Back to basics - 40mm singlet lens from Thorlabs

[JMC]

This was a project I started thinking about last year. A while ago while searching for information I came across something called a Hanovia Kalosat Spectral Diffusion lens, which was a large format lens with a single quartz element. Having failed to locate one for sale (I guess they are very rare) I thought, why not make something similar.

 

My version is based around a Thorlabs 40mm focal length, 1" diameter, UV silica plano convex lens with no coatings on it (I also have a biconvex 40mm lens too). I got a bunch of other fittings from Thorlabs at the same time so I could add an adjustable aperture, make it into an M42 mount, and add a 52mm filter ring on the front. Very impressed with Thorlabs, great to deal with. This is what it looks like;

 

 

 

 

 

And here it is on the camera with a LaLaU filter attached.

 

 

Screwed pretty much all the way into a slim M42 to Sony E mont adapter it allows focus almost to infinity. The sun came out today, well for a few minutes anyway. So I got a couple of quick shots of the garden using the multispectral A7III. These were converted to monochrome in photoshop and reduce in size for sharing.

 

LaLaU, aperture closed all the way down (approx f40), ISO8000, 1/10s

 

LaLaU, aperture partial closed (approx f5), ISO8000, 1/160s

 

R72, aperture closed all the way (approx f40), ISO1000, 1/640s

 

Not going to throw away all my other lenses just yet, but might be fun to have a play around with. Might try with a 50mm lens, or even try getting a CaF2 lens at some point.

[Andy Perrin]

Haha, yeah, I've heard people say uncorrected singlets have lots of aberrations for years now, so I never tried one, but I see they were not exaggerating. Good for art's sake?

 

I love ThorLabs. They are such nice people, and they ship very quickly, give you free snacks, and all their stuff fits together like LEGO for optical engineers.

[Stefano]

Haha, yeah, I've heard people say uncorrected singlets have lots of aberrations for years now, so I never tried one, but I see they were not exaggerating.

Yes, and I just said this to Dabateman here: https://www.ultravioletphotography.com/content/index.php/topic/3749-what-is-the-magical-ingredient-in-u340-to-block-ir-and-can-we-all-petition-hoya-or-schott-to-tripple-it/page__st__40. Yes, you can form an image, but it will be usable only in the center.

[Stefano]

I guess it's difficult to build your own lens with multiple elements.

[Stefano]

Try this: go in a room where there is a window and a wall on the other side (maybe use a paper sheet). Using a magnifying glass, project an image of the window on the wall. You will see that it is reasonably good only in the center. And it will be upside-down.

[Stefano]

I linked myself... using a smartphone it can happen

[Andy Perrin]

Haha, yeah, I've heard people say uncorrected singlets have lots of aberrations for years now, so I never tried one, but I see they were not exaggerating. Good for art's sake?

 

I love ThorLabs. They are such nice people, and they ship very quickly, give you free snacks, and all their stuff fits together like LEGO for optical engineers.

 

Yes, and I just said this to Dabateman here: https://www.ultravio...t/page__st__40. Yes, you can form an image, but it will be usable only in the center.

Yes, you are included in that remark, but also Alex H and Klaus (who said it privately, since he is not on the board).

[Stefano]

This lens experiment makes me wonder... I know that our brains flip the images in our retinas... but does a camera do that as well?

[Andy Perrin]

Of course. The image is upside-down in the camera. If you are trying to diagnose a light leak, this is an important fact to keep in mind.

[dabateman]

Funny,

I was able to order a $12 fused silica single lens elements. So thought why not. I will let you know how my project turns out.

I will be trying just a 185nm, using my 254nm/185nm ozone light and filter. So being monochromatic should help.

Image should look better than the pinhole.

 

[OlDoinyo]

Slick-looking build for a homebrew lens, well done (although the peripheral streaking/blurring makes me wonder if it is not a flat-field lens, but some kind of curved-field.)

[ulf]

How have you oriented the lens?

I think the optimal orientation is to have the convex side outward.

[JMC]

Yep, this was with convex side facing away from the camera.

[nfoto]

Slick-looking build for a homebrew lens, well done (although the peripheral streaking/blurring makes me wonder if it is not a flat-field lens, but some kind of curved-field.)

 

A single element lens of any coverage angle has to show a lot of field curvature and spherical aberration. JMC nicely demonstrated this fact

[ulf]

A single element lens of any coverage angle has to show a lot of field curvature and spherical aberration. JMC nicely demonstrated this fact

Not so much field curvature and spherical aberration with a longer FW as I can show here:

For this image I used a fused silica plano-convex lens, FL150mm, Ø50mm from Oriel with a S8612, 2mm UG2A, 2mm filter-stack and a full spectrum modified Sony A7III.

 

The distortion is surprisingly low and some of its fussiness is due to vibrations in the camera support.

As I didn't expect much image quality no remote or image stabilisation was used.

[nfoto]

QED

 

Using a smallish aperture helps as well. Old long focal length lenses, often fallaciously called "telephoto" lenses, tended to be slow and sometimes had surprisingly good image quality despite a very simple optical layout. The angle of view had to be very narrow, though.

[ulf]

I cannot stop down my setup as it originally was intended as a collimator for my spectrometer.

I don't know lens design well enough to know where in axial direction it is best to place an iris or aperture baffle.

It would be interesting to see how sharp I can get the image stopped down.

 

Help is appreciated if anyone here know.

[nfoto]

Try putting an iris next behind the lens.

[dabateman]

Try putting an iris next behind the lens.

 

I think Ulf ment at what distance behind the element. As in directly behind as the mount plate or in the helicoid, many mm away from the element.

[ulf]

I think Ulf ment at what distance behind the element. As in directly behind as the mount plate or in the helicoid, many mm away from the element.

That is correct and I think that is what Birna ment with her answer.

 

I will eventually 3d-print some suitable big washer-shaped disks with different apertures to experiment with and return with the results, hopefully this weekend.

[nfoto]

We're back to the era of Waterhouse stops -- only now, 3-D printed....

[Lou Jost]

Does anyone know how to make an aplanatic lens by adding one or two more elements? That would be really useful, and it might work, especially in long focal lengths, and especially if we use it with narrow-band UV filters so we didn't have to worry about CA correction. I'm trying to build something like this to make UV-C tube lenses for microscope objectives.

[colinbm]

What magnification are you looking for ?

[Stefano]

I have designed some lenses using WinLens3D, I am busy these days but I could try to simulate some.

[Lou Jost]

9 hours ago, colinbm said:

What magnification are you looking for ?

 

 

Not really a particular magnification, since it is a tube lens.

 

I'm interested in focal lengths of 200mm, 300mm, and 400mm. Object is at infinity. Stop is on the object side of the lens system, about 23mm diameter. Material is fused silica. Diameter of the elements can be 1 inch or 2 inches.

 

The commercial UV-C tube lens from Thorlabs cost $4000+. So there is a big incentive to build my own.