Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Will a Coma Corrector fix this?


Recommended Posts

Hi,

I have a new 200P DS, and I'm finding that I cannot get the whole view into focus at once. This is particularly true with the 28mm 2 inch eyepiece that is supplied, but is also partially true of the 2 Paradigm (18mm & 12mm) eyepieces that I have.

With the 2 inch eyepiece the outer 20-30% is out of focus when the central portion is in focus. So is this a problem with the scope or the eyepiece? Would a coma corrector fix this? This is very frustrating when trying to find a fuzzy, as every star that moves into view starts off looking like a fuzzy!

I've not really had a chance to take may pictures with it yet, so have not discovered how much of an issue coma will be for that.

Thanks,

Adam

Link to comment
Share on other sites

Do the OOF stars look like little seagulls similar to the photo below, if so then thats Astigmatism and is inherrant in your eyepiece.

Cheap eyepieces make this seem worse while better more expensive ones do help a little to correct it.

I have this in my 16" LB if I use the cheaper plossls then at least 30% of the FOV is awful, if I use my WO UWAN's then it's only the last 5% thats affected.

I don't think a coma corrector will correct it, as it's not coma.

post-13619-13387746449_thumb.gif

Link to comment
Share on other sites

Unless you are using expensive wide-field eyepieces (eg: Naglers) what you are seeing is astigmatism introduced by the eyepiece. This is a common issue with budget wide field eyepieces when used with fast scopes. A coma corrector will not help with this as Mick says.

The irony is that you fork out a couple of hunded on a premium wide field and the astigmasim is gone but you can then see the coma inherant with the fast newtonian design - this is when a coma corrector can help though.

Link to comment
Share on other sites

John is correct, first sort out your astigmatism by buying the best eyepieces such as naglers, pentaxes or Uwans then buy a coma corrector to sort out your coma.

In theory you should be left with a perfect view :eek:

Link to comment
Share on other sites

Thanks for all the advice, I couldn't tell if the fuzzies were seagull shaped, I just recall them being fuzzy. I think I still need to perfect my collimating skills too.

I certainly don't have the budget to buy those sort of eyepieces.

Link to comment
Share on other sites

I've looked at these descriptions of coma and astigmatism . It seems that the key difference visually is coma is a one sided aberration a bit like a comma, or a short fat exclamation mark; and astigmatism is like a bar on either side of the star and crucially the bar flips from horizontal to vertical on either side of focus.

Next time the clouds go away I'll be checking! I suspect my last outing wasn't helped by less than ideal collimation either, I further suspect that it'll probably be both issues.

Adam

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • 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.