Sky-Watcher 0.9x Coma Corrector
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 Sky-Watcher 0.9x Coma CorrectorSky-Watcher 0.9x Coma Corrector 

Sky-Watcher 0.9x Coma Corrector

£159.00
  (4 Reviews)
✓ 2 year warranty

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2x in stock shipped 1-2 working days

About this product

Model:  sw_coma_corrector
Part Number:  20233

Suitable for use with Newtonian reflector telescopes with f-ratios f4-f6 but is optimised for the new Sky-Watcher Explorer DS f/5 telescopes with 2-inch focuser.

Acts as a 0.9x reducer so a f5 Newtonian becomes f4.5 and f4 becomes f3.6. 

For imaging with a DSLR camera a Sky-Watcher DSLR-M48 Ring Adapter is also required. 

Also includes adaptors for visual astronomy with 2" eyepieces. To use with 1.25" eyepieces you will need a suitable 2" to 1.25" adaptor.

Threaded for 2" filters.

Requires 55mm back focus.

Customer reviews

Average Rating (4 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
My Coma is Corrected
Wednesday, 22 July 2020  | 

When I bought my Explorer 200pds I checked out the forums to find out if a coma corrector was a "must have" or a "nice to have". The opinion seemed to be divided around an F5 scope - basically "you might get away with it"

My plan was to build my new setup incrementally - add stuff as the need arose. Initially working visually all was fine - after all you only concentrate on the middle of the eyepiece. When I started imaging I was really pleased - mainly because I had acquired an image of what I was pointing at. As I started to process I noticed the stars at the edges were off. It wasn't quite what I was expecting, the looked faded and streaky - like driving into a snow storm at night,

The more I processed the more I became aware of it.

So I ordered a coma corrector.

The difference is immediately obvious. Stars are sharp and bright right the way across the frame. The image is flat and sharp. Removing coma just makes the image come to life.

As a far as I can see there are no downsides - stars are round and there is no distortion. I did notice a slight flare when I photographed Vega (my preferred focus star), but I have not been able to reproduce this.

I have not especially noticed a great benefit from the focal length reduction, but that's kind of a bonus.

I am impressed and wish I'd bought one at the outset.

As a note to new scope buyers. If you are intending to buy a Reflector and you primarily want to image - you will need a coma corrector. This one does what it is supposed to and won't break the bank.


Rating (max 5):  
Read this if you Have a 150Pds!
Wednesday, 3 June 2015  | 

Corrects the coma on my Explorer 150Pds almost perfectly across the field of view of my Canon 450D.
I was however disappointed to find that because it also acts as .9x reducer the focuser has to be wound in so there's only 7mm of inward travel left. The problem with this is that the inside edge of the focus tube protrudes in front of the primary mirror causing images of bright stars to have bite marks in them and all stars are slightly D shaped. This would be forgivable if it was made by anyone other than Skywatcher but because the 150Pds is one of the scopes this CC is specifically designed for I find it very poor.
The problem can be fixed by cutting the inside end of the focus tube to make it shorter but this does mean its possible to wind the focuser too far out so that it comes off its mounting wheels.


Rating (max 5):  
Good Round Stars All the Way to the Corners
Monday, 23 February 2015  | 

Using this CC with a Skywatcher 130PDS mounted on an EQ6 AZ GT. My camera is a modded Canon 100D DSLR.

So far....so very good. All sharp pinpoints all the way out to the corners.

Nothing more to add. What it says on the tin.


Rating (max 5):  
Perfect accessory!
Wednesday, 21 August 2013  | 

I bought this coma corrector for use with my Skywatcher Explorer 150PDS. It does exactly what it advertises and does so well above its price. This coma corrector gave me perfectly coma-free images on my large ATIK 383L+'s CCD sensor, with no internal reflections produced. I have zero complaints and would happily buy again.

Please do remember that if using this with a CCD camera like myself, you will need to have 55mm (+/- about 2mm) of spacing between the bottom of the 2" thread and the CCD sensor. This is easily achieved with a combination of spacers. If imaging with a DSLR however, the Skywatcher DSLR adapter will automatically take care of the required 55mm spacing.

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