DOF calculator

[Mark von Kanel]

when using a DOF calculator is the subject/focus distance measured from the sensor or the end of the lens? i think its the sensor but i cant seem to find anywhere that actually states that. i know it sounds a little picy to ask, but when photgraphing smaller stff with my macro lens its a 15 cm difference which makes quite a difference in the DOF calculation.

[Inkanyezi]

In most cases you don't need to worry about this, as there is a rather small difference in distances. Generally it should be measured from the sensor plane, but at scales of 1/1 and larger, it is not feasible. I don't know what DOF calculator you have, and I haven't even thought of using one for macro/micro work, so I cannot say how yours will work when you approach natural size on the sensor. At distances of 20 times the focal length and beyond I think it is a moot point from where exactly it is measured.

Simply put, I don't think there is a DOF calculator that could present a correct evaluation for macro distances, but you are free to write one. More interesting than actual distances would be the span of the DOF, and maybe your calculator will give a close estimation of it?

Another approach is to use the circle of confusion as a guide, and it is generally at its smallest at f/8. At very close distances with a macro lens, it is the equivalent, depending on type of focusing mechanism. For an IF lens, it is still f/8 although the actual focal length will have decreased with focusing, and with a lens that elongates, it will be f/4 at 1/1 ratio. Very often is it better to have small part of the image tack sharp than having all of it blurred. For stacking, narrower differences in distance are needed with a larger aperture, in order not to get unsharp bands between sharp slices. It all depends on how you wish to render your image.

[Mark von Kanel]

Sorry Uban my post was a little misleading im using a macro lens but it isnt a macro shot im trying to capture if you look at this thread it will show you what im trying to do

My Bee problems

im using the calculator on here and at 55cm distance i get 2.3 cm at 70 cm i get 3.9cm DOF which is quite a lot for this kind of shot im not even certain that this lens choice is optimal for this picture ill have to play with different combinations and see what works.

[krispix]

Hi Mark,
The short answer is that the measurement is from the focal plane (i.e. the sensor), but depth of field is not a sharply defined thing (no pun intended). Every part of your image is described on the sensor as a circle, known as the Circle of Confusion, at its optimum point of focus it appears sharp. As the point of focus moves further away so the circle becomes wider with less and less defined edges. There is a field where the subject matter is 'Sharp' by all accepted definitions and this is encompassed in the much touted, Depth of Field. This does not mean that anything within that band will be sharp as a tack and anything outside will be out of focus. It just means that anything within the field will be, to all intents, in focus and as you move away from that field things become less so.
Try to use the depth of field you have calculated as a guide to the zone where things will appear acceptably sharp although at the edges of that they may not be as sharp as you might wish.

[Mark von Kanel]

Thanks chris,

I did read the tutorial and to tell the truth there was little new to me but i couldnt for the life of me find a definition of focus/subject distance although it seemed logical that it would be the sensor i prefer to know rather than guess and getting my wife to pull her bee hive to bits every time i want try some new settings for some reason upsets her and the bees

[ajohnw]

The best dof calculator for macro work I have come across is this one which doesn't mention focal distance at all. Just magnification.

http://www.savazzi.net/photography/applet101.htm

That can be used. Say a bee is 6mm long and the sensor is 24mm across at 1:1 it would take up 1/4 of the frame. Or use the mag ratio's often engraved on the lens.

There is a more usual dof calculator here

http://www.mystd.de/album/calculator/

If you enter the values that are usually engraved on macro lenses you will probably find that at the distances stated on the lens the magnification this calculator gives are higher than those engraved on the lens. Lower magnification means more dof.

I have a suspicion that dof focal distances are calculated from a lens's nodal point but that's based on looking at sketches and not taking much notice of the sums.

John
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[Mark von Kanel]

I can feel some experiments with a tape measure coming on!

[Glenn NK]

I can feel some experiments with a tape measure coming on!

My feeling is that this is a better approach.

DOF is a very fuzzy concept (literally) and DOF calculators are interesting but of limited value. I think their best application is as a learning tool. Perusing sites where there is a high ratio of pro photographers, I rarely see DOF come up as a topic in itself.

If you need more DOF, and are close to the subject, focus stacking can be an effective alternative to smaller apertures, but pretty well useless for moving subjects.

Glenn

[William W]

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

[Mark von Kanel]

thanks bill its 1 am here im in bed and ive had to get up and go and see if my body hsa a phi on it!!

[William W]

Mostly all SLR (Single Lens Reflex) cameras do.

With Mirror-less it is a bit of hit and miss I have found: my newer Canon Powershot camera does not: but my Fuji X Series does.

WW

[Peeshan]

"The Film Plane (which is the ‘Sensor Plane’) is identified by the Greek letter 'phi', (φ) , on the outside of your camera" Wow I've always wondered what was that for.

About DOF calculator you could check the smart phones apps. At least for android there is one named "Hyperfocal"- you just enter your camera model and desired focal lens and can save the sheet with all apertures as a picture, or change the aperture and distance to subject and it gives you near and far limit, DOF and hyperfocal. Could be useful in your case.
To be honest I never remember to use it, but as Glenn NK said it's an interesting tool for learning.

