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 Post subject: Comet PanStarrs
PostPosted: Thu Mar 14, 2013 9:23 am 
I saw comet PanStarrs last night.

This is my first blog so don't know if I'm doing it right!
Was cloudy at 6pm where I live - Eccleston.
Decided to go north to Jubilee Tower which is up on the fells to the east of Lancaster
on the way to the Trough of Bowland.
This is a great vantage point with unimpeded western view from Cumbria to Snowdon.
Some light pollution from Heysham/Morecambe and Blackpool but nothing to the north or east or in the foreground.
I got there just before 7pm to find other observers including the secretary of the Lancaster and Morecambe Astro society and other members.
The crescent moon was clearly visible above the clouds but the comet was hidden.
I set up my telescope and five minutes later the clouds moved and revealed the comet!
I spent time viewing, and let others view through my scope. The tail was clearly visible.
By the time I got my camera out and set up cloud had drifted across and obscured the comet again.
I hung around for another hour but to no avail. I think the comet was below the horizon by then. It was bitterly cold so I went home.
Who will believe me without the photo?
Lesson learned - get the camera out first!

Steve Read


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 Post subject: Re: Comet PanStarrs
PostPosted: Thu Mar 14, 2013 1:39 pm 
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Well done Steve - your enterprise in "going mobile" was rewarded.
I think that everyone to the East of you was more hampered by the clouds.


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 Post subject: Re: Comet PanStarrs
PostPosted: Fri Mar 15, 2013 12:11 pm 
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Although I wasn't able to see the comet on Wednesday, I did manage to image the Moon much closer to the Western horizon than I'd imagined was possible from home.
From the back-garden my view to the West is blocked by the house, so I was experimenting with what I could catch over the side-gate. Following Carl's practice at the Broomes Farm Observatory, I was using an "overhead camera", with my tripod set at maximum height (hence I needed the step-ladder to reach the viewfinder:
Attachment:
File comment: Pentax DSLR and 50mm lens mounted on tracking platform at >2m above ground!
highcam.jpg
highcam.jpg [ 162.92 KiB | Viewed 7674 times ]

But this did enable me to see the Moon down to about 10 degrees above the horizon:
Attachment:
File comment: The Moon sinks towards my "artificial horizon" (the nearby houses). This is a stack of 1 & 2-sec images taken at 1-min intervals.
darkmoon2a.jpg
darkmoon2a.jpg [ 50.36 KiB | Viewed 7674 times ]

and catch "the Dark Side of the Moon" (illuminated by Earthshine):
Attachment:
File comment: 5x 2-sec images with 50mm lens at f/5.6
darkmoon.jpg
darkmoon.jpg [ 7.92 KiB | Viewed 7674 times ]


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 Post subject: Re: Comet PanStarrs
PostPosted: Sun Mar 17, 2013 10:11 am 
I think you were unlucky there Ross. Your sky looks clear except for the ribbon of cloud which is sitting on the horizon and obscuring the comet.
There is a pretty good site much nearer to me on the top of Parbold hill, which I've been to
a few times recently looking for Mercury and Mars just after sunset, but it's always the same story - that ribbon of cloud which obsinately sits on the horizon obscuring the target objects.
BTW there is a light pollution map in the April issue of Sky at Night magazine showing how much we suffer from light pollution in this area, but it also shows where it's dark if you want to travel.
Looking forward to your talk on Tuesday.


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 Post subject: Re: Comet PanStarrs
PostPosted: Tue Mar 19, 2013 10:22 pm 
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Follow-up from tonight's talk by Ross:-
Taken with a Canon 600D and Sigma 600mm F/8 Cassegrain Mirror Lens
http://www.flickr.com/photos/thedavewalker/8554731591/
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Processed:-
http://www.flickr.com/photos/thedavewalker/8556569886/
Image

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 Post subject: Re: Comet PanStarrs
PostPosted: Thu Mar 21, 2013 12:55 pm 
Frustrated by the fact that Panstarrs is behind a 100ft Oak tree in my garden I spent some time checking my planetarium software for its position. I notice that there are a number of other comets close to C/2011 L4 (Panstarrs). In fact there are two other Pannstarrs - these are C/2012 S4 (Panstarrs) and C/2012 V1 (Panstarrs). However V1 is approx magnitude 15 and S4 is approx magnitude 19! Bearing in mind that L4 is about magnitude 6 there is a difference of 13 magnitudes between it and S4 and as a difference of 5 magnitudes is a brightness difference of 100 that makes S4 unbelievably fainter! (A difference of 10 mags is 10000 X fainter, a 15 mag difference is 1 million times fainter -I will leave you to do the exact Maths (see my article in the Journal recently and spreadsheet if you want to work out the exact value if you are new to this). There are also other comets in the vicinity. In the chart below I have marked magnitudes on some of these.
Len
Image


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 Post subject: Re: Comet PanStarrs on 2-Apr
PostPosted: Sat Apr 06, 2013 8:03 am 
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Whilst I was away in South Wales over Easter I finally managed to capture comet C/2011 L4 PanSTARRS with our new modified Canon 300D camera:
http://www.boltonastro.co.uk/gallery/displayimage.php?pid=1204&fullsize=1
I was using my Pentax-A 50mm f/1.4 lens (stopped down to f/5.6), having found the "infinity focus" position the previous evening (by taking a series of five pictures of a bright star at different settings - it turned out that around "15m" on the lens-barrel was about right).

I went out just after 5am, so I was still able to see Polaris to align my tracking platform, but the sky was already too bright to see the comet (and M31) without binoculars. I took 10x 15-sec images, and then as the sky was brightening rapidly stopped down to f/6.3 and took another ten.

Having shown one of my RAW images at our Show & Tell meeting that evening, I spent a couple of hours the following day taking the calibration frames and processing in IRIS. Remember that although I've reduced the background to black in the final image, I was actually shooting against a bright sky, so the contrast wasn't great.

Meanwhile, we'd managed to see the comet from Ladybridge after our meeting, using a number of 'scopes and binoculars, and Shirley and Dean even managed to get an image of it too:
http://www.boltonastro.co.uk/gallery/displayimage.php?pid=1205&fullsize=1


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 Post subject: Re: Comet PanStarrs on 19-Apr
PostPosted: Sun Apr 21, 2013 2:21 pm 
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Now that the comet is in Cassiopeia, it's visible from my back garden - low down in the North-East after twilight, so as as the sky was clear on Friday evening I decided to have a go at imaging it with my 8" SCT (reduced to f/6.3).

Shortly after sunset I set up the tripod, mount and 'scope (with LPR filter and focal reducer fitted), and attached the camera. Then I was able to shoot a dozen flat-fields, using the twilit sky as my evenly-illuminated background. Next I fitted the lens-cap and shot my offset frames, and (once the camera had cooled) some 1-min dark-frames too.
By this time I could see Polaris, so I did an approximate polar alignment (using my polar-scope). Then I powered up my Celestron CG5 mount, set the date and time and selected Last Alignment (one I'd done back in September, I think?). I called up Caph from its Named Stars database, and then used the Sync function to get a good alignment for the Cassiopeia region from this star. I also used this star to optimise my focus, using the x2 magnifier in my right-angle viewfinder attachment: http://www.boltonastro.co.uk/forums/viewtopic.php?f=4&t=425
I'd previously determined from Cartes du Ciel that the comet would be close to the star SAO 21361 (which is in the Celestron's GoTo database), so I planned to use this as a target to get the comet in the camera's field of view. I took a 20-sec exposure to check, and could just make out a "faint fuzzy" on the LCD screen on the back of the camera, so I knew I was on target. Then I tried a 60-sec exposure to check how bad the trailing was, and satisfied myself that it would be acceptable.
So I programmed my interval timer for 30x 1-min exposures with 1-min gaps between them (if I exceed this 50% duty-cycle with my Pentax K110D it heats up too much and all my images are lost in pink noise!) and left it running for an hour.
At the end of this hour the comet was about to set behind next-door's shed, so I fitted the lens-cap and did another ten dark-frames before packing everything away for the night.

