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DPChallenge Forums >> Photography Discussion >> Why do long exposures take a long time to process?
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08/12/2008 11:41:44 AM · #1
I took some star streak pictures last night, using a 15 minute exposure, and every picture took 15 minutes to process after that. But, a while ago, i did a 30 minutes exposure, and the picture came up in less then a minute.
Any ideas what's going on here? I am using a Nikon D70s
08/12/2008 11:44:08 AM · #2
i think it may have something to do with the size of your memory card and how many images you have on it.
My camera takes only a few seconds, no matter the time frame, while my boyfriend's takes up to a minute...
Do you have a large memory card or a small one?
08/12/2008 11:44:15 AM · #3
You may have the auto noise reduction on. The camera effectively takes another exposure (as long as your original) with the shutter closed and uses that noise to cancel out the noise from the first picture.
08/12/2008 11:48:26 AM · #4
@missxmisery, i am using an 8GB CF card.

@DrAchoo, i guess i should go and read the manual, thanks for the suggestion.
08/12/2008 11:54:38 AM · #5
lol when i saw "long time in processing" i knew it was a D70, mine takes about these time to process a picture, its damn annoying , especially when you are in freezing condition and photographing Aurora borealis :D
08/12/2008 11:57:02 AM · #6
Originally posted by ahmadbaara:

photographing Aurora borealis :D

that's still on my to do list :)
i tried twice on my trip to Iceland. First night was perfectly clear with no activity. Second night the activity was really high, but it was way too cloudy.
I did manage to get something on the first night though, purely by accident. This was not visible to the naked eye.
' . substr('//farm3.static.flickr.com/2244/2203041194_a4a4a041b2_s.jpg', strrpos('//farm3.static.flickr.com/2244/2203041194_a4a4a041b2_s.jpg', '/') + 1) . '

Message edited by author 2008-08-12 12:01:57.
08/12/2008 12:07:13 PM · #7
i got a few decent ones, sadly i dont have membership on dpc to post them, but this a link to my facebook album

every second on that processing time and 15 degrees below was worth it

//www.new.facebook.com/album.php?aid=16203&l=f4065&id=504087757



Message edited by author 2008-08-12 12:12:43.
08/12/2008 12:09:29 PM · #8
@ahmadbaara, link's not working
08/12/2008 12:12:45 PM · #9
Most likely what DrAchoo mentioned is the culprate. From the D70s manual page 133 ;)

with NR on.

"Noise reduction takes effect at shutter speeds of
about 1 s or slower. Time required to process images
more than doubles;..."

-dave
08/12/2008 12:13:27 PM · #10
Originally posted by PlayWithFire:

@ahmadbaara, link's not working


hmmm i tried it out, it works for me, try copy pasting it :S
08/12/2008 01:42:18 PM · #11
ahmadbaara, now it works. nice pics! that's exactly when i was in Iceland

@dknourek, thanks for reconfirming. I'll do a test tonight.
08/12/2008 02:28:16 PM · #12
Originally posted by dknourek:

"Noise reduction takes effect at shutter speeds of
about 1 s or slower. Time required to process images
more than doubles;..."

-dave


Agreed, and I'll specifically say:

Turn on "Full Menus" via CSM.

Then go to "Shooting" menu.
Check "Long exp. NR" (noise reduction of exposures longer than 8s -- this definitely applies to you) -- set it to "OFF"
Check "High ISO NR" -- consider setting it to "OFF" as well, depending on what ISO you are using and your post workflow.

These settings can even slow you down if you shoot raw, since they effect the camera-generated previews in the NEF file.

I'm glad to hear someone got some shots of the shower last night -- I checked every hour until sunrise, and my entire area (within 100 miles of me, according to online wx maps) was covered by clouds. :( I'll try again tonight...
08/12/2008 02:54:07 PM · #13
@cdrice, so whatever noise reduction the camera does can be achieved in post processing? If that's the case, i have no desire to ever have it turned on. I try to never use high ISOs since the noise level is just unbearable.
I always shoot in RAW, just in case i would like to work with the image later.

As for shooting the shower, i didn't really get any good meteor shots, just star streaks. In one picture, if you zoom in, there's a very faint one.
08/12/2008 03:08:43 PM · #14
Originally posted by PlayWithFire:

@cdrice, so whatever noise reduction the camera does can be achieved in post processing? If that's the case, i have no desire to ever have it turned on.


