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Nemo Andrea

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Nemo Andrea

Hello Everyone,

 

I just joined the forum, so a quick introduction is in order.

 

I have fairly recently started infrared and UV photography, but the UV photography is giving me some trouble (isn't it always?). I will discuss below. I also like to do macro photography and microscopy, the higher resolution the better. I have found this forum to be a useful resource for UV stuff and camera talk so I decided to join!

 

Hope to read and maybe participate in discussions here,

 

Nemo

 

-----

 

I unfortunately don't have the means to get the nicer high sensitivity detectors such as found in the sony a7s line, so I am currently working with converted ancient relics. This works fine for infrared, but UV is giving me unexpectedly low signal, so I figured you might be able to help me figure out whether or not this is a property of the sensor or I should just get used to it with this type of old camera. But first some pictures I suppose.

 

post-261-0-14044000-1564482264.jpgpost-261-0-86353900-1564482307.png

 

So as you can see infrared (720nm filter) works just fine.

 

About UV then. I am working with an ancient canon 1000D which I ''modified'' for full spectrum (read: took out the internal hot mirror and lowpass/dust shaker thing; and replaced with nothing). As a lens, im using the Nikon AF 50mm F/1.8D, which should work well enough for UV as per https://kolarivision...-compatibility/. Finally, as a UV pass filter I am using Kolarivision's one (details here: https://kolarivision...ss-lens-filter/, although I am sure you are well aware of it).

 

When I take UV pictures, there is certainly a UV signature in the images ((sun)glasses are dark), sunblock looks fairly dark, but not super dark. Additionally, in daylight shooting, there appears to be a significant amount of the visible spectrum coming through. When I take images under blacklight this is of course not the case (but here too long exposures and max iso wide open are required)

 

However, the exposure times needed are longer than i'd expect. I need to shoot wide open with the nikon lens (f/1.8, APS-c sensor) at 1/4s exposure iso 1600 to get a decent image. Ive read some things about canon sensors being not as well suited for UV photography, and the ''normal'' colours of the outdoors image suggest (i'd like your take on this) that maybe this particular sensor (identical to the one in the canon 400D) is just not very sensitive to UV and that therefore the long exposures are required making visible and infrared wavelengths bleedthrough become a problem. This seems somewhat consistent with what is said here: https://blogs.msmvps...uv-photography/, where the author mentions he has seen some reports that the canon 1000D only goes down to 380nm.

 

Below I have an image of a flower in UV. The flower leaves were homogeneously orange-ish in visible, and in "UV" it appears there is some difference between the ends and near the base of the leaves, but as you can see there is a lot of what appears to be visible ish light in the image still. (greens in particular). I don't get any false blue or yellows. Note that this is not at all the right white balance, this was set on grass for infrared... I can send the raw file if that is any use.

 

post-261-0-41791300-1564484211.jpg

 

If you know more about this particular sensor, or think it is plausible that this sensor is just not very sensitive to UV, then I might purchase a nikon d3100 or something and ''modify'' that one as well. Still, i'd like to hear your take on this before I spend some money on this.

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I think that you should be able to get a UV photograph in the higher range 375 - 400 nm with the Canon 1000D and the Nikon 50/1.8D under the Kolari UV-pass filter when the UV illumination is good. (I have that filter and know it to be a good one although it does require slightly longer exposures.)

 

Usually at f/8, say, any UV exposure is longer than the equivalent visible exposure by anywhere from 8-12 stops depending on gear used. So your 1/4" @ ISO-1600 would not be considered off the mark.

 

However, there is *clearly* something wrong because the flower does not have the proper appearance for a UV photograph of that type of flower. You are getting Visible contamination, possibly also IR contamination, from somewhere.

 

Let's start here:

  • TEST 1: When you are shooting UV, do you have the viewfinder window covered or closed? Visible and IR light can leak through the viewfinder and wash out UV photos when shooting UV outdoors in the sun light or shooting indoors from ambient light through windows or from lamps. Make some UV test shots in strong sunlight with the viewfinder window covered and with it open. If you see a big difference, then there's the problem. If you don't have a viewfinder cover for the Canon, cover it with your thumb. (You can order a viewfinder cover later.)

