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01-02-2012, 10:54 PM   #1
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Long exposure shots (camera)

Hi, I'm still new, and I'm very much interested in getting into long exposure shots, so far I have the k-r. When I put it on bulb mode and I set it for a 4mins exposure, I need to wait another 4 mins before I can shoot again, I was wondering if there's a much faster "recharge" Pentax camera option "exposure wise". (Cause I hate to put it on a 30min exposure, and have to wait another 30mins just to find out that something went wrong,)

Thanks.

01-02-2012, 11:16 PM   #2
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There should be a "long exposure NR" off option in the menu
01-02-2012, 11:55 PM - 1 Like   #3
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QuoteOriginally posted by kaiserz Quote
(Cause I hate to put it on a 30min exposure, and have to wait another 30mins just to find out that something went wrong,)
Yeah, I hate when that happens.

It's called DARK FRAME SUBTRACTION (DFS) and most digicam makers think it's vital. Take a long shot; then take an equally long shot with the shutter closed; then subtract the noise in B from image A. As suggested, you can set LONG EXPOSURE NR to OFF on some cameras, but then you may be left with a noisy frame. I just bite the bullet and find something else to do while the DFS process takes place. Read a book. Use another camera. Eat, drink, get married. Play solitaire. Whatever. Think of it as an exercise in learning patience, like walking a cat on a leash.
01-03-2012, 12:11 AM   #4
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This is why you do your exposure test shot at a very high ISO, so you can then do the math and do your much longer low ISO shots with less chance of waiting all that time to find out your guess was wrong.

01-03-2012, 01:09 AM   #5
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If you don't mind a little photoshopping you can stack exposures with special software.
I know that photoshop extended can do it but also free software use in astro photography.

Instead of 1x 30 minute you take for example 60x 30 seconds exposure, it looks more work but you shot isn't spoiled when for example a car drives by and shines his light into the camera.
01-03-2012, 09:33 AM   #6
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@pinholecam I guess that's the Slow shutter speed NR for the KR

@RioRico Thanks ricorico (:! You always make life much more easier for me (Cause you make it always easy for me a newbie to undestand (: ) And wow I didn't even know that the camera takes 2 exposure (But what do you mean by shutter closed? If I decide to put the camera in the bag and go, will it affect the image?) And now I'm assuming that all pentax sensors have this DFS If that's the case then I guess I better bring something fun for me to do while waiting hehe

@Mike Cash Yes sir, I've been actually doing that.

@Anvh so you're saying, That I can stack 60 photos with 30 secs exposure, and this can be done with one photox60? That is very interesting to know. (I would do more research on that. And If It is gonna be much more work, I think it's gonna be fine cause If you can do it in the comfort of your home with your heaters on and a hot coco beside you while playing music or watching a movie vs out in the wild where you're in the middle of nowhere and is almost freezing cold. I guess the extra work is worth it (: )
01-03-2012, 12:05 PM   #7
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The long exposure NR may be necessary to avoid heat noise on the sensor. But not all cameras are the same. I experienced purple noise blobs on the K-200D after about 10min's, but you can test your camera by: turn off LE-NR, closing off all light sources to camera (I did this with caps on and inside dark cupboard), and take some some long exposures and see what noise patterns you get.

Apparently the noise is ISO, time and temperature dependent, so you can correct with static dark images.

Or the stacking route as alternative to LE-NR or post processing.

My first experience with LE noise in thread: https://www.pentaxforums.com/forums/photographic-technique/126655-star-trail-...urple-hue.html

Explanation from http://blog.starcircleacademy.com/20...posures-part2/
"Locally caused heat noise is noticeable in some cameras and is due to the heat of electronics in proximity to the sensor. In my opinion this problem is a design flaw in the camera. However this kind of noise is repeatable so LENR can help correct it. The “Pink or Purple Glow” that results from this flaw was discussed in Part 1."
01-03-2012, 12:15 PM   #8
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QuoteOriginally posted by kaiserz Quote
But what do you mean by shutter closed? If I decide to put the camera in the bag and go, will it affect the image?
Nope.

