Do I really need a coma corrector?

[emadmoussa]

Some of my eyepieces tend to show trailing around the edge in f/5 Dob. I never used a coma corrector before, but will be effective handling some of the uncomfortable eyepieces?

I was looking at the Baader Mark III, it seems to have good ratings.

Anything I should be aware of?

[Tinker1947]

No....

[emadmoussa]

No....

I thought so..

[YKSE]

Emad, It depends how much coma your eyes and brain can tolerate when you have a faster scope

The main advantages with Baader Mark III

1. Zero magniifcation

2. light weight and cheaper than Para corr.

The main draw back is that you might need different spacers for different EPs, if you have many EP need to use it, if'll be quite some fiddling in the dark.

http://www.baader-planetarium.com/pdf/mpcc_e.pdf

Para corr is better in this aspect, but bigger and more expensive, the 1.15x magnification means the 100 deg FOV becomes 85 deg instead.

[emadmoussa]

Emad, It depends how much coma your eyes and brain can tolerate when you have a faster scope

The main advantages with Baader Mark III

1. Zero magniifcation

2. light weight and cheaper than Para corr.

The main draw back is that you might need different spacers for different EPs, if you have many EP need to use it, if'll be quite some fiddling in the dark.

http://www.baader-planetarium.com/pdf/mpcc_e.pdf

Para corr is better in this aspect, but bigger and more expensive, the 1.15x magnification means the 100 deg FOV becomes 85 deg instead.

Most EPs are fine. Some are intolerable, but again...I don't use these much in the reflector.

[Luke]

Do you need a coma corrector (CC) for an F5 dob? For me, the answer is yes and no

I used two F5 Skywatcher dobs without a CC, and had many great views. The edges were a little bit ropey, but I tended to focus centrally. So no, you don't need a CC for F5.

With my F5 GSO dob, I was slightly disappointed with the optics compared to the SW dobs (though I loved the GSO mechanics, making it close to a tie). I wondered if a CC would help, but most of what I read said it's borderline at F5, don't expect much of a difference...

But I got a Paracorr 2, mainly for my F4.3 dob, and when I  tried it in the GSO, wow! It really tidied up the view! For me, it's been the difference between mild disappointment with the optics versus thinking it's a sweet view. So yes, you do need a CC for F5 :grin: And I think the view is generally better, not just at the edges,  though that's where it makes most difference. Views seem a bit more punchy across the field, with a hint of a refractor feel to it.

Being serious, it's one of those personal choices and I suspect some people will think it is worth it, and some won't. I have no idea why it's made such a difference in the GSO. Could it perhaps be that the central spot is not central and somehow the CC helps if the collimation is slightly out??

Any thoughts of replacing the GSO with a SW have gone. It's here to stay now - unless I see a second-hand Orion Optics UK F4 12 inch dob for sale!

[emadmoussa]

Do you need a coma corrector (CC) for an F5 dob? For me, the answer is yes and no

I used two F5 Skywatcher dobs without a CC, and had many great views. The edges were a little bit ropey, but I tended to focus centrally. So no, you don't need a CC for F5.

With my F5 GSO dob, I was slightly disappointed with the optics compared to the SW dobs (though I loved the GSO mechanics, making it close to a tie). I wondered if a CC would help, but most of what I read said it's borderline at F5, don't expect much of a difference...

But I got a Paracorr 2, mainly for my F4.3 dob, and when I  tried it in the GSO, wow! It really tidied up the view! For me, it's been the difference between mild disappointment with the optics versus thinking it's a sweet view. So yes, you do need a CC for F5 :grin: And I think the view is generally better, not just at the edges,  though that's where it makes most difference. Views seem a bit more punchy across the field, with a hint of a refractor feel to it.

Being serious, it's one of those personal choices and I suspect some people will think it is worth it, and some won't. I have no idea why it's made such a difference in the GSO. Could it perhaps be that the central spot is not central and somehow the CC helps if the collimation is slightly out??

