What can I do with this single quartz lens ?

[colinbm]

What can I do with this single quartz lens ?

I have a quartz, yes it passes UVC, single lens, that is 70mm dia & 13mm thick, but only curved on one side.

It can burn paper at about 80mm, so is that the focal length ?

Can I make this into a lens for my camera ?

[dabateman]

70mm diameter is huge. See if it fits a 72mm filter ring with curve side facing subject. Then use step rings to get to a M42 helicoid. Then mount that on your camera. Once on, adjust the helicoid until you see something. First take a picture of a tape measure across the width of the frame. Your Sigma Fp sensor is 36mm wide so you can read here to calculate the focal length:

https://www.photonstophotos.net//GeneralTopics/Lenses/Optics_Primer/Optics_Primer_05.htm

Then if you like it you can buy an aperture ring adapter.

[colinbm]

Thanks Dave

I was hoping it was this simple, I have a M42 aperture ring so all good.

Ok, so just step rings down to 52mm then to a M42 & the aperture ring, then to a M42 helicoid & the M42 Sigma fp adapter & bob's your uncle....

[dabateman]

Try to get the element as close as possible to that aperture ring. If you bought a M42/M52 ring than a 52mm to 72mm step up would work best. If you got a M42/M42 aperture ring then M42 to m52 step up and 52mm to 72mm step up to the 72mm element.

The helicoid will be behind the aperture control ring to your camera mount.

 

You can calculate your maximum aperture based on the ring opening diameter looking down through the front element. Divide that by your calculated focal length. As in if it ends up being 100mm focal length and you measure 25mm looking down through the front of the element, than you have a maximum F4 lens.

This may help or confuse, you may need to read it twice:

https://www.photonstophotos.net//GeneralTopics/Lenses/Optics_Primer/Optics_Primer_11.htm

 

Reading all the posts doesn't hurt. Most of Bill's primer is short.

[colinbm]

Thanks Dave

I guess the curved side faces forwards ?

[dabateman]

Yes best should be curve side of element facing the subject. Or away form sensor.

You can try both ways, but the contrast and sharpness will be best with the curve facing the subject.

[colinbm]

Helicoids & M42 spacers on, it measures 130mm from glass to sensor, at infinity.

The aperture ring that I have is for SA mount to M4/3, so not good at the moment. I'll make up some black card apertures & try them.

[colinbm]

I made some apertures, 12mm, 10mm & 8mm, to play with tonight.

[colinbm]

I am getting 1:1 ratio image with a focal length of 260mm & a working distance of 250mm in front of the lens.

[ulf]

I would also add a baffled lens hood in the front, as these builds often is sensitive to light entering sideways, but not used for the image.

As the iris will need to be stopped down rather much, the front opening can also be rather small without any problem with vignetting.

A rectangular opening just slightly bigger than needed in the front end is the most effective design.

Similar principle as used with this kompendiu:https://www.ebay.com/itm/313299390628?hash=item48f21950a4:g:X0UAAOSww-tfrvoR

[dabateman]

Any good images? The focal length of commercial lenses is typically reported from infinity focus. Nice that you can push it to macro. But I have a feeling its designed for macro as a reading lens that you move over a book to enlarge the words.

 

Did you find a good sharp aperture or were many wider ones good? If many than a control ring may be worth the purchase. If only one than just cut that and keep it there.

 

So you might have a quartz lens after all.

The pathway for a UV photographer now seems to be:

1. Get interested in UV

2. Buy a full spectrum camera.

3. Buy a cheap lenses capable of UV

4. Buy a filter stack.

5. Get stuck buying more lenses or more filters.

6. If avoid or break through 5, buy a spectrometer.

7. Make a quartz or fused silica lenses.

 

You, Jonathan, Ulf and I have all gone through these stages.

[colinbm]

Thanks Ulf, I'll try that when I get a thicker 72mm filter ring, the one I have now is just holding the lens, then I'll be able to use this 72mm filter ring with the baffle.

[colinbm]

Thanks Dave, don't forget your membership to the club....EDIT you did mention yourself.

 

I want to see how far the Sigma fp reaches in UV, I'll have to find some more 10 or 12mm band pass filters below 340nm, down to 300nm.

[dabateman]

I am assuming your aperture is Sigma SA mount to m43rds. Than if you have a M42 female to Sigma SA mount adapter, then you could buy one of these to make it work for this build:

https://www.ebay.com/itm/Macro-Extension-Tube-for-Olympus-Panasonic-Micro-4-3-/332834493606?_trksid=p2349624.m46890.l49286

 

Its has a front m43rds mount that unscrews to a m52 thread. Then there are various thickness m52 threaded tubes and finally a m52 to m43rds mount adapter. You ca use the front to make your aperture ring useful and the tubes to give you a hood for your lens.

 

Otherwise the aperture rings Ulf showed work well and you can decide based on your tests the maximum opening and threads.

 

You will need a 72mm to 52mm step down ring for the front. Though to use this and it should help a little with flare.

[ulf]

Thanks Ulf, I'll try that when I get a thicker 72mm filter ring, the one I have now is just holding the lens, then I'll be able to use this 72mm filter ring with the baffle.

Many metal lens hoods have a female thread at the front edge that might be used. The thread is normally also a filter thread, but one or two steps bigger that the male thread.

 

The baffle could be cut through stiff black paper and taped on, during experimentation.

You might also use a M42 extension tube as a hood like I did in my builds.

[colinbm]

Good thinking Dave, yes I have a M42 female to Sigma SA mount adapter.

I'll get the M4/3 tube set.......that is M42 threaded ?

[dabateman]

Good thinking Dave, yes I have a M42 female to Sigma SA mount adapter.

I'll get the M4/3 tube set.......that is M42 threaded ?

 

No oddly its all 52mm threads. But that works well for hoods on filters and other mount adapters.

 

I originally got it to add 52mm front thread to a reverse mounted lens.

[colinbm]

No worries I can cope with 52mm & I have a bunch of 52mm macro tubes.

 

Here is a 1:1 macro with the 70mm quartz lens with a 8mm aperture.

 

[Stefano]

That's sharp! There is what looks like a UV hotspot, and the lens has been stopped down quite a lot, but that looks good.

 

Can a longer hood reduce the hotspot? Does it work like it does with flares?

 

Also, just curious, do you know if your lens is aspheric or spheric?

[Stefano]

Actually, f/8.75 is really not a lot. This looks promising.

[colinbm]

Thanks Stefano

I don't know about lens types, sorry.

I will do Ulf's suggestions tomorrow & see how it goes.

I had some mylar / polyester film on the flash so it is only putting out down to about 300nm.

[dabateman]

130mm focal length/ 8mm (if thats what you see looking down) = f16

 

If we use 260mm at 1:1 then your F is 32.

 

So that is about what I would expect.

If thats good you may not need the aperture ring and just stay there.

 

Yes a hood will help with that hot spot.

It also might be due to reflection within you helicoid tubes. Adding flocking will help.

 

The fun thing about building lenses is you have full control and can improve them.

[colinbm]

Thanks Dave, I see what a bit of tweaking can do tomorrow.

[JMC]

Very nice Colin, that looks really good, especially for a single element lens. Good to see more people building their own kit.

[colinbm]

With this 70mm quartz lens I have infinity at 130mm from the quartz to the sensor, with the 36mm to 90mm helicoid attached, & I can get a range from infinity to 700mm fully extended.

That with a 50mm range of the lens, at 130mm it is at infinity focus & at 180mm close focus at 700mm.

1:1 ratio at 265mm extension.

 

Set at Infinity.....

 

 

 

Set at close focus, 700mm to subject from sensor....