Comet imaging

[Ric]

Hi all, I was hoping to chase and image a few comets over the weekend, weather permitting.
:camera:

I have never actually tried this before so I was wondering if the more comet savvy members have any tips to help me out. I have hunted around for a few websites but they seem to be orientated towards the seasoned imager rather than the beginner.

all help and ideas greatly appreciated :)

[Merlin66]

Most, if not all of the Southern comets at the moment are pretty faint, like 12 mag + so likewise they are very small with little tail. Photography would be similar to Deep Sky Object. Long guided exposures with largest aperture.
The comet usually "glows" visibily a shade of green due to the OIII emissions so a suitable filter may help to build up the image and reduce sky glow.
So, prime focus and 2 -5min on a CCD would be a starting point.
When they get "big and Bright" you can move to tele lens piggy back on the scope.
Hope this helps.

[RB]

Yep I agree with what Merlin66 said, Ric.

When they're brighter it's great to try imaging these beauties.

Here's one I did earlier this year of C73/P using a DSLR and 200mm lens.

http://www.iceinspace.com.au/forum/attachment.php?attachmentid=13156&d=1149393506

[rogerg]

The only thing I can add (limited experience photographing comets) is you need a way to track the comet and photograph the comet at the same time. They often move at a reasonable pace.

I used to either do short exposures prime focus and stack them, manually tracking the comet between exposures, or take exposures piggyback and track the comet through the scope.

Now with my guide scope more options would be available...

Roger.

[Ric]

Hi all, thanks for the info and tips they are greatly appreciated. That is a fantastic image RB.
As I would be using the DSI II with the f3.3 focal reducer for imaging and using the drizzle technology which I feel gives me the best images I can use that to track the comets while imaging as well. As you say Roger, I would have to keep the exposures short to avoid star trails and stack them afterwards.
Merlin66, at the moment I only have a UHC filter by Astronomiks for cutting out light pollution and enhancing nebula details and the Meade DSI II RGB filters, so I am still in the process of researching what filters do what and which are the most suitable for my needs. Does the OIII emissions require
a special OIII filter?

Thanks all for your help

cheers

[rogerg]

Actually it's the stars that will end up trailed, and the comet should be not trailed :)

Roger.

[Ric]

Thanks Roger for the clarification.

cheers

[Merlin66]

This is a "must" link for anyone chasing comets
http://www.skyhound.com/sh/comets.html

For faint comets, I wouldnt bother with filters. The UHC will help against sky glow, but the OIII is fun to use on brighter comets with visible tails, it separates the gas tail from the dust one.
I'd question using the f3.3 reducer on such small objects, the image scale will be very small and athough you may pick up an image it will not be big enough to show any detail.

[Ric]

Hi Merlin66, thanks for the link, I just had a quick browse and it is very informative. I bookmarked that one to go back to and have a good read.

Thanks also for the advice regarding the focal reducer, so much to learn. :D

cheers

[spearo]

Hi All,
I've never imaged a comet but the urge is growing.

I'm still unclear about how to go about tracking the comet.

I have a C9.25 with a William Optics in 125mm guiderings on top.
I use a Toucam modded inthe WO and a Canon 20Da on the C9.25.

What I need to figure out is how do I get the mount to track the comet so I can take long exposures?

The MOunt wants to track in either north or South mode (of course I currently use South) or Lunar or Solar or none at all.

I think all these would work against long tracking of the comet wouldnt they?

unless I leave the mount's tracking alone as per usual and just try to lock the comet itself in the WO guidescope and try to track that?

I'd fully expect star trails and have no problem with that

any input on how I track the comet?
thanks
Frank

[Merlin66]

There are three ways to guide on comets:
1. Using a guide telescope with a FL x2 to x3 the "camera" FL, witha cross wire eyepiece ( 12.5mm) and the MkI eyeball. Make corrections as necessary to hold the head of the comet on the crosswire.
2. Using the webcam/ ST4 guider to lock onto the comet and auto guide ( Guidemaster etc) this needs a bright nucleus.
3. Work out the movement of the comet from its ephemeris and prepare a "correction" chart for the movement in RA/Dec and pulse the drives as necessary to virtually guide.
The starting point in usually #1

[fringe_dweller]

:rofl: :lol:

hey if they get big and bloomin bright enuff, a 10-20 sec tripod shot is all ya need :eyepop: :lol:
Personally I'm not a big a fan of trailed star tracked on comet shots, altho they are important and vital, and often have the best deepest details usually, of course, and on faint ones it often matters, they are completely unnatural looking from aesthetic/purdy picture point of view imnsho.

[Outbackmanyep]

Hey F_D!

I use my equatorial fork mounted CELESTRON 8" SCT, and i guide with a radial guider and.... (forgive me!)....a Meade 9mm Series 4000 guiding eyepiece.
My camera is a Minolta 7000 AF camera, and i have a "AA" external battery carrier that can give me 3 times as much battery power as "AAA" holder gives me.
Troubles i have are photolabs processing my pics, BUT i have found a very nice fellow in Port Macquarie that has spent hours adjusting my pics for next to no extra cost!

If you have a copy of the july/august issue of Australian Sky and Telescope mag, theres a pic i have in there of 73P/S-W 3C, using a radial guider i have to guide on stars and not the comet, i too am thinking of going to a guide scope but can't afford it as yet.
Because i guided on the stars and 73P's close proximity to earth the comet had a very large apparent motion, which during the 15 min exposure caused the comet to trail, the pic in the mag didnt print out as bright as my original shot unfortunately!
The only way to combat the guiding problem through the telescope is with an autoguider in conjunction with a separate guide scope attached to the main scope. The problem i have discovered from my research into it would be DIFFERENTIAL FLEXURE.
To minimize this problem you'd need a good solid mount and mounting rings or mounting system with the guide scope.
I was contemplating looking into sitting a 80mm Williams APO on an aluminium bracketing arrangement and getting rid of my normal finderscope...on top of that i'd need to balance my whole assembly!

