Some experimental DSO test shots using an ASI224 and a Goto Alt Az mount.
ASI224 is stated to be a very low read noise camera (<1-2e) with high sensitivity (peak QE 70-80%). Hence wanted to see what results I could get with <5 sec subexposures.
Another motivation is that on most weekdays I usually don’t bother setting up the EQ mount as I usually only have 1-2 hours of observing time. I know the results will not match long exposure photography but wanted to see if this camera could provide an acceptable compromise for these sessions... almost like a hybrid imaging/EAA experience.
Nexstar 8SE Goto Alt Az 8” SCT scope at f/4-f/5 and the ASI224 connected to my Surface tablet
Software used was FireCap (to capture FITs), DSS (for stacking) and Photoshop Lightroom & RAW Therapee for basic stretching and color balancing (kept processing to a minimum).
Some initial observations:
• The camera is very sensitive. In live view with gain at 300-400 I regularly see up to 14 mag stars
• Even short exposures produce enough SNR for reasonable results vs. my DSLR and CCD which produce a sea of noise at 1-5” subexposures
• I found that for certain DSOs I have to image at a 300+ gain to ensure I have enough stars for DSS to align but as a result I am definitely losing information to clipping even after stacking hundreds of frames
• Maybe with a larger scope (12-16”) I could get away with using a lower gain but I don’t have one so no way of confirming
• The camera I have seems to be exhibiting high amp glow from the electronics at all gain settings. The impact gets really amplified when you stack hundreds of frames (vs. tens of long exposures frames where the SNR is much higher) EDIT: using max for stacking dark frames and lower gain mitigates this to an extent but certain DSOs with limited bright stars in FOV are challenging to stack.
• Stars appear a little blobby even after I have checked focus multiple times (using both FWHM and a Bhatinov mask). Maybe an IR cut filter could mitigate this given the high IR sensitivity of the camera. Tried using my Meade IR filter in front of the Antares 0.5x FR but getting reflections likely due to the high FR being applied. Need to figure out a solution here.
My initial takeaway is that there is potential here but issues exist (may just be due to my lack of expertise or maybe I am just asking for too much and technology just hasn’t caught up yet ).
All comments/insights/guidance welcome...
Edited by Astrojedi, 06 August 2015 - 09:30 AM.