Any thoughts of replacing the GSO with a SW have gone. It's here to stay now - unless I see a second-hand Orion Optics UK F4 12 inch dob for sale!

I thought the views through my 10" GSO were pretty good. Only one or two EPs were doing my head in. Having said that, I'm upgrading to Skywatcher 12", so perhaps less need for a CC

[Bart]

I used a GSO CC in my 16" LB F4.5 and yes it makes a difference. However, I found as I went on that the coma bothered me less and less. Especially if at med to high mag. I did use it in the 10" GSO F5 and found it wasn't really necessary. Yes it helps, especially at the high FL, low mag EPs, but really, I've just found I don't use it much now. If the coma bugs you, use one, if it don't.........

Barry

[Rustysplit]

I find that although coma is quite tolerable, the view with a CC is just so much cleaner, so why not use one? Sure at med/high powers the difference is negligable, but at low power/wide fov, for me it is so much better.

[Luke]

That's interesting that it didn't make much of a difference to your GSO, Barry. Wonder why it did with my 10 inch GSO F5?

The Paracorr 2 has a slight Barlow effect, so as far as I know that would allow a greater tolerance for the collimation. Or perhaps you got a better GSO mirror??

I used a GSO CC in my 16" LB F4.5 and yes it makes a difference. However, I found as I went on that the coma bothered me less and less. Especially if at med to high mag. I did use it in the 10" GSO F5 and found it wasn't really necessary. Yes it helps, especially at the high FL, low mag EPs, but really, I've just found I don't use it much now. If the coma bugs you, use one, if it don't.........

Barry

[Scooot]

I don't think I'd use my 26mm Nagler much without the CC, but I leave it in all the time now and I think it improves the views of all my eyepieces. I'm not too bothered that it reduces the FOV slightly because I didn't think it was a useable FOV without it.

[AlexB67]

I thought the views through my 10" GSO were pretty good. Only one or two EPs were doing my head in. Having said that, I'm upgrading to Skywatcher 12", so perhaps less need for a CC

Not much in those two I would have thought. The SW is 4.9 your GSO is 5. So if anything slightly more of a need.

Personally I am in no rush though, will probably get one at some point, that said, If I had any large FOV eyepieces in my f4.7 like an 82 degrees I would really want one.

My only gripe with some of the options presented as already pointed out, how much of a fiddle it may be versus how often would you use it. I am not a fan of barlows already and extra gadgets changing in an out, and the cost and fiddling with spacers.

Perhaps it is okay, but it may be worth thinking about how much it is going to cost extra with the spacers you need. Asmuch a paracorr may cost the roof, it does seem to be the ideal solution to me due to their adjustability all in one package, neat

[John]

If you stick to 68-70 degree apparent field eyepieces then you may well not see too much coma even at F/5. If you decide you want some well corrected 82 or 100 degree pieces then you may change your mind as these are seeing much more of the off axis field and coma increases as you move away from the optical axis.

Some of your eyepieces will show astigmatism at F/5 (eg: the Hyperions) though but those are probably the ones you would not use with such a scope anyway.

[Bart]

That's interesting that it didn't make much of a difference to your GSO, Barry. Wonder why it did with my 10 inch GSO F5?

The Paracorr 2 has a slight Barlow effect, so as far as I know that would allow a greater tolerance for the collimation. Or perhaps you got a better GSO mirror??

Luke

Maybe it did, and I'm just comparing it to the effect it had in the 16" !!! Sometimes I doubt myself!! I definitely felt it was less necessary in the F5. I stuck it into the LB tonight for the double cluster - too many stars to miss

Yes, I definitely fretted a bit when I got the F4.5 at first, but found the coma was like my bad back, it's there all the time, I just don't notice it a lot if the time....

Maybe the CC is like the Solpadeine, it's nice to get a bit of relief sometimes!!! Ha!

Barry