23 replies to this topic

[dabateman]

I think for most the transmission around 370nm will be most important for a lens, as cameras are more sensitive in the UVA range and 365nm LED are cheap.

For these tests, I have two 365nm LED bulbs positioned above the subject flower on a tilted block of PTFE. I used ISO 200 and tried to use F8 for each lens. I have my 370bp15 filter stacked with Baader Venus U filter to block all IR.

I first took an image with my UAT at F8, ISO 200 and liked the look of 1/2 shutter speed. Then I would take an image with a test lens at F8 (if reasonable) then wide open to get an idea. Through out the test I would re-image the UAT to ensure I still like the same shutter speed for the main subject.

First Image with UAT F8, ISO 200, Shutter 1/2:

Crop:


Last image recorded UAT F8, ISO 200, Shutter:

Crop:

I think the best reference lens will actually be the Nikkor EL 80mm F5.6, old metal version. Surprising to me it was faster than the UAT. I liked shutter speed of 1/3 seconds which would be 2/3rds a stop faster at 370nm than the UAT!

Nikkor EL 80mm F5.6 old metal version, at F8, shutter 1/3:

Crop:


Results:

Sigma 30mm F2.8 Art M43rds F8, 1/1.6, 1/3rd slower than UAT, 1 stop slower than EL80
Wollensak 25mm f1.5 Clean, F8, 1/2, Same as UAT, but 2/3rds slower than EL80. Also Not an F1.5 lens, seems to be F2 lens with same shutter speeds. Wide open best was 1/25 second shutter speed.


Panasonic 12.5mm F12 M43rds, its a fixed F12 lens 2.5 seconds 1 stop slower than UAT, 1 2/3rds slower than EL80


Panasonic 35-100mm f4/5.6 compact lens, very bad for UV didn't get good image with Just Baader venus filter

igoriginal 35mm f3.5 at F8, 1/4, 1 stop faster than UAT, 1/3 stop faster than EL80


Panasonic 15mm F1.7 F8, 2 seconds, 2 stops slower than UAT, 2 2/3 slower than EL80


Panasonic Leica 25mm f1.4 at F8 15 seconds, 5 stops slower than UAT, 5 2/3 slower than EL80


Panasonic 45-200mm version 2, at F5.6 10 seconds,


Panasonic 42.5mm f1.2 M43rds at F4, 15 seconds,


Quantray 24mm f2.8 Macro in Nikon mount, F8, 5 seconds, 3 1/3 stop slower tahn UAT, 4 stops slower than EL80.


Nikon 105mm f2.8 Macro D, F8 1/1.3 seconds. Only 2/3 slower than UAT, 1 1/3 stop slower than EL80


Tamron Adaptal 24mm f2.5, F8 1/1.6 seconds. Only 1/3 slower than UAT and 1 stop slower than EL80


All the above results are cropped from the full image which is much larger for some of the lenses.

[Cadmium]

They use to say that the pinker it looked the deeper it transmitted.
So, using the same white balance, on a scale of pink to blue, pink is deeper UV and blue is higher UV.

[dabateman]

Yes forgot to say all were shot and are posted with the exact same White balance. So you can go nuts looking for the more yellow or "pinkier" image.

The Panasonic 45-200mm is clearly pushing hard on the 380nm end of my 370bp15 filter.

I was also surprised with the Nikon 105mm macro, a usable AF UV lens for Nikon people.
The Quantray is slow, but the detail it pulled out is amazing. Also this is a very wide angle lens.

Edited by dabateman, 10 July 2019 - 08:30.

[Cadmium]

I don't see 'yellow', I see pink and violet, pink meaning deeper UV transmission, violet meaning less UV transmission.
So for example, the Panasonic 45-200 would have the worst UV transmission, and 42.5 is second worst, just based on color.
A little hard to judge which of the pink ones is most pink without seeing them side by side.

Edited by Cadmium, 11 July 2019 - 05:51.

[dabateman]

I think its best if others want to continue this, to use the Nikkor EL-80 f5.6 old metal lens as reference. However, the igoriginal and my Steinheil lens were about 1/3 of a stop faster. So using that I have calculated the following estimated T₃₇₀ values.

igoriginal 35mm F3.5 T-mount lens (soft) T₃₇₀ = 3.5

Steinheil Edixa-cassaron 50mm f2.8 M42 (soft) T₃₇₀ = 2.8

Reference Nikkor EL 80 mm f5.6 M39 (Good) T₃₇₀ = 6.3

Pentax UAT 85 mm F4.5 M42 (Excellent) T₃₇₀ = 6.3

Wollensak Cine velostigmat 25mm F1.5 C-mount (Soft) T₃₇₀ = 2.8

Tamron Adaptall mount 24 mm f2.5 (Soft) T₃₇₀ = 4

Quantray 24 mm f 2.8 Macro F-mount (Sharp) T₃₇₀ = 13

Nikon 105 mm F2.8 Macro D F-mount (good) T₃₇₀ = 5

Sigma 30 mm F1.4 4/3rds mount (Soft, low contrast) T₃₇₀ = 4

Olympus 35 mm F3.5 Macro 4/3rds mount (Sharp) T₃₇₀ =7

Canon 65mm MPE Macro T₃₇₀ = 22

Micro four thirds lenses:

