More ASI2600 Testing

The ZWO OAG finally arrived this past Monday and I was able to do some initial testing of the 2600 on the EdgeHD11.

Getting the spacing just right was a challenge but I had ample spacers in my shop, and ZWO provided a good variety with their cameras. 

My final configuration is as shown in the pic below; from left to right - nosepiece to mount to the Moonlite Focuser on the EdgeHD, ZWO OAG, 15mm spacer, ZWO Filter Wheel, 2mm adapter and ZWOASI2600. The placement of the 15mm spacer behind the OAG was chosen to allow the guide camera mounting to clear the filter wheel so that it could be rotated to get the pick-off prism to be centered over the long axis of the sensor. 

Initial test exposures yielded very good results, as can be seen in the following images. Since these are single, unprocessed images (except for stretching), the dust motes and vignetting are obvious.

Starfield 300sec

M82 in Ha 300sec

I was very pleased that the f/10 focal length of the Edge produced even less vignetting at the corners than with the f/5.7 WO GT102. Since I had already verified that proper post processing with good flats eliminated the vignetting with the GT102, I should have no problem with the edge images!

However, the placement of the spacer behind the OAG caused serious vignetting in the guide camera view, so much so that finding guide stars became a big problem.

What I had forgot to account for was the longer path of the light cone entering the guide camera. I needed to add 24mm of spacer to the camera. Now the ZWO's pick-off prism is fairly small, and coupled with the guide camera's sensor distance being a bit excessive the effect is like 'looking through a straw'. This needs to be corrected. I decided to move the 15mm spacer in front of the OAG, mounting the OAG flush with the filter wheel. A thin 0.5 mm spacer was used between the nose piece and the 15mm spacer to act as a stop when the assembly is attached to the Moonlite's 2" adapter. The pick-off prism will be a bit rotated from the center of the sensor's long axis but should still be out of the light cone. Now all I have to do is wait for clear skies to test this out.