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UltravioletPhotography

[Filter Test] Baader-U vs. Precision-U(old)


Andrea B.

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Introduction

It is a given that both the Baader-U and the Precision-U (old version) leak some small amounts of Visible and IR light.

We already know from our experience of using both filters in our work that they both produce satisfactory UV photographs.

So the primary purpose of this test is not to determine whether the filters leak, per se,

but rather to get some practical information about using these filters.

 

Equipment: Nikon D600-broadband + Nikon 105mm f4.5 UV-Nikkor

 

The D600 was set to a Neutral [4,0,0,0,0] Picture Control and a particular white-balance preset to enable best judgement of proper exposure. For each shot I chose an exposure that kept my Lab Spheres 99% white standard from blowing out in the red or blue channel because I wanted to use the standard for white balance. This means that the UV exposures could probably be pushed a bit more if they did not contain this bright standard.

 

The photos were converted in Photo Ninja using a D600 colour profile preset to present a standardized UV colour palette. Only minor tweaks were made to the endpoints of the histogram to the Black and White points. No other edits were applied.

 

Please do not read too much into the exposure times. The afternoon light was very clear and steady, however I did have to move twice when a tree shadow began to encroach on my set-up. And outdoors, all exposures change with time.

 

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Baseline Photographs

The first photograph provides a baseline Visible image to illustrate the subject matter.

The next two UV images give a UV baseline photo for each UV-Pass filter in full sunlight with no artificial UV illumination.

Note that the UV signatures of both flowers were satisfactorily captured in each case.

 

1. The Subject: Rudbeckia hirta 'Denver Daisy' on left and Leucanthemum x superbum on right together with Color Checker Passport and Lab Spheres 99% Reflective Standard.

baaderUvirCut_100213wf_15939origPN.jpg

 

2. Baader-U: Filter used alone.

The UV signature of the right-hand L. x superbum is very dark.

Typically, I would further edit this photo to open up the shadows a bit in order to see more of the UV-dark details.

baaderUonly_100213wf_15949origPN.jpg

 

3. Precision-U(old): Filter used alone.

The Precision-U(old) captures the UV pattern with slightly different false colours and slightly more open shadows.

This is beneficial to seeing the very dark UV signature of the right-hand L. x superbum.

precisionUonly_100213wf_15996origPN.jpg

 

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Trapping 'Pure' IR Leaks Past 800nm

In the this experiment I stacked the Baader-U and then the Precision-U(old) with a B+W 093 pure IR-Pass filter to try to trap any IR leaks beyond 800nm in 15" and 30" exposures in full sunlight. The photos were white balanced against the Labsphere 99% standard, but no other edits were applied. The results of this experiment were interesting. The Baader-U seems to have some pure IR-leakage and the Precision-U(old) does not.

 

To review, the Baader-U transmission chart shows tiny IR bumps between, approximately, 735-750nm, 800-825nm and 860-875nm.

Kindly note: Long exposures like this are bound to trap even the smallest amount of leaked IR.

Please Remember: For typical UV exposures under 4 seconds, this IR leakage is not significant enough to seriously contaminate the UV exposure.

 

B+W 093 IR-Pass Filter: This is a pure IR-Pass filter beginning around 800nm and reaching 50% transmission at 830nm. It is equivalent to RG 830 glass or a Wratten 87C. Reference: Filter Handbook: B+W Filters, page 29.

 

4. Baader-U + B+W 093 IR-Pass Filter: 15"

The Baader-U shows some IR leakage past 800nm in a 15" exposure.

baaderU+093ir_15sec_100213wf_15977origPN.jpg

 

5. Baader-U + B+W 093 IR-Pass Filter: 30"

Compare this Baader-U 30" exposure to the next Precision-U(old) 30" exposure - very interesting.

baaderU+093ir_30sec_100213wf_15979origPN.jpg

 

6. Precision-U(old) + B+W 093 IR-Pass Filter: 30"

There is some contamination on the top and left but there is definitely not any IR leakage past 800nm from the Precision-U(old).

