To Paracorr or Not to Paracorr...

[niallk]

Hi,

I think I'm becoming conscious of coma in my 15" f/4.5 scope. I've never personally seen the effect of a paracorr, and I was thinking of doing a little poll here to see at what focal ratio people would recommend a coma corrector. My EPs are Naglers and a Pan24 - no 100° EPs in my case.

If enough people respond with f-ratio and yes/no for coma correction, it perhaps it would lend itself to me posting a little chart of paracorr use vs focal ratio (possibly vs afov if reported too if that makes sense to do??).

Perhaps f/4.5 is on the cusp of it being an obvious decision...?

Thoughts & comments really welcomed + thanks!

-Niall

[Stu]

I use a SIPS with my 16" f4.5. Used with a variety of eyepieces but including Ethos and Nagler. Works very well

[Scooot]

I use a paracorr with my f4.5 16". The last couple of nights when imaging it was attached to my camera, so when I was finding things I was using my 17.3mm without the coma corrector, and I was very aware of the difference near the edges.

[scarp15]

I also use a paracorr, with my 14" F4.6. I consider that it is a nice and to an extent beneficial accessory to have. I am not overly sensitive to coma near to the edge and used the scope for over a year prior to investing in a paracorr, I still sometimes opt not to use. My eyepieces are a mix of ethos, delos, TV plossl and a Pentax XW. 

[alan potts]

My Dob is F4.3 and I was not that bothered with coma using Panoptics, I have 3 of them 41mm 35mm and 24mm. I could live with it on these eyepieces especially the 41mm.

Going wider to Naglers and Ethos I was not so impressed and coma annoyed me.

I have not used any of my Delos on the scope or my Pentax. The Paracorr which is the older MK1 model does a great job and makes them sharp to the edge with all the eyepieces I have tried out. I think it is a must really at F4.3 but I also like the wider FOV the 41mm Pan gives and at lower magnification I can live with it.

I will close with this which I have stated a few times, why pay TeleVue money for sharp edges and then accept the opposite, the only downside of a Paracorr is the cost.

alan.

[estwing]

I don't think that I could bare spending all that money and not getting the best view,so the paracorr is just another step towards getting that view and at F3.9 that's the deal..

[RCompassi]

I never bothered too much on visual use, but using a camera, it has a nice difference:

No CC (extreme corners and center crop):

With GSO CC (extreme corners and center crop):

[faulksy]

hi niall , i have a similar scope to you, and used it for around 6 months without a coma corrector, in te end i decided i wanted a better focuser so i went featertouch with sips and once steve (swampthing) helped me tune it up te difference was staggering real clean come free views even in my 21e. big outlay but worth it

[Paul73]

My scope is f4.7. I have Mk1 Paracorr. I notice a difference in the 82° eyepieces but not enough to justify the reduction in FOV.

It does get used, but not essential at all.

Paul

[estwing]

anything below 4.3...I would have to get one...others may put up with it..fair enough.

[jam1e1]

Use mine with 10" 250pds skywatcher newt, the other night I just did quick session in garden without it,used 12mm nagler, noticed the difference quite quickly towards the edges. Note for visual only as I don't image. In my opinion it's an essential bit of kit for getting towards as best view as possible, as estwing says

[YKSE]

My scope is f4.7. I have Mk1 Paracorr. I notice a difference in the 82° eyepieces but not enough to justify the reduction in FOV.

It does get used, but not essential at all.

Paul

Use mine with 10" 250pds skywatcher newt, the other night I just did quick session in garden without it,used 12mm nagler, noticed the difference quite quickly towards the edges. Note for visual only as I don't image. In my opinion it's an essential bit of kit for getting towards as best view as possible, as estwing says

That's 1:1 to the question I asked a year ago 

[niallk]

That's 1:1 to the question I asked a year ago

Thanks to everyone for the great responses so far - and yes there are lots of threads on this here and on CN - my apologies for bringing up the topic yet again.

Given the amount of dob owners here (show us your dob thread!), I had a notion of looking at the stats as one goes from f5 or greater down to sub f4 if enough people responded, and seeing where people generally agree that a paracorr is definitely worth it. For example, I didn't have any notion of getting one for my 10" f/4.7.

I will be continuing without a paracorr for the moment - I think my next purchases this year will be a rechargeable 12V battery, and Interstellarium.

I am keeping an eye out for a 2nd hand paracorr though (eg mk1)...

