A first attempt at M51

Posted on June 10, 2020 by james

Through March and into April I attempted to image Messier 51 with my Skywatcher ED80 and Atik 314L+ (mono).

I ended up with twenty-six five-minute luminance exposures and nineteen three-minute exposures for each of red, green and blue for a total of a fraction over five hours of imaging time.

This is the processed luminance data, scaled down to half size:

I was pretty pleased with that, but my final colour LRGB image I think needs more work. Partly I suspect it’s because I captured the colour data at 2×2 binning so it needed to be scaled up to match the luminance. Partly it’s my lack of skill at processing. I shall definitely return to this another time…

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Possible meteorite image?

Posted on June 10, 2020 by james

I suspect long exposure images that catch genuine meteorites burning up are not that common and I try quite hard to explain any unexpected trails on my images as satellites or aircraft, but this one doesn’t seem to fit and I can’t decide if it is or it isn’t.

It’s interesting that the brightness of the trail fades a little in the middle and seems a little uneven. I don’t think that would happen with a man-made object, but I just can’t make up my mind.

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Guidescope in need of TLC

Posted on June 10, 2020 by james

I recently purchased a used Celestron 80mm guidescope with a focal length of 600mm. Normally I’d probably have gone for another ST80, but in fact I wanted this one to use with a slightly longer focal length OTA anyhow, so the extra focal length of the guidescope suited me.

I really couldn’t get it to work though. The guiding was utterly unreliable. It was only when I looked at the images from the guidescope in detail that I think I might have uncovered why:

That really doesn’t look good to me. I’m going to put it to one side for the time being and see what I can do to sort it out later.

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Interesting guiding drift plot

Posted on June 10, 2020 by james

In relatively poor seeing recently, the drift plot for guiding in Ekos showed up like this:

An interesting pattern, I thought, like three circles on a line through the centre of the plot. I can’t explain either the circles or the fact that they appear to be centred on a line at an angle through the plot. More investigation required I think.

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Odd diffraction spikes from a refractor

Posted on June 10, 2020 by james

The other night I was framing an image using my 80ED and Atik 314L when I noticed that some stars in one corner of the image had odd diffraction spikes:

I couldn’t see what the problem was at all at the time, and ended up having to take the entire telescope/filter wheel/camera assembly apart to find out. It seems a small sliver of some material (plastic, possibly?) had dropped onto the edge of the objective lens, presumably in a position where not all incoming light from the field of view could make it onto the sensor, thus it only affected stars near the it’s position.

A quick clean off and the artefact completely disappeared the next night. Not something I’ve ever seen happen before.

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Odd Maksutov reflections

Posted on June 10, 2020 by james

The other night when I slewed to a bright star to check the focus on my Skywatcher 127 Mak I got this image from the ASI174MM camera:

I’m thinking the off-centre ring must be a reflection of the bright star, but the question is what is causing it? My best guess at the moment is that perhaps it is a reflection off the sensor cover that is again reflected by the back of the filter being used at the time, but I guess it could also be a reflection off the front of the filter and/or a reflection back from the secondary. I hope the ring isn’t central because the star isn’t central and that it doesn’t also mean something isn’t square to the optical axis.

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Darkstar restoration, part 6

Posted on June 10, 2020 by james

I think the next step has to be sorting out the spider and secondary mirror assembly.

Now I’ve had some time to consider options, what I’d really like to do is to build a secondary assembly similar to those used on more modern newtonian models, using two pieces of round aluminium bar (one cut at 45 degrees for the mirror mounting). TS sell such items though they’re far from cheap so I’ll have a go at making one myself. I can then mount the plate that I already have on the end and fit the mirror to that.

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Darkstar restoration, part 5

Posted on June 10, 2020 by james

The new stainless bolts arrived, but I’ve had little chance to get out to the workshop so this morning I got out and started work on fitting the new focuser. This took a little longer than planned as I realised halfway through that I would have to remove the focuser body from the backplate to get access to the lower two holes on the backplate in order to mark up the tube for drilling the new mounting holes (and actually it makes fitting easier, too). There are four grub screws in the edges of the backplate that can be slackened off to allow the focuser body to be rotated and backing them out a little further allows it to come away completely so it’s not hard, but for the fact they seemed to be done up exceptionally tight to start with. The tiny Allen key I had to use was flexing rather more than I was entirely comfortable with before they began to turn.

Anyhow, all sorted now.

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Robert Brown Focuser Controller build, step by step #13

Posted on June 10, 2020 by james

Woohoo! It lives, Igor!

I did wonder why the tests to turn the motor an entire revolution weren’t actually turning the spindle very far until I remembered that it has a 27:1 gearbox on. Easily missed, that one 🙂 And I have the buttons cross-wired as compared with the LEDs, but that’s just a question of switching a connector around the other way on the pin header I think. And the buzzer now works, though I don’t recall actually doing anything to fix that.

So now I need to decide which telescope I’m going to put it on and make up a suitable bracket. Then probably re-balance everything thanks to hanging another half kilo of motor on the end of the OTA.

Oh, I almost forgot — need to adjust the current limiting resistor on the stepper driver board too.

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Robert Brown Focuser Controller build, step by step #12

Posted on June 10, 2020 by james

I have some 24AWG cat5 patch cables that are no use to me any more, partly because they’re not good enough for gigabit ethernet and partly because they’re not assembled very well (they were supplied with Sun Microsystems kit, too; you’d think at the prices they used to charge they could afford to supply decent patch cables). I’ve chopped a length of about a metre out of one and soldered that into a DB9 plug. Looking at the tables for stranded 24AWG a single conductor should be good for 1.4A, but obviously the other wires and insulation in the sheath will lower that. I think it should at least be ok for testing whilst I find something else with larger conductors. I can’t tell what size the wires are on the motor body. No larger than 22AWG I’d say. Certainly not as big as 20AWG. Obviously they’re in free air though.

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