Bay Area, CA Stellarvue SV4, SV70ED Orion 127 Mak, ST80 Pentax K10D (full spectrum mod with cooler) Losmandy GM11 with Gemini 2 My Astrophotos on flickr and on Astrobin and where I write about my efforts
Terry Danks Photography: Birds, Scenery, a little astrophotography too. http://danks.netfirms.com/home.htm Equipment List: Too embarrassed to list it all. Roll-off-roof Observatory Constructed Fall, 2013
Quote:Quote:So 9 hours of tracking (without guiding)can be done with a careful drift alignment.I am not sure if this is possible without modeling. The stars move at different rates at different parts of the sky due to refraction. Stars track at sideral rate at the Meridian. So without modeling the sky with modeling software like The Sky, I am not sure it is possible to track perfectly even with perfect polar alignment.For example in my case. One night before the sky got dark, I polar aligned my mount and slew the mount to a bright star near target DSO for imaging. I centered the star with my imaging camera and the sky was still not dark. I went inside the house to watch TV until the sky got dark. 30 minutes later I went outside to check if the star is still centered of my camera. It drifted in RA direction. I wondered why it drifted in RA and later I found out about refraction.I believe autoguiding is necessary even with perfect polar alignment and without modeling.Peter
Quote:So 9 hours of tracking (without guiding)can be done with a careful drift alignment.
14.5" Starmaster with ServoCat and Argo Navis 1966 Unitron 4" Model 152 EQ Tec 140 TV NP101 f/5.4 APO Telvue .8 Focal Reducer FLI ML8300 and CFW-2-7 filter wheel Astrodon Gen2 RGBL 2" filters Baader 2" Narrow Band Filters Borg 50mm Guide Scope/ATIK Titan Guide Camera AstroPhysics AP900 Losmandy GM-8 Gemini
Quote:Yes, but it's not yet clear what caused the drift during guiding. That's what this thread is about.Other stated that with perfect polar alignment you can image for 9 hours unguided and I assumed that modeling of the sky was not included so I don't think it's possible due to refraction in the sky.Peter
Quote:That's probably because you always use autoguiding to correct any refraction. I also have A-P mount and do the same thing you do. Without modeling and perfect polar alignment, I don't think I can trust unguided imaging for 9 hours unsupervised.Peter