Coma Corrector for Visual Use

[Littleguy80]

With nothing but clouds in the forecast, I find myself with time to plan more Astro purchases ? I’m considering a coma corrector for my 10” F4.7 dob. I have 100 degree eyepieces and do notice a bit of coma. I think a TV  Paracorr or SIPS are a bit on the expensive side. @Stargazer McCabe gave me a great run down on the Explorer Scientific HR offering. I’ve also seen that Baader do a visual version of their MPCC, which looks to be the least expensive option. 

I’d very much appreciate your views/experiences of these or any other coma correctors and whether you’re glad to have one as part of your setup. 

Thank you!

[Paz]

I've got a TV Paracorr 2 but it is fair to say they are expensive. I stalked the second hand ads for a long time and never found one, in the end I got one new but with a discount from an astro fair. I find it helps, my reflector is f4.6. A difficulty is remembering to change the setting when need be and being able to see the settings in the dark so that you can set it correctly.

 

[rl]

I've got the Explore Scientific HR coma corrector in my 8" f/4.5 scope and it works really well. It gives a flat image plane as well as coma correction which means that the overall view is very good indeed with eyepieces also having a matching focal plane, which includes all the more expensive Televue offerings. The view of the moon at *200 with everything in perfect focus all at once is seriously impressive.

Downsides; the screw thread adjustment can be a bit of a pain to set in a hurry. The Paracorr tuneable top idea works better in practise. But to be honest it is not that big a deal since there is a compromise setting that works well enough with most of my eyepieces, but it might bug the perfectionists. Also, I find the view through the HR a bit "warm" in the same way as some criticise Nagler eyepieces. But on balance it's a really good bit of kit. 

If buying secondhand make sure you get the two camera adapters with it.

 

Regards. RL

[Tim]

17 minutes ago, Paz said:

I've got a TV Paracorr 2 but it is fair to say they are expensive. I stalked the second hand ads for a long time and never found one, in the end I got one new but with a discount from an astro fair. I find it helps, my reflector is f4.6. A difficulty is remembering to change the setting when need be and being able to see the settings in the dark so that you can set it correctly.

 

Another shout for the TV Paracorr here.  I write the setting letter A-H on the eyepiece case to help me remember, but with practice you soon switch between views easily, and helpfully my most common EP's in my f4 dob are either A or H setting, and easy to do in the dark. Yes they are expensive, but you can jse them photographically too if desired, and, well, you'll never need another one

[Louis D]

I use the GSO/Revelation coma corrector.  As far as I know, it's the cheapest 4 element, field flattening CC on the market.  It requires the addition of a 15mm spacer ring between the optical element and the eyepiece holder to achieve best correction for eyepieces that focus at the shoulder.  If you parfocalize your eyepieces to within about 5mm of the shoulder, correction is pretty similar to spot on and you never have to adjust anything.  It introduces about 10% magnification and requires about 10mm to 15mm of in-focus.  You can also use the optical element alone with a T-ring for DSLR photography.  It allows me to reach focus with only a 10% barlow effect.  Even at f/6, the effect on 65+ degree fields is dramatic at the edge.  The field is flat to the edge and correction is 95% of the way to perfection.  The 5% of coma which is left is extremely hard to detect.  I do remove it at high powers because it introduces some spherical aberration on axis which limits the finest detail visible on planets.  It is not noticeable at all with exit pupils larger than 2mm.

[Littleguy80]

As if to put temptation under my nose, there’s now a TV Paracorr 2 on ABS. £400 seems a lot though. I’m pretty sure I’ve seen them go for around £325 before. 

[estwing]

mate I really wouldn't bother...save your money.

[estwing]

not at F 4.7...not worth it unless you're going bigger and faster.

[Louis D]

On 07/10/2018 at 05:17, Littleguy80 said:

As if to put temptation under my nose, there’s now a TV Paracorr 2 on ABS. £400 seems a lot though. I’m pretty sure I’ve seen them go for around £325 before. 

Seriously, start with the GSO/Revelation one to see if you like using one first.  After having used one for several years now, I have no desire to move up to the marginal improvement at f/6 of any Paracorr.