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[NOT GOOD for UV] Sigma 24-105mm f/4

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#1 Bernard Foot

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Posted 07 April 2021 - 10:21

Here is a simple test of how the Sigma 24-105mm f/4 (full-frame lens) works with a Baader U. The two images are WBed as for a Focotar-2: I was not able to do a custom WB for the Sigma shot using RawTherapee as RawTherape was reporting no green channel.

The shot using the Sigma required about 6x the exposure for the Focotar-2.

Sigma 24-105mm:
Attached Image: Sigma 24-105 at 50 Baader WB for Focotar LoRes.jpg

Focotar-2:
Attached Image: Focotar Baader (1) WB for Focotar LoRes.jpg

The diference is obvious. The Sigma shot is much more monochromatic indicating that it is passing only a part of the UV range that the Focotar-2 passes.

So I would conclude that the Sigma 24-105mm is not really suitable for UV photography. (No surprise there!)
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#2 Andrea B.

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Posted 07 April 2021 - 19:15

Given that this is not a technical assessment of or transmission chart for the Sigma 24-105/4, then this topic should be placed elsewhere.
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#3 Bernard Foot

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Posted 07 April 2021 - 20:07

View PostAndrea B., on 07 April 2021 - 19:15, said:

Given that this is not a technical assessment of or transmission chart for the Sigma 24-105/4, then this topic should be placed elsewhere.

Suggestions?
Bernard Foot

#4 Stefano

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Posted 07 April 2021 - 20:30

The section that matches more to me is "Techniques, Tests & Gear". We don't have a "non-technical lens tests" section (do we need it)?

#5 Bernard Foot

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Posted 07 April 2021 - 20:40

View PostStefano, on 07 April 2021 - 20:30, said:

The section that matches more to me is "Techniques, Tests & Gear". We don't have a "non-technical lens tests" section (do we need it)?

Yes, that's probably the only other place to put it. But if people are looking for info. on lenses they'll go to UV Lens Technical Data, so I think all information about lenses should be in there. Perhaps we need a new section there.
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#6 Andrea B.

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Posted 08 April 2021 - 05:56

The thing is -- we already know that modern complex, multi-coated lenses mostly do not make the cut for reflected UV photography. We've known that for years. So why give such lenses any page space at all? In this technical section I want to see transmission charts and assessments of lens quality only for reasonably UV-capable lenses. If you start trying to list all the lenses not good for UV, then you will have hundreds (thousands?).
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#7 Bernard Foot

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Posted 08 April 2021 - 13:03

View PostAndrea B., on 08 April 2021 - 05:56, said:

The thing is -- we already know that modern complex, multi-coated lenses mostly do not make the cut for reflected UV photography. We've known that for years. So why give such lenses any page space at all? In this technical section I want to see transmission charts and assessments of lens quality only for reasonably UV-capable lenses. If you start trying to list all the lenses not good for UV, then you will have hundreds (thousands?).

OK - well just delete it then. I don't seem to have that option. We'll assume that all other members can somehow absorb the knowledge that you and a few other members have without it being mentioned anywhere. Heaen forbid that a few kilobytes should be wasted on setting down something that you already know.
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#8 UlfW

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Posted 08 April 2021 - 13:59

I think there might be a value of keeping information about lenses like this, tested, but not good for UV, as reference when someone wonder.
A negative result is also a result.
Sometimes there are modern lenses with modern coatings that in a limited way work for UV, like my Sunex SuperFisheye.
With some luck we might discover others even if I think they will mostly be primes and not complicated zooms.

The information would then fit well in a new subsection here.
If the storage space is a problem the images could be shrunk.
-
The information needed in such posts could just a Bernhard posted here be the difference i exposure time and some images, separately WB-ed for each lens.
The post above use the same WB from the Focotar. That blue colour gives a hint of the difference by the colour
A third WB for the zoom itself would give a hint of how much less colours an UV-bad lens gives.
I expect the big difference here with this type of scene would be the long exposure time, but also much less variation in the colours.

Edited by UlfW, 08 April 2021 - 14:05.

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#9 nfoto

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Posted 08 April 2021 - 14:29

I think we should reconsider the null hypothesis here. Let us assume any lens is bad for UV, then report only on those which prove useful in some way or other. We likely will end up with more useful information that isn't swamped by data noise in this manner.

#10 Andy Perrin

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Posted 08 April 2021 - 15:20

I’m fine with this being in the Techniques, Tests, and Gear section but I agree that we shouldn’t put it in the section devoted to lens tests of ones that are meant to work well. I vote move the post.

