| Author | Thread |
|
|
10/23/2006 06:33:53 PM · #1 |
Anyone else experienced the disproportionate length of time it takes to write a frame to the card when the exposure has been a long exposure.
This is on the 5D, and it appears to be the write time is equivalent of close to the exposure time. So for a 30sec exposure the image take 30 seconds to write etc.
Anyone else seen this? is there a way to speed this thing up?
Its bloody annoying.
|
|
|
|
10/23/2006 06:36:49 PM · #2 |
It might be a noise reduction system. I don't know about your camera, but on some when you take a long exposure, the camera will take an equal time dark exposure and subtract out things like hot pixels from the scene.
[/url] |
|
|
|
10/23/2006 06:37:09 PM · #3 |
does the 5D do a dark frame ? (to reduce noise )
if so find a way too turn it off - though you may be faced with hot pixels & uneven exposure ..
|
|
|
|
10/23/2006 06:47:31 PM · #4 |
| 20D is the same. Did a shot for 7minute exposure, took 7 min. to write. I do have the noise reduction on. Not sure if it makes a diff. |
|
|
|
10/23/2006 06:48:20 PM · #5 |
I know the Canon 350XT in the noise reduction will take a long time. If I take say a 5-minute shot it takes 10 minutes to complete (5 min exposure + 5 minute write). I did a 30 minute exposure once with the NR on and it took an additional 30 minutes to write.
I don't know much about the 5D but I think this maybe happening. Does it have NR and an option to turn it on or off?
|
|
|
|
10/23/2006 07:24:33 PM · #6 |
| The write to card time is not affected by the length of the exposure. What you're talking about is the noise reduction feature introduced in the 20D (and used by the 30D and 5D) where the cam is taking a dark-frame after the exposure itself. If you're doing a 7 minute exposure, the cam will take a 7 minute dark frame, do the image subtraction in-camera, and then write the result to the card. |
|
|
|
10/23/2006 08:14:34 PM · #7 |
| depeding on the final result(what the photo is of) i have found the 5d to not need the noise reduction so we turned it off. |
|
|
|
10/23/2006 08:45:03 PM · #8 |
Originally posted by Elvis_L:
depeding on the final result(what the photo is of) i have found the 5d to not need the noise reduction so we turned it off. |
I highly recommend leaving it on...especially if you are doing 30 min exposures.
|
|
|
|
10/23/2006 09:00:08 PM · #9 |
| FWIW, most serious amateur astronomers don't use the in-camera noise reduction either. They shoot their own dark frames (often several) and then average and subtract them in PP. |
|
|
|
10/25/2006 02:52:16 AM · #10 |
Definitely a noise reduction issue.
Write speed is constant as the same number of pixels are being saved in both situations.
Over a long exposure the sensors "heat" up leaving bright pixels and high noise. Taking a second blank frame reveals these extra noisy pixels allowing the camera to either patch "hot" white pixels with interpolated data from surrounding pixels or subtract the difference value of a "warm" pixel from the first exposure. This works due to the fact that the noise per pixel should be the same for each exposure. My Panasonic LX1 does the same thing albeit only 1 minute exposures. Casio's exlim ex-750 was able to do a quicker dark frame due to a better algorithms i suppose. Another technique i have used is image stacking, manually taking several exposures of the same scene with the aid of a tripod, then averaging the exposures to average the noise in the scene, this is handy as both my cameras have noisy sensors. |
|
|
|
10/25/2006 01:45:09 PM · #11 |
Check CF-2. You have a choice of on, auto, or off.
The 5D can take a few shots in sequence with NR on, but you have to wait for the dark frame to complete once the buffer is full. If you take several shots in sequence, I think the 5D only takes one dark frame and uses it for all the shots (based on the timing of when the buffer was cleared.) If you use different shutter speeds, the buffer takes longer to flush (this may be because one dark frame is taken for each unique shutter speed.) |
|
|
|
10/25/2006 01:49:30 PM · #12 |
Yes, it's the dark frame noise reduction what have you.
if the exposure is 30 sec then there is a 30 sec exposure made of the 'dark frame' and the noise is subtracted. Should reduce hot pixels and noise.
you can turn it off or on as mentioned.
Insert gratuitous night shot from the weekend. :D
|
|
|
|
10/25/2006 02:28:03 PM · #13 |
I'd leave noise reduction on. You will wind up with a lot of hot pixels and a lot of noise otherwise. I found this out already and had to go back and re-shoot. There were hot pixels everywhere. There were at least 3 groups of them visable and more when you zoomed in.
|
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2026 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 01/07/2026 06:01:26 AM EST.
