Jump to content
UltravioletPhotography

Suitability of 250mm f5.6 Superachromat for UV


Recommended Posts

I recently got hold of a Hasselblad 250mm f5.6 Superachromat, as I wondering whether this might be suitable for UV imaging. The lens has 6 elements in 6 groups, and (I believe) no T* coating. I was thinking that it might make a good longer focal length UV lens given the construction.

 

To try it out I mounted it on my Canon EOS 5DSR monochrome conversion, and using a Baader U, compared it against the 105mm Rayfact UV lens. I used ISO800 and f11 for both images. I collected a white balance shot using a PTFE tile and white balanced the monochrome images in Darktable. Both images taken at the same distance to the subject. The 105mm macro image was then cropped to give a similar field of view (the 250mm image is uncropped but with reduced resolution for posting here). Images taken in direct sunlight but about 30mins apart (fickle, UK weather) so the light was similar bu not identical.

 

Please excuse the ugly mug being photographed, but I was the only subject available, so there was a lot of running backwards and forwards and using the timer for these. I wear glasses (these are not sunglasses but they have a UV protective coating on them and are transparent in visible light).

 

Firstly the 250mm SA. f11, ISO800, 1/2s exposure.

post-148-0-97028600-1533038002.jpg

 

Secondly the 105mm Rayfact. f11, ISO800, 1/8s exposure.

post-148-0-25103900-1533038067.jpg

 

There is a weird colour cast with the white balanced images - looks to be a green halo around the edges of the image, which is odd for a monochrome camera, but it happened with the full sized image of the Rayfact too, so doesn't seem to be limited to the Superachromat lens. I normally shoot this in jpeg mode, so don't always look at the RAW files. Perhaps a result of the dichroic coating on the Baader U. No special processing was done on these - nothing specific to monochrome images - these were processed as a normal RAW file.

 

Overall the the 250mm SA was about 2 stops slower than the Rayfact 105mm in the UV. When I've done tests with normal camera lenses in the fact they are typically around 4 stops, or sometimes more, slower than a dedicated UV lens. It looks therefore as though the 250mm SA lens makes quite a good UV lens, being only a couple of stops slower than a dedicated UV lens.

 

Has anyone used this lens before for UV - I did a quick search but couldn't find anything on it? I'll be doing more analysis of it in the future, including hopefully assessing it on my spectral sensitivity setup, to see where the transmission drops off.

Link to comment
Andy Perrin
Interesting. Why did you white balance the monochrome conversion rather than just desaturating it?
Link to comment
Just to try it out really. Some people have mentioned to about white balancing in the past, so thought I would give it a go. Strange effect though.
Link to comment

If that’s you, who’s the kid in your avitar ?

The avatar was me when I was a bit younger and less stressed (but is still one of my favourite pictures of me). The avatar picture was taken using a lensbaby, and is very 'flattering'. What's the old quote "it's not the years, it's the mileage".

Link to comment

Jonathan, that looks like a good telephoto find. The angle of view on a m43rds camera is also interesting. I still need to test out my Lentar 400mm and 450mm lenses. But Cadmium posted already some interesting results.

 

The white balance results are very cool. You may have found great portrait set up for uv. To get green leaves and a central portrait zoon.

Link to comment

Overall the the 250mm SA was about 2 stops slower than the Rayfact 105mm in the UV. When I've done tests with normal camera lenses in the fact they are typically around 4 stops, or sometimes more, slower than a dedicated UV lens. It looks therefore as though the 250mm SA lens makes quite a good UV lens, being only a couple of stops slower than a dedicated UV lens.

What do you mean with "normal camera lenses" you have tested?

 

It would be interesting to see the same test with your full spectrum converted rgb-camera.

Link to comment

Ulf, typical modern Canon camera lenses, with lots of lovely coatings and glues between lens elements.

 

I did try with my RGB one but the issue was length of exposure. As it was about 2 stops slower than my monochrome camera at the same ISO and f stop settings, I couldn't keep completely still for the 2s needed and ended up with shaky/blurry images.

Link to comment

You can't hold still for just a second.

 

Sounds like something I have said to my kids. You could try f5.6, that would give you the two stops, but you don't have autofocus on that lens, so guessing the thin plane maybe hard. You will need a model.

Although all joking aside, the portrait at that focal length does look better. Much more slimming, without fully flattening your noise. Definitely a good portrait lens.

Link to comment

Ulf, typical modern Canon camera lenses, with lots of lovely coatings and glues between lens elements.

I hoped you had some more UV capable, but less expensive lenses to compare with, like a EL-Nikkor 85mm or 105mm.

Link to comment

It was difficult to get the plane of focus right David, with me being photographer and model, hence f11.

 

Ulf- strangely enough the one group of lenses I don't have are the El Nikkor enlargers.

Link to comment

@Andrea,

Have you tried to force that conversion on an IR image? I will have to see if that works as it would be similar to a monochrome camera if a 830nm filter or above were used.

I just noticed they extended the beta to September 1, so will have to try some tests

Link to comment

For longer UV-capable lenses, you can't go wrong, imo, with any of the Pieskers. They are usually very reasonably priced. All are very well-made, long triplets except for the 250/4.5 which is a doublet!

For a 400mm I use the Tele-Picon 400/4.5 in M42 mount. This requires a serious tripod.

Even the 250/4.5 can be a robust handful.

 

Good luck.

Link to comment

A doublet ?? !! ?? Doesn't it have a lot of aberrations?

However I certainly do not know much at all about lens design, so that may be a dumb question. :lol:

Link to comment
  • 1 year later...

Update.

 

I ran the Superachromat 250mm lens through my lens transmission measurement. Well, this has been a perfect example of wanting something to be better than it actually is (not good practice for a scientist). When I originally tested the lens I assumed that without coatings or glued elements it would be ok for UV and I wanted it to be good.

 

Turns out the transmission is not that great. This is my measured spectra;

post-148-0-64860400-1565261829.jpg

 

It doesn't really go that deep into the UV, and the max transmission isn't that great either. While it may be great for visible light imaging, I certainly wouldn't recommend rushing out and buying one for UV. However the Zeiss documentation does reckon this is a good one for IR (up to 1000nm at least).

Link to comment

Well it was about 2.3 stops slower than your quartz lens on the Monochrome camera. So not too surprising. Since tested on monochrome camera, it was hard to tell the color cast.

 

Thank you for the results.

Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...