Diffraction limited pixels... Really?

[WayneF]

CA and diffraction are different properties, but neither helps sharpness. I can't say I am ever bothered with CA, I don't view at 100% often.
But if you have tried and verified your case, then great. I am impressed by actually trying.

My overall point was:

In general, instead of blindly believing everything we hear on the internet (about image pixels being too small, which is too much resolution),
we should actually try stopping down (for example, f/22, or more), not routinely, but when we seriously need more depth of field.
When it helps, it helps (obviously and dramatically). Not in every case, but it helps tremendously in many cases.
This is why the f/stops are provided. They work, really well (short lenses are a special case however, needing more image object size to counteract).
But we are dumb to always shut out the valuable f/16 and f/22 from consideration, merely based on some poor hearsay opinion (other than our own).

If we claim to believe it matters, then we should be able to see it.

 

[Stoshowicz]

I hope Im not taking this conversation off track, but math just isnt my strong suit, but you guys seem very comfortable with it. So I just want to ask a specific question... I have the D7100 and I use the 70-300mm vr zoom lens on it.
Mathematically ,, What are the settings for optimal clarity in my final image at its nearest focus which is about 1.5m (or more if I need to move back) ?
for a dragonfly which is three inches long and three inches deep , and I want the whole thing clear tip to tip, ,
just the best it can do, all things considered together. So I can just set my camera to that as a standard dragonfly setting,
Trial and error takes forever when one has multiple factors involved.

 

[J-see]

Maybe someone knows how to calculate this but it won't be an easy formula.

A maybe easier approach to the problem is using some measuring tape and then go the distance until the preferred size fills the sensor. That's the distance you'll need.

At that point the bug is about 1/32th its size relative to what's on your sensor (762/24) and it should be possible to calculate the minimum aperture for the required DOF.

 

[WayneF]

My own notion is there are no special dragonfly settings. And without experimenting, I can't answer specifically. 1.5m is about 5 five feet, and 300 mm DX would have a field of view width of 4.8 inches there, so I suspect you are at 300 mm.

That 1.5m is pretty much the absolute closest focus the 70-300 can do. If you need the subject closer and larger, you could add a "close up filter" to the front lens threads, to make it focus closer, therefore to see a larger subject in a more narrow view. Sometimes called "Close up Lens", but it is just a simple magnifying glass attached to front of lens. It is not the best optical situation (macro lenses are better, but they lose the 300mm benefit). Close up filters are in two classes, cheap single element models, and more expensive double element models (maybe $100 class, with more correction, less color fringing, etc). The Canon 500D closeup filter is a double element, and very well regarded. Not sure it is available in 67mm thread size? You have to stop down considerably with these closeup filters (to keep frame edges sharp), so if you have enough light, I'd start at f/16 or f/22 for this special case (with or without the close up filter). Stopping down is greater depth of field (greater zone range actually in focus), and it better corrects the optical issues of the closeup lens.

But clear tip to tip is the major issue, its never that easy up close. It is more about procedure than gear. Your camera angle should position itself so tip to tip wings are in one plane at the same distance everywhere, one focus distance for all the wing span. That's the only way to get it all sharp, up if very close. Stopped down aperture is the way to try, but a proper camera angle is important.

The 300 mm lens offers to f/40, which is extreme (much less so at 300 mm), but it is there for that purpose. f/40 will require a lot more light (four fstops more than f/10. So high ISO or shutter speed will go to slow), so you may need a close flash to do it. Such magnification efforts are not really point&shoot, it is something we learn to deal with. First day will not be the best day.

I'd say experiment with f/16 to f/40, pick what you like.

 

[J-see]

I was just punching the numbers in some DOF calculator and apparently you got 2.64cm DOF with a 300mm at 1.5m distance.

The dragonfly is 7.62 cm which would force you to go back to some 3.5m to get that DOF.

At f/32

To add; 70mm at 1.5m using f/9 provides about the same DOF.

