Various Lens Comparisons - UV & IR

[bvf]

Following Andy's post comparing El Nik 80 & Cassaron, here are some comparisons I did recently. These finally persuaded me that the Focotar 2 was better than the Cassar S for a 50mm UV lens. The Cassar S seems to perform better in UV than it does in visible.

 

The top row is a crop at centre of the image - the area shown is approximately 1/30 of the full image width. The middle row is at extreme corner (APS-C sensor) with no re-focusing - the area shown is about 1/35 of the full image width. The bottom row is extreme corner with refocussing. The set of rings at the centre was different to that at the edges. The difference betwen the middle and bottom rows gives an idea of curvature of field issues.

 

In all cases, the camera was moved for the various focal lengths to give approximately equal image sizes.

 

The 345 nm and 850nm images were made to give a narrower wavelength band than the Baader U and R72 images and reduce the effect of chromatic abberation.

 

All exposures were f/8, ISO 100.

 

The lenses used were:

 

Canon EF STM 50mm f/1.8

Steinheil Cassar S 50mm f/2.8

Leitz Focotar-2 50mm f/4.5

El Nikkor 80mm f/5.6 (old-style metal)

El Nikkor 105mm f/5.6 (old-style metal)

Igororiginal 35mm f/3.5

Canon EF 28mm f/2.8

 

Visible:

 

Baader U:

 

345BP25 filter:

 

R72 filter:

 

Midwest Optical BN850 filter:

[Stefano]

Yes, the Focotar, although not being perfect, is definitely sharper than the Cassar at the edges. I think IgorOriginal lenses don't perform as well because they are handmade, and aligning the elements is not easy.

[Andy Perrin]

I think so too. That IgorOriginal is noticeably decentered.

[Andrea B.]

Bernard, this is a cool test. Thank you !

 

Would you be so kind as to list at the beginning of the topic the complete names and focal lengths of the lens you tested? That would make your topic even more useful as a reference.

Something like this: Leitz Focotar-2 50/4.5

 

Comments:

• Did you refocus before making the BaaderU photos? I ask because The El-Nikkors seem less sharp in the center in UV than I think they should be - especially given that all photos were made at f/8.
  

• I am not surprised that some lenses are less sharp in the corners particularly if the lens is not flat-field.
  

• The fact that some lenses may be a bit less contrasty than others seems not a cause for concern as we can make small contrast boosts either local or globally in the converter. (Too much contrast boost, of course, can cause other problems.)
  

• Of particular interest is possible evidence of astigmatism in a couple of the lenses? That is not decentering as there is a pie-shaped blur on both sides of the photo and the pie pieces are along an angular axis.
  
  • Visible, Second Row (unrefocused corner), second from left, Cassar S.
    
  • Visible, Second Row (unrefocused corner), right-most, Igoriginal.
    

• A possible point to be made here is that one cannot just toss together lens elements into a helicoid without putting the construction on an optical bench and adjusting elements for proper alignment to avoid blur and astigmatism. However, any readers should take this particular comment of mine with a "grain of salt" given that I have no personal experience doing this myself.
  

[Andy Perrin]

The fact that some lenses may be a bit less contrasty than others seems not a cause for concern as we can boost contrast either local or globally in the converter

Andrea, I disagree with this somewhat because the loss of contrast can only be compensated for to a degree. We have only so many bits per pixel and if the contrast is too low then stretching them causes posterization and things.

[Andrea B.]

I'll modify that.

How's this:

 

"The fact that some lenses may be a bit less contrasty than others seems not a cause for concern as we can make small contrast boosts either local or globally in the converter. (Too much contrast boost, of course, can cause other problems.)"

 

That is actually what I was meaning when I wrote it. I had been thinking about the Coastal Optics which some have thought to be slightly less contrasty than the UV-Nikkor, but not in a bad way.

[bvf]

Andrea:

• I've added the lens descriptions
  
• Yes, each lens was re-focussed for each filter.
  
• Yes, the corner reslution is bound to be less than at the centre.
  
• I agree that the cause of some of the loss of image quality is astigmatism - esp. with the Igororiginal.
  

[bvf]

Here's a bit more at the shorter focal length end. I'm ashamed to say that I forgot I had a UV-friendly 28mm Lithagon in a drawer, and so didn't test that.

 

So the lenses tested here were:

 

IgorOriginal 35mm f/3.5

Soligor Enlarger lens 35mm f/3.5

Canon EF 28mm f/2.8 (couldn't get a 345nm image)

 

The Soligor is clearly superior to the Igororiginal.

 

I'm surprised how poor the Canon 28mm looks - although it is wider angle.

 

Visible:

 

Baader U:

 

345BP25:

[Andrea B.]

[Editor's Note: Bernard, I added a UV Lens tag to your topic. So you will see my name on the Edit line unless you make another edit yourself. I just wanted you to know why my name was there.]

[Cadmium]

Bernard, Great work!

Try a 'real' Kuribayashi 35 f/3.5 sometime if you can find one.

I have been looking for a good Novoflex/Noflexar 35mm to compare, It was always the gold standard of 35mm prior to the Kuri.

This one looks good, but haven't been able to make myself buy it:

274285155313

[ulf]

Bernhard,

 

A very nice set of comparisons.

What is the test target?

 

One important thing to remember when looking at these pictures: "at extreme corner (APS-C sensor)".

On a full frame sensor the bad behaviour of many of the lenses are much worse.

 

I am glad to see that you finally have accepted that the Focotar-2 50mm is superior to the Cassar S 50mm as I said.

When I compared my pair of those lenses, I did so on a ful frame camera.

