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UltravioletPhotography

[INDEX] Lens Spectra with Jeweler's Spectroscope by Dmitry


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Hi,

The Sigma 30 mm f:2.8 was released in 2013 and is in production. I bought mine second hand, so I am not sure about the date of manufacture of my copy. Autofocus does work reliably in UV only under strong illumination, and autoexposure with my Olympus E-M1 usually needs a bit of compensation. It is a sharp lens. Usable in UV, if one is not too picky, from f:3.5 to f:16. It suffers from some focus shift, especially noticeable when focusing at the minimum distance of 30 cm. It is also cheap even though it is labelled as an Art series objective by Sigma.

https://www.sigmaphoto.com/30mm-f28-dn-a-29935

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From Pedro's recommendations, I too have the Sigma 30mm f2.8. The one in question is the newer one with the smooth focus ring. We haven't tested the first one that came out.

Mine is similar using recently a filter test method. I can't see anything using a 340bp10 filter. But a 370bp15 filter works.

On my full spectrum converted Em1 I can use the Sigma 30mm f2.8 with my 390bp25 filter hand held for uv video or regular uv images. Works quickly and usually a great option. Autofocus works very well.

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Dmitry, can you perhaps point to a more precise link for one of these that is exactly the same as the one you are using?

The one I have shows visible violet right on the very edge, so nothing is seen with the Baader U (eBay # 220692058016).

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I have no Baader U to check my copy. It looks same as link to ebay (including paper box and leather case), but I purchased it via aliexpress.

 

Tried to look by bare eye with zwb3 2mm, it's very dim on main spectrum, you need camera and long exposure to see second-order.

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Did you modify the one you have in some way so that you could see a wider view when looking inside the eyepiece?

The one I have only has enough viewing width in the view finder to show the visual spectrum when viewed with my eye, none of which shows up to my camera when viewed with UV only.

Perhaps if the view finder end was removed (which I have not found an easy way to do)? But as is, I would not recommend buying this particular item I got for UV, unless I can get it to work some way.

 

The eyepiece end 'looks' like it might screw off, but it definitely doesn't come off, perhaps threaded (not for sure), but also perhaps glued.

Width of field view is not adequate to view wider than visual, as is.

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Anyone?

Don't get the one I got, I don't recommend it for this use.

I took it apart, a vise grip to the body and some long channel locks to the eyepiece, twisted it off.

Eyepiece was glued in place. No threads.

Looks like the front of the unit has the slit + a lens.

The back end eyepiece section contains a type of prism, 45 degree cut with a thin membrane/film diffraction grating applied to the 45 degree cut glass prism surface.

The prism/grating is glued into the removed eyepiece housing.

Because the prism/grating is glass, I don't see an easy way to remove it from the eyepiece end/housing without destroying the glass.

In order to view a wider angle of the prism/grating the eyepiece housing would need to be removed from the prism/grating,

and there is still no guarantee it would view a wide enough range if the metal end housing was removed.

This one will not work for UV as designed.

 

Has anyone else tried this yet?

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HANDHELD DIRECT VISION SPECTROSCOPE

 

A real beauty! Great for demonstrating spectra from any visible light source. Precision made heavy duty stainless steel construction with an Amici type 3-element prism assembly, variable optical slit and adjustable eyepiece. Easy to use: Optical slit adjusts by rotating the knurled end piece, and focus is slip type. Contrast and resolution of the spectrum is changed by adjusting the slit opening. Both emission and absorption spectra can be viewed. 4 inches long by 1 inch diameter on the slit end. New with wood case. Edmund has a similar spectroscope for $272.00

 

The scale is not linear like the diffraction grating & has no second order.

The scale is like a log scale, it is expanded at the UV end (which is where we are interested) & is compressed at the IR end.

Mine reads, with the aid of a full spectrum camera, from 360nm to 920nm. Why it is restricted to this range I don't know.

 

You can search my posts for some pictures of it & spectra.

 

https://www.surpluss...tem/I1479D.html

 

http://www.ultravioletphotography.com/content/index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=12512

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The question I have is what attenuation does this device have in UV? If it is not transmitting UV well at the low wavelength end, it will be misleading for lens tests, I would think?
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The band graphs look OK, but this is completely undocumented.

I don't know which one to get, the one I have doesn't show a wide enough view for 'second order' anything,

I don't know what set up is used for focusing on the eyepiece, I don't know what tube it is mounted in.

There is a photo, but a lot of information is left out.

So until I see a complete and specific parts list and precise instructions for assembling this lens mounted set up, I have stashed my now dissembled copy in a drawer.

I am going to wait for more specific information and someone or other to try this beside just me and tell how they got it to work.

I am frustrated with it, and I have $30 less in my wallet.

I think maybe building one from scratch with 1000 line diffraction grating may be a better way to go.

I just thought this was suppose to work easier.

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Ulf, Yeah, seen a few like that, but the link you posted is a good one for sure.

Sorry if I sound frustrated, just thought it would work better, easier... with out much fussing around, given that it is already built/made...

oh well, always fun to tear something apart I guess. ;)

Thanks again.

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