Looking for advice on photographing the Milky Way

StewartR

StewartR

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Stewart
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Next month I'm going on holiday to somewhere where I expect the night skies to be really clear and really, really, really dark. Plus it's a new moon. So I'm hoping to get some good "starry sky" photos, and in particular I'd like to get the big sweep of the Milky Way if possible. But I'd appreciate some help.

Lens choice
Obviously I have access to pretty much any lens I want. I shoot with a Canon 40D, so I think a Canon 10-22mm is going to be the main tool for this. But what about a fisheye? A Sigma 4.5mm fisheye has a 180-degree circular field of view, so it will give me the entire sky. Would that be worth trying? Any other ideas?

Long exposure technique
I have the option of borrowing a tracking mount. The owner says "it's battery powered and is good for 1-2 minutes at 50mm". Is that worthwhile? I'm assuming that I'll use some sort of stacking program to combine multiple images and bring out the details - in which case, do I need a tracking mount or could I get by with lots of exposures of (say) 30 seconds or a minute each? (I assume stacking software can compensate for the earth's rotation?)

Camera settings
What sort of ISO is best? Low ISO because it produces low noise, though longer exposures would generate more hot pixels? Or higher ISO to keep the exposure times down? And what sort of aperture? Wide open (f/3.5-ish) to maximise the light falling on the sensor? Or f/8 because that's where the lens is sharpest?

I'll probably only get one opportunity like this, so I'm very keen to make the most of it. Any help gratefully received.
 
I've tried a few night shots in the past Stewart and would have these general observations.

If you have access to a tracking mount, make use of it. Even at 50mm, stars will start to show evidence of trailing at 30 seconds or so. Obviously, with a shorter focal length like the 10mm you may be able to get away with longer. The tracking mount will allow you to take longer exposures without this trailing becoming evident.

For deep sky objects I have used ISO 800 and upwards. The thinking behind this is that a lot of what can be captured in the night sky is very dim, so using a high ISO will give you every chance of capturing the faint stuff that makes up a lot of the milky way. If you are worried about hot pixels, you can take one or more dark exposures which can be used to remove these by the stacking software. The dark exposures should be taken at the same time and for the same legth of exposure as your imaging shots.

For the same reason I would normally shoot just a stop or two up from fully open. This gets you away from an aperture that the lens probably doesn't perform best at, but will still be open wide enough to allow in as much light as possible.

Possibly the biggest problem you might find is focussing. Really dark skies don't have much that the autofocus system can work with, and if you have live view available, this doesn't always provide much to focus on, even when zoomed in, if you are using a wide lens.

Hope you have fun and look forward to seeing your results.
 
Stewart, go with the tracking mount, it'll make things much easier. Obviously if you're wanting to include landscape, that will cause an issue, as the landscape will blur, but there was an article in this months sky at night magazine about that very subject (might be worth looking into it). Shoot a long sequence of tracked images, the more the merrier, as that will increase the signal to noise ratio, stack them using Deep Sky Stacker, which will allow for any slight variations between frames etc.

I'd suggest shooting at ISO200... that might sound odd, but the logic behind it does actually make a strange form of sense.

The theory goes that the sensor is only going to collect so much light during the exposure. The ISO setting does not actually make the sensor any more sensitive but rather amplifies the signal post capture, and also pushing up, the various noise levels (I can't remember the names) at the same time. ISO200 appears to be the ideal in terms of low noise and largest dynamic range. Have a look at my Orion image here to see what I mean about the ISO.

Some ballbark figures, this will vary depending on where in the sky etc you are shooting, but.. 18mm is about 30 seconds before trailing, 50mm is about 8-10 seconds before trailing becomes a problem when mounted on a static tripod. If you're shooting on a static tripod, if you get beyond about 3 minutes worth of exposures, you will get field rotation effects even with stacking.

For focusing, pick a really bright star (a planet will work nicely), set the lens to manual, activate liveview, zoom in all the way, and aim for the smallest dot you can manage, I find I need to push the ISO up to max to be able to see the star.

For reference, a 50mm is about right for a constellation the size of Orion, with an APS-C size sensor. I think the 10-22 will probably be your best bet. You can probably extend the 2 minutes tracking of the mount (an Astrotrac ??) to maybe 3 minutes before trailing becomes noticable at that sort of focal length, and the extra time will make a difference on what can be seen.

I hope that's of some help, have a great time, and look forward to the results.
 
I would take it out of its wrapper, slice in two with a sharp knife and turn it towards the camera to show the fluffy texture of the inside................................................................................................................OH.....not that Milky Way.
 
Excellent tips so far - couple of my 2ps

Agree with scarecrow - live view has been no help to me except when I managed to focus on a navigation buoy about 3/4 mile away.
I was recently told that the urbex mob use use laser pointers to focus in the dark (thanks Wilberoo). I'm now carrying a pointer in my kit but haven't used it for any star shots yet. I think you will be able to use it to focus far enough away to get that point to infinity in focus at a sensible aperture.

