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Fujifilm XF 27mm 2.8 Lens for UV...

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#1 D.Lafon

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Posted 20 September 2017 - 18:28

Hello everyone,

I have been using Fuji X-series cameras for about five years now, and I recently began experimenting with modifying some of the older and less expensive models for multispectral use. I have found that Fuji has a number of lenses that work wonderfully for infrared photography, including their newer 35mm f/2 and 50mm f/2 compact and weather resistant lenses. While the Fujifilm 27mm f/2.8 lens is one of my favorites for visible light photography due to its sharpness and compact size, it is not so good for infrared imaging due to a pronounced hotspot. However, I was pleasantly surprised to find that the Fuji 27mm f2.8 lens seems to do very well for ultraviolet photographs. Here are two quick experimental shots, taken hand held and without bothering to set a pleasing white balance or composition. The weather was partly sunny, and the first photo was taken in a shaded location on the north side of my house. First photo was taken at ISO6400, f/2.8, and 0.25 seconds, and the second photo is at ISO 1600, f/8, and 4 seconds with my arms braced against a sturdy object. I used a 2" Baader U filter over the lens, and it was affixed to an X-T10 camera converted to full spectrum by removing the internal cover glass, and installing a 1mm thick piece of Borofloat glass. I really am pleased to find an auto focus option for UV imaging, especially one that works on some of my favorite cameras, and I look forward to experimenting further with this set up.

Thank you,
D. Lafon

Attached Image: hemerocallis.jpg

Attached Image: rudbeckia.jpg

#2 OlDoinyo

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Posted 20 September 2017 - 19:10

It seems to have good sharpness. Have you checked the bandpass in any way?

How did you avoid getting dichroic ring artifacts with the Baader filter? My own efforts with this filter have been plagued by those.

#3 Andy Perrin

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Posted 20 September 2017 - 19:15

Hm, I'm not so sure this is a great UV lens (at least in the way we usually mean on this site, it terms of passing more of the shorter wavelengths). The photo is certainly ultraviolet with those flower patterns and a Baader on there. However, to see the flower patterns, you only need to get just below 400nm. I tried white balancing the image and could see very little false color, and I couldn't seem to eliminate the strange reds in the image, which we don't usually see? I was clicking on the rocks to set my white balance.

I'm curious what other people think!

#4 D.Lafon

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Posted 21 September 2017 - 06:11

Thanks so much for the replies. I welcome any recommendations or suggestions for further testing of this lens. I only have a few dozen quick snaps made with this lens so far, but I look forward to playing around with it again on a day with better sunlight. I would be happy to post some more results as I get the opportunity.

#5 JMC

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Posted 21 September 2017 - 14:36

Just to echo Andys comment, the exposure time seems quite long to me for this to be letting much UV through. For instance, with my UV modified Eos 7D, with a 40mm Canon pancake lens set at f4, and ISO1600, I get a well exposed shot in full sunlight at around 1/30s. Once you've got some shots in full sunlight it would be intersting to see what exposure you need for those.
Jonathan M. Crowther

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#6 OlDoinyo

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Posted 22 September 2017 - 01:25

I second Andy's assessment--I played with it myself in PS, including some manual color balancing and BGR rearrangement. I got the background to go grey, but I could not discern the usual cyan tinge on the Rudbeckia petals. They remained stubbornly white. The only chromaticity I saw was some faint pink on some of the other wildflower heads, due perhaps to long-wave absorption. I would say that this is consistent with a cutoff in the 370-390 range.

#7 Andrea B.

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Posted 22 September 2017 - 03:05

Regarding white balance: It can sometimes be difficult to properly white balance a jpg. Yes, the photo might be more monochrome in nature due to restricted UV in the capture. But I'm thinking that we just can't say for sure from only a jpg WB attempt?

