Andrew's Astronomy Blog

Friday evening was mostly clear albeit with a very bright moon. The original objective was to image the Sculptor galaxy (NGC253) which reaches 11 degrees above the southern horizon at this time of year. Unfortunately, there was a bank of cloud to the south which ruled this out. Plan b was the Orion Nebula.

The 20″ was tracking nicely and the Trapezium group of stars in the centre of the nebula provides a good guider reference. I dispensed with the luminance frames and just took 30 second red, green and blue sub-frames (20 of each) binned 2×2. This cuts image acquisition time which is important with the Alt/Az 20″.

Image processing was with Maxim, PixInsight and Photoshop. I’m using the trial version of PixInsight at the moment trying to get to grips with the very different method of processing. The background extraction process is exceptional but for final sharpening, levels and colour balance I used Photoshop.

My recent widefield nebula pictures of The Heart & Soul, Veil & Mu Cepheus left me rather flat with a disappointing lack of saturation and definition in the Ha regions. Suspicion fell upon the IR block filter in the imaging train but my first attempt at a replacement failed when it was a little too thick to enable my 75-300mm lens to focus.

Suspicion was confirmed when I found the original datasheet for the filter set where it was described as ‘Einsteiger filtersatz’ or Beginners filterset. The spectral response diagram showed a decline in light transmission after about 600nm. As the Ha line is at 656.28nm the filter was removing most of this light.

The second replacement was a Baader IR/UV cut filter in a 1.25″ housing that fits within the Geoptik adapter. As well as passing 98% of light upto 680nm this filter has the additional advantage of cutting violet light below 400nm.

A near full moon restricted me to relatively bright targets on the other side of the sky and the Veil nebula met the requirements. Focal length was increased to 200mm and 12 five minute sub-frames were acquired. Despite the less than ideal conditions the result is a huge improvement on my earlier attempt here: http://andrewluck.me.uk/?p=673

Last night was forecast to be clear until midnight so I loaded my portable setup into the car for the short trip over to the observatory. After last week, when 2 of us turned up for the regular tuesday night meeting, the evening was very well attended by club members. As the observatory was full I setup on the telescope pad outside.

Target for the evening was IC 1805 & IC 1848 between Cassiopia and Perseus and before the cloud closed me down I got 9 ten minute exposures. The camera was my QHY9C with the Canon 75-300mm zoom lens. I seem to be spending a lot of time with this combination at the moment with it’s 10 degree diagonal FOV and I’m starting to feel the lure of the 135mm f/2 prime lens with it’s faster light gathering and better colour correction. Maybe next year.

The second target for Saturday night was Mu Cepheus and IC1396 again. I’ve looked at this one recently but with the 10 minute sub-frames I was getting I wanted to see if there was any more detail possible. Nine 10 minute frames were stacked and then processed in Photoshop. The biggest problem area is around the Garnet star itself and there’s a dark ring I haven’t managed to eliminate yet. The problem is caused by the high difference in brightness between the star and nebula and I need to research some techniques for reducing this artifact.

Comparing this image with the previous one, there’s more subtle detail in the dark nebulae.

Another year is slipping by and the Autumn star party at Kelling is over. After missing friday due to illness we arrived on Saturday in time to catch the trade stands before they closed. From Altair Astro a new dew strap for one of my Canon lenses, dew heater for the red dot finder and a 2″ extension tube for the club’s 20″.

Of course, friday night was one of the best nights of the year. Various superlatives were being used to describe it and I missed it all. Saturday night was supposed to cloud over after midnight but, by the time we emerged from the bar at 9pm the sky was clear and that’s the way it stayed for the entire night until I packed up at 3.30am and retired to the tent.

With the chance of the sky clouding over I rushed the polar alignment and focus. Despite this, the polar alignment worked surprising well and I was able to take 10 minute exposures with the 75-300mm zoom set at 135mm. The focus was less good and I wasted some time before I realised and refocussed. First target was NGC 7000, The North American Nebula. After rejecting the out of focus images a couple had slight trailing leaving me with five 10 minute frames.

With a full moon in the sky last night was a test session for my new IR block filter and the Geoptik Canon lens adapter. Back focus is at a premium with this system with only 7-8mm to squeeze a filter into. The new filter appears to be slightly too thick but was within a whisker of achieving focus so there may be hope yet. Swapping the filter out I refocussed on Sadr and took 10 3 minute exposures at 135mm. A heavy crop of the field removed the worst of the background gradient introduced by the moon but some artifacts of this remain after processing.

The Veil nebula is something I’ve been meaning to take an image of since I got my QHY9 camera and last night was the first opportunity I’ve had. The skies are getting dark again after the summer twilight, there was no moon and conditions were pretty much as perfect as they’re going to get in the UK.

Using the Canon 75-300mm lens at a focal length of 100mm I took 20 5 minute exposures followed by 30 2 second flat fields. This lens is badly afflicted by vignetting and the flats compensate nicely. With Cygnus high in the sky and little moisture to reflect the ever present light pollution gradients weren’t a problem for this wide field.

The nebula doesn’t stand out particularly well against the backdrop of Milky Way stars in this image. To improve visibility, I’ve cropped the image fairly tight to the nebula as otherwise it’s rather lost amongst the stars.

Edit: Image replaced with reprocessed one.