How to calculate step size

[Scarodactyl]

Sometimes the browser will have it cached if you go back to the draft page in your history but usually not.

[rjlittlefield]

I wrote a long reply that seems to have disappeared. I thought I clicked "Submit." I don't want to have to attempt to recreate the message -- PLEASE tell me there's a way to retrieve a draft version of the message!

As far as I know, the forum software does not keep any sort of draft except when the "Save draft" button is pressed. If you had pressed that, you would have gotten a confirmation warning which you don't mention:

Please note that saved drafts only include the subject and the message, any other element will be removed. Do you want to save your draft now?

As Scarodactyl notes, sometimes you can find old writings in your browser history (but usually not).

--Rik

[rjlittlefield]

3. Clearly the step size calculator in Zerene Stacker is better than any of the ones I have discovered (although the one from PhotoPills looks promising). Would you consider making your calculator available online (for free)?

I updated the documentation to include a browser based version of the calculator. See https://zerenesystems.com/cms/stacker/docs/dofcalculator .

--Rik

[JKT]

3. Clearly the step size calculator in Zerene Stacker is better than any of the ones I have discovered (although the one from PhotoPills looks promising). Would you consider making your calculator available online (for free)?

I updated the documentation to include a browser based version of the calculator. See https://zerenesystems.com/cms/stacker/docs/dofcalculator .

Very nice!
Note: "DOF (wave optics) – diffraction-limited depth of field, calculated from effective effective and magnification"

[Pau]

I wrote a long reply that seems to have disappeared. I thought I clicked "Submit." I don't want to have to attempt to recreate the message -- PLEASE tell me there's a way to retrieve a draft version of the message!

Walter

First check the browsing history of your web browser, I remember to have been able of recovering a non uploaded post from there in few cases. If not, likely it's lost forever.

[JKT]

P.S. - All of the examples that we have discussed so far have been relatively simple and straightforward. (Hah!) What happens to the step size calculation when the macro rig is complicated by the addition of extenders, extension tubes, diopters, etc.?

I seem to recall this exact question was answered somewhere ... was it in Zerene help or in the discussion thread about the calculator development?

Coming back to this. The answer for the extension tubes and teleconverters - as long as extension tube is between lens and teleconverter where it should be - seems to be:

So if you have a base lens set on magnification m and know the effective aperture, pupil magnification and focal length at that magnification and know the amount of extension and TC power, you can calculate the new effective aperture and total magnification using those formulas. After you have the modified values for magnification and effective aperture, the dof calculation proceeds normally.

The problem is that for modern lenses none of the three lens properties at m are trivial. The focal length and pupil magnification can be interpolated from values on Photons to Photons, but the effective aperture seems more tricky. You may have to measure it for your lens from light loss. The value on Photons to photons is based on maximum opening in the lens. If the aperture is programmed for something else you are out of luck. I've done the calculation and polynomial approximation for MP-E65, EF 100 L, EF-S 60 and Sigma 70 A. I'll add EF-S35 and possibly EF 180 L & Tamron SP 180m, but then I'll be out of macro lenses.

[rjlittlefield]

Coming back to this. The answer for the extension tubes and teleconverters - as long as extension tube is between lens and teleconverter where it should be - seems to be:

Formula.png

So if you have a base lens set on magnification m and know the effective aperture, pupil magnification and focal length at that magnification and know the amount of extension and TC power, you can calculate the new effective aperture and total magnification using those formulas. After you have the modified values for magnification and effective aperture, the dof calculation proceeds normally.

I agree, and to my eye the formulas you show look correct.

The problem is that for modern lenses none of the three lens properties at m are trivial.

Yea, verily. You turn the ring, you really don't know what's happening on the inside.

the effective aperture seems more tricky. You may have to measure it for your lens from light loss. The value on Photons to photons is based on maximum opening in the lens

(Should be "Photons to Photos" -- no second "n")

In principle, the effective aperture could be calculated from measurements of the location and diameter of the exit pupil, IF you can separate the lens from the camera while maintaining the focus and diaphragm settings. Unfortunately this is becoming progressively more difficult as lenses get smarter. In quick test just now it looks like my new Canon R7 kit lens still does this if I set for manual focus, manual aperture, and hold down the DOF preview button while removing the lens with power on. But the physical layout of the camera makes this difficult, and I can't be sure what it's doing, and probably it violates warnings in the manual. Metering the light throughput seems much more practical.

One caveat: rather than trusting that any software "exposure" slider is behaving as expected, I would crosscheck by changing the exposure time to see how much more time is needed to get the same pixel values with a smaller aperture.

I would be interested to see what results you get for the MP-E 65 and EF 100 L. I have those lenses too, but have done very few careful measurements of them.