There at the corners the difference in both focus shift and sharpness is big.

 

Is is the El Nik 80 the one you got from me?

[dabateman]

Your igoriginal seems optimized for 345nm to me. Looks good there, thats interesting and not sure why. Are you sure its focus is correct at other wavelengths?

Its been years now since I have used mine, will have to play with it again, but they are no doubt all different.

 

[Stefano]

Were the photos converted to B&W? If so, in the originals you may see chromatic aberration, and this can indicate if the lens works better at certain wavelengths.

 

For example, if there is a lot of it in the Baader U images, then it means the lens works differently at different wavelengths. If not, and it is good at one precise wavelength (like 345 nm), then that wavelength isn't really different from the others, since the lens doesn't behave better or worse there. But these are just thoughts, just an idea I had.

[bvf]

 

Try a 'real' Kuribayashi 35 f/3.5 sometime if you can find one ...

 

I have been looking for a good Novoflex/Noflexar 35mm to compare ... 274285155313

 

I think the "if you can find one" clause is the key one. I think prices are pretty silly, too.

 

On the Noflexar, again the price is steep. Also, on the famous spreadshet (Klaus's?) the UV reach isn't brilliant (330nm) - which is important for tri-colour work where I'm using a 315BP20 filter.

[bvf]

What is the test target?

 

One important thing to remember when looking at these pictures: "at extreme corner (APS-C sensor)".

On a full frame sensor the bad behaviour of many of the lenses are much worse.

 

I am glad to see that you finally have accepted that the Focotar-2 50mm is superior to the Cassar S 50mm as I said ...

 

Is is the El Nik 80 the one you got from me?

 

The test target was the ArduCam one, which was suggested elsewhere on the forum. It doesn't have much on it, so I'd like to find another one. I may have to get a digital one that has to be printed off - should be good enough if I use the A3+ printer. BTW - the images were made at distances of about 1 metre or below, depending on focal length. This is the sweet spot for the enlarger lenses, but the camera lenses are probably optimised for longer distances, and so it's possible they are at a disadvantage here. But most of my UV work is close up.

 

Yes, the results would be a lot worse in the corner of a full-frame image. I suspect the Cassar S at f/2.8 would be pinhole quality.

 

I went through phases over the Focotar-2 vs. Cassar S question. First I favoured the Focotar-2 - mainly because I'd just spent money on it! Then I want back to the Cassar S because in a couple of shots it seemed to give better results - although I didn't do like-for-like comparisons. Anyway, now I'm back to the Focotar-2. And there's the snob value of having a Leitz lens on the camera!

 

And, yes, the ElNik 80 is the one you gave me. It is now my go-to lens for UV macro. And the 35mm Soligor enlarger lens was donated by Timber. If anyone else is looking for a home for their unused UV-friendly lenses ...

[bvf]

Your igoriginal seems optimized for 345nm to me. Looks good there, thats interesting and not sure why. Are you sure its focus is correct at other wavelengths?

 

I'm reasonably confident about the focussing - I was using LiveView with the magnifier. But of course there is always the opportunity for mistakes. I did re-do some of the tests (can't remember which) where the results looked odd, and got the sam results.

 

You're right, the IgorOriginal does look better at 345nm. I also commented somewhere above that the Cassar S seems to be at its best in UV. I wonder if the poor performance in visible is a chromatic error - if I can summon up the energy perhaps I'll do some narrow-band visible tests.

 

On the IgorOriginal 35mm lenses, my understanding is that he does not create the lenses by mixing and matching components from other lenses (although he does do that for some of his other lenses aimed at smaller sensors). I believe he just takes UV-friendly vintage 35mm lenses and converts their mount to T2 and the filter mount to 52mm - but the optics are as the original manufacturer made them. However, the source lenses come from various manufacturers (Prinz Galaxy, Soligor, ..., the (in)famous "Kuri clones" - just mentioning that to annoy Cadmium) so you might find that two different samples have different optical characteristics.

[bvf]

Were the photos converted to B&W? If so, in the originals you may see chromatic aberration, and this can indicate if the lens works better at certain wavelengths.

 

I just used JPEGs out of the camera - but the camera had been set to B&W output. So there was no colour fringing, but chromatic aberration would contribute to unsharpness. The purpose of the 345nm and 850nm images was to minimise the effect of CA in UV and IR, but as I mention somwhere above, I think there may be some CA in the visible images.

[ulf]

On the Noflexar, again the price is steep. Also, on the famous spreadshet (Klaus's?) the UV reach isn't brilliant (330nm) - which is important for tri-colour work where I'm using a 315BP20 filter.

I have confirmed that with my less famous, but more detailed data.

https://www.ultravio...m-f35-noflexar/

It indicates a 332nm cutoff at that for me annoying -3-stop level of 12.5%

The difference could be caused by either a bad wavelength-calibration, not compensated stray light in the measurement or difference in lens behaviors.

For serious measurements I try to eliminate all such errors as much as possible.

Errors caused by stray light in an array spectrometer iill shift the results towards shorter wavelengths.

 

There is a new section on the forum with a growing list of detailed UV-Lens data.

https://www.ultravio...technical-data/

[bvf]

 

There is a new section on the forum with a growing list of detailed UV-Lens data.

https://www.ultravio...technical-data/

 

 

Yes, I've been watching that. Looking forward to "someone" creating a summary comparative spreadsheet from this ...

[OlDoinyo]

Due to chromatic aberration, there is the possibility that lenses with narrower bandpass will incidentally produce sharper images than lenses with deeper cutoffs. To what extent is that what we are seeing here?