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.
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.
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.
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.
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; 14-09-2009 at 12:24 AM.
Reason: font?
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.
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.
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?
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!
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?