Long Exposures

P

Philx1979

Messages
987
Name
Phil
Edit My Images
No
Apologies first if this has not yet been asked, used the search function but cant seem to find out what i want to know.

When doing long exposures such as star trails, or night time scenes that last like 10 minutes or even daytime nd 10 exposures, how do you calculate how long to leave the shutter open or is it a case of trail and error, getting out there and trying it for yourself?

Or am i right in saying that as long as you haven`t got any direct or strong light facing the camera the shutter could be open as long as you want, night time scenes i`m refering too, and no longer than say 15 mins exposure.:thinking:
 
right while on the subject matter...how are those star trails photo made? I am thinking stars in the sky moves very slowly and to get a noticeable amount of movement on a photo you must be talking about 30min exposure?

how the hell you set that exposure?
 
bulb setting

but you can use multiple 30s exposures and mix it in prog called startrails, thus cutting down on light pollution too, i dont know much about it but others will fill you in im sure
 
ricky1980 said:
right while on the subject matter...how are those star trails photo made? I am thinking stars in the sky moves very slowly and to get a noticeable amount of movement on a photo you must be talking about 30min exposure?

how the hell you set that exposure?
Click to expand...

Woah ok bud, easy.

I`m a newb, sorry for asking i guess. I`ll just go out and try for myself.
 
Philx1979 said:
Apologies first if this has not yet been asked, used the search function but cant seem to find out what i want to know.

When doing long exposures such as star trails, or night time scenes that last like 10 minutes or even daytime nd 10 exposures, how do you calculate how long to leave the shutter open or is it a case of trail and error, getting out there and trying it for yourself?

Or am i right in saying that as long as you haven`t got any direct or strong light facing the camera the shutter could be open as long as you want, night time scenes i`m refering too, and no longer than say 15 mins exposure.:thinking:
Click to expand...

i use trial and error too, but the more experienced you get the less time it takes as you will instinctively know roughly where to start hth

i leant how to use a camera through forums like this and a lot of trial and error ;)
 
Cheers Cannock,, been reading elsewhere and getting some info aswell but thanks for your comments though, appreciate it.
 
I did a start trails picture one night. It was a 10 minute exposure at ISO100 f3.5, and I had to use some astronomy tools to remove the colour gradient from the light polution, even after processing, the sky still has a bit of a cast to it. The current thinking for star trails, is shoot in jpg 30s, ISO800, wide open or nearly, shutter to continuous and lock the shutter remote release button until the card fills, the battery runs out or the skies cloud over. Then use the startrails application to combine all the jpg's (it can't handle raw so not a lot of point using it). I've not done much in the way of non astro images at night, and the few I have tried were 30 seconds and under.
 
correct me if i'm wrong, but if you set the exposure too long arent you likely to burn out the sensor? i know when i've done 30 sec exposures before i start getting bright blue dots on the sensor
 
Star trails, I do the 30 second thing as others have said. Take a couple of test shots and have a look at the histogram to get an exposure that brings out as many stars as you can. Don't worry about the foreground, you take a separate exposure for that (either longer or shorter to expose it correctly).

For other night time shots, ie not star trails.. I just take a meter reading, or go off the 444 (more like 442 for digi) rule. That's exposing a scene by moonlight with a full moon, just the moon, so away from towns, etc.. a good place to start is 400ISO at f4 for 4 minutes (or 2 minutes on digi as you don't have reciprocity failure to worry about).
 
badgerbaiter said:
correct me if i'm wrong, but if you set the exposure too long arent you likely to burn out the sensor? i know when i've done 30 sec exposures before i start getting bright blue dots on the sensor
Click to expand...

Sounds like hot pixels. I've had no problems with the 10minute exposure. The exposures I took the other night for my astro captures were 2 and 3 minutes each, again no problems. I've seen astro images captured using 20 minute exposures and there's not been any problem with burn out of the sensor. The hot pixels in astro images are processed out in the stacking stage by using dark frame noise subtraction (works in much the same way as turning on long exposure noise reduction in camera, but takes less time to capture the images).
 
I have taken shots at 16 minutes and this is how I calculate the exposure.
Bump up the ISO as high as you can and set the maximum aperture. Take a 30 sec exposure and look at the histogram to check exposure. It doesn't matter about anything other than the exposure as you'll next adjust ISO and aperture to suit. If your ISO can go high enough and you have a wide aperture lens then 30 secs can be too long and you can let the camera metering do the job for you.
Once you're happy with the exposure, you have to do the maths. E.g. Original ISO 3200, Aperture 2.8 = 30 sec exposure. Desired settings ISO 200, Aperture f8. To calculate the time work out the difference in stops and add the necessary number of stops to the original time. In this case, 4 stops for the ISO and 3 stops for the aperture. 7 stops higher on 30 secs gives you 1 hour.
I find in most instances the test shot can be taken using the camera metering, but it depends on the aperture of your lens and your highest available ISO.
 
You must log in or register to reply here.
Back
Top