How super is the Olympus superapo?

[Scarodactyl]

I recently got my grubby hands on an Olympus UplanSapo 20x/0.75. Seeing an "s" in front of an "apo" is not always a good sign--some makers mean "semi apo" by this, which honestly seems intentionally deceptive when we already have a term for fluorite optics, but not Olympus--the "s" here stands for "super", meaning it's corrected for NIR in addition to visible light. I've actually had one of these before, but ended up selling it along with the microscope it was on before I could do more than basic tests with it. I also picked up a UplanFl 20x/0.5 a while back for an Australian acquaintance who takes great cross-polarization photos but doesn't have the same level of access to used optics as we enjoy in America, so aside from a nice 10x fluorite he's been stuck with the Nikon's chinese-made Olympus-clone achromats. With both of these on hand, plus a BX40 with an ultrawide head, I figured it was worth seeing how super the apo really is in comparison to a merely fluoritic objective. To the eye both give a very good image, though the S apo is visibly better.
Edit: This test is a bit apples and oranges since the difference in NA between the two is pretty huge, but I figure it's still worthwhile since someone might plausibly need to choose between the two.
The S apo has some ugly scrapes on the outside of the casing, but the glass is clear. The fluorite has good cosmetics but a small mark on the back lens, though it does not seem to affect performance--but if someone else does a test and finds different results, I am going to blame that and take zero personal responsibility.
I took a few shots of a fairly mediocre slide of acetominophen I had on hand, both in brightfield and with crossed polars. It's a fairly thick crystal layer so these comparisons aren't as perfect as they could be, which would matter more if this ended up being more ambiguous.
First the brightfield stacks, with crops selected from single images to best match focus.

UplanSapo 20x^

UplanFl 20x^
Click for larger but not full size, I resized down to 3000px width because of Imgur's upload limits.


The difference in detail is really obvious, center to corner. The fluorite's color correction is really not bad, but can't stand up to the super apo which really is clean corner to corner.

UplanSapo ^

UplanFl ^
For the cross-polarized picture I decided to compare crops from the stacks, since the individual pictures really aren't as nice with a slide this thick.


Anyway, this is another one of those really obvious test results--obviously any objective that a big four company is willing to call "super" is going to beat out a mere fluorite, and the higher resolution is going to make a big difference. But hey, I need to take test shots with them anyway so might as well share the results. I think these are both good options, but if you see a super apo at a good price I'd recommend snapping it up. I guess with the newer Olympus UplanXapos (super duper apos?) the merely super apos are yesterday's news, but I'd have trouble finding anything to complain about with this objective.
The comparison I'd really like to run is between the super apo and a Nikon 20x/0.75 planapo, but I am not sure how to do it logistically. The 20x is just too long to fit on a BX40.

[RobertOToole]

Nice results, I've always wondered about these.

20x NA 0.75, awesome, whats the downside other than cost, WD?

Also I didn't know about the X-line super APOs, interesting line!

Best,

Robert

[Lou Jost]

Don't you think the difference might mostly be due to the huge difference in NA between those two?

[Scarodactyl]

Nice results, I've always wondered about these.

20x NA 0.75, awesome, whats the downside other than cost, WD?

Mostly cost I think. The fluorite doesn't really have much longer working distance, though I guess it's less important when looking at slides.

Don't you think the difference might mostly be due to the huge difference in NA between those two?

For overall image quality yes, it does kind of swamp other effects. The difference in CA is a bit harder to see depending on what monitor I look at but it's there too--I should probably get a different subject to highlight that.

[Scarodactyl]

Well, if I'm going to do it better to do it right (or at least closer). Here's some shots of an eyepiece micrometer, wetted and with a cover slip put on top, bulb at full power for the best color temperature and all that. This should give a much better idea of the difference in CA.


The S apo performs pretty close center to corner, and the best center and corner are at the same focal point, while the plan fluor is not that plan out to the edge. There is still a hint of CA visible on the S apo in the corner though, subtle but present, and the contrast is not quite as good as the fluorite.

[Lou Jost]

That new test nicely shows the excess CA in the Fluor.

[viktor j nilsson]

I can't see the images. Is it just me?

Edit: I can see them now.

Great comparison. The Sapo is clearly superior in resolution and CA, but has slightly less contrast. Pretty much in line with expectations. The Fluor still looks pretty good, though.

[Scarodactyl]

I was wrong, the Nikon 20x planapo (the one that's sometimes cheap on eBay) barely fits onto the scope if the stage is put down as far as it goes.
Unfortunately the generic m25 to rms adapter I got on eBay is hot garbage, and the nikon objective isn't centered quite right. As such the two stacks of acetominophen I took really don't make for a good comparison. But I at least recentered the micrometer between the sapo and the normal apo to get some idea of the CA. I also had to resize the image from the Olympus down by 10% to get the images to match in size.
Anyway, long story short with those issues in mind the results are fairly close. Both show very good CA control and both had their best center and corner in the same shot. The Nikon does a bit worse in the corner, but the bad adapter may have some role in that.


The main difference, of course, is that the Nikon is reliably available for 300 bucks or under and unreliably for 100 bucks until that one guy runs out (if he hasn't already), while the Sapo is priced much higher. On the other hand it's not like you can practically put the Nikon on a nosepiece mixed with Olympus objectives--you're going to crash the long Nikon objective into the stage.

So overall I guess the answer to the thread title is: the Olympus is definitely an apo objective and it's a nice one, but it doesn't seem to be such an unbelievable apo that you don't see any tiny trace of CA. Doing so well against the Nikon 20x apo is a feather in its cap.

[Macro_Cosmos]

Consistent with what I've found last year.

CA, resolution, sharpness
Olympus 20x SApo dry > Nikon PlanApo 20x (not the OEM type that's corrected for a coverglass of 0.4mm) > UplanFL N 20x
Nikon 20x in this case is an 18x.

For contrast, just reverse the signs above and put ~= for the apos.

[Scarodactyl]

I wish I had a better rms adapter for the nikon. The acetominophen stacks were very similar but with center and edge so offset it's a losing battle to try and compare apples to apples.

[Macro_Cosmos]

I wish I had a better rms adapter for the nikon. The acetominophen stacks were very similar but with center and edge so offset it's a losing battle to try and compare apples to apples.

You can always get brass objective adaptors such as this: https://www.ebay.com/i/142378001230?chn=ps
RAF offers good ones too.

No-name aluminium ones are can be very bad. I get mine from amoyca/amoycal, a Chinese brand, it's decent, there do sell on ebay too I think.

[Scarodactyl]

I guess i should say I wish, but don't quite $30 wish, since it's not likely to be an adapter I'd use a lot. Thanks the for the link though, I'll keep that seller in mind--I got my set of 32-26/25s from thorlabs which were surprisingly well priced but most of their adapters are more expensive.
It would be nice to do a good head to head on a more interesting subject but I feel like there's enough here to say they're very similar. Minute differences in image quality are never going to be the determining factor between these two, not compared to price and parfocal length (or DIC prism compatibility of course). I'm certainly happy to do tests with limited implications for real-life decision making but I think I'll probably just let it sit.