Optimizing a lens for UV transmission

[Alex H]

So how "deep" in UV do you want to record? 350nm? 300nm? 200nm?

[lost cat]

So how "deep" in UV do you want to record? 350nm? 300nm? 200nm?

 

Somewhere between $ and $$

 

Its not so much about how deep into the UV but how much UV light I can get to become meaningful electrons and how good the image will look. It'd be nice to get images with 50% cutoff at 300 nm for bragging rights but as long as I can get most of the photons between 350 and 400 nm I'll happy.

 

For now I'm doing portrait work so I'd like to keep exposure to a minimum, both for the well being of my subjects and because they tend to move sometime during a long exposure.

 

Eventually I'd like to get into UV video as well.

 

 

 

[Cadmium]

Hi Lost Cat,

Yes, 88 is suppose to transmit slightly lower, but I can't detect any difference between 63 and 88 with my equipment, even at much thicker thicknesses than are used with lenses and filters.

However I can detect a slight color difference between both of those and 305 with thicker thicknesses, again much thicker than used with lenses and filters.

Acetone works, but it requires much more time.

Regardless of which adhesive you use, all of this takes some finesse, so you should practice everything a few times first using junk glass, filters, lenses... even the removal processes...

before you sit down to do anything with your lens elements.

Just my advice, because I have done this with filter glass enough to know it is not easy at first.

Once you practice some, then the process becomes easier, but the first time will probably not work out so well.

Practice makes perfect, so don't start with your perfect doublet... start with a couple old cheap skylight filters or such.

 

Here are a few things I Googled:

This is an old document from 1970, but the only thing I happened to find showing UV transmission info for Canada Balsam (it also mentions 305).

From the info in this paper, Canada Balsam looks good for UV, but I have not tested it or worked with it.

http://www.dtic.mil/.../u2/a308426.pdf

 

Search Enrico's page for "Balsam", about half way down, "The optical glue used to cement the layers must transmit UV (Canada balsam is not usable)".

I don't know the reasoning, but maybe Enrico can explain.

http://www.savazzi.n...tography/uv.htm

 

I have no experience using Canada Balsam, so I have no opinion or info about it. I have only used the adhesives I have mentioned.

I do have a couple old doublets that work fine for UV, which are probably glued with Canada Balsam. One has a small amount of delamination, but not enough to take it apart.

[Andrea B.]

....with 50% cutoff at 300 nm for bragging rights

 

UV Illumination is the hurdle there. I've never gotten anything much around 300 nm. Here is one of the attempts: http://www.ultravioletphotography.com/content/index.php/topic/1268-its-rough-down-there-at-293nm

[rfcurry]

Norland 72 has a lower viscosity than Norland 63, which I prefer as it allows for a thinner cement layer between elements. Both cements are similar in UV transmission.