JoBarg Loc: Pennsylvania

I recently read a blog of a 500 rule for nighttime photography.. The example was using a 14 mm lens full format camera. The calculation said 500 divided by 14 = the exposure time maximum before the "sky" moved.. Any info?

G Brown Loc: Sunny Bognor Regis West Sussex UK

that would be 28.5 of a second? That seems to be reasonable. On a crop sensor iso 100 at F10 gives a 30th of a second at 18mm. The sky won't move but focus and sharpness may be an issue.

try asking in the astro section

DirtFarmer Loc: Escaped from the NYC area, back to MA

It's going to depend on how closely you look at the image.
A few years ago I tried some night sky pictures using my 24-70. At 70mm I could just barely see motion with a 4 second exposure. 500/70 would be around 7 seconds. The main issue was focus.

Here is a multiple exposure, 5 shots, 2 seconds each, 15 second interval, 70mm lens. Manual focus, the dots are about 5 pixels across. The image is negative, since I think it's easier to see faint black dots on white than faint white dots on black. 7 seconds is about half the distance between dots.

pithydoug Loc: Catskill Mountains, NY

That may be a minimal rule meaning you can go longer depending on conditions and the effect you want. I shot this one at 50mm f/11 ISO 100 6:32 am EST. Basically just a hint of light, set to bulb for 400 sec for experiment. The Hudson river movement and cloud movement obviously smoothed out. Nothing magical about 400 just a WAG. How would it look at 10 min or 30 seconds would be quit different. Rules are interesting but long exposures can take on a life of their own. I do lots of long shutter especially with slow moving barges and lights on a bridge in the dark. The picture is nothing exceptional but to offer more ideas

(Download)

travisdeland Loc: deland, FL

Plenty of info on this-explanations, etc, if you just Google it

jerryc41 Loc: Catskill Mts of NY

Nikon, and others, suggest 20 seconds before "the sky moves." I've also seen 15 seconds as the limit. I wonder if that changes for shooting at the equator or the poles.

DirtFarmer Loc: Escaped from the NYC area, back to MA

Of course if you're shooting the pole star* it doesn't move much, but most people shoot in other directions. My 15 second example above was shot at about 45 degrees North latitude, but it's really the latitude (declination) of the star that counts, not the latitude of the camera.

* The "pole star" (Polaris, also known as the North Star) is not quite on the pole. It's approximately 0.7 degrees away from the pole. There is no comparable bright star at the southern pole.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

35.7 seconds.

Obviously shorter exposures would be better if you can deal with the noise of a higher ISO.

Ronsh Loc: Floresville,Tx.

Some follow the rule of 400, some 500, and others follow the rule of 600. The length of time changes with crop vs full frame also.

peterg Loc: Santa Rosa, CA

This guideline applies only to stars, not to clouds, moon, sun, Polaris, etc. It also depends on camera's ISO quality, post processing, final print size, etc. It's a good place to start.

imagemeister Loc: mid east Florida

The sky is always moving - question is, will you notice it ?

For gear choices, depends on the pixel density of your sensor( or how close you are looking/size of your print), and your tolerance for noise (ISO performance) ......20 seconds + or - exposure on a moderately wide angle lens is thought to be the longest practical limit for most scenarios.

imagemeister Loc: mid east Florida

I guess I should also mention the quality ( resolution) of your lens at wider f-stops also factors in. this will govern your aperture selection and affect your SS/ISO.

CaptainBobBrown

The 500 rule is a conservative algorithm for determining the maximum time in seconds you can keep the shutter open at a given focal length on fixed mount (as opposed to equatorial mount which compensates for earth rotation) before the earth's rotation (which causes stellar apparent motion) would be observable as light streaks. The longer your focal length the more magnification so the shorter the time of shutter opening before stellar motion becomes apparent as light streaks. It has nothing to do with lens quality or atmospheric conditions. If you are doing astro photography then you might care otherwise it's irrelevant but all that other stuff might be.

jeep_daddy Loc: Prescott AZ

Set up for Night Sky ImagesBefore You go into the Dark

Remove the polarizer or any ND filters, if attached, and replace with UV/skylight filter
Turn the brightness of the monitor on the back of the camera down to near minimum
Attached cable release (must have a lock for star trails), remote trigger or set timer to 2 seconds (will not work for star trails)
Turn off the image stabilization/vibration reduction on the lens/camera
Set the focus on the lens/camera to manual, focus lens at near infinity or distant object and mark or tape lens.
Set camera mode to manual
Set f-stop to the most open setting (usually f/2.8-f/4) and set ISO to 1600
Set color temperature to 4000k and make sure you are capturing in RAW
Set shutter speed per “Rule of 500” if you are just shooting a single shot, if shooting star trails set to around 20-30 seconds. (The rule of 500 is 500 divided by the lens mm. Example using a 14mm lens: 500/14=35 so can start with 35 seconds and then adjust it based on the image). Crop sensor cameras need to multiply lens focal length by crop factor usually 1.5)
Turn off any in-camera noise reduction
Set the lock up mirror if you are just shooting single shots
Set camera to continuous low or high shooting for multiple shots if shooting star trails
Check batteries to make sure you have plenty of power remaining both camera and flashlight
Check memory card to make sure you have plenty of storage (approximately 60-90 images every 30 minutes of capture for star trails)
Test shutter release to make sure everything is working before you walk on into the darkness
If not packing in, recommend removal of the strap on the camera and attach the camera to the tripod in the light, check to makes sure the camera is firmly attached.
Discuss plan and communication to control incidental light - I’m open, I closed, light painting, etc

Bobspez Loc: Southern NJ, USA

You won't see much at a 30th of a second unless you're in crystal clear viewing conditions. At 15 seconds you will see thousands more stars than at 1/30 second, but they will start to appear as slightly eliptical rather than round.