For my second photoshoot after deciding to give a serious effort to come back to astrophotography I chose another famous target – The Leo Triplet. I caught it during a short break in the clouds. The members of this group of galaxies are M65 (right top in the image above), M66 (right bottom) and NGC 3628 (the Hamburger Galaxy, bottom left). They are about 35 million light years away from us.
This shoot was done on a tracking mount, but without guiding, so I used 41 sub-exposures of 25 seconds each (so-called light frames). The relatively short exposure times were needed to avoid the trailing of the stars. My polar alignment was pretty good, though, so the tracking worked well. I used a stock (unmodified) Sony a7r mark IV camera on an 81-mm (478 mm focal length) refractor telescope with the aperture of f/5.6. The ISO was set to 800, following an example I saw online. For calibration, I took 25 dark frames (same exposure length as the light frames, with the lens cap on) and 25 flat frames (2-sec exposures with the same ISO and focus as the light frames, uniformly illuminated by a tracing LED light panel through a couple of T-shirts).
The image below is a wide field, which I cropped in to get the top image.
Generally, I think not much would be possible in this area of amateur astrophotography if people would not share they experiences in online forums and in their blogs. So here is a bit of what I learned in this photoshoot: for shooting the flat calibration frames, while it is common knowledge to select the exposure in such a way that the histogram peak of the resulting images is roughly in the middle or slightly towards the left (dark) side of the light intensity range, it is also crucial to make sure that the shutter speed is long enough to average out the banding caused by the LED light source. Since the ISO is fixed (it needs to match the light frames)
I was quite pleased with this image after stacking the images in the Pixinsight software. I did make a few beginner mistakes, though. The main one is that I decided to go for a second target during the same night instead of collecting more photons of these galaxies. Since then, I have aquired some new tools and techniques, both for the image acquisition and the processing, so I am looking forward to revisiting the Leo Triplet when the skies clear up. Waiting for a cloudless, moonless night is an exercise in forced patience – a benefit of the astrophotography hobby, I suppose.
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