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Back to basics - 40mm singlet lens from Thorlabs

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#1 JMC

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Posted 02 March 2020 - 13:42

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;

Attached Image: small 578A3202.jpg

Attached Image: small 578A3203.jpg

Attached Image: small 578A3205.jpg

Attached Image: small 578A3206.jpg

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

Attached Image: 578A7146 a small.jpg

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
Attached Image: DSC00184 uv lalau closed small.jpg

LaLaU, aperture partial closed (approx f5), ISO8000, 1/160s
Attached Image: DSC00187 uv lala u 5mm open small.jpg

R72, aperture closed all the way (approx f40), ISO1000, 1/640s
Attached Image: DSC00195 r72 closed small.jpg

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.
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#2 Andy Perrin

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Posted 02 March 2020 - 13:46

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.

Edited by Andy Perrin, 02 March 2020 - 13:48.


#3 Stefano

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Posted 02 March 2020 - 13:56

View PostAndy Perrin, on 02 March 2020 - 13:46, said:

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.ultravio...t/page__st__40. Yes, you can form an image, but it will be usable only in the center.

#4 Stefano

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Posted 02 March 2020 - 13:58

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

#5 Stefano

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Posted 02 March 2020 - 14:03

View PostStefano, on 02 March 2020 - 14:03, said:

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.


#6 Stefano

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Posted 02 March 2020 - 14:05

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

#7 Andy Perrin

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Posted 02 March 2020 - 14:05

View PostAndy Perrin, on 02 March 2020 - 13:46, said:

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.

View PostStefano, on 02 March 2020 - 13:56, said:

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).

Edited by Andy Perrin, 02 March 2020 - 14:07.


#8 Stefano

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Posted 02 March 2020 - 14:09

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?

#9 Andy Perrin

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Posted 02 March 2020 - 14:11

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.

#10 dabateman

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Posted 02 March 2020 - 16:50

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.


#11 OlDoinyo

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Posted 03 March 2020 - 03:54

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.)

#12 UlfW

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Posted 03 March 2020 - 17:07

How have you oriented the lens?
I think the optimal orientation is to have the convex side outward.
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#13 JMC

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Posted 03 March 2020 - 22:31

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

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Posted 03 March 2020 - 23:50

View PostOlDoinyo, on 03 March 2020 - 03:54, said:

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 :smile:

#15 UlfW

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Posted 04 March 2020 - 05:01

View Postnfoto, on 03 March 2020 - 23:50, said:

A single element lens of any coverage angle has to show a lot of field curvature and spherical aberration. JMC nicely demonstrated this fact :smile:
Not so much field curvature and spherical aberration with a longer FW as I can show here:
Attached Image: Screen Shot 2020-03-04 at 05.59.02.png
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.

Edited by UlfW, 04 March 2020 - 08:44.

Ulf Wilhelmson
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#16 nfoto

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Posted 04 March 2020 - 08:02

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.

#17 UlfW

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Posted 04 March 2020 - 08:40

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.

Edited by UlfW, 04 March 2020 - 08:41.

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#18 nfoto

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Posted 04 March 2020 - 08:44

Try putting an iris next behind the lens.

#19 dabateman

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Posted 04 March 2020 - 12:36

View Postnfoto, on 04 March 2020 - 08:44, said:

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.

#20 UlfW

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Posted 04 March 2020 - 14:36

View Postdabateman, on 04 March 2020 - 12:36, said:

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.
Ulf Wilhelmson
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