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DOF table for Canon 100mm macro
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Joyful



Joined: 19 Feb 2015
Posts: 143
Location: Cape Town, South Africa

PostPosted: Wed Oct 03, 2018 2:24 am    Post subject: DOF table for Canon 100mm macro Reply with quote

Hi Guys - I am making a powerpoint to show beginners the DOF on the Canon macro - something simple ?

Any suggestions

Thanks

Joyful
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Chris S.
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Location: Ohio, USA

PostPosted: Wed Oct 03, 2018 8:00 pm    Post subject: Reply with quote

Joyful,

Take a look at Table 2A in Rik Littlefield's DOF Estimates For Macro/Micro. While this is a portion of the supporting documentation for Rik's Zerene Stacker software, it is applicable to any macro shooting with the sort of lens you're talking about.

--Chris S.
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rjlittlefield
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PostPosted: Wed Oct 03, 2018 8:53 pm    Post subject: Reply with quote

Chris S. wrote:
Table 2A in Rik Littlefield's DOF Estimates For Macro/Micro. While this is a portion of the supporting documentation for Rik's Zerene Stacker software, it is applicable to any macro shooting with the sort of lens you're talking about.

Despite that I built that table -- or maybe because I built it, I have grave doubts that it's a good match with Joyful's audience.

The problem is that the Zerene Stacker table is different from virtually every other source they might see. It's great for what it's designed to do: guarantee that you don't see focus banding even when pixel-peeping a stacked image with an arbitrarily good sensor. But it accomplishes that goal by essentially scaling the size of the COC (circle of confusion -- geometric optics model) in proportion to the size of the Airy disk (diffraction blur circle -- wave optics model). That approach fully accounts for diffraction, but does not give "credit" for limited resolution of either the sensor or the viewer.

The numbers correspond well with other sources if you run down the middle of the bold section, which are the recommended settings for various size sensors. But outside that section, the numbers are different from other sources. For small apertures (large f-numbers, lots of diffraction), the ZS numbers are bigger than given by other sources, while for large apertures (small f-numbers, not much diffraction), they're smaller than other sources. The farther you get from the bold region, the bigger the discrepancy.

For beginners, I suggest instead to use the classic geometry model with standard values for COC. That will give results that "make sense" and do not introduce unnecessary confusion.

Joyful, the standard formula is that:

DOF = 2 * C * N * (m+1)/(m*m)

where:
C is the circle of confusion, typically chosen as 0.030 mm for full frame and 0.019 mm for APS-C,
N is the nominal f-stop setting for the lens (not corrected for close focusing), and
m is the magnification.

For example, 0.5X at nominal f/8 on APS-C will give DOF = 2 * 0.019 mm * 8 * (0.5+1)/(0.5*0.5) = 1.82 mm, which matches what you'll find on https://www.photopills.com/calculators/dof-macro . That's a pretty good match to the 1.3 mm that you'll see in the ZS table.

But at f/4, the standard calculation gives DOF = 2 * 0.019 mm * 4 * (0.5+1)/(0.5*0.5) = 0.91 mm, which again corresponds with photopills.com. But it's not at all a good match to the 0.32 mm listed in the ZS table.

Likewise at f/16, the standard calculation gives DOF = 2 * 0.019 mm * 16 * (0.5+1)/(0.5*0.5) = 3.65 mm, matching photopills.com but not matching the 5.1 mm listed in the ZS table.

--Rik
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Chris S.
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PostPosted: Thu Oct 04, 2018 12:58 am    Post subject: Reply with quote

I agree with Rik's points. In fact had started to write some of them, but decided that a simple tip to "take a look at Table 2A" might be a better way to begin the discussion needed for Joyful to define an answer appropriate to the particular audience and purpose at hand. Rik, thanks for providing the second sally into this discussion. Very Happy

A few thoughts:
    A "beginner" can take varied forms. In this case, the putative beginner has an interchangeable-lens camera and a dedicated macro lens. Such a person is often different from a beginner with a point and shoot. But we don't know if this beginner wants to stack focus or take single shots; pixel-peep or just post to the Web, etc.

    While many in our forum are comfortable with math, and the formula Rik provided is simple, lots of people in the outside world tune out at the mention of any mathematical formula.

    A table, on the other hand, may appeal better to a beginner audience. And a nice thing about this particular table is that it shows, visually, important basic ideas about how aperture, magnification, and DOF relate.

    I could imagine basing a beginner presentation on Table 2A, using it as a resource, but not presenting it as is. If I obtained permission to use it, and after giving credit to my source, I'd likely show the table as is briefly, then switch to a simplified version showing only the numbers in bold. I'd consider color coding these numbers for sensor size. I'd probably remark that the missing numbers to the right will produce fuzzier images, and briefly explain why (diffraction). Perhaps I'd mention that there are times when one might want to work in this fuzzy region--most of us did, before the advent of focus stacking, and not everyone wants images beyond Web size. And I'd probably mention that the missing numbers to the left may be too picky for practical purposes. But of course, this would depend on the audience and the goal of the lecture.

