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Is this normal? (Nikon PA 20/0.75)
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Macrero



Joined: 01 Sep 2011
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PostPosted: Mon Mar 30, 2020 5:00 am    Post subject: Is this normal? (Nikon PA 20/0.75) Reply with quote

Playing with my Nikon Plan Apo 20/0.75 I noticed that when retracting the spring-loaded front lens the whole assembly is moving and the rear part comes out of the barrel.



Can someone who owns this objective check if it behaves in the same way and report back? Thanks!

Best,

- Macrero
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Pau
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PostPosted: Mon Mar 30, 2020 6:18 am    Post subject: Reply with quote

Yes, it is normal.
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Macrero



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PostPosted: Mon Mar 30, 2020 7:06 am    Post subject: Reply with quote

Thanks Pau! I am re-testing it without coverslip. Pretty usable after editing. Will post some test stack later on.
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Macro_Cosmos



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PostPosted: Mon Mar 30, 2020 8:46 am    Post subject: Reply with quote

Incredible NA for a 20x. Easily feeds a 60MP sensor in theory. Looking forward to seeing the results
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Macrero



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PostPosted: Mon Mar 30, 2020 11:08 am    Post subject: Reply with quote

Yeah, 0.75 is impressive NA for this mag and I can live with 1mm WD. Unfortunately, the coverslip correction certainly and obviously affects IQ at that high NA.

This is a crop from a test stack with 150mm tube lens at 15X on sensor:

https://images2.imgbox.com/4c/1a/gEaLshyW_o.jpg

Did not come out well. Will try using shorter steps.
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Ichthyophthirius



Joined: 07 Mar 2013
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PostPosted: Mon Mar 30, 2020 1:09 pm    Post subject: Reply with quote

Hi,

There will always be spherical aberration without a coverglass. If you have the chance, experiment with a coverglass cap (small cap made from plastic tube to fit around the objective nose; coverglass glued to the plastic tube) and you might see an improvement.

Regards, Ichty
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Pau
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PostPosted: Mon Mar 30, 2020 1:19 pm    Post subject: Reply with quote

Macrero, do you have many no cover glass 20X 0.4 like Nikon or Mitu industrial objectives?
If so I would like to see a side by side comparison to see if spherical aberration can kill the NA advantage of the PA 20/0.75
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Macrero



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PostPosted: Mon Mar 30, 2020 2:24 pm    Post subject: Reply with quote

Ichty,

will try that, when I find the box with coverslips... Crying or Very sad

Pau,

many... no, actually I currently have only one no coverglass 20X - an Oly MPlanFl N 20/0.45. Well, a Nikon U20 too, but it is NA 0.33 only and is not a good reference objective.

From what I've seen in the few tests I shot with the Nikon, the NA penalty without coverglass is pretty significant.

Will make a comparison with the Oly tomorrow, though I am pretty sure it will (at least) match the resolution of the Nikon without coverglass and for sure will look better overall.
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Scarodactyl



Joined: 14 Apr 2018
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PostPosted: Mon Mar 30, 2020 4:26 pm    Post subject: Reply with quote

I use mine to image inside gems. Once you get under the surface of a stone it usually behaves pretty well across a range of depths, but if you have anything reflecting on the surface (cracks, dust spots) they streak really badly across a stack. Still, it is an insane deal at 100bucks if there is any context you can use it in.
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Mon Mar 30, 2020 4:30 pm    Post subject: Reply with quote

If your subject supports it, you could also put a thin layer of oil over your subject. But risky for the objective if you hit the oil.
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JKT



Joined: 28 Oct 2011
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PostPosted: Mon Mar 30, 2020 10:15 pm    Post subject: Reply with quote

I was blown away by the sharpness and now I want the 10x version too. ;-)

The first test with Raynox DCR-150 & Canon EOS RP: http://jkt.1g.fi/Xtra/Blasto%20GP%20-%20large.jpg.
Corner vignetting is likely due to M42 connection on FF camera. That I have fixed.

The sharp image circle is limited, so much shorter tube lenses are not that useful. Longer ones should work well due to low resolution of the RP.

Considering my targets, the coverslip correction is just what the doctor ordered. Smile
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Pau
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PostPosted: Tue Mar 31, 2020 12:48 am    Post subject: Reply with quote

Pau wrote:
Macrero, do you have many no cover glass 20X 0.4 ...


Oops! I thinked that I wrote any, not many Rolling Eyes
Macrero wrote:
Will make a comparison with the Oly tomorrow, though I am pretty sure it will (at least) match the resolution of the Nikon without coverglass and for sure will look better overall.


Please perform and post it
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Macrero



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PostPosted: Tue Mar 31, 2020 7:27 am    Post subject: Reply with quote

Lou,

I am afraid subjects won't get along with oil.

I had in mind Ichty's approach, and will try that once I find my coverslips...

Pau,

I was pretty optimistic saying that the Oly will just match the resolution of the Nikon without coverglass. It actually clearly outresolves it, and as expected, image looks much better overall.

Here is a quick comparison. Nikon with Apo-Gerogon 150 as tube lens, Oly with Componon 135. Shot in RAW, converted with same settings in Capture One 20. No additional adjustments/sharpening in PS.

Nikon:

https://images2.imgbox.com/a8/79/Eapf9Ior_o.jpg

Oly:

https://images2.imgbox.com/f1/f8/Ee96wWXc_o.jpg

Nikon with some levels adjusment and sharpening:

https://images2.imgbox.com/5d/50/VHgYGkxK_o.jpg

- Macrero
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Pau
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PostPosted: Tue Mar 31, 2020 7:46 am    Post subject: Reply with quote

Macrero, thank you very much for the test.
Of course I agree with your conclusion. Resolution is not bad but glare produces lots of apparent unsharpness. Another issue is the short WD conditioning illumination and likely also some scales out of focus
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Macro_Cosmos



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PostPosted: Tue Mar 31, 2020 8:02 am    Post subject: Reply with quote

Oly is the clear winner here despite the far lower NA. Nikon lacks the coverglass, not sure how well it will work with my slides for polarised light. Mine are all photographed at 10x, the 20x I use produces pretty poor results. Cover glass and polariser in the optical path, I guess it's too much for the 20x. Spherical aberration and the glare doesn't help resolution.

I had the chance to play with a zeiss water immersion objective lens, despite the high NA, without water it sucked. That's when I learnt that correct coverglass/immersion medium is crucial with these objectives. Your results are very helpful too.

First time I've seen scales like that, do you know the type of butterfly? If not, a wing segment phone pic should help. It looks incredible.
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