Any experiences with the Thorlabs 2x superapochromat?

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Lou Jost
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Any experiences with the Thorlabs 2x superapochromat?

Post by Lou Jost »

FOVs between 6mm-12mm (around 1.4x-3x on an MFT sensor) are the most important range for my orchid work, and the most difficult range for high-quality optics. The Printing Nikkor and regular macro lenses cover lower magnifications, and microscope objectives cover the upper end of this range and beyond, but really good solutions at 2x are hard to find. The Canon MP 35mm often wins tests here, but that is mostly on APS or FF sensor; at nominal f/4 (its sharpest aperture) which is an effective aperture of 12, I find it is a bit soft due to diffraction when used on my MFT sensor. To use the MFT hi-res mode, the EA should be kept under EA=8. I also find a bit of red fringing on some edges with this lens.

I see that Thorlabs has an expensive 2x "superapochromat" infinity-corrected objective with NA=0.1.

https://www.thorlabs.com/newgrouppage9. ... up_id=9895

This would be an f/5 but, being infinity-corrected, the EA would be 10, slightly better than the Canon. There is a formula somewhere on this forum suggesting that the EA equation should be modified by a factor of m/(m+1) which would make this EA=6.7, below my limit. So this may be an attractive solution for 2x. But nobody here has ever mentioned this lens. Is that because it sucks, or because there are better solutions?

There may be better solutions with coupled lenses, but the convenience of an objective that could be easily swapped out with other objectives is very attractive.

Anyone know this lens?

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Post by ChrisR »

Nope, never seen one.
Tried this sort of thing?
Image
Chris R

Lou Jost
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Post by Lou Jost »

Yes, I lost a bidding war on one of those yesterday, and I see there is one up today. But look at the working distance, 8.5mm. That sucks for a 2x. The Thorlab lens has a 50mm+ working distance. That means much less perspective variation during a deep stack.

ray_parkhurst
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Post by ray_parkhurst »

For MFT at 2x, I might suspect the Nikon 3xMM objective would win vs the 35MP. It certainly beat the 35MP handily in the center in my 2.4x shootout, but the question is if it can hold on out to the corner of MFT at 2x. It showed astigmatism at the extreme corners on APS-C at 2.4x. It looked great at 3x on APS-C, so maybe that tells you what it can do at 2x on MFT. Maybe operate near 3x and add a speedbooster?

All that said, as I also remember the 35MP needed stopping down for best corner performance, so perhaps it could be operated at bigger aperture on MFT. Looking at the shootout images though, the 3xMM was noticeably better in the center than anything else in the group.

Edited to add: that 2x superachromat looks very impressive. Would be interesting to do a shootout with that one.

Lou Jost
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Post by Lou Jost »

Ray, some time ago I had done some experiments with the 5x and 10x MM lenses and the Speedbooster. I found that they weren't too bad but that they had color aberrations, and the 5x did not have a high enough NA to use hi-res mode. I could beat the 5x with coupled lenses. At low m a finite lens has to be much faster than an infinity-corrected lens in order to give the same effective aperture. If the diffraction-limiting effective aperture is f/8, then at 2x an infinity-corrected objective (or reversed camera lens) on a tube lens needs to be f/4 (NA= 0.12) but a finite lens has to be f/2.7 (NA= 0.19).

mjkzz
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Post by mjkzz »

Mitutoyo QV 2.5x 0.14NA is apochromatic and telecentric, it needs 100mm tube lens, that Pentax 105mm that was discussed early can be perfect tube lens.

Or just mount a Mitty 5x on that 105mm so you get approximately 2.5x and 0.14NA

Lou Jost
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Post by Lou Jost »

Yes, that works very well at 2.5x, but I haven't been able to push it down to 2x with good corners, unfortunately. With the 2.5x QV and the 70mm Sigma macro lens as the tube lens, I did get good results almost to the corners, but not quite.

Justwalking
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Post by Justwalking »

Lou, if you are perfectionist then look machine vision lens Kowa LM1138TC. Exactly 2X mag for 4/3 sensor. Center and corner 120lp/mm. W.D. is about 80mm. But expensive too.

ray_parkhurst
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Post by ray_parkhurst »

Justwalking wrote:Lou, if you are perfectionist then look machine vision lens Kowa LM1138TC. Exaclty 2X mag for 4/3 sensor. Center and corner 120lp/mm. W.D. is about 80mm. But expensive too.
Welcome to the PM forum JW! Glad to see you here. Will be interesting to see your lens combo examples for discussion.

Lou Jost
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Post by Lou Jost »

Justwalking, thanks for the tip. I am indeed a bit of a perfectionist about this, though with a limited budget. Where would one find such a lens for sale? None on eBay now. What is its focal length and aperture, in case a vendor omits the part number? Edit- Never mind, I found info on the internet. Back focus is too short for MFT?

For this magnification I am also a big fan of coupled lenses.

Justwalking
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Post by Justwalking »

Lou Jost wrote:Justwalking, thanks for the tip. I am indeed a bit of a perfectionist about this, though with a limited budget. Where would one find such a lens for sale? None on eBay now. What is its focal length and aperture, in case a vendor omits the part number? Edit- Never mind, I found info on the internet. Back focus is too short for MFT?

For this magnification I am also a big fan of coupled lenses.
I saw it at this site
https://www.kowa-lenses.com/en/applicat ... 1/lm1138tc
I think it'is impossible to meet this on ebay

Lou Jost
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Post by Lou Jost »

I've now found it significantly cheaper at this site:

http://www.rmaelectronics.com/kowa-lm11 ... xel-rated/

$1179. That's high but not crazy high. But I wonder how badly things fall apart for magnifications slightly below or above 2.0.
Last edited by Lou Jost on Mon Jun 11, 2018 8:15 pm, edited 1 time in total.

Justwalking
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Post by Justwalking »

Welcome to the PM forum JW! Glad to see you here. Will be interesting to see your lens combo examples for discussion.
Thanks for inviting, Ray. I have post my pen already at "small sensor" topic.

Justwalking
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Post by Justwalking »

Lou Jost wrote: $1179. That's high but not crazy high. But I wonder how badly things fall apart for magnifications slightly below or above 2.0.
Wow! That cheaper indeed. I think with it's resolution is not problem to achieve 2.5-3x with short helicoid and to 1.0X with c-mount 0.5x back converter.
Last edited by Justwalking on Mon Jun 11, 2018 8:36 pm, edited 1 time in total.

Lou Jost
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Post by Lou Jost »

Justwalking, what if those resolution figures refer to resolution on the subject rather than on the sensor?

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