    It's worth mentioning that no DOF chart or formula does more than get a photographer into a safe area--there is always room for "season to taste." So a good general picture of things, with proper admonitions, is a good start for many people. The boldfaced numbers in table 2A strike me as a good start for many audiences.
So we are now three posts into a discussion. Very Happy I suspect that before Joyful gets the optimal answer for the audience at hand, there will be more back and forth.

--Chris S.

--fixed typo


Last edited by Chris S. on Thu Oct 04, 2018 2:12 pm; edited 1 time in total
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Joyful



Joined: 19 Feb 2015
Posts: 143
Location: Cape Town, South Africa

PostPosted: Thu Oct 04, 2018 4:00 am    Post subject: Reply with quote

Thanks Chris and Rik.

All I want to get across is that DOF is tiny, and stacking is a good way to go - and the table 2a does that ! Math will boggle them

Hold thumbs - I will be running a macro workshop of 4 hours a day on Sat and Sunday !

Rather nervous

Joyful
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rjlittlefield
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PostPosted: Thu Oct 04, 2018 5:10 pm    Post subject: Reply with quote

To be clear, I was not intending that the beginners would ever see the formula, only the numbers generated by it.

I rather like Chris's concept of focusing on the bold path down the middle of Table 2A.

That will very nicely highlight the two main points every macro photographer should know:
1) DOF gets small as magnification goes up, and
2) you have to open up to maintain sharpness at higher magnifications.

--Rik
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Joyful



Joined: 19 Feb 2015
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PostPosted: Thu Oct 04, 2018 10:20 pm    Post subject: Reply with quote

Thanks Rik - got it !

joyful
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rjlittlefield
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PostPosted: Thu Oct 04, 2018 11:01 pm    Post subject: Reply with quote

BTW, I hereby grant permission to use anything on the zerenesystems.com website for your presentation. That includes any of the material in my PowerPoint presentations, found as PDF in the Tutorials section.

--Rik
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Joyful



Joined: 19 Feb 2015
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PostPosted: Thu Oct 04, 2018 11:13 pm    Post subject: Reply with quote

Very kind of you - Thanks Rik ! I intend giving Zerene a boost !
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Chris S.
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PostPosted: Mon Oct 22, 2018 4:26 pm    Post subject: Reply with quote

Joyful, how did your two-day workshop go? Very Happy

--Chris S.
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Joyful



Joined: 19 Feb 2015
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Location: Cape Town, South Africa

PostPosted: Mon Oct 22, 2018 10:36 pm    Post subject: Reply with quote

Hi Chris -

Much better than I feared. I had prepared a massive 350 slide powerpoint, with target points to reach at specific times.

Managed to go according to schedule.

Got rated 10 out of 10 by some delegates, and as a result, have been invited to repeat the presentation in January.

very JOYFUL !!
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bs0604



Joined: 19 Feb 2013
Posts: 39
Location: Sarasota FL

PostPosted: Sun Oct 28, 2018 12:15 pm    Post subject: Reply with quote

a couple of beginner questions regarding DOF for stacking.
In rjlittlefields's entry the formula given uses m for magnification. but how do I know what the magnification is? f I am using a setup with 10x microscope objective m would be 10? But what about when I am using my 80 mm macro lens. What is m?
My other questions is in the link to the Zerene site the table lists values depending on "frame width" How do I know what the frame width is in my fujifilm pro 2 APS-C camera using my 80 mm macro lens?
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Joyful



Joined: 19 Feb 2015
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Location: Cape Town, South Africa

PostPosted: Sun Oct 28, 2018 12:26 pm    Post subject: Reply with quote

Hi bs0604 - To get your sensor width, look up the sensor dimensions in your camera manual. Make a note of this, as you need it to determine your magnification.
Now using a ruler in mm or smaller, take a photo of the ruler, and note how many mm you get into your field of view. Magnification is obtained as follows -
camera sensor width divided by field of view

My sensor is 22mm wide. My field of view is 2.2mm. Therefore my magnification is 10 !!

QED
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bs0604



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PostPosted: Sun Oct 28, 2018 1:13 pm    Post subject: Reply with quote

I actually just read this on another part of the forum. Might even have been you who posted it. Thanks. The "nominal f stop" in the formula is wherever I chose to put my camera's f stop?
When I finally get my extension tube set up to mount a microscope objective what f stop do I plug in to the formula as my camera system (fujifilm x pro2) has the f stop determined by a ring on the lens and my understanding using a microscope objective is that the extension tubes will mount right to the camera body and not use the macro lens and thus I won't be setting an f stop. ??
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rjlittlefield
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PostPosted: Sun Oct 28, 2018 1:35 pm    Post subject: Reply with quote

With a microscope objective, the simple approach is to just look up the DOF in Table 2-C at the end of https://zerenesystems.com/cms/stacker/docs/tables/macromicrodof (referenced earlier in this thread).

The NA will be stamped on the side of the objective.

If the exact NA that you have is not listed in the table, then you can use the formula that was used to make the table:
DOF (in mm) = 0.00055/(NA*NA)

--Rik
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