D.Lafon has indeed captured the UV-signature of these flowers. Whether or not the UV is in the range 350-400 nm or 370-400 nm range doesn't seem to particularly matter for a UV floral signature, per se. Given that a BaaderU -- peaking around 350 nm -- was used, I'd say that the Fuji lens did a good enough job of capturing some UV in some part of the 350-400 nm range using the long exposures or high ISOs. However, the long exposure or high ISO setting is a clue that the UV is not easily passing through the lens.

Remember that Bjørn's Theorem states that you can force UV through almost any lens --
if you have enough patience. :lol:
Andrea's Lemma states that eventually you will get tired of these long exposures --
and start saving for a Rayfact UV-Nikkor. B) :rolleyes:

I've had some luck with UV auto-focus using my (mirrorless) Panasonic Lumix GH1 conversion and its little zoomer kit lens. (I'm currently not home so apologies - I can't tell you what that lens is, don't remember.) The mirrorless lenses are smaller, but I don't think that they are really any "simpler" in terms of optical design. So I don't have an explanation for why I can do UV auto-focus with my Lumix or D.Lafon can do that with the Fuji gear. Maybe someone has some ideas about this?

[EDIT: I'm on a very slow tedious hotel wireless. I made some edits which I lost track of. Please excuse me for not being able to have properly marked them.]
Andrea G. Blum
Often found hanging out with flowers & bees.

#8 D.Lafon

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Posted 22 September 2017 - 04:25

Hello,

Thanks again for the comments and advice everyone.

Yes, I agree that shorter exposure times would be very nice. I am working on cleaning up an old Soligor 35mm, 3.5 that I bought at a flea market after reading advice from Mr. Enrico Savassi's excellent article, and that lens should hopefully help in that regard.

What intrigues me about this Fuji 27mm lens is that once I get the camera set up properly, I can put it in the hands of my son, or the young students in my science classes, and they can hopefully capture some of their own UV photos in bright sunlight without having to worry about manual focusing or working with flash units. A technically suburb lens or not; I have a feeling that the students are going to have lots of fun with this set up.

I will attempt some better photos with the lens as soon as I am able. Thanks again!

PS...

Andrea, when you have a chance, I would like to know more about the Lumix lens that you have had good results from as I have an Olympus micro 4/3 camera that I am currently interested in converting for student use as well.

Edited by D.Lafon, 22 September 2017 - 04:35.


#9 Andrea B.

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Posted 23 September 2017 - 16:43

Daniel, I was able to look up my Lumix lens online in good old Wikipedia. :)

There have been three Panasonic Lumix 14-45 lenses.
Mine is the first one labeled Panasonic Lumix G Vario 14–45 mm ƒ/3.5–5.6 Asph. Mega O.I.S which was sold as a kit lens for the original Panasonic G. The second version of this Lumix lens has a "II" in its label. The third version has a "PZ" in its label.

I note in passing that when converted, the Panasonic Lumix G line of cameras are very good for UV video (given good UV-capable lenses, of course).

*********

Another small note about white balance of the preceding jpgs. Daniel has very appropriately dialed down the saturation in those shots. If you want to get some false colour from white balancing one of those jpgs, turn the saturation back up a lot. You won't quite get the typical WB look, but you will get some differentation in false color.

Photo Ninja tweaks on JPG: Saturation increased to 75 from 50. White balance dropper on leaves. Cyan hue-shifted to yellow. Now see lurking blues & yellows revealed. WB still quite imperfect however. "-)
Attached Image: post-159-0-41440200-1505931556pn.jpg

******

Daniel, a noted UV/IR photographer, Boon Tang, used an Oly. May still do. Here is one link: http://myphotojourne...g-camera-setup/
Andrea G. Blum
Often found hanging out with flowers & bees.

#10 nfoto

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Posted 23 September 2017 - 20:01

Your lens probably gives up the 'UV ghost' pretty soon below 380 nm, if not a little before.

I noticed a similar behaviour when I did a shoot-out comparing a wide rage of lenses against my UV-Nikkor and Coastal 60 references. The 85/1.4 Nikkor AIS delivered razor sharp UV images, at peak performance not very different from the UV-Nikkor, but the chromacity simply wasn't there.