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05-13-2015, 09:55 AM   #1
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Long delay on long exposures

Using my trusty old *ist DS, it seems that it has gotten even slower than it used to be for a long timed exposure. I've used it many times for astrophotography, star trails, bright comets, meteor showers, etc, and I know there is a lag time or whatever you call it after ending the exposure. Almost all those pics have been using the timer, anywhere from 2 seconds up to 30 seconds (the max it will do).

Well, last night, I tried painting with light along with some friends. We all used the bulb setting on various cameras (mine was the only Pentax), and held the shutters opened for around a minute or so while the "painter" went around flashing the old barn or shining his flashlight on it. We used the old black cloth or cardboard over the lens, inbetween flashes.

Anyway, that said, when I ended my exposure, it took at least a full minute or so - it seemed like an eternity though - for my image to "process" so I could view it. A friend was using a Canon (I don't remember what model, but it was 4-5 years old he said), and his showed the image within 2-3 seconds! Wow, why such a huge difference?

He kept asking me, "how'd yours turn out", and all I could say was, "don't know, still processing".

Any suggestions or thoughts? Is that normal? Is something wrong? Is it just because my DS is older tech?

On my 30 second star photos, it never took more than maybe 20-30 seconds at worst. Could going up to a full minute make the camera have to work and process that much longer? It was kind of embarassing when everybody else there was looking at their images and I was still waiting.

Scott Smith - Astronomersmith

05-13-2015, 10:47 AM   #2
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QuoteOriginally posted by Astronomersmith Quote
Using my trusty old *ist DS, it seems that it has gotten even slower than it used to be for a long timed exposure. I've used it many times for astrophotography, star trails, bright comets, meteor showers, etc, and I know there is a lag time or whatever you call it after ending the exposure. Almost all those pics have been using the timer, anywhere from 2 seconds up to 30 seconds (the max it will do).

Well, last night, I tried painting with light along with some friends. We all used the bulb setting on various cameras (mine was the only Pentax), and held the shutters opened for around a minute or so while the "painter" went around flashing the old barn or shining his flashlight on it. We used the old black cloth or cardboard over the lens, inbetween flashes.

Anyway, that said, when I ended my exposure, it took at least a full minute or so - it seemed like an eternity though - for my image to "process" so I could view it. A friend was using a Canon (I don't remember what model, but it was 4-5 years old he said), and his showed the image within 2-3 seconds! Wow, why such a huge difference?

He kept asking me, "how'd yours turn out", and all I could say was, "don't know, still processing".

Any suggestions or thoughts? Is that normal? Is something wrong? Is it just because my DS is older tech?

On my 30 second star photos, it never took more than maybe 20-30 seconds at worst. Could going up to a full minute make the camera have to work and process that much longer? It was kind of embarassing when everybody else there was looking at their images and I was still waiting.

Scott Smith - Astronomersmith
Google "dark frame subtraction" and, yes, new cameras are much much faster, especially when you disable DFS
05-13-2015, 10:58 AM   #3
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It may be called Long Exposure NR on your camera, but dark frame subtraction is what it is doing. It does a dark frame (shutter closed) for the same amount of time you exposed as a noise reduction technique.

Last edited by mattb123; 05-13-2015 at 12:29 PM.
05-13-2015, 12:07 PM   #4
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QuoteOriginally posted by mattb123 Quote
It may be called Long Exposure NR on your camera, but dark frame subtraction is what it is doing. It does a dark frame (shutter closed) for the same amount of time you exposed for as a noise reduction technique.

Yes! Also, what memory card are you using? If it is a few years old you may want to purchase a newer and faster one.

05-13-2015, 01:46 PM   #5
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My K110D will do that. To stop it you have to turn off the NR.
05-13-2015, 09:46 PM   #6
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The 'dark frame subtraction' takes a second image with the shutter closed after the 'primary' image is taken; the duration is the same as the original exposure. This is (if I'm not mistaken) done for exposures longer than 30 seconds.

You can switch it off in the custom menu of the *IstDS; item 'noise reduction'; see the manual, page 140 and page 100.
05-14-2015, 11:03 AM   #7
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Wow, yall just learned me something! <haha> Seriously, thanks for that terrific informative response, everyone!

I am a little embarrassed that I didn't even know about that NR option, even though I've used the camera for at least 9 years! I just never ran into a situation where I needed it, I suppose. Even on my 30 second star trail photos, I realized it took a while to process, so I accepted that small amount of wait. But, the other night, using Bulb, and holding it open for at least a minute or more...big difference.

There was some discussion among the people there about turning off noise reduction, but I didn't realize my old DS even had that feature....so I didn't even check! Live and learn I suppose.

And to the person who asked about my card - yes, it is an older one, so that probably slowed it down some too.

I looked in my manual and found exactly what was suggested, so I changed it from "1" to "2". Now, next chance I get, I'm going to do a little test and see how much difference it makes. Thanks again for the suggestions and help!

Scott

---------- Post added 05-14-15 at 01:07 PM ----------

Now that you have given me a good lesson about my camera and its capabilities, I want to ask, does it make much of a difference? I mean, with NR on compared to NR off?
I know I'm going to try it out myself first chance I get, but I wanted to get your opinions too. Thanks again for the help!

Scott
05-14-2015, 11:38 AM   #8
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On a one minute exposure, it will make a one minute difference; on a ten minute exposure, it will make a difference of 10 minutes.

See my previous reply.

05-14-2015, 11:44 AM   #9
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QuoteOriginally posted by Astronomersmith Quote
[/COLOR]Now that you have given me a good lesson about my camera and its capabilities, I want to ask, does it make much of a difference? I mean, with NR on compared to NR off?
I know I'm going to try it out myself first chance I get, but I wanted to get your opinions too. Thanks again for the help!

Scott
It can make an significant difference, more so on older generation sensors, so only turn it off when you have no other option.
CCD sensors can get quite hot during long exposures, which can show as mis-colored areas on the image. And a lot of hot pixels can show up during long exposures.

Check the sample on this page where half of the image have NR applied (zoom in on the image).
Dark-frame subtraction - Wikipedia, the free encyclopedia
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