Infrared block, broad UV and visible pass filter?

[Avalon]

I seen people shooting just normal DSLR with UV pass filters and calling it ultraviolet photography while in fact it is violet or deep blue with very little UV. CFA and hot mirror are first barriers to invisible ultraviolet world.

BTW I forgot to mention that I have inherited from my grandfather all sorts of photography equipment. It's from Soviet era, used for old film camera's but lenses do have AR coatings so I could use them in future. He also used UV-C quartz lamps for something. Is there method to test UV-B transmission without UV-A, maybe specific fluorescence patterns?

Then I will aim for 380nm for now.

[Cadmium]

Once again, UVC is very dangerous. UVC lamps lose potency after a short time of use, the only way to test them is with a UVC meter, but you should not be using UVC, because you don't need to, and it is dangerous stuff.

Concentrate on doing something easy and basic first. Forget about UVC and UVB. The ONLY way to photograph even UVB is to have a converted full spectrum camera, use a special UV pass filter for the 290nm-315nm range, with a VERY special and VERY expensive lens (like a UV-Nikkor, costing about 7 grand these days), long exposure. Don't even plug your UVC light in. DANGER DANGER. You will end up blind and with skin cancer. You think I am just a scaredy cat?

[Cadmium]

You may have some reason, intent, fascination for wanting to photograph UVB and UVC, so why do you want to photograph those bands?

I am assuming you are not confusing fluorescence with UV, because there are some examples of UVIVF (visual fluorescence) that is induced by UVC and UVB,

but that is rare, but indeed it is doable.

So please explain your intentions, reasons. for pursuing UVC and UVB.

Thanks.

[ulf]

From what I read maybe using just single UV grade fused silica lens would be best, even better with special UV pass coating? There wont be optical zoom option but still possible to focus.

 

I just tried a single fl150mm, d50mm, plano-convex, fused silica lens with a Baader U and helicoid on my camera.

The lens reach down to at least 210nm if I remember correct.

The result is not very sharp, but still acceptable for simple testing of UV-B imaging.

 

I bought the lens-element, made by Oriel as surplus for $15, to build a big aperture collimator for my spectrometer.

 

For a wider spectrum there will be massive chromatic aberration.

[Andrea B.]

The most popular baader venus filter, peak is at 355nm, but due to camera sensitivity and solar radiation is mostly being used at 380nmm by most users.

 

I don't understand this statement. There may be more available solar UV at 380 nm, but the BaaderU is supressing most of that. Is there some confusion between transmission and sensitivity?

[dabateman]

@Andrea,

I now see after breaking my Baader venus filter this morning, that there are many different spectra for that filter. It does not seem to be standard set range filter. Mine was marked 325nm to 369nm #2458291. However, I had it when I still worked in a lab and tested its transmission profile. Mine hit 76% at 330nm and was still at 55% at 380nm. It has no signal at 325nm and falls off from 380nm ending just before 400nm. I still had 18% transmission at 390nm. I have seen some end at 380nm from random internet searches. I bought mine in October 2008, so It survived for just 10 years. I am now trying to figure out how best to try and fix it.

 

@Ulfw, I don't know where your Baader venus filter starts, but I doubt your seeing UVb. That looks more like UVA to me. All my UVb images are heavy in the green channel. With a 313bp25 filter and a recent 300bp10 filter I have.

 

@Avalon,

If your interested in building your own lens you should read this:

http://www.randombio.com/uvlens.html

[Cadmium]

"The most popular baader venus filter, peak is at 355nm, but due to camera sensitivity and solar radiation is mostly being used at 380nmm by most users."

 

The lens, the lens, the lens...

You can't see UVB with a Baader U, with any lens, and you will only see the range that the lens transmits.

 

Here is a graph showing three UV pass filters, and two UV transmitting lenses, one is a very good UV transmitting lens (Kuri 35/3.5), the other is only marginally good at transmitting UV (Nikkor 18/4).

 

You see how the lens truncates the UV pass filter, redefining the functional peak, range, and amplitude of the UV transmission.

