Any advantage to a 'faster' coma corrector?

[szymon]

I'm looking at possibly buying a Coma Corrector for my SkyWatcher Explorer 200P.  I can get the SkyWatcher one designed for scopes up to F5 from FLO for £100.  However, I've found a second hand SkyWatcher f/4 Aplanatic Super Coma Corrector for £90 second hand (but in good optical condition).

So -- are there any advantages to buying the aplanatic one for me?  The obvious one is if I upgrade to a faster scope in the future, but other than that, will it work just as well?  Better?  Worse?

-simon

[Tinker1947]

Coma Correctors i believe have upper and lower limits to what they will work in while it may work in a F4, it might not perform so well in a F5, i could be wrong, somebody will belong who does know.....soonish...

[laser_jock99]

The coma corrector must be matched to the F number of the scope. Some are designed to be used with only the fast F4 scopes for instance as is the one you mentioned (SkyWatcher f/4 Aplanatic).

The other possibilty is a corrector/reducer which will turn an F4 scope into an F2.9 photon hoover (or an F5 scope into into an F3.6). The disadvantage is they cost twice as much as most scopes and can be tricky to use (need perfect colimation and CCD spacing)

Once set up correctly they are distubingly fast- M51 in just 140 seconds....

[szymon]

Ok, so I'll be better off with the one designed for the F5 scope.  It also reduces by 0.9 so it will turn the scope into an f/4.5, which must be a good thing.

Thanks!

[Gomtuu]

The coma corrector must be matched to the F number of the scope.

I have to admit I didn't know this. That's what I like about SGL, always something useful to learn.