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UltravioletPhotography

Under <300 nm?


OlDoinyo

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Not much is said even here about photography in the nether band between vacuum UV (<220 nm) and 300 nm. Due to the ozone layer, the world goes dark below 280 nm, so all lighting must be artificial. There is a company called Ofil selling a camera called Daycor

 

http://www.ofilsyste...logy/index.html

 

which is designed to detect corona discharges on power lines, and it indeed operates in this band, at least for one of its channels. The thing is fearsomely expensive and its image quality is not up to serious artistic standards. I do wonder what filter it uses, however; would anyone here hazard a guess, and are such filters generally available? If such a filter were mounted on either a pinhole film camera or on a digital camera using all-reflective optics (e.g Makowsky Katoptaron,) is it likely that images could be obtained at all? Could one obtain night scenes from the 254.1 mercury line of street lights, or is this just fantasy?

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When using digital camera, you would need to remove not only ICF but also sensor cover glass, in order to get these wavelength just reaching the sensor. Microlenses and bayer array may still block them, so debayering may still be needed. My own tests with narrow band filters peaking below 300 nm were inconclusive.
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enricosavazzi

I remember I found a couple of web sites describing videocams with "naked" sensors (no glass window, no microlenses, no Bayer filters). They recommended never removing the lens from these cameras, for obvious reasons (these sensors cannot be cleaned, and might be damaged by humidity) and using only quartz lenses. On the other hand, I don't know whether some technical reason prevents the use of a fused silica window on these sensor chip carriers, considering that some grades of fused silica transmit well below 200 nm.

 

I have some unpublished data (not collected by myself, so I prefer not to release it without permission) showing a very modest response of a consumer-level CMOS Bayer sensor (equipped with standard window) well below 300 nm, but I would not call it usable for imaging. The practical limit for consumer-level Bayer sensors seems indeed to be around 300 nm.

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I have given one of the sensor cover glass (sensor window) from Sony NEX-5N camera to be tested for the transmission in UV. According to the results of the test, which I too can not publish, the glass does not transmit anything below 280 nm. Of course, it does not mean that all sensor covers are the same.
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enricosavazzi
Iggy: yes, it is one of the quartz/synthetic quartz materials I was thinking about. There might be other reasons than transmission spectrum why the sensors of some UV videocams are naked instead of covered with a window made from one of these glass types. I am only guessing, it might be something like thermal expansion coefficient not matching the ceramic package or difficulty of making a durable seal with these materials. Or it might simply be that these special sensors are runoffs from production lines that make ordinary consumer sensors and it would be too costly to modify the production line to change the window material, while it is simpler and cheaper to just skip the step of installing the window. The additional characteristics of these sensors can also be achieved by skipping production steps: don't print/etch the Bayer filters, don't print/etch the microlenses.
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EDITOR'S NOTE: UVP DOES NOT RECOMMEND THE EBAY CONVERTER "EEASSA" BECAUSE WE HAVE HAD 3 REPORTS OF BAD CONVERSION EXPERIENCES FROM THIS SELLER. He offers to fix the problems, but we feel the problems should not happen in the first place.

 

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There's a guy on Ebay, who sells full-spectrum-converted cameras with 'Spectrosil 2000' (instead of the conventional WG280 glass). He does the conversions, himself, and he is a MASTER at his trade.

 

His user name is: eeassa

 

I, myself, have ordered several of his offerings. My favorite, being a 'Spectrosil 2000'-converted Pentax K-01 body (essentially, a mirrorless version of the Pentax K-5). I bought it specifically for astrophotography (via mating to a Maksutov-Cassegrain type telescope). It performs brilliantly (a much lighter and compact package, and no "mirror-slap"-based vibration, but same exact sensor and processing engine under the hood as the Pentax K-5 DSLR. It has "focus peaking", too. Which is VERY useful, indeed. One of the first cameras ever to utilize this technology, when it was first released a couple years ago).

 

Although, as was already mentioned in this thread, the limiting factor will most likely be the sensor / array, and not the 'Spectrosil 2000' cover, itself. (Which is a shame, because this would mean that the Spectrosil 2000's full potential is wasted on such conversions).

 

I haven't ever gotten around to actually testing if my camera would transmit below 300nm, as I have no lens / filter combo which would permit for that. However, mated to my Meade ETX-105 telescope (of Maksutov design), I can probably attempt to test it on some stars of known spectral-shift and determine the camera's response that way (since some modern Maksutov-Cassegrain telescopes can transmit UV very well. Possibly even below 300nm, as these are mostly reflector-based designs, and not refractor-based. I'd have to test, to be certain).

