Photographing the night sky

I’m taking two trips to the U.S. southwest this summer, and I’m interested in photographing (35mm slides) the night sky, especially with some geological landscapes in the foreground.

What speed film should I use?

What focal length and shutter speed?

At what speed do star trails start to appear? And at what speed does the motion of the moon become apparent?

I realize that the moon will influence the brightness of the landscape, but will it also influence the apparent brightness of the stars if the moon is not in the picture?

I’d use ASA 100, or slower, simply because you’re gonna need a lengthy exposure to get decent trails. And this gives you the added bonus of a finer grain. I recommend stopping the lens down pretty much all the way. Use whatever focal length frames your shot pleasantly.

Star trails will begin to appear about about one minute, but they don’t really look like much until you reach at least a fifteen minute exposure. One-half hour to a couple hours is better, or even four hours. (obviously, though, if you’re taking four hour exposures, you ain’t gonna get to take very many.) If you point your camera at the North Star, you can easily calculate the degrees of arc the star trails will describe for a given length of exposure. One hour is 1/24th of a full revolution; thus, the star trail will imprint an arc of 15 degrees.

The moon will begin creating trails much sooner since it’s closer and also has it’s own motion relative to earth. However, the moon won’t ever look like anything other than a smear. You’ll probably want to avoid capturing it entirely. You’ll also probably want to avoid shooting even star trail pictures on nights with a bright moon. It tends to wash everything else out of the picture since you need a pretty lengthy exposure to get decent star trails.

Another thing you can try, is using your flash manually off camera to highlight objects such as trees, or rocks, in the foreground. Also, try tracing foreground objects with a flashlight - maybe even with a colored filter on it. Just trace the objects once or twice and leave the flashlight off for the rest of the exposure. These techniques work better than you might initially suspect. You need not shorten your exposure time to use these techniques.

Another thing you might consider, is making a flat black card to hold in front of the lens while you’re tripping the shutter. Cameras can shake a little bit when the shutter snaps open or closed. But if you have a flat black object in front of the lens, there’s no image to show that jitter. The longer focal length lens you use, the more important this becomes.

Poop. Lemme add a couple clarifications.

This assumes your main objective is to get star trails. If it’s the nightscape that you’re more interested in, then by all means, shoot when the moon is brighter. Unfortunately, it’s pretty difficult to obtain both star trails and a good nightscape.

And another point about film choice - you’ll want to select a film formulated for high contrast.

Finally, to allow for the longest exposures, you may need a neutral density filter. Or a polarizer.

Here’s some more good tips:

As a rule of thumb, on a clear night, the correct[sup]*[/sup] exposure for the moon can be calculated as f 8 at 1 over film speed. e.g. for 64 ASA film use 1/60 sec at f8 or 1/30 at f11, for 400 ASA use 1/500 sec at f8. Obviously at night it will be a challenge to get anything else exposed without flash.
*whatever that means

Remember to bracket your exposures. Also, note that this formula is for taking a photo OF the full moon, not of other things by its light.

I’ve had superb success in astrophotography of all sorts using regular ol’ Ektachrome 64. Current E6 films by Fuji or Kodak will work well. No need for extra fast films most of the time. (yymv of course) You’re going to be on a tripod anyways, might as well go for lower grain. Nothing more annoying than grain ruining a pretty night sky photo.

When processed, ask for the roll to be sent back to you uncut. This means you will have to mount your own slides, but it avoids the problems machine cutting and mounting has with astrophotography, namely, not being able to correctly judge where to cut. I always expose a couple of close up, out of focus flash shots of something at the beginning and end of the roll so I have framelines to gauge my cutting on.

Ooh, one more thing, don’t stop the lens down ALL the way. This often causes odd diffractions due to the iris blades. Most lenses are ‘best’ stopped down a couple or so stops from maximum. For and f 2.8 lens, this means that f 5.6 or 8.0 will probably give you the best results. Most photo mags lens tests will show this, look up any of them, plus my personal experience agrees.

Not a correction, merely a clarification. Lots of good advice already given in this thread.

Uh, you sure you don’t have this backwards? At ƒ2.8 a lens might be wide open - ƒ5.6, or 8.0, is well towards the open end of the aperture range on an ƒ2.8 lens.

I think, if you have a lens with a minimum aperture of ƒ28, you’ll wanna use an ƒ-stop of 16 or 22. Much like I stated in the third sentence of my first post to this thread.


