Sensitivity Index for PD170

[Shuf Shukur]

Hi Folks,

Would anyone know what the sensitivity index for the PD170 is?


Regards,

Shuf

[Mike Rehmus]

Not certain I've ever heard that term before, Shuf.

I don't know that there is a standard against which that camera could be measured.

Is it possible you are interesed in the equivalent of film speed ?

[Shuf Shukur]

Hello Mike,

Yes...the film version is ASA...:-)

I was browsing through a book which mentions the importance of determining the 'sensivity index' (something like that) of a video camera when setting the exposures from light meter readings, especially when shooting using key, fill & backlighting.

It mentions using wave form monitors, light meters etc...to determine this index and sounds all too complicated for me to fathom. And of course I don't have even a light meter! :-(

I've gone through the PD170 manual that came with the camera and there's no mention of this index. Oh...the book also placed the PD150 index at 400, which I believe means that to get the exposure, set the light meter at 400 and get the light reading from there...if it reads f5.6, then that becomes the correct exposure...

What I've been doing is, set the camera to auto iris zoom onto the face (say), and going to manual iris before zooming out. This is what I did for these interviews: http://malaysia.tv/?VID=666

Also, I've not yet used a 'multiple lighting setup' -- just a key light.

I've got a possible crack at a small corporate video work which involves interviews with key personnel and I would like to shoot with proper lighting, and I've read abit on getting the key, fill, backlight ratios right. But this wouldn't mean a thing if I haven't set the 'index' right -- it'll be like shooting stills with a 100 ASA film, but taking the light meter reading set at ASA 400....(I think)...

:-)

[Mike Rehmus]

OK, understand. But if you don't have a light meter, the index does you no good and most people don't use a light meter anyway. As you say, with a light meter, it is easier to set up lights.

However, if, for example, the lights are of equal wattage, then you can use physical distance to arrange the lighting ratios for the key and fill lights which is what most people do.

For fast setups, you fasten light cordage to the lamps with distance marks and use those to rapdly do the physical set up.

It is easy to do once you run some experiments in preparation for the real events.

[Shuf Shukur]

Thanks Mike. I shall try your suggestion.

Hope I can handle it

:-)

[Kell Smith]

Hi there all,
I do have a light meter - an old one - and am trying to see if it would be of much help. I have the same question as the original poster. Does anyone know the answer to this? Thanks. =)

[Don Bloom]

IIRC, a long time ago when the 150 came out someone did some tests to find the ASA of the camera. Not here at DVi somewhere else I beleive. Anyway again this is going back a long way and I might be off here but I remember something along the lines of 320 ASA.
I long ago gave up trying to figure it out and instead use zebras. Mike assessment of lights and using a string on it to mark setting is a trick I used back in the early 70s when I did still photography. It worked great with strobes as well as 'hot lights".
If one is insistant on using a light meter then I think I would start at ASA320 and shoot some tape load it up and see what it looks like. If need be you can tweak up or down from there.

[Dave Dodds]

When it comes to getting an exposure, it is probably more accurate to go by the zebras. If one were to rate the 170 at a certain ASA, it would be accurate under the specific settings used when rating but it won't respond consistently like a film stock. Also, there are a couple of levels of exposure within each f-stop. If you take a look and the camera reads 4.0, you have wiggle room so when your meter says 4.0, which part of 4.0 is right? There's a brighter and darker side of each stop. With your zebras, however, when you stop down enough to, say, leave zebras in the highlights or whatever your method is, you're there.

That said, I am an advocate of using a light meter for video work. Not for exposure but rather for ratios. You can eyeball it with the LCD but what you see is not what you get unless you're using a properly calibrated reference monitor. In this case, set your key light, get a measurement, and set your other fixtures and check. When you've got the ratio you want between the different sources, go back to the camera, expose for the key (using the zebras) and you're set.

Just my opinion. For me, using a combo of the zebras and a light meter (AND a monitor whenever possible) yields some very pleasing results.

Good luck.

~~Dave

[Shaun Roemich]

Shuf: my old PD150 had an equivalent ISO of between 400 and 500, based on MY experience shooting NTSC at 60i. Hope this helps.

Addendum: I used this method for location scouting looking at base light levels to see if ancillary (base) lighting was necessary for footage such as factory floors, showrooms etc. Actual exposure was "calculated" in camera using monitors and zebra.