Online Depth of Field Calculator

 

[Stoshowicz]

I was just punching the numbers in some DOF calculator and apparently you got 2.64cm DOF with a 300mm at 1.5m distance.

The dragonfly is 7.62 cm which would force you to go back to some 3.5m to get that DOF.

At f/32

To add; 70mm at 1.5m using f/9 provides about the same DOF.

Online Depth of Field Calculator

Yep Jsee , I think youre understanding the question I'm trying to ask. A person leaves their, my, house with specific gear,, thats fixed info.. the dragonfly proportions , again , are a fairly fixed parameter. I can alter my distance I can alter the light , I can alter all the settings on the camera.,, none of that is fixed , and so thats really what a person needs to know to get the maximum resolution out of the gear-- is how far they need to be from the thing and what aperture they need to use, with which focal length ( on a zoom).
Ballparking your technique , youre not really optimizing what the camera can do.
If I zoom back to 70mm maybe that diffraction thing stars affecting my resolution , but if Im out at 300mm then I start getting away from the sharpest resolution of the lens ,, but that still may be better than the diffraction.
If I close up my aperture , then I start to gain DOF , If I open my aperture , then I will need to back up to get the Dof again,, but if I back up , then I start start having a smaller image, ..
and so forth.
My point is however , that the optics should be able to be calculated and optimized ,, knowing the depth of the field one needs crisp clear,, and that will be particular for any given lens.
If One cannot actually know this information , then data about the airy disk and such , while very interesting , doesnt actually help more than to chimp the shot.
And this doesnt just apply to bugs , it would hold true for other things like product placement shots etc.

 

[J-see]

My point is however , that the optics should be able to be calculated and optimized ,, knowing the depth of the field one needs crisp clear,, and that will be particular for any given lens.
If One cannot actually know this information , then data about the airy disk and such , while very interesting , doesnt actually help more than to chimp the shot.
And this doesnt just apply to bugs , it would hold true for other things like product placement shots etc.

The unavoidable problem is that one can't calculate it all.

The composition is only constructed during the moment of the shot (unless you start with a specific goal). I could check the size of a specific spider and calculate exactly what magnification at what distance at which aperture covers all the DOF I require but that's only of use when I'm cataloging spiders and need species shots. When I'm not doing that, all this info about spider X requiring X, Y and Z suddenly falls apart when I'm trying to compose something that includes a part of a branch and a portion of the web. Suddenly all my calculated information is irrelevant.

Now what's there to do? Write down and calculate every possible option I could ever encounter? That's an option but I'd be busy until my last breath and would lack the time to actually shoot something. Or I could improvise in the moment.

I'm the improvising type.

There's nothing wrong with knowing your stuff and I'm the first to close down the lens, up the ISO or do whatever possible when such improves the end result. However; the moment any of these changes come at the expense of something and I'll have to find a compromise, I wonder about the why of that change. If the answer is that it'll improve my shot as a whole, I find it an acceptable solution. If the answer is because that's what you're supposed to do, I don't find that a good enough reason.

I go with my flow and hopefully the more experience I gather, the steadier that flow becomes.

 

[Horoscope Fish]

Yep Jsee , I think youre understanding the question I'm trying to ask. A person leaves their, my, house with specific gear,, thats fixed info.. the dragonfly proportions , again , are a fairly fixed parameter. I can alter my distance I can alter the light , I can alter all the settings on the camera.,, none of that is fixed , and so thats really what a person needs to know to get the maximum resolution out of the gear-- is how far they need to be from the thing and what aperture they need to use, with which focal length ( on a zoom).
Ballparking your technique , youre not really optimizing what the camera can do.
If I zoom back to 70mm maybe that diffraction thing stars affecting my resolution , but if Im out at 300mm then I start getting away from the sharpest resolution of the lens ,, but that still may be better than the diffraction.
If I close up my aperture , then I start to gain DOF , If I open my aperture , then I will need to back up to get the Dof again,, but if I back up , then I start start having a smaller image, ..
and so forth.
My point is however , that the optics should be able to be calculated and optimized ,, knowing the depth of the field one needs crisp clear,, and that will be particular for any given lens.
If One cannot actually know this information , then data about the airy disk and such , while very interesting , doesnt actually help more than to chimp the shot.
And this doesnt just apply to bugs , it would hold true for other things like product placement shots etc.