Unless you have a UV-Nikkor lens, you will not realize anything more than the peak provided by the Kuri x Filter on this graph.

With the Kuri, you will pretty much have a peak of 360nm for all those filters, including the Baader U.

You will have a peak at 380nm with the 18/4, and with a much reduced amplitude, thus a longer exposure time.

 

 

The lens matters more than the filter.

 

 

[Andrea B.]

Oh David, wow. I'm really sorry to hear you broke your BaaderU. I've done that and know how distressing this is.

 

The first BaaderU I had was the old IR-leaky version. Since then there have been 2 versions, at least. Although I cannot tell you whether differences in the labels indicates differences in the transmission.

 

Here is the labeling on them:

• Baader U-Filter 2" (CWL 350nm) #2458291
  
• Baader U-Filter 2" (HWB=325-369nm) optically polished #2458291
  

For the two examples I have with that 2nd labeling above, one is pink/green and one is pink/goldish-green.

So perhaps there have been 3 versions since the old IR-leaker ??

[Cadmium]

There are different vintages of the Baader U.

Mine is the Baader U-Filter 2" (HWB=325-369nm) optically polished #2458291.

[dabateman]

@Cadmium,

Is that the most recent one from Alpine Astronomical, that I see at B&H?

 

Well mine has a crack on the outer edge at least. There seems to just be 30mm of good filter in the centre region. So I am going to try a Gorilla tape method to hold and seal it back up. Amazingly I have been able to use 12.5mm filters recently with only 9mm of open filter in center on my Em1 without vignetting. So I have High hopes it will still be good.

The price has doubled over 10 years of ownership. So will have to wait a long time on a new one. Also the Astrodon Uvenus filter looks interesting at the same price point. So I am reading everything about that filter too.

[Cadmium]

I didn't get mine from Alpine or B&W, got mine from Astro Physics years ago, not sure how many years.

http://www.astro-physics.com/index.htm?titlepg

I am under the impression that Alpine is the central distributor for Baader in the USA, so basically any USA supplier, store, site, or listing of a new Baader U on eBay are all coming from Alpine,

and the prices are probably almost exactly the same.

I have more recently purchased a couple other special filters from Alpine directly.

 

Sorry about the crack. :(

[ulf]

@Ulfw, I don't know where your Baader venus filter starts, but I doubt your seeing UVb. That looks more like UVA to me. All my UVb images are heavy in the green channel. With a 313bp25 filter and a recent 300bp10 filter I have.

 

No I cannot see any UV-B.

My image was not an attempt to do that at all!!

 

I only wanted to show the image quality from a single good quality plano-convex fused silica lens with a well known UV-pass-filter. (UV-A).

The lens has similar or better UV-transmission than an UV-Nikkor 105mm, to 1/100 of the price, including helicoid, step rings... The penalty is a not so sharp image. :)

If someone without TAC-, Coastal- or UV-Nikkor-lens want to play with UV-B pass filters a fused silica lens-element might be an option.

 

A good quality plano-convex fused silica lens can also be used as an alternative to a pinhole for pinhole-testing the UV response of camera lenses.

[ulf]

My Baader U-Filter 2" (CWL 350nm) #2458291 is pink/goldish-green.

FHWB = 328nm - 384nm ± 1nm

 

The filter has this transmission:

 

 

The biggest IR-peak, slightly below OD4, is at 734nm.

[Cadmium]

Ulf, I especially like your second graph, for the fact that we seldom see such a graph for the Baader U, the only one I have seen that come close is the one Shane has on his site.

Actually, I am a little surprised about the 700nm peaks, what vintage/year is yours?

You did that with your USB spectrometer?

 

Sometime will you give me a shopping list of things to set up a spectrometer like yours with, then help me learn how to put it all together and use it?

It could come in handy. :-)

[dabateman]

Thank you UlfW for the Baader venus spectrum. Its a little different than mine, but not grossly different.

I too am curious by your spectrometer. Your to OD5 detail is excellent.

