Questions about photographing stars.

Kerri Rae · Apr 11, 2007

I take trips out to the country often and have been trying my hardest to get some decent pictures of stars without much luck. They always look blurry and out of focus.

I have a decent tripod (Using Rebel xti w/18-55 lens). I use the self timer to avoid any camera shake and although I've had much troubles with wind, I'm pretty sure that isn't the problem.

Any hints or tips you can offer?

zioneffect564 · Apr 11, 2007

I would maybe try a longer lens, say a 300mm+. For the blurryness i would check to see if you locked focus because the kit lens is going to be slow and like i said at that focal length its going to have a hard time finding what you want to focus on.

shorty6049 · Apr 12, 2007

from my experience in astrophotography, i will have to disagree with zioneffect... A longer lens is going to allow for MUCH shorter exposure times , unless you want the stars streaked. you can get a 30 second exposure with the stars only slightly trailed, at full wide angle, but as soon as you zoom in, that trail gets longer and longer with the same exposure. The blurring problem you're having is probably due to the fact that your focus is off.... i have a 50mm f1.8 lens that works like a charm for star photography. I just set the focus to infinity. On my kit lens though, infinity doesnt give me sharp stars and i need to turn the focus ring until i get sharp stars. I usually set the ISO really high so i can test the focus without having to do really long exposures. once i get focus right, i put the ISO down really low and turn the exposure up. Here's an example of what i've gotten with the 50mm.

Orion (with orion nebula)

shorty6049 · Apr 15, 2007

did i answer your question? have you tried it ?? are you reading this anymore?

RedDevilUK · Apr 16, 2007

i am

i am also interested in shooting the stars... so i read your post with interest.

i wont be home till weekend, so i cant try yet... but trust me i will (if there is a clear sky

)

grafiks · Apr 16, 2007

shorty6049 said:
from my experience in astrophotography, i will have to disagree with zioneffect... A longer lens is going to allow for MUCH shorter exposure times , unless you want the stars streaked. you can get a 30 second exposure with the stars only slightly trailed, at full wide angle, but as soon as you zoom in, that trail gets longer and longer with the same exposure. The blurring problem you're having is probably due to the fact that your focus is off.... i have a 50mm f1.8 lens that works like a charm for star photography. I just set the focus to infinity. On my kit lens though, infinity doesnt give me sharp stars and i need to turn the focus ring until i get sharp stars. I usually set the ISO really high so i can test the focus without having to do really long exposures. once i get focus right, i put the ISO down really low and turn the exposure up. Here's an example of what i've gotten with the 50mm.

Orion (with orion nebula)

How cool is that... I will have to give this a go now that you 'splained it. I've got a 50mm 1.8 on it's way to my door right now. Now I will have to go out in the country on a clear night. Thanks for sharing.

Digital Matt · Apr 16, 2007

If you are trying to record the stars, without showing the movement of the earth, you'll want to get an equatorial mount for your tripod. Careful focusing is also necessary obviously. The wind might be doing more than you think, so get yourself a decent size sandbag and hang it from your tripod to provide more weight and stability.

shorty6049 · Apr 16, 2007

ooh yeah, thanks matt i forgot to mention that. A lot of people do "piggybacking" which is when you get a piggyback mount for your telescope (on an EQ mount with a motorized clock drive) and align the telescope so it rotates around the axis that it creates with polaris. of course, if you do this, you NEED precision, especially with high magnifications or you will get trailing. and for anyone who wants to get an interesting shot, this thursday the crescent moon will be traveling between venus and the pleades star cluster which will appear to the west (venus is very bright right now) shortly after sunset. I know if its not cloudy, i'll be out there!

shorty6049 · Apr 16, 2007

here's a photo i took through my telescope of the orion nebula. As you can see, my tracking was NOT very precise, and i think its a bit out of focus, but definately shows the possiblities of astrophotography . I've converted it mostly to the blue channel because it had the most visual information in it, but through a telescope , the nebula appears grey, with long exposures you can begin to see the true colors, wich are white, blue , and red/magenta.

Kerri Rae · Apr 16, 2007

Yes, thanks everybody for your input! I don't get out of the city much so I haven't been able to test anything out, and I'm super broke so I'm in no rush to run out and get any equipment just yet, I just want to get some good shots with the lens I have (if possible). Thanks for your help!

Digital Matt · Apr 16, 2007

The best results with that lens are going to be had from f/8 to f/11. This is going to increase the length of time you'll have the shutter open, so you will for sure get some motion blur of the stars, but this can be a great effect, if you let it go long enough to make it count.

astrostu · Apr 16, 2007

Digital Matt said:
The best results with that lens are going to be had from f/8 to f/11.

Okay, I have to ask -- why does everyone say this? I honestly can't think of a good reason why a high f/-number is going to give you a better picture. But I've seen it over and over again on this forum, though no one ever says why.

shorty6049 · Apr 16, 2007

it gives you a sharper picture. With f1.7 you get that blooming like you can sort of see in the stars on my first picture. with f8 they woudl probably start to get some diffraction spikes. i like the lower f number though because i dont have to use such a long exposure

astrostu · Apr 17, 2007

shorty6049 said:
it gives you a sharper picture. With f1.7 you get that blooming like you can sort of see in the stars on my first picture. with f8 they woudl probably start to get some diffraction spikes. i like the lower f number though because i dont have to use such a long exposure

Maybe it's because I've never used an f/1.8 ... or lower than an f/3.5 on stars due to lens limitations, but I've never had issues with blooming, even on "long" exposures of 45 minutes. Stopping down the aperture would also decrease the number of stars that you could see by a significant amount. And when I want diffraction spikes, I put in a cross-screen filter.

shorty6049 · Apr 17, 2007

ya, thats why i always use 1.8, becasue thats where i get the most stars for my setup. people just say use f8 because thats the sharpest aperture for a lot of lenses. Its the "sweet spot" where you get the best results. i have taken daylight photos with f1.8 and f8 and can definately tell the difference in clarity across the field