Panasonic 12.5 F12 3D lens (Soft) T₃₇₀ = 22

Panasonic 15 mm f1.7 T₃₇₀ = 5

Panasonic Leica 25 mm f1.4 T₃₇₀ = 11

Sigma 30 mm F2.8 Art (sharp) T₃₇₀ = 4.5

Olympus 30 mm F3.5 Macro (Sharp) T₃₇₀ = 6.3

Panasonic 42.5 mm F1.2 T₃₇₀ = 20

Olympus 14-42mm f3.5/5.6 R2 T₃₇₀ = 8

Panasonic 35-100mm f4/5.6 T₃₇₀ = >45

Panasonic 45-200 F4/5.6 II T₃₇₀ = 51

Metabones Speed booster Ultra with 370nm filter has 4 stop loss of light, But using just Baader Venus filter the stop of light gained is used up, so neutral. Tested using Pentax UAT lens.

[Andy Perrin]

Quote

So, using the same white balance, on a scale of pink to blue, pink is deeper UV and blue is higher UV.

Sounds like a literal litmus test.

So if I understand this, you take the Baader and the El-Nikkor 80mm/5.6 and shoot a reference image at F/6.3. Then you shoot the other lenses and figure out what stop is necessary to give the same exposure?

[dabateman]

Andy,
What I do step by step:
1. set up a flower on PTFE block.
2. place two 365nm LED lights on this subject.
3. Place a 370bp filter stacked with a Baader Venus U filter (370 +BVU) on the lens.
4. Photograph the subject using F8, as all lenses seem to have at least F8.
5. Photograph the subject with lens wide open to ensure that its linear. In that if you calculate back the expected exposure time wide open it should match the exposure used to match the image recorded at F8. This was Not true for my Wollensak. My Wollensak at F2 was equal to F1.5.

Using this I predict the T value, with huge (I mean huge error) to what the lens may transmit at 370nm.

All that said, you don't need to do that.
Since you have the "reference lens" you can add a tight band pass filter to the EL-80 and then test other lenses, hopefully you have one of the Cadmium discovered 35mm f3.5 lenses as well and figure out your own exposure times. Then since we have the same reference lens we can figure out how it all fits in.

I am not photographing anything at F6.3, but based on the look that my 35mm f3.5 was about 1/3 stop faster than my EL-80, then I assume it to transmit 1/3 less light and thus its true T370 stop is 1/3 slower being T370 = 6.3 (5.6 + 1/3 stop). So that is how I calculated my T370 values. Of course the 35mm f3.5 may also not be perfect, but I haven't found one that is better yet. So it may be the best. Also since my 35mm was modified by Igor, it may not actually be F8. Its possible the aperture opening is different. One day I should measure it to make sure.

I hope that makes sense.

Edited by dabateman, 11 July 2019 - 20:41.

[Andy Perrin]

Ok, I'm still not sure I get it. You wrote:

Quote

Reference Nikkor EL 80 mm f5.6 M39 (Good) T₃₇₀ = 6.3

Shouldn't the reference be exactly F8 using the above procedure?

[dabateman]

Maybe if we want negative values. But I like to keep it positive. My 35mm was better remember.

So now your asking what is a T370 value and how does it help me?

Say you have both the EL-80 and the Nikon 105mm macro lens. Both have similar WB color range and similar sharpness. Now you need F8 depth of field for your subject and you don't have a lot of UV light. Well the Nikon 105mm macro lens will have a 1 and 1/3 stop slower shutter speed than if you used the EL-80 at the same aperture.

But now you don't need F8 depth of field and your doing a portrait. So you can crank that lens wide open. Then the Nikon 105mm macro will be better with T370 value of 5 at the F2.8 aperture.

Now you want to do a video and need the fastest UV lens. Then a Steinheil 50mm f2.8 will let in the most UV wide open. Problem is its crazy soft there and you will need to stop down to at least F5.6. Well its still better than the EL-80 at F5.6, letting in more UV.

Thats why we should think in T stops when we are gasping for the litte UV light we have.

[dabateman]

Also, a reference is something everyone should be able to get. They made lots of Nikkor 80mm EL lenses and they can be found cheap.
Just saw 9 on ebay now range from $50 to $150.
There are very few modified igoriginal lenses. I am not sure they all behave the same and Igor did clean and polish the elements and added seals. They currently sell for $120, and only 3 left.

