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03-30-2016, 08:20 PM - 4 Likes   #1
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Breaking the 30 Second exposure barrier with interval composite

I just wanted to share my method of creating long exposures using interval composite. I've written before on how to use this feature to replicate long exposures during daylight but in this post I talk about using it for nocturnes and for creating star trails. I think this is timely considering it looks like the K-1 will have a method of doing this in camera and hopefully it will be added to the K-3 series with firmware but in case it isn't here is a way to do it.

Breaking the 30 second barrier with a Pentax DSLR (Interval Composite Mode) | Wallace Koopmans Artlog



03-30-2016, 08:37 PM - 1 Like   #2
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Very creative photo. DA15, I presume?
03-30-2016, 11:00 PM   #3
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Good idea; also interval composite + average can be used to recreate a long exposure when a ND filter isn't available, for instance photographing a waterfall.
03-31-2016, 05:25 AM   #4
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QuoteOriginally posted by calsan Quote
Very creative photo. DA15, I presume?
It's actually the DA*16-50 I guess the * stands for star bursts

03-31-2016, 07:17 AM   #5
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Thanks for your work here. Can you comment on what "Save Process" does? Does it just retain the parameters? Do you have long exposure NR activated? Also, I use composites a lot, but "average" the exposures. Why not "average" the exposures rather than "additive" -- have you calculated the exposure and set exposure up manually for a 2-minute exposure? Can you also do something with "bright" composites? I have not investigated that yet.
03-31-2016, 10:22 AM   #6
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QuoteOriginally posted by Marktax Quote
Thanks for your work here. Can you comment on what "Save Process" does? Does it just retain the parameters? Do you have long exposure NR activated? Also, I use composites a lot, but "average" the exposures. Why not "average" the exposures rather than "additive" -- have you calculated the exposure and set exposure up manually for a 2-minute exposure? Can you also do something with "bright" composites? I have not investigated that yet.
Thanks for the questions Mark. The save process setting will in addition to creating the composite save each captured image as a separate file.
The reason I do not use average in this case is that I want all the exposures to be summed. If you use average then items like the flashes will be diminished by each subsequent exposure in essence they will be averaged away. Average is good for other things like smoothing flowing water ect.
In this case I arrived at the 2 minute exposure by metering with a higher ISO setting. I don't recal the exact values at this moment but say you get 30 seconds at f4 with an ISO of 3200 then if you were to lower the ISO to 800 it would be 120 seconds to achieve the same exposure.
03-31-2016, 10:34 AM   #7
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Could you not avoid the short gap between exposures by using a wired release cable (or a good IR remote) and using (additive) Continuous Multi-Exposure (instead of Interval Composite)?
03-31-2016, 10:40 AM   #8
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QuoteOriginally posted by biz-engineer Quote
Good idea; also interval composite + average can be used to recreate a long exposure when a ND filter isn't available, for instance photographing a waterfall.
I tried this out last week on a sunny shore with breaking waves and found that the effect differs very much from the result with a ND filter. I used 10 pictures for the compositions. In comparison to the smooth result you can expect with a filter the glittering drops and other bright details of single pictures shine through and lead to frizzy compositions.

03-31-2016, 10:51 AM   #9
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QuoteOriginally posted by Pete_XL Quote
I tried this out last week on a sunny shore with breaking waves and found that the effect differs very much from the result with a ND filter. I used 10 pictures for the compositions. In comparison to the smooth result you can expect with a filter the glittering drops and other bright details of single pictures shine through and lead to frizzy compositions.
Yes, sure. When I used image composite, I stopped down to f16 or f22 that already lengthened the exposure time to about one second; I wanted 6 seconds, so I stacked 6 shots.
03-31-2016, 10:56 AM   #10
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QuoteOriginally posted by Pete_XL Quote
I tried this out last week on a sunny shore with breaking waves and found that the effect differs very much from the result with a ND filter. I used 10 pictures for the compositions. In comparison to the smooth result you can expect with a filter the glittering drops and other bright details of single pictures shine through and lead to frizzy compositions.
Remember that to get comparable results, you'll need comparable total exposure time. 10 shots is a bit more than 3 stops - not that much. Personally, in bright light I think that this technique is best used in combination with the use of an ND filter, to let you turn a weak or mid-strength ND filter into a much stronger one...
03-31-2016, 11:02 AM   #11
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good one. bookmarked.
03-31-2016, 12:02 PM   #12
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QuoteOriginally posted by Painter Quote
Thanks for the questions Mark. The save process setting will in addition to creating the composite save each captured image as a separate file.
The reason I do not use average in this case is that I want all the exposures to be summed. If you use average then items like the flashes will be diminished by each subsequent exposure in essence they will be averaged away. Average is good for other things like smoothing flowing water ect.
In this case I arrived at the 2 minute exposure by metering with a higher ISO setting. I don't recal the exact values at this moment but say you get 30 seconds at f4 with an ISO of 3200 then if you were to lower the ISO to 800 it would be 120 seconds to achieve the same exposure.
"The save process setting will in addition to creating the composite save each captured image as a separate file."

Aha! Thanks for that answer. The camera retains your last settings, I think, so it had to be more than remembering just the settings.

"If you use average then items like the flashes will be diminished by each subsequent exposure in essence they will be averaged away."

Yep, I understand. Thanks for that, too. Very good work.







03-31-2016, 12:22 PM   #13
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QuoteOriginally posted by Painter Quote
The reason I do not use average in this case is that I want all the exposures to be summed. If you use average then items like the flashes will be diminished by each subsequent exposure in essence they will be averaged away. Average is good for other things like smoothing flowing water ect.
Great write-up, thanks so much for sharing!

I have a suggestion for ways to handle the issue (quoted above) in post-processing as well.

When you have your stacked images aligned, group them as a smart object, then duplicate the smart object so you have 2 identical stacks. In the top smart object, use the averaging mode "minimum" (or "maximum", I can't remember which), which picks the lightest pixels in the stack and sums them. This will composite all of your flashes.

Then, on the 2nd smart object, use the averaging mode "mean". This will average away all the noise and average out the flashes.

Then, using layer masks, brush the flashes from the top stack back in on top of the "mean" smart object. In the end you're left with the bright bulbs blended immaculately in with an averaged stack (at lower noise than the ISO you shot each frame with).

I shot this (link below) on a K-5iis a few weeks ago to string together headlight trails at sunrise. This was 23 frames shot in burst mode over 2.5 minutes of total exposure (6.5 seconds per frame, thanks to an ND filter).

https://www.instagram.com/p/BDRcff-Kkpu/

Anyway, back on topic, if this could be done in-camera instead of relying on a memory-heavy PP workflow, I'm all ears and excited for this ability in new cameras.
03-31-2016, 01:44 PM   #14
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QuoteOriginally posted by Doundounba Quote
Could you not avoid the short gap between exposures by using a wired release cable (or a good IR remote) and using (additive) Continuous Multi-Exposure (instead of Interval Composite)?
Perhaps each variation has its purpose. This way though allows for easy adjustment of the exposure time by the setting of the number of exposures and the automating of the process including setting a specific start time IE enough time for you to get into the scene yourself.

---------- Post added 03-31-2016 at 01:53 PM ----------

QuoteOriginally posted by Pete_XL Quote
I tried this out last week on a sunny shore with breaking waves and found that the effect differs very much from the result with a ND filter. I used 10 pictures for the compositions. In comparison to the smooth result you can expect with a filter the glittering drops and other bright details of single pictures shine through and lead to frizzy compositions.

Yes you would need to capture many more short exposures to approach any type of smoothing. It works best at extending already long exposures. This images was created using that technique.

03-31-2016, 06:31 PM   #15
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QuoteOriginally posted by Painter Quote
Perhaps each variation has its purpose. This way though allows for easy adjustment of the exposure time by the setting of the number of exposures and the automating of the process including setting a specific start time IE enough time for you to get into the scene yourself.
For sure, if you need to be *in* the frame, or actively producing something in the frame (like activating a flash or doing light painting), then interval composite is the way to go! (Unless you have an assistant.) But for star trails, I would imagine (since I've not done it) that continuous multi-exposure would work better to avoid little gaps in the trails. BTW, when using interval composite, this "gap" problem can also happen with fast moving clouds - and this I've seen. Instead of having a smoothed out cloud, you get multiple well-defined lines, as if there were N separate clouds in the shot, where N is the number of exposures taken.
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