DOF calculator

[DanK]

Mark,

I shoot a lot of bugs, and frankly, I don't think a more precise understanding of the numbers will help. It is possible to use image stacking in a circumstance such as yours if you are steady and fast enough, and have a flash that will refresh fast enough, but I can't do it. I have never managed to stack bug shots, even though I stack flower shots all the time. My solution is to:

--use a diffused flash. Without that, you don't have much chance of getting a small enough aperture to get a reasonable DOF.
--keep the subject as close to parallel to the sensor as you can.
--start at f/13 (nominal aperture).

Nominal vs. effective aperture is explained in the macro tutorial on this site. Basically, effective aperture is smaller (larger number) at macro distances. Canon cameras (which I shoot) show the nominal aperture. I believe that some Nikons show the effective aperture.

This usually works. E.g., this shot, which is higher magnification (hence narrower DOF) because I shot it with a 36mm extension tube:



If f/13 is not enough, you could go smaller. You will start getting some diffraction (remember that the effective aperture is narrower), but with the increased DOF, the image may appear sharper anyway. I have shot macros with nominal apertures up to f/22 that look fine printed at 8 x 10 inches (roughly A4).

You can see the effect of not being parallel to the sensor in the next shot. Check out the back of the abdomen--clearly out of focus.



One last suggestion: I have been shooting bugs for maybe 6 years, and even after that much time, most of my shots fail, usually because either I or the bug moves enough to ruin focus. A standard solution is to take a bunch, moving the camera very slowly to regain focus. A monopod helps a lot for that. You just have to be patient, and be happy that digital makes all the unsuccessful shots free.

Good luck.

Dan

[ajohnw]

Maybe some examples of what I was getting at will help. This is the full frame view.



This may load slowly as it's a 100% crop to show what that captures. Saved at 80% quality which should help size wise. SOC jpg with no processing in or out of the camera. It will enlarge a lot in the light box if clicked on.



These will be a bit smaller than the OP's bees. They were taken on 16mp micro 4/3 at F14 so another 16mp camera with a larger sensor for the same sized view would need more magnification and consequentially would have less dof available. On the other hand on m 4/3 as the pixels are rather small I am getting diffraction effects in some shots especially on insect eye detail, either that or pixel aliasing. If that then more magnification would help get rid of it. I feel I have seen signs of both at F14. I've also taken shots that don't reduce well because the detail is lost when the image is web sized. PP can help with that but only so far.

Stacking in micro work is largely aimed at getting round diffraction effects. Life gets tough in this area. It's possible to relate F ratio to resolution and in real terms on that basis 2 to 3 times the resolution required by the specimen are needed so for shots like this one F ratio's of 1 or eveb faster might be used. There is plenty of info about on the man's site if I remember correctly but I know some one who does this sort of thing for a living and largely listen to him. And make my own mind up of course. I have an interest in this area which is one of the main reasons I have been working on my PP.



John
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[Mark von Kanel]

Dan / John.

Just goes to show how much i have to learn on this subject and how much practice i need! but this is all great stuff and i will get there in the end.

Thanks for all this help its great!

[ajohnw]

I might get assassinated by the microphotography mafia for telling people to think about how much mag is needed and also in the extreme how fast an F ratio. For some reason nobody spells it out. Probably because for microscope users it's so obvious.

John
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[Mark von Kanel]

To Tell truth John it just went whooooosshhh straight over the top of my head! ill do some reading and see if it can sink in!

[Mark von Kanel]

Hi Guys taking all of your advice on board i took this today. ive put it on a separate thread and if you could add your non DOF advice their it would probaly help a wider selection of peeps who arnt interested in DOF!!

[krispix]

The (still) correct technical term is "Film Plane", even in this modern world of digital sensors.

"Film Plane" is still surviving for TR&D, Technical Papers, Texts and Examinations, in this digital era.

The Film Plane (which is the ‘Sensor Plane’) is identified by the Greek letter 'phi', (φ) , on the outside of your camera:

WW

Hmmmm! Must be something to do with being upside down in the Antipodes.

Here in UK it's referred to as the Focal Plane and always has been (going back to my 1949 textbook anyway), as for the use of the lower-case Phi - Well, it does look like that, but you'd have to view it on its side (as your picture). Viewed from the normal perspective (from behind the camera) it's merely a circle with a line, which matches the Focal Plane, running through it.
In reality, it doesn't matter what you call it, or what you believe it is, as long as we all know what we're talking about.