Lens transmission in the UV - latest update

[Cadmium]

Earlier today, I was gluing something with UV curing adhesive, and I was wearing my UV goggles for that task.

Then while later I was Googling something, and I realized I was still wearing my goggles.

So in fact I was doing a quick goggle Google.

[ulf]

Earlier today, I was gluing something with UV curing adhesive, and I was wearing my UV goggles for that task.

Then while later I was Googling something, and I realized I was still wearing my goggles.

So in fact I was doing a quick goggle Google.

Some week ago I returned from a bike ride, forgetting that I was wearing my well covering over-sun goggles.

When looking at my main 30" monitor to check something at Google, I thought the backlight in he monitor was broken as the screen was very dark.

Fortunately it was just the effect of crossed polarisers that fooled me.

 

I felt a great relief after finding the cause.

The monitor is high of end type with a wide gamut and not cheap.

[enricosavazzi]

So, if we know what the elements are made of, can we "predict" the transmittance, more or less?

For example, the UV-Planar, which reaches 320 nm, has 5 elements:

• 2 calcium fluoride elements (99% at 350 nm)
  
• one lithium fluoride ele (99% at 350 nm)
  
• one fluor crown glass Schott FK-3 ele (99% @ 350 nm)
  
• one flint glass Schott F1 ele (90% at 350 nm).
  

EDIT - removed irrelevant post.

[bvf]

A while back, I ran a few lenses for Timber, just to see what they all look like for transmission in the UV.

 

So now I'm lusting after a Soligor 35mm/3.5 or Autocrat De Luxe 50mm enlarger lens - but all that's on ebay at the moment are Soligor camera lenses and non-De Luxe Autocrats.

 

Have you ever done the same testing with the lenses I have - Cassar S and Kuri 35mm/3.5? It would be interesting to know whether it's worth keeping my eye out for a Soligor or Autocrat De Luxe. (I've also got a metal El Nik 105mm which I thought was pretty good, but it doesn't come out briliiantly on your graphs.)

[ulf]

Bernhard, remember that the UV-transmission limit is not the only parameter that might be important when choosing lenses for UV-photography.

All depends on what type of imaging you are optimising for.

 

Here are some of the parameters I can think of just now, there are more:

• UV-transmission limit - Important if you want to go deep into UV and struggle with light-sources and sensor limitations.
  
• Sharpness, also over the entire image area.
  
• Good speed, and low losses in the spectra of interest.
  
• Low focus shift, possibly also into IR.
  
• Ability to focus close enough for the intended motif - Macro?
  
• Ability to focus at infinity - Nice for landscape photos in UV.
  
• Wide FOV, if wanted - often difficult for deeper UV and also with small sensors.
  
• Ability to reach high magnification for macro.
  
• A practical working distance, especially for macro.
  
• A working way to mount and exchange filters.
  

The Cassar-S 50/2.8 and Kuriabashi 35mm/3.5 are known to have a deep UV-reach. Also the Focotar-2 50mm goes quite deep.

There has been many versions of Soligor 35mm/3.5.

Some goes just as deep as the one Jonathan has found, I have found two that do, but his model seams to also have an unusually low general attenuation in the pass-band.

[bvf]

Thanks for that input, Ulf.

 

Actually, I'm pretty happy with the Cassar S: it is reasonably sharp, although I have to stop down to f/8 to get good IQ, and its focal length on an APS-C sensor is not ideal so I sometimes have to make panoramas. It can take filters, and can focus to infinity (although UV landscapes don't do anything for me). It works fine for macro with bellows and tubes (although the El Nik 105mm is my main choice for this). I rarely use the Kuri.

 

So I like the Cassar S, but if I could get a bit more UV reach for not too much £££ then I'd like to give that a go. That's why I was interested in the Soligor.

 

A question for you: the Soligors that you have, are they camera versions or enlarger versions (like the one that Jonathan tested)? I would guess that the enlarger version has a different formulation and coating to the camera versions.

[ulf]

The Soligors I have are camera versions.

One is the same as the second Soligor Jonathan measured with a serial number beginning with KA.

One is a slightly more modern variant. None of my lenses have that great general transmission Jonathan found, but still the deep UV cutoff.

