Working distance & focus - Canon 100mm macro w/Kenko tub

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rjlittlefield
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Post by rjlittlefield »

JimGnitecki wrote:So, redoing my math to allow for the APS-C sensor size of 14.8mm x 22.2mm:

The actual vertical height of the "Highlighter" lettering is approximately 3/64" = 0.047".

On my computer screen, the photo frame of the resulting shot is 5.5" in height. This corresponds of course to the 14.8mm height of a Canon APS-C frame.

The Highlighter lettering in this frame is approximately 1-1/8" high. This means it is 1.125/5.5 = 0.2045 of the vertical height of the frame.

That makes the image of the highlighter word in the frame 0.2045 x 14.8 = 3.03 mm high or 0.119"

0.119" divided by the actual height of 0.047" = 2.54X actual size

Is that correct?

Jim G
That looks like the correct idea.

But I doubt that the number is very accurate, because of the difficulty of measuring by eye something as small as approximately 3/64".

I suggest repeating your procedure, but measuring something like say the width of the whole string HIGHLIGHTER. Or even better, just photograph a ruler. (Hint: what did you use to measure the height of the "Highlighter" lettering?)

--Rik

JimGnitecki
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Post by JimGnitecki »

rjlittlefield wrote:
JimGnitecki wrote:So, redoing my math to allow for the APS-C sensor size of 14.8mm x 22.2mm:

The actual vertical height of the "Highlighter" lettering is approximately 3/64" = 0.047".

On my computer screen, the photo frame of the resulting shot is 5.5" in height. This corresponds of course to the 14.8mm height of a Canon APS-C frame.

The Highlighter lettering in this frame is approximately 1-1/8" high. This means it is 1.125/5.5 = 0.2045 of the vertical height of the frame.

That makes the image of the highlighter word in the frame 0.2045 x 14.8 = 3.03 mm high or 0.119"

0.119" divided by the actual height of 0.047" = 2.54X actual size

Is that correct?

Jim G
That looks like the correct idea.

But I doubt that the number is very accurate, because of the difficulty of measuring by eye something as small as approximately 3/64".

I suggest repeating your procedure, but measuring something like say the width of the whole string HIGHLIGHTER. Or even better, just photograph a ruler. (Hint: what did you use to measure the height of the "Highlighter" lettering?)

--Rik
I just edited my posting to reflect the actual image size per the Canon specs (15.0 x 22.5mm), while you were posting.

But yes, I want to find something that ap[proaches full width of the frame, BUT I want to photograph something more detailed than the lines on a ruler, because those are pretty rough. I want something detailed enough to give me some idea of what level of fine detail I will be actually able to discern on really small insects with small eyes, antennae, hairs, scales, etc.

It seems obvious to me that the sensor resolution is high enough to make sensor resolution a "does not matter anymore" deal. Canon says there are 19 actual megapixels (rated at 20+ megapixels) in the 70D's sensor, which means there are almost 3600 pixels in the height of that 15.0mm image. That's way beyond the pixel density that my computer screen can display, and its enough pixels that at 600 dots per inch printing, you could make a photo printout of a truly raw (uncompressed) file that would NOT require ANY dot interpolation whatsoever.

And, the 70D uses dual pixel CMOS (phase, versus contrast) autofocus in Live View mode, and enables 10X magnification of the point of focus, so focusing is pretty accurate.

The limitation is therefore clearly the lens.

Getting a macro sized image is only good if the quality of that image is good enough to see the level of detail desired.

To assess that lens limitation, I need a "challenging" very small subject to photograph under controlled conditions. An actual 1/4" sized insect would be pretty ideal, but I don't want to kill an insect while doing a lab experiment just so that it does not move during the process, so I need to find a suitably detailed subject of like size! Perhaps a very detailed flower head or rock or seashell or . . . ?

Jim G
Last edited by JimGnitecki on Fri Sep 15, 2017 9:10 pm, edited 1 time in total.

rjlittlefield
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Post by rjlittlefield »

Check your windowsills and light fixtures. It would be surprising if they don't contain some nice already dead flies and moths. They'll be dusty, but still quite detailed.

--Rik

Lou Jost
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Post by Lou Jost »

Just stick a ruler in front of your lens and be done with it. The tests for detail can be done with other subjects.

JimGnitecki
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Post by JimGnitecki »

Lou Jost wrote:Just stick a ruler in front of your lens and be done with it. The tests for detail can be done with other subjects.
I see your point: SEPARATE the 2 tests. Do a simple magnification test using a ruler, to determine raw macro magnification capability, and then do a quality of image test using a very detailed object. Makes sense.

I have a lot to learn about this new obsession . . . My wife simply doesn't "get" the sudden interest in insects, but she is warming up to it, despite her fear of "creep spiders and bugs" when I point out some of the gorgeous details in macro insect images posted online . . . :D

Jim G

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Post by Deanimator »

banania wrote:Hello, you can also use teleconverters like Kenko 2X teleconverter.
I often use my ProMaster teleconverter with my Tokina 100mm macro lens, with and without the ProMaster extension tubes. I'm pretty happy with the results.

JimGnitecki
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Post by JimGnitecki »

Keep the info and ideas coming. This is all new to me, but utterly fascinating! :D

Jim G

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