8” f5 Newt Coma Star Test using Baader Mk3 CC

[Startrek (Martin)]

Although clear, conditions last night on the South Coast were poor but I wanted to test my Baader Mk3 coma corrector spacing on the 8” f5 newt
I had already proven my 6” f6 scope in Sydney earlier in the week with a spacing of 56mm sensor to coma corrector, coma free to edges
Picked a dense Star field near the Statue of Liberty Nebula and captured 8 x 5 minute dithered guided subs using the 56mm spacing
ZWOASI2600MC
PHD2 Guiding around 0.90 arc sec error
Processed this morning and coma is virtually eliminated from the corners
Pretty happy with a successful outcome with both scopes using the Baader Mk3 Coma corrector

Here’s some images
Original version ( ignore the halo around the star , due to conditions)
Cropped versions in each corner

Thanks for looking

[Rerouter (Ryan)]

Could you try as extreme as 58mm to see if it overcorrects. Have a thread about a theory on these

[Startrek (Martin)]

Originally Posted by Rerouter

Could you try as extreme as 58mm to see if it overcorrects. Have a thread about a theory on these

Haven’t got spacers to extend out to 58mm
Sorry
But I’d suspect that it would overcorrect and depending on your focal ratio would change the level of correction
I’m just happy I’ve resolved my issue first go at it with 2 different scopes

[RyanJones]

Hi Martin,

Looks like that scope has corrected well too. It’s interesting that there’s no real difference between correcting the f/6 and f/5 and yet my f/4 needs 3 times the spacing increase. Do you have a single sub of both you can send me ? I’m interested to see what it looks like in CCD insoector ?

Cheers

Ryan

[Startrek (Martin)]

Ryan
My subs out of the 2600MC are 50MB fits files so can’t send but I did check all 8 subs in the corners with ASTAP and the stars were 95% 100% coma free. Only the top RHS corner of the frame near the edges showed a very slight coma when you zoomed in , hardly noticeable and not worth worrying about
Yes it is strange about f5 and f6 newts with same spacing to eliminate coma but their focal lengths only differ by 100mm , f6 being 900mm fl and f5 being 1000mm
I’m sure faster optics ( f4 and lower ) are harder to get spacing right
Thanks
Martin

[etill (Elliot)]

That looks well set up for both those scopes. My 200mm F/4 vixen doesn't quite get corrected all the way out to the edge with the Baader. I have also noticed in some tests that the stars at the centre of the field are bloated a little bit when I do get the spacing as good as I can when compared to no corrector.

I picked up a paracorr 2nd hand and have yet to swap it in since the baader still works very well and I don't really want to pull it all apart and go through the process of getting the spacing right again. I am planning on doing some comparisons when I do that to see if the paracorr is as good as they are supposed to be.

[Startrek (Martin)]

Originally Posted by etill

That looks well set up for both those scopes. My 200mm F/4 vixen doesn't quite get corrected all the way out to the edge with the Baader. I have also noticed in some tests that the stars at the centre of the field are bloated a little bit when I do get the spacing as good as I can when compared to no corrector.

I picked up a paracorr 2nd hand and have yet to swap it in since the baader still works very well and I don't really want to pull it all apart and go through the process of getting the spacing right again. I am planning on doing some comparisons when I do that to see if the paracorr is as good as they are supposed to be.

I use my Paracorr type 2 for visual use only (12” goto dob ) and when I use my ethos 100 deg eye pieces, stars are coma free to edge of field , that’s a really wide field too
There are positive reviews from folk who use it for imaging , you just have to use the correct Televue adapters to set it up correctly

[multiweb (Marc)]

Looks well dialed in. Great.

[Sunfish (Ray)]

Thanks Martin. Great post. Well set up.

[ChrisV (Chris)]

Okay I'm convinced!
I'm adding a bit to my spacing. I've never really tried too hard with this as my big issue has been tilt