There are similar lenses by other brands, that are thought to be of the same general optical design.

You can read more about that on our member Enrico's excellent site:

http://www.savazzi.net/photography/35mmuv.html

 

My Soligors look like the ones here: http://www.savazzi.net/photography/35soligor.html

[JMC]

Hi Bernard, I've not run the Cassar S yet, but it one of the better 'non dedicated' UV lenses I have in terms of amount of light it lets through. As for the Kuri, I have a graph somewhere, and it is very good.

 

I seem to remember Timber saying something about that Soligor 35mm f3.5 enlarger lens not being able to cover a full size sensor. Not sure what the actual coverage of it is.

 

Sorry, I'm snowed under with work at the moment and haven't had time to do any updates to my threads or sort out new data.

[bvf]

Well, I'm still lusting after a Soligor 35mm enlarger lens. But I did manage to get an Autocrat de Luxe 50mm, and have compared it against my go-to UV lens, the Cassar S: I don't have the scientific kit a lot of othe rmembers have, so I take photos through both lenses and compare the results visually. I tested two things - image sharpness, and UV transmission.

 

On image sharpness, the two lenses seem very close. The Cassar may be a tad sharper, but I may be imagining that. My tests were at f/8 with a subject distance of about 1 metre. I'll try at close-up and macro distances when I've adapted the Autocrat (which doesn't have a filter mount) to let me reverse it.

 

In terms of light transmission, the Autocrat appears to be better. But this may just be down to inaccurate aperture markings on one or both lenses. Here is what I found, showing how much faster the Autocrat appeared to be compared with the Cassar - all at f/8:

 

Visible 1.3 x

Baader U 1.8 x

380nm 1.8 x

345nm 1.4 x

315nm 1.3 x

 

Weird that the transmission ratio is higher in the longer-wavelength UVA region than in the neighbouring wavelength regions.

[nfoto]

Your narrow-band filters most like have lower peak transmittance than the Baader U.

[Cadmium]

If you can find one, get a Kuribayashi 35mm f/3.5, or the Kyoei 35mm f/3.5, those are identical, except for the cosmetics of the focus ring,

those are the best of any UV friendly 35mm lens in my oppinion, and they have no focal shift either if that is ever a factor for your work.

[bvf]

I've got one - or at least an Igororiginal clone. Coudn't detect any difference in UV capability compared with the Cassar S. The deeply recessed front element prevents my using small 25mm filters, which is where the UV reach would be most apparent. I ought to check it out for image quality, although I suspect a cheap 35mm lens is not going to work as well as a cheap 50mm lens for the same area of coverage.

 

Lack of focal shift would be a plus, but I have a process for handling that now. And the fact I can't use my 3 x 25mm filters (for colour separation work) on the Kuri makes that benefit less useful.

[ulf]

I've got one - or at least an Igororiginal clone. Coudn't detect any difference in UV capability compared with the Cassar S. The deeply recessed front element prevents my using small 25mm filters, which is where the UV reach would be most apparent.

And the fact I can't use my 3 x 25mm filters (for colour separation work) on the Kuri makes that benefit less useful.

 

Sometimes it is possible to build inwards closer to the front element with step down rings.

Their smaller inner thread is often accessible from both sides of the ring.

That is making it possible to mount the filter inside the step-down ring to shift the filter closer to the front element.

It could be repeated several times for deeply recessed front elements.

[bvf]

That's a useful idea.

 

Unfortunately, it won't help me here. I've cemented the 25mm filters into 49mm mounts, as I've standardised on 49mm. I arranged it such that the filters protrude from the back of the filter mount so that they are a bit closer to the lens - but that was not enough for the Kuri. Now that's causing me problems with the Autocrat, because the front element is not recessed at all. So I'm going to have to add some rings to move the filter away from the lens!

[bvf]

I've done some comparison shots now to look at the sharpness from the various lenses at my disposal.

 

First of all, using my full-spectrum camera. I did these shots in UV through a Baader U. With the adapters I have at the moment I couldn't focus the Kuri and Autocrat at the same distance, so I compared each separately against the Cassar:

 

 

The Cassar is the clear winner. No point in using the Autocrat de Luxe, and only use the Kuri if you need the wider angle.