In most cases yes, but you still must take the time to shoot the dark frames. Some random thoughts:
- When you shoot very long exposures like star trails, you should experiment with breaking up the exposure into 5-minute segments. This will both keep sky background exposure within reason, and also give you noise reduction through averaging. Specifically, you'll reduce random noise by the square root of the number of exposures (e.g., random noise is reduced to 1/4 of it's single-frame levels for 16 averaged frames). Note that you'll need to start the next frame immediately after the previous one has finished, or you will have gaps once they are combined.
- After you shoot your "light" frames (your actual images), put your lens cap on and shoot a series of dark frames. These should be shot at the same air/camera temperature, ISO and exposure time as your light shots. Shoot at least 8 dark frames and average them in post processing, then subtract the averaged frame from your combined light frames. Subtracting a dark frame reduces fixed-pattern noise, a different kind of noise which is not affected by averaging light frames.
- For star trail shots, use your camera's lowest native ISO (100 or 200 as the case may be). You don't want or need higher ISO, the trails will just get too crowded and overexposure will eliminate color from your trails. Experiment to find the best combination of ISO, aperture, exposure time and number of exposures. Using this technique, your total exposure time is limited only by your power source.
08/12/2008 03:14:50 PM · #15
Originally posted by PlayWithFire:

@cdrice, so whatever noise reduction the camera does can be achieved in post processing? If that's the case, i have no desire to ever have it turned on. I try to never use high ISOs since the noise level is just unbearable.
I always shoot in RAW, just in case i would like to work with the image later.


If you are shooting only raw, then the only NR you are seeing on your actual exported images is whatever you do in post. The in-camera NR is only applied to the thumbnail preview in the nef file (which you probably discard, depending on what software you are using) and/or JPG images (if you shoot in a JPG or RAW+JPG mode).

Some people argue over which is best (in-camera vs. post), but I think weighing that against all the other benefits of shooting raw, I still shoot raw for my high-iso shots.

If you are shooting raw, you can turn off all the in-camera NR, as well as level-out the settings in your "optimize image" menu (also in the "Shooting Menu") -- those settings only apply to camera-generated JPGs and the nef preview thumbnails.

Originally posted by PlayWithFire:

As for shooting the shower, i didn't really get any good meteor shots, just star streaks. In one picture, if you zoom in, there's a very faint one.


Bummer. The perseids have been a bust for me the last several years in a row (even just viewing, much less photography).
08/12/2008 04:26:50 PM · #16
@kirbic, thanks a lot for the very useful information. I plan to read over it a few more times, and certainly clip it for future reference.

@cdrice, i don't understand too much about the whole RAW vs JPEG, and i don't think i care for now. Once i learned that RAW preserver the information better then a JPEG, i stopped shooting in RAW. Maybe when i am better photographer, i will learn such minor nuances.

I have learned so much :)
08/12/2008 06:13:16 PM · #17
Kirbic, in Photoshop, how do you:
1) "average" frames
2) "subtract" frames?

I assume there are blending modes for each, but I don't recognize those specific terms.

Thanks!
08/12/2008 08:02:37 PM · #18
Originally posted by levyj413:

Kirbic, in Photoshop, how do you:
1) "average" frames
2) "subtract" frames?

I assume there are blending modes for each, but I don't recognize those specific terms.

Thanks!


Frames can be truly "averaged" or they can be combined with more sophisticated mathematical algorithms. For simple averaging, doing it manually in Photoshop is one option.

To average several layers:
1.) Load the images to individual layers
2.) Set the opacity of the first (background) layer to 100%
3.) Set the opacity of the second layer to 50%, the third to 33%, the fourth to 25%... keep the blend mode set to "normal."
4.) That's all there is to it! For more sophistication, other software is normally used. I'll leave it as a research exercise to google "image stacking" and do some reading :-)

To subtract one image from another:
1.) Load image 1
2.) Load image 2 as a second layer
3.) Set blend mode on image 2 to "difference"
4.) You've just subtracted image 2 from image 1

Message edited by author 2008-08-12 20:04:19.
08/12/2008 09:36:39 PM · #19
Great, thanks!
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