I really like the detail you are getting in M51, very nice work indeed cheekygeek!

Thanks for the encouraging comments! I must have just been fortunate, because I'm not sure what part of the process you are saying requires patience and not blowing out the subs too much.

I don't have my sheet in front of me but I would say that I probably rejected between 50-60% of the subs (and that they all were 45 second exposures or less at ISO 800. I only kept the ones with round stars and that appears to be in decent focus.

Just an update: I have to admit that my O-GPS1 has lit a little fire in me for astrophotography, and for me it has been a "gateway" to understanding the basic principles of astrophotography. I've sold my O-GPS1 and ordered a Vixen Polarie unit. The day after I did that, a local astronomy club member contacted me with a nice little German Equatorial Mount set-up that he was selling for $325. It consists of an Orion Skywatcher Pro mount, with DC Dual Drive upgrade and Intelliscope upgrade (a push-to computer system for location). It has also been modified with an auto-guider interface. I don't yet have a scope to put on it (my 8" dob is too big for this modest 20 lb capacity mount), but I will be experimenting with both the Polarie and the DSLR on the GEM going forward.

I will be happy with whatever solution gets me 3 to 5 minute subs for stacking with lenses in the 200-500mm ranges.

For which I thank you. Here's one from my first session with it:

Wonderful! Looks like you got the hang of it quick.

To take it to the next level, do a series of exposures of the same object and stack the RAW files in DeepSkyStacker (free software). It will, no doubt, bring out some of the nebulosity around those baby stars.

Thanks! I took a fair number of shots at a couple of different exposures intending to stack, but didn't get enough good ones. DeepSkyStacker being Windows only I can't run it, but I'm looking into the alternatives.

Nebulosity 3 supports the Mac (but I only use the Windows version). You can download a trial and the full version is a reasonable $80.

Looks like one of the best options for Mac. Pity it doesn't offer the same camera control as for Canon, but I guess that's Pentax's fault for dropping tethering support.

Astrotracer: Electronic Compass Accuracy & Long Focal Lengths

My city-based "observatory" is a fourth floor balcony with reasonably onobstructed view from the south-east to the north-west. Being surrounded by re-inforced concrete and othe magnetic objects, errors in the electronic compass readings are to be suspected.

Therefore, I have started a series of systematic comparisons of Astrotracer compass readings towards fixed landmarks against true geographical directions, as I get them from Geosetter. My findings so far, as illustrated in the following three images are that compass readings are reasonably accurate towards to south, but errors increase systematically and rather significantly as I move towards north:









Having learned this, I felt tempted to try out a really long lens, my Tamron Adaptall-2 SP 350mm f/5.6 mirror lens together with a 2X teleconverter pointed near the meridian (which is unfortunately also the direction towards central Copenhagen):



Orion's Sword with the great Orion Nebula, M42
Pentax K-5; Tamron Adaptall-2 SP 350mm f/5.6 + Tamron SP F-series 2X Teleconverter.
Best 27 images out of 48 at ISO 3200 and exposure times 15, 10, 8, 4, 2 and 1 second stacked in Deep Sky Stacker.

Of course, a 700mm f/11 system isn't the very best "nebulousity system" but results are actually better than I had hoped for. A slightly differently processed M42 image and more star tests in this post: https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/195236...ml#post2594296

B.R. / Steen G. B.