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xaprb
Joined: 28 Jan 2021 Posts: 171
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Posted: Fri Apr 26, 2024 1:22 am Post subject: Improving Mirror Lens Contrast |
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xaprb wrote:
Here is an article on a way to reduce stray light in catadioptrics and reflecting telescopes, which improves contrast markedly.
https://retrofocal.com/articles/improving-mirror-lens-image-quality/
The synopsis is that mirror lenses and reflecting telescopes show the sensor a reflection of itself, which hazes the image, but the spot that forms that reflection doesn’t participate in making the image, so it can be blackened. |
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Alun Thomas
Joined: 20 Aug 2018 Posts: 655 Location: New Zealand
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Posted: Fri Apr 26, 2024 5:09 am Post subject: |
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Alun Thomas wrote:
An amazingly simple idea, it is surprising it hasn't been addressed by designers. It would seem that the effectiveness of the manufacturers sensor coatings would also be a factor. However, as noted, the best idea could be that shown in the link. |
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RokkorDoctor
Joined: 27 Nov 2021 Posts: 1419 Location: Kent, UK
Expire: 2025-05-01
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Posted: Fri Apr 26, 2024 8:56 am Post subject: |
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RokkorDoctor wrote:
Interesting concept.
Almost seems too obvious to be true; given that some mirror lenses already contain internal baffles and cones to block stray light and reflections, one would have thought something as simple/obvious as this would not have been overlooked. But then that sometimes does happen.
Also, reflection of film was less of a problem than digital sensor reflections are, so maybe it wasn't considered as much of a problem then. _________________ Mark
SONY A7S, A7RII + dust-sealed modded Novoflex/Fotodiox/Rayqual MD-NEX adapters
Minolta SR-1, SRT-101/303, XD7/XD11, XGM, X700
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connloyalist
Joined: 22 Jul 2020 Posts: 345 Location: the Netherlands
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Posted: Fri Apr 26, 2024 9:24 am Post subject: |
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connloyalist wrote:
Very interesting!
Regards, C. |
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Himself
Joined: 01 Mar 2007 Posts: 3244 Location: Montreal
Expire: 2013-05-30
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Posted: Fri Apr 26, 2024 11:00 am Post subject: |
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Himself wrote:
Anyone with a mirror eager to give it a try?
I don't have one but I'm curious. _________________ Moderator Himself |
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connloyalist
Joined: 22 Jul 2020 Posts: 345 Location: the Netherlands
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Posted: Fri Apr 26, 2024 11:31 am Post subject: |
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connloyalist wrote:
Himself wrote: |
Anyone with a mirror eager to give it a try?
I don't have one but I'm curious. |
Eager, yes. But sufficiently confident of my skills, no.
Regards, C. |
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marcusBMG
Joined: 07 Dec 2012 Posts: 1316 Location: Conwy N Wales
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Posted: Fri Apr 26, 2024 5:04 pm Post subject: |
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marcusBMG wrote:
Very detailed article, I am interested to try this out, I have more than one tamron 500mm so can compare.
It's a bit curious as to who wrote this piece, the webpage/website has no info.... _________________ pentax ME super (retired)
Pentax K3-ii; pentax K-S2; Samsung NX 20; Lumix G1 + adapters;
Adaptall collection (proliferating!) inc 200-500mm 31A, 300mm f2.8, 400mm f4.
Primes: takumar 55mm; smc 28mm, 50mm; kino/komine 28mm f2's, helios 58mm, Tamron Nestar 400mm, novoflex 400mm, Vivitar 135mm close focus, 105mm macro; Jupiter 11A; CZJ 135mm.
A classic zoom or two: VS1 (komine), Kiron Zoomlock... |
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Ernst Dinkla
Joined: 30 Nov 2016 Posts: 408
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Posted: Sat Apr 27, 2024 9:05 am Post subject: |
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Ernst Dinkla wrote:
RokkorDoctor wrote: |
Also, reflection of film was less of a problem than digital sensor reflections are, so maybe it wasn't considered as much of a problem then. |
Still there is a way longer period of mirror lenses used with film, on a variety of tasks and with film emulsions that have different reflection values. Possibly the film reflection was less visible while more uniformily spread than the hot spot reflection of a sensor is. Anyway contrast loss would still be measurable. Maybe a lower T-stop number had better marketing value than enhanced contrast.
Digital sensors were already used in astronomy before the general photography sector could buy them. Mirror lenses more common there.
All together it is a mystery why nothing on this subject has been published before.
