T-stops, shutter speed, video (originally posted in Panasonic is Developing a New, Smaller 35-100mm

bikerhiker

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I see what you are saying, if for artistic reasons you want to constrain your shutter speed to be constant throughout your production then yes of course you have to use other exposure or lighting controls. But that is not a limitation of the cameras at all nor is it in any way related to your frame rate beyond the aforementioned restriction that typically the shutter speed must be at least faster than the frame rate. That's probably why everyone is confused with what you are saying.

And thanks for the link, that explains the 2x rule as being typically the most aesthetically pleasing.
Thank you for re-affirming that I create art. My speaking art can sometimes confuse people.

Cheers! :biggrin:
 

bikerhiker

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Most cameras{especially in an auto mode} will automatically set the shutter speed to 2x the frame rate but that is just to make things simple for the user. Some have limitations and that may be what Nikon was telling you about their camera - it specifically couldn't do it. At work I have 2 Panasonic AF100 pro camcorders and I can set them either by shutter speed or shutter angle{speed 1/24th - 1/250th and angle 10-360 degrees}{not all speeds/angles are available for all frame rates however}{Oh I can also set the frame rate as low as 12FPS and as high as 60FPS}.

Now I do use the 2x guideline for most things so that the motion blur looks natural. As a general rule you can't change the shutter speed/angle WHILE filming although some cameras will even allow that. So when you are filming and you need to adjust the exposure you do it with aperture and/or ISO/gain{proper term for video}. ND filters are also used but you can't switch them in the middle of filming. Many high end camcorders have ND filters built in BTW.

Here are the reasons why you would want to change the shutter speed/angle.
If you go faster than the 2x the image will be sharper with more strobe effect{think stop motion unevenness}. This look gives a retro film look as many old film cameras used shutter angles less than 180 degrees. If you go slower there will be more blur to the images and less strobe. Both are often used for dramatic effect.
But you don't get strobe effect with faster shutter speed on a digital still camera nor do you get less strobe effect with slower shutter speed if you are talking about taking a 1 frame shot. Which was what I was trying to say all along. You can freely adjust shutter speed with a digital still camera to COMPENSATE for light loss of any lens you mount it on and this compensation is done via TTL metering and built-in Shutter sensor monitor when you are making a still. It's all automated. All of these effects you get from raising shutter speed above frame rate simply does not exist in a still photograph. If a movie maker needs to vary the frame shutter speed to account of difference in the transmission light loss like that in a digital still camera, then you'll have a few frames with strobe like effect and then a few frames without? Wouldn't that make people sick watching that kind of movie? I certainly can see where you are coming from. You can definitely set a Nikon D800 to shoot movies at 1/500 sec and higher, but what they say is that unlike a still camera, the shutter speed is not meant to compensate for exposure variance but rather to create as you said the blur effect being sharper stop motion or news reel like or cinematic blur with slower speed. But then, nobody is stopping anyone to create HDR using different aperture settings and merge them together and call it sharp rather than setting different shutter speeds and keeping the aperture fixed. Does this limit the use of a digital camera? Yes it does, only if you want to create sharp HDR. No one can say you can't create crappy fuzzy and blurry HDR. Same with movies. :biggrin:
 

Cruzan80

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Which was what I was trying to say all along. You can freely adjust shutter speed with a digital still camera to COMPENSATE for light loss of any lens you mount it on and this compensation is done via TTL metering and built-in Shutter sensor monitor when you are making a still. It's all automated. All of these effects you get from raising shutter speed above frame rate simply does not exist in a still photograph.
Nobody is arguing that you can adjust shutter speeds for a still shot. Doesn't have to be done thru TTL at all. You can compensate for light loss any number of ways. Of course you don't get frame rate effects for a single frame. This still doesn't say anything about the original point of your argument, which was that the lens couldn't be f2.8 due to physics, and he was confusing f and tstops. It went far afield, and is still just as off as when you made the first post.
 

speedandstyle

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You can definitely set a Nikon D800 to shoot movies at 1/500 sec and higher, but what they say is that unlike a still camera, the shutter speed is not meant to compensate for exposure variance but rather to create as you said the blur effect being sharper stop motion or news reel like or cinematic blur with slower speed.
Yes, generally speaking you do not pick a shutter speed for exposure reasons with video. However you can if you need to. I have done it a time or two when I was shooting low action at low light levels. I used a slower shutter speed one time because I had already boosted the gain{ISO} as high as I could{or was willing to without horrible noise} and the lens I had was not very fast. This gave me the extra exposure I needed and although the motion was a little blurry it wasn't too bad since it was just a guy speaking and walking on a stage{they wouldn't let me add more lights! and the available light was bad!}.

This is my final post on this matter - if you wish to discuss t-stops and video more then let's move it over to the t-stop thread I linked to earlier.
 

bikerhiker

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Nobody is arguing that you can adjust shutter speeds for a still shot. Doesn't have to be done thru TTL at all. You can compensate for light loss any number of ways. Of course you don't get frame rate effects for a single frame. This still doesn't say anything about the original point of your argument, which was that the lens couldn't be f2.8 due to physics, and he was confusing f and tstops. It went far afield, and is still just as off as when you made the first post.
But the basis of T-stop is to administer a rating in terms of light transmission loss, so you don't have to change the aperture of different lenses from a prime lens to a zoom lens to maintain identical brightness of the frame. This can only indicate that any movie film maker who decides to use a fixed shutter speed can be assured that he or she has the same DOF and the same brightness of each frame if a lens of T/4 are used (prime and zoom) if that what is called for the exposure. But in a still film camera, even if say the lens is truly about 1 stop under than rated f/stop between a prime and a zoom lens, the TTL metering will compensate this by opening the shutter longer. If you let the movie camera adjust exposure by changing shutter speed for each frame like that of each frame if you change lenses, then you will have different motion blur created in the movie. The point of the argument is that, today's lenses T-stop rating is very close to f/stop, but there are some people who still believe that T-stop is still 1 stop slower than f/stop. You have your own views, I have mine so let's say we can always agree to disagree.

Cheers!
 
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