Anna Uio

I happened upon another reference to the concept I was trying to discuss on http://www.dpreview.com/learn/?/key=focal+length in the first paragraph in particular > Larger sensors or films have wider FOVs and can capture more of the scene. And a depth of field adapter give you in effect a full frame sensor :) Cheers, Anna

Hi all, Anybody have any experience using Tcp compact fluorescents as light sources? I saw some Par30 4100K in a shop window a liked the color and light, so I asked the owner what they were. On the web I then saw they have a variety of color temperatures. Cheers, Anna

Thanks Dave. That's exactly what I thought I was saying, or what I was trying to say at least :) I certainly never meant to imply that the focal length of a lens somehow changed from camera to camera! And my actual original question was only to wonder why people do not talk about this more. It has such a huge effect on how you shoot a scene. With a larger format, you don't have to use as wide angle of a lens to "take in a scene" and thus you can shoot with less of the "huge in the foreground, tiny in the background" that I think is the most recognizable characteristic of stuff shot on video cameras. Even supposedly big chip cameras that still don't get anywhere near 35mm film. I dream of the day when larger frame cameras like the Red become more popular and come more down even more in price. Cheers, Anna

Here is a nice video review of the Canon EOS 5D Mark II, a full frame (35mm) digital SLR that can shoot movies. The reviewer talks about getting greater "coverage" with the larger format than is possible with normal small chip video cameras when using a lens with the same focal length. Just looking at their example clips one can see how much more of a scene can be shot without resorting to as wide angle lenses and the associated perspective. As another example, search for online for medium format photographs and notice how they "look different". The difference is again that you can see so much of the scene but without using wide angle perspective. Finally, one can watch films shot in 70mm and see this. Warning: once you learn to see it, you will hate anything shot on tiny video cameras, including the best 2/3" prosumer models :) http://www.vimeo.com/2596405 Cheers, Andrew

Here is a nice web page that calculates field of view from focal length and format: http://www.mat.uc.pt/~rps/photos/angles.html My question wasn't about how this works, but rather asking why it is so seldom discussed compared to depth of field. The weird wide-angleness/tiny field of view of video cameras is what makes everything shot on them so recognizable and looks so bad in my opinion, not the depth of field. It creates such bizarre geometric relationships between objects in the fore, mid and background. Cheers, Anna

Howdy, Whenever I read about 35mm lens adapters for video cameras, there is always lots of discussion of depth of field. That's great, but no one ever seems to mention another consequence of having a much larger equivalent film gauge, namely MUCH wider field of view without having to use a short lens or back the camera away from the subject. Am I missing something? Isn't this important too? In comparing my own cameras with different sensor sizes ( 0.25in to 0.55in ), the difference has an enormous effect on the geometry of shooting a scene, i.e. relative placement and motion of objects in the frame, especially when the camera or subjects are moving relative to each other. Cheers, Anna

Hi all, I often see dynamic range values thrown around in discussion, and I wonder what's standard. What is a typical dynamic range for film? What is the highest dynamic range for film? What's typical prosumer camera have? What about a typical consumer level camera? Just trying to get the big picture here :) Cheers, Anna

> But the image off a video camera isn't a wide range Not true. The range of video cameras keeps getting wider as we move to more precise analog to digital converters. Currently the precision of the A/D converters is exceeding what can be represented in standard storage formats. Hence the move to more bits per pixel and logs. There is a huge reason to capture store a wide range or latitude. You can recover/use all the detail in the shadows and highlights that is lost in normal range film or video. If the range is wide enough, you can just forget about exposure settings during shooting and do it later in post. Photographers talk about high dynamic range all the time. For decades there have been techniques for taking multiple low dynamic range shots of the same scene at different exposures and combining them to get a single high dynamic range image. Now they can do it with just a single shot in todays digital cameras. I can't wait for prosumer video cameras to become like the viper. I've coded lots of effects video filters that work ok with standard range images but will benefit immensely from increased precision and range. Also, people keep saying that the CCDs in a camera aren't linear. But that doesn't matter. The software inside the cameras knows about this non-linearity and straightens it out in the stored image. Cheers, A

This link might be useful too: http://en.wikipedia.org/wiki/Logarithmic_scale Cheers, A

Mathematicians & engineers have been using logarithms for hundreds of years. Slide rules used logarithms for calculations before computers. Every high school student learns about them, although it is hard to understand what they are useful for at that age :) There are probably lots of web pages on line that explain why logarithms are useful in diverse fields whenever large ranges of scale are to be considered. A start for anyone who wants to learn about them would be to google "logarithm". Also the link http://en.wikipedia.org/wiki/Logarithm, but that may be a little too mathematical for some. As Video Editing software is moving to 32-bit floating point representation of numbers, instead of 8, 10 ot 16 bit integer, the need for logarithms or square roots is beginning to fade away, since floating point numbers have the "log" thing built into them in a way that you don't see it and just forget its there. Oh, and people keep referring to regular video as linear, but its not. A power function, x^0.45 (which is about the same as square root) is used to compress the range of values. This is pretty wonky and won't scale up as devices become more precise and have larger dynamic range/latitude. Finally, 10bits can be used to store 2^10 distinct values, regardless of where they are distributed logarithmically or using square root. Logarithms naturally allocate the same level of number of value across each "stop" or doubling of intensity. Power functions don't do that, so some stops get allocated more precision than others. Also, it is not really true that logs allow you to store a 16 bit number in 10 bits. Rather, logs allow you to store an any-bit bit number (8-bit, 16-bit, 32-bit, 128-bit) in a smaller number of bits by discarding precision evenly across stops, as opposed to keeping precision in the larger numbers and discarding it in small numbers as simple truncation would do. Cheers, A

If you store the logarithm of the signal, it is then a simple matter to undo it with an exponential in post to recover the original signal exactly (up to quantization error due to the 10-bit integer encoding). Logarithms are THE natural way to capture a big range of scale (from tiny to huge) in a fixed amount of space with equal precision given to each "stop" or doubling of size. Floating point (decimal) numbers in computer are all stored this way. Traditional video cameras take the square root of the levels (more or less) to achieve a similar precision across a wide scale, but this does not scale up to higher and higher ranges. Log scales perfectly, because that's exactly what its for! :) Cheers, Andrew P.S. I'm not associated with the company that makes the Viper. I just code video processing filters.

Hi all, After a number of experiments, I've come to the realization that all of my video cameras shift the black point to zero and that there is no way to disable this "feature". This effect is often referred to as left-justifying the histogram. While it may be a useful creative choice, it is certainly not something you want forced on you, as it will make color correction in post impossible. Each frame gets offset by a different amount depending on the level in darkest part of the frame, and any offset other than zero will make it not possible to use RGB gain perform color balance. Nor will any other color correction method likely work across a whole scene from beginning to end with varying light levels. The image below shows an example of this behavior. The curtain was lit from the left and the right by identical light sources, one farther from the curtain than the other. So both the light and shadow parts of the curtain are receiving considerable light, and there is nothing black in the scene. Looking at the RGB histograms, you can see that they have obviously been left justified so that the minimum (blue channel) becomes zero. This very much changes the image, causing the shadows to become much, much darker and more saturated than they should be in this light filled shot. Note that film would not do this. It is a very artificial thing to do. I don't know what to think of this. It seems awful. The cameras I've tested are Sony Fx-1, Sony Hc-1 and Canon Gl2, and they all do it. I'd be curious to hear comments/thoughts from other people who regularly works with color adjustment in post. Cheers, A