EDIT: We are not sure of the source of the IR leakage in this photo. I have speculated that it might be from the D600 IR shutter monitor or from my filter step-ring fittings.

precisionU+093ir_30sec_100213wf_16031origPN.jpg

 

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Trapping Red/IR Leaks Past 695nm

In this experiment I stacked each of the UV-Pass Filters with a Red + IR-Pass filter, the B+W 092, to try to trap any near-IR leaks beyond 695nm in 15" and 30" exposures in full sunlight. I then compare the results to the previous experiment. The photos were white balanced against the Labsphere 99% standard, but no other edits were applied. Again, the results were interesting. Both the Baader-U and the Precision-U(old) show leakage under the 092, with the Baader-U leakage being somewhat less. There are also colour differences between the filters after white balance. I don't know what that signifies, if anything, because false colours are at play here.

 

To review, the Baader-U transmission chart shows tiny IR bumps between, approximately, 735-750nm, 800-825nm and 860-875nm.

Kindly note: Long exposures like this are bound to trap even the smallest amount of leaked IR.

Please Remember: For typical UV exposures under 4 seconds, this IR leakage is not significant enough to seriously contaminate the UV exposure.

 

B+W 092 IR-Pass Filter: This is a Red + IR-Pass filter beginning at about 650nm and reaching 50% transmission at 695nm. It is equivalent to RG 695 glass or a Wratten 89B. Reference: Filter Handbook: B+W Filters, page 29.

 

7. Baader-U + B+W 092 IR-Pass Filter: 15"

There is obvious leakage by the Baader-U under the 092.

Is it Red leakage or IR leakage, or both? I don't know. Let's just call it 'near-IR' leakage.

After the white balance step, the photo shows some blue false colour.

baaderU+092ir_15sec_100213wf_15963origPN.jpg

 

8. Baader-U + B+W 092 IR-Pass Filter: 30"

Interestingly, the amount of the Baader-U's near-IR leakage under the 092

does not increase as much as I thought it would with a doubled exposure time.

baaderU+092ir_30sec_100213wf_15965origPN.jpg

 

9. Precision-U(old) + B+W 093 IR-Pass Filter: 15"

Compare this to the first Baader-U 092 15" photo to see that the Precision-U(old) has slightly stronger near-IR leakage.

Again, I don't know if this is Red leakage or IR leakage, or both.

Most likely, the near-IR leakage of the Precision-U(old) is in a different portion of the near-IR waveband from the Baader-U.

precisionU+092ir_15sec_100213wf_16010origPN.jpg

 

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IR Leakage Test Conclusion

I would say that in these long 15" and 30" exposures, the Baader-U has wider overall IR-leakage than the Precision-U(old) and that the Precision-U(old) has slightly stronger near-IR leakage than the Baader-U.

Again I feel that I should remind you: we know from extensive experience that for purposes of UV documentary photographs, both filters satisfactorily capture UV signatures.

Because of slightly different UV transmission and minor colour differences, editing will be different for work produced with each filter with respect to white balancing, opening up shadows or other such tasks.

 

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Controlling IR Leakage in Both Filters (if you feel you really must...)

If you stack BG39 or S8612 filter glass with either your Baader-U or Precision-U(old), then the minor IR leakage they have is cut even further in spite of the fact that the both supplementary filters also pass some IR.

 

10. S8612 UV/Vis-Pass Filter: This is a blue-green filter which passes UV and Visible wavelengths and which can serve an IR-block. The S8612 glass is very similar to BG39 glass. Note that both these BG filters do pass some IR. Here is a transmission chart from Schott's optical filter catalogue: Schott: Glass Made of Ideas, 2009. I darkened the graph along the 1% line to make it more obvious. At 700nm both filters go below a 1% transmission of IR.

BG39_S8612_Chart.jpg

 

11. Baader-U + S8612 + B+W 092: 30"

This long exposure shows no IR leakage.

baaderU+092ir+s8612_30sec_100213wf_15971orig.jpg

 

12. Precision-U(old) + S8612 + B+W 092: 30"

This long exposure shows no IR leakage.

precisionU+092ir+s8612_30sec_100213wf_16025origPN.jpg

 

13. UV Photograph with Baader-U + S8612

Here is the Baader-U UV photograph with additional IR blocking.

