Some advice on Coma correctors

Hi there,
Hoping some of you folks might be able to advise me.
I have an Orion SPX 200 ie an 8 inch F4.5 Newt that I am quite happy using with a Baader 8-24 Zoom eyepiece for visual use only on a GOTO mount. I believe its well coliminated using a Baader Laser and subsquent star tests are as expected. I notice that I have to readjust focus if I alternate between items in the center of the field of view or at the edge. This even happens with star clusters like M13. Folks at Orion UK tell me that this is coma and I should consider a coma corrector. Reading all the blurb especially the Baader MPCC info, I get the impression a coma corrector is a must for Astro photography and if you use super wide eyepieces. However I am not into either. So based on my equipment, would a coma corrector be any use to me?
Donal

Hi,

problem you have is related to very fast dobsonians F 1/5 and bigger. Coma corrector is just half of problem and I dont think it would improve view much (even MPCC is good choice for visual obs). Second part are eyepieces. Cheaper eyepieces (such as Baader) are not good with fast dobsonians. Theory in short: rays on fast dobs are comming in too wide angle, and most eyepieces does not correct it.

You need eyepieces which works well with fast dobson, most likely Televue Nagler, Panoptic or Radian.

Other option is to use barlow lens to extend your focal ratio. Lot of eyepieces have build in barlow.

And last option is to shield part of primary mirror to make focal ratio smaller.

Just my 2 cents, I have 16" f 1/4.3

Hi Janek,
Thanks for the info. Suspected as much. I bought the zoom for use with a F10 SCT and then the Newt just arrived.
Donal