Burgess/TMB fix - for Mike Hosea

Mike,

How did you fix the glare in your Burgess/TMB eyepeice(s)? Could you please post some pictures?

Dmitri

I'm not sure it is totally fixed on the 9mm.

On the 4mm I installed Protostar flocked paper on the inside of the black barrel. This wasn't enough because most of the problem is due to the retaining ring on the field group. It may not help much, but it can't hurt. Note that there is a lip several mm wide at the bottom (it's hard to see). You just want to install the flocked paper above the lip where the barrel has uniform ID. The lip fits down beside the field group cell when the barrel is installed and has no access to light.

With the barrel removed and sitting flat on the table, I unscrewed the retaining ring on the field group and carefully set the barrel (now with loose optics) aside. Then I measured the ID and thickness of the ring, cut a strip of flocked papaer, and installed it. Some precision is needed here because the thickness of the paper may be enough to cause vignetting (just reduced brightness) as it is, and you don't want overlap or a gap. I used the conical end of a pencil to seat the paper properly with force from the inside. Then I reinstalled the retaining ring in the barrel, just snugging the retaining ring (no "tightening") and reinstalled the barrel.

Now I can't be sure if this is enough, either, because I also have a cardboard baffle on the outside from a previous (and only partially successful) attempt to fix the problem with baffles on the inside and outside. I can't remember the ID of the baffle (just a bit less than the diameter of the field lens clear aperture), but I just cut it from something like a cereal box, painted it flat black, and pushed it on the outside.

I call this "aggressive baffling" because I wasn't concerned about introducing vignetting at the edge of field, and I may have gotten a little. I've just had one evening with it for use on Mars, and I did not see any glare. The moon has not been available to me during an observing session since I performed these modifications, but when I hold the eyepiece up to a light bulb at arm's length and examine the exit pupil, it looks good, just a circle of light in a sea of black. Previously, the specular reflection off the retaining ring and other surfaces in the field group were almost as bright as the exit pupil itself.

I may be able to take some pictures tonight.

BTW, it's clear that the field lens retaining ring is most of the problem. If a suitable replacement is offered by Burgess, I suspect it will make a dramatic improvement.
--
Mike

Mike,

While we are at it, how do you compare the two? Does Nagler 9mm make Burgress 9mm redundant? (I think you've got both.)

Dmitri