Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

A lot of coma - normal ??


Recommended Posts

I took this last night, 20s unguided with 400d through a SW 250px.

There seems to be a lot of elongated stars not just at the edges but much further in. I used to imaged with a refractor (ED80) and didn't realise this would be such a problem. I was wondering is this a normal amount or is my collimation not great? I did collimate the scope the last time I used it last week, and was 95% happy with it. Can you please have a look and advise me if this is normal. I have read about the MPCC flattener, is this something that I would see a benefit from using?

Thanks

Adam

post-15548-133877409359_thumb.jpg

post-15548-133877409366_thumb.jpg

Link to comment
Share on other sites

Coma is a fact of life with Newtonians, Adam - the MPCC works very well with these instruments as I hope you can see from any images taken with my 8" or 10" Reflector by me since March this year. To get one to work with the Skywatcher range may well require a custom adapter as the standard Skywatcher 2" adapter projects out too far to achieve focus with the correct spacing of the MPCC from the film plane.

Link to comment
Share on other sites

WOW, that's some difference. I bought the 250 specifically for imaging, to go along with the ED80, so it looks like the MPCC is a pretty essential piece of kit if I want to get the most out of the scope.

I'll need to look into that too. (Not to mention the buy the stuff for mounting the sopce too :rolleyes: )

Link to comment
Share on other sites

Adam, this is the system that I use with my CCD camera but you would need something different for your DSLR camera. Essentially, you need a low profile 2" EP adapter that fits the Skywatcher focus tube so that the MPCC is inside the actual focus tube. The first image is my custom adapter and the second image is the adapter with the MPCC attached at the left hand side.

baader_adapter_photo.jpg

Baader_plus_adapter.jpg

Link to comment
Share on other sites

The mod I did is not a long term solution I modified the focuser mounting plate so I could mount the focuser on the inside of the OTA.

The problems are the focus wheels can no longer be used, there is not enough room ( not a problem for me as I have a homemade servo focuser made from the servo from an old remote control car)

the big problem is the drawtube now slightly enters the light path.

When I can afford it I will get a skywatcher low profile focuser.

Mike

post-13376-133877409681_thumb.jpg

Link to comment
Share on other sites

Steve, dose your custom adapter alow for a filter wheel in the imaging train while still keeping the 55mm (I think) between the MPCC and Chip?

Mike.

Unfortunately not, Mike, I currently only use OSC CCDs, however, I reckon it could be adapted to suit - there's 23 mm to play with, is that enough for your filter wheel?

Link to comment
Share on other sites

I spoke to Bern at modernastronomy, and he has given me the good news that the mpcc filter will work fine with my scope without any modification. Good news, and hopefully helpful to anyone else interested. He told me that because the dslr focuses already without the mpcc, that the mpcc only adds to the back focus.

Regards

Adam

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.