in macro DOF is a tad bit harder to control and any adjustment results into a more severe change.

Been sick , but Im fine now,
IMO
Landscape Dof is going to be completely different than macro because you are working at distances close to hyperfocal. In the macro you just dont have that inequal and handy phenomenon.
While I suppose you are correct that , the advantage of the increased dof of small apertures may never be exceeded by the increased softness of image,( Im not sure- I suppose it depends on the size CoC that you use) Im thinking that what makes a greater difference than tightening the aperture initially is to just zoom back and reduce focal length. ( if youre not using a prime).

 

[WayneF]

Hyperfocal does not apply to Macro (infinity is not a concern ). Also, in landscapes with a close near subject, it often seems better to directly focus on the near subject than to use hyperfocal. Saying, at least don't focus in front of the near subject, that does not help infinity either.

Macro and landscape are different DOF situations, but stopping down more (like f/22) obviously helps both in many cases. That is what it is for. Maybe extremes are less true at wide angle focal lengths, but otherwise stopping down is usually an obvious improvement (in those cases when we need more DOF).

Point is, always avoiding f/16 like the plague is often the wrong answer. DOF is not about pixel size. Both do affect Maximum resolution, but we are concerned with the one actual picture, the Actual resolution of a specific scene. So instead of letting the talk about comparing pixel sizes spook us away from this advantage, we should simply try it (f/16, f/22, maybe f/32) in those cases when it helps. Seeing is believing. Try it.