Astrophotography
One of my main goals in setting up this site was to share my pictures. I got involved in astrophotography for the first time in the Spring of 2005 with my C9.25 and Meade DSI . It was fun, I acquired several photos by Fall 2005, but I was a little disappointed with the results. Unfortunately I had very little time to pursue this aspect of the hobby until the Spring 2007 when I started again - this time with CGE1400 and Canon Digital Rebel XTi. The results were much better - partly due to better equipment, partly due to more experience. Next step was to acquire Hyperstar - a tool that converts 15" SCT into something like 8" APO refractor ... I did it in September 2007. The next fundamental hardware related step was to acquire modified DSLR - the one with original IR/UV filter replaced with the astronomical one allowing good transmittance around H-alpha emission line (656.6nm). I made this step in December 2007, and I used this opportunity to upgrade from Xti to 40D, which uses 14 bit ADC unit (16,536 levels) versus 12 bit ADC in XTi (4,096 levels). Pleiades were the first object photographed with 40D.
My current imaging setup consists of Canon 40D modified by Hutech (with my wife's Digital Rebel XTi kept as a backup) attached to CGE1400 (prime focus), usually with Celestron f6.3 focal reducer (it produces f7 system with C14), sometimes at f11, and often with Hyperstar (at f1.9, see below). C14 field of view at f11 is approximately 19.5'x13', while at f7 it is 31'x20'. F6.3 focal reducer introduces some vignetting compared to f11: below on the left there is a flat field frame at f11, on the right there is a flat field at f7. It can be corrected with flat field frames. Since required exposure time for a single frame is measured in minutes (up to 6 min so far) I need an autoguider. For this I utilize Meade DSI attached to Celestron C80ED piggybacked on CGE1400. For image acquisition and camera control I use Craig Stark's Nebulosity, and for autoguiding I use his PHD program. An example of an f11 image is Owl Nebula, typical f6.3 images are M51, M94 or M63
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C14 flat frame at f11 |
C14 flat frame at f7 |
C14 flat frame at f5 with GEG |
Imaging setup with f6.3 focal reducer |
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In September 2007 I got fantastic tool for astrophotography: Hyperstar from Starizona. It converts Schmidt-Cassegrain telescope into a flat field corrected Schmidt camera with focal ratio f1.9. F1.9 allows for short exposures where previously very long ones were needed: 1 minute exposure at f1.9 is equivalent to around 12 minutes at f6.3! The field of view is appropriately larger: 113'x75' for C14. It is very easy to set up, after one overcomes the fear of removing secondary mirror and attaching something big and heavy to the corrector plate. The additional obstruction from Canon Digital Rebel XTi is quite small, below on the left there is a an image with defocused star showing the shadow of secondary mirror mount (Hyperstar is of course smaller than that, so it doesn't show) with some parts of Canon protruding on the left and right with cables. Illumination of the sensor is quite good, much better than with the f6.3 reducer, as shown on the flat frame displayed below. The other pictures show assembled CGE1400 Hyperstar system almost ready to go (dew shield is missing). A very important thing to remember when setting up a Hyperstar is to run the cables from the camera along the scope's OTA and tie them to the back: there should be no stress on the corrector plate coming from cables. I tie them to the handle on the back of C14, leaving the cables just loose enough between the handle and the camera to allow camera rotation if needed. Since then I acquired many images with Hyperstar, some examples are Pleiades (no reflections!), Veil Nebula Complex (a mosaic) or NGC6992.
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