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-   -   The concept behind using a 1/60 shutter for 30f (https://www.dvinfo.net/forum/canon-xh-series-hdv-camcorders/103714-concept-behind-using-1-60-shutter-30f.html)

Shiv Kumar September 17th, 2007 01:01 AM

The concept behind using a 1/60 shutter for 30f
 
I do understand the principle of a shutter and the various effects one can achieve using the shutter. However, even thou a 1/60 shutter for 30f or 1/48 shutter for 24f makes sense (kind of like a gut feeling), to the point that I did this even before reading anywhere that one should... I now realize that I don't truly understand the reasoning?

I have shot some footage using a very high shutter and don't see any difference really.

Appreciate anyone throwing some light on this.

Thanks.

Shiv.

Jack Walker September 17th, 2007 02:28 AM

Shutter speed in motion pictures (that has slopped over to video trying to look like film) is related to shutter angle and the amount of motion blur that is judged appropriate to make a projected motion picture film look good.

Traditionally, film has used a 180 degree shutter angle, resulting in 1/48 of sec shutter speed at 24 frames per second. Read this:
http://en.wikipedia.org/wiki/Shutter_angle

So for 30p, an equivalent shutter speed based on a 180 degree shutter angle, and relative motion blur, would be achieved at 1/60 sec.

(In still photography, abpit 1/60 is considered the slowest speed that can be hand held without getting blur from the photographer's movement. 1/60 is too slow for shooting things in motion.)


Also, 1/60 is an optimal speed for video in the U.S. (1/50 in Europe) because it matches the cylce speed of electricty and won't cause flicker with electric lights of certain types.

You can use any speed shutter you want for video, with the result showing differently depending on what is being photographed and your own sensitivity to flickering things.

(Apparently a 165 degree shutter angle, that equates to 1/50 sec., has also been common in motion picture cameras.)

Erik Norgaard September 17th, 2007 03:13 AM

Quote:

Originally Posted by Jack Walker (Post 745429)
In still photography, abpit 1/60 is considered the slowest speed that can be hand held without getting blur from the photographer's movement. 1/60 is too slow for shooting things in motion.

The thumb rule I have learnt is that shutter speed should be double focal length, so if you use a 50mm (35mm photography) you should set shutter to at least 1/100 sec. I don't know how this translates into the non-35mm world.

This protects against intraframe shake - but for video I guess we're more worried about interframe shake.

Rick Llewellyn September 17th, 2007 10:47 AM

Match blur to frame rate
 
Ignoring film and artistic questions, shooting at a faster speed than 1/(frame rate) will result in discontinuous blurs.

For example, shooting 30p at 1/60 shutter speed at a row of telephone poles will result in a pole bluring, then an equal size space without the pole, then the blurred pole reappears in the next frame. The result is sort of a picket fence look from a single pole.

Same would hold true for 24 fps and 1/48 shutter speed. 60i at 1/60th won't have that problem because the pole would be continuously imaged.

Having said all that, I usually shoot at 30F and 1/60th. Especially in HD and hand held, I find a faster shutter speed helps keep the resolution. Also I shoot at very high shutter speeds when I shoot from a moving platform like a boat when I plan on using stabalization software in post.

Rick

Brian Keith Moody September 17th, 2007 11:12 AM

There is a good article on video shutter speeds here:

http://www.videomaker.com/article/10418/

Josh Laronge September 17th, 2007 12:19 PM

Quote:

Originally Posted by Erik Norgaard (Post 745440)
The thumb rule I have learnt is that shutter speed should be double focal length, so if you use a 50mm (35mm photography) you should set shutter to at least 1/100 sec. I don't know how this translates into the non-35mm world.

This protects against intraframe shake - but for video I guess we're more worried about interframe shake.

Actually, the rule is 1/focal length. So for a 50mm lens the minimum would be 1/50 of a second. A seasoned photographer can hand hold 1/25 on a wide angle lens without seeing camera shake. Of course if you hang out at Starbucks, you might want a shorter shutter speed.
--JL

Jack Walker September 17th, 2007 12:41 PM

Sorry, I didn't meant to cause so much confusion.
When I said 1/50 or 1/60 I meant when using a standard lens, which on an SLR would be 50 or 55mm, or so.

It was normally considered that one could go down to 1/30 if one was very steady (with this lens).

Of course, these days, with IS lenses and smaller than 35mm sensors, the rules are different.

Eric Muehling September 18th, 2007 07:38 PM

Here are two recent examples of where I used short or long shutter speeds.

Nature: raindrops on water. The high shutter speed (1/500) captured the raindrops as sharp circles (not blurred by their motion). I liked the effect. It recorded raindrops just as I imagine raindrops on water. The ND filter was set to zero so the lens aperture closed down to provide as much depth of field as possible.

Nature: moose standing in the woods at dusk. On a tripod, a low shutter speed (about 1/3 second) resulted in very acceptable footage (the animal was standing more-or-less still). A faster shutter speed could have been used by increasing the gain, but that would have caused image noise.

Shiv Kumar September 19th, 2007 12:51 AM

Eric, Jack, Josh, Brian, Rick,

Thank you all for the information and links. It is much appreciated.

Rick,
I need to try the "dicontinuous blurs" theory, so I can better understand what you mean. So when you say "shooting a row of telephone poles", do you mean panning from one pole to the next (from the front, ie perpendicular to the line of poles)? Would appreciate some explaination so I can simulate this.

Eric,
I think you forgot to post the links to the videos :)


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