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Can Sony/Minolta DSLR be used for reflected UV?

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Alex H View Drop Down
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Topic: Can Sony/Minolta DSLR be used for reflected UV?
    Posted: 07 November 2010 at 19:37
A qustion from a fellow member about Sony cameras and photography in the ultraviolet spectrum in this thread Lenses for Infrared (IR) stimulated me to write up and post here some of my observations. The question is: Can Sony DSLR cameras be used for photography in reflected ultraviolet spectrum?. In short - yes, but....



Before You continue reading, I have to make a statement. Large part of the information on this post is based on findings by other peoples, in particular Andrea Blum, Shane Elen, Vivek Iyer, Bjorn Rorslett and Klaus Schmitt, and I will try to acknowledge all of them and link to their web-sites. My personal observations refer only to Sony-related stuff and my own tests described below. Also, everything in this post refers to reflected ultraviolet in the range of of approximately between 300 nm and 400 nm (UV A, near UV, long wave UV, etc). It is not to be confused with the UV-induced fluorescence photography.



1) Why bother? Just like when taking pictures in the infrared spectrum, the purpose of UV photography is to get an image of something we can not see with our own eyes, but other organisms can. Many insects and birds can see in the UV spectrum, for example. So here are two example of flowers captured in visible spectrum and reflected UV as camera sees it (reflected UV is presented in monochrome or violet rendition here, even though many DSLR record UV in the red channel).



Visible spectrum







Reflected UV







Visible spectrum







Reflected UV









2) What lens to use? There is a lot of information on the web about lenses that are suitable for UV photography. Ideally, You would want to use a lens that transmits as much UV as possible, such as those made from quarz/fused silica. Many of suche lenses are listed on the web site maintained by Klaus Schmitt. The most notorious example is UV-Nikkor 105 mm. Unfortunately, they are very expensive and not always readily available. For the most complete list of lenses suitable for UV please look at this discussion on the NIKONGEAR forum prepared by Andrea Blum with contribution of many Nikongear forum members. It is one of the most complete and up-to-date source of information that I know about, together with the blog maintained by Dr. K. Schmitt (use Goggle to find it). In any case, all lenses that are useful for the UV photography are manual focus and can, with some adaptation, be used on any DSLR camera. In fact, many of them come in a range of mounts and need to be adapted for use on Nikon cameras too.



3) What filter to use? Again, the most recommended filter for UV is Baader-Planetarium UV-pass filter. Please note that there was an older version of this filter with some infrared leakage, but the recent version is optimised dor 329-365 nm transmission and completely block visible and infrared spectrum. There are other filters listed on NIKONGEAR. Most of the older and generic UV pass filters (like Kodak Wratten 18A) also pass a lot of infrared and need to be used with IR-blocking filters to perform properly. Unfortunately, many IR-blocking filters also block some of UV. Please read this web page for the details.



4) What source of UV to use? The best one is sun. Several brands of flashes and LED lights can be used to illuminate objects in the studio. There was a dedicated UV flash made by Nikon (SB-140) for example. Regular flashes have some sort of UV-blocking filter installed in front of the flash-tube, or a UV-blocking coating on the flash tube itself. Most commonly recommended for modification are the Nikon SB-14, Vivitar 283 (NOT to be directly connected to digital cameras without special adapter!), Vivitar 285 (NOT to be directly connected to digital cameras without special adapter!), Vivitar 285HV ("digitally safe"), Metz 45CT and 60CT series (again, older versions of these flashes have high sync. voltage and SHOLD NOT to be directly connected to digital cameras without special adapter!). I use Vivitar 285HV modified according to these instructions by Shane Elen. Unfortunately, Vivitar 285HV model was changed during production period. I have one copy of the flash that works fine after removing the plastic UV-blocking filter. The other one has UV-block coating on the flash tube. Remember that UV light is harmful for your eyes



All what I wrote above is camera brand independent. This is a good read about the simple start-up setup for UV photography written by an expert with many years of experience, Dr. Klaus Schmitt, who was very kind answering my multiple questions and giving very useful advice. Another very informative site is maintained by Bjorn Rorslett with many useful tips, examples and picture galleries.



Now the last question. Are Sony and Minolta DSLR cameras useful for reflected UV photography? I was wondering about it since I bought my A100, as there was no information about it to be found on internet. All other DSLR brands were discussed, at least in some details. The most commonly used are of corse Nikon, Kodak and Fujifilm DSLRs. Some Olympus and Pentax models are used too. Again see this link. Also, it is often said that CCD cameras are more useful for the UV photography, but it is not entirely true. Properties of the low-pass filter influece the final result as much as properties of the sensor (see below). Basically, any camera can record some UV if the exposure is long enough. But is it of any use? Currently, I am not interested in modifying my DSLRs. All my observations are based on "off-the-shelf" bodies.



Fortunately, Sony DSLR A100 does have suitable UV responce. Here is my best example with less then suitable equipment: 50mm F/4.5 enlarger lens in a DIY focusing helicoid, B&W UV-pass 403 filter and Tiffen hot mirror filter, under the sun light. Exposure time was 20 seconds with ISO 100 for UV shot. Granted, increasing ISO and using better lens would cut exposure times to "usual" 2-4 seconds.



Sony A100, visible spectrum







Sony A100, reflected UV







But then I got myself what Dr. Schmitt recommends as a good starter kit: Nikon D70, Noflexar 35mm lens and Baader U2 filter. I took it and Sony A100 for a test to botanical gardens. Unfortunately, is was too windy and I did not have UV-flash at that time to stop the motion. Most of my resulting pictures were fuzzy because of the wind, and I have nothing to show You now. I learned two things, nonetheless:



1) My unmodified Sony A100 has UV sensitivity close to my Nikon D70. Under the bright californian sun the exposure times for good pictures would be within 1-4 sec range with ISO400, depending on the F-stop used and the lens. Pretty good.



2) My Sony A100 (unlike Nikon D70) sometimes showed leakage of light through the OVF, which created a flare on final image. So the OVF has to be closed or at least kept away from the direct sunlight.



Unfortunately, I sold my A100 when I got SLT-A55 and can not re-do the tests right now. I will try to borrow it in the future again and provide You with some better examples. But, ... I recently did some not very scientific tests comparing the UV responce of D70, Sony A100, Sony A290, Sony A700 and KM5D. In this case the results are a little disappointing. Setup for this test was simple: ?Helianthus? flower; Noflexar 35mm lens stopped down to F/5.6; Baader U2 filter; modified Vivitar 285HV flash connected via PC cord and adapters; cameras fired at 1/80 sec (slower than flash sync. speed). Please remember that, even though I tried to use standartized and reproducible setup, I suggest You to treat these results with caution. And if You see any mistakes in my setup - please correct me!









Nikon D70, visible spectrum, ISO 200, flash 1/16 power.







Nikon D70, reflected UV, ISO 800, flash full power (+16EV comparing to visible).







KM5D, visible spectrum, ISO 200, flash 1.16 power, -0.5 EV in post-processing.







KM5D, reflected UV, ISO 3200, flash full power. Still very much underexposed and the noise is problematic.







Sony A700, visible spectrum, ISO 200, flash 1/16 power, -0.5 EV in post-processing.







Sony A700, reflected UV, ISO 3200, flash full power. Still very much underexposed.







Sony A100, visible spectrum, ISO 200, flash 1/16 power.







Sony A100, reflected UV, ISO 1600, flash full power. Still very much underexposed.







Sony A290, visible spectrum, ISO 200, flash 1/16 power.







Sony A290, reflected UV, ISO 3200, flash full power. Still very much underexposed.







What are my conclusions from this rather crude test.



1) All tested cameras do show some sensitivity in the UV spectrum and are capable of showing a characteristic color-pattern of the Helianthus flower.



