F-Stops and video format

[Jonathan Gentry]

I have the DVX100a. I will be shooting a fishing video that will be converted to DVD and VHS and sold. I have a few questions:

Should I shoot 30p or 60i?
What is the best use of aperature when shooting video out of doors say from a boat? Should I put the aperature in auto mode or set it and leave it? I was thinking on some partly cloudy/sunny days conditions would change so I though that auto would be best but not sure.
Last is there a white balance setting that I should use for this type of work or should that also be in auto?

Thanks for the help!

[Daniel Hollister]

these are all variable. 30p will give the film a much more cinematic look. the good thing about sending it to DVD would be that the DVD can retain the native 30p information (as opposed to a 60i conversion). what are you shooting exactly? if you are shooting something to be cinematic-looking i would definitely shoot 30p or 24p.

in terms of aperature, that's entirely up to you. you will probably need both the ND filters active, but i would still leave the iris on manual. set it to something decent and leave it. cloud movement wont necessarily change the lighting that much, but even if it does, it's just a small touch of the iris control. the problem with putting it on auto iris in bright light is that the whites might become blown and the camera will compensate on that by closing the iris too much, leaving the actual subject dark.

as for white balance, just bring a white sheet of paper (or something pure white) to the actual location with you, and right before you film, zoom in on it and white balance.

[Bogdan Apetri]

In fact, what is the progression of the f-stops on this camera? Half-stops, it seems.

Somebody asked this question in April but never got an answer. Why are the (half) f-stops different on this camera compared to the majority of other lenses?

[Jeff Donald]

Some manufactures choose to use the mathematically correct numbers and others choose a historically correct number. Rounding up or down can cause differences too.

[Barry Green]

What do you mean, different? The DVX is calibrated in proper f-stops, but also shows the numbers that are halfway in between (so you have f/2 and f/2.8, and halfway inbetween you'll see f/2.4).

But the f-stop setting is more variable than that. It looks like the iris is calibrated for at least three settings between half-stops, if not completely continuously variable.

[Daniel Hollister]

hmm..... no, there's nothing else in between f/2 and f/2.8 except f/2.4...

[Jeff Donald]

Is there a menu option to change from 1/3 stops to 1/2 stops? If you have a camera set to 1/3 stops you would also have f/2.2 and f/2.5, but f/2.5 sometimes gets rounded to f/2.6

[Bogdan Apetri]

Barry,

When I say different, I mean that the half-stop numbers are sometimes different from regular lenses, but it might be just that, having mathematical correct numbers instead of rounded numbers. Usually, manufacturers round f-stop numbers.

Yes, I've noticed this myself, it seems that each stop is divided in 6 increments! But only the full stop and the half stop appear in the viewfinder (or the LCD screen), right?

I wonder why this degree of precision, having 6 steps from one stop to the next. It is generally awknowledged that 1/3 of a stop is the finest degree of precision, taking into account all the other factors. On the other hand, we don't have processing, printing etc with video, as opposed to film (where differences greater than 1/3 stops are somehow lost).

I was just looking for a way to use Blain Brown's tables from his Cinematography books, where everything from F-Stops to ASA numbers and distance is calculated in differences of 1/3 stops.

[Bogdan Apetri]

If we work within the Zone system with the DVX100A, and we say that Zone V is middle gray (of course), then how many stops - or zones - would this camera generally have above and below this middle exposure value, all the way to pure black and up to pure white?

From your experiences...

[Barry Green]

<<<-- Originally posted by Daniel Hollister : hmm..... no, there's nothing else in between f/2 and f/2.8 except f/2.4... -->>>

There's nothing marked, but if you view it on a monitor and manipulate the iris ring, you can clearly see that the image changes in brightness in more steps than just what the display says. For example, between 2.4 and 2.8 there are two clear brightness changes possible, which leads me to think the iris ring is calibrated in 1/6 stops.

At 2.4 there's one level of brightness. Then as you start closing the ring, you can detect a darkening, but the display still says 2.4. Keep turning the ring and you'll see another darkening, and the display will still say 2.4. Keep turning it again and it'll darken again, and this time the ring will say 2.8.

So it looks like you can have 2.0, 2.0 + 1/6, 2.0 + 2/6, 2.4, 2.4 + 1/6, 2.4 + 2/6, then 2.8.

[Barry Green]

<<<-- Originally posted by Bogdan Apetri : Barry,

When I say different, I mean that the half-stop numbers are sometimes different from regular lenses, but it might be just that, having mathematical correct numbers instead of rounded numbers. Usually, manufacturers round f-stop numbers.

Still trying to track down where the difference is. I haven't done still photography for years, but all the lenses I have are marked in whole stops, following the tried-and-true numbering system, which is doubling stops based on 1.0 and 1.4.

So:
1.0 1.4
2.0 2.8
4.0 5.6
8.0 11
16 22

The DVX has all those. Plus it has mathematical "half-stops" represented in the viewfinder, which are just the average between two whole stops (so, between f/4.0 and f/5.6, you'll see f/4.8). My old still-camera lenses don't have markings for half-stops so I don't know how else it's done. Are you saying there's a different numbering system for half-stops?

[Barry Green]

<<<-- Originally posted by Bogdan Apetri : If we work within the Zone system with the DVX100A, and we say that Zone V is middle gray (of course), then how many stops - or zones - would this camera generally have above and below this middle exposure value, all the way to pure black and up to pure white?

From your experiences... -->>>

This is a test I keep meaning to run, but haven't gotten around to yet.

In the meanwhile, you can look up Michael Phillips' testing in the American Cinematographer magazine. I believe he found about 7 stops of latitude, about 1.5 to 2 stops above, and 5 to 5.5 below.

[Jeff Donald]

A total of seven stops of dynamic range is very difficult to obtain in DV and takes very careful lighting. More commonly I can get 5 to 6 stops of dynamic range. Seven stops takes very careful lighting of the shadows and highlights.

See this recent discussion on how F-stops are obtained.

[Tom Hardwick]

In answer to your questions Jonathan, my answers would be 60i for the smoothest video, locked exposure a definate, and locked white balance a necessity. Don't white balance on a white or grey card as that will dilute the beautiful sunset etc.

Remember that on replay the camera readout is to the nearest half-stop only, so take those with a pinch of salt. Also remember that on cameras with built-in automatic ND filters (not the 100A) like the Canon MVX3i, the Sony PDX10, the Panasonic MX350/500, the readouts are totally wrong - the apertures are extrapolations of f4.8 plus whatever ND was on axis at the time.

tom.

[Bogdan Apetri]

Barry,

Yes, I meant the half stops not the full stops. Sometimes like Jeff said, the numbers are rounded historically and sometimes the manufacturer just puts the mathematical correct number.

One more question Barry (not directly related): I saw that you've published an anamorphic adaptor guide. Somewhere you mention that you have compiled a focus chart UPDATED for the DVXA. Well, I have taped the old DVX focus chart and used it ever since on my A model, with good results. Are the numbers really different for the advanced model? And, on your chart, do you go below 50? Anyway, I plan to buy your guide when I get back to the States in late August.