I do hope the writer archived a list of his disc measurements for the popular mirror lenses
he tweaked. I guess with a 3D printer at hand it would even be possible to make the proposed cones to fill in the voids between the light paths. Black 3.0 painted for low reflection. _________________ Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
March 2017 update, 750+ inkjet media white spectral plots |
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jamaeolus
Joined: 19 Mar 2014 Posts: 2965 Location: Eugene
Expire: 2015-08-20
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Posted: Sun Apr 28, 2024 4:25 am Post subject: |
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jamaeolus wrote:
Fascinating. I have a cheap Tokina I might try this with. _________________ photos are moments frozen in time |
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xaprb
Joined: 28 Jan 2021 Posts: 171
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Posted: Mon Apr 29, 2024 12:03 am Post subject: |
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xaprb wrote:
Regarding film's differing reflectivities, I thought the same thing about film. But I was reading an article about Maitani's design process for the OM-1, which metered off-the-film. If I recall correctly, in the interview he stated that he got samples of every film stock available on the market, and metered off them, and found them all within 10% of each other, validating that off-the-film metering would work OK. Then he went ahead and designed the system and it worked well. There weren't very many cameras that metered off the film, but the ones that did (several of the OM, as I recall, as well as the Minolta CLE) metered quite well. So maybe film stocks aren't as different as one would think? |
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Ernst Dinkla
Joined: 30 Nov 2016 Posts: 408
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Posted: Mon Apr 29, 2024 7:19 am Post subject: |
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Ernst Dinkla wrote:
xaprb wrote: |
Regarding film's differing reflectivities, I thought the same thing about film. But I was reading an article about Maitani's design process for the OM-1, which metered off-the-film. If I recall correctly, in the interview he stated that he got samples of every film stock available on the market, and metered off them, and found them all within 10% of each other, validating that off-the-film metering would work OK. Then he went ahead and designed the system and it worked well. There weren't very many cameras that metered off the film, but the ones that did (several of the OM, as I recall, as well as the Minolta CLE) metered quite well. So maybe film stocks aren't as different as one would think? |
That the OM system worked is already an indication film reflected a measurable amount of light. I was thinking whether the film emulsions gloss differences could shift the reflection between diffuse to more directed light. _________________ Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
March 2017 update, 750+ inkjet media white spectral plots |
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Slalom
Joined: 10 Dec 2017 Posts: 158 Location: Stourbridge
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Posted: Mon Apr 29, 2024 8:28 am Post subject: |
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Slalom wrote:
I have an OM2N and it has two sensors at the bottom of the mirror box, only effects exposure when film is fully visible and static.
Now thinking it through, it is getting difused light at the bottom of the box, So reflections are also difused. Less trouble forthe unused bit of the mirror. |
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kds315*
Joined: 12 Mar 2008 Posts: 16651 Location: Weinheim, Germany
Expire: 2021-03-09
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Posted: Tue Apr 30, 2024 11:14 am Post subject: |
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kds315* wrote:
Interesting as I have quite a few such lenses and some do have lower contrast...
_________________ Klaus - Admin
"S'il vient a point, me souviendra" [Thomas Bohier (1460-1523)]
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Lomo Уфар-12 f2.5/41mm
Lomo Зуфар-2 f4.0/350mm
Lomo ZIKAR-1A f1.2/100mm
Nikon UV Nikkor f4.5/105mm
Zeiss UV-Sonnar f4.3/105mm
CERCO UV-VIS-NIR f1.8/45mm
CERCO UV-VIS-NIR f4.1/94mm
CERCO UV-VIS-NIR f2.8/100mm
Steinheil Quarzobjektiv f1.8/50mm
Pentax Quartz Takumar f3.5/85mm
Carl Zeiss Jena UV-Objektiv f4/60mm
NYE OPTICAL Lyman-Alpha II f1.1/90mm
NYE OPTICAL Lyman-Alpha I f2.8/200mm
COASTAL OPTICS f4/60mm UV-VIS-IR Apo
COASTAL OPTICS f4.5/105mm UV-Micro-Apo
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stevemark
Joined: 29 Apr 2011 Posts: 3977 Location: Switzerland
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Posted: Wed May 08, 2024 9:15 pm Post subject: |
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stevemark wrote:
Interesting information - thanks for sharing.
There's also another problem adding to the low contrast of certain reflex lenses (in fact most of the well known 8/500mm lenses!) - see Fig. 2 & 3 in Nikkor Tale 13:
https://imaging.nikon.com/imaging/information/story/0013/
Nikons 2nd gen reflex 8/500mm lens has a much better central contrast compared to e. g. the Minolta MD 8/500mm RF lens indeed.
S _________________ www.artaphot.ch |
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