[george013]

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

I've tried to look up the definition of Focal Plane, there are different. I stick to the plane perpendicular to the optic ax and through a focuspoint. So pointing to infinit the distances of the focal plane and the film plane are equal, measured from the optical middlepoint of the lens.
All the formulas I've seen of the calculating of the DOF are based on the possibility to change the filmplane within the tollerance given by the accepted CoC. All measured from the optical middlepoint of the lens.

Using the DOFmaster you can check it. Select a 100mm lens and put the subjectdistance at 10cm. Your DOF will be 0. Select for the distance 9cm and your DOF will be negative. So if you want the exact subjectdistance, and you measure from the film plane, you should correct this with the film-pane distance. I don't know how to do that, it's just theorie.

George

[Mark von Kanel]

well its sunday and ive little else to do so it was my intention to carry out just such an experiment our George

[Mark von Kanel]

Hi Peeshan, is that your real name if so can you add it to the "real name" area of your profile so that we know who to chat with? Normally i wouldnt be that interested in accurate DOF calcs it only because of the My Bee problems thread that i want to nail it right down normally its a case of "do i want the background in focus or not" unfortunately for this particular photo i need to be precise and because of the nature of the subject i need to be as prepared as possible.

[george013]

Hi Peeshan, is that your real name if so can you add it to the "real name" area of your profile so that we know who to chat with? Normally i wouldnt be that interested in accurate DOF calcs it only because of the My Bee problems thread that i want to nail it right down normally its a case of "do i want the background in focus or not" unfortunately for this particular photo i need to be precise and because of the nature of the subject i need to be as prepared as possible.

Mark,
You've got a Nikon. Did you try "controlemynikon". http://www.controlmynikon.com/. I think it has got a solution for your problem, both the dof and the distance from the bees..

George

[Mark von Kanel]

Hi george, i have this program but shooting tethered with a pc outdoors is more than i wish to contemplate! because the queen is constantly moving using a tripod for the camera is also difficult so ive been shooting hand held. even if i did do this with the camera on a tripod im not sure how the program would help. could you explain how you would use it for me please?

[george013]

Hi george, i have this program but shooting tethered with a pc outdoors is more than i wish to contemplate! because the queen is constantly moving using a tripod for the camera is also difficult so ive been shooting hand held. even if i did do this with the camera on a tripod im not sure how the program would help. could you explain how you would use it for me please?

I don't have that program and I don't shoot little animals. What I figured out is that that program takes a certain amount of shoots with a just difference focus. I would say that if you think you're able to take one shot handheld, you should be able to use the program. Take a laptop with the program installed, connect it to the camera, aim it on the bee-queen and let your queen handle the laptop at your command.
I'm not sure if it will give you that wanted result, it's just an idee. Once you have a serie of shots, you can decide which you want to use and/or stitch.

I 'often' see beekeepers using cigarsmoke to drug the animals. Maybe you could ask if that would give you some more time.

George

[Mark von Kanel]

Hi George

i think that you mean focus stacking the idea is like you said, a series of shots are taken with a pre programed slightly different focus point, these images are then combined in a program to give you a single image which is entirely "in focus"

unfortunately for this to work all of the images need to be identical apart from the focus point, so you have to use a tripod and the image needs to be stationary. so it wont work for this scenario, which is why im paying so much attention to DOF/COC

i am getting there with overyones help on here, please keep the ideas coming

[ajohnw]

The main use for the film plane marker was for calculating magnification etc with bellows. Manufacturers were also helpful at the time and provided tables which I still feel should come with all macro lenses. All of the dof calculators seem to assume a single element lens so wont give precise results. The only people that could do that for a given lens are the manufacturers. The calculator I posted that uses magnification came from an experts book so would be unlikely to be like the others. The diffraction warnings on that can be important.

I've shot more macro of late because it's a lot easier than using 50mm or what ever lenses on reversal rings on film so have decided to take the approach used on a microscope which I do use a lot at times. DOF and magnification have exactly the same problem as macro on a camera except it's much worse as the magnifications can be rather high. Just translating this to camera use the 1st thing to do is to distance the camera so that the magnification obtained shows the detail at the level that it needs to. In this respect macro is no different to any shot so people should have some idea how big things need to be in the viewfinder to record detail well. This means the camera is set up for the minimum magnification that will do the job rather than higher than in needs to be resulting in less dof. There is a tendency for me to think in terms of how many pixels are underneath the subject or what sort of crop size will be needed and how big that crop can eventually be. Again that's no different to taking any shot. A bit like using telephoto on birds etc and being unable to fill the frame.

Then in th OP's case I would bracket F numbers and use the preview. The simple dof calculator could also be used once the camera is set up and as I suggested I think people will always be working at a lower mag than the calculator thinks so there will be a safety margin.

It might be worth remembering that the dof calculators are generally based on full frame final image size of 12x8in what ever the sensor size is but that is based on fairly high resolution prints as our eyes are concerned viewed from 10in - not PC screens so often things are no where near as bad as they may seem.

John
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