I have a feeling you can crunch all the numbers you want but, once you're out in the field actually attempting to shoot this notoriously difficult subject, methinks you'll be chasing your tail with all this. Far be it from me to squash a good conversation but I keep coming back to the idea that, while there is clearly a degree of science involved in the art of photography, in the end it's still far more art than it is science.



/wet blanket
....

 

[WayneF]

I have a feeling you can crunch all the numbers you want but, once you're out in the field actually attempting to shoot this notoriously difficult subject, methinks you'll be chasing your tail with all this. Far be it from me to squash a good conversation but I keep coming back to the idea that, while there is clearly a degree of science involved in the art of photography, in the end it's still far more art than it is science.



/wet blanket
....

That's my notion too, you try what you've got and think, and then do what you need to do to get what you want.

Your best guide is your experience last time.

 

[Stoshowicz]

Yep guys , thats really somewhat reasonable , I do shoot the dragonflies all the time though , I have hundreds of shots , some of which are on flickr.. my personal experiences aside , Im suggesting that its not this impossibly huge number of results covering a large number of circumstances,
Mr. Jsees point there is valid , if I hadnt already defined what my depth of field needed to be exactly.. three inches.
Mr. Horoscope fish, well I dont want to number crunch out in the field either, I agree ,, thats my point ,, but ,, neither do I want to be guessing.
Mr Wayne F , my experience ' last time out ' doesnt tell me whether I have already reached the limits of what the camera should be able to do.

Id like to convert yall to an idea here ,, which you may have encountered on your own,, I dunno ,,"what exactly is the best this thing can do?".
I read one day far back , that the larger the aperture , the sharper the image in the focus plane.
So for maybe a year , I was shooting with the camera wide open.
Not surprisingly I got a good deal of color fringing against the sky ,etc, so I reduced my aperture and found out that at the smaller end I began to lose clarity there was a tradeoff to be made.Then one day I read that the lens wasnt as sharp zoomed all the way out, so I zoomed back a bit and found out I still was losing resolution but now it was because the image was smaller. Somewhere inbetween there is a tradeoff.
Then I read this particular lens was sharpest at aperture f11 and ,on another chart, when zoomed back to 135mm ,
But taking pix , It seemed that I was actually seeing the best resolution in the cropped end result zoomed all the way back out to 300mm at F22 for something about eight feet away.
Then I tried focus on something as close as I could get and got my best closest resolution at f11 and 200mm. Ughh!

Thats far too much math for me , I dont have the patience , and Im not going to sit around punching numbers into a DOF calculator as my dragonflies take off for parts unknown.

But its clear to me , that since there are trade offs being made - there is an intersection point optimum for each parameter
(aperture , angle of view )
And there may in fact be a single sloped line describing the optimum of the combined parameters for a given lens. It may be that only the manufacturers have enough data to draw it up.. but if known , you could compare the choices you made , to the best choices you could have made. Without this combined parameter , you just do not know whether you are getting the best out of the lens. YOU ARE GUESSING . Yes you may be roundabouts that very best quality by virtue of your experience , but you also may be trending to use too much aperture , or too little -too close or too far, too much zoom , too little zoom. Or perhaps this lens isnt the one you should be using. Professionally you could be wasting time taking shots that were close , but not good enough. You calculate exposure , or at least you have the camera do calculation, and youd be willing to calculate Dof for its own sake .. why shouldnt you be able to calculate or set a shoot up, for greatest sharpness?? (when thats what you need)

