iso\gain in filmcam mode question

Ed Kishel

Ed Kishel

Veteran
In Barry's book on page 216 it states the low setting for gain is equal to 0db (or no gain applied). Now in film cam mode iso200 is the lowest you can set the switch to. So it's safe to assume iso200 is the same thing as 0db/no gain applied- when the switch is set to L? There is no such thing as iso000.

And in this case, L for "low gain" is not really "low gain applied", but "no gain applied". Might seem like a no brainer, but I am slowly figuring out this camera want to be sure.

Thanks,
 
THe switch has two functions.

It operates as a GAIN switch in Video Mode and an ISO Preset when in Film Mode.

Both switch functions are exclusive of each other as are the functions.

Dont over think it except you may want to consider that the camera (sensor) is natively ISO 400. ( I believe)
 
so if I go into the menu and set the L position (for the gain switch) to ISO400, that will result in adding zero gain to the picture. Assuming I leave it on the L position.

These are my settings:
L: ISO200 (= 0db gain)
M: ISO400 (= +6db gain)
H: ISO800 (= +12db gain)

Does this sound right?

EDIT: I meant this....
L: ISO400 (= 0db gain)
M: ISO800 (= +6db gain)
H: ISO1600 (= +12db gain)
 
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My reading and understanding is

ISO 200 = -6dB

ISO 400 = 0dB

ISO 800 = +3dB

All approximations.

Still dont think you want to equate ISO to dB when in film camera. Totally wrong way to work with f-stops and the calculations of exposures
 
I won't equate the two- I just want to know what setting will have no "artificial brightness" added. It was easy to tell when gain was added with the hmc150- it said it on the screen.

In Barry's books- gain is defined as "an electronic amplification of the video signal, in other words artificially making the picture brighter".

Is any ISO above 400 defined as the same? If so, then the two are equal, functionally speaking- even if the numbers/settings on either side don't equal each other exactly.
 
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Ed Kishel said:
I won't equate the two- I just want to know what setting will have no "artificial brightness" added. It was easy to tell when gain was added with the hmc150- it said it on the screen.

In Barry's books- gain is defined as "an electronic amplification of the video signal, in other words artificially making the picture brighter".

Is any ISO above 400 defined as the same? If so, then the two are equal, functionally speaking- even if the numbers/settings on either side don't equal each other exactly.
Click to expand...

ISO 400 is 0db (L on a HMC150).

BUT the AF100 can be essentially noiseless below 1600ISO. We use it occasionally at 2000ISO and get noise equal to HPX170s at 0db gain.
 
You said:

EDIT: I meant this....
L: ISO400 (= 0db gain)
M: ISO800 (= +6db gain)
H: ISO1600 (= +12db gain)
Click to expand...


That is the problem using dB :
In theory +/- 3dB is a factor of x2 so ISO 800 would be +3dB ...if ISO 400 was 0dB. (ISOs are also a factor of 2)

The Reverend is right. There is no discernible difference in the ISOs when eyeballed.

In photography...ISO and Gain are not functionally the same.
 
Shooter said:
My reading and understanding is

ISO 200 = -6dB

ISO 400 = 0dB

ISO 800 = +3dB

All approximations.

Still dont think you want to equate ISO to dB when in film camera. Totally wrong way to work with f-stops and the calculations of exposures
Click to expand...

what iso would you assign the "L" switch in film cam, iso 200 or 400?
 
What ever you need it to be for the particular shoot.

Set them up (all 3) for your convenience once you have considered the circumstances that will arise.
 
Confused by this; isn't there a better way? I've heard of so many different ways to help create a shallow DoF - but lowering ISO was never among them.
 
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Iso and gain are two different ways of describing the same thing.

6dB of gain is the same as doubling the ISO.

400 = 0dB
800 = 6dB
1600 = 12dB
3200 = 18dB

Every time you add 6dB you're doubling the gain/amplification. It is equivalent to opening up the iris by one stop, or doubling the exposure time (except that those techniques actually double the light hitting the sensor; increasing gain 6dB doesn't add light but it does increase the brightness but amplifies what it has to a degree where the resulting image is as bright as if you'd doubled the light. )
 
Not saying the only way, but if you decrease gain to underexpose slightly, you can open up the iris a bit to compensate, thereby giving shallower DOF, no?
 
Steve R said:
Confused by this; isn't there a better way? I've heard of so many different ways to help create a shallow DoF - but lowering ISO was never among them.
Click to expand...
Well... That is one of the points of debate between the old guard, and the new wave of DSLR shooters. Us old film guys would have considered it madness to go changing the ISO from shot to shot, for purposes of manipulating the aperture. But the new wave does it all the time.

On an hpx170 or hvx200 it would be a bad idea. But on the af100 it is really pretty consistent from 200 to at least 800, so changing iso for purposes of exposure (at least in that range) seems to be a valid technique.
 
Iso and gain are two different ways of describing the same thing.
Click to expand...

So what would the Gain be for ISO 250, ISO 320, ISO 500, ISO 640....?

ISO and ASA have traditionally been the way one describes "light sensitivity" in photography and the f-stop has a direct relationship with them both. (ISO and ASA are virtually interchangeable as a reference). F-stops and ISO / ASA are all a factor of 2.

The chart you show Barry (if correct) shows exactly how difficult it is to use dB for photographic purposes. The ISO shows a factor of 2 and the dB ... well who knows...log?, linear?.... (dB does not even relate to a light meter , lens or wfm ...)

Ask the gaffer to give you 7db on the fill , 4dB on the backlight and 9dB on the key. Then calculate it so the AC can set the lens for ...who knows what! (Auto exposure maybe)

:-)

BTW: In AUDIO 3dB is doubling the gain. (pressure in audio terms). ie. 3dB = a factor of x2.

Just a few reasons why dB is not the way to work in photography.
 
I've always thought that, if you had ample light and were stopped down to your ideal exposure and sharpness - and you needed to open up for shallower DoF - you'd drop in ND corresponding to the number of stops you opened up (...vs. drop the ISO within the scene).

The former felt like "cutting light", whereas the latter feels like "decreasing sensitivity" - and they don't seem the same in my brain for some reason.

Which method would result in a better image?
 
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