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UltravioletPhotography

Unscientific mirror lens test


StephanN

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Motivated by these threads https://www.ultravio...technical-data/ and https://www.ultravio...-uv-at-the-zoo/ , I decided to run my mirror lenses through a quick test - and I have more of them than I remembered :blink:

 

I own the following lenses, all in M42-mount:

  1. MC 3M-5CA 500mm, f/8
  2. MC 3M-6A 500mm, f/6.3
  3. Soligor 500mm, f/8, /11, /16 (via a aperture weel, but I restricted myself to f/8 [Edit]this one is T-mount with EF-adapter[/Edit])
  4. MC MTO 11CA 1000mm f/10

I took some shots in UV, VIS and IR, using the following cameras:

  1. UV: Canon EOS 6D, bayer-removed, internal X330C filter (I only show these, I also took control shots with the S8612, but on this subject the difference is basically half a stop in terms of brightness. Also good luck trying to fit a filter to a front lens of 105 mm, or squeeze it in somewhere at the back. For this basic comparison I didn't think it worth the hassle)
  2. VIS: Canon EOS 5DSR
  3. IR: Canon EOS 6D, fix converted to 700nm

First an admission: not all of them were taken off the tripod, because especially with the 1000mm, I would have had to carry a very hefty tripod, and only had my small Manfrotto befree. So don't look too closely at sharpness, I rested the lenses on my rucksack and had to almost lie down to focus, so please go easy on me. If properly focussed, the Russian 500 f/8 and f/6.3 do have really good quality, and even the 1000 does not fare too bad, one just has to have a rock steady base, a lot of patience to focus in life-view, and no wind whatsoever :smile:

 

Also, it's not possible to handhold the 500mm for UV-shots, but definitely for shots in VIS and IR, or at least leaning on something stable will be enough. That's why I'd be interested to see how far it reaches into UV, because this is a lens which might tag along on tourist trips, being quite small for a 500. A travel tripod will also be more than enough to stabilize this lens.

 

In terms of bokeh, I chose bad subjects, because not shooting into the light there are not many of them :wink: What else, yes, distance to the building in front was about 190 m.

 

Now, the photos, in post the only thing I did was to use a profile for white-balance to make the IR more easy on the eye, and to tweak exposure on the UV, to make them all about the same.

 

MC 3M-5CA 500mm: UV, 0.6s, f/8, ISO 800 (-1 in LR)

post-176-0-54421000-1613745967.jpg

 

MC 3M-5CA 500mm: VIS, 1/60s, f/8, ISO 100

post-176-0-35153800-1613745977.jpg

 

MC 3M-5CA 500mm: IR, 1/60s, f/8, ISO 100

post-176-0-87309200-1613745986.jpg

 

 

MC 3M-6A 500mm: UV, 0.6s, f/6.3, ISO 800 (-1 in LR)

post-176-0-27440700-1613746253.jpg

 

MC 3M-6A 500mm: VIS, 1/100s, f/6.3, ISO 100

post-176-0-10829500-1613746273.jpg

 

MC 3M-6A 500mm: IR, 1/60s, f/6.3, ISO 100

post-176-0-90674200-1613746262.jpg

 

 

Soligor 500mm: UV, 0.3s, f/8, ISO 800 (-0.5 in LR)

post-176-0-19107800-1613746422.jpg

 

Soligor 500mm: VIS, 1/100s, f/8, ISO 100

post-176-0-60164100-1613746429.jpg

 

Soligor 500mm: IR, 1/60s, f/8, ISO 100

post-176-0-61800300-1613746437.jpg

 

 

MC MTO 11CA 1000mm: UV, 8s, f/10, ISO 800 (-1 in LR)

post-176-0-77049600-1613746660.jpg

 

MC MTO 11CA 1000mm: VIS, 1/100s, f/10, ISO 200

post-176-0-48534500-1613746770.jpg

 

MC MTO 11CA 1000mm: IR, 1/40s, f/10, ISO 100

post-176-0-00844100-1613746779.jpg

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Well done Stephan - I would have liked to do this but didn't have all the gear.

 

I'm not familiar with the X330C filter, and what you mean by its being "internal" - can you explain?

 

Is the Soligor 500mm a mirror lens as well? If so, can you explain a bit more about how you adjusted the aperture?

 

Although I am interested in seeing how these lenses handle UV, I don't think there is any pratical application for what I do - it's a ridiculous lens for indoor use, and out of doors landscaps ar going to be murky in UV and shutter speeds will be too long for animals etc. But I'm looking forard to trying mine for IR.

