How good is the Baader U at suppressing IR?

[JCDowdy]

I have a question to all UV photographers here using the Baader U-filter.

 

Is it possible that the Baader filter leaks above 1200nm?

 

I am asking this because my Nikon D7100 is modified with the Spectosil 2000 Fused Silica Glass in front of the Sensor. And if you check the datasheet from this material will let pass UV from 170nm all the way to IR frequencies over 2000nm. I am asking this because I founded out that it makes a difference if I am using the Schott KG3 or not, which should not make any difference at all because the KG3 filter is just blocking above 1300nm and I have been told that the Sensor from my camera isn't sensitive in this range any more???

 

The sensor, irregardless of cover glass, is essentially blind by ~1100 nm so any filter transmittance at longer wavelengths is irrelevant.

[nfoto]

Bjørn,

 

 

Wolfgang's nighttime UV efforts which led to the initial discussion raises the question of how much total out of band spectrum was recorded not just IR.

 

Perhaps a more realistic simulation might be to stack a Schott GG420 or yellow Hoya K2 type filter with the Baader U.

 

I'll make an effort combining the Baader U with the trustworthy Nikon filters in my possession: Y48, Y52, R60 then. Just need a weather change.

[kogakunippon]

The sensor, irregardless of cover glass, is essentially blind by ~1100 nm so any filter transmittance at longer wavelengths is irrelevant.

 

The guy converted my camera said its around 1200nm.

[Andrea B.]

While all these experiments are interesting, I do not think we are learning anything we do not already know.

We know:

• All the UV-pass filters can have IR forced through them if using strong IR and no UV or very weak UV.
  
• The BaaderU (and many other) UV-pass filters have areas of IR "leakage".
  
• The newest BaaderU has strong supression of its IR leak, probably OD5.
  
• To successfully use a UV-pass filter for general UV photography the supression of IR must be OD3 or better. More usefully, the supression of IR should be OD4 or better.
  
• There is no glass substrate for UV-pass filters which does not have an area or IR transmission.
  

It takes many, many layers of "hard coating" to fully suppress IR transmission in a UV-pass filter.

 

LINKS to some of my IR stress test experiments:

 

UV-Pass Filter Test III: Baader-U vs. Precision-U(old)

 

U360+BG40, U360+S8612, BaaderU: IR Leak Test

 

Baader-U: Test for Red Leak

[Cadmium]

I have a question to all UV photographers here using the Baader U-filter.

 

Is it possible that the Baader filter leaks above 1200nm?

 

I am asking this because my Nikon D7100 is modified with the Spectosil 2000 Fused Silica Glass in front of the Sensor. And if you check the datasheet from this material will let pass UV from 170nm all the way to IR frequencies over 2000nm. I am asking this because I founded out that it makes a difference if I am using the Schott KG3 or not, which should not make any difference at all because the KG3 filter is just blocking above 1300nm and I have been told that the Sensor from my camera isn't sensitive in this range any more???

 

Hi Wolfgang, What thickness is your KG3? Are you using it alone or stacked, if stacked with what filter(s) have you seen the difference with?

What difference does it make? Can you show an example?

[Cadmium]

Hm. The Baader U I'm using obviously is much less less prone to IR leakages. This reminds me of the first generation of the Baader.

 

I could not possibly have acquired my exhibited results if the filter in question leaked IR in this manner. I do have tried night^* shots with exposures up to 2 minutes with the Baader U and these appear exactly the same as those done in daylight at much shorter exposure times.

---

^* still light on the night sky thus impossible to get longer exposures this time of the year. I live at a high latitude and summers are bright.

 

I suggest that my Baader is not anything unusual, and that it would perform exactly as yours does at night, remember what you said about ratios, what we are doing here is pushing things to the point where there is only one side of the ratio, making the minuscule into the the whole. We are removing the UV from the ratio. Mine is a typical 2012 Baader U. It is definitely not one of the "first generation" Baader's that had the stronger IR.

Your results may show something a little stronger if you test your Baader U with some lower NM longpass filters.

If anyone wants to duplicate my results, here are the camera settings I used for each of my shot: 60s, f/8much, ISO 200, and sunshine (except the UV shots have a different exposure time).

I used a Nikon D7000, and of course a Kuribayashi 35mm f/3.5 lens.

 

 

[Cadmium]

Steve, A very good test, it allows us to pinpoint the leaks. The Baader U appears to have most of its leakage in the 700-800nm range, but some above that as well. The UVee 360 has almost all of its leakage in the 700-800nm range and none above that. The LUV U has most of its leak in visible light - 610-700nm - and only a soupcon of NIR. The dark leaves in the RG610 image also would indicate visible light. You might want to try something below 610nm to see how low the leak goes. I had one annoying leak in a filter I was making that was really hard to find with the spectrophotometer, but was obvious using your approach, above. Thanks. Regards, Reed

 

 

The LUV U has a forced leak around 680-690nm, that is why the 610nm filter shows more of it than the 695nm filter does. Nothing in the lower ranges (495nm shows the same as 610nm).