  • TEST 2: There might be other light leaks? We try to find these by putting on the lens cap and making some long darkframe exposures, 15"-30", in the light and then in the dark. If the darkframe photos made in the light are showing any washed out areas while the darkframe photos are made in the dark do not, then you have a light leak of some kind. Some cameras have in internal IR shutter monitor which can contaminate UV photos, but I don't think that is the case for this Canon. Sometimes I use a small flashlight and shine it onto potential problem areas (below) when making these test darkframes.

Over the years I have detected light leaks in various places:

  • the viewfinder, as mentioned
  • open port doors
  • lens aperture windows
  • top LCDs
  • around the mount if it has become warped
  • around mount adapters which do not fit properly
  • add-on lens helicoids when extended too far

So please try these two tests and get back to us with the results and we will go from there.


 

375 - 400 nm: This higher range of the UV waveband is a legitimate waveband in which to capture a UV photo with non-UV-dedicated gear. In fact, most of us who have UV-dedicated gear do not often shoot below, say, 350 nm. There's just so little light available in that range. Probably 365 nm is the peak UV shooting point due to the prevalence of 365 nm UV-LED torches and lamps. But the waveband in which we can attempt reflected UV photography is only 100 nm wide and, as noted, illumination is the big problem. BTW, there are UV-pass filters available which are optimized for the 375 - 400 nm waveband. Consult the Filter Sticky in the Reference section.


 

The thing about Canons being unusable for UV is mostly myth. We have all kinds of DSLR and mirrorless conversions being used here on UVP. The only brand I have not yet seen converted is the newer Fuji X type. (I'm sure someone has one somewhere. Just haven't seen them here.)


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Well, I put on my techie hat in the preceding and completely failed to say "Hello" and "Welcome to UVP" to Nemo Andrea. So hello and welcome to UVP! We hope you enjoy the website and find some answers. We will be looking forward to your contributions. We are a friendly, small group with rather slow forum action. It is a nice little corner of the UV world.
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Andy Perrin

Hi Nemo Andrea (more Andreas! To go with our Andys and Marks I suppose).

 

Yeah, you will know you have a UV photo when it looks all magenta in daylight white balance. UV photos do take a long time to expose properly relative to IR, however. There is only 5% UV in sunshine and nearly half IR.

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Nemo Andrea

Thank you for the tips!

 

I have done some initial testing on slightly overcast weather.

 

I have always covered the viewfinder with 2 layers of duct tape (premium solutions, I know), but to be safe I tested the following (as I can imagine it is infrared transparent)

 

I tried 30sec iso1600 (I suppose the iso isnt too important as long as its consistent) with the viewfinder pointed up (towards light) outdoors and in a dark cabinet. Lens was stopped down to f22, and had a lens cap. The proper exposure with the UV filter (lens wide open) is about 1/3s under this lighting and iso. The two exposures at 2 orders of magnitude more light then yield detectable, but minor differences in the histogram, which are both very minor compared to the properly exposed image. Hence I think this rules out the viewfinder.

 

Histogram outdoors

post-261-0-31483700-1564504997.png

Histogram indoors (dark)

post-261-0-74276000-1564505010.png

 

Then I figured the likely culprit is the adapter for the nikon to canon mount.

Here when pointed at the sun (lens cover on lens stopped down) at 30s iso1600 there is a visible bright patch at one of the sensor sides, whose location is independent of the camera angle.

post-261-0-52838200-1564505210.jpg

and histogram

post-261-0-10511100-1564505429.png

which again in my eyes seem to suggest that this is also insiginifcant.

 

I suppose that since the colours in my images appear to be spatially correct, the IR/Visible contamination must be somehow getting through the lens.

I put the lens wide open with the lens cover on the lens and again exposed for 30s iso1600 pointed at the (bright) sky. Under the assumption that the lens cover is an ideal seal, this provides the amount of leakage through other openings of the lens I suppose. At the very least an upper bound on the leakage. At these settings there is a decent amount of light getting through, but nothing that would make me convinced that this is showing the problem. Stopping down the lens to f22 makes this particular type of leakage dissapear.

post-261-0-09665900-1564506280.jpg

post-261-0-53878700-1564506294.png

 

This leaves me still a bit puzzled. Since the filter certainly covers the area coverd by the lens cap, and all light that doesnt pass through this area is insignificant, it must either be a fault in the filter (which I dont suspect) or something about the lens (which should also not be a problem) or it is something about the sensor (which you mention is also likely not the case).

