Two newb questions

J

jordini99

Active member
Hey all,

so I'm fairly knowledgeable and adept with a DVX100 and similar cameras, but there's a few things about the 7D that I still don't fully understand...

1. What exactly does "grading" mean? Why have I never heard this term before except when referring to 7D footage?

2. What exactly is dynamic range and what should I do with it?

3. Could someone please explain to me what the difference is between full frame and a 1.6 crop? I've searched around and still can't find a clear answer that my constantly overloaded student brain can comprehend :P

Thanks!
Jordan
 
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In short...

In short...

1. Used to be referred to as color correcting but that term seems to be a misnomer now.

2. The number of stops between detail in the blacks to detail in the highlights that a camera is capable of producing.

3. Try Ginkgo Biloba. :)
 
Haha, thanks Terry!

So with dynamic range then, is there some setting I should be using to modify it? Or should I just leave it alone? Also, is it connected highlight tone priority? What is that anyway?

Also, what is jello/moire?
 
I don't own a 7D but I believe the general consensus is to leave HTP off as it increases noise.

To increase dynamic range turn your contrast settings in-camera all the way down so the least amount of contrast is applied to your video. That way you have more room to grade it later if you want.
 
Oh and jello is the result of the each frame in the video not being read off the sensor all at once. Basically it reads the top line in the sensor, then the one below, then the next, until it has read the whole sensor and created a frame. As a result, if something is moving across the frame sideways, it will have moved between the time the camera read one line and the time it read the next, creating a scew in the final frame. Here is an extensive article on it if you are still confused (with examples/animations):

http://www.dvxuser.com/jason/CMOS-CCD/

Moire is basically a result of the sensor being 18 megapixels but used to create HD video (which is like 2 megapixels). Someone else can probably explain it better but essentially the idea is that when the camera takes 2mp images from an 18mp sensor many times a second certain artifacts are introduced. Here's an article on it (scroll down to where it says, "OK, but how does this apply to the HDSLR?"):

http://www.dvxuser.com/articles/article.php/20
 
Aaaaand the difference between a 1.6x "crop" sensor and a full frame sensor is just a size difference. A "crop" sensor is slightly smaller (thus the term "crop" - because it only captures part of the image a full frame lens would project on it).

All it means for normal people like us is that a full frame sensor is usually better in lowlight and gets a narrower depth of field by a few stops. And a full frame sensor is more expensive.
 
If you haven't encountered the term "grading" before reading about the 7D, then you probably haven't done too much reading about filmmaking. I see it all over the place. But then again, the places that I frequent tend to be more hardcore about filmmaking instead of mere videography. I'm certain that there's plenty of talk about grading DVX100 footage around here as well.

Actually, color grading is not exactly a synonym for color correcting. The term "color correction" strictly refers to "correcting" color anomalies in the footage. Color correcting is actually the first step in color grading. Grading refers to altering the colors of the footage in a drastic way to achieve a distinctive look.

Dynamic range is not something about which you should concern yourself too greatly. What matters most is that the footage looks good to you. Most prosumer camcorders, such as the EX1, especially, have more dynamic range than any of the DSLRs. Yet the people who frequent the DSLR forums here prefer the image from DSLRs, in general. Dynamic range is connected to, and sometimes used as a synonym for, exposure latitude. What this means, in practical terms, is how easily shadow and highlight detail are clipped, which limits the amount of freedom that you have to under- or overexpose. In other words, on a camera with limited dynamic range or latitude, you'd better get your exposure right, or else adjusting it in post will severely compromise your image.

There's a long thread in the Technical Discussion sub-forum about increasing the dynamic range on the 7D.
 
Moire is an example of the phenomenon known as "aliasing." Aliasing refers to artifacts in an image that are the result of inadequate signal sampling. Barry Green's article, linked above, provides an excellent explanation. But the real reason why it exists on the 7D (and 5D) is because of an inferior down-sampling technique used to take an HD-resolution image from an 18 MP sensor. If it were done right, then moire would not exist. The GH1 has a better down-sampling method, so moire is almost completely a non-issue on it.

You can avoid or decrease moire by:
1) slightly defocusing the lens
2) using a soft focus or diffusion filter, or the Caprock Anti-Moire filter (Isaac Brody has found the 2.0 version to be the best)
3) avoiding subjects that produce moire (basically any fine, repeating patterns, most famously brick walls)
 
Jester2138 said:
Aaaaand the difference between a 1.6x "crop" sensor and a full frame sensor is just a size difference. A "crop" sensor is slightly smaller (thus the term "crop" - because it only captures part of the image a full frame lens would project on it).

All it means for normal people like us is that a full frame sensor is usually better in lowlight and gets a narrower depth of field by a few stops. And a full frame sensor is more expensive.
Click to expand...
That's not the whole answer.

You forgot to emphasize the fact that the size difference between a crop sensor and a full frame sensor results in a change in field of view on any given lens. Of course, anyone who isn't familiar with SLR photography doesn't need to worry about this, but it is an issue worth mentioning, and it could cause further confusion.

The "1.6x" number refers to how much the field of view changes. On a full-frame camera, a 50mm lens produces a "normal" field of view, i.e. the FOV of our own eyes. But 50mm on a 1.6x crop sensor would give a much narrower FOV. In order to achieve that same narrower FOV on the full-frame camera, you would need an 80mm lens (on the full-frame camera). (50x1.6=80)

BUT, please note that using a crop sensor does not change the actual focal length, magnification, or focusing properties of the lens. The DOF changes a little bit, but that's the only thing other than FOV. If you never work with full frame, then you don't need to worry about the "crop factor." But if you're switching between image formats (i.e. crop and full frame), then it is important to know.

It's also important to know when reading about lenses. A lot of articles presume that you're working with full frame, so they might say that a 24mm lens is a "super-wide" lens. But if you buy such a lens with that expectation, then you'll be disappointed when you put the lens on your 7D. The best thing to do is simply memorize a table of focal lengths versus FOV. On a 1.6x crop sensor camera, use this:

~12mm = ultra-wide
15-17mm = super-wide
20-24mm = wide
28-35mm = normal
50mm = portrait
70mm+ = tele

For full frame, use this:
16-20mm = ultra-wide
24-28mm = super-wide
35mm = wide
50mm = normal
70-100mm = portrait
135mm+ = tele
 
Thanks for the clarification!

And yeah, in terms of grading, I'm definitely more of a TV/video guy than film. What you said about colour grading/correction makes sense - we usually just use the term "colour correction" as an over-arching phrase that includes both "fixing" colour and making it look "better."
 
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