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Example pictures taken with PrimaLuceLab UV filter

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#21 UlfW

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Posted 11 May 2019 - 13:37

I have the PrimaLuce UV filter too.

It is interesting for artistic IR leaky-type of UV-images.

IMHO the IR-leakage isn't that tiny.
I measured the transmission and OD in IR is between 2 and 3:
Attached Image: Screen Shot 2019-05-11 at 15.21.52.png

I tried to tame it without limiting the shorter end too much by stacking it with a B-410, but it wasn't enough to kill the leakage.
B-410 has a deeper UV transmission cutoff than S8612 or BG-type filters.

Unfortunately I have not kept any of the test images.
Ulf Wilhelmson
Curious and trying to see the invisible.

#22 enricosavazzi

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Posted 20 May 2019 - 23:11

View PostUlfW, on 11 May 2019 - 13:37, said:

I have the PrimaLuce UV filter too.

It is interesting for artistic IR leaky-type of UV-images.

IMHO the IR-leakage isn't that tiny.
I measured the transmission and OD in IR is between 2 and 3:
[...]
I happened to update my web page on the PrimaLuceLab U recently, but had not seen the last couple of posts. See in particular the updated part about the Optolong Venus U filter, which may be the same as the (now apparently discontinued) PrimaLuceLab U:
http://savazzi.net/p...alucelab_u.html

The linear transmission graph at https://www.optolong...-filter-venus-u seems to agree with Ulf's log graph of the PrimaLuceLab U in the preceding post.

Looking again at the test pictures on my page, I strongly suspect that the washed-out false-blue in some of the tests is at least in part a NIR leak. They look like the NIR leaks I have seen in some of my U340-10 filters like the Thorlabs one.
-- Enrico Savazzi

#23 UlfW

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Posted 21 May 2019 - 04:50

Enrico,

When looking at your images of the PrimaLuceLab U, I see an important difference compared to how my filter look.
My filter is just coated only on one side. The coating has the same copper colour.
The opposite side is uncoated showing the black ionic glass substrate.

I think your filter has less IR-leakage than mine, due to the second dichroic coated face.
I remember that the foliage had a much more intense blue tone in my images, just as some images earlier in this topic.
Ulf Wilhelmson
Curious and trying to see the invisible.

#24 enricosavazzi

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Posted 21 May 2019 - 07:37

It seems that there are two versions of the PrimaLuceLab U, the one with different dielectric coatings on either side that I got, and the one without dielectric coatings on one side (or perhaps just AR coating on this side) that you got. Possibly the missing coating on one side helps to reflect NIR, which might be the reason why yours may have a more pronounced NIR leak.

It would be interesting to hear from other owners of this filter (Alex for example) which of the two variants they got. It is of course not a good thing that this filter is/was sold in two different versions without any information on this being disclosed by the seller or maker. Skipping the coatings on one side of course makes the filter cheaper to make, but probably not worth it if it means a significantly poorer performance with respect to our use of the filter.

I can find only one picture of one side of the Optolong Venus U, so we don't know whether this one also has dielectric coatings on only one side. Its price appears to have been cut on the PrimaluceLab web site ( https://www.primaluc...ltraviolet.html ), but has this been done by compromising on its performance? This filter appears to be made in China, which as a whole is not a good sign given our experiences with Chinese filters.

The Asahi Spectra XRR0340 ( http://www.savazzi.n...ml#asahispectra ) has dielectric coating on only one side, but this does not prevent it from having a higher NIR rejection. It also largely cuts off the 370-400 nm band, so it gives monochromatic (false yellow) results with most subjects. Its price is much higher though (the 25 mm size costs almost the same as the 2" PrimaLuceLab U and Optolong Venus U).

Edited by enricosavazzi, 21 May 2019 - 07:41.

-- Enrico Savazzi

#25 enricosavazzi

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Posted 29 May 2019 - 21:17

I had a chance to try again the PrimaLuceLab U in the field, this time with full spectrum Sony Alpha 7 II and CoastalOpt 60 mm Apo.
Edit: To make it clear, the version of PrimaLuceLab that I used for the following pictures is the one with dielectric coatings on both sides (one side copper-colored, the other side gray).

First an example of the custom white balance I used, which I set with the Baader U. This picture is also taken with the Baader U:
Attached Image: SUV04094s.JPG

With the same white balance and the PrimaLuceLab U. The tonality is almost exclusively false yellow:
Attached Image: SUV04092s.JPG

Attached Image: SUV04172s.JPG

Things change if the subject includes a large portion of green plants. This forces a longer auto exposure (the camera is trying to expose for the very UV-dark foliage):
Attached Image: SUV04195s.JPG

Attached Image: SUV04178s.JPG

I suspect that much of this false green is NIR contamination. So it really depends mostly on which subject we are shooting. The NIR contamination does not seem to be important, unless the subject is largely green vegetation, which reflects little NUV but a lot of NIR.

PS - This can be verified by enhancing the green channel of images and changing the overall color balance to better distinguish the green areas, which reveals that the false green is indeed already present in underexposed areas, and therefore not immediately obvious:
Attached Image: SUV04147s.JPG

Edited by enricosavazzi, 30 May 2019 - 07:50.

-- Enrico Savazzi