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Extension Tube DoF Calculator

Discussion in 'Web Sites of Interest' started by daft_biker, Mar 31, 2009.

  1. daft_biker

    daft_biker Action Man!


    Good enough for most purposes I expect and interesting even if you don't really care too much. This one for one of my lenses says f/1.4 at 1.5:1 gives even less DoF than I can get at 5:1......must find something to try it out on :D
  2. Malcolm_Stewart

    Malcolm_Stewart Well-Known Member

    I was surprised to see DoF in microns for an example I tried. Could explain my recent oof results... I doubt it - more likely camera shake.
  3. daft_biker

    daft_biker Action Man!

    I think it's pretty normal for DoF in (true) macro to be given in microns. One thing I got from that calculator was that I'm now more convinced that the DoF table for the MP-E 65mm was calculated to give 10x8 inch prints from 35mm and isn't much use now.

    For this shot it says I should get 1.584mm but I think it's closer to 1mm. (BTW the bigger size of that image is 4.5MB and is straight out of DPP if you click the link to original size) Still no idea how to calculate it more accurately for my lens!
  4. wbm

    wbm Member

    I've just came across this post (hello everyone, by the way!) just as my macro calculator page has been updated to handle the MP-E 65 with any Canon DSLR. Serendipity or what? :)

    Give it a go at http://www.flybacon.com/Cameras/Macro.aspx -- you'll need JavaScript enabled for the MP-E 65 to become an option in the extension-tube selector. Let me know how you get on.

  5. daft_biker

    daft_biker Action Man!

    Thanks Ewan and welcome :)

    Have just tried the the one for the MP-E but am getting weird results (no idea if javascript is enabled on this work PC). What focal length and minimum focus distance should be set for the MP-E? Could you pre-fill those fields and max/min apertures when the MP-E 65mm option is selected and only leave the camera and output size options to fill?

    Also, just out of curiosity, can DoF for the MP-E be calculated with the same formula as used for a standard 50mm on some tubes? The reason I ask is that when putting extension on the 50mm all the lens elements are moved the same distance but the MP-E has several groups of elements that all move different amounts as you increase magnification....is it always the same focal length?

    The only niggle I have with the MP-E being in with the extension tube set is that I can't select a DoF table for the MP-E + a set of Kenko tubes (I know the manual says they're not compatible but they seem to work just fine :cool: ).

    Saw some nice night shots of Leith on your site...are you local? I'm about half an hours walk from where they were taken :)
  6. wbm

    wbm Member

    That should happen already. You'd get a big warning box on the page if you loaded it without JavaScript enabled, so I guess it isn't that.

    Try holding down the shift key while clicking on the refresh button (this forces a refresh of all cached files for the page.) The results would've ignored whatever you had in those fields and used the MP-E's values (65mm, f/2.8-f/16, mfd is 24cm, FWIW) anyway.

    The results might look a bit out, but this is because most other D.o.F. tables have been created for a circle-of-confusion (basically the minimum size that an out-of-focus dot can be and still appear acceptably sharp) of 30um, whereas I use two sensor pixels (if you don't select an output size) which can be as little as 9.4um (on a 50D or 500D).

    If you try selecting A6 as an output size for 1.6 crop sensors, or A5 for full-frame, you'll get results similar (c.o.c of 28um and 32um respectively) to other D.o.F tables.

    I don't know how to calculate the magnification of the MP-E plus extension tubes (with d.o.f. calculations, everything relates to magnification and aperture only.) That's why I put the MP-E option in the extension tube selector. ;)

    If you know what magnification you get from the MP-E plus tubes, I'll add them to the page.

    Glad you like the shots. I'm Embra born 'n' bred, living in Bellevue at the moment, so not so far from Leith either.

  7. daft_biker

    daft_biker Action Man!

    Sweet...thanks :) My DoF calculations are usually guesswork :eek:

    About 6.3:1 I think -
    this pic is about as accurately as I can measure it with the tubes on. There are folk that stick a 2x convertor on them too though! (not me....yet ;) ).

    Bellevue?.....just a few streets away from Dundas....even spookier :eek:
  8. wbm

    wbm Member

    (starts hearing Twilight Zone music...) :)

    When I tried plugging in a custom extension tube length to give a 65mm lens 5:1 magnification at infinity (325mm) then added another 68mm of tubes, I get 6:1 for the magnification which seems in the same ball-park as your measured value (the lens might easily change focal-length when focusing so the measured result would differ.)

    As it is quite easy for me to add extra extension-tube lengths to the results, I've put in an extra option to show my results with 12mm, 25mm, 36mm and 68mm extension tubes. I haven't put in any correction for your measured results, that'd be too much work this late at night...

  9. wbm

    wbm Member

    I've now updated the MP-E results with extension tubes to match the measured x6.3 magnification with 68mm tubes, extrapolating the others (seems the lens is more like a ~62mm lens when set to x5)

  10. daft_biker

    daft_biker Action Man!

    Thanks :cool: Am having trouble getting the right result out of that one too....am using the IE that came with Vista but get this URL when I select the MPE + tubes option :D Doesn't seem to give the right results when I try filling all the values....seems to calculate for a normal 65mm on tubes at lower magnifications. Does it work for others?

    Not that I have a practical use for measurements smaller than I could hope to turn a focus rail by hand when focus stacking....I just think the numbers look cool :D
  11. wbm

    wbm Member

    That URL indicates to me that you've got a bad copy of the script files, not sure why though. Have you tried shirt+refresh again? I've tested it with IE8, Opera 9.64 and Firefox 3.1b3 on Vista and XP and they all work fine (although it looks rubbish when IE8's compatibility mode is switched on.) Most odd.

  12. daft_biker

    daft_biker Action Man!

    I'll try it from work when the boss isn't looking ;) Might be using a mobile as a modem that causes problems as it defaults to loading low res images and may not be refreshing all that it should when clicking calculate.
  13. wbm

    wbm Member

    If the page is working correctly, and JavaScript is enabled, then all the calculations are done in your browser without contacting the flybacon.com server at all, so I don't think the mobile modem is a problem (unless it connects via a proxy server that is caching the script files. Try browsing to to attempt to force the proxy to reload the scripts to see if this is the problem.)

  14. daft_biker

    daft_biker Action Man!

    Thanks Ewan...will give it a try. Using Opera mini 3.1 on a mobile at the moment and hardly anything works with that! Anyway, the reason I posted the link in the firt place was because the calculater is better than anything else I've seen for stuff like my 24mm on 12mm of tubes when space is really tight (20mm of tubes makes the working distance pretty much unworkable..a few mm), 50mm with tubes if it's still to tight to use something longer and 100mm with tubes for avalable light(&tripod) stuff. The calculater worked brilliantly for all that stuff where I can (hopefully!) use accurate figures :cool:
  15. wbm

    wbm Member

    Try http://www.flybacon.com/Mobile/Macro.aspx - it works fine with Opera Mini on my phone. This is a much cut-down version of the web-page, so should load faster too (but you can't use custom tube or output sizes.)

    For the MP-E 65, you can leave the aperture values etc. as is, it will ignore the values anyway. I've not added the MP-E with extension tubes yet.


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