The Steinheil Edixa in M42 mount is very rare. I have only seen it on ebay once.
But of course as I type this I found one on ebay now. But it is 5x more than I paid for mine.

Edited by dabateman, 12 July 2019 - 00:09.

[Andrea B.]

When UltravioletPhotography.com started out years ago as a board on the very first Nikongear (which eventually evolved into Fotozones after the second Nikongear split off from it), there was a UV/IR photographer RKPhotog (Robert Kerr) who compared lenses in a manner similar to what David is experimenting with.

RKPhotog used the Novoflex 35/3.5 as the reference standard. (We all seemed to have a Novo 35/3.5 in those days.) He converted the exposures of each lens into total EV values and scaled them against the Novoflex total EV base value. You can find a few of RKPhotog's comparisons in the Lens Sticky that I managed to hang onto over the years. For example, RKPhotog tells us that the Schneider-Kreuznach 135/5.6 Componon-S in T2-mount shoots -1.33 EV below the Novo 35/3.5 on a D40 under a BaaderU UV-pass filter. (Note that the camera and filter must be included in any comparisons.)

I don't recall the particular details of how RKPhotog set up his comparison shots. But I can tell you that if you include different amounts of reflectivity in your scene because of framing (or whatever), then you are going to skew the results. The best thing to shoot for lens comparisons like this is a good old blank wall, a very large one, which is EVENLY lit. This is not easy in UV. But a good sunny day helps. Or an array of UV lamps if working indoors. Stick some small thing in the middle of the wall to focus on. Now you have a better chance of meaningful comparisons.

There might be some old hand who remembers this kind of Novoflex comparison and who might remember further details of how best to set up the comparison scene and make the shots.

*******

For a given camera and filter, I sometimes compare lenses by shooting in monochrome and making an exposure which pushes the brightness histo all the way to the right without hitting the right-hand wall. The scene being shot must again be "fair" (something like the evenly lit wall as described above).

If you are only finding a 1/3, 1/2 or 2/3 total EV difference between lenses, then that is not particularly meaningful. The slightest reframing can shift total EV easily by these fractions. Especially if outdoors. Or if shooting mixed reflectivity.

Added about 5 minutes later: When shooting comparisons, be sure to turn off settings such as increased dynamic range, active D-lighting, shadow boost or whatever your particular camera has. These settings can affect exposure times in some cameras. Keep contrast at a "normal" level. If shooting color, keep saturation at a "normal" level.

*******

Corrections always welcomed by me for anything I write. As an editor I don't have an editor. So when I forget something or write too fast or something gets befuddled, then I want to know so that we can continue be a good source of UV/IR photography info for everyone. Thanks!

[dabateman]

Andrea,
I like the flower on a PTFE block, better than just flat PTFE block. The flower lets you know how sharp and detailed the lens is in UV. I like the Quantray 24mm, its sharp, but slow. The Tamron 24mm is faster in UV but not nearly as sharp. Also the Steinheil might be the fastest, but not usable wide open need to stop down. Whereas the Sigma 30mm f2.8 lens is sharp wide open, so is usably faster at T370 = 4.5 vs stoping down the Steinheil to at least f5.6 (T370 =5.6).

Just PTFE wouldn't tease that out.

Also I am not doing this scientifically, by correctly measuring the illumination differences off the PTFE block. I will leave that to others. I am just eye balling it. So thats why I don't make big claims and only claim within 1/3 to 2/3rds stop differences.

Yes the filter used for the test will have a huge effect. The Baader venus filter is too broad band. A tight band pass filter is ideal to just look at a low wavelengths. Using the 365nm LEDs help as well as thats there peak light. Using a Baader the difference between the lenses is much less and then you're stuck looking at blueness in the image. A good full spectrum converted camera shouldn't have much effect, if it does than not well converted and may have plastic or wrong glass on the sensor. But settings are important, you want consistency.

Having the camera and tripod in one spot is ideal. Now that I think about the order. I may have moved it for the Quantray lens test. As I tested my C/Y 135mm f2.8 YUS lens which needed 6 feet minimum focus distance, which was bad to get a good image. Then the Canon 65 MPE, which needs to be really tight. So I may need to retest and compare that one. But maybe ok as just looking at my last image again I am not far off from alignment of my fist image, with UAT. So should be ok.

Edited by dabateman, 12 July 2019 - 08:05.

[SteveE]

The largest 370bp15 I can find is 25mm. Won't this skew results for lenses with a larger front element?

I have been planning to do something similar, this is what I was thinking of for my protocol:

• Mount a 365 torch with a U340 filter to the hot shoe of the camera. This is so the portion of the illuminated spot viewed by the lens remains constant. I have a bracket for this.
  