--Rik

[JKT]

I agree, and to my eye the formulas you show look correct.

Thanks for checking! I at least checked that the extension part gives same final result when applied at once or in two parts.

(Should be "Photons to Photos" -- no second "n")

Now that makes MUCH more sense! I guess I misread it once and never checked.

One caveat: rather than trusting that any software "exposure" slider is behaving as expected, I would crosscheck by changing the exposure time to see how much more time is needed to get the same pixel values with a smaller aperture.

In this case it is Canon software with Canon RAW files, but the point is valid. I've used it a long time and the numbers have always seemed to match when I change ISO, time, aperture or flash power. I have not done a detailed check, though.

I would be interested to see what results you get for the MP-E 65 and EF 100 L. I have those lenses too, but have done very few careful measurements of them.

Well, those results I already have, so...
EF 100 L:

MP-E65:

The unit in those is aperture value, so 1 means one stop down from set number. The 0-point for MP-E may not be quite accurate for obvious reasons.

I mentioned on this or another thread that 100 L has an interesting behavior around m=0.5. The fitting does not try to duplicate that.

The data points at 0.3, 0.4 ... 1.0 have duplicate measurements, though one set was missing the zero value, so that is adjusted - with same value for all the points in that set. The oddity takes place at the same magnification, where Photons to Photos shows that the limiting aperture location changes, so I think it is intended. I was surprised with the two additional points between old ones being on the curve, though.

[4odonates]

Well now we’re getting somewhere! Thank you, thank you, thank you for making your excellent DoF/step size calculator available online, Rik!

I’m surprised and delighted the calculator works with relatively little input. (For example, focal length of the lens isn’t required.) Would it help or hurt to input as much information as I know? (Maybe it’s a wash.)

Regarding my long reply that disappeared I’ll get back to everyone after I see whether I can recover my post by looking at browser history. Thanks to all who made that suggestion!

Walter

[rjlittlefield]

Well now we’re getting somewhere! Thank you, thank you, thank you for making your excellent DoF/step size calculator available online, Rik!

You're very welcome. It should simplify my life also, when questions come up.

I’m surprised and delighted the calculator works with relatively little input. (For example, focal length of the lens isn’t required.) Would it help or hurt to input as much information as I know? (Maybe it’s a wash.)

In the closeup/macro/micro regime, calculations get simpler when you allow the optics to be described by magnification and effective aperture.

All that stuff about focal length and working distance and whatnot is just a way of getting to magnification and effective aperture anyway.

I think the main value of putting in more information is only to help clarify for yourself how things fit together. For example the diffraction limited wave optics DOF is determined entirely by magnification and effective aperture. The result may be less sharp than what you think you need (as specified by a small COC), or maybe you can actually live with some more blur (as specified by a large COC). If so, then you'll get the suggestion to consider using a larger or smaller aperture, to better match the sharpness you said you needed.

--Rik

[4odonates]

Bad news: I was unable to recover a draft version of my long post by looking at Web browser history. Oh well, it was worth a try. Thanks to everyone for the suggestion!

Most of the lost reply is moot now that Rik released an online interactive version of his excellent DoF/step size calculator. A lot of what I wrote was related to my efforts to get Rik's older Microsoft Excel spreadsheet to work. But since you asked, Rik, I was using Microsoft Excel for Mac 2011, Version 14.0.2 (101115). Now you know.

I'll post another follow-up reply if I remember anything important I forgot to mention.

Thanks!
Walter

[Chris S.]

Bad news: I was unable to recover a draft version of my long post by looking at Web browser history. Oh well, it was worth a try. Thanks to everyone for the suggestion!

Sorry to hear this, but not surprised. Having lost a post or three myself, I now usually compose long posts in Microsoft Word, then paste them into the form here at the forum.

--Chris S.

[4odonates]

Hi Rik! May I have permission to use several screen captures from your new online interactive DOF Calculator for a blog post tentatively planned for Tuesday, 21 February 2023? Of course credit will be given to you. [Would you prefer a specific URL or email address for the credit?]

The primary purpose of the blog post is to illustrate how I used your calculator to determine the "safe step size" (with 20% overlap) for focus bracketing with all of my basic macro photography rigs.

Thanks, Rik!
Walter

[rjlittlefield]

Sure, permission granted.

Use the URL of the calculator, https://zerenesystems.com/cms/stacker/docs/dofcalculator . If anybody wants to reach me they should be able to figure it out from there.

When you get the blog post made, please let me know the URL. Thanks!

--Rik

[4odonates]

Thanks for permission to use screen captures of your DOF Calculator, Rik.

My blog post is online at the following address …

https://waltersanford.wordpress.com/202 ... alculator/

Corrections and/or suggestions for improvement are invited and welcome.

Walter