Rule of 500?

[Nova2000]

Hi

I use a tracker for ap. I was wondering if I go to a place where I couldn't Carry my tracker how would I do ap. Can you'll exactly explain to me the rule of 500.ill use focal lengths of 250/200/55. Bright objects like Andromeda galaxy and orion nebula. 

Thankyou 

[Victor Boesen]

divide your focal length with 500 and you get the max exposure you can use without getting any star trailing.

[Nova2000]

Victor, you mean to say 250/500 or 500/250?.does the position of the star affect this? I mean if the star is closer to the poles or celestial equator. 

[Victor Boesen]

15 minutes ago, Nova2000 said:

500/250

sorry, i meant divide 500 with your focal length just like above.

[wimvb]

The exact formula is (should be) dependent on declination or altitude of the target. In practice however, it all depends on how much star trailing you can live with. Besides, photgraphic lenses may have other issues, such as aberration, which can be worse than mild star trailing. In the end you will have to experiment. Whatever you choose, the total time on target is also important. Aim for as many (100+) exposures as possible, escpecially since you will be using a high ISO setting. The only real way to fight noise with short exposures is to take many.

 

Good luck

[Nova2000]

Thanks wimvb I'll be shooting the Andromeda mostly tomorrow. I'll take 200_500 2sec shots at iso 1600 at f-5.advice accpeted