question about shooting stars - timed exposure

I am interested in trying out some times exposures this weekend as it has been particularly starry lately here and very clear skies (below freezing temps).

LAst time i gave this a shot the pics were horrible, barely any stars visible and blurry etc. I used a tripod, 30 sec exposure, mirror lockup and 17-40L at 40mm.

I knwo these can be done, as I have seen stunning shots before. Can anyone point me in the right direction settings wise? I do not have a cable release, so i imagine some of the blue must be due to that.

thanks

You have to think minutes not seconds for star trails photography. Have a lookhere, this should get you on the right track.

Hope this helps.

MLU isn't needed. You won't expose any signficant light during the short period of unwanted vibration.

What aperture did you use? Star photos are all about aperture... since the points of light are moving across the frame shutter speed has no bearing on exposure. Your only control for exposure is aperture. Shutter speed controls the length of the trails.

Basically you want to go relatively wide open but staying in the sweet spot of the lens.

This is 20 minutes, f/5.0, Canon 18-55 EF-S @ 18mm, ISO 400. Next time I'll use ISO 100 because ISO 400 was too sensitive (I darkened this image a bit). The lighter areas to the right are bits of chimney smoke that were blown into the shot.

AF probably doesn't work with the lens pointed straight into the dark sky.

also, some lenses (e.g. my 16-35) will focus *beyond* infinity (something about temperature compensation or some such), so you can't just flip it to manual focus and zing to the infinity stop -- it will be out of focus.

so you have to do some experiments.

first, the focus. crank the ISO all the way up, open the aperture all the way. eyeball the focus thru the viewfinder, or if that's not possible, line up the infinity symbol with the mark on the lens.

start with a 15 or 30 second exposure. after taking a picture, review it, zoom all the way in, and see if the stars are in focus. if they are not, move the focus ring a little bit in one direction and repeat. if the result is a little better, then try again moving a little bit more in that direction. if it's worse, then rotate the other way. tedious!

next comes exposure. decide what aperture you want to shoot at. keep the ISO cranked up. find a shitter time that yields a satisfactory exposure (sky color, other element exposure). now if you want a shot with less noise, drop the ISO down and compensate by multiplying the shutter time appropriately (double the time for every ISO "stop").

here are some examples from a recent trip to Yosemite...
http://nobot.2y.net/pi​ctures/20041031-yosemite/?9 (12 minutes)
http://nobot.2y.net …res/20041031-yosemite/?10 (45 minutes)
http://nobot.2y.net …res/20041031-yosemite/?11 (10 minutes)
http://nobot.2y.net …res/20041031-yosemite/?17 (lit only by moonlight -- 3 minutes at ISO 400)

have fun and enjoy those clear nights!

here is a pic at 15 seconds, i didnt even mean to capture it, but somehow it happened and i think it looks cool

Byte size: ZERO | Content warning: NOT AN IMAGE

Also, when photographing stars or other point (emissive) light sources, the relative aperture, or f/ stop is less relevant than the absolute (diameter) aperture. So a 200 mm f/8 is as fast as a 50 f/2 for capturing stars. It'll just capture a smaller area of the sky.

These are great tips guys, but can't you damage the senzor if you keep it open for 20 mins ans something bright, let's say the moon, comes into the picture?

Shouldn't think so - it's not going to be hitting the same spot on the sensor the whole 20 min. Of course, if it makes it into the picture, it'll probaly blow out the star trails anywhere near it, so you might as well pack things in at that point. But even a full moon exposure should be f/16 at 1/ISO.

Hop on down to the bookstore and pick up the latest issue of PC Photo. It has a very neat article about astrophotography using digital cameras.

A buch of cool tips you might not have thought about too.

-Pete

One other point, if you use a 300mm lens vs a 50mm lens, it will take less time to get star trails. Just remember that you bring up the fstop, decrease the shutter speed accordingly.

Hey guys, these are great tips thanks. I was limited to 30 mins, as for bulb i understood i would have to sit there with my finger on the trigger so to speak the entire time on my 10d. Is this not correct?

I may go pick up the wired remote this week in order to try this out again this weekend at the farm (less ambient light). Is the ~$130 TC-80N3 remote from canon the cheapest there is?

As for the focusing PAST infinity, this was my problem. I realized it when i came inside. I slapped it over to the infinity loop and it went past infinity. I should be able to get some decently focused shots at least this time. I wasn't even so much after trails my first shot (altho they do look stunning).

How can i ensure that i dont get condensation inside my lens and body after being out in sub freezing temps for 20 mins?

the TC-80N3 is nice for having timer and intervalometer features. there is a cheaper ($60) version without the timer and stuff. it has a release button that you can lock, so you can just use your watch as a timer.

http://www.canoncompan​ystore.com …?ProductDetail=​2393A001AA

i don't think you'll see it inside the lens & body if you don't dismount the lens. you may get fogging on the front of the lens and eyepiece once you come back inside though. did you notice fogging inside the first time?

Ah I will look for this timer this weekend. I dont need the interval shooting etc, as if i do anything like that it will be tethered to my laptop.

Didnt notice much fogging last time, just a bit between the lens front element and my UV filter.