High Dynamic Range?

[Stephen Finton]

Lorin,

The 8 settings to the left of the exposure bar on the HC1000, TRV950 and PDX10 are where the ND filters come into play. My guess is the HC1 DOES have undocumented ND filters built in. The camera stops at around an f-stop of 4 and then starts using ND filters, which the camera cannot accurately measure. That's why it doesn't go any higher than 4(I can get my HC1000s to 4.8). There's a way to see if the camera is using ND filters by placing it in AUTO EXPOSURE and shining a mini MAGLITE down into the lens while watching to see if you notice any little blades flip into view way back in the back of the camera. These are the ND filters. Give it a try and get back to us!

P.S. Make sure it is on manual shutter!

[Joe Carney]

Geez, after reading all this techincal stuff, I need an aspirin. hehehe

I thought modern CCDs and CMOS chips basically processed their images at higher than 8bit, than dithered down to 8bit (different than compression BTW). There is a whole science and business surrounding color dithering (fooling the eye into seeing more color than is actually there in the end result)
Many patents are involved in doing this, and it sort of explains why the expensive rigs like Davinci and Flame get away with charging more, since they offer the option of working in higher than 8bit color.

What is really weird is the graphics card manufactureres could give us more color, but wont. Chicken and egg stuff I guess.

[Andre De Clercq]

Joe I don't think that dithering is involved in the 10 (or more) bit to 8 bit conversion. This is being done through a HW lookup table (LUT). Spacial/temporal halftoning (dithering) is more related to output signal processing.

[Gerald Lunn]

Stephen and Lorin,

I've been doing a little experimenting with my HC1, comparing it with my old GL1. I took video in all sorts of lighting situations from a fairly dark indoors to bright sunlight and drew up a table comparing the data codes between the 2 cameras on auto exposure. Max gain of the amplifier on the darkest subject was 18dB. Both cameras use 1/60sec as min shutter speed. The GL1 has a manual 4X (I checked the ratio) ND filter which was used in the brightest scenes but I took account of that in the calculations.

What I found was that as you go from darkest subjects to brightest subjects there is about a 2.5 stop (6X) automatic change in the HC1 sensitivity between the point at which the amplifier gain gets to 0dB (very shaded outside scene) and a bright outside scene (not the brightest). At the same time as the sensitivity is changing the aperture goes from f1.8 to f4.8 and the shutter speed goes from 1/60 to 1/125. Further brightening of the subject is then compensated by a faster shutter speed - up to 1/250 in my case.

Thus there does not seem to be any doubt that something is giving the change in sensitivity. I have looked in the lens as Stephen suggested but see no ND filter flipping down. In any case I found that the sensitivity change is not sudden but gradual, meaning that there is some sort of 6X (only 2.5 bits) gain change in the DSP. It is probable that with 14 bit resolution in the AD converter they are giving up this 2.5 bits to add to the range of useable light level.

The lens can only stop down from f1.8 to f4.8 (about 7X light range) - it's only a 2-blade control.
The amplifier is 18dB (8X)
"Bit adjustment" gives 6X
The shutter (in my case) went from 1/60 to 1/250 (4X)

This gave a total adjustment range of 7X8X6X4 = 1344 (just over 10 stops)
although more is possible for extremely bright scenes by using a faster shutter.

I hope that this analysis is useful and makes more light than heat or fog!!!

Gerald

[Gerald Lunn]

Adding a little to my diatribe yesterday.....

I can now see why it is that Sony does not give direct manual control over aperture. The range they have chosen to use is only from f1.8 to f4.8 - not giving a lot of flexibility in depth-of-field etc that normally come from that control. The limited aperture range however is beneficial from the point of view of the optics design - I'm sure it makes it easier for Zeiss to get the best definition over the whole telephoto range. My GL2 goes all the way from f1.6 to f11 which is a much more useful range but the resolution required is much lower.

Does anyone know what the range of aperture is on the FX1/Z1?

Gerald

[Andre De Clercq]

Higher f-numbers for those small sensor structures would kill HDV resolution due to diffraction effects. Even when the ideal (=diffraction limited) optics would be used.

[Stephen Finton]

Originally Posted by Gerald Lunn

Stephen and Lorin,

I've been doing a little experimenting with my HC1, comparing it with my old GL1. I took video in all sorts of lighting situations from a fairly dark indoors to bright sunlight and drew up a table comparing the data codes between the 2 cameras on auto exposure. Max gain of the amplifier on the darkest subject was 18dB. Both cameras use 1/60sec as min shutter speed. The GL1 has a manual 4X (I checked the ratio) ND filter which was used in the brightest scenes but I took account of that in the calculations.

What I found was that as you go from darkest subjects to brightest subjects there is about a 2.5 stop (6X) automatic change in the HC1 sensitivity between the point at which the amplifier gain gets to 0dB (very shaded outside scene) and a bright outside scene (not the brightest). At the same time as the sensitivity is changing the aperture goes from f1.8 to f4.8 and the shutter speed goes from 1/60 to 1/125. Further brightening of the subject is then compensated by a faster shutter speed - up to 1/250 in my case.