#11 Andrea B.

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Posted 08 April 2021 - 18:26

Andrea: The thing is -- we already know that modern complex, multi-coated lenses mostly do not make the cut for reflected UV photography. We've known that for years. So why give such lenses any page space at all?

Birna: Let us assume any lens is bad for UV, then report only on those which prove useful in some way or other. We likely will end up with more useful information that isn't swamped by data noise in this manner.

I am going to move the two posts.

But here is what I suggest.

Use a title prefix of [NOT GOOD for UV] or [BAD for UV]. This will highlight the main point and also show up in a Lens Tag search which produces topic titles.
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#12 Bernard Foot

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Posted 09 April 2021 - 09:07

View PostAndrea B., on 08 April 2021 - 18:26, said:


Birna: Let us assume any lens is bad for UV, then report only on those which prove useful in some way or other. We likely will end up with more useful information that isn't swamped by data noise in this manner.

I am going to move the two posts.

But here is what I suggest.

Use a title prefix of [NOT GOOD for UV] or [BAD for UV]. This will highlight the main point and also show up in a Lens Tag search which produces topic titles.


That makes sense - but I'll probably adopt Birna's approach for ther future (not that I have any more lenses to try out).
Bernard Foot

#13 nfoto

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Posted 09 April 2021 - 09:25

I have heaps and heaps of lenses and easily could flood UVP with negative comments regarding their UV performance. Which frankly is a temptation I can resist.

#14 UlfW

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Posted 09 April 2021 - 10:06

All of what you say makes sense and I agree that the null hypothesis is a good idea.

I think a simple summary of the difficulties with modern lenses could be good to have.
We might place it in an easy to find location with a good topic name to help new people understand better.

This is my first attempt for such a text:


There are a few main things that limit UV-transmission.
  • Advanced AR coating attenuates UV, if it is not designed specifically for a good UV transmission.
  • Each lens surface count. Many AR-coated lens surfaces add up and give more attenuation.
  • Many types of modern optical glass has also bad UV-transmission.
  • The transmission is attenuated more if the glass passed is thick.
There are very few modern lenses that are even limitedly usable for UV-photography.
Lenses, if not specially designed for UV, should have a simple optical design, with few elements or groups and lenses should not be thick and should not have advanced AR coatings.

Please feel free to use it or improve it.

Edited by UlfW, 09 April 2021 - 10:07.

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#15 StephanN

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Posted 09 April 2021 - 11:53

As a newby one of the first data I would like to have whether my lenses work for UV, next being the info which other lenses work.

Ulf's suggestion of a summary is good, so why not make this similar to the sticky list, just call it "lenses crappy for uv" or something simular.

This could avoid uvites repeating tests which other people have performed already, like in the recent thread about the Samyang 14. I've tested my version long ago, but never bothered to post it here, since it was the expected result that it's a crappy lens for UV.

Certainly the same is true for almost everybody around here, and searching through hundreds of topics starting with "lens not good for uv" just to find the few ones which say "yabbadabbadooo, found a lens which is not crappy for uv" may seem a bit of a waste of time.

Just my 2c
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#16 UlfW

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Posted 09 April 2021 - 12:40

View PostStephanN, on 09 April 2021 - 11:53, said:

" just to find the few ones which say "yabbadabbadooo,"
https://www.youtube....h?v=GPjp84cjEXM
The lenses do not have to be that old to be UV-capable :grin:

Edited by UlfW, 09 April 2021 - 12:41.

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#17 Andrea B.

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Posted 09 April 2021 - 20:55

I think a simple summary of the difficulties with modern lenses could be good to have.
We might place it in an easy to find location with a good topic name to help new people understand better.


The Lens Sticky has contained such information for years now.
I can always rewrite info in that Sticky to improve it.



For now, No, we are not going to have a Bad-for-UV lens list.
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#18 StephanN

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Posted 10 April 2021 - 07:50

View PostAndrea B., on 09 April 2021 - 20:55, said:



For now, No, we are not going to have a Bad-for-UV lens list.

If the sticky-text is updated a bit, and people read it :grin: (myself haven't read it in months, tbh), there's no ned for the baddie-list
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#19 UlfW

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Posted 10 April 2021 - 08:49

View PostAndrea B., on 09 April 2021 - 20:55, said:


The Lens Sticky has contained such information for years now.
I can always rewrite info in that Sticky to improve it.

Well informed members likely have read that.
The information might be even more easy to find if it was in a separate topic with a suitable name, placed by the Lens sticky.
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