 

[Horoscope Fish]

And there may in fact be a single sloped line describing the optimum of the combined parameters for a given lens. It may be that only the manufacturers have enough data to draw it up.. but if known , you could compare the choices you made , to the best choices you could have made. Without this combined parameter , you just do not know whether you are getting the best out of the lens. YOU ARE GUESSING . Yes you may be roundabouts that very best quality by virtue of your experience , but you also may be trending to use too much aperture , or too little -too close or too far, too much zoom , too little zoom. Or perhaps this lens isnt the one you should be using. Professionally you could be wasting time taking shots that were close , but not good enough. You calculate exposure , or at least you have the camera do calculation, and youd be willing to calculate Dof for its own sake .. why shouldnt you be able to calculate or set a shoot up, for greatest sharpness?? (when thats what you need)

First of all, I do think you're chasing the wind because I don't think this calculation would yield much on a practical level. Even if you *were* able to calculate the optimal combination of focal length, aperture, distance to subject and so forth for any particular lens (and this assumes there even IS such a thing) I think the entire formula is for not because of the highly dynamic nature of light itself. Possibly under studio conditions where the amount, angle and temperature of the light used can be controlled... Possibly. But I doubt it. And I doubt the return would be worth the time and trouble invested.

Just my two cent's worth, of course, and if you wish to pursue this line of reasoning I wish you nothing but good luck and better shooting!

....

 

[Eyelight]

Dragonfly 3" framed in camera at a 6" subject size

3.30" DOF - 200mm, f/16 @ 94" distance yields roughly 10" image cropped to 6" final image
3.05" DOF - 200mm, f/22 @ 77" distance yields roughly 8" image size cropped to 6" final image
3.05" DOF - 300mm, f/22 @ 115" distance yields roughly 8" image size cropped to 6"final image
3.54" DOF - 300mm, f/45 @ 89" distance yields roughly 6" image size

While 200mm is probably cleaner than 300mm and f/16 is probably cleaner than f/22, all have to be cropped except for the 300mm @ f/45, which likely is not the crispy one. Bear in mind that the DOFs above are considered where the acceptable sharpness ends based on viewing criteria that may or may not suit the final image. Also, the DOF is spread in front and behind the focus distance, so for these to work, the focus has to be selected with care.

But then, where's the shutter speed and ISO been while we were maximizing the DOF. Either one or both have been going in the wrong direction for sharp images.

So, this answer is not so much an answer as it is an exercise in why there is no single answer.

Would diffraction be noticeable in any of these shots? Seems more likely that a slower shutter speed or higher ISO would have greater impact.

In a way, the dragonfly question lends to Wayne's point because using an aperture less than f/16 pushes the subject even farther away to keep the DOF above 3". To use f/11 we need to move back to roughly 14' and end up with a 12" image that has to be cropped to half the horizontal resolution. However, it could yield the best final image.... maybe.

 

[aroy]

First of all the sharpest region of a lense is usually two or three stops away from wide open. That is where detailed reviews help. They have sharpness vs aperture well mapped out. Some lenses are reasonably sharp wide open (Super Telephotos), as they are designed for it, but even there a stop or two will yield sharper images.

I believe that going for higher F stops to achieve better DOF is worth it. After all if I get a reasonably sharp shot at F22 (or F32), it is better than a shot where half the image is out of focus. My 105mm AIS macro goes upto F/40, and when I try shots they give me quite a good DOF, and that is what I am interested in.

 

[dslater]

First of all the sharpest region of a lense is usually two or three stops away from wide open. That is where detailed reviews help. They have sharpness vs aperture well mapped out. Some lenses are reasonably sharp wide open (Super Telephotos), as they are designed for it, but even there a stop or two will yield sharper images.

