Posts Made By: Doug Scobel

Since installing blow-across fans on my 13" Dob, I'm finding that I'm now blowing a lot of dust and dirt into the scope and onto the primary mirror. I'm looking to install some kind of simple, low restriction air filters to the outside of the two fan intakes (see picture). Ideally, I would be able to remove them for cleaning/replacement, by attaching them with Velcro.

Any suggestions?

Thanks,
Doug

Hopefully no hurricanes this year.

Doug

Here is an image of the huge sunspot group beginning to cross the sun's face. I took it this morning around 08:45 EDT. The large complex is active region (AR) 10808, the very small spot to its upper right is AR 10809. North is at the top.

I took the image afocally, using my Nikon Coolpix 800 digital camera, through my 8-inch f/8 Newtonian reflector with a 7-inch aperture Baader solar filter. The camera was mounted to a 14mm Tele Vue Radian eyepiece, and then digitally processed using Paint Shop Pro.

This spot is just starting to cross the solar disk, so get your solar filters out and take a look. It is impressive!

Doug

Does anyone have any polishing/figuring experience with so-called black rouge? It's a black form of iron oxide (as is red rouge). Got Grit sells it.

I'm about to embark on a refiguring project and I'm considering using it instead of Cerium Oxide. It's advertised to polish slower and produce a better polish than CeO2.

Is it worth a try?

Doug

How reasonable is it to expect to get every last bit of primary ripple out of a small, plate glass mirror?

I'm working on a 4" f/11 sphere, made of plate glass. I think it's an old mirror out of a Dynascope (I just have the mirror, not the scope) that exhibited a turned edge and some zones. I thought a refiguring was in order before making a grab-n-go planetary scope out of it. Getting a zoneless sphere has not been much of a problem, but getting rid of the last of the primary ripple has been difficult.

Using cerium oxide was a disaster - severe dog-biscuit - so now I'm using zirconium oxide. Much better, but still no cigar. I'm going about as slow as I can go, and as lightly as I can go, and maintaining good contact, but I just can't get rid of it all. My own guess is that the relatively fast speed of zirconium oxide combined with the high coefficient of expansion of plate glass just won't let me get it any smoother.

And how much primary ripple is too much? I know, a subjective question. It's quite noticeable under the Foucault test, using a moving-source slitless tester, which I would imagine to be quite sensitive. I'll try to get a picture of the mirror tonight and post it.

[edit] I've added an image. There are still some things to correct, such as a TDE of a couple millimeters, and a slight bump in the center (although it will be covered by the secondary). Those I know how to deal with, but the primary ripple is what I'm most concerned about.

Any thoughts?

Thanks,
Doug

Hi, all, I'm working on a 6" f/4.5 mirror. All polished out, attempting to figure.

The mirror has a large and deep central depression, roughly 3.5" in diameter. It's left over from an earlier attempt to parabolize with a too-hard lap (too much overhang, long strokes, hard lap, result - dug a deep hole). The outer zones are relatively flat.

What is the best way to eliminate it? Some books say stick with 1/3 diameter center over center strokes, with mirror on top, and eventually it will work itself out. Others say it's best to use a deformed lap, depressing the central facets using a circle of waxed paper a little smaller than the depression while pressing. I want to concentrate the action in the outer zones, but I don't want to create some other defect that will make matters worse, like turning the edge.

Any ideas?

Thanks,
Doug

Hi, Jim, I'm trying to come up with a design for plywood rotating rings for the 6" f/4.5 Newt I'm working on now, so I'm interested too. I need to mate it to a Vixen Great Polaris. Parallax rings look great but that much cash is out of the question for me. If/when I come up with something that works, I'll post.

Doug

I need to do some touch up work inside my scope (screw heads, etc.) and I'm wondering what you folks have found to be the flattest, blackest, best-covering brush-on paint. I've considered spraying some Krylon Ultra-Flat into a cap and then brushing it on, but I expect it would be a little thin and not cover real well. What do you all use?

Thanks,
Doug

I recently acquired a Meade Deep Sky Imager Pro (monochrome) with Autostar Suite and RGB/IR filter set (won it at the BFSP). I own a Vixen GP mount that has been hypertuned, but with just an RA drive, though it would be easy to add a dec drive. On the mount is a 6-inch f/4.5 Newtonian. I would like to attempt some deep sky imaging, starting with monochrome and eventually "graduating" to color. I have a couple questions borne of my ignorance regarding this camera:

Does one have to guide? IOW, can exposures be kept short enough to obviate the need for guiding?

Can I set it up to simply acquire images and use some other software to stack and align them?

If I do need to guide, then can Autostar be made to work with the Vixen drives?

Any and all advice is welcome.

Thanks,
Doug

I would like to hear other folks' results using the new 3.2mm Burgess/TMB planetary series eyepiece.

I finally got a chance to test mine last night in my 6" f/4.5 and I was quite disappointed. It has a lot of off-axis astigmatism. Only about the middle quarter or third of the FOV is what I would call sharp. Keep in mind I was using an f/4.5 scope, which puts extreme demands on eyepieces. But for example none of my Radians (I own three) exhibit this and are sharp all the way to the edge. Yes I know that Radians are more expensive but sharp is sharp.

So I'd like to hear others' experience using this eyepiece in either fast or slow scopes. My expectation is that it works much better at slower focal ratios.

Thanks,
Doug