Baader MPCC coma corrector spacing???

[yobbo89]

Dang, btw does your oag rotate the pick off or does it rotate the camera?

[UlteriorModem]

The OAG is rotatable around 33 degrees. Its a bit of a trick but can get the pick off prism on the 'short' side of the chip. It can be a little fiddly but yea usually you can get it positioned nicely. It has three 'ears' that can rotate then lock it down. Trick is getting the part with the three ears in the right orientation to begin with. But once set, it stays there.

It's the ZWO OAG.

[UlteriorModem]

Well I got to try the RCC-I out tonight, first light.

The tropical storm took and abrupt right and ended up drawing cooler dryer air in.

Anyhow, at first I put it in the drawtube with the stop ring in place. I could not reach focus, not enough inward travel.

So I removed the stop ring and put the hole damn thing in there right up to the OAG. As it turns out it is almost exactly as long as the draw tube. With that change I was able to reach a focus.

I have examined a few subs and while there better there is still some defect. I suspect tilt.

So the sequence is off and running and the subs look pretty good at first glance. Good contrast, no moon for a change

I will analyze things a little more pics comming I promise

[UlteriorModem]

A quick update. I found out that the RCC-I states a spacing of 94.5mm from the M48 threads, and 91.5mm from the stop ring if used.

Since I had removed the stop ring and was still using the 91.5mm spacing it was a few mm short. Added a 5mm extension ring to bring it to 95.5 mm. Pretty close.

Will get a chance to try it tonight.

[UlteriorModem]

I have reached my absolute wits end after tonight with this.

The 8" astrograph is going back in it's bag!

Alot of time and money went into this 'project' and none the better for it.

Let's just say I did not have a good night and leave it at that.

[yobbo89]

dang tom, sorry to hear that, same tilt problems in the corners ?

[UlteriorModem]

dang tom, sorry to hear that, same tilt problems in the corners ?

Actually made some progress on it. Posted a full frame image in the AP deep sky section.

In a nutshell I got frustrated trying to work with CCD Inspector trying to work out the tilt. Eventually I got fed up with incoherent readings and errors from the program.

I decided to take the camera off and move the tilt plate all the way down flush with the camera body, the 'default' if you will. I was really just looking for a starting point.

When I put the camera back in an took a few subs I said "Hey that's not bad" and just let the sequence go for the rest of the night (after touching up collimation). Unfortunately I did not take the time to refine PA but it was not too bad.

I think two things had happened, the spacing got moved in ever so slightly, maybe 1mm, and the tilt was greatly reduced. Havent had much time to further analyze with CCD inspector but a quick visual inspection of the frames was a pleasant surprise!

NGC1038 1 by Tom Whit, on Flickr

[yobbo89]

yeah, ccd inspector needs a large star field spread out on the image, it works poorly for for example nebula targets .

[yobbo89]

huh, your coma correction is better then my skywatcher aplanatic .. , you have a little tilt in the right side top and bottom, but ahh that should be very managable in software processing with distortion correction .

[UlteriorModem]

Evidently I was told it was due to the stars on the edge of the field being so distorted that they were not being calculated as stars so it only saw stars near the center of the field. That was before I reset the tilt ring.

Kept trying and putting up an error message about the stars not being spread out enough, regardless of where I pointed.

Sounds reasonable. Again haven't had a chance to check things again now that it seems sorted.