QuoteQuote:
And now I'm assuming that all pentax sensors have this DFS If that's the case then I guess I better bring something fun for me to do while waiting hehe
Yup.



That 'shutter-closed' part of DFS happens automagically in the camera. If you think you got the exposure right and don't intend to re-shoot from the same positions, then sure, toss the camera in a bag and go. Otherwise, bring a book or knitting or game or libations or partner or whatever. Have fun!

01-03-2012, 05:24 PM   #9
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I've done exactly what RR suggests while roaming around through the mountains near my home shooting at night. Rather than hang around waiting for the dark frame subtraction to happen I just toss the stuff in the car and motor along to the next spot. The camera doesn't care where it is while it does the processing. The shutter isn't open, so it certainly doesn't have to be sitting perfectly still on the tripod still aimed at the scene you just shot.

Adjust shooting ISO to give an exposure roughly equal to no more than the time you think it will take you to move to your next shot and you'll have little to no "down time" waiting for the processing to finish so you can shoot again. For example: if it is going to take you 15 minutes to go to your next spot, then adjust so your shot at the current location is about 15 minutes at most.
01-03-2012, 06:21 PM   #10
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Thanks guys! everyone here is a great help (:
01-04-2012, 05:42 AM   #11
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As the DFS is in effect postprocessing, you could presumably do very similar back at home, in a more controlled way. You could take a long exposure of the inside of the lens cap, identify the locations of hot pixels, and fix those locations in your photos. Could even set up a photoshop macro or something, to do it automatically. Advantage of doing it yourself rather than letting the camera do it for you is that you know exactly what it's doing, and what it's not - I've read that DFS can lower image quality in some way. Also means you don't have to wait for it to finish after each shot
01-04-2012, 06:42 AM   #12
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As far as hot pixels go, Lightroom will fix those for you automatically. I don't think the problem is entirely one of hot pixels, though.

The one time I did some long night shots with DFS turned off I came back home and upon reviewing the results wished I had left it turned on.
01-05-2012, 03:59 AM   #13
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So I'm gathering that a Pentax DSLR would be useless for lightning photography. You can't wait for NR because in that time you may miss 4 or 5 good shots. I'd love to get a K5 but if there's no way to turn this function off then I guess I'll have to look elsewhere!! The K10D allowed NR to be turned off but I believe this was stopped after that model.
01-05-2012, 08:13 AM   #14
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QuoteOriginally posted by Timbuctoo Quote
So I'm gathering that a Pentax DSLR would be useless for lightning photography. You can't wait for NR because in that time you may miss 4 or 5 good shots. I'd love to get a K5 but if there's no way to turn this function off then I guess I'll have to look elsewhere!! The K10D allowed NR to be turned off but I believe this was stopped after that model.
You can turn it off with the K5, not sure about the k7 though...
btw you can turn it off in the K20D with the help of some scripts and Debug menu.
01-05-2012, 08:25 AM   #15
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QuoteOriginally posted by kaiserz Quote
@Anvh so you're saying, That I can stack 60 photos with 30 secs exposure, and this can be done with one photox60? That is very interesting to know. (I would do more research on that. And If It is gonna be much more work, I think it's gonna be fine cause If you can do it in the comfort of your home with your heaters on and a hot coco beside you while playing music or watching a movie vs out in the wild where you're in the middle of nowhere and is almost freezing cold. I guess the extra work is worth it (: )
Yes to explain it simplere you can make from 3x 10 second photo a 30 second photo.
It's called exposure stacking and it's quite popular with astrophotography.

Here are some software that you can use.
Startrails application
DeepSkyStacker - Free

here is a read about it.
How Image Stacking Works



You can also up the ISO so instead of a long exposure at ISO100, it might be better to shoot at ISO1600 and then stack the photo to average out the noise.
Most noise is random is if you've 6 images you can quite effectively remove the noise.

This a ISO1600 photo taken with the K10D, handheld though so sorry that it isn't perfect.
http://fc02.deviantart.net/fs51/f/2009/336/0/1/Grote_kerk_1_by_Anvh.jpg
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