Kevin_A OAGs were never good quality stars in my opinion since you have to use an inferior part of the flattener when using a bigger sensor camera for imaging.
How true that is.
If the part of the image plane where the OAG resides is good, why not use it for a larger image, instead of wasting it on an OAG :-).
Except for 16" SCTs, I have never understood why people like using OAG. Nor the "Duo" cameras.
SBIG gave up after inventing the "duo" scope and sold as the ST-7. ST-4 was the first and the last camera to have two chips. ST-4 was the first camera that had the guide pins, that is why those pins are called ST-4 today.
http://www.company7.com/sbig/products/st7.html
I still have my SBIG 8300; that one once had the reputation that the Sony IMX571 based cameras enjoy today.
I regret sending Sam an email about the two camera ST-7 a year or two ago. He got one of his flunkies to jury rig one up (guy used to do product support, not engineering). But I'd warned him about all the shortfalls of a dual camera system, which he of course does not include in the Duo documentation. To ZWO, everything is a rush job to get the next bundle of money. And then abandon support to go the the next money making scheme. Nothing is studied properly.
I also now regret telling Sam about how well the RST-135 worked as a mount. He went off and copied that too, but without really studying the minutiae of the RST-135. It puzzles me (... it is a puzzlement... The King And I) the Chinese blindly copy things without first trying to understand how they work. The leaky tantalum capacitor was a good example, and exploding LiON batteries is another. Both were missing a critial ingredient that stabilized the chemistry. The copied (stolen IP) ones lacked them cause fires, and I think the expolding batteries caused lives to be lost.
At least the ZWO mounts won't kill anyone, and it serves them right, now that the Chinese are copying themselves, and with more stable mounts. At least two companies now have starin wave mounts with much better measured guiding -- only one of them recently distributed in the US by Agena. They all use the same strain wave gears; so we know the tracking glitches are how ZWO is incorporating the gears, not the Chinese gears themselves. In addition to real EE who can design USB interfaces, ZWO also needs to hire real ME who can design mounts.
After those two things, I have now sworn off telling Sam about neat ideas to implement. I was expecting him to start some real investigation, but he simply took off and got his people to copy things superficailly. Unfortunate for the ZWO mount customers, I don't think there is a way to get rid of the mount glitches short of a full recall (like they did with the leaky ASI2600), and I don't think they will do that.
Chen
