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The 22" mapstar mirror

mapstar

By mapstar
in DIY Astronomer

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mapstar
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Hi all, I began this journey way back in Oct 2013 so it has taken a while to get to where I am at present but thought it about time I put my experiences down. Wanting a larger scope than the 8" I had

mapstar
mapstar

Hi all, It's been a long time in the creation and the update is a little late so after apologies here it is. As I left the thread last the mirror was in the hands of John and he informed me every day

mapstar
mapstar

Hi all, It's been quite a while since I last updated the thread and posted a few images.  So here is what has happened and where it stands at present I spent a total of five days working with John on

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mapstar

mapstar

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What is chordal ?

Derek

As AJohn says it's the chord of a circle. Working the edge at present I'm only doing a short chordal stroke.

The centre of the lap does the most work so where ever you concentrate this it has the most effect.

Moving it nearer the edge works that part more although caution is required as too near the edge as you can appreciate will just accentuate the edge problem.

John had said that it may be a case of going round in circle's (ha ha) between working the edge then the middle to rectify the problem I have

As AJohn states maintaining a press area for the Lap is essential as a raised centre will press the Lap hollow so not working the edge when I return to it.

Damian

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Physopto

Physopto

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Hi Damian,

I wondered about that, (the lump in the middle and shape on the pressing). Hope it works for you. I know when things are not going to plan it can get demoralising to say the least. When it happens to me on anything,  I just tend to get angry with myself, becoming more centred and stubborn, I hate giving up.

As I said I tried two instances of I.E. open with different pictures of your tests in view, the effect is difficult to see for an untrained eye.

Thanks for the updates and explanation. I went off to Utube for  a search about chordal strokes. So got it now.

Best of luck Damian.

 Derek

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mapstar

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Evening all,

I only had an hour on the mirror today mainly just smoothing the centre down.

Took some more image's with fewer lines as these will probably show change better. 

Inside ROC

post-28847-0-55903100-1428612654_thumb.j

Outside ROC

post-28847-0-42130700-1428612648_thumb.j

I have a central hill which can be seen with the wavey lines in the centre but prove's that glass has been removed from the outer zone. A foucault test would show this better as it gives an image of the overall smoothness of the sphere and I may post some just for reference.

More work maybe tomorrow, where I will do some more smoothing then a long press and back to the edge to hopefully progress some more

Damian 

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alan potts

alan potts

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Damian,

I hope all is going well though I know it is a slow process. Is this your first mirror as it is a big one. I made a 12 inch back in 1976, tried my best and still had to get it tickled up by someone that knew how. Back then there was no such thing as on line help or coma correcters that I knew of.

Keep at it and good luck.

alan 

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mapstar

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Damian,

I hope all is going well though I know it is a slow process. Is this your first mirror as it is a big one. I made a 12 inch back in 1976, tried my best and still had to get it tickled up by someone that knew how. Back then there was no such thing as on line help or coma correcters that I knew of.

Keep at it and good luck.

alan

Cheers for the post Alan

Very ambitious I know but yes it is my first mirror so the process is even longer as I'm feeling my way along, although with a good guide it's a bit easier.

I may get some more work on it this aft but I have a few bits to make up for Rich and his mirror blog (crashtestdummy) if you also want to check that out as he's doing the same.

Damian

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Physopto

Physopto

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Hi Damian,

 You talk about taking time to do the mirror! well last night I just managed to get my Active Optics to work after nearly 14 months. Spent 5 hours last night with it. 3 hours in vain then Eureka Ta Daaaa! 2 hours of perfect guiding within 0.2 pixels, wow!

Mirrors PA PISH POSH. :p

Keep going, you'll get there.

Derek

Edited by Physopto
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mapstar

mapstar

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Hi Damian,

 You talk about taking time to do the mirror! well last night I just managed to get my Active Optics to work after nearly 14 months. Spent 5 hours last night with it. 3 hours in vain then Eureka Ta Daaaa! 2 hours of perfect guiding within 0.2 pixels, wow!

Mirrors PA PISH POSH. :p

Keep going, you'll get there.

Derek

Now there's a long term project  :eek:

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Physopto

Physopto

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Well you go from a high to a low. Been waiting for a camera rotator arriving from the States. Arrived today and guess what: wrong threaded end. They sent a male 92x1 mm fitting instead of a female. Partly my fault and partly theirs. So awaiting a reply to my email now to see what can be done, as I cannot find the correct bit on their site. You win some and loose some :mad:

How's that edge doing?

Derek

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mapstar

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Well you go from a high to a low. Been waiting for a camera rotator arriving from the States. Arrived today and guess what: wrong threaded end. They sent a male 92x1 mm fitting instead of a female. Partly my fault and partly theirs. So awaiting a reply to my email now to see what can be done, as I cannot find the correct bit on their site. You win some and loose some :mad:

How's that edge doing?

Derek

Hi Derek,

Yes things from the state's sometimes are not quite what we expect. No work on the mirror today I'm afraid, as I was readying a second table top mod like mine for Rich (Crashtestdummy blog) to take home with him to hampshire.

Edge is the same grass is cut though :grin: 

Damian 

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barkis

barkis

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Let us try to keep this thread on topic folks.

Anyone with their own projects running, make a thread of your own and don't post in this one.

I'm sure Damian would prefer continuity, with no interruptions.

Ron.

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mapstar

mapstar

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More work this afternoon folks once I've finished work and done a few chores.

I have Rich visiting this aft at some point and will be good to see him

A long chat with him about each others mirror making and how to fit the new flag stone table top to his existing table frame. By the looks of it he has a similar edge problem to me so will probably be viewing my notes with interest

Will be nice to see some progress this week and fingers crossed I'll be able to grace you akk with some image's of a smoothly spherical mirror.

So the plan is to smooth the centre a little more, long press and then work the edge again.

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