 

I cannot really think of anything else to test at the present, but any further suggestions are very welcome.

 

Nemo

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Andy Perrin
That filter may have an IR or visible leak. We usually stack UV filters with S8612 1.75mm or 2mm in these parts to cut IR leaks. Try that.
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Do you have available a flower like a Dandelion, Rudbeckia, Sunflower or Bidens? Those flowers have a central UV-dark bullseye. I'd like to see what happens when you make a photo of a flower like that.

 

A good Kolari UV-pass filter would *not* let that much visible light pass through. So there might indeed be something strange about that particular filter. It happens sometimes that a batch is not perfect.

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http://www.ultraviol...-straightedgeu/

 

In that topic I showed both raw and finished results for the KolariU, the BaaderU and the StraightEdgeU-Gen1. Use those photos as a guide to what you should be getting from the Kolari.

 

*********

 

I do not permit light leak to the extent shown in your histos. I want to see almost nothing on the left hand side.

 

*******

 

Can you see anything through that Kolari UV-pass filter when held up to strong visible light (but not the Sun please!)??

 

********

 

If your particular combination of sensor, filter and lens were a poor performance combo in reflected UV, we would still expect to see a UV-like image which would be somewhat dimmer than normal and probably very noisy. We would not expect a visible image such as you show with all that green.

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Nemo Andrea

Hi Nemo Andrea (more Andreas! To go with our Andys and Marks I suppose).

 

Yeah, you will know you have a UV photo when it looks all magenta in daylight white balance. UV photos do take a long time to expose properly relative to IR, however. There is only 5% UV in sunshine and nearly half IR.

 

The images do look very reddish under daylight WB, but so do all images (with IR filter or without any filter), so I guess I will have to look at bit closer at the WB reference images.

 

Thanks for the suggestion

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Nemo Andrea

Do you have available a flower like a Dandelion, Rudbeckia, Sunflower or Bidens? Those flowers have a central UV-dark bullseye. I'd like to see what happens when you make a photo of a flower like that.

 

A good Kolari UV-pass filter would *not* let that much visible light pass through. So there might indeed be something strange about that particular filter. It happens sometimes that a batch is not perfect.

 

I'll have a look around, it's a good idea.

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Nemo Andrea

http://www.ultraviol...-straightedgeu/

 

In that topic I showed both raw and finished results for the KolariU, the BaaderU and the StraightEdgeU-Gen1. Use those photos as a guide to what you should be getting from the Kolari.

 

Ah, great to have a direct reference!

 

*********

 

I do not permit light leak to the extent shown in your histos. I want to see almost nothing on the left hand side.

 

 

Even considering the fact that this is for an exposure duration 100x longer than for a suitable exposure (at least suitable with what im getting with my filter)?

 

*******

 

Can you see anything through that Kolari UV-pass filter when held up to strong visible light (but not the Sun please!)??

 

Looking at a few household lamps (warm-ish to neutral temp) at reasonable distance, I can see the outline of the lamp (rather dimly) and a blue tint. I don't know if its uncommon, as the filter still has some transmission close to 400nm, and I can see my 405 and 395nm leds. I am not sure if the amount of light getting through is too much, but I suppose the human eye is not a suitable measurement tool for that anyway.

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Considering the ratio of UV/Vis/IR in sunlight, even a little non-UV light leak can be contaminating.

 

Same thing I see with my Kolari. Never hurts to try the good old eyeball test (not against the Sun of course) just to verify there is nothing blatantly obvious. :lol: Almost all of our UV-pass filters pass a little tiny bit of violet near 400nm. And 390-400 nm would probably photograph as violet in most cameras. (Side note: some older cameras tended to record violet as blue. It is a difficult capture. The near-400 colors are much better in newer cameras. Although we really do not encounter true reflected violet very often! Most of what we think as violet has a blue component.) Anyway any little violet leak is *not* one we consider damaging because it is just a small extension of what we want to shoot and really does not contaminate. Some folks like violet-leak UV-pass filters for a slightly different finished look (usually not accompanied by WB. But that's another topic.)

