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Edmund (?) 175mm doublet as tube lens

 
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jnh



Joined: 27 Apr 2015
Posts: 99
Location: US East Coast

PostPosted: Sun Mar 08, 2020 3:49 pm    Post subject: Edmund (?) 175mm doublet as tube lens Reply with quote

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.

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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Sun Mar 08, 2020 4:22 pm    Post subject: Reply with quote

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



Joined: 27 Apr 2015
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Location: US East Coast

PostPosted: Sun Mar 08, 2020 4:56 pm    Post subject: Reply with quote

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

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Lou Jost



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PostPosted: Sun Mar 08, 2020 4:59 pm    Post subject: Reply with quote

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.
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Macro_Cosmos



Joined: 15 Jan 2018
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PostPosted: Mon Mar 09, 2020 1:05 am    Post subject: Reply with quote

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.
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jnh



Joined: 27 Apr 2015
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Location: US East Coast

PostPosted: Thu Mar 19, 2020 5:57 pm    Post subject: Reply with quote

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:

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Macro_Cosmos



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PostPosted: Fri Mar 20, 2020 12:44 am    Post subject: Reply with quote

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.
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jnh



Joined: 27 Apr 2015
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Location: US East Coast

PostPosted: Fri Mar 20, 2020 6:47 am    Post subject: Reply with quote

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-x-175mm-fl-mgfsub2sub-coated-achromatic-doublet-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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