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Old 17-06-2018, 09:05 PM
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muletopia (Chris)
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Failure with compensation

On Friday evening I wenout to try for my first comet image.Panstarts-c/2016mi and Vales-P2010 H2 were said to be available. The forme being much brighter seemed like a first step. But cloud in that part of the sky stopped that, So try for the fainer Vales.

So I took 10 8.5 minute shots on a Canon 60Da at ISO 6400 at prime focus of my Mewlon 210. The guiding was off axis using a ZWO ASI120mm.

Well I could not see anything that hinted at a comet in any of the ten shots.
So I just stacked the shots to produce a rather attractive star field.

The guiding was adequate as shown in the PHD2 screen dump.

So how do you find comets with a DSLR?

Chris
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  #2  
Old 18-06-2018, 11:49 AM
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PKay (Peter)
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Hi Chris

Nice star field.

Don't know anything about comets (imaging that is).
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Old 18-06-2018, 12:40 PM
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redbeard (Damien)
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Hi Chris,

What software/information did you use to locate the comet?

What I have done in the past is updated the program Stellarium with the comets details and then compared the sky to what I see on screen. Then with a little trial an error took a single shot with a duration relative to the magnitude of the comet to see if it is in frame, once found, then take a series of photos.

There is also a web site that can show where the comet is in the sky each night but I don't know the website. Search on IIS forum as you should find some info. Search for words like 'ephemeris' and 'comet'. Then as before look at the map from the website and compare with the sky.

Often someone from IIS will post that info for current comets too.

Cheers,

Damien.



Quote:
Originally Posted by muletopia View Post
On Friday evening I wenout to try for my first comet image.Panstarts-c/2016mi and Vales-P2010 H2 were said to be available. The forme being much brighter seemed like a first step. But cloud in that part of the sky stopped that, So try for the fainer Vales.

So I took 10 8.5 minute shots on a Canon 60Da at ISO 6400 at prime focus of my Mewlon 210. The guiding was off axis using a ZWO ASI120mm.

Well I could not see anything that hinted at a comet in any of the ten shots.
So I just stacked the shots to produce a rather attractive star field.

The guiding was adequate as shown in the PHD2 screen dump.

So how do you find comets with a DSLR?

Chris
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Old 21-06-2018, 12:56 PM
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sil (Steve)
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Quote:
Originally Posted by muletopia View Post
So how do you find comets with a DSLR?

Chris

Typically guesswork for me.


Your star map source needs to be good if thats what you're following. I've yet to find any that is perfect but Starry Nights (PC) and Sky Safari (idevice) are accurate enough.

First thing is before heading outside it I fire up the programs and update with their latest data as comet data changes often with observation data. Next I sketch a simple starmap of the region on a piece of paper, the major stars and distinctive star formations and where the comet is meant to be in relation to them. I do DSLR from a regular tripod with a 200mm lens, so I have to star hop a little to get it pointed to the correct region, I'll take a test shot with a higher iso and longer exposure (expecting trailing) then I can compare that star field on camera to my iphone in Sky Safari, to make sure I have it pointed in the correct general area.

Next I note where the comet appears in sky safari and zoom in on camera image to same location and see if i can see it there, might have to scroll around a bit until I spot the faint coma. sometimes the comet is very obbvious in the frame sometimes its too faint but comes good after stacking/processing. My aim here is to make sure The comet is actually there or if I cant spot it that I am capturing where the software says it should be at that time.

I typically know which way the star field will drift across the sensor so since I'm shooting untracked I try to position the camera such that the comet is to one side of center frame and will drift across the center during my shoot. I then adjust for my actual capture settings and use a remote shutter to run off 100 shots, Then I recheck star position and readjust camera direction if the comet is nearing the other frame edge and repeat the process several times so I get a few hundred shots, usually they all contain the comet with a high percentage near the center of the frame where lens distortions are lowest.

To process in PixInsight I star align the whole lot as first registration to deal with field rotation then a second registration using comet align to "lock" the comet as it drifts against the star field. When I integrate the stars get mostly removed but the comet ends up as crisp as I can get it. Just doing a regular align or only comet align the starfield rotation is still there and if the comet has a tail you smear details.

Sometimes its a matter of point and pray. But stay commited, I screwed up a few times by second guessing myself and repositioning my camera a couple of times to try to get the sky covered and found later I completely missed the comet and if I'd left the camera alone for my usual routine the comet would have just drifted into view.

Comets are often too faint to see on a dslr though they may be there in the raw data. The skyhound maps I started with I found were wildly wrong predictors for me, so was stellarium (if the comet was in the database) but Starry Nights and Sky Safari very very close and give a good enough match to my processed files. So you may need to do a bunch of test runs to firstly photograph a comet and then see what your software tools predict for the location of the comet in relation to the starfield for the time and location of your photograph. Also look at the faintest stars in the photograph and look them up in software to guage what the limiting magnitude is of your capture gear, so you know if you are hunting for a comet around that magnitude you just may not be able to capture it. (using the comet subs you captured do a regular star align and process to determine the faintest magnitude stars you are able to see in the image, if you comet aligned a lot of star data gets lost in processing and becomes unreliable to measure from.) I'm sure theres better and more accurate method to figure out how faint your imaging gear can capture but this does the trick for me (from memory, been a few years, I could go to mag14 and comet chasing bore that out too.

in simpler terms, I Point and Shoot to capture comets
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Old 21-06-2018, 03:33 PM
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Merlin66 (Ken)
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All the current comets can be displayed in Cartes du Ciel.
The necessary guiding rates / direction can be sent directly to PHD2 (See the PHD2 Help menu "Comet tracking")
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Old 21-06-2018, 04:23 PM
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LewisM
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The image is very black clipped - back it off and post it again - move the black point back to the very tail end of the curve.

Then we might be able to properly stretch the image and see if anything is there. I tried stretching what you posted, and there is a HINT of something...
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Old 22-06-2018, 10:52 AM
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cometcatcher (Kevin)
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Stellarium is good, and it's free. Just load up solar system objects under the F2 key - plugins - solar system editor - configure - solar system - import orbital elements in mpc format - select comets - select mpc's observable list of comets - get orbital elements - mark all and add to list.... and holy cow that's a long list! But you're done.

Now you only need 30 seconds to pick up a comet brighter than mag 11, at least in a big Newt. Keep taking 30 sec subs around the area until you find it.

C/2016M1 (Panstarrs) is about mag 9 at the moment.

This is one of the best comet finding pages. http://www.aerith.net/comet/future-s.html
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Old 08-07-2018, 09:33 PM
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muletopia (Chris)
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For LewisM

I have been away for several weeks, hence this tardy post.

Lewis, attached is the reduced output of the stacked fit file from Nebulosity.
Saved as jpeg and reduced with paint.
So it might be possible for you to find the "hint" you found in the black clipped version.

Chris
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