Quote:
Originally Posted by strongmanmike
I've just ordered a 12" F4.9 skywatcher flex tube GOTO dob ..yes a miracle  I haven't had a usable visual scope since 2006
The scope will be purely for casual visual observations and I was wondering how necessary a coma corrector is with this model and if you think it is necessary which one do people use or recommend?
Cheers
Mike |
Hi Mike,
Welcome back from the Dark Side
I have the same scope, good choice!
The answer, as Raymo pointed out, depends...
Firstly, with a tracking DOB, it is not generally noticeable.
(with a non tracking DOB, you tend to put your object into one side of the eyepiece, and watch it drift across the field of view. So changes due to coma may be obvious on the outer edges).
Also, coma is more noticeable with the more widefield eyepieces.
TeleVue says:
Quote:
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All Newtonian/Dobsonian telescopes can benefit from using a Tele Vue Paracorr (Parabola Corrector) to eliminate coma in the image. Coma is the effect that makes off-center stars appear like little comets (it becomes more apparent as stars move closer to the edge of the field). Any Newtonian/Dobsonian telescope will benefit from the use of Paracorr, but those from f/3.5 to f/5.0 will see the greatest results. For example, the size of the diffraction-limited field expands by an incredible 36 times in area for an f/4.5 mirror! Stars at the edge of the field will improve so dramatically, that (using top-notch Tele Vue eyepieces) the image will look the same anywhere in the field. It also prevents faint stars from disappearing at the edge of the eyepiece field. This is not only aesthetically pleasing, but it also greatly reduces the need to constantly nudge the scope to keep the object centered in the “sweet spot.” Paracorr essentially makes an f/4 scope perform like an f/8. Just insert it into your 2" focuser like a 2" Barlow (it has a 15% [1.15x] magnification factor) and add Tele Vue eyepieces to suit your needs. It’s a recipe for perfection, when you use Tele Vue eyepieces.
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I have a TeleVue Paracorr, but it does add a bit of weight (especially with an Ethos eyepiece) and I don't always use it.
Some people have looked through my scope (without Paracorr) and said they could not detect any coma (eg astropolak) others have said it makes a noticeable difference (eg Rick Petrie).
Why don't you duck up to Bretti this week and have a look through mine at a very Dark site. Or as Raymo says, just try it first.
