A few days ago it came to my attention that Darryl's (Kokatha man) ADC is built with the wedge prisms mounted in a reversed manner to those in the ZWO ADC I was given to test back in early November. Thinking that it could possibly be my ADC that was the outlier as mine was a test unit, I asked a couple of others to check theirs--- Sean Walker's is like Darryl's, while Paul Maxon's is built like mine. So there are examples of both out there.
Either way of building the ADC is 100% correct--- both work equally well. But between them, the initial setup in a given scope is different: In several previous posts I've made describing how to use the ZWO ADC, I described that with an inverting scope that the prism levers and white nylon scale ring screw (a.k.a. datum screw) needed to be on the left side--- initially thinking that all were made like mine. However with the prisms mounted as in Darryl's, the prism levers and datum screw need to be mounted to the right in an inverting scope. The best way to describe this is that some are built left-handed, and others are right-hand ADCs. They simply have different dispersion correction polarity which is fixed by mounting the right-hand ADC to the scope with their bodies rotated 180° vs. the left-hand ones.
In notifying Sam Wen of ZWO about this, he thinks this occurred because of multiple staff members assembling the units. While they are working to standardize the assembly procedure from now on--- and I'm not sure which way will be the standard--- it's always possible that some opposite polarity ADCs will be produced. For background, I also own a Pierro-Astro which is right-handed, and have tested an ASH ADC which is left-handed. I do not know if the direction of those other brands is standardized though, and it's always possible that there are examples of both with those models too.
Attached is a ZWO ADC polarity test image that you can test your ADC's correction polarity with. The answer will determine if your levers should be pointed to the left or right when used in an inverting telescope--- please click on the thumbnail for the full size image.
In the center you'll see a large white disk with a small black center with subtle color fringes simulating spectral dispersion. To either side of the image there are also grey silhouettes of left-hand and right-hand ADCs shown with their levers spread apart and with the ring scale datum screw between them representing a proper horizontal reference.
Holding your ZWO ADC at arm's length from your monitor and while looking through the ADC with one eye, view the dispersed central disk and spread the levers to try to cancel out the color fringing. You should find that you'll correct the color fringes only with your ADC levers to one side and not the other, roughly matching either of the silhouettes.
So now you should know if your ADC is left or right-handed in a inverting scope. But what about use with a diagonal, which corrects the image vertically? First of all, using a diagonal complicates things so I don't recommend it. But if you have to, you'll find that an ADC with left-hand prism levers will need to be used with the levers to the right when used after a diagonal (the eye/camera end). The reverse is true with a right-hand ADC.
Comments and questions certainly welcomed.
Edited by John Boudreau, 26 January 2016 - 04:03 AM.