Comet photography planning
Sometimes you can read in newspaper that there is a comet up in the sky. If you live in a city it's not easy or almost impossible to see them. But if you take the car out where there is a dark sky you maybe have a chance to see them. Even better if you can take a photography of them. I have done that from my heavy light polluted place, and sometimes little bit darker place.
Here is the comet 41P Tuttle Giacobini Kresak that I took from a darker place not far from city:
This comet is still up there (12th April 2017) and I plan to try to photography it again, now it's more brighter. And that is what I will write about here, how I plan it with CdC star charts and briefly about my equipment.
For me a bright comet is of magnitude 3, this one is at the best magnitude 6. But you take what you have.
First you have to know something about comets, you can visit my Astronomical Dictionary and follow the links under Solar System:
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2: My travel equipment
Here is a list of the equipment I normally use today when I need to be transportable:
This is only a short summary over my equipment.
Most DSLR cameras will be fine I think. But it's much easier if there is some way to do several photos by automatic (timelapse function). Some cameras has it built in. In my case I use an intervalo meter to control the camera.
Most lenses between 24 mm to 300 mm will be ok, prime lenses are normally better than zoom lenses. It's much more difficult with longer focal lengths. It depends very much on your mount how long focal lengths you can handle. In my case 150 mm is ok on a full frame camera. Big aperture give more light, but even with my Sigma APO 150mm f/2.8 I have to set down the aperture to f 4.0 if I want low vignetting and sharp stars.
The core of a comet is almost a point object, but the halo around the core could be big, and the tail very big. The tail can be from nothing to couple of degrees or even more 10 or 20 degrees. The tail is the most beautiful so chosen your lens focal length to cover the tail and a bit more according the forecast of how big it's expected to be.
Long time exposure control:
I have an aftermarket intervalo meter, not very expensive, 40 Euro. With 30 seconds exposures you get around 100 images per hour and with 1 minute exposures around 50 images. We have almost three hours of real darkness in middle of April on our latitude 60 degrees (Stockholm, Sweden).
Red dot finder:
With a telephoto lens it can be difficult to aim the camera at the object, comets are weak but from a star chart you know what stars are nearby to aim for. To make it easier I have bought a Red dot finder. I have not used it yet.
This is how it looks, Canon EOS 6D with the Sigma 150 mm f/2.8 APO lens and the Red dot finder on top.
Normally you have a mount that is motor driven to follow the stars. You normally have that to follow comets too. Comets when they are at brightest can move very fast relative the stars because they are so close to Earth then. Then You have to shorten the exposures or have a more advanced mount were you can set the speed to that the comet has. It depends very much on your focal lenght how complicated it will be. I can do that on my EQ6 mount, but it's very heavy and I don't bring that mount with me.
Here you can see the Star Adventurer mount with camera and lens mounted on the tripod:
Here is my project about this mount and if you scroll down you can see my equipment list in detail:
I always had problem with dew on the lenses when doing astrophotographing. Now I have built a heating band that I wrap around the lens. It's wiser if you buy a over desk heating band, they are not expensive.
It depends on a lot of things, darkness of sky, comets brightness, comets speed relative stars, focal length, motor driven mount or not.
In my case with a 150mm lens, a simple motor driven mount, and a comet that doesn't move to fast at the moment.
Normally I set the ISO setting to 800 for deep sky objects which give better dynamic. But in case of comets the stars will be trails so the dynamic isn't that important. Better to get better data on the comets weak tail. My camera a Canon 6D has it lowest readout noise at ISO 3200 and that is important if you do many short exposures. Maybe ISO 1600 is the best compromise in this case.
Because the comet moves relative the background stars you can't have to long exposure times. In my case here maybe not longer than 60 seconds.
Lens aperture settings, very common that I set it to f/4 for all my camera lenses. Wider opening only give more light in the center, the vignetting give bad result at the edges. The lens is also relative sharp at f/4.
With a wide angle lens you can test to shot with just a tripod. Maybe at most 20 seconds with a 20 mm lens at high ISO 1600 or ISO 3200 if your camera can handle that.