Thus there does not seem to be any doubt that something is giving the change in sensitivity. I have looked in the lens as Stephen suggested but see no ND filter flipping down. In any case I found that the sensitivity change is not sudden but gradual, meaning that there is some sort of 6X (only 2.5 bits) gain change in the DSP. It is probable that with 14 bit resolution in the AD converter they are giving up this 2.5 bits to add to the range of useable light level.

The lens can only stop down from f1.8 to f4.8 (about 7X light range) - it's only a 2-blade control.
The amplifier is 18dB (8X)
"Bit adjustment" gives 6X
The shutter (in my case) went from 1/60 to 1/250 (4X)

This gave a total adjustment range of 7X8X6X4 = 1344 (just over 10 stops)
although more is possible for extremely bright scenes by using a faster shutter.

I hope that this analysis is useful and makes more light than heat or fog!!!

Gerald

So the HC1 uses shutter speed to attenuate light past f-stop 4.8? UGH!

[Lorin Thwaits]

Originally Posted by Stephen Finton

So the HC1 uses shutter speed to attenuate light past f-stop 4.8?

Try this test: Set the shutter speed at 60, film a sequence including bright light, experiment with all 24 settings of the exposure, and then play it back with the "Advanced Data Code" on. The reading in the lower-right corner of the screen claims that it stops it down to f8. Each of those 24 settings became the basis of this article I wrote for mywebsite:

http://hdvforever.com/hdv/exposure

-Lorin

[Gerald Lunn]

Lorin,

Obviously my tests were a little misleading. I did not try fixing the shutter at 1/60 for my main set of tests - I was using the full auto mode - wanted to see what happened to aperture, gain and shutter. In that mode the aperture stopped at f4.8 and then the shutter speed was varied for brighter conditions. Maybe they are trying not to get too much depth of field, or maybe the definition suffers slightly at smaller apertures due to diffraction.

Anyway, I have tried your "24 steps with the shutter fixed" and I actually got a slightly different result. You found 8 steps at f4 and a minimum aperture of f8. I found 7 steps at f4 and a minimum aperture of f9.6 (then "Closed")!!!

So we can now say that the min aperture varies with the camera manufacturing run - either f8 or f9.6. It remains to be seen which will end up as the final choice when they are in full production.

I think you are probably close on your bit range adjustment. They must use something like this to give the 12X change in gain required for the 7 steps (3.5bits) at f4 (8X or 3 bits in my case). I see that you have presumed that the MSB is only adjusted by 2 bits with much more significant changes in the LSB. This would lead to the picture getting a little dimmer at low light levels (which it does). Good work!

Gerald

[John Yamamoto]

Lorin, thnaks for ur info, I mange to get a very good exposure control on HC1E
be short, first set shutter to 1/50s. well u may set to any as u prefer. then use exposure notch to get max iris. 1.8 but not gain. simply move the notch to far right and back 6 notch.

so now u get the max iris and no gain to shoot better DOF.
if u prefer f1.8 to shoot , when it's too bright, iu may need to add a ND filter.

i use zebra to get my reading and refer as IRE or zones.
again i find if u set at zebra at 70 IRE , it's about 3 notch plus to 100 IRE or 3 notch down to 50 IRE.

use the histogram to see ur zones, it's very handy too.
i just remeber how it go whne i reading one tone, ( says a grey card or white paper) and set to the IRE i want.

to my own taste i when i use auto i set the AE to -4 and i find the reading is matching with 50 IRE.

so in a quick set up, may just set AE -4 and do the reading then lock it or ajust to what u like.

I, find the dynamic range is quite OK on Cmos.

enjoy.
J.M.

[Rodolphe Pellerin]

Lorin and others,

If you look at the lens (with a loupe), you can see 2 ND filters moving like a curtain when you change the exposure. They appear at (F4 +1). F4 is +5 fom the left. So (F4 +1) is +6 from the left... ;-)

ND1 filter:
Between F8 and F4 ND1 filter is always on. 0 (close) to +5 from the left.

ND2 filter:
At (F4 +1) exposure +6 from the left, the ND2 filter is engaged but not fully. Each incrementation moves the filter from the top to the bottom of the cmos imager.

At +14 from the left there is no filter until the end...

You can clearly see the effect when you do that :

- zoom max
- point to a small source light
- defocus with the ring
- start exposure from the left (close) and start to increment

Note: The ND2 filter is not a full size filter (maybe 1/3 of the cmos imager). At (F4 +5) or +10 from the left, you can see the shape of the blured light divided in 3 distinctives areas. First area from the top : no filter. Second area from the top : ND2 filter. Third area from the top : ND1 filter.

Maybe there is a combination of this with a bit shifting of the EIP... Any suggestion ?

It results in very interresting Bokeh... I love this cam !

Rod.