Lens transmission in the UV - latest update

[JMC]

I have some new data to add. 3 lenses this time;

 

1. The Sirchie KSS100b 60mm f3.5 lens, as discussed here - https://www.ultravioletphotography.com/content/index.php/topic/3402-60mm-f35-c-mount-uv-lenses-on-ebay/page__view__findpost__p__28777

2. Carl Zeiss 60mm f4 UV Objektiv Exakta mount, as discussed here - https://www.ultravioletphotography.com/content/index.php/topic/1973-carl-zeiss-60-mm-f40-uv-objektiv-1/page__view__findpost__p__13698

3. Asahi Takumar 35mm f4, m42 mount

 

These were measured on my usual setup, with an average of 3 scans, and a boxcar smoothing of 2. A dark spectra run immediately after the scan was subtracted from the lens transmission spectra.

 

 

Couple of points to note.

 

The KSS100b and Asahi 35mm f4 lenses had very small diameter maximum apertures (the KSS100b looks to be a lot smaller than the 3.5 written on it, as discussed in the thread linked above). As such I cannot guarantee that some of the light beam wasn't blocked by the aperture blades for either of those lenses. This would reduce the overall amount of transmission, but not the distribution as a function of wavelength (so their absolute transmission may be slightly higher than shown here). The KSS100b is behaving like the UV Nikkor type lenses in terms of transmission, so I have no reason to doubt it wont be giving good transmission down to 250nm and even below.

 

The Zeiss UV objektiv was easier to run, so I am more confident that this is a real measurement of absolute transmission. This is the only lens I've tested which seems to fall between the 'UV Nikkor', 'Asahi UAT' type of lenses which transmit down to well below 250nm, and the old enlarger lenses/accidental UV lenses which transmit down to the 320-340nm region. I believe this is similar to how the transmission curve for one of the Jenoptik 60mm f4 lenses looks, although I don't have one of those to test. Interesting lens.

[Andy Perrin]

That certainly is a reassuring graph, Jonathan (for dabateman and I, I mean). What are you doing about the hotspot issue? I coated mine in the Acktar Metal Velvet.

[JMC]

That certainly is a reassuring graph, Jonathan (for dabateman and I, I mean). What are you doing about the hotspot issue? I coated mine in the Acktar Metal Velvet.

No problem Andy, and sorry it has taken so long to get done. Regarding the hotspot, not sure yet. I only received the lens a few days ago (it's been on a long journey around the US, then to Austria, before finally making it to me in the UK). I believe Edmund Optics stock that Acktar material, so may get some there, or somewhere else if I can find another UK vendor. I do also have the black paint from Culture Hustle which I've used before. It wont be quiet as effective, but should be very nearly as good (and free, as I already have some).

[dabateman]

Jonathan, thank you that looks far better than I ever would have expected. Full 10% higher transmission than the UAT from your post #21, which was averaging 60%. Also your UAT has significant dip in 300 to 313nm range.

 

What is going on with the Zeiss 60mm f4 UV? Is that advertised as a quartz lens or just good for UV? It looks similar to curves I have seen for the Kuri 35mm. Might be just WG280 glass.

 

Do you plan to try and run the KSS UVC filter? I know that would be hard as you don't have the ideal lights. Would need a calibrated deuterium lamp. But if you can scan it I would like to see what you get.

I am confident my is as written with excellent IR blocking.

I wish my other filters had as strong IR block with the same excellent transmission in the labelled peak wavelength.

[Cadmium]

Jonathan, Andy mentioned that lens has a lot of chromatic aberration in UV.

https://www.ultravio...dpost__p__31311

 

Have you noticed any so far?

[JMC]

David - given it is described as 4 quartz elements, I would have hoped it would have been pretty good transmission. With regards to the dip in the UAT spectra, I think that is due to CaF2, which the KSS100b doesn't have. Although now I look at it again there is a small dip in the KSS100b profile in the same place, although that could be noise. No, the Zeiss 60mm f4 is not described as a quartz lens as far as I know, just one which was suitable for UV imaging. It is a triplet, and I presume they have used glass with good UV transmission properties. The transmission curve looks a bit like the Jenoptik 60mm f4 APO macro lens, as that one drops steeply around 280-300nm. The Kuri would drop much sooner, and have zero transmission by 300nm.

 

I will be running the filters. I can run down to 250nm (and up to 800nm) with filter transmission, although that is right at the bottom end of the spectrometer sensitivity. Hopefully I'll be able to get an ideal of peak transmission %, but accurate measurement of blocking wont be possible. At best I trust my system to OD3-4 measurement. I hope the get the filters tested in the next week.

 

Steve - not tested yet. Not got the bits to fit it to a proper camera at the moment. They are ordered.

[Andy Perrin]

Incidentally, my comment on the CA issues with this lens is based on my experience using it with a full frame camera and an APS-C. The lens was intended for a much smaller sensor, and might be fine in the middle of the image circle in that case.

[dabateman]

Thank you Jonathon.

Since you and Andy now have Dony cameras, if you get the correct adapter it seems to be able to mount allowing infinity focus on the E-mount that Andy tested. My C-mount adapter is too narrow or the lens is too fat, that I need to adapt to M42. So I loose infinity focus. I am not sure if a broader adapter works on M43rds. I will have to see. I only need 3mm extra diameter. I might mill that off one, or just use it as is.

[Andy Perrin]

I don’t think I have infinity focus either (although it seems to get to 10-15m).