2) All of the tested cameras has much lover sensitivity than the Nikon D70 under the same condition, They all need one (A100) or two (other cameras) EV of exposure to produce recognizable flower patterns, but to obtain good quality image, the exposure times should probably be increased by at least two-three EV comparing to the Nikon D70.



Now some speculations: Even though, KM5D uses CCD sensor, which was manufactured in the same year as D70 (2004 - introduced with KM7D) and has similar pixel pitch and maximum resolution - it has a very different UV response. I do not know who made sensors for KM5D, but Nikon's sensor was manufactured by Sony. Either sensors were made by different companies, or the low-pass filter used in KM5D camera has very good UV-blocking properties? I do not know. These are pure speculations though. Also, as You can see, unmodified Sony cameras have much lover UV sensitivity than the Nikon D70 too. I do not know if this is the property of the sensor, low-pass filter or combination of both.



Acknowledgements

I would like to thank, pleno titulo, Andrea Blum, Shane Elen, Vivek Iyer, Bjorn Rorslett, Klaus Schmitt, and many other people for all the useful information about photography in reflected UV spectrum they share with us.





And now some fun:



UV image overlayed over visible image in Photoshop.







PS: Note to the moderators. There are some pictures in this thread, which were done with non-a-mount camera (Nikon D70). They are put here for comparative and educational purpose only. I hope it does not violate the rules of the forum too much. If You think this post will better fit somewhere else, please move it. Thanks, Alex

Edited by Alex H - 29 September 2012 at 12:53
 



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Bass View Drop Down
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Post Options Post Options   Quote Bass Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2010 at 22:56
Alex, thank you for all the time you must have spent putting this thread together. It is packed full of information for the 'A' mount user wishing to learn and get into UV and full spectrum photography.

I couldn't find any information on the net for Sony / Minolta UV photography, or UV capable lenses. I hope a mod / admin could add this thread of interest as a sticky, along with the Lenses for Infrared IR Dyxum Sony Minolta thread - thanks!

Your images are fantastic Alex, thanks for posting them. I can see why the D70 has such a following for Ultra Violet photography, the results are impressive. However, as the A100 is an A mount camera, it seems to produce excellent results 'off the shelf'.

How much 'better' would a camera (A100 for example) be that had been converted to full spectrum and was used with UV-pass / IR-Block? This seems to be the cheaper option than having a dedicated UV conversion

Thanks again for an excellent thread - I hope some more A mount UV converts come forward!
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2010 at 23:15
Originally posted by Bass Bass wrote:

Your images are fantastic Alex, thanks for posting them.


I am glad You found it useful.

Originally posted by Bass Bass wrote:

How much 'better' would a camera (A100 for example) be that had been converted to full spectrum and was used with UV-pass / IR-Block?


I do not know. No-one tried this before. It might be worth trying or it might be not. For example Nikon D70 is good enough for the conversion for peoples on the budget. Especially since the camera itself can be had for less than the conversion service. I am currently not in the financial position to try it.

Originally posted by Bass Bass wrote:

This seems to be the cheaper option than having a dedicated UV conversion.


Dedicated UV conversion is not offered commercially for Sony DSLRs as far as I know. Advanced Camera Services offer it for three Nikon bodies only and is very expensive. So far I only heard about one DIY dedicated UV conversion, but it was not very easy to get the filter cut.

If I learn any more, I will post it here.
Alex
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Post Options Post Options   Quote Micholand Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 19:33
Alex, a very clearly written and illustrated contribution thanks for putting in the time and effort to make this for us    
/Michael

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Post Options Post Options   Quote Edinator Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 19:51
I've converted my A100 into a full spectrum camera (replaced hot mirror with clear glass). If I can get a hold of a UV pass filter i'll try it. But as far as I know, hot mirrors only block IR light. UV light is generally not strong enough to affect the colours in a visible light image.
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 19:57
Originally posted by Edinator Edinator wrote:

But as far as I know, hot mirrors only block IR light. UV light is generally not strong enough to affect the colours in a visible light image.


Not necessarily. Indeed, low pass filters are designed to block IR, but their other properties may come from the material used. Just like camera sensors are not specifically designed to be sensitive to UV, but they are.

