30D low light -HELP!

Last night I decided to try and capture some star trails, so I set up at the bottom of the garden in pitch darkness and tried some test exposures. I made 2 captures, both at 4minutes with different apertures to get a feel for the light. Both looked pretty good, but I decided to go with f/8.

I released the shutter and set my stopwatch for 30minutes. After waiting patiently I let the latch go on my remote release and waited to see the results... The red CF access light came on and "Busy" flashed on the LCD, but no image. After waiting 5 minutes, I gave up. The only way I could unlock my camera was to open the BATT compartment. What did I do wrong?

The 4minute exposures came up straight away, so why did my 30min exposure lock up the camera?

Any advice would be greatfully recieved! Many thanks!!

Do you have long exposure noise reduction on? If you do, it will take the same amount of time as the exposure to reduce noise. So your 30 minute exposure will take an additional 30 minutes following the actual exposure.

the longer the exposure the longer the write to the card.
not 100% sure but i think a 30 min exp will take almost as long to write to card

Ah, ok... just reading about that now in the manual. It says that the long exposure NR is activated after 1sec, so why didn't my 4minute exposure take another 4 minutes to write??

Are you sure NR was on for that exposure?

I've always left it in AUTO. Is it best to switch it off for very long exposures? Will I be able to correct the noise in PP???

on my 350d its either on or off no auto

i left that option always on, should i turn it off if i shoot in daylight or high speed short exposure? and what if i don't use it even with long exposure can that be bad for shots to be so noisy and can't fix even with Noise reduction softwares?

Tareq wrote in post #2153405
i left that option always on, should i turn it off if i shoot in daylight or high speed short exposure? and what if i don't use it even with long exposure can that be bad for shots to be so noisy and can't fix even with Noise reduction softwares?

It won't kick in for normal daylight exposures, so you can leave it on. I turn NR off for test shots when doing long exposures, but always turn it back on before taking the shot I hope will be a winner Try some test shots with NR off at higher ISO's and see what you think.

totalbeginner wrote in post #2153194
I've always left it in AUTO. Is it best to switch it off for very long exposures? Will I be able to correct the noise in PP???

Long exposure NR is either on or off. There is no 'auto' setting for it. If you choose to leave NR off, you can use a program like Noise Ninja to correct the nose in the PP phase.

C.FN-02 Long exp. noise reduction

0: Off

1: Auto
For 1 sec. or longer exposures, noise reduction is performed automatically
if long exposure noise is detected. Setting this to [Auto] is effective in
most cases

2: On
Noise reduction is performed for all exposures 1 sec. or longer. Setting this
may reduce the noise even for exposures which would not have been
noise detected/reduced at the [Auto] setting.

I think the above probably answers my question. I guess it's possible that the AUTO setting didn't detect any noise during the 4minute exposure and so the image was "written" fairly quickly. However the 30min exposure probably produced detectable noise and so the write time would have been 30min also.

Many thanks for all your help!

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Tech Tips by Chuck Westfall August 2006