Read about what is meant by diffraction limited.

It seems counter intuitive, but somewhere in between wide open and fully stopped down is best for astrophotography. In many lenses, that stop is closer to the open end than the closed end.

This applies to both film and digital imaging, btw.

It depends what you’re going for. Most lenses have maximum performance (i.e. optical sharpness) about one to two stops from their maximum aperture. So a f/2.8 lens will have its maximum sharpness usually at about f/5.6.

If you’re going for maximum depth-of-field (which tells you how much of your image is in acceptable sharpness before and beyond your focusing point), then you want the highest posisble f-stop (smallest aperture).

Personally, though, the difference in sharpness often takes a trained eye to point out. For high-quality glass, it’s only the difference between being really sharp and really, really tack sharp. I generally do not take this into account in my photography. I would shoot most night scenes at f/11 with Fuji Velvia 50.

That may be a reasonable rule of thumb for non-astronomical photos, where you have objects at different distances. Stepping down to F/16 or smaller can improve sharpness by increasing depth of focus.

But if you are photographing a flat object at a set distance (and the night sky is essentially “flat” with a constant distance of “infinity”), and if your focus is dead on, then you want to step down only 1 or 2 steps from wide open. Any larger and the aberrations get worse; any smaller and diffraction degrades resolution.

Interesting. That’s a nice link. Thanks for the info.

Here’s a good discussion I found.

Scroll down to the comments and look for the “combined lens/film resolution” chart.

Often in regular everyday photography, the difference is very slight, maybe even not noticable ata ll in printing or projection. But in astrophotography, it can make the difference between resolving stars as points vs being fuzzy disks.

One of the few Dope things I’m actually good at. Thanks. And as I stated before, I wasn’t correcting you, merely clarifying for the specifics of astrophotography.

I should add that I was suggesting a smaller aperture simply as a means to increase exposure length.

My digital camera will do up to ~15 second exposures, and I’ve caught some interesting shots of the aurorae, stars formations, etc.

Using a flashlight is interesting… try not to expose the end of it to the camera or you’ll get a bright spot. You can also insert yourself in the shot multiple times if you feel like it. :slight_smile:

To avoid camera shake at the beginning, I either trip the shutter with my infrared remote, or (more usually), just set the timer. This also allows me to be far enough away to avoid fogging the lens on cold nights.

Yep. I understood that. I’ve got a buddy who used to be pretty heavy into astrophotography. panache45 may not, however, be as concerned with sharpness of celestial bodies though, since he looking to shoot star trails. I doubt he’s got an equatorial mount or a motor drive for tracking.

Good idea for the trails, then. A neutral density filter can also help, as with your recco of staying with slower speed film.

I don’t have it available online, but I once took a photo of a Houston freeway exchange during the middle of an overcast day with an ASA/ISO 12 B&W film that I pulled to be a stop slower in processing, stopped down to f/32, with a 2X and a 4X ND filter and the resulting long shutterspeed rendered the moving cars invisible. All you could see was the empty freeway interchange with downtown buildings in the background. (1977 or so, can’t remember exactly) Yes, I had some vignetting, but I cropped that out of the prints. A motorcylce cop pulled up as he was curious what I was doing. I made an extra print for him.

So, the point is, there are interesting things one can do with long exposure, star trails being one of them.

The fact that the Moon is closer is irrelevant: As far as any Earthbound optics are concerned (at least, any optics smaller than a few hundred meters), the Moon is an infinite distance away. And the Moon’s proper motion relative to the stars is much slower than the stars’ daily rotation through the sky, and in any event, it’s in the opposite direction (so the Moon will actually move a bit slower through the sky than will the stars).

For photographing the Moon, remember that it’s a big rock illuminated by direct sunlight. So the same exposures, film, and aperature that you’d use to take a picture of a mountain in daytime, will also be good for pictures of the Moon (at any time it’s visible). Forget about getting the Moon and stars in the same shot, though, unless you use some multiple-exposure tricks.

Incidentally, with a long enough exposure, etc. on a moonlit night, you can actually get pictures apparently of a well-lit landscape, complete with blue sky. There’s some subtlety to it, though, which I don’t remember the details of, due to the nonlinear response of film.

The moon lights up the entire sky and wash away all but the brightest stars. So even with multi-exposures and other tricks, there’s no way to get a decent photos of stars on a moonlit night.