I got a clearer picture of the comet last night, despite the moonlight being even brighter than on Sunday. This time I was using an old
Starlight Xpress MX716 camera (which I picked up a few months ago for under £100:
viewtopic.php?f=9&t=862) fitted with a
Meade f/3.3 reducer, on the back of my
Celestron C8 SCT. I'd not tried this combination before, but it worked very well.
And as an experiment, I was running without any Light-Pollution Reduction filter, so I could only manage exposures of 60-sec without the background becoming too saturated. And this bright background did show up the vignetting of this optical system all too clearly:

- Stack of 40x 1-min from the MX716 with the f/3.3 reducer and no LPR filter. (South is at the top at this stage of the processing).
- vignette716.jpg (25.04 KiB) Viewed 3693 times
Of course a proper flat-field would have compensated for this effect, but I found the Local Estimation Gradient Removal in
IRIS was a good quick-fix.
So here is my final image, which does show a hint of the comet's tail:

- Comet LINEAR on 18-Aug. 40x 1-min using MX716 on C8 at f/3.3.
- 2016a8_18aug.png (224.61 KiB) Viewed 3693 times
The small gaps in the trails of the background stars are due to me omitting a few of the 1-min exposures which were too badly trailed by my unguided mount, but the large gap was due to an unexpected phenomenon: a major power-cut. It was good news that all the streetlamps went out, but although I was running my mount from a 12V battery and the laptop had its internal battery, I was still using a mains power-unit for the SX camera, so it didn't record any data.
And then when the power was restored a couple of minutes later, my neighbour's security light came on, so I had to wait for that to re-set before continuing my captures.
