Telescope Polishing- Update

Almost polished mirror

Almost polished mirror

As you can see, the mirror is polishing pretty good but it is taking a long time to do, they weren’t lying when they said rouge is really slow, not to mention incredibly messy.  The large grey mass is on the back of the mirror- I got careless during the 3rd grade of abrasive and accidently set the mirror down face up. See post (here). All of the scratches you see are on the backside of the mirror.  Also, after repeated “cold pressing” sessions, the mirror refuses to polish from the center to the edge.  I have heard of this before, and it usually causes a turned edge.


As you can see above, the area in the middle is not polished yet.  This is often hard to distinguish from the ground surface on the back, but at the right angle, I can see it.  I was lucky enough to capture it in the picture.

Unfortunately, the lap in the previous post was ruined by dropping it, I am reckless sometimes.  Then I made a new lap, and let it sit too long after pouring it and it hardened before I could put in the curve.  The next lap polished a lot and then, for some reason, the lap started to crack around the edges.  It eventually came off so now I have to make another lap.  The books don’t lie, polishing with rouge and pitch are not easy.


Up close with Rouge and the polishing process.

Polishing operation, as always covered with Rouge

Polishing operation, as always covered with Rouge


Focal Length Test

As I progress through building my telescope, it is important to know and understand the focal length, or distance where all of the light from the star forms into an actual image at one point.  There is a simple yet effective way to do this.  You don’t need much, but a checklist is helpful.

When I perform this test, I use:

a bucket  halfway full with clean water

a tape measure that extends to about 100 inches

the mirror (duh)

a piece of chalk or card to mark the distance

and a white poster board (optional but it helps)

Here is the setup:

So here’s the steps from Building a Reflecting Telescope:


As you can see, the process is so simple and straight to the point that I will agree not to explain what is being depicted.  My results came out well as expected.  I was aiming for an f/12 telescope, which would yield a 48 inch focal length, and it came in at 47 inches.  No harm done, as an inch will not effect the performance in the least bit.

As I was grinding on the weekend, I am on the last 2 abrasives; aluminum oxide 9 and 5 micron.  It is said that when grinding has been successfully completed, the mirror will feel like the finest satin to the touch, and newsprint can be read through it.  It’s already unbelievably smooth, and not quite able to read through, but nevermind.

I caught a snag while finishing my abrasive: I scratched the mirror’s surface near the edge.  I’m not quite sure how it happened, but my best guess is that somehow, dirt of some sort got between the glasses, and scratched.  If this furrow was near the center, I wouldn’t be stressing over it as much.  It takes about 3 times as long to remove such a thing at the edge than one near the center, as the glass naturally grinds out fastest at the center.  Oh well.  I knew that I would get a scratch at some point, but I’m happy it wasn’t during polishing, or I would have been in some serious trouble.

Hope to be finishing this project soon, because I’m itchy to look through this telescope!


Less than Transparent Skies

The growing dilema in amateur astronomy is light pollution and other related sources.  In the mid city, forget about all of the NGC’s or IC’s you’ll be lucky to see all of the Messiers.  I have faced this problem everytime I go out with my telescope.  The LA county fair is in full swing right now, and that pretty much rules out the entire southern sky.

I don’t have any problem with the fair, it’s just that it turns an already not transparent sky into something that can’t be described without seeing it firsthand.  If you live far away in the country, you don’t have much problem with this.

Anyway, I am finishing up the Mesier project, 70 objects are very close now! I need only about 15 more Messiers, but this is hardly any compared to how many I have observed.  Pretty much all of these were observed in town, in badly polluted skies.  Before going out with the telescope, I look at the color of the daytime sky.  If it is a deep blue, it will be a decent night.  However, if it is pale blue and the area above the horizon is a dirty smog color, it will not be worth going out for deep sky.  I have been limited to planets and the moon on nights like that.

I can’t wait to see dark skies, even acceptably dark sites like Mount Baldy are well worth the trip.  By the way, the blog appearence and theme has been changing a lot lately and I have finally found a look that I am satisfied with.  I haven’t observed too much as school is really in full swing now.  I have also been blogging less, like one to two posts a week.

If you ever get the chance to pull the trigger on one of Astro league, programs, it is HIGHLY reccomended you start one.  Mesier one is awesome for learning and taking notes on these bright and detailed astronomical objects.

Clear Skies