Astronz
Coma Corrector 2"
Coma Corrector 2"
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Suitable for Newtonian telescopes from f/4 and slower.
This coma corrector can be placed completely inside a 2" focuser and offers a high grade of correction and also a low degree of vignetting. The generous back focus of 70mm allows the use of off-axis-guiders.
M48 thread connection for good field illumination. M48 x 0.75mm (2") Filter threads. Offers 44mm of illuminated field diameter - even full format sensors can be used. Long working distance (70mm) - enough space for off- axis-guiders and filters.
There is no change of the focal length of the telescope
Connection:
- Telescope side: 2" barrel with 2" female filter thread
- Camera side: M48x0.75 male thread - fits directly to further adaptions, filter drawers, off-axis-guiders and more. Includes a T2 (42mm) adapter ring.
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Can't fault AstroNZ - clear communications throughout, and prompt shipping. This coma corrector does reduce coma quite a bit on my 150/750 Skywatcher newtonian, but it does suffer from significant chromatic aberration which needs dealing with in post-processing. I've had one of these before and it was the same. Given that it was half the price of the next cheapest option, I can live with it until I can justify an upgrade.
Weather and work mean I haven't yet had a chance to try out the coma corrector under the stars, but based in my short experiments with viewing tree branches about 150 m distant from my telescope, it looks like this coma corrector is doing a good job at bringing the entire field of view into focus. This is with a 10" F4.7 Newtonian, and with a full frame (35 x 24 mm) camera. Note that this corrector is a rebranded GSO come corrector (I don't think AstroNZ will mind me saying that), and so it does need 70-80mm back focus (so you'll likely need 20 to 30 mm M48 extension rings depending on what you're doing), and despite what the website says, it does also lengthen the scope focal length by a factor of ~ 1.1, so you lose a bit of field of view, but not much.
All in all for the price, I think this is pretty good value, and a great place to start you want to sharpen the stars across the field of view.
Unfortunately, the Coma Corrector comes without instructions. It comes with a separate T-ring, not labelled, so I had to ask what it was. With the Coma Corrector in my 12" Dob, I haven't been able to bring my eyepiece to focus, so how well it works I can't say yet. After searching online forums, I discovered that a spacer needs to be inserted in the coma corrector, so I'm going to need to work out what size spacer I need, and buy it.