Astro photo processing instructions here...
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
hiro Canon EOS 5Dmk2-sp2 by Seo san Takahashi FSQ-106ED with reducer, extender, and "hiro design" off axis guider, version 2 Lenses by Nikon, Leica, and Zeiss Takahashi EM-200 temma 2 jr / Kenko Skymemo-R Starlight Xpress Lodestar Autoguider http://www.flickr.com/photos/hiroc/
Scopes: 12.5" Dob w/Lightholder mirror, Astro Tech AT8RC, TPO 8" Imaging Newt, Intes MK-67 Deluxe, Tak FS-60CB, Tasco 10TE, Coronado PST
Quote:All image trains have flexure due to gravity. Some have more than others for a given load. The other consideration is the critical focus zone. In general for fast systems any flexure present will show up far more than for slow systems.That being said there are two components to flexure. The amount you have when adjusting focus and the dynamic change due to mount orientation while collecting data. The dynamic change can be partly overcome by an OAG rather than a guide scope. It is this myth of guide scope flexure that comes from this dynamic flexure due to orientation.Your image shows elongation of stars due to non orthogonality of your sensor to the optic axis. It is not field curvature. It is sag in your image train. I have been setting up an F3 system with a focal length of 600mm and a sensor that is 36.8x36.8 mm. This very fast system was very sensitive to flexure. The best solution was to stabilise the image train completely by restraining the camera with an adjustable frame.See image below.Here is an animated gif of two crops from two 16 minute exposures.http://d1355990.i49.quadrahosting.com.au/2012_07/tightT.gifThe difference is a firm tighten of the adjustments that hold the camera.Without the frame there would be about ten pixels of movement per exposure.This is 10x16 minutes of 3nm NII of NGC6334 and NGC 6357. 10MBhttp://d1355990.i49.quadrahosting.com.au/2012_07/ngc6334&6357_ITS.jpgThis image is the proof that the image train stabilizer works!Bert
flickr photos: http://www.flickr.com/photos/24719437@N03/
Quote:Your image shows elongation of stars due to non orthogonality of your sensor to the optic axis. It is not field curvature. It is sag in your image train.