I had some very wicked internal reflection problems. Here is what I have learned?
First, do you know about Actar Black? This is a very high tech flocking from Israel that is VERY black. It is expensive, but if you are going to pay almost as much for sticky black velvet, you might as well get good stuff.
I have used their "stray light control kits" which for $129 worked well for me.
https://www.acktar-store.com/store/stra ... kit-mv236/
I have no idea about UK customs but it got here to the US quickly and no customs issue.
However in my war on stray light I have gone further.
Your biggest enemy is actually the diameter of the tube you are using. M42 tubes are tiny, the Mitutoyo and the tube lenses have MUCH bigger image circles than you might think, and when you have a small diameter tube the reflections of light from the side of the tube occur at very shallow angles. Even Actar black has a trouble with this.
Increasing the diameter of your tube helps ENORMOUSLY. I found this out by doing ray tracing, but it is pretty obvious once you think about it.
Of course the little M42 tubes are convenient, so it's up to you. I switched to Thorlabs SM3 tubes - these happen to fit 72 mm x 0.75 filter threads, so it is not hard to use adapters to get to the larger diameter. I was able to do this without making custom parts with Raynox 150, 250, and Mitutoyo.
When I moved to PhaseOne from Canon, I abandoned tubes altogether and went to an aluminum square wall tube that is ~100 mm internal dimensions. That is convenient for the PhaseOne, and square tubing is easier to mount than circular, but I did have to make custom end caps.
Either SM3 or the 100mm square tube would be great with flocking - way better than M42 tubes with the same flocking.
However, I went overboard while I was at it. Inside the square tube, or the Thorlabs SM3 tubes I use 3D printed baffles that are designed to force light to bounce at least 3 times before hitting the sensor. Even a mediocre black plastic will absorb 90% of light. So one bounce is 0.1, and three bounces is (0.01)^3 or 0.00001, or 99.9999% absorptive. Baffle edges give some of that back, but not much. That is vastly better than you can do with any flocking. And it is pretty cheap - the baffles on my macro rig was like $60 to print at Shapeways. It is more trouble - I had to write the software to make the baffles.
Nathan
