Edmund (?) 175mm doublet as tube lens

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jnh
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Edmund (?) 175mm doublet as tube lens

Post by jnh »

Haven't posted here in a long time, but I thought this might be worth mentioning. I had a surplus lens doublet sitting around for the longest time, and given some other stuff it came with, it most likely is from Edmund. I just tried this as a tube lens, swapping out my Raynox 150. I didn't run any scientific tests, but subjectively it looks just as good or even better than the Raynox. Below is an example of a poppy seed taken with the Mitu 20X and the doublet.

Image

Lou Jost
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Post by Lou Jost »

On my screen this does not look very sharp. Would be nice to see a comparison.

jnh
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Post by jnh »

Here's a seed with the Raynox. Different seed, slightly different lighting, hence the not very scientific comparison.

Image

Lou Jost
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Post by Lou Jost »

Yes, I see, the doublet does look better. But a controlled comparison should be done. And perhaps it would be helpful to use a subject that has more fine detail, like a butterfly wing.

Macro_Cosmos
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Post by Macro_Cosmos »

EO achromatic doublets are quite decent as a tube lens. I've had some success with FL=200mm ones at work.

Never thought about doing a test though, I just assumed it wouldn't be as good as something dedicated to the task.

jnh
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Location: US East Coast

Post by jnh »

Didn't have a butterfly wing or a silicon wafer around, but I run a more systematic test with a bank note (of non-US origin). Used the 10X Mitutoyo (it's sharper than my 20X) this time, but illumination etc. was all identical.

The below images were stacked in Zerene and sharpened in Affinity (same parameters for both of course). Also, the Raynox image seemed a bit dimmer (exposure times were the same for both stacks), so I made a slight brightness adjustment to account for that. Also had to apply some jpg compression to account for the file size restriction.

The doublet still appears a tad sharper, I'd say:

Image

Macro_Cosmos
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Post by Macro_Cosmos »

I think the raynox edges here. The doublet yields more contrast though which appears to be sharper, but for fine details, I see a bit more in the raynox.

That said, as I recalled correctly, the Raynox is an f=208mm lens while the EO achromat is 175. NA stays the same, so the EO should give decent sharp centres. It's at a lower magnification however. Equalising the two seems to yield identical outcomes. I definitely will not be able to tell between the two in a true blind test.

What's the part number for the EO doublet? I have a cabinet of those, could run a test on them all.

jnh
Posts: 160
Joined: Mon Apr 27, 2015 7:34 am
Location: US East Coast

Post by jnh »

Not sure about the part number, as this came out of some surplus pile, so I can only speculate that it's this one:
https://www.edmundoptics.com/p/25mm-dia ... lens/2670/
Part #32-884; they also have a 200mm version of this doublet btw.
Looking forward to the results, if you run tests with yours.

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