special quest: UV lens > 100mm wanted

[19_blackie_73]

Hey guys,

I'm working on a research project and we are using methods in the uv range to see what happens (wavelengths ~250-350nm). As a weapon of choice we are using a phantom v2011 with a F-Mount. For this we have at the moment a ~100mm lens capable of uv and it works fine on other projects, but because of space problems, we need to be quite far away of the object so we would need a longer lens. Problem is, I didn't find any lenses with f-mount longer than the 100ish mm. optimum would be a 200mm, but everything greater than 150mm would help a lot, because we could use more pixels. 

If we would work outside the uv range, using a teleconverter for our existing lens or just buy a off-the-shelf nikon tamron whatever lens, wouldn't be a problem, but we need uv capabilities.

AFAIK simple extension tubes wouldn't help, would they?

If anybody has suggestions, I'm very thankful!:)

 

Greetings

- 19_blackie_73

[whoisjaya]

On 01/06/2018 at 4:59 PM, 19_blackie_73 said:

[...]

AFAIK simple extension tubes wouldn't help, would they?

[...]

I think they'd just allow you to set your focussed point closer to your front element.

 

Couldn't really find a lens suiting your needs, though, sorry...  

Edited June 3, 2018 by Jonas_2909
Typo

[porina]

I haven't really looked, but the only UV lenses I'm aware of are those made by Coastal Optics. They only go to 105mm so not really helping here.

 

Extension tubes allow you to reduce focus distance, so that wont help either.

 

To my understanding, the problem with "normal" photographic lenses going into the UV range are two fold: one, they're not corrected into the UV range so performance will probably suck. Secondly, many glass types used absorb UV so transmission might be a bit rubbish. You could simply try your luck, see if you can borrow or rent some lenses in the desired focal length range, and see how they perform. Fixed focal length lenses are more likely to perform well here as they will be simpler, and avoid any with image stabilisation functionality.

 

There are two other areas that might be investigated, but not without their own different sets of problems.

 

Firstly are mirror lenses. These were a fad for low cost longer focal lengths, but the use of mirror as primary optic has the benefit of not dispersing different wavelengths. I don't know how the mirror coatings work in UV though so that would be an area for further research. Also, I believe they generally weren't pure mirror designs, but catadioptric, so you still have some glass element(s) in there.

 

On a parallel note, I'm wondering if astronomical telescopes might be a candidate here. From memory, the Coastal Optic lenses designed to work at UV made copious use of Fluorite elements, in part for their UV transmission properties, and some astronomical refracting telescopes also use these elements. Not saying they're designed to work well into the UV, but it might help transmission rate. Unless you drop serious cash into this area, designs may be doublets or triplets, so very simple optically speaking. For this application, it compares well against photographic lenses, where zoom lenses may have 20+ elements. I have to say, I'm very out of date in this area so I can't give example scopes to look at.

 

The possible problem with the above two suggestions is that focal lengths may be longer than desired, probably not going to fund much less than 400mm.

[19_blackie_73]

On 2.6.2018 at 12:30 AM, Jonas_2909 said:

I think they'd just allow you to set your focussed point closer to your front element.

 

Couldn't really find a lens suting your needs, though, sorry...  

yeah that was my problem too, thought maybe another person might have more luck than I had. Thank you anyway

On 2.6.2018 at 1:02 AM, porina said:

I haven't really looked, but the only UV lenses I'm aware of are those made by Coastal Optics. They only go to 105mm so not really helping here.

 

Extension tubes allow you to reduce focus distance, so that wont help either.

 

To my understanding, the problem with "normal" photographic lenses going into the UV range are two fold: one, they're not corrected into the UV range so performance will probably suck. Secondly, many glass types used absorb UV so transmission might be a bit rubbish. You could simply try your luck, see if you can borrow or rent some lenses in the desired focal length range, and see how they perform. Fixed focal length lenses are more likely to perform well here as they will be simpler, and avoid any with image stabilisation functionality.

 

There are two other areas that might be investigated, but not without their own different sets of problems.

 

Firstly are mirror lenses. These were a fad for low cost longer focal lengths, but the use of mirror as primary optic has the benefit of not dispersing different wavelengths. I don't know how the mirror coatings work in UV though so that would be an area for further research. Also, I believe they generally weren't pure mirror designs, but catadioptric, so you still have some glass element(s) in there.

 

On a parallel note, I'm wondering if astronomical telescopes might be a candidate here. From memory, the Coastal Optic lenses designed to work at UV made copious use of Fluorite elements, in part for their UV transmission properties, and some astronomical refracting telescopes also use these elements. Not saying they're designed to work well into the UV, but it might help transmission rate. Unless you drop serious cash into this area, designs may be doublets or triplets, so very simple optically speaking. For this application, it compares well against photographic lenses, where zoom lenses may have 20+ elements. I have to say, I'm very out of date in this area so I can't give example scopes to look at.

 

The possible problem with the above two suggestions is that focal lengths may be longer than desired, probably not going to fund much less than 400mm.

Thank you for your long answer   I'll see what I can find, I'll talk to some guys at our facility next week and see how we will setup tests - need to verify some things anyway, so maybe I'll just try one of my personal lenses (using nikon stuff myself) and test uv capabilities. Also I'm trying to find some mirror lenses and see if they fit there where they need to go - but more than 200mm is probably not useful as far as I can tell right now, but I will need to do some tests. I tried to simulate and calculate some stuff, but at the moment these numbers are quite far off from reality.