 

Just for the hell of it, I thought I'd do the same on a full frame (visible only camera). I threw in a Canon 50/1.8 to see how a modern lens compares:

 

 

No surprise, the Canon is best. Then the Cassar, followed by the Autocrat, and the Kuri trailing well behind.

[JMC]

Bernard, I'd be careful about calling that Igoriginals lens a 'Kuri'. He puts them together from bits of lenses and I have yet to see any meaningful work done to compare them with the real ones. I have one of his 28mm lenses, and I'm not blown away by it. I also have a real Kuribayashi 35mm f3.5 lens, and the build quality is in a completely different league.

[bvf]

Yes, I tried out one of his home builds as well.

 

But his Kuri clone is nothing like that. It's a genuine Kuri or one of the re-branded versions which he converts to a T2 mount and 52mm filter mount. I have no reason to believe the lens is not the real thing. Certainly in terms of UV transmission it does what it's supposed to. It's just that the Cassar is a better lens, partly because of its longer focal length.

 

[JMC]

Bernard, this is worth a read a some point, if you've not seen it already;

 

https://www.ultravioletphotography.com/content/index.php/topic/2795-about-lens-clones/page__view__findpost__p__21498

[bvf]

Hmmm, interesting.

 

To be fair, the comments seem to be suspicion and what-might-be rather than fact, but nevertheless cause for concern. I couldn't find the Sigma Quattro article that is referred to, to see the photos taken with the clone.

 

Genuine Kuris/Keois are hard to come by and are expensive, but the equivalent Soligors, Optomaxes, Prinz Galaxies, etc. are relatively common and cheap. Perhaps I'll get one of these to try out. It's a bit of a minefield because there are so many variants in the metalwork that I may not get the right glass inside. I guess the answer is to look for one that is identical in appearance to those pictured in articles by Blum, Savazzi, et al.

[dabateman]

Bernard,

The Igoriginal 35mm f3.5 is not a Kuri and can't be. He took multiple different clones apart, switched lenses, cleaned them, added seals, glued in 52mm step in ring and labeled them clones. I think the Igoriginal 35mm is closest to the Soligor or Galaxy.

 

See here:

http://www.savazzi.net/photography/35mmuv.html

 

See Johnathan's spectral tests here:

https://www.ultravioletphotography.com/content/index.php/topic/3406-lens-transmission-in-the-uv-latest-update/page__hl__soligor__fromsearch__1

 

 

This assumption of mine is based on the markings on the barrels, and the barrel grips. But even this maybe wrong as he did swap lens elements.

 

So if you can get your hands on a real Kuri, it would be the best 35mm that is not quartz.

[bvf]

Thanks for the help everyone.

 

My favourite UV lens is the Cassar S, followed by the metal El Nik 105mm - I'd love to know how they compare with the real Kuri.

 

I can only use my "Kuri clone" with the Baader U (because my 25mm 315 & 345 filters are too far from the front of the lens), so I guess UV reach is not so important as the shorter wavelengths (where the camera is much less sensitive) get swamped by the longer wavelengths. But certainly the image quality is of concern: actually, I remember when I bought the lens from Igororiginal the lens that was delivered was absolutely dreadful for IQ - he replaced it without problem, but it does support the contention that it was a doctored lens.

 

There is a genuine Kuri on ebay at the moment - but at a price of £235, which I'm not prepared to pay. So I'll get one or two of the rebrands, which are going for £5 - £30. From what I can see on the various links you've provided there's nothing to choose between these and the real Kuri. When I get these, I'll do a comparison with the "clone" I have and let you know.

 

In the meantime, if anyone has any data comparing the Cassar S and El-Nik 105 with the real Kuri ...

[Timber]

So now I'm lusting after a Soligor 35mm/3.5

This enlarger lens is APS-C only, it does not renders Full Frame.

[bvf]

Thanks, Timber. Fortunately my FS camera is APS-C. All I need now is to find one of those Soligors ...

[Timber]

Thanks, Timber. Fortunately my FS camera is APS-C. All I need now is to find one of those Soligors ...

Where about you live in the UK? If you happy to pick it up in London you can have mine as I moved to FF and it only collecting dust on my shelve. Drop me a PM if you are interested.

[bvf]

Generous offer, Timber. I'll PM you.