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12.5in mirror - Ronchigram after 5hr polishing

Started by BABOafrica, 03/29/2013 05:30AM
Posted 03/29/2013 05:30AM Opening Post
I'm doing a 12.5" mirror (my first attempt at doing a mirror). After 5 hr of polishing with rouge (I don't have any CeO), this is the Ronchigram.

I don't know how far inside focus, but definitely inside.

I'm mainly pleased that I have been able to get as far as doing a Ronchigram and taking a picture of it.

Any comments are welcome.

Clears,
Joe

Attached Image:

BABOafrica's attachment for post 57334

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm
Posted 03/29/2013 05:52AM #1
Very nice! And a good photo too.

I suspect there are many others like myself who have been watching your progress reports from the side lines. I am impressed with what you have accomplished so far. There are some very knowledgeable folks here who will be able to help you through the final figuring stages when the time comes. Congratulations on a fine job so far.

dan
Posted 03/29/2013 07:04AM #2
Joe, the mirror is looking very good. I think you should keep up with the stroke (s) you are using. I'm not an expert in interpreting Ronchi, but it looks like a very slight TDE on the last 1/4 inch. This should polish out with the way you are working. I too am very surprised at how well you are proceeding. This is not a trivial accomplishment, you certainly have an aptitude for this.

George

Posted 03/29/2013 11:35PM #3
well done

Early days close to a good sphere nothing to be concertned about.

A little bit of a hole in the centre and a slight tde.

keep to the basics press well don't polish for too long (as it can distort the lap) and alternate your stroke.
I usually do a 1/3 w mixed with number 8 and centre over centre also alternating mirror on top and tool on top.

I always warm her up with mirror on top to reduce risk of scratching.
You could try shortening the stroke a little closer to completion and that tde will reduce.

Pyrex is hard and rouge is slow but polishes beautifully. Its a good idea to use your back and straighten the arms as you can injure your arms and elbows if not careful repetitive strain injury.

I polished an 18 inch by hand once

keep up the good work
Posted 04/02/2013 07:11AM #4
Here's another pair of Ronchigrams. The first is INSIDE RofC, the second is OUTSIDE.

Clears,
Joe

Attached Image:

BABOafrica's attachment for post 146928

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm