Measuring exposure

A

araujofh

Veteran
Hello folks,

Everyday I learn new things related to camera work, but, since I dno't have much experience with film cameras, I don't know much about exposure metering. I tend to use the zebra detect. That is, I play around with the iris until I get rid of them. But, I know there more professional ways to do this.

What is the procedure you guys use? And how do you know when you have a good exposure?

Could someone give me a pointer to a site that explains f-stops in details?

I know the relationship between the f-stops and exposure. But, the numbers to me don't mean anything. Since I just use the iris dial to adjust my exposure, which I control via the zebra detect, I don't really look at the numbers.

Thanks in advance

Fidel.
 
Re: Measuring exposure

F-stops are basically the amount of light the iris STOPS from getting into the lens.

Put in simple terms, f/1 would be admitting as much light as the lens is possibly capable of (yes, I know that's oversimplifying it, and there's been f/0.95 and f/0.7 lenses before, but this is for the sake of illustration).

Each additional f-stop cuts that amount of light in half.  So f/1.4 admits half as much light as f/1 does.  F/2 admits half as much light as f/1.4, and so on and so on.

The numbers are based off of two base numbers, f/1.0 and f/1.4.  Each new f/stop number is seen by doubling the previous number, for example:

1.0   1.4
2.0   2.8
4.0   5.6
8.0   11 (rounded down from 11.2)
16    22

So if you remember 1.0 and 1.4, you can calculate the rest of the sequence easily.

The other numbers the DVX iris wheel shows are half-stop increments, so between 2.0 and 2.8 (which are both "whole" stops) you'll find 2.4 listed, which is a half-stop, which is equivalent to halfway between 2.0 and 2.8, and lets in 75% as much light as f/2.0 does (since f/2.8 lets in 50% as much light as f/2.0 does).

You can think of the f/stop notation as a diameter formula for the lens iris.  Whatever "f" stands for (and it can't mean "focal length of the lens", although I've heard it described as such), when expressed in the term of f/2.0, would mean an iris size of "f" divided by 2, which would let in 1/4 as much light as an "f" divided by 1.  (think in terms of a square: if you divide the length of a side of a square by 2, the overall square is 1/4 the size as the original: a 2" x 2" square has an area of 4 sq inches, but cut that size in half and you get a 1" x 1" square, with an area of 1 square inch, which is 1/4 the area of the 2x2 square).

So to get half as much, you need to divide not by 2, but by 1.4.  If you take the 2" side of the square and divide that by 1.4, you'd get a square of 1.42" x 1.42", which has an area of 2 square inches.  And 2 sq. in. is 1/2 as much as the original 2x2 square's 4 square inches.

So to get half as much coming in, you need to divide by 1.4.

Therefore, the numbers you divide "f" by are:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22

And each successive number lets in half as much as the previous number.
 
Re: Measuring exposure

Wow, this was the best explanation on f-stop I have ever read. Have you ever considered writing a book on camerawork? You should! I know you have written the Anamorphic manual and just read good reviews about it.

Now, what about the other questions I have asked. Do you guys also use the zebra detect to measure your exposure? Or you use other methods?

Thanks a lot for the f-stop explanation.

All the best

Fidel.
 
Re: Measuring exposure

I'm considering doing a book/DVD combo that would basically be everything the anamorphic adapter guide is, except for the camera itself, going into shutter speeds, strobing, DOF, DVX vs. film, up-rezzing, all that other stuff. If I knew people would buy it, I'd leap into it. Probably have to charge around $40 to make it worth doing, as it would take a while to do...
 
Re: Measuring exposure

Barry I think that is a great idea. Especially if you got real in depth (which you always do) explaining all of the menu and camera setups. Examples of when to set this to that etc. Maybe some footage showing each setting. $40 would be too cheap. For such a great tool and learning guide to not only the DVX, but videography in general. Plus the amount of work involved making such a DVD. If you got started tomorrow, should take you what 8 weeks or so....right? What are you waiting for? I just busting your balls. I know I would buy one, and I think that I know a lot of sh***t when it comes to video and my DVX. Amazes me about the amount of information that you and Jared know.
 
Re: Measuring exposure

[quote author=Barry_Green link=board=news;num=1092500547;start=0#3 date=08/14/04 at 20:40:35]I'm considering doing a book/DVD combo that would basically be everything the anamorphic adapter guide is, except for the camera itself, going into shutter speeds, strobing, DOF, DVX vs. film, up-rezzing, all that other stuff. If I knew people would buy it, I'd leap into it. Probably have to charge around $40 to make it worth doing, as it would take a while to do...[/quote]

I would buy it for sure. But don't forget to include about the ways of measuring exposure.