 

But, just so you know. There is one guy who uses 'Spectrosil 2000' for conversions. The only one on the web that I know of, in fact.

 

Here is a link to the same model which I've purchased from him:

 

http://www.ebay.com/...=item2a4072df28

 

(I've even supplied him with comparison photos of some of my own results, after purchase.)

 

However, many of his other full-spectrum offerings (Canon, Nikon, etc.) are 'Spectrosil 2000' conversions, too.

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Thanks!

 

My D600-bb is my only cam currently with a clear internal filter because it was converted by Life Pixel.

 

My other bb cams are 'naked' -- have no glass of any kind except whatever their original sensor pack is constructed from.

Thus no worries about fluorescence or refractive index or glass purity of the replacement glass.

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Hmmm. Now, what if this "eeassa" fellow were to make a conversion using a "de-bayered" sensor, with just Spectrosil-2000 placed in front of it?

 

As Enrico stated, the thermal setting may not be stable enough to even bother with such an experiment. Unless he (or someone else) knows of a way to design one.

 

Until (or unless) that were undertaken ... then, as stated, the full potential of using 'Spectrosil 2000' glass on these conversions is wasted.

 

Oh, well.

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@ Andrea,

 

Indeed. :-)

 

(Unless one is THAT hung up about preserving the camera's original focusing capabilities, including auto-focus functions ... of which, a properly-cut cover glass is necessary.)

 

However, there are other perceived advantages of Spectrosil-2000 covering a de-bayered / naked sensor: Protection of the sensor, itself. After all, we UV photographers often photograph in less than ideal environments. As is: wind-blown dust, grime, etc.

 

No?

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@ JCDowdy,

 

Yes. My Panny G-5 is also a Spectrosil 2000 conversion (and also from eeassa).

 

Those two (Pentax K-01 and Panasonic Lumix G-5) are "eeassa" purchases. He's not cheap, either.

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@ JCDowdy,

 

No, scratch that. I have an Olympus E-P1 that is also a Spectrosil 2000 conversion from eeassa.

 

So, make that THREE models that I own, which use that glass.

 

Geez. I have TOO many full-spectrum bodies, don't I?

 

Hoarder, I am. Ugh.

 

(That doesn't count my full-spectrum bodies with convensional Schott WG280, from other sellers, such as Lifepix, among others).

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If the sensor cover glass does not transmit to the same level as Spectrosil (and the test I have seen show that it indeed does not), than the use of Spectrosil instead of any WG-type of Schott glass in the full-spectrum converrsion makes only sence from the marketing point of view.

 

My first question would be - what is the surface quality of that Spectrosil and is it AR coated. I have purchased some uncoated Spectrosil from a reputable seller of optical glass. I paied good money just to find out that the surface of this glass is full of microscratches and also extremely susceptible to mechanical damage. Contrary to the sensor cover glass. I had "opened" four sensors for de-bayering - the cover glass that is used in Sony cameras is very tough.

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Live View renders focusing problems due to internal filters or lack thereof moot.

 

Besides which most non-UV-dedicated lenses used for UV will have their own kinds of focusing problems even with a clear internal glass filter to maintain the flange focal distance. You can only do so much compensatory adjustment of the focus plane internally.

And even when using dedicated UV lenses which are considered to be APO across UV/Visible/IR, I'm here to tell you that sometimes you still need to adjust focus when switching between UV/Vis/IR. It is just that the amount of compensatory adjustment needed is much more subtle.

Thus Live View has been a true blessing (for me anyway) in the UV world (with sufficient illumination as I always must be careful to add).

 

Unless you seal the clear cover glass to the sensor stack you still risk getting dust, pollen and so forth where you don't want it. The clear glass used in our commercially converted cameras is not sealed to the sensor stack. Eventually the whole shebang has to be taken apart and cleaned. Thus, for me, it seems easier simply to omit the clear filter if you are a really heavy outdoor shooter as some of us are.

 

Once you grind into the sensor stack all bets are off its longevity and its ability to withstand intense UV without changes. I would fear that the grinding would leave things just uneven enough to cause reflections if a cover glass were added. But certainly a protective cover sounds like it would be useful for de-bayered/de-microed sensor stacks.

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If the sensor cover glass does not transmit to the same level as Spectrosil (and the test I have seen show that it indeed does not), than the use of Spectrosil instead of any WG-type of Schott glass in the full-spectrum converrsion makes only sence from the marketing point of view.