 

At this point the only thing I can think of to look at next is a photograph of a known floral UV-signature. We are all very familiar with how those are supposed to look both raw and finished. So might be able to come up with a better diagnosis if we can look at one of those. I'd like to see the raw and the jpg. I'm not sure where you live*, but sunflowers are often available in grocery stores or at florist shops.

 

Some things to look for:

Deciduous tree leaves in UV are typically UV-dark. The sky is usually very UV-bright. Grass is UV-dark. Some white painted buildings produce a nice false-purple/blue after white balancing. As you have observed sunglasses (good ones anyway) should be UV-dark. People's skin in UV varies, but some freckling should occur. A UV photo made at a good long distance will be very hazy because the short rays are scattered so much. Some flowers have UV-dark bulls-eyes and those are used a lot for testing.

And of course we have hundreds of other photos here for you to compare to.

 

I'm sure you will get some more suggestions from the members as they stop by. We'll figure it out eventually.

 

*EDIT: You live in the Netherlands of course as I belatedly noticed on your post! :lol:

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Forgot to ask this: What conversion app are you using? Some converters in the past could not handle UV files well. And some converters still today cannot attain the grey/blue/yellow/black/white in the white balance processing.

 

Although I must say that I've never seen a bad converter turn a UV file into a visible file! :rolleyes:

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I just checked the Big 3 retail conversion shops in the US and they all offer conversion of Canon 1000D for full spectrum use. And thus for UV use. So the sensor itself is not the issue here.
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Nemo Andrea

Alright, I have some more findings that may help identify the cause of the issue.

 

I found some sunflowers, so lets look at the images. It was a bit overcast, but I took images when the sun came through. I assume it should be bright enough to see something, but I don't know if clouds attentuate UV significantly more than visible and therefore only making UV photography possible (irrespective of exposure time) during super sunny days.

 

Normal visible shot (smartphone)

post-261-0-37700600-1564593201.jpg

Canon with filter on, whilte balance set on gray tile.

post-261-0-89614400-1564593215.jpg

Canon with filter on, white balance set to 5200K.

post-261-0-26813500-1564593208.jpg

 

Here I dont see any of the characteristic UV signature. Then a quick check on some glass objects. (white balance set to 5200K again)

 

> A regular drinking glass and transparent (in visible) glasses with UV coating.

[in UV]

post-261-0-25745100-1564594119.jpg

[in infrared 720nm]

post-261-0-69791000-1564594128.jpg

[in UV white balance set to the magenta(?) sky]

post-261-0-06472900-1564594634.jpg

 

> A regular drinking glass and sunglasses that are semi opaque (blue) in visible.

[in UV]

post-261-0-27287600-1564594137.jpg

[in infrared 720nm]

post-261-0-21203500-1564594144.jpg

 

 

So the fact that the glasses (the transparent in visible and infrared one is most conclusive I think) seem to show that there is some contribution of UV to the images. While I suppose today wasnt super sunny, I also get the greens and visible colours (i.e. colours that match the visible) in my images when we had a heatwave here with temperatures of 36 degrees so I'm not sure that could be all.

 

let me know of any of these images ring any bells or resemble any of the unprocessed files or effects you observe in UV.

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Nemo Andrea

Forgot to ask this: What conversion app are you using? Some converters in the past could not handle UV files well. And some converters still today cannot attain the grey/blue/yellow/black/white in the white balance processing.

 

Although I must say that I've never seen a bad converter turn a UV file into a visible file! :rolleyes:

 

I use DxO Photolab 2 as my primary photo editor. Unfortunately it is limited in terms of white balance, to the extent that I need to first set the white balance in camera for infrared. I also use Gimp for channel swaps and I have some adobe programs for colour profiles.

 

Maybe its just really good software that can infer the correct colours ;)

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Andy Perrin

Those glasses should probably be opaque? My filter starts around 370nm, though, so I'm not sure what a (working) Kolari would do.

post-94-0-00932100-1564597044.jpg

post-94-0-88750400-1564597051.jpg

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If that is a Sunflower (which of course it appears to be :) ), then you are not recording UV at all or you are not recording very much UV. I say this because there is *no* UV-dark ring at the base of the petals. There is not even a darker yellow or orange colour at the base of the petals.

