Odd objective: Optem 2.5x

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Scarodactyl
Posts: 1619
Joined: Sat Apr 14, 2018 10:26 am

Odd objective: Optem 2.5x

Post by Scarodactyl »

I spotted this weirdo on eBay--an Optem 2.5x/0.09 objective. Not marked Plan, not marked Apo, not marked HR, and not listed or mentioned anywhere I can find online. I was interested because a high quality low magnification objective parfocal with my mitutoyos is still on my wishlist. I have a mitutoyo 2x and a mitutoyo 1x, and while I like and use both of them they are in a lower tier than other Mitutoyo objectives, with a good image in the center but pronounced CA outside that central area. It was also pretty inexpensive so worth a go.
Initially it looks just like Optem HR objectives, with a long black body.
Image
However, the bottom of the barrel unscrews, leaving a much shorter body. In fact all the lens(es) are at the very top of the objective, much like some simpler traditional 4x objectives. Interestingly it didn't seem to cause any issues removing that bottom shroud, though I didn't exactly stress test it.
Image
It definitely gives you a big increase in working distance.
Image
Now for the real question: how is the image quality? It's a pleasant surprise. Much like Optem HR objectives this one is not planar at all--it has pronounced field curvature. Unlike HR objectives, however, the corners do come into sharp focus at some point so it can stack out. In a head to head with a Mitutoyo 2x, the 2x was best in the center and corner in a single shot, while the Optem required 17 shots to make a reasonable stack, and I am not sure I did fine enough steps.
Image
Here is the optem resized to align with the Mitutoyo. As expected the image is brighter given the higher NA to magnification ratio.
Full size mitutoyo image: https://i.imgur.com/iQV6L4j.jpg
Full size optem image: https://i.imgur.com/OEPFb9G.jpg
Now the crops. I have brightened the Mitutoyo to match the Optem.

Center:
Image
Mitutoyo
Image
Optem

The optem is clearly more detailed, as you would expect. Neither shows bad CA.

Edge:
Image
Mitutoyo
Image
Optem

The mitutoyo's CA is so bad it's affecting the resolution, while the optem mantains a nice crisp image.

Corner:
Image
Mitutoyo
Image
Optem

Hochi mama!

So when it comes to pure image quality the Optem easily outclasses the mitutoyo 2x on aps-c center to corner as long as you're willing to stack it out. The optem is still not distortion free nor is it completely CA free, but it's definitely much better.
There are a couple other niche considerations. The Mitutoyo 1x and 2x do really poorly with through-lens epi illumination on subjects that are not strongly reflective--you get a central hotspot on any target that isn't bright enough to push it under the noise threshold. The optem does not seem to suffer from this problem. However the Mitutoyo 1x and 2x objectives are compatible with my Nikon DIC prism, while the optem is not.
This is what DIC looks like with the Mitutoyo 2x:
Image
And the optem 2.5x:
Image

There's also the issue of having to do a deep stack on this type of subject confusing helicon, making it want to make mistakes like this on the stacking:
Image
That might be a problem with my quick manual stacking though.
In some ways this feels like an objective designed for photomacrography, in that planarity was not a concern but it does provide a fairly crisp and decently color-controlled image, all with quite good working distance. Of course if you want to shoot at 2.5x there are better options--I imagine the Laowa would easily outclass this objective. Still, it is a very pleasant surprise, and if it worked with my DIC setup I would sell my mitutoyo 2x and put this on my nosepiece instead. As is it will probably be more of a pinch hitter.
Edit:I was wrong, the 2.5x has stayed on my nosepiece this whole time while the 2x is now reduced to a pinch hitter.
Last edited by Scarodactyl on Tue Mar 08, 2022 3:12 pm, edited 3 times in total.

RobertOToole
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Re: Odd objective: Optem 2.5x

Post by RobertOToole »

Thanks for the sharing the info, nice discovery!

Better results than I would have guessed.

I see a ten fold price increase on these in the immediate future #-o :D

Best,

Robert

Scarodactyl
Posts: 1619
Joined: Sat Apr 14, 2018 10:26 am

Re: Odd objective: Optem 2.5x

Post by Scarodactyl »

Thanks! That might be, if anyone can ever find another one. I haven't been able to find any information, but I did drop Optem a line asking if they have any more information and if it might possibly still be offered for sale.

RobertOToole
Posts: 2627
Joined: Thu Jan 17, 2013 9:34 pm
Location: United States
Contact:

Re: Odd objective: Optem 2.5x

Post by RobertOToole »

Scarodactyl wrote:
Tue Feb 22, 2022 3:59 pm
Thanks! That might be, if anyone can ever find another one. I haven't been able to find any information, but I did drop Optem a line asking if they have any more information and if it might possibly still be offered for sale.
If they don't respond, let me know, I have a contact I can message.

Best,

Robert

Scarodactyl
Posts: 1619
Joined: Sat Apr 14, 2018 10:26 am

Re: Odd objective: Optem 2.5x

Post by Scarodactyl »

Thanks! I suspect you'll have more luck than me. The closest I found was a reference to an HR 2.5x/0.11 as part of the A-Zoom2 system, but it was only mentioned in a brochure and not pictured. The brochure also did not mention the 20x/0.60 and had the older black and gold styling, so I assume it was fairly old.

Scarodactyl
Posts: 1619
Joined: Sat Apr 14, 2018 10:26 am

Re: Odd objective: Optem 2.5x

Post by Scarodactyl »

I just heard back from Optem--in a surprise to no one this objective is no longer made. Given how little evidence there is that it was ever made that tracks.

Scarodactyl
Posts: 1619
Joined: Sat Apr 14, 2018 10:26 am

Re: Odd objective: Optem 2.5x

Post by Scarodactyl »

This one has become a permanent fixture on my nosepiece, and I've only broken out the mitutoyo 2x once for a DIC shot of a full crystal face. It also seems to have a pretty wide image circle and it plays well with my mag changer, easily filling my eyepieces on the 0.62x setting and only showing some corner shading vs hard vignetting with more complex objectives.
What I don't get is that it does all that while appearing to be essentially a single lens, maybe a doublet? How is that possible? Makes me wonder if one could get good results with an achromatic doublet in a simple 3d printed shell. Might be worth firing up the 'ol surplusshed lensfinder for some experiments.

I would love to compare it with the lwd 2x (or kwd qv 1x), or especially the qv HR 1x/0.084 which I just learned about.

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