Optimal Thickness of S8612: Discussion

[Andy Perrin]

Quote

 But the real optimizations lie in the areas of good UV illumination, a sensor with good image quality (high dynamic range and low noise), a very UV-capable lens, and practice. Put some effort into learning to use well what you have, into refining your image making skills both in the field and in the editor.

YES, this! You get way more for your money and effort from a good flash and camera body, and a not-bad lens (which includes Kuris, the Igoriginals, the EL-Nikkors - it doesn't need to be quartz, which doesn't actually help too much).

[Andrea B.]

it doesn't need to be quartz, which doesn't actually help too much

 

not sure I'd go so far as to say quartz doesn't help too much........

[lukaszgryglicki]

True, but I was asking because I'll buy another S8612+U set with 52mm size in addition to my current 67x2mm S8612+U-360 - I was wondering what to order, considering 1.75mm instead of 2mm - that's it.

 

S8612+U-360 stack is perfect, but really slow, my Kolari-only UV stack is a lot faster, seem not to leak IR, but have no idea what the actual transmission looks like. I've posted many photos from Kolari here on the forum and people confirmed that it seems not to leak IR. I think it just shifts top transmission a lot closer to 400 or even 405 nm than S8612+U-360 stack (RAWs are a lot "bluer" than 8612-U which are red-orange by default).

 

Actually Kolari UV is easy handheld with Nikkor 50/1.8 AFD while S8612+U-360 (2mm both) seem not to be handheld even with Soligor 35/3.5 (which has good UV transmission) - but I only tested the latter today, 50-80% overcast skies, December and 52 degrees north... so ... UV very low?

 

I wonder how Kolari UV-pass transmission looks like and what is it made from? I have a "good" batch, not leaking IR, quite up-to-date (it is 2 months old).

 

[ulf]

2 minutes ago, lukaszgryglicki said:

my Kolari-only UV stack is a lot faster, seem not to leak IR, 

Or you have not yet been in a situation prone to IR leakage, or learned to identify it fully.

It is often see best with really dark UV-signatures, especially when the illumination has a bad UV/IR ratio.

For IR leakage it is always good to have margins.

Going from 2mm to 1.75mm will increase the speed just marginally. You lose much more IR suppression.

 

[lukaszgryglicki]

This is what I already know, but didn't know when I originally asked this question. This forum makes me learn a lot, actually, never learned more from any forum.

 

[Andy Perrin]

56 minutes ago, Andrea B. said:

it doesn't need to be quartz, which doesn't actually help too much

 

not sure I'd go so far as to say quartz doesn't help too much........

With exposure? I mean, maybe with color, but the camera gain goes way down in UVB, so unless you have a monochrome conversion, why would quartz help all that much? I have one quartz lens, the KSS 60mm, and I don't recall it being dramatically faster, although it is a little faster than my other "accidental" lenses.

[lukaszgryglicki]

I have both mono & bayer - but don't have quartz lenses... was considering UV8040BK2 - skipped due to huge chromatic aberration (chromatic sounds silly in UV, but u know what I mean).

[Andy Perrin]

Lukas, I have my eye on that DIY quartz aspheric lens (79mm) that Jonathan built from Thorlabs parts. The price for the new lens is about $400 (in round numbers) which doesn't seem crazy for a quartz lens to me. His test photos seemed nice and sharp.

[lukaszgryglicki]

I take it blind.

 

[Andrea B.]

Andy....but the camera gain goes way down in UVB, so unless you have a monochrome conversion, why would quartz help all that much?

 

Point taken.  I think I was thinking more about a mix of fluoride and quartz elements. 

 

 

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Łukasz: ....wonder how Kolari UV-pass transmission looks like and what is it made from?

 

I have this for the KolariU: 365FWHM40. 50% transmission at peak. Half-max 340-380 nm. Min OD 3.5. Ave OD 4.3.

 

Given that the KU is an absorptive filter, then there are only a few possibilities for its substrate - something equivalent to (or maybe equal to) U-330, U-340 or U-360. Given the peak at 365 nm, I would reasonably surmise the U-360 equivalency. And there is probably a blue-green cemented layer to provide the IR blocking and cause the low transmission rate. Given the reasonable price of (US)$199, I am going to guess that the substrate is one of the Chinese ZWB types, but I do not know for sure.

 

I am looking for a chart which I thought we had here. Haven't found it so far. 

Here is the chart from Kolari Vision. But these linear charts are not too helpful because we can't see where any Vis or IR bumps might be. I've always thought that the KU had pretty good IR-blocking.

 

[Doug A]

There's a "mechanical" disadvantage to the Kolari. No front filter threads. I could live with not being able to use a lens cap. No lens shade seems like an invitation for flare and loss of contrast. 

 

Thanks,

Doug A

[lukaszgryglicki]

My Kolari has front thread - I've put UV filter there (by "UV" I mean cheapest protection one - it is not blocking any UV as 99% of UV filters).

 

[ulf]

5 hours ago, Andrea B. said:

I have this for the KolariU: 365FWHM40. 50% transmission at peak. Half-max 340-380 nm. Min OD 3.5. Ave OD 4.3.

 

Given that the KU is an absorptive filter, then there are only a few possibilities for its substrate - something equivalent to (or maybe equal to) U-330, U-340 or U-360. Given the peak at 365 nm, I would reasonably surmise the U-360 equivalency. And there is probably a blue-green cemented layer to provide the IR blocking and cause the low transmission rate. Given the reasonable price of (US)$199, I am going to guess that the substrate is one of the Chinese ZWB types, but I do not know for sure.

 

"Min OD 3.5" was considered as a pretty good IR-blocking, four years ago. No we know better and prefer one magnitude more to say pretty good IR-blocking.

 

The low transmission in the graph from Kolari might be not so bad if the graph is showing the full transmission including surface losses.

Many manufacturers of UV-pass filters hav graphs showing the internal transmission only.

 

The thickness of the filter stack would be valuable to get a better guess of what materials used in this filter.

 

When I measure thickness of delicate glass, disks I normally cover the measuring surfaces on the micrometer tool with tape, that then is cleaned with alcohol, before I measure the thickness of the stack.

Maybe someone owning a KolariU could measure how thick the glass stack is?  

[Doug A]

7 hours ago, lukaszgryglicki said:

My Kolari has front thread - I've put UV filter there (by "UV" I mean cheapest protection one - it is not blocking any UV as 99% of UV filters).

 

Strange. The Kolari I'm looking at says only 1 side is threaded. https://kolarivision.com/product/uv-bandpass-lens-filter/

 

Thanks,

Doug A

[Andy Perrin]

There was also that “bad batch” of KolariU filters floating around for sale still, so you don’t know until you get one whether it works okay. (Andrea, related to that, I think you are right about the substrate…)

[lukaszgryglicki]

14 hours ago, Doug A said:

Strange. The Kolari I'm looking at says only 1 side is threaded. https://kolarivision.com/product/uv-bandpass-lens-filter/

 

Thanks,

Doug A

I bought it from Kolari website, not from eBay etc. Double checke dnow - it has thread, but I would say very very short - not all my protective filtrs can be screwed-in. The one I use as protection makes only about half of single turn (say 180 degrees) but it is enough for it to fit.

[Andy Perrin]

The bad batch was sold directly by Kolari (and they even switched filters for people who complained afterwards, the problem was with quality control, not customer support thankfully).

[lukaszgryglicki]

Yes, I know about this "bad batch" - I was lucky not to get a filter from that batch.