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my war with stray light - 3D printed baffles everywhere

 
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nathanm



Joined: 02 Jun 2016
Posts: 222
Location: Bellevue, WA

PostPosted: Fri Aug 26, 2016 7:02 pm    Post subject: my war with stray light - 3D printed baffles everywhere Reply with quote

I recently put together a new macro system http://www.photomacrography.net/forum/viewtopic.php?t=31197, and unfortunately was met with some serious stray light problems.

Initially what I was a faint hint of structure in the shadow areas. Then I started taking exposures of a black, or mostly black field. I got things like this



or



These are with different lenses.

Needless to say this was disappointing. I did a careful analysis and discovered that there were multiple sources of the problem. The key issue was that the camera was attached to the bellows system by a Mamiya bellows adapter, and that adapter plus the camera itself were the source of the four spots of light. So I set out to eliminate that, and other sources of stray light.

Around that time longtime forum member elf had a post on 3D printing lens hoods
http://www.photomacrography.net/forum/viewtopic.php?t=31316&highlight=baffling+affair. So I designed a set of lens hoods for my macro lenses that used the "3 bounce principle" - the baffles are spaced so that any stray light must bounce at least 3 times before it hits the sensor. A normal lens hood has just one bounce. This vastly improves the stray light suppression. Here are some of my hoods.



The one at the back that is just a cylinder is an internal baffle that goes between the tube lens and camera in this Mitutoyo system that I put together
http://www.photomacrography.net/forum/viewtopic.php?t=31604

I also made a baffle for the camera adapter side - the bayonet connection to the camera is handled by a RAF Camera adapter - the 3D printed baffles sit inside it to mask the offending parts of the camera flange throat that were giving problems with the Mamiya bellows adapter.

The good news is that it all works! The annoying flare is totally gone. The decisive part was the camera adapter, but the hoods won't hurt under some lighting situations.

I offer all of this in case other people on the forum have stray light problems...


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