The 610nm filter shows 610nm and above, 690nm (see graph). If you want me to test it at 665nm (etc.), I will.

I remind you these are not leaks, they are forced, and have no UV to IR ratio present making the exposures 30 or more times as long.

The Baader U shot and the LUV U shot look exactly the same to me when the UV is not blocked, and the filter is used normally.

 

RG495 shot added, is identical to RG610nm shot.

 

The graph below: shows LUV U graph (Red/IR, 680-690nm suppressed to 1E-04).

 

LUV U used normally, and white balanced (CNX2).

[Cadmium]

Wolfgang, Here is what I recommend, this will answer a lot of questions for yourself about the results of what you are doing.

Shoot one of your night time UV shots, just like you would normally do, shoot it on a tripod.

Then stack that same filter with some common red filter like R25 or R29, those are about 600nm longpass filters, they will block UV and transmit Red/IR above 600nm.

Then shoot the same shot on the tripod, using all the same settings, and make sure you use the same exposure time as the UV shot you just did.

Now compare the shots and see what you think, and please post the two shots here, the comparison will be quite interesting!

This will be a much better starting point, and a better way way to analyze your situation, using your own filter for your situation.

[nfoto]

Cadmium: " I remind you these are not leaks, they are forced, and have no UV to IR ratio present making the exposures 30 or more times as long."

 

A statement that cannot be repeated often enough when we deal with the peculiarities of our filters or filter stacks.

 

Plus we also should keep in mind what the intended purpose of the makers of a given filter and the scope for it . An example: in the film days, the B+W 403 was considered a cheaper alternative to the Kodak 18A for UV photography. A purpose for which it worked well using b/w film, not equally well in combination with colour films. Today, we realise that the specific "UV colour" appearance on film was largely due to out-of-band leaks, thus in hindsight the perceived poorer performance of the 403 simply meant it had a different distribution of leak(s) than its Kodak Wratten counterpart.

 

Enter digital era and 'full-spectrum' modified cameras, and now the B+W 403 is an unmitigated disaster as its transmitted so much outside UV proper that any UV-specific feature simply was blown away. However, these days now it serves as a very useful filter for colour IR photography bringing forth a beautiful blue sky without need for the usual 'channel swap' technique. Just forget it as a UV filter though unless stacked with strong IR-blocking filters such as the S8612.

[Andrea B.]

We need to write The Ultimate UV-Pass Filter Guide.

A significant portion of all this information is in the Filter Sticky, but perhaps the title is not catchy enough! :D :D :D

[enricosavazzi]

I have a question to all UV photographers here using the Baader U-filter.

 

Is it possible that the Baader filter leaks above 1200nm?

 

I am asking this because my Nikon D7100 is modified with the Spectosil 2000 Fused Silica Glass in front of the Sensor. And if you check the datasheet from this material will let pass UV from 170nm all the way to IR frequencies over 2000nm. I am asking this because I founded out that it makes a difference if I am using the Schott KG3 or not, which should not make any difference at all because the KG3 filter is just blocking above 1300nm and I have been told that the Sensor from my camera isn't sensitive in this range any more???

As mentioned by John (JCDowdy), the sensor is essentially blind by 1,100 nm. As always, "essentially" and "practically" have limitations and qualifications, and if you throw a lot of radiation at the sensor with a 1,200 or 1,300 nm source, the sensor will record "something". That something may be true 1,200 or 1,300 nm radiation at the tail of the sensitivity range of the sensor, as well as the 1,000-1,100 tail of the radiation spectrum of the source.

[Andy Perrin]

I've tried stacking a 900nm NEEWER with this Omega 1110AELP filter (which has a major visible leak, since it's meant for a GaAs sensor), and I definitely see SOMEthing, as enricosavazzi puts it, but I have to expose for quite a while. You can see where the cut-on is for this one, and it's a bit before 1100, so probably most of what I'm seeing comes from the left end...

[OlDoinyo]

No experimental data here, but a brief thought about what various sorts of out-of-band contamination might look like with a standard Bayer sensor, based on the usual channel sensitivities. (I decline to speculate about laminar sensors such as the Foveon, due to the complex post-processing used to reconstruct the channels:)

 

Edit: I tried to format this as a table but the editor eats tabs and spaces; sorry for illegibility.

 

Band Appearance (RGB) Appearance (BGR)

 

400-420nm Deep Blue Deep Red

 

420-600nm Unlikely to be recorded

 

600-760nm Red* Blue*

 

>760nm White or pastel color**

 

* May be of varying chrominance depending on exact wavelength

 

** May be skewed by the white balance of the image; hue unpredictable, especially if UV and IR white balances are very different.

 

Notably, none of the cases predicts that bright green could be the result of out-of-band contamination.