I havent got the money as yet for the 80mm APO so i intend to do more research into the set-up, hopefully someone might be able to enlighten me!

The trailed star shots on comets are a result of nature!
The comets motion against the background sky just cant be ignored and although those pics are excellent pics, and John Drummond from NZ has taken some really superb pics, you'd certainly need to go through a lot of expenditure to get those set-ups to be able to take those pics and the knowledge of how to put it all together is a feat in itself as well!
Long exposures are required for the fainter comets and their natural progression against the background stars unfortunately cant be solved!
I will just keep on doing what i am doing, guiding manually in conjuntion with PEC and getting better at it, cos it requires a lot of practice and patience and the results are worth it!

Theres so many different set-ups to image comets, id say start with something simple and uncomplicated and work your way up like i am doing! :-)

hope that helps!

Cheers!

[fringe_dweller]

Chris/OBMY, checked out your shot, great effort, wow another film person - we are getting rarer by the day
15/20 min is a long time to be guiding a single shot, EDIT: on a star, at that magnification of a moving object! thats more the issue than the comets apparent motion over time, in your pic. you need a more sensitive imaging device than 400 iso film/camera and take shorter exp. and stacking have you tried 800 speed film?
Ive seen great results of high power comet stuff with just cheap webcams out there, there was some beauties earlier this year.
I would be piggy-backing your film 35mm camera and taking widefields with some nice prime lenses in the 50 - 200mm, even up to 300mm, range rather than prime focus? and using 800 speed film for even shorter exposures - a lot easier? but thats just me, i'm fairly lazy :)

[spearo]

Ok
Thanks for the input
so given my setup (C9.25 on CG5 with a WO80mm in 125mm guiderings on top and a toucam) I can pretty much either
1) take lots of short exposures and stack not worrying too much about the different coment motion compared to the stars
20 guide on comet head manually while I expose longer
3) if bright enough get the Toucam locked on the comet heat to autoguide

thanks for the info

If anyone has ever done #3 above successfully please PM me so I can discuss the finer art!

cheers
frank

[Ric]

Hi OBMY, I noticed that you mentioned you use a Minolta AF camera. I have Minolta Dynax 300si with AF/manual switch but no bulb setting to keep the shutter open, are there any ways around it that you know of. I would like to try my hand at some imaging with a 50 - 200 lens.

cheers

PS: thanks for all the input as well guys, it's been really helpful to me as well.

[CometGuy]

Comet SWAN might be about your best bet at the moment as its still around magnitude 8 and low in the evening sky near Altair. Its not moving too fast so you should be able to take several minutes of exposure before trailing becomes evident (at 200mm focal length at least). Even a short exposure should show it.

The next chance for a brighter comet should come in the second half of January 2007 as Comet McNaught rounds the sun and is pretty bright (unfortunately its low in twilight so will have to be really bright to be seen well). At the moment its mag 8 (but not visible from the southern hemisphere) and should get a lot brighter :)

Terry

[Outbackmanyep]

The reason i tried a 15 min exposure was to try and get more fainter stars in the shot, if i had 800 ISO at that time i would have done a 5 and 10 min exp.
I do use 800 ISO film BUT its getting hard to get up here, i have 2 rolls now, one i just finished and ones in the fridge!
I have to get more but for some reason photo shops seem to be running out of Fuji Superia X-tra!!!!!
I can buy it in bulk but they wanted nearly 60 bucks for 5 rolls of Fuji Reala.....
So im keeping my eye out!
Have tried Kodak Max 400 film and its crap as far as im concerned, way too much blue for me so i steered clear of it!

Cheers! :)

[fringe_dweller]

we always buy our film in packs/ of 5 and stick 'em in the fridge, its the only way to go imo.
Our fave 800 (fuji NPZ) is rumoured to be phased out, and a new one in its place - altho i would be surprised if its any different as the NPZ is what all hollywood uses for 35mm film stock/movies, I think, so we are kinda in the movie/show biz :P, even tho they use digital a lot now, ever notice how blue leaning some movies tend to be ;) flattering to peoples skin tones to.
The best Kodak astro film is the E200 - altho a bit slow for you?
the other 35mm film fuji that is famous is the expensive but very nice fuji provia 400, reversible stuff, can have developed as a neg or a slide, $25 a single roll!

[Outbackmanyep]

G'Day Ric,
Im not familiar with the Dynax cameras but i know i recently purchased on ebay a Minolta 7000 Maxxum, 2nd hand but in good condition, for about $130 Aus, The Maxxum's are the same as the 7000 AF cameras but they were released in the U.S.A. as "Maxxum", so they're basically the same camera!
You might be able to try ebay and get a great deal, although just be warned that it can be risky business! I have a friend in Texas who will receive it and send it to me, that way i can tell if its been damaged at all...
Have you tried your manual to see if there is a way to find out if it has bulb setting or not??
I know on my camera it says in the manual to use BULB setting through the "M" mode......

Other than that only a camera specialist can advise you on what you can do with your camera.

Cheers! :D

[Outbackmanyep]

I have seen on ebay people in Canada selling bulk rolls of 800 ISO Fuji film, but they're all out of date! :P
I have heard that Agfa was also a good film, especially the 1600, but i havent located any, my rule is if i can't get 800 get 400....

Have a look at this pic of P1 McNaught!!
http://kometen.fg-vds.de/pix/2006P1/2006P1_26112006.htm

AWESOME!:D