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UltravioletPhotography

Baader U, U-360, UG11, ZWB1 stacks compared


Cadmium

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I sure hate seeing that nice peak at 325nm get "shifted" !! But the IR certainly does get blocked.
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Some deep blue is also sneaking through, according to that trace. This may be less troublesome than IR, but it is worth pointing out.
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I've never found a smidgen of violet to be all that much problem in UV photography. After all it is somewhat arbitary where UV "begins". The BaaderU does this also. The AndreaU does slightly more so. Both work quite well for UV photography. If strict results are needed for scientific work, then just apply more blocking. Of course, I agree with making the observation for any & all filters. :D
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This is why I am of the opinion, for what it is worth, that optimal relative out of band blocking should preferably be ≥4.

 

John, yes and then again no. Perfection is the enemy of practical. I think that buying OD3 and carrying an extra blocker for the few times it is needed is the least expensive way to go. And illumination is always a problem for UV - even more so for OD4 UV. To get high UV transmission with OD4 out-of-band blocking is prohibitively expensive for the typical UV photographer who simply wants some landscape/flower/sunscreen type photographs without exceptionally long transmission times.

 

I have a foot firmly on each side of the OD3/OD4 fence. :lol:

 

This brings to my mind another problem we face. No one is making these filters for the UV photography generalist. The filters are being made for astronomy, industrial and scientific work. It is difficult to find filters which take our needs into account. No collimated light. Non-oxidizing surfaces. No IR leakage at all. No violet leakage. Nice high transmission around peak. Every filter I have has some problem.

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I sure hate seeing that nice peak at 325nm get "shifted" !! But the IR certainly does get blocked.

 

Keep in mind that all lenses, other than a few very expensive lenses also truncate ('shift') the uv transmission in the same amount, and often even more than the BG glass.

This happens with a Baader U also, you are limited by the lens, it will 'shift' your peak nm, peak amplitude, and exposure time.

So depending on your lens transmission profile, you are left with similar bandwidth regardless of all these filters except the ZWB1 stack which needs more exposure time.

The lens rules.

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The lens rules.

 

Yes I understand what you are saying about the truncation and shift of transmission with most of our 35/3.5s.

But I have the UV-Nikkor and it will pass that 325nm peak at the highest transmission. :D

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I will illustrate this idea about the lens again.

There are several common reasons why people use absorptive UV filter stacks instead of a Baader U.

1) cost

2) size

Neither of these would be an issue for a UV-Nikkor owner.

For lenses with larger filter threads than 52mm, none that I know of will transmit UV deep enough to even realize the full bandwidth of an efficient stack.

Some old lenses will definitely transmit UV deeper than others. My best UV lens is the Kuribayashi 35mm, which I have used with almost any UV results I have shown.

 

Here is an April 2012 topic by Klaus on Nikongear (now fotozones) which includes this factor.

http://www.fotozones...y-a-simulation/

 

Here is my simple illustration of what I am talking about comparing the Baader U and the UG11 stack (LUV U) and U-360 stack (UVee):

post-87-0-59086700-1454484275.jpg

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Cadmium, what does "internal transmittance" mean for a stack? Are you just multiplying the internal transmittance of each individual filter together, scaled by their thicknesses?

 

Also, I keep reading "LUV U" as "love you."

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Cadmium, what does "internal transmittance" mean for a stack? Are you just multiplying the internal transmittance of each individual filter together, scaled by their thicknesses?

 

Also, I keep reading "LUV U" as "love you."

 

Hi Andy :-)

I am using Internal Transmittance (Ti) because I can't find a way to plot combined (stacked) graphs in T (transmittance).

T graphs use Ti data x Reflection Factor of each glass type:

https://en.wikipedia...i/Transmittance

 

LUV U is my name for the UG11 stack in this topic. UVee is my name for the U-360 stack in this topic (aka 'UVee 360').

'LUV' is my abbreviation for Longwave Ultraviolet.

"U" as in Baader U, Andrea U... Wombat U (the name 'Wombat U' is not yet in use as far as I know).

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Oh, we should talk! My code calculates reflectance factor from the refractive indexes and also includes the multiple reflections off all surfaces. I don't have a table of the internal transmittances for all the glasses, though. I inputted the data for UG11 and BG39 for my own stack, and I'll run that one through soon, when I get time (jobs...so annoying). If you have the individual numbers for the other glasses, I can run those? It's just a a pain entering them from the PDF files into MATLAB.
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Hi Andy :-) MATLAB is cool. The Schott filter program should be able to do combined T graphs, but I have never figured out how to make it do it. The math is all there in the code, but I have not found a way to get the program to use it.

It will of course plot T graphs for a single glass type.

Yes, the inputting takes care and patience for sure. The Schott program has all/most of the Schott glass data already in it, and I have added others.

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  • 2 weeks later...

Okay! I have got my MATLAB code up and running (and producing diabatic graphs...) for my 2.5mm BG39/2mm UG11 stack. Here are the resulting curves.

 

I ran the stack both with and without reflections, and also just the UG11 filter with reflections for a baseline. Reflections probably don't make much difference, which I suspect most here had already concluded.

post-94-0-64719400-1455315272.jpg

post-94-0-60740100-1455315287.jpg

 

From playing with the code, reflections start to make a major difference as the thickness of the filters decreases. These are quite thick, so I'm losing a lot of light but the reflection losses are much smaller than what's being absorbed by the glass.

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Hi Andy :-) That is excellent what you have done with MATLAB! Thank you for posting that.

 

Although your stack is a bit thick and low on the UV transmission for my personal taste, I used your stack formula to compare,

and your Internal Transmittance (Ti) matches up with what I get for that same stack.

If you ever get a chance to use the Schott filter program, please see if you can find a way to get it to draw combined graphs in T instead of Ti.

I think there may be a way to do it in that program.

 

This is also a good example of how using S8612 is better than using BG39. Although those two types of glass have the same suppression of Red/IR,

S8612 transmits UV better.

 

post-87-0-60686600-1455335136.jpg

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