This is because most lenses are not diffraction limited. They have aberrations and usually it's the outer region of the lens that contribute the most to the aberrations. Stopping down masks out the outer regions of the lens removing these aberrations and yielding a diffraction limited result. ( Since stopping down also increases diffraction, it is easier for the stopped down lens to be diffraction limited. ). There are examples of diffraction limited lenses that do not improve when stopping down. The newest Nikon 600mm f/4 AF-S is an example - this lens actually performs best wide open. Other examples are the old Ultra-Micro Nikkor industrial lenses - these lenses all perform best wide open - stopping down reduces resolution in these lenses.

However, for this discussion regarding DOF, I believe we're making an implicit assumption that we have an ideal diffraction limited lens.

 

[dslater]

Dragonfly 3" framed in camera at a 6" subject size

3.30" DOF - 200mm, f/16 @ 94" distance yields roughly 10" image cropped to 6" final image
3.05" DOF - 200mm, f/22 @ 77" distance yields roughly 8" image size cropped to 6" final image
3.05" DOF - 300mm, f/22 @ 115" distance yields roughly 8" image size cropped to 6"final image
3.54" DOF - 300mm, f/45 @ 89" distance yields roughly 6" image size

While 200mm is probably cleaner than 300mm and f/16 is probably cleaner than f/22, all have to be cropped except for the 300mm @ f/45, which likely is not the crispy one. Bear in mind that the DOFs above are considered where the acceptable sharpness ends based on viewing criteria that may or may not suit the final image. Also, the DOF is spread in front and behind the focus distance, so for these to work, the focus has to be selected with care.

But then, where's the shutter speed and ISO been while we were maximizing the DOF. Either one or both have been going in the wrong direction for sharp images.

So, this answer is not so much an answer as it is an exercise in why there is no single answer.

Would diffraction be noticeable in any of these shots? Seems more likely that a slower shutter speed or higher ISO would have greater impact.

In a way, the dragonfly question lends to Wayne's point because using an aperture less than f/16 pushes the subject even farther away to keep the DOF above 3". To use f/11 we need to move back to roughly 14' and end up with a 12" image that has to be cropped to half the horizontal resolution. However, it could yield the best final image.... maybe.

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

 

[Eyelight]

If we stop and think about the images we take and the ones that are in the box (throw back from Kodachrome), there are not that many that diffraction is going to impact. Here is why. Sharpness is relative to blur. There are images with blurry subjects that look great because the background is blurrier. There are very few images that every single square nanometer is perfectly sharp, so we are fine with blur and use it every day to our advantage.

One other reason, is the only focused part of an image is the focal plane. The DOF in front and behind the focal plane is falling off immediate; just doesn't get unacceptably sharp til the front and back edge of the DOF, which is arbitrary depending on what you plan to do with an image.

However, good to understand the things that impact every aspect of what I'm trying to do.

Good discussion. Good questions and replies.

 

[Stoshowicz]

Horoscope Fish
Assume Nikon standard daylight from above, maybe 5600 Kelvin. Im just trying to find out whatever is optimum using conventional standards and I know that in the field, I would always be hovering around that optimum configuration,, but Id at least be hovering around the actual optimum rather than a subjective and questionable 'trial and error fudged optimum'.
I'd have to actually give the methodology a try, before I said it wasn't useful to know the best settings for my lens.

 

[Stoshowicz]

I like that complete coverage as well. Yep I see those rules of thumb and the usual sharpness charts. The problem with those charts is the number of factors has been reduced to simplify the actual situation.

 

[Stoshowicz]

This commonly used lens ( I checked last night) only goes to f32. Assume the focus is properly centered. Shutter speed is 1-250th of a sec ( sync speed) the iso is 200, and any additional light needed is to be supplied with the on camera flash.

Yes I agree that Wayne's point on the significance of the diffraction plays a part in defining that which would be optimum.
and Yes I think that physically altering distance will also play a part in the calculation , both of which are why DoF calculators dont answer the question.

 

[WayneF]

I'd have to actually give the methodology a try, before I said it wasn't useful to know the best settings for my lens.

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.