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RMallon
2002-Nov-06, 01:07 AM
Hello all,

I just bought a second hand Celestron 8" Star Hopper Dobsonian. It looks brand new, just one or two little hickies on the tube. Other than that it looks like the scope has sat unprotected, up-right in a back room for a long, long time collecting tons of dust.

Needless to say the primary and everything else looks like a major league dust bunny with a fuzzy mask on.

I've removed all gear from the tube, i.e. the primary with its mount, eyepiece mechanism along with the secondary mirror and have set aside. Used a rag on the inside and outside of the tube.

What's a good cleaning procedure with the first surface mirrors? And too on the dobsonian mount, do the small teflon pads need anything like silicone or wax?

Thanks for any tips or direction,
Randy
Austin, Texas

<font size=-1>[ This Message was edited by: RMallon on 2002-11-05 20:09 ]</font>

aurorae
2002-Nov-06, 01:50 AM
What's a good cleaning procedure with the first surface mirrors? And too on the dobsonian mount, do the small teflon pads need anything like silicone or wax?


On the mirrors, only clean them if they really really need it, as some dust won't hurt anything.

You can find instructions for cleaning mirrors in books like StarWare or Backyard Astronomer's Guide.

First, I get some surgical cotton, distilled water, and a clean spritzer bottle.

The technique is to first rinse the mirror with distilled water (spritz it down good, get the big chunks of dust off), then pour some distilled water (with no more than 1 drop of dishwashing liquid) on the mirror, and use the surgical cotton to lightly (apply no pressure, just let the weight of the cotton do the work) swirl from the center of the mirror out. Frequently turn and replace the cotton.

Finally, rinse with distilled water. Rinse thoroughly. Any water remaining can be left to dry, or can be sopped up with a corner of the surgical cotton.

I usually clean the mirror while it is still on the mount, but if you take the mirror off, a good idea would be to support the mirror in a sink with a lot of towels (to cushion it against any shock or accidently dropping it).

Finally, as to lube for the Dob's alt and az bearings, don't apply anything unless it is needed. I have used a good silicone based car wax (like turtle wax) to good affect. Usually, teflon on ebony star formica makes a good motion with no "sticktion" and won't need any extra lubrication.

David Hall
2002-Nov-06, 05:08 PM
A quick google search brings up quite a few hits on mirror cleaning, such as this one:

http://members.aol.com/bemusabord/cleaning.html

RMallon
2002-Nov-06, 10:22 PM
Thanks for the write up and the link.
After cleaning the primary lense I held it up to a bright light to look thru the back side. Saw a few hundred pinholes of light coming thru the backside. Guess a bit of this is normal breakdown of mirror's reflective coating. Imagine after a length of time it'll be due for a fresh mirror coating.

Brought out the scope last night for its 'first' light. Saturn was on a low rise in the east about 10pm. Nice viewing with the 24mm eyepiece that the scope came with. Wonder what other sizes I should buy? I do have a 4mm along with a Barlow lense with the old 6" Newtonian I have. The 4mm really ups the magnification but sure is a loss of sharpness. Get what you pay for I guess.

Need to rig up my Coolpix 990 on it too and attempt some astro shots.

aurorae
2002-Nov-07, 09:13 PM
On 2002-11-06 17:22, RMallon wrote:
Thanks for the write up and the link.
After cleaning the primary lense I held it up to a bright light to look thru the back side. Saw a few hundred pinholes of light coming thru the backside. Guess a bit of this is normal breakdown of mirror's reflective coating. Imagine after a length of time it'll be due for a fresh mirror coating.


Yes, you are right. Eventually, the mirror will need to be recoated.

As to eyepieces, it depends on how much money you have. /phpBB/images/smiles/icon_smile.gif

As to loss of sharpness with the 4mm eyepiece, the seeing on any particular evening (or even minute by minute) as well as the quality of the optics limits the amount of magnification you can get without significant loss of sharpness.

