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Grant Privett

I've been doing astronomy for 50 years (eek), so I am probably not giving it up any time soon.

Astronomy has changed and over time my interests have evolved from planetary observing, into meteors, through variable stars and, finally, to the deep sky. These days I'm especially interested in imaging of various sorts but find making pretty pictures increasingly dull. Its just not a challenge anymore - todays's kit pretty much does it for you. 

I generally use a 250mm f4.3 Newtonian on an EQ6 and Starlight SX694 camera from a site in Wiltshire near the Dorset border where the sky is mag 21. I also have sporadic access to a Celestron 11" RASA.

Fortunately, given the UK weather, I like programming and so write my own MS VB6 code to run a Starlight camera and interface it with TheSkyX software. Its a worthwhile skill for when I finally retire and get the chance to observe more - I want to make the most out of every night. I've also taught myself Python 3, which is useful but was designed by an idiot.

My current software project is writing code to resample images of variable nebulae in such a way as to allow quantitative  comparisons to be made, while my observing interest is in seeing how far a 250mm can be pushed and, also, satellite imaging.

2019 Jan 30

20:26 UTC

Gyulbudaghian's nebula as seen on a very windy night. The wind was howling roiund the RASA and on occasions you wondered if you needed to hang on to the roof or watch it blow away. So, anyway, I stuck with 20s exposures and even then some of the images are a bit blurry. Gives a feel for the approximate form at the moment though.

Later in the evening I went over to 60s frames and had a look at Comet 64P/Swift -Gehrels. Easy to image but no obvious tail.

The field of NGC1275 was pretty impressive too. Loads of galaxies. Very rich area. Unfortunately as I was fighting the wind a lot of the time (must be me age)  I didnt get the chance to sort out a flat - so this is just the central portion of the image.

Similarly for IC1613, the local group galaxy was worth a look. I've been meaning to image it for years, but never got round to it. Must start imaging mor of the deeper local group galaxies. This was a bit like IC10 - a bit bright too be a challenge - though it is a bit bigger than IC10.

2019 Jan 28

22:10 UTC

Finally managed to get a night out after a miserable few weeks of cloud.

The wind was howling though, so some images are a tad blurred (went down to 20s exposures at one point to reduce the failure rate) and the wind made it freezing (it was 1C) so I should perhaps have checked the focus more often. 

Either way got some useful stuff.

2019 Jan 12

22:52 UTC

While working out how to use Virtual Dub (sounds like a Bob Marley record from the 70's) I came across a bunch of pics from La Palma. Its pretty difficult to take a bad picture there. So heres one...

2019 Jan 11

22:52 UTC

The run of bad nights has sent me back to some old data to have some fun.

I dug out 3 sets of images I took with a 10" f4.3 Newtonian and a Starlight SX7. For 2 of the 3 sets I used a linear polariser - pretty low quality - and on the final set captured a  normal unfiltered image. I used the unfiltered image as the luminance and green band while the 0 degrees and 90 degrees filtered images were used to synthesise the red and blue. 

The effect is interesting, so that any colour you see in the frame isnt down to the wavelength of light, but the polarsiation state of light leaving the nebula. With a highly ionised gas and a magnetic field there was bound to be contrast. Theres other games you can play using the degree of linear polarisation to things clearer but this is a start.

2018 Nov 22


2018 Nov 18

14:26 UTC

As winter is clearly on the way I decided to have a go at some variable nebulae again.

Tried McNeil's nebula (any excuse to image M78) with 34x120s and 2x binning on a Trius 694 using a 0.279m f2.2 Celestron RASA. As has been said, therea bit there but its only just visible - I estimated it at 1.5% of sky count. I forgot to autoguide but still got a tolerable result. 

I also had a go at Hind's nebula (NGC1555) adjacent to T-Tauri and found it broadly similar to last spring.I was worried the sampling wouldnt be up to it but it looks good enough to me. I set up too late for a flat field unfortunately.

In addition I had a bash at Gyulbudaghian's nebula. That was looking particularly nice. It looks slightly more dramatic when it has the full fan shape, but this was pretty good and I especially liked the fine detail. Reminded me of V900 Mon - which I didnt get round to.

And yes, I do know some images need mirroring...

2018 Nov 1

20:37 UTC

The Pelican nebula captured with the Celestron 11" RASA. Love the detail in this object and wanted something to picture after an evening messing about with the CCD/corrector plate separation. About 18 years ago I imaged it with a different system - an 8" f4.3 Newtonian and a Texas 255 based CCD boasting a swanky 344x244 pixels. The field was a lot smaller, the noise much greater and it was much harder work to get something respectable.

And did I mention the Super Polaris mount, the peak QE of 0.35 and that it predated PHD?

Cue: Montry Pythons Yorkshiremen sketch... rolled up newspaper...tell the kids of today that...etc etc

2018 Sep 11

10:25 UTC

I've finally managed to unequivocally see the Zodiacal Light and photograph it. I've been to several quite dark places but usually theres been too much going on, or the weather has been bad, the Moon was up,  or I didnt have a camera. This time things worked out okay. I had a new Samyang 14mm f2.8 lens with me and a Canon 1100D to hang it on. I got the attached picture high up on the island of La Palma in the Canaries at new moon just before astronomical twilight ended . 

Once I was decently light adjusted, it really did look like there must be a town nearby - but all of those were below the cloud layer. 

In the dark clear skies of La Palma it was a lovely sight!

2018 Sep 8

2018 Aug 18

15:19 UTC

Its often said that the Samyang 14mm f2.8 lens manual lens is a bargain for doing wide field images of starfields and landscapes. With the smaller frame size of a Canon 1100D or Canon 700D series cameras it gives a field 90 degrees across, while on a full frame Canon 5D it gives a whopping 110degree field of view. Its a very clever design of more than 10 lenses with multiple glass types, coatings and even aspheric lenses. Typically, they appear on the second hand market for a bit over £200 - the cost of lenses has risen significantly since the referendum.

The problem is that people tend to forget that these are mass production items - assembling that many components accurately and maintaining build quality is non-trivial. There will be poor batches, there will be poor random examples and the camera they sit  on may be duff too - the CCD being non-perpendicular to the optics by as little as 50microns can be enough to mess things up. 

So, when I bought one second hand  - with guarantee happily - I wasnt suprised that things were not quite right. I took a 10s exposure of the summer triangle and the surrounding sky and then looked closely at the shape of star images off the central axis.

The image attached shows the view at the left top corner of the image and at the top right of the image. The difference is very obvious. Pretty much the whole of the left side of the image was superb. Really good for the cost of the lens - the Canon equivalent costs 7x as much.

Suffice to say its going back to the supplier. Though I am looking for another as I borrowed a Samyang from Mark Radice a few months ago and that gave a great response across the whole field. 

Moral of story - don't believe in perfect manufacturing. When you get a new lens - test it immediately.

2018 Aug 17

23:18 UTC

After the M101 image I spent sometime wondering why the stars are so blobby. Especially as it wasnt a hideously turbulent night. Eventually, I realised the RASA really is sensitive to the CCD-Corrector separation and I only guessed it initially - being more concerned with the pointing accuracy.

I added a couple more spacer rings and the star images tightened up a lot. More work needed but gradually getting there. So to test it I took a few frames of the Bubble Nebula and M52. The moon was still up but that didt stop me seeing the tighter PSF.  Looks like the IR and visible is now nearly in focus at the same position.

2018 May 6



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