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Saturday, January 28, 2012

It doesn't Bode well for the new flat...

This latest test of correcting the collimation of the AT8RC demonstrates that it will produce a virtually coma-free image as seen in the image of M81 (Bode's galaxy) below. This is good! However, I screwed up on creating the new flat. My white sheet apparently got loose and I left the camera on high gain (1600 ISO) rather than 100 ISO where it was supposed to be. Doh. Before post-processing, the imaged flat was not what I was expecting. Ran the image workflow anyway just to see. Need to remake the flat.

I suspect though it may not help much as that even with a marginally imaged flat, the previous addition of the field flattener had significant impact on post-processing out the uneven signal levels due to optical curvature.

So, before reverting back to using the flattener lens, I will take another round using a deep sky filter for comparison.

Thursday, January 26, 2012

Collimation step two...what step two?!

Waited almost an hour for scope to cool down outside this evening. For the optical star test, all the provided extension rings needed to be added including a 2" eyepiece extension. Three-star aligned scope using the 1.5" insert and both a 15mm and illuminated reticle piece. Tracked on Sirius to conduct test. It is a wonderfully clear night, again.

Looked just fine. Nice round concentric circles. No warping as focused in and out. Pin point focus also provided sharp diffraction spikes across the entire field of view. Very nice.

Started taking shots of M81 without the field flattener. Have to say, the brighter image seen in the test shots was pleasing. No filter either, we'll consider this a test run on the new collimation.

Need to remember to not remove camera until after I've been able to create a new flat with this change to the optical configuration

Sunday, January 22, 2012

AT8RC collimation, step one...

There are some frightening online postings regarding attempts by other users to collimate the AT8RC telescope. Hmmm. This does not sound good. So, I dug out and read the manufacturer instructions. My takeaway? DO NOT mess with the primary mirror screws! Check. From my readings, those who have, managed to truly make it worse and then spent many hours, days, and other tools to get it back. This should be simple, why is everyone making it sound so hard?

The Astro-Tech collimation instructions emphasize use of a Chesire eyepiece with a light source. This kind of eyepiece has a mirror with a center hole, and the mirror is tilted precisely in a 45 degree angle such that you can visually inspect the appearance of concentric rings with an external light source. Well, my vision ain't what it used to be, so I used my Orion LaserMate Deluxe collimator which is a chesire piece with a laser as your external light source. Brilliant. Much better than my visual acuity.

Removed the extension rings and put the focuser assembly directly to the back of the scope. Turned on the laser collimator. Surprise! The secondary was not in collimation. The return beam point was off center by at least one of the LaserMate's target rings. Out comes the Allen wrench. Took a few minutes to figure out the "loosen-tighten" pattern on the secondary adjustment bolts, then fairly quickly centered beam point and tightened alignment screws. Cool.

Next step in collimation, the star test. Results will be in the next post.

Clear Skies!

Close-up On Rosette Nebula

Near the center of the Rosette Nebula in the constellation Monoceros is an attractive open cluster. My daughter wanted another try at this deep sky object, after her first attempt a few years ago. I think we fared better this time, though still did not collect as many frames as we would have liked.

Nearly 400 frames from our new front driveway in the cul-de-sac. Given the amount of ambient light we had to deal with, I think it would be better to take this shot with a filter. Pushed post-processing on this one and added my own unsharp mask manually at the end.

Having second thoughts about continuing to use the field flattener. Why?! Well, the AT8RC is *supposed* to be largely coma free and the flattener is just another lense reducing transmission of photons in the optical chain. Was the field really that bad before? I don't recall. Maybe the RC scope needs colimation. When the image is finally processed, it is always cropped into my poster template. Wouldn't any aberrations in the outer field be removed? I recall images taken before the flattener were brighter. What about optical curvature? Well, calibrating each image frame with the flat takes care of that. Just need to create a new flat without the field flattener in place. Hmmmmm...haven't I been here before?