Is it worth 50p? (C9.25 on ABS)

[johninderby]

Another case of the parts needed (matched corrector and mirrors) would cost about as much if not more than a whole new OTA.

Celestron C9.25 StarBright XLT without corrector plate.

http://www.astrobuysell.com/uk/propview.php?view=57608

John

[Earl]

Are these not matched on manufacture?

Nice office bin though?

[Dunkster]

Is it not possible to string the secondary up with wire and fake it as an RC or does the corrector really make that much difference?

[johninderby]

The corrector is there to correct for the spherical aberrations of the primary mirror. Without it the scope is useless. They are produced as a matched set at the factory so you can't just simply replace the corrector with one from another scope as it won't be matched to the primary mirror.

This link has some basic SCT info.

http://uncle-rods.blogspot.co.uk/2008/08/sct-mythology.html

John

[Dunkster]

Good read - thanks!

[Zeffer]

Yes, enjoyed that!

[4lefts]

without wishing to offend anyone (might be someone from here that's selling...) - how do you misplace the corrector from a scope like that?

[Dunkster]

Misplace? LOL

[E621Keith]

A SCT can still be used with a cracked corrector, but a SCT with no corrector is useless. The OTA needs to be sent back to Celestron to find a corrector which will match it.

After reading some ATM articles on making Schmidt corrector plate, it's clear it's a case of making the corrector plate first and the grind a mirror to match it. The vaccum process used for making the corrector is not very precise and it's easier to make a mirror with the precise error and aberration to correct for the corrector plate, rather than the other way round. I suspect this is also done at Celestron, but only at an industrial scale.

In summary, a SCT without a corrector plate can't be fixed without also re-figuring the primary mirror, so an intact primary mirror is no different from a glass blank.

For those interested: an article on making an SCT

http://www.considine.net/drowesmi/pfaff/pfaff.htm

[Tim]

I'd be interested to see the effects on the image if two SCT's had their correctors swapped.

But no, not my C9.25 or my C11 as a donor thanks

[Stu_2011]

A SCT can still be used with a cracked corrector, but a SCT with no corrector is useless. The OTA needs to be sent back to Celestron to find a corrector which will match it.

After reading some ATM articles on making Schmidt corrector plate, it's clear it's a case of making the corrector plate first and the grind a mirror to match it. The vaccum process used for making the corrector is not very precise and it's easier to make a mirror with the precise error and aberration to correct for the corrector plate, rather than the other way round. I suspect this is also done at Celestron, but only at an industrial scale.

In summary, a SCT without a corrector plate can't be fixed without also re-figuring the primary mirror, so an intact primary mirror is no different from a glass blank.

For those interested: an article on making an SCT

http://www.considine.net/drowesmi/pfaff/pfaff.htm

Is it really done this way? i.e. make the corrector and then grind the mirror to match? You need tooling to grind shapes on an industrial scale and thats not that easy to change. I'm guessing they produce a whole lot of corrector plates and mirrors and then go through and match up pairs. Celestron and Meade talk about hand matched optics which implies this is the way they do it.

Thanks

Sent from my iPad using Tapatalk

[Keiran]

I am sure that i remember somebody from Hereford making a dob out of SCT mirrors, I dont remember there being a corrector on that... I may be mistaken though

[E621Keith]

Is it really done this way? i.e. make the corrector and then grind the mirror to match? You need tooling to grind shapes on an industrial scale and thats not that easy to change. I'm guessing they produce a whole lot of corrector plates and mirrors and then go through and match up pairs. Celestron and Meade talk about hand matched optics which implies this is the way they do it.

Thanks

Sent from my iPad using Tapatalk

You're right, they probably do it in an industrial scale by making lots of correctors and mirrors with known error and then match them.

[Peter Drew]

A F2 Dob with a spherical mirror and no corrector would give some interesting star images!