I have read a book on camerawork and it basically says that there are three ways of making sure you are exposing correctly: auto-iris, manual iris via zebra stripes, and with a light meter.

I understand the first two, because I do them. What about the lightmeter? Do you use the lightmeter to read the f-stop and then you adjust the camera to that f-stop?

About the book/DVD combo, why don't you anounce it on the News section, to see people's reaction? Let's make a questionaire and see how many would buy it. That way, you would know if it would be worth it or not.

I bet a lot of people would buy it.

All the best

Fidel.

PS: It would be nice to have a combo like this for lighting as well.
 
Re: Measuring exposure

Barry please make the dvd. I am still learning about the DVX100 and I know several other people who recently purchased the camera and a dvd of this sort is on top of their wish list. Also, here is an article (Digital Cinema Society) in reference to the SDX900 which could be a prototype for the DVX100, but I think a dvd is a better choice than a book.

"I would like to thank Robert Goodman for making “Goodman’s Guide to the SDX 900” available to all owners of the camera. As an SDX owner and recent recipient of the book, I can tell you that this is much more, and is in addition to, the standard operation manual that comes with any camera. This is a bound book with high quality color graphics. It features high resolution
pictures of the various “looks” achievable with the camera and then gives you the precise settings to obtain those looks. What’s an even greater improvement over your standard camera manual is that this one is written to the Cinematographer, or user of the camera, as opposed to the
engineer. It tells you what you need to know in clear, easily
understandable language. Personally, I would rather spend my energy trying to master the art of cinematography rather than being unduly burdened with electronics. In other words, I just want to be told what I need to know to make pretty pictures, and this book does that. I urge Panasonic and other manufacturers to commission similar books/dvds for all their cameras. This is a really great asset to the Cinematographer."
 
Re: Measuring exposure

GARP! (sound of me gagging)...

That guide goes for $125! Perhaps I'm a little underpriced at thinking $40-$50 for a guide + DVD? ;D

Well, I think I'll do it...
 
Re: Measuring exposure

When you make it I'll buy it too! :)

If you want to know who would buy it, make a poll and ask. You'll have a rough number then.
 
Re: Measuring exposure

As a video novice, I give my tall salute to members of this brilliant and mighty forum. You are giants in this universe and no one can rival your depth of knowldege and generous, cooperative spirit.

I just purchased my 100A and can't wait to start exploring its remarkable capabilites. Which leads me to Barry's upcoming DVD on the DVX100A. Mr. Green, you are a Great Respected Master, Sir. And you know it!

May I humbly suggest that I would be willing to pay you $100 for the DVD you create. I bought a Birns & Sawyer DVD ("Panasonic DVX-100: Tips,Tricks & Basic Operations") for $50.00 and that was an utter waste of time and money. The product did not even remotely live up to its name. The vaguely useful segment was by Nancy Schreiber ... barely.

In fact, if I may even more humbly suggest, you would have a strong subscriber following if you decided to launch a site with short ongoing tutorials. I'll be the first in line ... and from what I've read about your highly regarded position here ... I'll also probably be the first to be crushed in the stampede by your loyal followers. Small price to pay for such an incredible reward.

And the title for your upcoming DVD? "Everything You Wanted to Know About Your DVX-100A But Were Afraid To Ask". I would be highly privileged to shine your DVD jackets before they ship out. If you would allow that, Sir.

I await your creation - spellbound.
 
Re: Measuring exposure

Okay, everyone thank Alumna for setting the new price. The DVD/book combo will now be $100.

;D ;D ;D ;D ;D

Seriously, thanks for the nice words, and I'll try to make it well worth whatever the eventual price ends up being! :)
 
Re: Measuring exposure

It'll be a while. Certainly not before the end of this month. Depends on how many articles and subjects I can think of! ;)
 
Re: Measuring exposure

It happened again. Barry posted a response to a question and I printed his response and put it in my 3-ring binder of "DV HOW TO."

Barry: if you ever lose your notes on for your book combo, just let me know b/c I've got a back up for you in hard copy. OH, and I'll still buy the book/DVD when you finish.

Thanks again for a great lesson.
 
Re: Measuring exposure

Hi guys,

I have another question.

I have been reading a book on digital photography and I came to read about histograms. Is there an equivalent of histograms in camcorders?
I would probably guess that the equivalent to photoshop's histogram in a video editing software, would be a vectorscope, right?
But, is there something like this in camera? What is the equivalent of this on the DVX, for example?

Thanks in advance

Fidel.
 
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