Composition - bump the ISO and use widest aperture to take a 10s ish exposure. Nothing worse than wasting an hour to find the composition was wrong.

Dew may form on the lens. You will often see reference to heaters under the camera which solve the problem - solution will depend on how sheltered you are.

Keeping warm is a problem. I've used a fishing shelter, sleeping bag and kept myself amused with an iPod while watching the stars. Something to nibble - I prefer Mars to Milky Way ;)

You will need a stopwatch - although most cameras have timers built in, none of them are any use in the pitch black.
 
For the dew, if it's an issue, try one or two of those hand heaters... but you want to keep the heat away from the body, as that will cause greater thermal noise in the capture. I forgot to mention to take some darks... cap the lens, and take 10 to 15 shots at the exact same settings, this will remove thermal noise, hot pixels, fixed pattern noise etc from the light frames when you stack them with DSS. If you get any vignetting with the lens of choice, you need flats, set the camera to aperture priority, and shoot something that's evenly illuminated, do not allow anything to change, including focus. DSS will use these to remove any vignetting and sensor dust.

Make sure you have some way to lock the focus and zoom rings, masking tape should work fine, as the tracking mount swings around the change in orientation could change something for you.

As for a timer, if you have a timer remote that works brilliantly, if not, my 450d displays an exposure time on the LCD during a bulb mode exposure, so that'll work for getting exposures of the same times. (if it's out by a second or so either way, it doesn't seem to make any difference).
 
jgs001 said:
As for a timer, if you have a timer remote that works brilliantly, if not, my 450d displays an exposure time on the LCD during a bulb mode exposure, so that'll work for getting exposures of the same times. (if it's out by a second or so either way, it doesn't seem to make any difference).
Click to expand...

Yeah, but in the pitch black you won' be ale to read it.
Don't touch the camera to turn on the backlight and don't shine a torch at the camera....
I found my phone has a very good stopwatch buried in the games folder....
 
canonrebel said:
I would take it out of its wrapper, slice in two with a sharp knife and turn it towards the camera to show the fluffy texture of the inside................................................................................................................OH.....not that Milky Way.
Click to expand...

There is always one!
 
DuncanDisorderly said:
Yeah, but in the pitch black you won' be ale to read it.
Don't touch the camera to turn on the backlight and don't shine a torch at the camera....
I found my phone has a very good stopwatch buried in the games folder....
Click to expand...

I don't need to touch the camera to turn it on. If I leave the display active on the camera when the exposure starts, the display counts all the way through to the end. No handling required... even for 20 minute exposures.
 
In your case Stewart I'd say Stacking, not tracking!

Shooting at the wide end of a 10-22 for the big splash of the milky way you'll be better off with a lot of darks, a lot of medium 15/20 second exposures and letting registax or some such do all the maths and the clever stuff.

Star trailing when shooting wide isn't such a problem that way. Here's a 10mm shot, 59 second exposure..

4114856605_50dc636caf.jpg


Link to full size

Hard to give solid advice on ISO as a lot depends on just how dark it really is where you are and how fast the lens is. Noisier pictures can be worked on in the software if you shoot a dozen or so 'dark' frames with the lens cap on and the camera normalised at the ambient outdoor temperature.

Putting a 50mm on 40D for sky shots is well worthwhile and that's where you'll get to see colours you can't readily pick out by eye. Longer exposures will start to 'smear' the stars as they begin to trail so your chance of a tracking device might be worth an experiment - but you'll be getting. I was surprised how narrow the field of view was with a 50 on a crop when I was shooting the Leonid meteor event last August. Good for bits of the milky way and enough to actually make out tiny little galaxy shape objects.
 
Stewart
i would also suggest the tracking option but beware it would have to be polar aligned very accurately for 1 to 2 mins exposure, otherwise you will get field rotation over several minutes worth of shots making the images much more difficult to align. I would also use a low ISO (typically 400 max) and I wouldn't recommend in camera dark frame subtraction as that will make any field rotation problems twice as bad, just take the shots seperately at the end of the session and then subtract in software! ..

edit: Sorry for got to say If you do have a really good site then 2 mins (in total) of exposure will give an excellent image anyway!
 
Hi Stewart,

Whereabouts are you heading? Hubby and I will be visiting Natural Bridges National Monument in Utah in a couple of months, as part of a longer trip to the area. It's an "international dark skies park" and we are also hoping to photograph the Milky Way as well as some star trails.

Looking forward to seeing your attempts and hopefully learning from your experience ;)
 
3183931614_156ab899a2_o.jpg


That was taken in Death valley the year before last and is an amalgumation of around 40 shots at around 12mm, 30 seconds and ISO800 at f/4. I didn't use a mount.

Although it looks ok (after going through deep sky stacker) the corners did end up blurred and odd due to the program not understanding the lens distortion and stars going out of frame so bear in mind you may have to crop the edges to get a better shot.

