Crater

Attached is an image showing an example of a DSO image that can be obtained using an Alt-Az mount. When obtaining the image the equipment I used comprised : Camera : Modified Canon EOS 1100D DSLR plus Light Pollution Filter. Telescope : SkyWatcher 130PDS Reflector plus Coma Corrector. Mount : SkyWatcher AZ GOTO. Capture Software : BackYardEOS. This was imaged on 06 Feb 2015. Exposures were, 30s at ISO 1600, effective f/4.5, using 20 Light frames and 20 Dark frames. The rather short exposure and high ISO being necessary with an unguided AZ type mount in order to prevent star trailing and field rotation. A second set of exposures was also obtained in order to achieve more detail in the bright core of the nebula. This core was over exposed in the first set, whose purpose was to obtain detail in the nebulosity. Exposures for this second set were, 30s at ISO 200, effective f/4.5, using 20 Light frames and 20 Dark frames. When stacking, I was very selective and used only 9 and 8 of the 20 Light frames in each set respectively after rejecting any frames showing signs of star trails or star distortion. Deep Sky Stacker (DSS) was used for all stacking. The output file from DSS for each of the above two sets was processed using both Photoshop CS2 and StarTools. The two different results were then merged using the Layer Masking facility in Photoshop in order to obtain the required High Dynamic Range of this nebula. This prevents the bright core being overexposed, while allowing the detail in the nebulosity to be seen. This Layer Masking technique is that advocated by Jerry Lodriguss on his website. The final image obtained is better than a similar attempt a year previously, as the star shapes and colours are improved. Firstly, I believe that this is because I used a reflector telescope rather than the non-apochromatic refractor in the previous year. Secondly, because I now used a DSLR that had been modified. This modification allows more of the red content of the nebula to be recorded.