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Old February 16th, 2010, 09:32 AM   #1
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Hoodman SDHC and overcranking

I am new to this so please bear with me. I have tried to do forum searches on my question as best I could. But I am still fuzzy on some details.

Q: I am planning a shoot on chain saw safety. It will be going to DVD and web d-load. I do not plan to overcrank, but I do want the least amount of motion blur as possible if I slo-mo the footage in post. I need the audio so overcranking is not an option.

I am under the impression that if I shoot 720 60p with the shutter speed set to 1/60 or even 1/120 I will not be overcranking but will still get better (less motion blur) slo-mo (by reducing rate in editing, not in camera) than by shooting 720 30p or 1080 30p.

I am not worried about my 2 sony SxS cards, but I have 1 hoodman 16g SDHC card/adapter. I am concerned that maybe even 720 60p 60fps might exceed the 35mbs write speed limit I have read about with SDHC cards.

TIA, Rob

Last edited by Rob Lagerstrom; February 16th, 2010 at 09:32 AM. Reason: added clarification
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Old February 17th, 2010, 04:29 PM   #2
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all sounds good.
using 60fps in the lower resolution will give you the same frames you need, the difference being it wont use as much data , so compression will be higher than an overcrank. plus you get your audio.
then in post you slow it down, instead of it being automagically slowed via the taged frame rate it is.

so how do you work on the compression issue so you have a good picture?
with a good clean solid picture , instead of flailing about or doing walk arounds and stuff like that. with a good solid background NOT Moving and your subject inside that frame moving all over, the compression codec can just keep repeating the background with not much data required to display it.
oh but your going to be following the chainsaw, with the background moving right?
Ok reverse that, with a good solid FOLLOWING of the subject, so the subject is repeated in the frame as the background changes.
if lots of stuff is moving in the frame then your more likly going to want more data and less compression. its all about how many pixels in the frame will change, be that color, movement, light/luma, or even vibrations that shift the data to the other pixels changing them. the more SOLID you are on say a good tripod, the more a compression codec can deal with the issues.
if your all over the place with your picture, then you will prefer more data for the compression, when you go to slow it down.

once slowed down the humans will more easily spot all the flaws in the compression.

Untill you actually set the overcrank, the data rate does not go high, so a poor SDHC card that will not work overcranked, can still work at a high frame rate, because the (compression) data rate itself doesnt change.

that is my understanding of it so far.
if you havent TESTED what you are going to do at home, by running the adpated SDHC in a hard overcrank and changing all the pixels to simulate the intended subjects you are filming, then one might say your not ready to go yet :-)
Re-learning everything all over again, one more time.
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Old February 19th, 2010, 07:25 AM   #3
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720 60p motion blur

Wow! Thank you for such a informative and detailed answer.

The only times I will be needing slo-mo is to show the chainsaw making specific cuts, and to add interest to the viewer. My camera will be on a tripod so the only motion is the chain saw in action.

Thanks for instructing me on the best way to minimize compression artifacts

I don't have a chain saw for testing, otherwise I would probably not need to post my question. Your answer does apply to many other fast action situations I am sure I will encounter.

Last edited by Rob Lagerstrom; February 19th, 2010 at 07:35 AM. Reason: added info
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