 

Would you please put a raw version into Dropbox and provide the link? Then I'll run it through Photo Ninja and Raw Digger and see what I come up with. Each UV-pass filter has a characteristic raw histogram. So we will see if your photo has that, or not.

 

When you post a photo for analysis, please also provide aperture, exposure time and ISO value. That info also helps tell us what's going on.

 

Experiment: Try making the sunflower photo on tripod with a dark thick towel wrapped all around the camera and lens mount. Let's see if anything changes at all. You *must* rule out contamination by light leak.

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Nemo Andrea

Those glasses should probably be opaque? My filter starts around 370nm, though, so I'm not sure what a (working) Kolari would do.

post-94-0-00932100-1564597044.jpg

post-94-0-88750400-1564597051.jpg

 

Thanks for the images, thats what I hope to see eventually! I think what I am getting is mix of visible (perhaps some IR as well) and a bit of UV, as shown by the images above, the fact that strong sunscreen looks a bit darker than bare skin (but not quite the dramatic darkness that you can find online. So I am certain that there is some UV contribution to the images, however when I compare the images to what you have and other images on the forum it is clear there is too much visible.

 

At the moment I have two possible explainations that I still consider?

1. The sensor is just comparatively insensitive to UV (on top of the low intensity of UV that is normal), hence the ratio visible/UV is skewed significantly more to visible than in your cameras.

2. The Visible/UV ratio of sunlight in my location is not suitable where I am

 

Have you ever taken UV pictures under cloudy conditions? Does that still work (save for longer exposure times), or do clouds filter out too much UV to prevent visible contamination? (I took the flower pics above under direct sunlight, but it wasnt too warm today (~20C).

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Forgot to say: On overcast bright days there is sufficient UV to make photos outdoors. And on cloudy bright days, same thing. Exposures just get longer, the more clouds there are. If the sky is really dark/cloudy/rainy, then you might not get much with non-dedicated UV gear. But if it is daytime, you will get something. Temperature has nothing to do with it other than when it is hot, it is summer and we have more UV. In the winter we have less UV outdoors to work with. But still enough to make photos.

 

Unless you are in a cave somewhere in the Netherlands, you can shoot reflected UV there !!

 

Please try my leak-covering experiment mentioned in Post #20. Your problem is not with the sensor. As mentioned, if the problem were with the sensor, then you would get a dull, dark, very noisy photo. The problem is that visible and IR light is not completely blocked.

 

edit: it is HOT here where I am and I am making goofy errors when I write. :D :D :D Pls excuse any typos or ogher stuff. I just wrote an absurdity about how close the sun is to the earth and started laughing and forgot to correct it for a bit. Fixed now.

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Andy Perrin

UV under cloudy skies works fine. Sometimes it gives nicer photos for portraits because it's more diffuse lighting.

 

At the moment I have two possible explainations that I still consider?

1. The sensor is just comparatively insensitive to UV (on top of the low intensity of UV that is normal), hence the ratio visible/UV is skewed significantly more to visible than in your cameras.

2. The Visible/UV ratio of sunlight in my location is not suitable where I am

I don't think either of those is likely! We have members in the Netherlands who take UV pics all the time. Also, nearly all sensors have similar UV response once the blocking filter is removed.

 

The most likely explanation is that there is something up with the filter, in my opinion.

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Have you ever taken UV pictures under cloudy conditions?

 

I've made reflected UV photos in the rain and in snowstorms. As long as it is daytime and there is some light, then a long enough exposure will record the UV.

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Nemo, thank you for permitting me to work with your raw files in order to determine what is going on.

Here is a Photo Ninja conversion of both files which seems to show that you are getting a little bit of UV. But not much.

 

This was a non-standard conversion for reflected UV files. The false-blue and false-yellow are too intense. The false-yellow in these photos should be very dark in a typical reflected UV photo of a sunflower. The tips of the flower should be false-yellow or pale false-yellow. The background foliage should be greyish or maybe have some grey-glue tones.

 

(If you want to try this conversion in your DxO app, then white-click on the tips of the flowers and turn off any camera profiling. Adjust exposure/highlights/shadow sliders as needed.)

 

Now I'm going to run the files through Raw Digger. BRB.

 

5200K_WB_f1.8_iso800_1_10spn.jpg

 

gray_WB_f1.8_iso800_1_13spn.jpg

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