So this entire imaging session was completed with minimal set-up (no Bahtinov mask or auto-guider, and without even taking my laptop outside!), all within two and a half hours (of which I spent no more than 30 mins outdoors). "Simples!"

Then the following day I spent an hour with IRIS (and my comet-stacking Excel spreadsheet http://www.boltonastro.co.uk/members2/index.php/fp/Software/Excel-comet-calculator-for-IRIS/)to produce my final stacked image and load it into the Gallery:
http://www.boltonastro.co.uk/gallery/displayimage.php?pid=1218&fullsize=1


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 Post subject: Re: Webcam imaging of Comet PanStarrs on 13-May
PostPosted: Tue May 14, 2013 7:05 am 
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Although the comet is much fainter now it is higher in the sky, so last night I decided to try it with my LX-webcam. I have a Meade f/3.3 reducer which fits on the back of my Celestron C8: this results in quite a "fast" imaging system over the the tiny area (1/4" diagonal) of the webcam sensor. But it's a while since I used this line-up. so I needed a couple of experiments before I got the right combination of extension-tubes and adaptors fitted.

I had my CG5-GT mount set up and polar aligned (just using the polar-scope) before 10pm, and soon after ten it was dark enough to line up on Gamma Cephei (the comet was right beside this bright star last night). This allowed me to experiment with the focal reducer line-up and then focus with my "cardboard cut-out" Bahtinov mask. I had my laptop set up on a folding table (an old green-baize card-table, just like the one Keith uses) beside the 'scope, so adjustments were easy. But as soon as I'd finished this, it clouded over! :(

Happily the clouds soon cleared again, so I was able to take a series of 10-sec images (the twilight sky was still too bright for longer exposures). But I wondered why I could see a single diffraction-spike on the bright star: this turned out to be due to our telephone-wire hanging right across the line-of-sight! :o

After a while, I was able to go up to 21 and then finally 62-sec exposures, before a solid cloud-bank rolled in soon after 11pm. I took this opportunity to do a series of dark-frames, and then packed away.
I'll do the bias-frames & flat-fields later today (whilst the camera is still on the back of the OTA).


Last edited by rwilkinson on Wed May 15, 2013 9:33 pm, edited 1 time in total.

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 Post subject: Re: Webcam imaging of Comet PanStarrs on 13-May
PostPosted: Wed May 15, 2013 7:53 pm 
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rwilkinson wrote:
I needed a couple of experiments before I got the right combination of extension-tubes and adaptors fitted.
Attachment:
File comment: Using my converted webcam in an f/3.3 imaging system
dsocam.jpg
dsocam.jpg [ 215.28 KiB | Viewed 7433 times ]

Unlike many camera systems which require the 'scope to be re-balanced, this one is actually lighter than a 2" star-diagonal and eyepiece!

Using the f/3.3 reducer and webcam I do have a smaller field-of view than with the f/6.3 reducer and DSLR, but it's still adequate for compact DSOs and comets:
Attachment:
File comment: Comparing fields of view of my imaging systems
panstarrs_13may.jpg
panstarrs_13may.jpg [ 40.07 KiB | Viewed 7433 times ]
and it is actually easier to use (aiming and focussing with an adjacent PC screen), since I don't have LiveView on my DSLR.

I've been processing the images today, and got a reasonable result from a combination of my 20x 21 and 11x 62-sec exposures:
http://www.boltonastro.co.uk/gallery/displayimage.php?pid=1238&fullsize=1
And in the process of doing this, I've discovered an improved calibration technique for 8-bit webcam images, and how to embed the time & date information into my files so that IRIS can compute the comet's track for stacking (using the INIT_DATE command).


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