March 26 2012
Well, its all starting to fall into place.
After a terrible time with my last attempts at astrophotography (namely trying to shoot M45) which, inevitably, has been consigned to the depth of digital hell, I think I am getting there. I was so close to throwing in the preverbal towel last time I was in too minds whether to take advantage to the week of clear nights we have been offered.
I am glad to say that I did decide to dust myself off and get out imaging!!!
Last night was about getting the small things right, stuff I often have neglected in my efforts to get something recorded to share. I also used it as a chance to try a few new (well new to me) things.
Last night I was actually using my scope rather than lenses on my DSLR. When I have previously used my scope I have struggles with various issues such as balance, polar alignment and focus. Having nailed most items I wanted to get my focus spot on. With this in mind, over the weekend, I decided to try our a home made 'Y' mask. For those who don't know about 'Y' masks they are touted as a good alternative to Bahtinov masks which can be fiddly to self construct, especially if your ham-fisted like me!
Simply put a ‘Y’ mask is, err well in the shape of a 'Y' and is used to create the diffraction spikes on a star to allow accurate focussing. The idea is that all the diffraction spikes should align and nicely intersect on the centre of the star showing good focus. The underlying principles in the use and construction of a ‘Y’ mask are the same as those used for Bahtinov masks. The width of the 'limbs' can be the same order as that used in a Bahtinov mask and an angle of around 20 degrees, from the vertical, is also good.
My mask, not having the equipment to measure angles, was constructed with the upper parts of the 'Y' each at 45 degrees from the vertical i.e. at right angles to each other. The width of each limb was also set at 10mm, which is wider than the calculations for a Bahtinov mask for my scope thus making my ‘Y’ mask around a third order mask. Increasing the limb width was primarily done to aid stability of the mask and prevent sagging over the 10” aperture of my scope. A couple of foam blocks at the extremities meant easy attachment to my scope and I was all set.
Well, I can say it worked a treat. Using the live focus on my DSLR I could clearly see the additional diffraction spikes and managed to focus well using Venus as a reference as it wasn’t quite dark enough for anything else. It was also useful to note the diffraction spikes created by the spider vanes of the secondary which, when out of focus, doubled up and when in focus went to single spikes.
So my night started well!
Focus sorted and locked off (not done this before!), polar aligned and star aligned.
Too easy - right!
After selecting to image the double cluster in Perseus I proceeded to calibrate my guider and ran into a bit of trouble. PHD kept reporting back that there was not enough star movement when calibrating in the W, after some head scratching and quick conversations with the guys online at AstronomyShed I manage to sort this out and get myself guiding. It was only going to be a quick session lasting from around 9 until midnight.
Setup and focussing - Big tick in the box!!!!
As well as this I also wanted to try and nail my flat frames as whenever I use my DSLR I get nasty vignettes. Initially I thought these vignetted were light leakage from the viewfinder - I can safely say this is not the case as I have been covering my viewfinder and still getting the same result. My flats were to be taken the following day, so stripping down my setup was done carefully to keep everything in place. My flats were taken using an embroidery ring and pillow case over the end of the scope, with the scope taken outside in the shade as direct sunlight was too bright.
Flats - Another tick in the box!!!
So what did I get - a shock, thats for sure. A pleasant shock though!!!
The image below is a little noisy due to no darks and the data possibly being stretched more than it should, but I'm pleased with the results. I am also beginning to get the hand of PixInsight as well, so shall be soon purchasing a full license once my trial ends.
Stacked in DSS, edited in PI
29 x 5min subs and flats.
No comments:
Post a Comment