There is not much change from the first Baader-U UV photograph (#2 above).

baaderU+s8612_100213wf_15957origPN.jpg

 

14. UV Photograph with Precision-U(old)+ S8612

Here is the Precision-U(old) UV photograph with additional IR blocking.

There is some colour shift from the first Precision-U UV photograph (#3 above).

precisionU+s8612_100213wf_16004origPN.jpg

 

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Trapping IR Leaks in IR-only Illumination

I had wanted to try to show, as per Bjørn's suggestion below, that repeating the IR leakage tests in IR-only illumination would yield similar results to the IR leakage tests made in full sunlight. It appears as though this is true, but I'm having trouble determining whether I have "pure enough" IR illumination using my little IR-LED hotshoe light. Also, this IR LED light source - even when combined with some light from an (impure) Incandescent light bulb - does not seem strong enough to boost exposure times above 30 seconds. So I'm going figure out how I can set this experiment up better before I post anything here.

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Hi Andrea,

 

Thanks for this test that should be indeed very helpful for anyone interested in UV-photography. Personally, the only filter that I own and use which has an acceptably low IR leakage is the Baader U 2”. I was thinking that the Precision U would be good as a backup and also because it has a more usual size of 52 mm. However, when comparing your first two UV shoots I would conclude that the Precision U has a visibly higher IR leakage, at least under the test conditions that you have applied here. I think the yellowish cast in the areas that are UV-dark with the Baader are a clear indication of that leakage. – Or do I get something wrong?

I also noticed that you and Bjørn use almost exclusively the Baader U for the images that you publish. Is that mainly to standardize, or because the filter has an edge over the other alternatives in your experience?

Best wishes and thanks again,

Nico

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I would conclude that the Precision U has a visibly higher IR leakage, at least under the test conditions that you have applied here. I think the yellowish cast in the areas that are UV-dark with the Baader are a clear indication of that leakage. – Or do I get something wrong?

 

Well, Nico, please be patient until all the results are posted. It is not all that clear to me what is going on. The Baader-U and Precision-U both leak different things in different places. So we shall see what we can learn about that - in a practical sense.

 

Look at the two baseline photographs above. Both are satisfactory UV photographs. The Baader-U photo slightly obscures the right-hand Leucanthemum signature without further work. The Precision-U provides a better overview of the Leucanthemum signature. (Remember, colour does not matter here.)

 

It is what I call "by Historical Accident" that Bjørn and I use the Baader-U in our botanical work. :rolleyes:

 

The original 1.25" Baader Venus filter was a leaky mess as are the B+W403, the Hoyas 340/360, the Astrodon and the old Schüler. This is because all these filters were developed primarily for astronomy use. I think Bjørn used to stack his Venus filter with some BG glass to improve the results in botanical work. I've posted some Filter Tests here that show the leaky filters can be used successfully if stacked with BG39 or S8612 if one is aware of potential stacking side effects such as longer exposures or possible flare problems.

 

When the new, improved Baader-U came along we both jumped on it because it only leaked minor amounts of Vis/IR and so did not need to be stacked with an additional IR blocker. The Precision-U did not come along until very much later. So Bjørn and I both have years of documentary work done with the Baader-U.

 

Recently I see that the Schueler has been improved and that the LUV filters are being offered. So we now have a nice variety to choose from. Eventually I hope to be able to get some of the newer ones for testing.

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I agree such tests can be informative. Kudos to anyone willing to take the time to conduct these.

 

However that being said, one has to put the observations into the proper perspective. Any filter will, given long enough exposure, show leaks outside its designated passband. A trivial fact we should never ignore. So, the more useful way of testing is setting up the subject as for UV photography, but for a "blind" comparison replace the UV illumination by an IR source keeping all other factors (aperture, exposure time, ISO) identical. That will tell the practical importance of the filter's transmission curve. Is the IR-illuminated frame (achieved under standard conditions for UV) anything than jet black when no UV light is added, an IR contamination is present. To give reproducible results, the setup should be run in total darkness apart from the light source tested.

