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Grant Privett

I've been doing astronomy for 47 years, 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 and 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.

My current software project is writing code to automatically locate asteroid/NEO trails on large field of view imagery, while my observing interest is in seeing how far a 250mm can be pushed and satellite imaging.

Local society membership: Shropshire

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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2018 May 4

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19:40 UTC

Recently I've been using a 11" Celestron RASA which operates at f/2.2 - which means that objects that in the 90's and early 00's used to cause problems due to their size now fit comfortably in the frame - even when using an imager rather smaller than a full frame DSLR. An example was NGC4565. I recall this in the 90's being too big for the Texas 255 (3.4mmx2.4mm) CCD I used then. In fact it sprawled all the way across the diagonal and off the edges.  

Today things are rather different with the definition of "What is a large deep sky object" shifting somewhat.

So, attached is an image showing NGC4565. Its the full frame Trius 694 image. Created by summing 25x 60s frames. Should have dithered them to get the noise down a bit but the pic is still usable. Cannot imagine what it would be like on a Starlight Trius 35. Feel free to lend me one :)

2018 Mar 29

19:31 UTC

A while back I was at the 2017 solar eclipse in the US. I took some images at 800ISO, 1/40th sec with a humble Canon 1100D and combined them to get a luminance frame. I then looked at the images I had used a linear polarisation filter on and used those to code the R, G and B responses of an LRGB composite - one for each angle of filter rotation. The result will be shown here shortly.

The main difference between this and an image I put up soon after the eclipse is that in this one the images have been manual aligned. 

It aint perfect and I could have done better with a higher quality lens and camera, but as I didnt buy the lens until the day before we travelled, and it was held at 300mm zoom using gaffer tape, I don't feel too ashamed. 

2018 Mar 22

21:49 UTC

Managed to get outside again and get some imaging done. This time I was mainly testing some software changes.  I ran some code I had written, which chased down 10 or more geostationary satellites in 5 minutes -which was kind of fun. Pretty easy to do with TheSkyX and VB6 but I don't like TheSkyX controlling the camera so I let my own code handle all that. 

Anyway... went after NGC2437 - the cluster in Puppis - and the embedded NGC2438 planetary nebula. Was pleased to see I caught them quite well despite their low altitude (Declination -14degrees). It is a rather nice simple pairing. Had  expected the stars to be more bloated.

2018 Feb 24

21:21 UTC

Recently, I've been messing about with a Celestron RASA 11" and a Starlight H18 - its a nice combination. Mostly I look at nebulae, but I got curious about how clear the dark lanes would be in M31 and so took an image. The scope wasnt autoguided but I tried a 240s exposure while I was waiting for my chosen target to clear a tree.

What amused me wasnt the amount of detail in a single frame - quite respectable - but the fact that the galaxy core saturated. Really quite strongly. I had to back off to a 60s frame and even then it was borderline. Might have helped myself by not using the camera in 2x binned mode, but thats what I had a flat for :)

Worth remembering if you are considering one of these.

Example shown. 

I also slipped in 16 minutes worth of imaging of Hind's variable nebula. Alas, I was still on 2x2 binning, but it does at least show the broad features.

2018 Feb 12

23:08 UTC

Last night I had a quick look at M78 - partly because I think its one of the prettiest nebulae and partly because McNeil's variable nebula lies close by.

Unfortunately, the image size limit makes it hard to see both well. Will supply a FITS copy to Callum.

 

2017 Oct 23

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21:55 UTC

Jeremy Shears asked if anyone had an image of Crux knocking about. A couple of colour images are shown here. These were taken using a Canon 20D from Australia and a Canon 1100D from New Zealand. Used a simple fixed tripod and quite short exposures. Had to throw away the image edges due to (cheap) lens distortions.

The monochrome picture was taken in New Zealand using a Starlight H18, a Nikkor 20mm lens and a fixed tripod again.

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2017 Sep 29

23:54 UTC

While in Hawaii recently, I got a chance to sample the delights of a mag 22 sky again - at the top of Haleakala.

I had intended to take a decent 14mm lens this time (I visited in 2014 as well), but instead made do with the 18-55mm zoom that came with my Canon1100D. Its not a great zoom lens, and its not a great camera by modern standards, added to which I only used a tripod to mount the camera.

I took  a series of 6s 6400ISO f3.5 exposures with the arrangement and later tried to align them using AstroArt6. It didnt do a bad job, but i did have to crop the image quite a lot as the star images at the frame edges were really quite horrible. The vignetting was a little fierce too.

Either way, given that I didnt take half the frames I had intended to because two colleagues had decided to join me - one of them wearing shorts - and if we didnt get down the mountain again by 10pm all the eateries (apart from McDonalds an Zippy's) would be closed. 

Despite that, the attached image gives a feel for the sky there. Milky Way absurdly bright - we mistook it for a cloud initially, there was some about - constellations at weird angles and far more stars than I am used to. A wonderful place. 

The image covers Sagittarius and Scorpius pretty well.

2017 Aug 26

17:54 UTC

Managed to make it to the centre line in Idaho. Fearing hideously bad roads we left our hotel in West Yellowstone for the 106mile drive at 4am. We took a "pretty" wibbly-wobbly route to avoid Rexburg where the population was expected to more than double on eclipse day, but only saw a few dozen cars in the predawn light. So we ended up in the desert about 10 miles east of Terreton (AKA Nowheresville) with about 80 other RVs, SUVs, cars, motorbikes and quad bikes.  The very aptly named Sage Junction. People were excited, friendly and very happy - and that was before anything happened. The 4 hour wait passed very fast.

The eclipse itself was far prettier than that I saw from the shore of the Black Sea in 1999. Thats probably the difference between dry desert air and maritime humid air. Either way the corona looked bigger and more detailed than I had seen previously and the diamond ring more breathtaking. We took 9 family and friends with us and several who had never seen an eclipse before were totally gobsmacked by the fantastic view. There were wild grins all round as the light vanished. 

Had intended to take pics for a minute and watch for the final 75 seconds, but instead watched and took photos throughout. Processing them will take some time. They look quite nice, even when taken using only a 30 year old f5.6 100-300mm canon zoom lens hung on a Canon 1100D and fairly light weight tripod.

The trip back was harder. A 6 hour haul where we at one point stopped completely for an hour - one of our party got out to walk and we didnt overtake him for an hour. But as we had Pringles, water, cookies and fruit, no one cared. Months of prep paid off.

A very, very good day. 

Whens the next one?

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