• In the conference room at work we have an entire wall that is painted with projection screen paint.
  Place the camera at a fixed location on the massive conference room table, with a UV filter (Baader U or U360) on the lens, illuminating the wall with the attached UV torch.
  The torch will be adjusted and clamped so that center of illumination falls on the wall at the central axis of the lens.
  Care will be taken when changing lenses so as not to disturb this alignment.
  There is no IR in this room.
  
• Use freshly charged batteries in the torch and monitor the illumination during the testing session with a Solarmeter 5,7
  
• In aperture priority mode, with standardized settings, including spot metering, record the indicated shutter speed for all apertures.
  
• Convert the readings to EV100 (https://www.scantips...posurecalc.html or formulas in a spreadsheet)
  
• I already know some lenses deviate at either end of the aperture range, so find the area in the middle where the EV100 is constant.
  
• Also measure the reference lens in each testing session.
  
• Compare the EV100 values obtained for the lens under test with the reference lens to get a relative performance value in stops.

I was going to use my Kuribayashi Acall 35mm f3.5 for a reference lens, but after reading this thread, I will try to get an EL-Nikkor 80
Does this sound like a worthwhile exercise?

Edited by SteveE, 12 July 2019 - 16:44.

[Andy Perrin]

Considering I can barely understand either of these protocols and the necessity of finding a 370 bandpass, I’m thinking I will not be doing this anytime soon. Like, having the T stop of a lens be smaller than the F stop doesn’t compute for me, even though I see how you are doing the computation. I guess we can at least compare lenses within one person’s inventory but not across photographers.

Edited by Andy Perrin, 12 July 2019 - 16:54.

[dabateman]

Steve,
That sounds more detailed than what I did and you will get a more accurate profile for the lens through out its aperture range.

Yes the 370bp15 filter is just a 25mm filter, that I mounted in cheap Chinese 25mm UV filter. The filter I got was was thin enough and small enough to just mount in the 25mm UV filter without modification. However it leaks a lot of IR, so your set up with out IR may work. Other wise I should be stacked with either a Baader Venus filter (As I did) or a S8612 filter.

This is the thread describing how I mount the 25mm filters:
https://www.ultravio...__fromsearch__1



As for front element size, maybe. However, most UV capable lenses seem to have a very small front element. So I don't think this is an issue.
These were some of my measurments:

Pentax UAT 85mm f4.5, front diameter about 18mm, Rear diameter about 15mm
EL-Nikkor 80mm, front diameter about 18mm, Rear diameter about 20mm.
Steinheil Munchen EDIXA 50mm f2.8 front about 17mm, Rear about 16mm
igoriginal 35mm f3.5 lens front diameter about 23mm, Rear about 12mm
Sigma 30mm f2.8 M43rds Art lens front about 14mm, Rear about 23mm.
Wollensak 1" cine velo stigmat front and rear dameters are about 18mm and this lens has a 25mm front filter thread.


Andy,
The T stop will always be less than the F stop of a lens. This is because the T stop takes into account light lost due to glass elements, coatings and air transitions. Thus why you will Cine lenses which in the photo world are know as F2.8 lens will be reported with T stop value of 3.2.

I am Olympus users so I know this example which may help. The Panasonic Leica 25mm f1.4 lens is small and has 9 elements and some good coatings. Its T stop value at typical 550nm was measured as 1.8. Not bad. Now the Olympus 25mm f1.2 lens is huge as 19 elements, but even though its an F1.2 lens all those elements lead to light loose and its T stop is the exact same, measured as 1.8.
Hope that helps.

[Andy Perrin]

dabateman, you read my comment backwards.

Quote

The T stop will always be less than the F stop of a lens. This is because the T stop takes into account light lost due to glass elements, coatings and air transitions. Thus why you will Cine lenses which in the photo world are know as F2.8 lens will be reported with T stop value of 3.2.

3.2 is greater than 2.8. T-stop is greater than F-stop, not less. I know how they work. But you have the T370 of the EL-Nikkor 80mm as 6.3 while its F-stop is 8!

Edited by Andy Perrin, 12 July 2019 - 20:13.

[dabateman]

Andy,
Sorry for the confusion. The maximum aperture of my Nikkor 80 EL is f5.6. So I am saying that the T370 at F5.6 is 6.3.

[Andy Perrin]

Ok that makes sense. It does seem really really complicated to me.

[SteveE]

There appear to be several different versions of the EL-Nikkor 80mm f5.6 lens.
Different mount sizes (32/39mm), different bodies. (Black&chrome vs full length fluted), etc.
How do we unambiguously identify the one we are going to use as a standard reference lens?
I am guessing the black&chrome 39mm mount one?
Could you post a picture of the one you have that you are using as the standard?

[Andy Perrin]

He did say metal version explicitly (and that is the only one anyone uses around here anyhow).