mirror shift

[shoelevy]

hi guys....think many of you would know i jus bought a new G8 ota.
when i first tried it on jupiter, although on a low magnification of 81x, the mirror shift was terrible!

can anyone help?

[VinSnr]

hi guys....think many of you would know i jus bought a new G8 ota.
when i first tried it on jupiter, although on a low magnification of 81x, the mirror shift was terrible!

can anyone help?

when u say terrible, how terrible is that?

On my Meade, image shift is only noticable around 142x and it just moves very little to be even distracting.

Try this, turn your focuser all the way to the max and then turn back the other way to the max. Do this a few times to even out the grease that could be on your primary baffle.

[shoelevy]

well
terrible meaning at 160x, jupiter can shift from centre of view to completely outside.
i tried the method you've mentioned
it's better but still quite significant compared to my 5"

how else can i remedy it?

[VinSnr]

well
terrible meaning at 160x, jupiter can shift from centre of view to completely outside.
i tried the method you've mentioned
it's better but still quite significant compared to my 5"

how else can i remedy it?

Oh gosh..that's very bad!!

You have two choices. One is to talk to OPT and tell them that they sent you a really bad OTA. Tell them about this image shift thing. Problem is, once Celestron scopes are out from US, the warranty is null and void. The only way to obtain waranty is to send the scope back to US by using a US address. Work with OPT and see if they can help. See, this is the problem of getting a new OTA....

But the lesser pain way is to get a Crayford focuser. Attach it to the back of the SCT and forget about using the stock focuser.

If Jupiter can leave the FOV at just 160X, you can't even do star test with this scope! How much turn do you require to get Jupiter out of FOV? Is it very little turn? Or is it that Jupiter keeps moving out of the FOV as you turn?

Also, which way do you turn to get Jupiter out? Does it happen on both ways?

[Airconvent]

This is very bad. I was under the impression OPT will test the item for you prior to shipping it out. Was thinking of buying something from them too and they have this full complete test at a certain cost. I wonder how comprehensive it is.
Is it possible the mirror assembly gotten in transit ?
Possible to remove it to re-tighten something?

Vince : For your crayford solution, do you mean to permanenly leave the stock focuser at one position, attach the crayford focuser to the eyepiece slot and to focus from there? Is this a better solution in general? Logically seemed so since there is lesser movement adjusting a small assembly than mechanically adjusting the whole primary mirror. How much does these focusers cost? Any issues using them?

cheers
rich

[shoelevy]

well...if i turn one way to get the planet in view then turning the other way would get it out of view
just a slight turn and it'll be out.
it moves to a position then it'll stop moving even if you continue to turn it
and the warranty is still valid with OPT.

Airconvent:i'm just probably one of those unlucky ones because they have no stock for the c8 and shipped one directly from Celestron warehouse. So if there's any problem it should be with celestron.

[VinSnr]

This is very bad. I was under the impression OPT will test the item for you prior to shipping it out. Was thinking of buying something from them too and they have this full complete test at a certain cost. I wonder how comprehensive it is.
Is it possible the mirror assembly gotten in transit ?
Possible to remove it to re-tighten something?

Vince : For your crayford solution, do you mean to permanenly leave the stock focuser at one position, attach the crayford focuser to the eyepiece slot and to focus from there? Is this a better solution in general? Logically seemed so since there is lesser movement adjusting a small assembly than mechanically adjusting the whole primary mirror. How much does these focusers cost? Any issues using them?

cheers
rich

Rich, even if they do the test, they won't test for image shift. For OTA, they just check to make sure that it is cosmetically ok and the focuser is turning and the lens has no dings and stuff like that. They won't put it under the stars to test.

The popular crayford is from William Optics...costing US hundred odd dollars from Astromart. I donno how much it cost new....never believe in buying new for accessories.

To use the crayford, you turn the primary mirror all the way back and leave it as it is. Then dun touch the focuser anymore. To focus, use the crayford. Solve your image shift problems 100% of the time. The only problem with crayford is for those that use fork mounted tube such as LX-90 or LX200. For these scopes, the length of the crayford will hit the base of the OTA.

[VinSnr]

well...if i turn one way to get the planet in view then turning the other way would get it out of view
just a slight turn and it'll be out.
it moves to a position then it'll stop moving even if you continue to turn it
and the warranty is still valid with OPT.

Airconvent:i'm just probably one of those unlucky ones because they have no stock for the c8 and shipped one directly from Celestron warehouse. So if there's any problem it should be with celestron.

But shipping the scope back and forth will most probably buy you another OTA in Astromart!

Just get the crayford and solve it.

[shoelevy]

if i buy the crayford then the image shift will be there...in chinese its cure symptoms not problems

oh ya...if i use the crayford can i still do astrophotography?

[weixing]

Hi,

if i buy the crayford then the image shift will be there...in chinese its cure symptoms not problems

If you use a crayford focuser, then there will be no mirror shift at all... you are no longer moving the primary mirror when focusing.

oh ya...if i use the crayford can i still do astrophotography?

It shouldn't be a problem as long as you can find a way to connect your camera to your scope...

Have a nice day.