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Nico: to elaborate the answer on the Baader U-filters already presented by Andrea; yes it was a result of history and what filter alternatives were present at a given point in time. Initially I considered the non-standard (for photography) 48 mm thread cumbersome, but it turns out to provide some unexpected advantages as well. This is because it is easy to install these filters inside adapters so you can do UV with lenses otherwise impossible to attach a filter to.
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I've carefully marked this post as incomplete because I haven't yet had time to put up all the IR leakage tests. Nor have I written all my commentary yet. Could be I already have exactly what you have suggested....... :rolleyes:
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Hi Andrea

 

nice set of tests for showing the potential for Baader U and Precision U IR leakage. However, if you were to re-take image 2 and 3 with the IR filters in place but not change the exposure you would obtain almost black images which would require an exposure adjustment of around 6 stops to make an image out of the IR leakage. I think this would put the following statement into context.

For typical UV exposures under 4 seconds, this IR leakage is not significant enough to seriously contaminate the UV exposure.

 

There is some contamination on the top and left from the D600 internal IR shutter monitor, but there is definitely not any IR leakage past 800nm from the Precision-U.

you attributed the IR contamination in these images to IR shutter monitor. However, comparing image 11 and 12 seems to contradict this assessment. Image 11 and 12 were captured under the same DSLR parameters the only difference being one was fitted with the Baader U and one the Precision U, and yet only one displays IR contamination and one doesn't. This feature appears fairly prominently in a couple of the Precision U experiments, 6 and 9, however it also appears to be present to a lesser degree in the Baader images. This casts doubt as to the source of the IR artifact.

 

Have you tested the D600 with long exposure, High ISO, NR off, and body cap on (no lens, filter etc), viewfinder covered, wrapped in black cloth or preferably tin foil and place in a "black hole"? If IR LED leakage is present then its pattern should match those seen in the above images.

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Andrea,

 

You should try the new, thinner PrecisionU which has the object surface A/R coated. The anti-reflective coating - centered at 350nm - protects the PrecisionU from scratches and corrosion, while increasing the UV transmission by 2-4%. The cladding has been eliminated.

 

Best regards,

Reed

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You should try the new, thinner PrecisionU which has the object surface A/R coated. The anti-reflective coating - centered at 350nm - protects the PrecisionU from scratches and corrosion, while increasing the UV transmission by 2-4%. The cladding has been eliminated.

 

Good to see that you are still in search of perfection. :D

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Shane - I'm so glad you stopped by to give me some input on this experiment !! I will definitely follow through with your suggestions. Thank you!!!

 

I have amended my comment about the IR "contamination" to make it more speculative and included the possibility of misfitting step-rings. I'll get the darkframe experiment done soon. Then perhaps I can make a more definitive statement.

 

In UV photography, it is rather amazing how the least little thing can contaminate the photo. I left a port door open on the left side of the D600 one day and got IR contamination. Then there are lens windows, bent or dinged lens mounts, too flexible step-rings, "windows" on enlarging lens, viewfinders and on and on. Gotta keep the roll of duct tape handy.

 

Reed - I suppose I should designate my Precision-U as "version 1" or something like that?? Are the old and new Precision-U visually different? I can't afford an upgrade currently. Perhaps next season. :D

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  • 3 weeks later...

The new Precision is definitly better

here is an example taken with the Panny GH3-UVIR and the UV-Nikkor105 at 4.5

 

Compared are the Baader U, the first Precision and the new one,

all 3 without (left) and additionally with (right) the Makario IR Neutralisation NG Filter (this stops the IR but not that much the UV and is intended to take visual pictures)

Exposure times are 4,6,6s without and 6, 10,10s with the NG

 

I still have to work on the WB for the GH3, all pictures developed from raw with the identical Settings

 

 

(name of Makario filter corrected)

post-21-0-37902700-1382997456.jpg

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