Coma Corrector?

[Starwiz]

In the never-ending quest to improve the quality of my images (which is strongly correlated to the reduction of money in my bank account), I want to improve the star shapes that I get at the edges of my frames.  I think this is coma.

The image shows a zoomed-in portion at the top left-hand corner of my latest image.  I get similar in all four corners with the stars trailing towards the corners.

So, do I need a coma-corrector, or is there another way?

I'm using a SW200p (F5) and ASI1600mm-Pro with filter wheel.

Thanks

John

 

 

[alan potts]

It certainly looks exactly like the coma I can get with my 18 inch F4.3 Dob, I got a Paracorr by TeleVue which has a slight magnification factor, x.15 if I recall correct. There is no doubt it is an excellent piece of equipment but with a sizeable price tag. There are others available I am sure but as to how good they are that another matter. I went with the TeleVue because all my eyepieces are, they say it works perfectly for AP, which I am sure it does.

Alan

[Starwiz]

12 minutes ago, alan potts said:

It certainly looks exactly like the coma I can get with my 18 inch F4.3 Dob, I got a Paracorr by TeleVue which has a slight magnification factor, x.15 if I recall correct. There is no doubt it is an excellent piece of equipment but with a sizeable price tag. There are others available I am sure but as to how good they are that another matter. I went with the TeleVue because all my eyepieces are, they say it works perfectly for AP, which I am sure it does.

Alan

Thanks Alan.  That looks a great bit of kit, but I may have to do some saving.

John

[Ships and Stars]

I wanted the Paracorr, but due to price and inability to find one second-hand, I ended up going with a second-hand Explore Scientific HR coma corrector in as-new condition for around £175 I think.  It is adjustable or 'tuneable' like the Paracorr, so no need to buy additional spacers etc like some of the others require. I've only used it a few times, but on a 100deg Ethos eyepiece at f3.95 in a big dob it does the trick nicely. It adds 1.15x mag I believe. I've also used it as a spacer to obtain the right focus with other EPs I have that are either too far out with the normal 2" spacer and too close without. I think the Baader line is a fair bit cheaper but seem to recall they require additional spacers. I'm not any more familiar with the Baader line than that, am sure others who do AP (I'm visual only) will chime in here soon.

[alan potts]

I bought mine about 3 years ago and I don't believe I have ever seen a secondhand one. I personally believe TeleVue are as good as any on the market for all their product and in many cases better. This better though is only very subtle in the case of many eyepieces I have tested and written about on here., I feel the same will be true of the Paracorr.  EXSc is very good gear too and even some SW stuff is not far behind for much less, I am sure given a bit of time many others will chip in with what they have for much less than the price on the TV.

Alan

[Starwiz]

18 hours ago, Ships and Stars said:

I wanted the Paracorr, but due to price and inability to find one second-hand, I ended up going with a second-hand Explore Scientific HR coma corrector in as-new condition for around £175 I think.  It is adjustable or 'tuneable' like the Paracorr, so no need to buy additional spacers etc like some of the others require. I've only used it a few times, but on a 100deg Ethos eyepiece at f3.95 in a big dob it does the trick nicely. It adds 1.15x mag I believe. I've also used it as a spacer to obtain the right focus with other EPs I have that are either too far out with the normal 2" spacer and too close without. I think the Baader line is a fair bit cheaper but seem to recall they require additional spacers. I'm not any more familiar with the Baader line than that, am sure others who do AP (I'm visual only) will chime in here soon.

 

15 hours ago, alan potts said:

I bought mine about 3 years ago and I don't believe I have ever seen a secondhand one. I personally believe TeleVue are as good as any on the market for all their product and in many cases better. This better though is only very subtle in the case of many eyepieces I have tested and written about on here., I feel the same will be true of the Paracorr.  EXSc is very good gear too and even some SW stuff is not far behind for much less, I am sure given a bit of time many others will chip in with what they have for much less than the price on the TV.

Alan

Thanks both.  Some useful info to consider there.  Time for me to start doing some research for when my wife asks what I want for Xmas.  😉

John

[alacant]

Hi

How about correcting the coma in software? Anything which allows you to make masks will do and most astro processing software will have their own one-click version. That way, you avoid having to pass the light through glass, which always seems to introduce more aberrations.

Cheers and HTH

 

[Starwiz]

1 hour ago, alacant said:

Hi

How about correcting the coma in software? Anything which allows you to make masks will do and most astro processing software will have their own one-click version. That way, you avoid having to pass the light through glass, which always seems to introduce more aberrations.

Cheers and HTH

 

Thanks.  I'll research that too.

John

[dph1nm]

The Skywatcher Aplanatic corrector is very good in my f4 Quattro (for which they are designed). Not sure how well they work at f5?

NigelM

[Starwiz]

2 hours ago, dph1nm said:

The Skywatcher Aplanatic corrector is very good in my f4 Quattro (for which they are designed). Not sure how well they work at f5?

NigelM

Thanks Nigel.

John