Thorlabs 79mm UV aspheric lens for imaging

[dabateman]

Well if you only plan to use monochromatic filters, than fresnel lens made from PMMA are super cheap and provide as Reed shows above excellent UV transmission.

 

I have a couple that I was planning on stacking to create wide angle lenses. The only major problem is very high rainbow like chromatic aberrations. But as a single element, they aren't horrible.

 

I haven't seen people here use PMMA elements yet, but that would be another cheap light weight UV capable option. I like them for cuvettes and protection. It looks like you can buy optical grade elements for under $20. I may have to test a build lens using just PMMA to see how it compares to fused silica. It can kind of see to 255nm.

[Stefano]

That is an interesting option. One can begin with a PMMA element and then upgrade it with quartz/fused silica if he(she) is satisfied with the results. Or just keep it depending on the needs.

[ulf]

I haven't seen people here use PMMA elements yet, but that would be another cheap light weight UV capable option. I like them for cuvettes and protection. It looks like you can buy optical grade elements for under $20.

Where?

 

Plastic lenses are very sensitive to scratching, if not coated with some tough protection coating and that might affect the UV-transmission.

[Stefano]

I think that if one is careful they can last for a while. In your lens the element is deep inside because of the hood you put, and that probably protects it too.

[dabateman]

 

Where?

 

Plastic lenses are very sensitive to scratching, if not coated with some tough protection coating and that might affect the UV-transmission.

 

These ones maybe worth testing:

https://www.ebay.com/itm/363385956337?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

Or this

 

https://www.ebay.com/itm/182628191096?ssPageName=STRK%3AMEBIDX%3AIT&var=485188936989&_trksid=p2060353.m1438.l2649

 

This is one of the fresnel lens I purchased that can see into UVC:

 

https://www.ebay.com/itm/184248841161?ssPageName=STRK%3AMEBIDX%3AIT&var=691955520222&_trksid=p2060353.m1438.l2649

[Andy Perrin]

At those prices, I wouldn’t care about scratching. Buy ten at a time and replace them when they get scratched.

[ulf]

At those prices, I wouldn’t expect any high quality either.

Condenser lenses very rarely need a high imaging quality and quality production costs money.

There are definitely good camera lenses that can use a few plastic lenses, but they are probably produced to higher standards.

It is not that easy to injection mould ticker plastic parts to a the high dimensional standards needed for a good quality lens, due to uneven thermal shrinkage.

 

I think modern plastic prescription eyeglasses are milled in precision specialist milling machines, but normally they strive in working with materials especially attenuating UV and far violet.

[Stefano]

The quality will not be super high but I still think it can be pretty good. An aspheric molded PMMA lens should produce good images. If the imperfections are lower than the chromatic aberration for example, they won't be the limiting factor.

 

Thorlabs does sell molded glass and plastic aspheric lenses, they claim near diffraction-limited to diffraction-limited performance but they are not good for UVC. Their acrylic doesn't even reach 300 nm.

 

Link: https://www.thorlabs.com/navigation.cfm?guide_id=2344

 

Transmission of the materials they use: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=16#50EC2073-AAC1-4C1A-815E-609B0742F562-16 (it seems I can't make a direct link. Go to "Graphs" to see them).

[ulf]

It is absolutely not impossible to injection mould plastic precision lenses, but it is expensive if they are not produced in high volume.

Creating an injection moulding tool for that kind of precision lens is very expensive.

One example of such are lenses for Blu-ray drives to be mounted in computers. They are fantastic designs optimised for 405nm, 650nm and 780nm with different NA for each wavelength.

 

The aspheric lenses at Thorlabs are also tiny and not very practical for photography in our typical applications.

 

There might be some mass market out there needing big diameter plastic aspheric PMMA lenses with good optical quality, but I have no idea of what that can be.

[rfcurry]

I notice that from Edmond Optics the price of PMMA lenses does not increase dramatically with the increase in FL.

https://www.edmundoptics.com/f/molded-acrylic-aspheric-lenses/13209/

 

Fresneltech has some interesting aspheres - https://www.fresneltech.com/polymer-aspheres

 

Knight Optical sells them by the pound - https://www.knightoptical.com/stock/default/lenses/plastic-lenses.html

 

Sinoptix is clear about the trade-offs between glass and plastic - http://sinoptix.eu/portfolio-item/pmma-injected-aspherical-lens/

[Andrea B.]

Good links! Thanks.

[dabateman]

An alternative might just be that positive meniscus SvBony 0.5x focal length single lens.

I just played with one mounted in a 25mm filter ring and its focal length is 58mm. It can see from 300nm and up and is multi coated. You could buy one cheap, a 25mm ring to remount it correctly curve side away from sensor, a m42 to C-mount adapter, an aperture control ring, a 17-31mm helicoid and a slim your camera to m42 mount quite cheap as a first UV capable lens. You can then add a 25mm to 52mm step up ring to use standard filters.

58mm/20mm is about f2.9, so not slow, but dreamy there. It does need to be stopped down.

I should take a couple shots to show it off as I just screwed one together. I think its lost here so will creat a new thread.

[dabateman]

I scanned my 25 year old plastic lens from my forever flashlight and it was PMMA. Its a 36mm diameter aspheric lens. But boy was it soft. Not worth the time with an old PMMA element. It needed a 35-90mm helicoid so was most likely around 100mm focal length. My PMMA fresnel lenses are also not the best for sharpness. Very odd aberrations, with a reverse spherical effect. The center can get very round and soft as the edges sharpen up. Reversed it was very low contrast But had an interesting look. Just a toy lens like a Holga.

 

The SvBony element is by far the best low cost choice. Sharp across the frame on a m43rds camera.

[Avalon]

I was wondering long time about building single aspheric lens inspired by simplicity of the eye and it's also much more budget friendly option, maybe there are even lower cost sellers. More popular material such as BK7 wont cover full range UV-A range? Can you show curvature of the lens and do image quality testing with square board?