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Looooong Exposure Photography


Nigeyboy 6 537 United Kingdom
22 Jul 2009 2:26PM
Hi all

I am off on my hols next week to North Norfolk. I am planning on some early morning trips to the beach, and some of the broads. However, I am also planning on trying some long exposure photography - by long, I mean 10 mins plus. I want to try and capture star trails over the sea. I will be using a 400D with 2 x NB2-LH batteries in a grip.

My question is, has anyone else tried this? If so, what sort of results have you had? I am worried about noise, and battery life, so if anyone has any tips, that would be great!!

Cheers all

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Metalhead 7 1.9k 2 England
22 Jul 2009 2:32PM
There was another topic a couple of months ago about star trails and the like. One thing mentioned then was the use of stacking software (and maybe even Photoshop?) and taking lots of shorter exposures and stacking them together to get effectively the same time but with much less noise.

Another great tip in that other topic was to use a remote lead that is locked to "On" and have the time as 30 seconds (or less), so the camera literally continues taking 30-second exposures until the memory card is full or the batteries die! You just sit back, relax, and stack the images in software when you get home....

It's on my list of things to try too. Good luck!
Metalhead 7 1.9k 2 England
22 Jul 2009 2:33PM
Actually, using Photoshop you could stack all the images as layers on one file with different transparencies - that's probably how they do it in Photoshop.
fauxtography 9 6.6k 36
22 Jul 2009 2:33PM
Enable the long exposure noise reduction in your menu, this will reduce the "dark noise" from sensor heat. It will mean, however, that you will not be able to take another photo for as long as your exposure (as the camera takes a dark frame of the same duration).

The longest exposure you can get on a single battery is over an hour in duration though that will depend on ambient temperature a little and battery condition.
Metalhead 7 1.9k 2 England
22 Jul 2009 2:41PM
To save you time and battery power out in the field, you can take a photo with your lens cap on for the same amount of time as your long exposure shot when you're back home, then deduct that "dark frame" from the original image.

That way you don't have to wait for the camera to do that step of the process and you can get on with your next shot.

I haven't tried any of this, but I'd imagine the "dark" shot needs to be on exactly the same settings, which you could set in Manual mode, to reflect the original long exposure shot.
Tandberg 11 1.2k 2 England
22 Jul 2009 2:48PM

Quote:Enable the long exposure noise reduction in your menu


Did it once on a cold dark night

Never again,and if i'm honest made no difference in the end.was a 5D i was using at low iso.

Not worth the hassle doing it
But thats just my opinion
Dave
Nigeyboy 6 537 United Kingdom
22 Jul 2009 2:53PM
Thanks guys - I guess its just a matter of getting out there and experimenting. Problem is, I am sure that clear nights will be fairly rare, so don't want to waster any time I get!!

Anyone have info on stacking images using PS (I have CS-3)?
fauxtography 9 6.6k 36
22 Jul 2009 2:55PM

Quote:To save you time and battery power out in the field, you can take a photo with your lens cap on for the same amount of time as your long exposure shot when you're back home, then deduct that "dark frame" from the original image.

That way you don't have to wait for the camera to do that step of the process and you can get on with your next shot.

I haven't tried any of this, but I'd imagine the "dark" shot needs to be on exactly the same settings, which you could set in Manual mode, to reflect the original long exposure shot.



That's exactly what the long exposure noise reduction is. It takes a 2nd shot for the same length of time. Merging the 2 shots together by the camera takes seconds. It is the 2nd exposure that takes the time, so doing it the old fashioned way will take just as long and also require time after the capture. The three things that need to be the same, are duration, iso and temperature. The noise is created by heat within the sensor. The longer the exposure the more heat that is generated and the hotter it is, the more noise there is.

Dave it all depends on what sort of dark noise your camera generates, the colder it is, the less it will generate... maybe you are lucky and have a nice cool running cam Wink

Here's a sample of dark noise and the benefit of a dark frame (either in or out of camera)
Metalhead 7 1.9k 2 England
22 Jul 2009 3:03PM

Quote:doing it the old fashioned way will take just as long and also require time after the capture.


Thanks for the info there. I just thought you could save time sat out in the middle of the night waiting for your camera to take a black 10 minute shot if you could do that at home at a later date. Maximises your time out under the night sky.

But if the temperature needs to stay the same too for the dark frame, I guess you're better off relying on the camera's noise reduction done straight after the main shot. Sitting at home the next day doing a 10 minute shot won't keep the circumstances exactly the same, even if the camera settings are the same.

Thanks for the link to the examples. The few times I've played with night sky shots I haven't had the pink noise as you've displayed in the examples.

Incidentally, there's a lunar eclipse on August 5th...
Nigeyboy 6 537 United Kingdom
22 Jul 2009 3:06PM
So does this noise reduction function do the 'stuff' in the camera then? Or do i have to blend in PS?
Tandberg 11 1.2k 2 England
22 Jul 2009 3:07PM
Mate i think you know i shoot a fair few long exposures in summer and in the cold weather.

I shot one 10 min expo that needed another 10 minutes on top of that

Time is money as they say,But time was for me freezing my knackers off for 1 shot. I thought Balls to that Wink

So i went back to single exposures for long exposures and i can honestly say i never had a problem with noise.

So i just dont capture second blank frames of any kind
Dave
fauxtography 9 6.6k 36
22 Jul 2009 3:11PM
That shot is from my old 300D it did generate a fair bit of dark noise, in that very particular pattern.

If you can keep your camera sensor at a known temperature (some astrophotographers cool their sensors) then you could in theory create a "bank" of dark frames to apply at home later.

I have two DSLR bodies, so i tend to alternate while night shooting, i.e. use one while the other is doing a dark frame.
Nigeyboy 6 537 United Kingdom
22 Jul 2009 3:12PM

Quote:Incidentally, there's a lunar eclipse on August 5th...


oooo - Thats cool!! Fingers crossed its clear . . . .
Tandberg 11 1.2k 2 England
22 Jul 2009 3:13PM
Good thinking batman
But we dont all have 2 cameras do we eh

If that works for you (Great)
Dave


PS I have 3 Wink
fauxtography 9 6.6k 36
22 Jul 2009 3:15PM

Quote:So does this noise reduction function do the 'stuff' in the camera then? Or do i have to blend in PS?


If you select the long exposure noise reduction in your camera menu it is all done in camera.


Quote:Time is money as they say,But time was for me freezing my knackers off for 1 shot. I thought Balls to that


LOL! me too.


Quote:So i went back to single exposures for long exposures and i can honestly say i never had a problem with noise.


Newer cameras seem better at controling the "dark noise", my 300D was really bad for it.

Nigeyboy... do some test shots before you go... see what sort of dark noise your camera generates, if it doesn't generate a lot, then there may be no need for the extra dark frame.. and that'll save you time.

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