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I've had the camera converted to b/w, with all internal filters removed (maxmax), and they installed the X330C internally. This filter blocks all but a bit of IR, and because getting rid of the Bayer-filter improves sensitivity to UV, an additional filter like the S8612 does not change much, even though, to be on the safe side, I use the filter whenever possible. Of course, this also depends on the subject, but with today's photos, the ones with the S8612 are a bit darker and the trees may be a teeny-weeny-winy bit darker, but that's all.

 

The Soligor is basically this lens here: https://www.bidorbuy...s_T2_mount.html , and I was wrong in my first post, this one came with an EF-adapter, not M42. The built-in filters look like aperture "filters" to me, and they are labelled "F=8", "2X=F11", and "4X=F16" (possibly also some sort of ND-filter?), you can see the wheel protruding in the last two photos.

 

I agree that for distance landmarks UV will not work, but say, I want to take a photo of a statue on top of a palace, and see more than just a small speck, then the 500 would be quite usable (and portable!). But I did get them some time ago, not with UV in mind, but with reach in a small package. [Edit]And one can stick it on an ordinary camera as well, and the dimensions are pretty small: diameter 83mm, length 139mm, if this is correct: https://www.ebay.com/itm/MC-3M-5CA-lens-CCCP-MTO-500mm-F8-Maksutov-Mirror-Telephoto-Lens-M42-Vintage/283820290574?hash=item421501f20e:g:TxUAAOSw8o9d732e [/Edit]

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Wow - that Soligor lens went for 11 Rand - that was a bargain! Sounds like the "aperture control" are just ND filters - my Tamron came with some ND filters + some others. The instructions say there should always be a filter present - even if it's just the clear-glass one they provided. I assume your F8 aperture filter is just plain glass.

 

The Tamron is the same diameter as the 3M-5CA, but only 10cm long (inc. the mount). It's probably lighter too. Annoyingly Tamron claimed it was fine as a hand-held lens, and so didn't provide a tripod thread - so I've made a crude cradle to fix it to a tripod. I'm looking forward to being able to try it out.

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I was just reading about these 500mm mirror lenses. Do you have the 3M-5A or the 3M-5CA?

The 3m-5ca is apparently the same as the 3M-5SA. The 5CA is updated version at half the weight of the original 5A.

 

3M-5CA:

Focal length: 500mm

The weight: 620g

MDF: 4 meters

Diaphragm: F8.0 fixed

Front Filter Diameter: 72mm

Landing thread: M42

Manufacturer: LZOS (Lytkarino Optical Glass Plant, Lytkarino)

 

That UV response looks quite impressive.

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Wow - that Soligor lens went for 11 Rand - that was a bargain! Sounds like the "aperture control" are just ND filters - my Tamron came with some ND filters + some others. The instructions say there should always be a filter present - even if it's just the clear-glass one they provided. I assume your F8 aperture filter is just plain glass.

 

Pity it wasn't me. But goes to show that if one wants something, it may pay off to check different bidding platforms around the world :smile:

 

 

I was just reading about these 500mm mirror lenses. Do you have the 3M-5A or the 3M-5CA?

The 3m-5ca is apparently the same as the 3M-5SA. The 5CA is updated version at half the weight of the original 5A.

 

3M-5CA:

Focal length: 500mm

The weight: 620g

MDF: 4 meters

Diaphragm: F8.0 fixed

Front Filter Diameter: 72mm

Landing thread: M42

Manufacturer: LZOS (Lytkarino Optical Glass Plant, Lytkarino)

 

That UV response looks quite impressive.

 

I have the "MC 3M-5CA", and it states "Made in USSR", diameter 8cm, length 15cm. Sounds exactly like what you're describing. It does show the c inside triangle inside the circle, which is the corporate symbol of LZOS. It came in one of these neat black leather cylinders, together with three or four filters. There is no tripod mount, because if you mount the camera, the lens is not heavy enough to really give you any problems.

 

Hm, who knows, the original 5A might be even better for UV, but if it's twice the weight (and probably larger as well), ....

 

But I can see, I'll have to find some way to measure lens-transmission around 340 nm, just to see how far these exotic lenses reach, probably by trying to fit a bandpass-filter over the light source or inside the rear mount of the lens.

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If they have mirrors only they should go deep. I'm not a fan of the ring bokeh, but they may be useful even for UVC.

 

On a side note, I discovered that LiF (lithium fluoride) is the deepest UV-transmitting material known. No other material goes deeper. It goes down to about 110 nm, so a lens made of LiF will go that deep, and it is impossibile to make lenses for deeper UV. That said, mirrors should go deeper, so theoretically lenses like this may allow you to go below 100 nm, which is a very dark and basically unexplored world.

