Kevin_A Strange how WO decided to use a focus knob the size of a Mack truck!
Not only that, and I wonder why no one else has mentioned it yet -- that focuser on the Pleiades 68 is not very usable with a ZWO EAF (should be OK with some of the other electronic focusers, especially the high end Q-Focuser.
As it is, you can see a change in the Bahtinov spikes with just 5 to 10 EAF steps! This is a disaster unless you only move in one direction. Otherwise, the ZWO electronic focuser's backlash will eat you alive. I was seeing so much backlash it was a royal pain. What I did today is to move the EAF over to the 10:1 shaft.
No ugly black knobs in sight now, and the ZWO 90mm rings are just on a 3/8" riser.
With the EAF attached to the fine focuser, it takes about 5000 EAF steps to move the internal drawtube by 1mm. Or about 5 steps per micron. I have seen backlash that is as large as 50 for the ZWO EAF -- that would now be just 10 microns at most, and should be within the CFZ of theis OTA, even if it is an f/3.8.
Good thing I am installing the rack handle at the top (between the ZWO rings), otherwise the position of the EAF will be right where a handle would have been with my usual set up.
The thing must have lots of glass towards the "back", since the scope is back heavy, even without instrumentation, with the handle in between the two tube bands (like their ugly handle with all kinds of mounting dovetail for a finder or something).
The other thing I did was to throw away their rough Bahtinov mask (do people actually use that crap?) and use the three mounting holes to hack a couple of step-up/step-down rings. You can see the Kase mounted here:
I have a large 105-82mm setp down ring coming from Amazion. That should be less Rube Goldbergish that what you see above. I will drill three M3 holes, and it will be properly attached.
Between this and attaching the EAF to the fine focuser, I can now try to do the EAF ∆ to discover (objectively and mathematically) the actual backfocus. With the EAF on the rough focuser shaft (they actually showd that in their manual :-), and the useless Bahtinov mask (I am very convinced no one at William Optics ever studied Fourier Transforms), the EAF ∆ methoud would have been impossible. We get to now discover how clean their image plane design is.
I managed to remove the camera angle rotator cover by using a semicircular lens filter wrench; that thing is torque in by some monster. But I can see the four push pull tilt screw groups now. However, the screw groups are not placed at the four corners of the image frame. The are up/down and left right. So, I need to puzzle a bit on how to adjust my bottom edge left/right tilt. (Or, it is really coming from the ASI2600.)
Anyhow, I will be mounting an ASI6200MC on it next. I want to know if this thing can cover more than an APS-C (although I would be perfectly happy with just APS-C at 270mm focal length). That's right, plate solve says that with my current backfocus setting, the focal length is 270, and not 260mm as they claim, so my copy is really more like an f/4.0. The ASI6200 test should tell me if the tilt is on the scope or on the camera.
I am not done tweaking backfocus yet, and the scope already feels like a keeper. that I might use often. The spot sizes are definitely not as tight as the Baby-Q (both in their published nspot diagrams, and when I imaged the stars). The Takahashi has a snap to it, that the Chinese and Taiwanese scopes all lack however much I try to focus it. Gramted, I couldn't focus well last night because of the poor Bahtinov mask (it should be criminal to sell that crap)and the EAF step size.
Chen