RMallon
2002-Nov-08, 02:19 AM
Rigged up a crude eyepiece adaptor and tried a few shots with my digital camera this evening just about an hour ago.
Top one is with a bit of camera optical zoom and sharpening. Second and third is with a bit of Barlow power.
Eyepiece is a Celestron 25mm. Sure beats the old binoculars. May try a shot or two of Saturn later on this evening.
http://home.austin.rr.com/rmallon/DSCN3952.jpg
http://home.austin.rr.com/rmallon/DSCN3913.jpg
http://home.austin.rr.com/rmallon/DSCN3911a.JPG

<font size=-1>[ This Message was edited by: RMallon on 2002-11-07 21:25 ]</font>

Charlie in Dayton
2002-Nov-08, 07:40 AM
Excellent photography! Am considering same eventually after upgrading scope. Details on that camera and its settings please. Still gonna have to get one with a time exposure setting of some sort...those cheapo cameras at walgreen's won't hang open like needed.

Again, great work! Post those Saturn shots soon!

RMallon
2002-Nov-08, 12:25 PM
I used my Nikon Coolpix 990. It's a 3.3 megpixel.
The local camera store wanted 120 bucks for a little lense adaptor and a t-adaptor. Skipped on that expense for now and made my own for about 5 bucks. Used a plastic medicine bottle along with a bit of corrective surgery.
Tried a few shots of Saturn. Posting will have to wait a day or two.
Here's a run down of the settings for the above shots......
<center>http://home.austin.rr.com/rmallon/a1.gif<center>
<center>http://home.austin.rr.com/rmallon/a2.gif<center>
<center>http://home.austin.rr.com/rmallon/a3.gif<center>

Timm
2002-Nov-08, 02:38 PM
Great Pictures...

Post Saturn!

Russ
2002-Nov-08, 07:53 PM
RMallon:

You've gotten some good suggestions about cleaning your mirror, but... I thought you could use an additional tip or two. /phpBB/images/smiles/icon_wink.gif

1) Spraying the mirror with distilled water: The idea is to float the dust & whatever, off the surface to avoid scratching the finish. This will take LOTS of distilled water. DO NOT try to rub or otherwise use mechanical force on the surface.

2) If the surface still needs cleaning, eg. has grease or similar gunk on it, repeat the above process with PURE denatured alcohal. Again the idea is to float the gunk off if possible.

3) If there is still stuff on the surface, then and only then, get out the surgical cotton. Flood the surface with PURE denatured alcohol then use the cotton. The technique is to start at the center of the mirror and take ONE swipe straight out the the edge. DO NOT push down on the cotton. Discard the piece of cotton and get a new, clean piece and repeat. The pattern should be like spokes on the mirror. You should not see anything but clean mirror after each swipe. Again you are trying to float the gunk off not scrub it off.

The reason for all of this ritual is to avoid scratching the aluminum coating on the glass. Which is very easy to do, by the way. Do not clean the mirror any more than absolutely necessary. If you keep the tube properly dust protected, once every 3 or 4 years should be plenty. Good Luck. /phpBB/images/smiles/icon_biggrin.gif

RMallon
2002-Nov-09, 02:55 PM
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<BODY>Had fairly clear skies last night other than the usual Austin humidity
hanging in the air. The wind was buffeting the telescope so it was difficult to get a steady shot of anything.
I had driven out a bit to a new neigborhood addition, paved streets with no houses. Was pleasantly surprised to see another party of three stargazers present. I joined them for about an hour. They were using a 8" Schmidt Cassegrain with a lot of nice bells and whistles.


http://home.austin.rr.com/rmallon/DSCN4098a.jpg
After Jupiter began its climb after midnight, I "attempted" a few shots. As you can see I'm needing to invest in a better quality Barlow lens and other eyepieces. Of course the distance has a bit to do with it too, being apx,...483m miles away. The three little gray smudges are moons. Again, I removed the hot pixels and sharpened both photos a little.

When on site it's hard to see digital photo playback results on the camera's dinky LCD viewing screen. May try connecting the camera with a USB cable to a laptop for onsite playback. (speed up that instant gratification /phpBB/images/smiles/icon_smile.gif



http://home.austin.rr.com/rmallon/DSCN4088a.jpg
The Saturn photo faired a bit better here. 770m miles distant. Digital pixeling is a bit of a problem. When removing excess noise I may have removed some of the background exposure.

<font size=-1>[ This Message was edited by: RMallon on 2002-11-09 09:57 ]</font>