Thanks again

[alan potts]

The Mk1 normally goes for around 150 quid S/H and bear in mind it will hold that mark. The other downside for me is they do have an impact on the FOV as they increase the F/L by 15%. If only we could have a sub F2  24 inch mirror with a Paracorr, imagine the wide field views that would give, maybe one day who knows.

Alan

[John]

You could buy some less expensive wide field eyepieces and mask the coma with some astigmatism

More seriously though, one of the attractions of my F/5.3 12" dob was that it was unlikely to need a coma corrector despite my peculiar taste for hyper wide eyepieces. In the main I've found that to be so but I can just see a little coma creeping in right at the edge of the field of my 21mm Ethos eyepiece. I have the feeling that even with my scope a Paracorr would tighten things up out there a little

[RikM]

I don't use one with my 10" f/4.7. It would definitely be a help but at the moment it is way down the priority list.

[Luke]

Tidies up the corners a lot with my F4.4 dob (SW400P) and 21mm Ethos. To my surprise, greatly improves the view with my F5 GSO880 10 inch dob, but I wonder if perhaps the mirror dot is not central or something else is amiss, it takes the optics for me from being slightly disappointing to being quite nice actually. Given how many people say F5 is marginal for the Paracorr, it does make me wonder why there is such an obvious difference with my scope.  I really should get around to checking if the spot is definitely central.

[swamp thing]

The Mk1 normally goes for around 150 quid S/H and bear in mind it will hold that mark. The other downside for me is they do have an impact on the FOV as they increase the F/L by 15%. If only we could have a sub F2  24 inch mirror with a Paracorr, imagine the wide field views that would give, maybe one day who knows.

Alan

Alan

You will not get a wider FOV in an f/2 than an f/4, exit pupil and the human eye prevent it.

If you are looking for big FOV you are wasting your time looking at big scopes.  To rule out Paracorr on these grounds is wrong.

[alan potts]

Steve,

Thanks for putting me right on that point but I was not really ruling a Paracorr out because of this, don't forget I have one. I just thought it would be nice to have a massive scope with a short F/L hense lower power wider field, that is not possible as you say the Exit Pupil would be massive, it was just a bit of banter really but you are absolutely correct to highlight the fact to other readers.

Alan

[niallk]

Thanks for all the feedback.

I'm keeping an eye out, and plan to get a paracorr. I'll probably also overtime revisit my eps ... eg my high mag option with +15% focal length, and possibly wider fov.

In the meantime, I'll still very much be enjoying the views whenever the sky is clear

All the best,

-Niall

[niallk]

I guess a paracorr is a no-brainer for the guy with the 14.5" f/2.55 [!!!] dob... :)

http://www.cloudynights.com/topic/502484-a-slow-dobsonian/#entry6632804

[YKSE]

I guess a paracorr is a no-brainer for the guy with the 14.5" f/2.55 [!!!] dob... :)

http://www.cloudynights.com/topic/502484-a-slow-dobsonian/#entry6632804

That is a cool scope to look at, I'm kind of wondering what's view looking through it?

Stacking THREE paracorr in the focuser, the scope can reach f3.9, still faster than TV eyepieces are good for, and the eyepiece train might be as long the the scope itself.

[Sporadic Dobstronomer]

That is a cool scope to look at, I'm kind of wondering what's view looking through it?

Stacking THREE paracorr in the focuser, the scope can reach f3.9, still faster than TV eyepieces are good for, and the eyepiece train might be as long the the scope itself.

I'm not so sure....

If you look here:

http://www.loptics.com/articles/fast14p5/fast14p5.html

You can see King Nagler himself testing the Paracorr on this telescope.  From the text they were all happy with his eyepieces too!

[YKSE]

Yes, Paracorr helps, should we expect anything else?   The question is: Do we know to what extends paratcorr works? Are coma correction done to a satisfactory level?

Any way, reading more on that homepage, we can see that he has got a couple of sub f3 scopes on order every year since,so the business is surely going on well.

[alan potts]

Believe it or not I was only joking when I said F2, I had no idea such scopes existed, Calvin's F3.9 is the fastest I know of on site. The new Paracorr I believe states it is good down to F3 but as TeleVues are only tested to F4 maybe some abberation nasties creep in the edges. Calvin seem happy with the Televues he has in his super fast scope so I guess the wheels do not actually come off bang on F4, it will be a gentle decline.

alan