Three (relatively) inexpensive 50x Objectives: generic "LMPlanFl" vs Generic BD Plan vs Mitutoyo M50

[Scarodactyl]

Hi everyone. This week I got my hands on three 50xish objectives which I needed to test out, so I thought I might as well run them head to head to head to see how they'd do.

They are: A solid black generic BD Plan 40x which I got cheap on eBay, a Mitutoyo M50 objective (presumably off an Akashi hardness tester, I am not 100% sure what Akashi does or who made these objectives) provided by user jnh, and a generic "LMPlanFl" (wonder if that violates an Olympus trademark?) off of a Unitron Examet 4 metallurgical microscope (a whitebox Chinese product). All three are infinity objectives with a 45mm parfocal length.

The BD plan 40x/0.65 is a clone of Nikon's infinity CF Plan BD 40c from the infinity corrected metallurgical optiphots, immediate predecessor to the Eclipse series. They have an unusual M27x0.75 thread. The working distance is 1mm, short but workable.

The LMPlanFl 50x/0.55 was from a Unitron Examet 4 and the same one is offered on the newer examet 5. I haven't found other Chinese objectives with the exact same specs but I imagine it could be bought direct. It has RMS threads and a whopping 7.9mm working distance putting it well ahead of the other two.

The Mitutoyo M50/0.65 (and Mitutoyo M objectives in general) are familiar to anyone who's searched for mitutoyo objectives on eBay before. Previous tests of this line have gotten decent results, but there are a few versions (both infinity and finite, plus a 50x/0.55 version). Unlike their M Plan Apos the Ms are normal short metallurgical objectives with a short working distance meant for coaxial illumination. They are not plan rated. Working distance is shortest of the bunch, under 1mm.

The target is the excellent wafer that Macro_Cosmos distributed a while back, shot with coaxial illumination. The single images are stacks to deal with any lack of planarity (only an issue on the M50), the depth of features and any lack of flatness in my stage. Crops are from individual images. It's possible I missed perfect focus on some features but it's pretty close if so.

First the BD Plan (click for full size stack)


Center

Corner

Edge
This one is nice to use visually, and feels similar to finite Nikon BD plans, some lateral CA but mostly in the far corners, noticeable but OK axial everywhere.
Overall I was very impressed for a no-name objective at a very affordable price!

Next up the LMPlanFl


Center

Corner

Edge
I think this one is nominally rated for 22mm, but it seems to perform well even on aps-c, especially given its long working distance. It looks better than the BD plan in the center though there is some obvious lateral CA in the corners.

Finally the Mitutoyo M50


Center

Corner

Edge
This one is quite non-planar as this single image shows:

Contrast is not as good as the other two and it doesn't quite cover APS-C. Color correction is not awful in the center but rather bad in the corners. All this with the shortest working distance as well. I'd take either of the others over it but it's still not bad if you stack it.

Overall I was pretty pleased with both of the Chinese objectives for the price, I would avoid this particular Mitutoyo objective but others in the line may be better. The LMplanFl in particular seems to do quite well with a relatively long working distance.

[RobertOToole]

50x comparison, nice!

The BD Plan is not so bad!

What do those things cost anyway?

I should try to dig up some crops of a 50x Mitutoyo M Plan I bought for $100 with a mint condition barrel but a huge chip in the front element. 100% fine IQ, the chip had zero effect on IQ. Fact was it was better than my $600 M Plan 50x Mitutoyo with mint glass.

Best,

Robert

[Scarodactyl]

I'm not sure what they cost new, but the BD plan was 35 bucks shipped (hence my inability to resist it).
Microscope Central is asking just over 1k for the LMPlan 50x https://microscopecentral.com/products/ ... 1067207733 (though that one isn't marked as a fluorite, but I am not sure that that actually means it's a different lens). A few times what I paid for the entire microscope it came on.

[Scarodactyl]

I had almost forgotten this objective but I'm trying to clear out some of my backlog and came across it again. It's a Nikon E plan 50x/0.75 epi which came free with a nosepiece I bought. I figured I should try it with the BD Plan as a comparison. I need to take photos anyway to make sure they're in decent shape before selling (especially with a cosmetically challenged one like this E Plan)--I don't know when the next time anyone will be considering one of these objectives might be but might as well share my findings.

I noticed that my fine focus was slipping very slowly, enough to have an effect on my last stacks. Moving the coarse focus a bit, refocusing down with ultracoarse led to no slipping. That's not a great sign but whatever. For this stack I felt like I really needed a fine focus for my fine focus--the wafer was very slightly tilted and both objectives show significant axial CA, though the BD Plan was worse on that front. With very fine steps in the stack it almost all stacked out which is nice.
Once again the overview is a stack (and click for full size), center middle and edge are single frames.
BD Plan:


Center

Corner

Edge

E Plan:


Center

Corner

Edge

Overall I think the BD plan is clearly better, and oddly I feel like I don't really see more detail with the E plan in spite of its higher rated NA, though the E plan has less axial CA (though plenty of lateral!). Of course the E plan is being pushed way out of spec, since it likely has a rated FN of 22. Overall not one to seek out for photomacrography on aps-c.

[Scarodactyl]

Reviving the old thread to throw one more point in the generic BD plan's favor. The outer shroud unscrews easily and the inner lens is exceptionally skinny. I 3d printed a cap to cover up the df light path.

For a 0.65 NA it still has unimpressive working distance but for my subjects anyway lighting isn't an issue, and having a lower NA 50xish that's a bit more tolerant of shooting through media is nice for when a subject is a bit too deep for my 50x/0.8.
This line of nikon cf bd clones is still sold, I'll dig up the link later.

[bralex]

Am I missing something that the BD Plan is marked 40x?

[Scarodactyl]

Am I missing something that the BD Plan is marked 40x?

I should have written '50xish', since the lmplanfl is also not working at 50x since it wants a 180mm tube lens (it's around 55x here).

[bralex]

Heh, ok. I wondered if maybe you grabbed the wrong lens for photos. Makes sense then!

[heyitsmedusty]

Where did you source the generic LMplanFL?

[Scarodactyl]

Where did you source the generic LMplanFL?

It came on a Unitron examet 4.