Paging Fuzz - Lyrid meteor shower ?'s

**nobueno** · 04-21-2012, 07:51 AM

Fuzz (and everyone else) - you seem to be quite an expert of astrophotography, how would a mere mortal like me go about getting a shot of the Lyrid meteor shower? heard the best time to see it will be before dawn on sunday morning. I have a t2i w/ the 18-55 and 55-250 kit lenses and the 50mm prime. figured i would head up to the mountains and set up shop far from any light source but beyond that i'm at a loss. 50mm prime opened up to 2.2 iso up to 3200 and put it in bulb mode? about how long can the lens stay open w/out making star trails? will i even be able to pick up the meteors as quick as they'll be zooming through the sky? thanks in advance guys

**OverTurn** · 04-21-2012, 04:12 PM

General rule for the star trails question is to divide 500 by your focal length (in 35mm terms)...so if you're shooting 50mm on a 1.5 crop sensor, that's 500/(50*1.5)=6.6667 so you only have a little more than 6 seconds before you start to trail. I think I did that right at least.

**iscariot** · 04-21-2012, 06:29 PM

Originally Posted by OverTurn

General rule for the star trails question is to divide 500 by your focal length (in 35mm terms)...so if you're shooting 50mm on a 1.5 crop sensor, that's 500/(50*1.5)=6.6667 so you only have a little more than 6 seconds before you start to trail. I think I did that right at least.

Not even close, the answer is 9.

**Fuzz** · 04-21-2012, 07:08 PM

First thing will be to make sure you're pointing in the right direction -- the shower will be between Lyra and Hercules (more info here).

I've seen several versions of the exposure length formula:
1000 / (focal length x crop factor)
600 / (focal length x crop factor)
250 / (focal length x crop factor)

600 seems to be the most commonly cited one -- technically the exact formula depends on your location declination (and camera pixel pitch); I'm guessing 600 is average for the US. At 50mm on a crop, you'll probably be okay somewhere between 7-10 seconds -- I'd suggesting shooting some test frames to gauge what's acceptable to you (you may well be okay going longer at 10sec).

50mm at f/2.2, ISO3200 will work, but as OverTurn pointed out, you'll have to shoot a lot of frames. Just make sure you have enough room on your card and battery charge, and shoot continuously.

The trickiest part will most likely be focusing -- you cannot just set the focus ring all the way since lenses focus past infinity. One method -- point to a bright star (nearby Vega in Lyra is a good candidate), zoom in 10x in LiveView and focus manually until the star is the smallest. If your camera doesn't have LiveView or LV zoom, then trial and error is the way to go. Note that the focus point does move with large changes in temp (so if you set your focus in the early evening, it may well change when you start shooting much later).