[ulf]

Ulf, I especially like your second graph, for the fact that we seldom see such a graph for the Baader U, the only one I have seen that come close is the one Shane has on his site.

Actually, I am a little surprised about the 700nm peaks, what vintage/year is yours?

You did that with your USB spectrometer?

 

Sometime will you give me a shopping list of things to set up a spectrometer like yours with, then help me learn how to put it all together and use it?

It could come in handy. :-)

 

I bought my Baader U new last spring. It is the latest version AFAIK.

The peaks are rather low and can be seen in other measurements too.

I am quite confident that they are real as a similar measurement of my S8612/U-360-stack show no peaks.

The low level parts of the graph are a result of 10 000 spectra averaged both binwise and wavelength-wise.

To reach OD5 is a complex task completing. When everything is stabilised and verified it is more than one or two hours work to obtain one composite graph.

 

The graph I posted is a composite of very many different measurements for different parts of the spectrum.

Each section is carefully optimised for what I needed to measure to overcome the limitations of an array-spectrometer. It is a divide and conquer method.

 

An USB spectrometer is just one component in the measurement setup. Then you need good collimators, optical fibres, filters, a suitable stable lightsource, and a way to mount and align all components in a proper way.

It is also essential to verify and recalibrate the wavelengths-calibration of the spectrometer. For that you'll need a calibration light source.

 

I can eventually give you a shopping list, but if you intend to buy everything new it will cost you like a new Rayfract 105mm, maybe more.

I got my specially configured spectrometer as surplus from a company that sold three of them on eBay last summer.

Then I posted about the auctions here on the forum, but I don't think anyone here was interested and bought any of the two remaining spectrometers.

[dabateman]

Wow, I am amazed you got that with a usb spectrometer.

That gives me hope I could afford and piece something together that I will be happy with. I am solo not in a lab. So a 2 hour acquisition doesn't matter. Better would be 4 hours, then I could sleep in the collection times.

 

[Cadmium]

You need a Rayfract 105mm to do a spectrometer test of a filter?

[Andy Perrin]

I think he meant the price was similar.

[Cadmium]

Oops, yeah, read that wrong.

[ulf]

Wow, I am amazed you got that with a usb spectrometer.

That gives me hope I could afford and piece something together that I will be happy with. I am solo not in a lab. So a 2 hour acquisition doesn't matter. Better would be 4 hours, then I could sleep in the collection times.

Not two hours acquisition!

 

Total actual acquisition time summed from all different measurement sessions needed is maybe 10-15 minutes. Between the sessions there is recalibration of reference and background levels, reconfiguration of the setup and data processing of the results from the sessions to generate the final composite spectrogram. It is a lot of manual handling.

If I did this often I would be faster, but not faster than down to 40-50 minutes if everything went without any problem.

 

To reach this dynamic range I cannot trust the stability of a background calibration older than 1-2 minutes despite a rather good, stable lightsource and spectrometer.

The measurements are not a simple - push the button and wait two hours for the result -operation.

You have to understand what you need to do to avoid all the limitations and pitfalls in the process.

 

I think I do that now after much experimenting and learning with the spectrometer setup.

My background of designing specialised measurement systems for thirty years has been of some help to identify problems and ways around them.

[ulf]

I think he meant the price was similar.

Correct.

[dabateman]

UlfW,

Thank you. I did kinda figured that. The short cut I guess would be 5 USB spectrometers with over laping ranges. The sensitivity and stability when I looked seemed good for a maximum range of 200nm.

I am really impressed that you can recalibrate and adjust that quickly though. I guess that is when you know you equipment and experience kicks in.

I remembered grad students taking a month for optical alignments in confocal microscope systems. But thats a different beast.

[ulf]

The two main obstacles to overcome is internal crosstalk and dark reference drift in the spectrometer.

Then comes the general system noise. That can be a thermal noise from the sensor array, or noise from the electronics, or both.

[Avalon]

Speaking of spectrometer maybe prism can be used test UV transmission? It should be possible to calculate spectrum by refraction angle.