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Sensor reflection
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PostPosted: Sat Apr 27, 2019 1:06 pm    Post subject: Sensor reflection Reply with quote

Hi. Sometimes i´ve had sensor reflections when using my Auto Sears 55mm F1,4 M42 lens (and Sony A7 RII Camera). I tested to fix this with painting matte black paint on the back lens element. (se picture red marking). It seems to work but i have to do some more photo shooting. Have anybody tried anything similar ? I tried some black marker felt pen at first but the matte black paint seems to work better. Maybe other similar (Tomioka??) lenses have another solution for the back lens that avoid sense reflections ?
#1


PostPosted: Sat Apr 27, 2019 2:01 pm    Post subject: Reply with quote

I've never heard of this type of fixing before. I've heard of adapter issues, which could be fixed flocking the inner part of it, or sensor reflections, that's got to do with the sensor filters. Painting the thread on cold on top of anodized thread,sooner or later (sooner) will make loose the paint inside the sensor compartment, that's why I don't see it.


PostPosted: Sat Apr 27, 2019 4:18 pm    Post subject: Reply with quote

I painted my sensor black instead. Works like a charm :p


PostPosted: Sat Apr 27, 2019 4:19 pm    Post subject: Reply with quote

Sensor reflections are usually caused by flat rear elements that directly reflect light that has already bounced off the sensor back onto the sensor, i.e. it is essentially two parallel flat mirrors facing each other and (some of) the light bounces back and forth. Aperture blades that are a bit too reflective on the rear side can also be problematic.


PostPosted: Sat Apr 27, 2019 6:20 pm    Post subject: Reply with quote

D1N0 wrote:
I painted my sensor black instead. Works like a charm :p


Well, that is supposed to be the last solution, isn't it?


PostPosted: Sat Apr 27, 2019 7:51 pm    Post subject: Reply with quote

I will test if it works on similar shots that have ben problematic and se if it works.


PostPosted: Sat Apr 27, 2019 8:05 pm    Post subject: Reply with quote

I have other lenses with flat rear element, Auto Chinon multi coated 55mm F1,4 M42, Auto Chinon 55mm F1,4 M42 (Tomioka) , Auto Mamiya Sekor 55mm F1,4 M42, no problem with sensor reflections on them.


PostPosted: Sat Apr 27, 2019 9:44 pm    Post subject: Reply with quote

Maybe these last one's got better coatings on the inside lenses which prevents sensor reflections?


PostPosted: Sat Apr 27, 2019 11:04 pm    Post subject: Reply with quote

There was a report here someplace about a conversation with Tamron at trade show saying the rear element of 90mm 52B, 52BB, is not coated, hence the reflective hot spot in center of frame due to reflections from elements inside the lens on the sensor/film. Reducing aperture size makes reflection worse, which should be a clue to cause.


PostPosted: Sun Apr 28, 2019 2:43 am    Post subject: Re: Sensor reflection Reply with quote

Not sure how similar these are but I have a 50mm f1.4 Sears EE in M42 all metal. It has 6 blades painted black and does a ninja star for one of them. Seems pretty dark inside, no itis. Rear element convex mostly purple coating with some yellow. Front element I see more yellow and some purple.

From the photo your rear element appear to have a similar coating.

It needed a pin to be hot glued, but the M42 mount doesn't leave much for reflection once it is screwed in. Not that I have seen.

What exactly does sensor reflection look like?

If you post a sample I can test on APS-C a6300 or a6000 and look for the same.


PostPosted: Sun Apr 28, 2019 3:23 am    Post subject: Reply with quote

Chardin wrote:
I have other lenses with flat rear element, Auto Chinon multi coated 55mm F1,4 M42, Auto Chinon 55mm F1,4 M42 (Tomioka) , Auto Mamiya Sekor 55mm F1,4 M42, no problem with sensor reflections on them.
I have a couple of Mayima/Sekor 55/1.4s -- they both get aperture shaped hotspots when stopped down.


PostPosted: Sun Apr 28, 2019 3:53 am    Post subject: Reply with quote

It look something like this, in the center of the picture the dark area are a bit lighter.
#1


PostPosted: Sun Apr 28, 2019 11:31 am    Post subject: Reply with quote

I'm not seeing it...


PostPosted: Sun Apr 28, 2019 12:56 pm    Post subject: Reply with quote

I see it in the middle of the brown structure. Brighter and a bit purple, washed out.


PostPosted: Sun Apr 28, 2019 1:56 pm    Post subject: Reply with quote

Chardin wrote:
It look something like this, in the center of the picture the dark area are a bit lighter.


All I can tell is that it is stopped down a lot. You are not using a camera converted for IR, right?

Is this supposed to be a crop? The image size is 1250x434.

BTW, when do the spring flowers bloom in Sweden?


PostPosted: Tue Apr 30, 2019 8:28 pm    Post subject: Reply with quote

The Camera are Sony A7RII. The picture are cropped from full frame pic.
The flowers are in bloom right now, its going too fast.


PostPosted: Tue Apr 30, 2019 9:01 pm    Post subject: Reply with quote

Chardin wrote:
The Camera are Sony A7RII. The picture are cropped from full frame pic.
The flowers are in bloom right now, its going too fast.


I still can't see it enough that it would catch my attention. Maybe you were wearing a white t-shirt which caused some reflection of light against the foreground subject.

One thing I did was to add flocking tape to the contact pins inside the camera sensor box. I noticed they were still exposed when the manual focus adapters were attached.

I can't comment on how diffraction would play into this. What others have been saying about hot spots when stopping down; I thought that was related to IR photography and specific AR coatings. I have never noticed this phenomenon.

I also can't say how the possibility of oily aperture blades would increase internal light transmission as it is stopped down. I assume yours is oil free.


Regards


PostPosted: Wed May 01, 2019 8:40 am    Post subject: Reply with quote

To be honest, I can't see a problem here either.
The change is almost imperceptible, and you would get more significant brightness distribution delta when boosting local contrast.
Which is, again, a non-issue.


PostPosted: Wed May 01, 2019 6:15 pm    Post subject: Reply with quote

Blazer0ne wrote:
...Maybe you were wearing a white t-shirt which caused some reflection of light against the foreground subject...


Astute observation imho!!!

The principle behind recent cameras which see around corners & through objects; in-frame light reflected from out of frame objects.

In this case like assistant holding reflector light onto subject. Could this be cause?


PostPosted: Sun May 12, 2019 11:51 pm    Post subject: Reply with quote

A rectangular baffle eliminates stray light from hitting the sensor, and further reduces reflected light from hitting the lens, and then reduces re-reflected light from hitting the sensor again. A baffle will cut down ~40% of the total light paths, so I'd guess it would reduce the re-reflected light significantly, maybe by as much as 78%