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07-20-2020, 06:37 AM - 2 Likes   #1
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Interval shooting and the camera's buffer.

I've spent the past few nights shooting Comet Neowise and have had some results that I am very happy with...particularly when you factor in the almost zero effort the K1 makes you expend.

I fancy trying some of the time-lapse type shots I've seen about the place and think the best way to do this is to use the interval shooting and then do something magic in Photoshop, rather than the Interval Movie Record which (again, I think) would result in lower resolution results?

My query is...if I wanted to take, say, a hundred 30 second exposures, would I have to leave a similar time between shots to allow the camera time to record the data? It's seemed to me over the past few nights that anything like a 20 second exposure allows the camera to be used more or less instantly again, but anything over that seems to render the camera inoperable for a length similar to the exposure.

Am I making sense?!

Thanks

Example shot....

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07-20-2020, 07:48 AM - 1 Like   #2
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it seems to me that you did it well
07-20-2020, 07:55 AM   #3
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Thanks - time lapse next!
07-20-2020, 08:47 AM - 1 Like   #4
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Recording the data takes very little time (less than a second) but if you employ noise reduction, the camera will have to take a dark frame (with the shutter closed) equal in length to the exposure you used, so that might be what you're referring to. Without noise reduction, you probably will be ok with most any practical interval between shots.

Out of curiosity, is the shot that you attached done unguided, with the K-1 Astrotracer, or guided on a mount? Did you let the camera meter the exposure (green button)? Was that a morning or evening photo?

Great shot!!

07-20-2020, 09:35 AM   #5
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Oh, that makes sense. Fantastic...I had noise reduction on both Slow Shutter and High-ISO set to auto. I'll give that a go.

As for the shot, it was just plopped down on a tripod with Astrotracer turned on (having carried out a precise calibration), and then I gave it 20 seconds at f4.5, ISO 1600 and the 70mm end of my 24-70DFA lens. It's a doddle! As for the exposure, I simply had an educated guess and then twiddled with it in Photoshop to bring out a bit of the tail.

Thanks
07-20-2020, 09:36 AM - 1 Like   #6
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QuoteOriginally posted by osbourne one-nil Quote
...It's seemed to me over the past few nights that anything like a 20 second exposure allows the camera to be used more or less instantly again, but anything over that seems to render the camera inoperable for a length similar to the exposure....
Look for Slow Shutter Speed Noise Reduction in your camera menu. Turn it off.


That feature, when enabled, takes an extra dark frame after each long exposure. The shutter stays closed during the dark frame, the noise pattern is analyzed, then the noise is subtracted from your exposure.
07-20-2020, 09:45 AM   #7
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Brilliant thanks. So I could achieve the same result by taking my own dark frame and using the right software? It does sound like a useful feature but only at the right time!
07-20-2020, 10:26 AM - 1 Like   #8
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Also, don't forget that the shutter speeds aren't quite as advertised! A "30 second" exposure is really a 32-second exposure (True Shutter Speeds compared to Nominal Shutter Speeds - Actual Measurements - PentaxForums.com), so if you are using interval shooting, you have to set the interval long enough for the correct exposure length, plus a second or two to write the data.

So, for
QuoteOriginally posted by osbourne one-nil Quote
if I wanted to take, say, a hundred 30 second exposures,
an interval of 33 or 34 seconds is about right. (Do a test before the next comet shoot!!!!!)

07-20-2020, 10:41 AM   #9
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There'll be a K1-iii by then.
07-20-2020, 11:39 AM   #10
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QuoteOriginally posted by osbourne one-nil Quote
There'll be a K1-iii by then.
QuoteOriginally posted by AstroDave Quote
(Do a test before the next comet shoot!!!!!)
I meant like TONIGHT! i.e. the next shoot - not the next comet!
07-20-2020, 12:20 PM - 2 Likes   #11
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I don't have the K-1 but with my K-3, K-3ii, and K-500 when I do things like that I just put the camera in manual mode with a drive mode of continuous fast, connect my release cable and flip the switch. I've never hit the buffer with exposures longer than a few seconds, at 1 or 2 seconds I likely would, but at and beyond 4s I've never had a problem. I've done 2+hour night time lapses that way several times and not had a problem.

I see that the mention of dark frames has been brought up and my advise there is to turn it off in camera. Instead take your own dark frames at the end of the session and take a bunch of them. Almost all astro image processing software supports dark frames and will combine and average out a pile of them giving a much truer representation of the systematic error which is then removed from each light frame. This produces much better results than the in camera dark frame subtraction. The reason for this is by averaging a bunch you drive the true random noise down dramatically which is actually surprisingly strong. So by driving the random noise in the darks down you are better able to correct just the systematic error instead of randomness. To overcome true random noise you just need a bunch of light shots which increase the signal to noise ratio. When I take dark frames I do so when tearing down and packing up which takes 10 to 15 minutes so I end up with around 60 to 75 darks (I am usually doing astrotracer shots of 20s). Be sure cover the view finder as well as have the lens cap on so you don't get light sneaking in and always take them at the same ISO and shutter speed as your light frames.

A couple of timelapses I did:

Last edited by MossyRocks; 07-20-2020 at 12:22 PM. Reason: Didn't think the video links would eat the text
07-20-2020, 01:11 PM   #12
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QuoteOriginally posted by AstroDave Quote
I meant like TONIGHT! i.e. the next shoot - not the next comet!
Haha! You over estimate my locality's ability to have two clear nights in a row (and my ability to say up to the small hours and function the next day). Having said that, the clouds are breaking....

---------- Post added 07-20-20 at 01:12 PM ----------

QuoteOriginally posted by MossyRocks Quote
I don't have the K-1 but with my K-3, K-3ii, and K-500 when I do things like that I just put the camera in manual mode with a drive mode of continuous fast, connect my release cable and flip the switch. I've never hit the buffer with exposures longer than a few seconds, at 1 or 2 seconds I likely would, but at and beyond 4s I've never had a problem. I've done 2+hour night time lapses that way several times and not had a problem.

I see that the mention of dark frames has been brought up and my advise there is to turn it off in camera. Instead take your own dark frames at the end of the session and take a bunch of them. Almost all astro image processing software supports dark frames and will combine and average out a pile of them giving a much truer representation of the systematic error which is then removed from each light frame. This produces much better results than the in camera dark frame subtraction. The reason for this is by averaging a bunch you drive the true random noise down dramatically which is actually surprisingly strong. So by driving the random noise in the darks down you are better able to correct just the systematic error instead of randomness. To overcome true random noise you just need a bunch of light shots which increase the signal to noise ratio. When I take dark frames I do so when tearing down and packing up which takes 10 to 15 minutes so I end up with around 60 to 75 darks (I am usually doing astrotracer shots of 20s). Be sure cover the view finder as well as have the lens cap on so you don't get light sneaking in and always take them at the same ISO and shutter speed as your light frames.

A couple of timelapses I did:
number one
number two
That's very helpful - thank you! Great videos by the way...really like those!
07-20-2020, 01:16 PM - 1 Like   #13
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QuoteOriginally posted by osbourne one-nil Quote
That's very helpful - thank you! Great videos by the way...really like those!
I figured they would show what is doable and at least the results I get. In the description on their respective page I have the info on what camera, lens, iso, shutter speed and I think even the f-stop that was used. One was shot with a 50mm and I think a 4s shutter and the other was shot with a 28mm and 10s shutter if I remember correctly.
07-21-2020, 01:33 AM   #14
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I needed sleep last night but I pointed the camera at Polaris, asked it to take 500 shots, did something in Lightroom and Photoshop (I'm not sure what really) and got this. Nothing exciting at all but at least it proves that it works!

https://www.flickr.com/gp/pierspalmer/690N4d
07-21-2020, 06:12 AM - 1 Like   #15
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QuoteOriginally posted by osbourne one-nil Quote
I needed sleep last night but I pointed the camera at Polaris, asked it to take 500 shots, did something in Lightroom and Photoshop (I'm not sure what really) and got this. Nothing exciting at all but at least it proves that it works!

https://www.flickr.com/gp/pierspalmer/690N4d
That's a very good learning step. Star trails can often be done when sky conditions are less than optimal, such as some clouds or light pollution.


You can also use those images to create a single still image with the stars forming curves. Photoshop can do it, but StarStax is much easier StarStaX – Markus Enzweiler
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