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  #21  
Old 13-09-2009, 08:18 PM
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multiweb (Marc)
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Quote:
Originally Posted by DavidU View Post
It seems odd as Petes Omega pic is really very good wo a flattener
That's what I don't get. Peter's picture shows no coma and extremely negligable field curvature. But have you seen the first pic in this thread? Even my newt uncorrected wouldn't be that bad.
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  #22  
Old 13-09-2009, 08:27 PM
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I wonder why a Hyperbolic is acting like a very short Parabolic????
Odd indeed
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  #23  
Old 13-09-2009, 08:35 PM
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David,

Hence my original post, I just don't get it!
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  #24  
Old 13-09-2009, 08:52 PM
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Grahame

It is strange looking image - but I'm sure you will figure it out.

How did you check the focus? I'd like to see a shot taken with a Bahtinov mask over the scope, then one with it removed. To me it looks like the stars at the edge of the image are way out of focus. Although the ones at the center look in focus, perhaps they are not and the field curvature is making the ones at the edge look a lot worse.
The situation could also be made worse if your new focuser is not square for some reason. To me it looks at bit worse at the top than at the bottom of the image.
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  #25  
Old 13-09-2009, 08:55 PM
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Also look at the diffraction spikes on the bright stars - they aren't lined up properly.
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  #26  
Old 13-09-2009, 09:07 PM
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Check collimation how do the focal rings appear out of focus ae they concentric

I know when collimating mine two ehads are better than one

a recent Ronchi test conducted on my mirror indicated nothing out of the ordinary
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  #27  
Old 13-09-2009, 10:18 PM
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Originally Posted by Grahame View Post
Wow Peter! what camera was this image taken with?
SBIG STL11000. Field cropped to APS size. The scope was out of the box.
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  #28  
Old 13-09-2009, 10:43 PM
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That first image is very strange. I have not seen this with my scope. Does the scope focus uniformly when using an eye piece? Even without the Tak flattener it does not produce stars like that. I have gotten similar stars with the QSI as Peter did. It is just a little under APS. My 40D has not produced stars like this either without the flattener.
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  #29  
Old 13-09-2009, 10:57 PM
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Quote:
Originally Posted by DavidU View Post
I wonder why a Hyperbolic is acting like a very short Parabolic????
Odd indeed
Possibly two reasons, it's either not been figured properly or the indexing of the primary and secondary are out by 500 light years!!!. Which is both a case of shoddy workmanship and slap together "I'm going home in 10 minutes" negligence.
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  #30  
Old 13-09-2009, 11:23 PM
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mmm needless to say at the next possible chance using a Bahtinov Mask photos of the results will be posted - I would hate to have to follow this up with the dealer for some kind of faulty primary/secondary thats for sure.

Thanks guys!

Grahame.

Last edited by Grahame; 13-09-2009 at 11:24 PM. Reason: font?
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  #31  
Old 14-09-2009, 06:44 AM
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Good luck Grahame. In reality, if it's that badly out, it's not fit for its purpose, and you have every right to ask for a replacement under consumer laws.

Dave
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  #32  
Old 14-09-2009, 08:46 PM
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Thanks Dave, I will give the collimation a go (bahtinov mask is in the process of being made) will post the before and after pics soon.

Grahame.
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  #33  
Old 14-09-2009, 09:13 PM
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Grahame....try this...before you do anything else, focus on stars about 10-20% away from the edge of the frame.

You may be surprised at results
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  #34  
Old 28-09-2009, 02:43 PM
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Hello All,

Finally had a good weekend to head out and do some more test images. Using a bahtinov mask and focusing around the 15-20% from edge of field technique produced the following results:

Shot One - not looking to bad (might be a little soft on focus)

Shot Two - back to Eta Carina and seems the problem is still there (Much less obvious than the first example in this thread)

This was again using a canon 50D without any field flatteners.
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  #35  
Old 28-09-2009, 02:53 PM
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Quote:
Much less obvious than the first example in this thread
But the problem is still there. Can you post an image you took with the bahtinov mask on?
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  #36  
Old 28-09-2009, 03:08 PM
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Hi Graham

Some of my first images showed top left same as yours

replaced the focuser with a moonlite

and re colimatted

seemed to have fixed the issue

also check tracking
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  #37  
Old 28-09-2009, 03:15 PM
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Graham, the left side of the images look bad.
Can you measure the distance from the inside of the OTA to the edge of the secondary holder with a dial vernier to see if it is concentric?
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  #38  
Old 28-09-2009, 03:46 PM
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Looks like a focuser slop issue, or a collimation issue to me... The ETA shot looks a lot like focuser slop... make sure you lock up the focuser TIGHT when you're ready to image.. Real Tight!
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  #39  
Old 28-09-2009, 04:02 PM
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There is a couple of things in those images.

In the first one I can see baffle rings, they are really obvious. That combined with the out of focus stars on the outside of the field indicates that the field is not flat. Return the scope, it clearly has problems.

In the second image the stars are out of focus on the outside of the image and sharp in the center. Collimation should be addressed but this will not stop the out of focus stars. Are you absolutely certain that collimation is done correctly?
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  #40  
Old 28-09-2009, 04:03 PM
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Quote:
Originally Posted by TrevorW View Post
Some of my first images showed top left same as yours

replaced the focuser with a moonlite

and re colimatted

seemed to have fixed the issue
Did the focuser it look like this?
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