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In the ebay ads I see the front glass is glass with spray coating of mirror material in the center and the back of the lens has at least one glass element. So at best the reach if BK7 would be 313nm.

 

There is a mirror only mirror lens that some forum user here have. I just remember reading that the image quality wasn't great.

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Even reflective telescopes (I have one) have lenses. They have mirrors in the main tube, but have lenses where you look at the image. So the transmission of the lenses is the limiting factor.
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There is definitely glass at the back end, but I don't know how to get rid of and still get an image.

 

For my purpose of doing uv-cityscapes a reach of 320nm would be more than enough.

 

So, to ask a really dumb question: is there an easy way of determining whether the lens reaches down to X nm? Not using proper devices, but say: Take a photo of flower Y, and if you see this spot then you've got it?

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So, to ask a really dumb question: is there an easy way of determining whether the lens reaches down to X nm? Not using proper devices, but say: Take a photo of flower Y, and if you see this spot then you've got it?

Usually colors would help. As stated by me before in this forum, 340 nm should appear green. But you have a monochrome sensor, so it isn't as easy.

 

You should probably try bandpass filters,if you see through a 320 nm bandpass your lens can reach 320 nm, more or less. If you have a diffraction grating and a mercury lamp you could try to see which lines you can see.

 

I think that unless you use special equipment it isn't easy to determine a lens reach.

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is there an easy way of determining whether the lens reaches down to X nm? Not using proper devices, but say: Take a photo of flower Y, and if you see this spot then you've got it?

 

Do you have a bandpass filter at the wavelength you're interested in? If so, how about putting that in front of a UV-friendly flash gun and seeing if the lens can see the light?

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No mirror lenses are great for IQ, and so I had a question as to whether it would be as well to use a traditional telephoto with shorter focal length and enlarging the image. So I compared the Tamron SP500 with equivalent crops from the excellent Canon 200mm f/2.8 L.

 

When viewing the images full size on the monitor there was no real difference betwen the SP500 (at its one and only indicated aperture of f/8) and the Canon 200mm at f/8. However, with the Canon at f/2.8 the SP500 is clearly better. And if you enlarge the images, you can see a slight advantage of the SP500 over the Canon at f/8.Of course the Canon images would also be limited by noise and pixellation at larger enlargements.

 

The results were similar in visible and IR (850nm LP filter).

 

I have to say that the I find the out-of-focus areas of the SP500 unpleasant compared to the Canon.

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bandpass filters

diffraction grating

bandpass filter

 

Ja, trying to avoid having to buy bandpass filters (unless I follow up on the tri-colour UV thing), gratings, etc., just to test one or two lenses, so sort of hoping for a cheapskate-solution. Unfortunately, TANSTAAFL also applies, here, or so it seems :cool:

 

Generally about mirror IQ: I did a bit of a search on the internet, and seems that sometimes the mirrors are clamped too tight leading to distortions, and the lens can be "relaxed", which basically means unscrewing everything there is to screw, screwing it back together, just a little less tight, and hoping for the best. This page for example http://www.stricklin...russentonne.htm also contains a paragraph in English how to relax a mirror lens. But if one really wants to get into mirrors, the astro-crowd are quite experienced, because it's a cheap way to get close to the sun and stars. Fun fact: the 1000 mm also goes by the name of "Russentonne" in German, which translates roughly to "Russian barrel".

 

For me, I'm satisfied that with the small 500 f/8 I can take near-UV photos, and of course, VIS and IR, so I'm definitely considering it adding to my bag for the next city-trip. Also, the infamous doughnut-bokeh depends very much on the subject and direction of light; in the photos here there is almost no trace of it.

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  • 8 months later...

The Goema/Makowsky 500mm optic is a glassless two-mirror Schiefspiegler optic, so such things have existed. I have even posted a photo or two taken with it on this  board. Mine seems to roll off below about 345 nm for reasons I have never been able to understand. The refracting 400mm and 600mm Novoflex optics appear to have somewhat better bandpass.

 

Mirror lens designs are not inherently inferior to refracting designs, but many of them have been cheaply made, being marketed as budget substitutes for the traditional (and very expensive) baseball-bat refractors. These cheap mirror lenses have poor image quality. There is also the issue that mirror optics with secondary mirrors in front of the primary mirror sacrifice certain modulation transfer function ranges, giving images a somewhat smudgy look. That said, most astronomical telescopes, including the best on earth, are reflecting designs.

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It just might depend on what the mirror is.  Silver has an absorption that Jonathan showed well with pure flakes at the point of UVB.

If its aluminum,  than should be ok, but the image quality wouldn't be as good.

 

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  • 8 months later...

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