ZWO OAG, ZWO helical focuser, ZWO EFW 8 filter wheel, ASI290MM mini guide camera and ASI1600MM Pro imaging camera

ZWO ASI290MM Mini ToupTek OAG Equipment Coma
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Andy Wray avatar
Andy Wray avatar
Just wondered whether anyone is using the above combination and how it is working for them when connecting to a coma corrector with 55mm back focus?

I believe that it would work as follows:

* The OAG would connect to the coma corrector directly
* I'd need to remove the 5mm spacer from the OAG before connecting the helical focuser
* The ASI290MM mini would need to be pushed right into the helical focuser as far as it would go
* The only spacer I would need between the OAG and the filter wheel would be the 11mm spacer I already have.

If I've done my maths right, I would probably need to set the helical focuser to about 1.5mm to achieve focus on the guide camera.

I hope someone has this setup and could confirm.
Engaging
John Noble avatar
John Noble avatar
Sounds about right for the 290 MM Mini. I use a similar set up with the 2600 MM and a 174 MM Mini as the guider. I have the filter wheel screwed directly to the camera without the 5 mm tilt plate. The OAG L is also screwed directly to the filter wheel and the tilt plate is screwed to the telescope side of the OAG L. I don't have any spacers to get to 55 mm (12.5+21+16.5+5=55).

Hope that helps.

John
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Andy Wray avatar
Andy Wray avatar
OK, I received the OAG and helical focuser today and the description of the setup seems to work as per my original post (only so far tested in daylight); albeit I'm nearer the 2mm mark on the helical focuser rather than 1.5.
Andy Wray avatar
Andy Wray avatar
OK, I'm not 100% impressed with the ZWO OAG V2:

* The ZWO 2" F5 coma corrector doesn't screw in that well to the OAG as it's threads are too long for it and it ends up hitting the prism stalk
* That means that my back-focus has extended by about 1mm
* I've now ordered a 9mm female to female T2/M42 adapter to replace the 11mm ZWO one and ordered some M48 and M42 spacers to get my image train just right

On the positive side:

* It is easy to adjust the position and angle of the ZWO OAG prism to get it in the right position
* Their helical focuser works really well for focusing the OAG
* The prism gives a nice clear field of view for the ASI290MM mini
* There are no issues in achieving matched focus using an ASI 290MM mini with this setup; you have two adjustments:  the position of the prism within the image circle so that you don't obstruct your main sensor (that makes no difference to the focal point) AND the height of the guiding camera mount point above the prism (that means you should be able to get your guiding camera right in the middle of the helical focuser range to give you plenty of focus adujstment).  

All-in-all:  not 100% seamless, but I can see how this will give me exactly what I need at the end of the day.
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