In any case, don't oversaturate the core of the comet, it don't look nice. Most of my comets photos don't look very god because of light pollution, taken with my telescope which I have on the balcony in city.
Buy new equipment:
If you looking for astronomy related equipment to buy I think you can have use of my list of links:
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3: Setup CdC for comets
To take a photography of something you must know where it's to point the camera at the object. Comets are weak and normally you don't see them. They also move relative the stars. You need a good Star Chart.
CdC or Skychart is a French Star Chart software. I use it to control my telescope but it could be used for a lot of other things too. You can use other software too if you prefer that.
It's free to download, you find it here:
But first you maybe want to know in advance if there is any comets coming up later, then you can visit Seiichi Yoshida's homepage.
Here is my earlier tutorial how to know if there is any comet coming up in the future:
In this case I already know which comet to look for, the comet 41P Tuttle Giacobini Kresak 2017. I repeat part of the earlier tutorial because I use different parameters here.
Now to how to setup CdC to show in detail how the comet moves over the sky. You should already have installed the CdC and be familiarly with it before proceed here.
In my case I want to observe and take photography of it the coming days. First step is to check the weather report. Are there any clear sky the coming days? I found that it maybe will be a clear sky the 19th April 2017.
Then I set this date in CdC like this:
Setup and date / time:
Maybe you get information already which time is optimal to observe the comet. If not start with 00:00:00. CEST stands for Central European Summer Time. UT +2 hours.
Move to next tab, simulation. CdC is a very clever program, you can simulate the comets orbit over the sky. How you set it up depends on the situation. This is my case for this comet. Mark Comet, set the number of steps to 9 day. Show only text info to every fourth step. Object name, date, magnitude and month and day could be wise to show.
Next step is to setup the comet parameters in CdC. Maybe this values is good, fainter comets and there will be to many on the screen and confusing. The tail length is good to have, then you can plan where on the sensor the comet should be without clipping the tail, but don't count on to see that much as this indicate on your photo.
This is important, new comet can come very fast, you must have the latest orbital data. You update orbital data under the tab "Load MPC file". Download and the update process start automatically.
Now when you have the date that you expect it to be a clear sky it could be good to know if the moon is up and when you have astronomical darkness at your place and date. Under the view tab there is a "Solar System Information". Click on that.
It's most comfortable to have the noon at left side of the time scale, mark the top left box. The red line is the time the chart show just now, the black area is the time when it's astronomical darkness. See the yellow line for the Moon. Here it coming up about when the darkness disappear. It could be important because comets has weak brightness, especially the tail that you really want to shot. But there isn't so common with clear sky either so don't let this stop you.Back to contents
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4: Display and print a chart
Start with a wide view to get an overview of the sky, also read my earlier tutorial for more details:
On the right side, choose 310 degrees. Here I also have chosen the south direction. Use the right scroll list to center the image. Can you see the comet 41P now? With the hour buttons above you can move back and forth in time to see when the comets is at its highest position in the sky. A rule is that you should at least have it 45 degrees above the horizon, but most comets don't reach that height. But remember it must also still be at a time when it's dark. In this case at the late season for astronomy the time windows with darkness was just two hours, and of course a clear sky. Try to find when it's optimal at your local place.
Here I have centered the comet, the field is reduced to 90 degrees and the direction is more to the east. You also see a red rectangle here. That rectangle marks the field of view of my Sigma 150 mm lens.
You setup up the rectangle in the setup display menu. You must know your lens field of view and it should be in arc minutes. There are 60 arc minutes (') in one degree. In my case with a full frame camera and a 150 mm lens it gives a field of view of 825' x 550'. I have also set up two finder circles, one and five degrees under Finder circle tab.
Now we want to print this star chart. Here I have as an alternative to print setup CdC to deliver it as a BMP file into Paint. Good if you want to add some text to the map, after you save it as BMP or JPG file and print it out.(click on the image to get a full resolution photo in a new window)
I have set it up to BMP file with resolution of 1920 x 1080 pixels. Black and white.Back to contents