 

Right. Which is why I said (above) that using Spectrosil 2000 on full-spectrum conversions, without removing all other light-path limiting covers and array, is mostly wasted potential. Indeed, mostly (if not entirely) a "marketing" (or even "bragging rights") result. Agreed. :-)

 

My first question would be - what is the surface quality of that Spectrosil and is it AR coated. I have purchased some uncoated Spectrosil from a reputable seller of optical glass. I paied good money just to find out that the surface of this glass is full of microscratches and also extremely susceptible to mechanical damage. Contrary to the sensor cover glass. I had "opened" four sensors for de-bayering - the cover glass that is used in Sony cameras is very tough.

 

Those are good questions. Something I have not asked the seller about. Thank you!

 

Not to mention, at the time that I had first gotten into buying full-spectrum-converted cameras, I was just doing IR photography and have not yet gotten into UV photography. So, I wouldn't have even thought of asking those questions, anyway. I was "UV ignorant", at the time, so to speak.

 

But, I suppose I can always send the seller a friendly message, and ask anyway (out of curiosity, if nothing else.)

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@ Andrea,

 

I am not talking about retaining focusing settings for UV work. I am referring to if you ever wanted to retain full auto-focusing abilities, for the times that you place S8612 filter over the front of your lens, and use the camera within a "normal color" job (like any other DSLR).

 

Some of us, you know, like to travel light sometimes (or are even faced by restrictions on how much we can pack away) ... and so, I like having a camera body that can do sufficiently well in UV (over a weekend trip), and STILL be used for the paid gig that I was hired for. In those cases (especially with faster-moving subjects, such as sports or children), your "live view" won't count for smack, if your auto-focus is still crippled. :)

 

But, yes, otherwise ... I agree. You're right.

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Seems like most of you are worrying about technicalities in a UV range in which you will never actually be shooting ?? !! ??

It cannot possibly matter whether your internal cover glass goes below 280nm or not, can it ?? !! ??

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I am not talking about retaining focusing settings for UV work. I am referring to if you ever wanted to gain back full auto-focusing abilities, by placing S8612 filter over the front of your lens, and using the camera again within a "normal color" job (like any other DSLR).

 

Here's my opinion --> if restoration of "full auto-focusing abilities" is what you want, then you will get closest to that by using Live View.

 

If you have both a clear internal filter replacing the ICF and an external S8612, in what possible way will this restore the original factory auto-focus settings?? There is no way this will match the original thickness and refractive index of whatever UVIR blocker was over the sensor originally. And usually a good commercial converter attempts an internal focus plane adjustment based on the focal length you tell them you want to use and based on the thickness and refractive index of their supplied conversion filter. So you would be trying to overcome that as well.

 

Once you have converted a camera, you have what you have and you can't expect it to behave like an unconverted camera. So much for traveling "light" !! I haven't traveled light for 7 years now. (sigh.....)

 

Restoration of "normal colour" in a converted camera happens only by making a good converter profile. The S8612 does not restore the original colour curves. If you have the original internal blocker, you could make that into a filter I suppose.

 

*********

 

Auto-focus is only an approximation anyway.

 

Guys, ya gotta be realistic about this stuff.

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@ Andrea,

 

Yep. I likely will NOT ever shoot anything in sub-300nm ranges. In fact, I currently don't even have any interest in it, truthfully. Hehe.

 

However, for the sake of asking "what if", which is part of the learning process after all, isn't it? :)

 

Oh, well. Back to work for me. Nice discussion, though. But, yes. Andrea = Voice of reason. Once again. :)

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@ Andrea,

 

White-balancing to a good performing "gray card", with S8612, gives me as good of a color reproduction as I ever have been satisfied with. Enough so (and close enough), that I can minimally tweak any remaining color-corrections, via post-photo editing.

 

Not to mention, I end up tweaking color balancing in post-photo edting even in NON-converted ("stock" cameras), half the time. So, what does it really matter?

 

(I have yet to use a DSLR that gets colors to my satisfaction, in-camera, every single time. Whether converted or unconverted).

 

On the other hand, there are scenes where I actually do not even want "exact color" reproductions, regardless of my color profile accuracy. (Ex: Some scenes are better to my taste, when biased in a "warmer" tone. Even though this may not be "accurate" or "true to life" color).

 

And that goes back to my assertion: Approximate color restoration (via S8612) is plenty enough, on site. Post-photo editing will likely be necessary, anyway. The only thing that really concerns me, in such cases, is to simply eliminate IR from the photograph. That's all.

 

But, anyway ... that is going off-subject, something that I don't want to hijack this thread with, hee hee.

 

I'll be back, though. Work is calling. Thanks, all!

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All these speculations about sensors aside, is there a readily-available filter anyone owns or has heard of in a reasonable diameter which would have the requisite bandpass/block? If the answer is no, then the whole discussion is indeed moot, at least for us ordinary mortals.
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