How To Get Great Night Sky Long Exposures !

Great Night Sky Long Exposures

That's not some Photoshop trickery!

This can all be done right in-camera...

The way to do this, is to use the 600 Rule.

It's based on motion as it relates to time, and becomes very useful for long exposure night photography when you want the stars become part of your image composition.

The 600 Rule allows you to quickly calculate the maximum exposure time required, that you can employ without producing noticeable star trails at any given focal length.


The formula is for full-frame cameras (and we assume you use a tripod).

If you use a crop-sensor camera, you'd need to adjust the formula to take that into account.

For example: If your camera has a 1.5x crop factor, try replacing "600" with "400".

A 1.6x crop factor would mean going from "600" to "375".

So, the formula goes like this:

  • 600 / focal length of your lens in mm = shutter time in seconds

If you are shooting at a 100mm focal length, then your maximum shutter time would be:

  • / 100mm = 6 seconds until star trails

For a 12mm focal length, it becomes:

  • 600 / 12mm = 50 seconds until star trails

At 50mm, the formula states:

  • 600 / 50mm = 12 seconds until star trails

You get the idea.?


Take 600 and divide it by your selected focal length to get the approximate exposure time.

1. The 600 Rule becomes extremely useful for images where you want to include the Milky Way or other fixed astral subjects as part of your image.

2. It allows you to quickly get an ISO and aperture based on an acceptably precise shutter speed.

3. The 600 Rule gives you the ability to use your lowest ISO setting, which reduces image noise and also gives you relative control of the effects of astral motion.

4. It's not a big deal, really. You're just compensating for the movement of an entire planet :)



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