From what I can read on the links I provided, there are Nikon and Fujifilm cameras that are more sensitive to UV when their low-pass filter is removed, independently from their sensors (CCD or CMOS), such as D40X, D200, Fujifilm Finepix S3 Pro, S5 Pro.

Alex


Edited by Alex H - 08 November 2010 at 19:58
 



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Post Options Post Options   Quote pdeley Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 20:49
Very interesting and very comprehensive Alex

Presumably this means the a200 and a230 will behave similarly as the a100, but the a290, a3xx, a5xx and FF alpha bodies will need to be tested to get any idea of their sensor's responses to reflected UV? Or do you expect most of them to do poorly because of their mostly CMOS-type sensors?

Did you shoot the a100 in manual mode or in aperture priority for the above shots? Do you think it matters a lot/a little for UV purposes that the a100 has shutter unlock for manual lenses while the a2xx don't?

Now I'm interested and sorry too that I gave up my a100!
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 20:50
Originally posted by Edinator Edinator wrote:

replaced hot mirror with clear glass


Just one question I forgot to ask before. What do You mean by clear glass? Is is a quartz glass? Thanks, Alex
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Post Options Post Options   Quote Edinator Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 20:56
I just cut a lense protector filter to fit the dimensions of the hot mirror. It wasn't a UV filter, just clear glass.
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 20:57
Originally posted by pdeley pdeley wrote:

Very interesting and very comprehensive Alex


Thanks Paul!

Originally posted by pdeley pdeley wrote:

Presumably this means the a200 and a230 will behave similarly as the a100, but the a290, a3xx, a5xx and FF alpha bodies will need to be tested to get any idea of their sensor's responses to reflected UV? Or do you expect most of them to do poorly because of their mostly CMOS-type sensors?


1) If I remember correctly, A200 and A230 use the same sensor but there was something about AA-filter that was different with these cameras. Have no idea if it will have any influence on UV.

2) Some CMOS cameras perform good in UV converted (with removed low-pass filter. One of them is Nikon D700.

Originally posted by pdeley pdeley wrote:

Did you shoot the a100 in manual mode or in aperture priority for the above shots? Do you think it matters a lot/a little for UV purposes that the a100 has shutter unlock for manual lenses while the a2xx don't?


Everything was shot in manual mode. Camera will not expose properly in A mode. So id does not really matter if it has shutter unlock or not. I do not know if modified camera will behave differently.
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 20:59
Originally posted by Edinator Edinator wrote:

I just cut a lense protector filter to fit the dimensions of the hot mirror. It wasn't a UV filter, just clear glass.


Thanks. Lense protector filter is not optimized for UV transmission. It may not be better for UV than the low-pass filter. That is my guess of course. For best UV performance, low-pass filter has to be replaced with quartz glass.

Alex
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Post Options Post Options   Quote Edinator Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 21:02
I see, too bad. I wasn't really planning on doing any UV photography which is why I didn't really give a second though to what glass I used. I just needed to get rid of that hot mirror :P
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Post Options Post Options   Quote Alex H Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 21:05
Originally posted by Edinator Edinator wrote:

I see, too bad. I wasn't really planning on doing any UV photography which is why I didn't really give a second though to what glass I used. I just needed to get rid of that hot mirror :P


It is completely understandable ;-) But it should perform great for IR.
I do not know many &-users who were interested in UV photography.
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Post Options Post Options   Quote Swede101 Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2010 at 21:56
Originally posted by pdeley pdeley wrote:

Very interesting and very comprehensive Alex
---

I agree indeed!


Originally posted by pdeley pdeley wrote:

---
Presumably this means the a200 and a230 will behave similarly as the a100, but the a290, a3xx, a5xx and FF alpha bodies will need to be tested to get any idea of their sensor's responses to reflected UV? Or do you expect most of them to do poorly because of their mostly CMOS-type sensors?
---

Both A290 and A390 has CDD image sensors. Their AA- Bayer-filter sandwich may be different from A100 though.

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