Re: RAPAS on Mach2

Terri Zittritsch

On Thu, Apr 16, 2020 at 05:25 PM, W Hilmo wrote:

No problem.  Likewise, I’m just trying to offer some suggestions.

Wade, I appreciate the calm dialog.    Thank you.

I tend to be overly verbose when I write, which probably overcomplicates things.  It probably wasn’t clear, but I’ve ever even used an eyepiece with my two main imaging scopes.  Everything that I’ve suggested is intended to be “imaging rig friendly” and fairly simple to do.

No worries.   

Regarding your previous attempts to image unguided, what kind of scope are you using?  I do most of my imaging with an EdgeHD 8, and I simply cannot do unguided imaging with it with any kind of regularity.  The issue is that the primary mirror just has too much movement, even with the focus clutches locked.  There is obvious star trailing after 3 minutes, and 5 minute subs are completely unusable to me.  I have to use an OAG.  An APPM model doesn’t really help a lot with this because the mirror movement seems to be non-repeatable.

I have numerous scopes, but most recently it's been a Stowaway and a TEC140.  The Stowaway was being used at only 492mm , with reducer/corrector while the Tec was being used at, I think plate solving thinks it's 1037mm.    I use the A-P corrector which seems to increase the focal length a little.   

I started AP with an SCT 'Franken-rig'  with lightweight wedge, fork, and a wild assortment of weights to balance the whole thing.  I ended up with OK images.   Once I bought an Atlas, I deforked the meade 8" and ended up with much rounder stars.   That lightweight wedge only had to be breathed on and it would wobble... a huge challenge. but I always got it to work.    With the Meade 8" on the Atlas, my primary exposure was 5 minutes, unless I was imaging something really bright, where I might reduce to 2 or 3 minutes, or really dim, and I'd go to 6 minutes.   I was able to do acceptable work there, although I can do much better now.   My SCT had no mirror lock, and it worked acceptably well.  My Meade didn't have any mirror shift either (I must have been lucky).    I have since re-forked it now, and use it for outreach a lot.. it gives amazing views in a small package.    In fact, usually better views than most of the clubs 10" reflectors, and one 12",  they bring to the events.    Before anyone poo-poos this, they aren't Lockwood mirror scopes, but at least one is done by a local mirror grinding pro, and my SCT gives them a run for their money.
I use a 400mm Orion guide scope and lode star with the TEC140.   With the Stowaway, I have a 240mm guidescope with AS290 (small pixels) for better guiding resolution, or so I think.

When you do an APPM run, how much of the time is spent waiting for the image to download?  I was using a CMOS camera with USB 3 downloads for a while, and it would download a 1x1 frame in just a couple of seconds.  My current camera is a CCD with USB 2, and it takes a *long* time to download a 1x1 frame.  To mitigate this, I do 5 second exposures with 2x2 binning whenever I plate solve (either inside of SGP or with APPM).  That speeds things up considerably.  I spend less than an hour to get 100-150 points.  I suspect that your DSLR can probably download a lower resolution as well.  The last time that I binned a DSLR was many years ago with a Canon 20D, and it lost the Bayer matrix information when binned 2x2, but that was no big deal for plate solving.

I do need to try binning, I do 1x1 today, and use an ASI1600 or an ASI071.   I stopped using DSLRs around 18 mo. or so ago.   So it does takes far too long.. much longer than USB3 would indicate it should.  Many people complain about this on SGPro, but they've not been able to fix it, or it's a driver issue and I've stopped following the discussion.     It is what it is at this point, and for AP it's not a huge deal.    I should try 2x2 binning, and even thought it's all software, maybe i'll result in smaller file transfer if the downsizing happens in the camera.  If it happens at the computer, not much to be gained.   CMOS sensors do not bin in the same sense that CCD sensors do.    Once the image is at the computer, the plate solve is quite fast and usually after the first solve, they all happen very fast.

My personal opinion that is unguided imaging is not something that interests me much.  It takes me about an hour to really dial in a new guider (what with focusing through my OAG and such), but once I’ve done that, it’s all automatic.  Since I always set up with the camera, OAG and guider at the same orientation, I don’t even need to recalibrate the guide software after setting up.

At this point just trying to see what the high performance of the mount gets me.   I know it's made much better than my Atlas's (I have an old and new pro belt drive), but so far I've not been able to get significant and consistently better performance.   My last time out, I was imaging M101 and my RMS was .64 arc sec and M101 is pretty high in the sky.    I acknowledge it could be all seeing too, so my wanting better performance could be a pipe dream.     It could be that living in Vermont I should have taken up a more reliable hobby, like quilting, rather than astrophotography given our lack of clear and stable skies.     But I am a gluten for punishment.   Most of my AP is done in the dead of winter, unshielded by walls or an observatory in frigid weather (certainly not a sissy... smile) and dealing with at least one gotcha a night that requires some amount of debug.  I guess if the Mach2 gets rid of the gotchas, it'll be an improvement.  

I am an EE semiconductor engineer myself, so I have a fondness for finely made mechanical things..   It is pretty!   


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