I have to say I have taken quite a few long exposures at night and have never had a problem with dew or condensation so it doesn't seem a major issue to me. What I do recommend however is you buy a timer remote release. You can get them on ebay for less than £20 and they are very useful. I've had to take 30+ shots at two minute intervals before I got the timer and it was a massive pain. I got the remote and now I just arrange the camera, set the remote and wait for the camera battery to run out or me get bored and stop it. For example I went back to the fire with my companions during the "shoot". As shown in this one. :p

3033471372_26e490ee21_o.jpg


Don't be afraid to point the camera at a light source when shooting star trail shots (if you do) as it's not a major problem.

Hopefully you get a much better milky way shot than mine, higher up (as opposed to below sea level) and cold as well as no light pollution (apparently Death valley is to close to Las Vegas for that...) would make that much better. :)
 
Wow. So many responses. Thanks everyone. I've clearly got some reading and thinking to do...

One more thing though.

Condensation
I'm expecting daytime temperatures around 31-32C, and overnight "lows" of around 25-28C. If I'm out photographing in the evening, say around 10pm, it should be 30C give or take. And I imagine the humidity will be highish (say 80%). Do I need to worry about condensation?
 
stunning. Library time for me!

Nick.
 
I really don't know if dew would be a problem or not... I made a dew shield for my nifty with some camping mat. Same for my scopes. If dew still gets to the optics a gentle application of a cool hair dryer from a distance works nicelybut that's under our winter climate...
 
jgs001 said:
Stewart, go with the tracking mount, it'll make things much easier. Obviously if you're wanting to include landscape, that will cause an issue, as the landscape will blur, but there was an article in this months sky at night magazine about that very subject (might be worth looking into it). Shoot a long sequence of tracked images, the more the merrier, as that will increase the signal to noise ratio, stack them using Deep Sky Stacker, which will allow for any slight variations between frames etc.

I'd suggest shooting at ISO200... that might sound odd, but the logic behind it does actually make a strange form of sense.

The theory goes that the sensor is only going to collect so much light during the exposure. The ISO setting does not actually make the sensor any more sensitive but rather amplifies the signal post capture, and also pushing up, the various noise levels (I can't remember the names) at the same time. ISO200 appears to be the ideal in terms of low noise and largest dynamic range. Have a look at my Orion image here to see what I mean about the ISO.

Some ballbark figures, this will vary depending on where in the sky etc you are shooting, but.. 18mm is about 30 seconds before trailing, 50mm is about 8-10 seconds before trailing becomes a problem when mounted on a static tripod. If you're shooting on a static tripod, if you get beyond about 3 minutes worth of exposures, you will get field rotation effects even with stacking.

For focusing, pick a really bright star (a planet will work nicely), set the lens to manual, activate liveview, zoom in all the way, and aim for the smallest dot you can manage, I find I need to push the ISO up to max to be able to see the star.

For reference, a 50mm is about right for a constellation the size of Orion, with an APS-C size sensor. I think the 10-22 will probably be your best bet. You can probably extend the 2 minutes tracking of the mount (an Astrotrac ??) to maybe 3 minutes before trailing becomes noticable at that sort of focal length, and the extra time will make a difference on what can be seen.

I hope that's of some help, have a great time, and look forward to the results.
Click to expand...

John mate, we had this discussion on Astrochat and IMHO you are simply not right with that low ISO theory. As you know I've done a lot of this stuff in practice, with my 20D and Vixen GP mount and found the optimum ISO to be 1600.

In my experience, you should use the highest ISO you can get away with. You will get considerably more exposures in the same session, and the improved SNR from stacking 8 times as many ISO1600 images will outweigh the lower noise from a handful of ISO200 shots. You also risk losing a smaller percentage of your overall exposure time to satellites, aeroplanes, itinerant cloud and tracking errors.

The advantage of using a 4.5mm fisheye is you will get 600/4.5mm = 133 seconds with a static tripod before star trails become apparent. At ISO1600, with a dark sky this should be enough to get good results. You may have trouble stacking shots taken with this lens however, on account of the field curvature, in which case a single shot with noise reduction, or manually subtracted dark frames, might be the way forward. I hasten to add, I've never used a fisheye that wide for astronomical use - just a Zenitar 16mm.f2.8 but have had problems stacking shots from that, especially with a fixed tripod.

Dave

PS I hope you aren't going away in June, as I was thinking of hiring your Sigma 4.5mm then (unless you've got two of them ;)).
 
Dangerous_Dave said:
I hasten to add, I've never used a fisheye that wide for astronomical use
Click to expand...

I do very little astrophotography, but it is one use to which I have put my Canon 15mm fisheye (180° corner to corner coverage on full frame) :)

200710_9714.jpg


Canon 5D. Single shot f/2.8, ISO 800, 48 seconds and some light PP in Adobe Lightroom (curves to enhance the contrast). It doesn't bear very close inspection, but I was pretty happy with it as a fairly casual shot from a back garden.

Most of the glow, on the right hand side of the frame, is from the City of Hereford about five miles away from where my parents live.

FWIW, I seem to remember reading somewhere that fisheye lenses were invented for wide field astro work.

edit: a slightly larger version [1600 x 1067] in case it's useful
 
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