Honeybadger152

2 minutes ago, Chriske said:

After a quick search found a few pictures from long ago...

 

Here you can see there's no mirrorsupport at the perimeter of that 10". The mirror is held in place by the central bolt that is glued at the back of the mirror.
Just below the mirror you'll see the neoprene ring (the pusher part of the flex unit).

Have you got a spare one of those that you don't use anymore haha

That's a pretty sick looking scope

14 hours ago, Chriske said:

I do have images somewhere, need to search my HD's.
But it works just perfect. As a matter of fact using this technique you easily can pull the mirror to any CC you require, from ellipse to hyperbola, as long the mirror is not to thick.
That's the beauty of the system.

So Chriske, it would appear this mirror is an f/4 rather than an f/8.

From what i have read it is super difficult to flex mirrors successfully at that ratio?

I ask all of you, just that Chriske has stated he has experience in flexing.

3 hours ago, davidc135 said:

Just to be clear. As Gonariu mentions above the F/4 primary works with a Bird Jones lens that acts like a x2 Barlow extending the focal length to 1000mm and at the same time hopefully correcting the spherical aberration.

David

So what would this mean should I want to parabolize the mirror? Would it become more like f/3.5 or does that ratio change based on its shape?

I understand that i would need to reposition the secondary + focuser and remove the correction lens

2 hours ago, davidc135 said:

Interesting plan.

Sounds like you have a 5'' f/4 sphere for a primary. As it is, it will have 1.75 waves of spherical aberration as against a basic standard of 1/4 wave 

To be evenly parabolised by the harness the primary will need to have an even thickness around the edge. And the overall thickness will play a part in the force needed.

It may be that the eyepiees that came with the scope, if they have H, HM or R written on them, would be unsuitable for a fast F/4 scope although OK for the slower F/8.

Although basic Plossls or Kellners don't cost much.

Another component to check is the size of the diagonal.

David

Hi David

The scopes rating

127mm mirror

f/1000mm

f/8

Eye pieces have  H on them

20mm

12mm

Then a super small one that i've gotten no use out of

3. something mm

3x barlow only 1 lens

So far i've had a good look at jupiter and its moons. That was from indoors with awfull light pollution.

On 22/09/2021 at 07:27, Chriske said:

As a matter of fact, many years ago it used to be standard procedure during telescopemaking course at our local club.
There are many things to consider using flexed mirrors.
The procedure has to be performed ab-so-lu-te-ly perfect. There no room for error.
After a while we abandoned the procedure because some course members were to sloppy during the gluing procedure.
But there's a reason why you should not do this. When a flexed mirror need a new coating, all companies will refuse that mirror. Reason : they will not put your mirror with a neoprene disk glued on it's back in their coater.

I don't suppose you have any before and after images Chriske? Demonstrating the improvement in optical accuracy?

I have been searching the net far a wide just for some sort of practical demonstration but can't find much at all.

10 hours ago, Merlin66 said:

What about trying the Kelley-Alder Mirror Flex System??

https://skyandtelescope.org/wp-conte...MirrorFlex.pdf

This is very intriguing. I can't help but wonder though why this wouldn't be common practice with spherical designs.

Surely the offset cost for the extra materials would be cheaper than the more expensive parabolising process?

Do you know anyone that's done it with before and after images?

I should have explained a bit more about my thoughts towards my query.

My intentions are to use the scope as is for now just to learn the ropes and to get a feel for whether it will become a hobby of mine.

Personally, throwing a grand or 6 at a setup doesn't excite me and this is no dig at anyone who chooses to do that.

I'm a bit of a tweaker kind of guy. I get a lot of satisfaction from squeezing as much performance out of things as possible. Modding/ adapting.

I like the idea of perhaps making my own telescope but I'm kind of learning that it's a bit pointless as the costs would likely exceed that of a purchased one.

Thanks for the input though

regards

Chris

So I recently purchased a second hand telescope since I've an interest getting into Astronomy. I knew that the scope wasn't great but at £45 and less than a mile away, I saw some value in it.

Being new I didn't want to invest much money at all.

The scope is a celestron ps1000.

As said before I'm aware it's certainly not something a seasoned amature would buy.

My question is...

Would it be possible to re-grind the mirror to make it parabolic?

Regards

Chris