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Old June 12th, 2006, 06:44 PM   #46
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ISO/ASA Speed of TC 3.0

For the ones that are interested, I tested the configuration to be roughly equivalent to 200 ISO. Given that the lens loses light through the zoom this is a variable number. The 200 ISO were measured at f2.8 and approximatly with 19mm lens.
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Old June 13th, 2006, 03:13 PM   #47
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Quote:
Originally Posted by Paolo Ciccone
Don't know directly. My only experience has been with the Mini35. It seems that the M2 is actually more "finnicky" than the Mini35. That's because it uses the stock lens and allows you to use, for example, Nikon SLR primes in order to get shallower DOF. I'm not too crazy about the design (stock lens+additional lens+upside down image) but in absence of other options (the Mini35 is way out of range for me) this can work.
No prob Paolo,

Since I started out as a fashion photographer, an upside image dosen't much bother me :)

What conversion does the M2 do? I have a ton of Nikon lenses, including a 13mm Nikon linear WA, but the exit grab is much less on a 1/3" block, so conversion (if any) is important.

Since the M2 is even more finicky than the Mini35, maybe the best bet is to place a Panny S35 between the HD100 and the action, you think?

Or, how about a set of f/.01 primes for the HD100, that should help with the DOF :))
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Old June 13th, 2006, 03:28 PM   #48
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Quote:
Originally Posted by Paolo Ciccone
For the ones that are interested, I tested the configuration to be roughly equivalent to 200 ISO. Given that the lens loses light through the zoom this is a variable number. The 200 ISO were measured at f2.8 and approximatly with 19mm lens.
Hi Paolo, how do you measure this?
I'm curious what ISO 'the low light setting' of Tim Dashwood is giving.
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Old June 13th, 2006, 03:34 PM   #49
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Quote:
Originally Posted by Enzo Giobbé
What conversion does the M2 do? I have a ton of Nikon lenses, including a 13mm Nikon linear WA, but the exit grab is much less on a 1/3" block, so conversion (if any) is important.
Ooooh, 13mm, I'd like to see that on the HD100. Don't know about the coersion. The M2 uses a ground glass, similarly to the Mini35, but it is in front o the stock lens. The Redrock Micro person I talked to said that you actually need to zoom in with the stock lens in order to frame the image from the ground glass. I guess this is one of the problems reported with the unit. If you touch the zoom on the stock lens then you're in trouble.

Quote:
Since the M2 is even more finicky than the Mini35, maybe the best bet is to place a Panny S35 between the HD100 and the action, you think?
That's assuming a lot. For example that I know what a Panny S35 is :)
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Old June 13th, 2006, 03:47 PM   #50
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Interesting...

Quote:
Originally Posted by Paolo Ciccone
For the ones that are interested, I tested the configuration to be roughly equivalent to 200 ISO. Given that the lens loses light through the zoom this is a variable number. The 200 ISO were measured at f2.8 and approximatly with 19mm lens.
In setting my exposure curve on a grad GS chart, I come up with a 320 ISO equivalent (wide open at 16mm zoom), but we are both in the same ball park that's for sure. I use 100% clip, maybe you are at 108% clip?

FYI, the stock lens works out to be a T1.5 on the wide end, and a T2 on the far end.

I have found that using a "400 slide" meter setting gives a good exposure compromise for the HD100 on Caucasian faces (when a meter is actually called for). Otherwise, I use a 80% Z setting on the hottest specular highlight for a Caucasian face, and adjust that for the subject's actual skin tone by setting the Z to more or less pattern blooming.
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Old June 13th, 2006, 03:48 PM   #51
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Quote:
Originally Posted by Marc Colemont
Hi Paolo, how do you measure this?
I'm curious what ISO 'the low light setting' of Tim Dashwood is giving.
I framed my DSC chart, lit it with even light from two sources at the same distance/angle. Verified that the grey area was showing as a even fuzzy line in the center of the chart in the WFM.
Changed the aperture until the grey area fell on the 40%-45% marker. Adjusted my light meter to give me the same exposure. Read the resulting ISO rating. It was 200.

Now, as I said, there is no way of rating this solidly because the lens is not constant across the range but my measurement was not at the two extremes so, it can work as a reference. If you go wide you'll gain some sensitivity, probably around 220. If you zoom in you loose "film speed".
Also, I played with the Gamma settings a bit. If you're in a low light situation you might want to switch the Gamma from "Cinelike" to "Standard". Standard gives you more light but its has a less balanced, IMHO, response. The "X" shape of the grayscale from the chart looks a little bit shifted toward the top. The Cinelike gamma seems to be more even and able to handle highlights better.
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Old June 13th, 2006, 03:53 PM   #52
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Quote:
Originally Posted by Enzo Giobbé
I use 100% clip, maybe you are at 108% clip?
Yes, I use 108%.

Quote:
FYI, the stock lens works out to be a T1.5 on the wide end, and a T2 on the far end.
Good to know, thank you.
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Old June 13th, 2006, 03:59 PM   #53
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Quote:
Originally Posted by Paolo Ciccone
That's assuming a lot. For example that I know what a Panny S35 is :)
Spiacente Paolo,

Panavision Super 35. Hahaha, that solves the DOF issue, that's for sure :)
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Old June 13th, 2006, 04:54 PM   #54
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Quote:
Originally Posted by Paolo Ciccone
I framed my DSC chart, lit it with even light from two sources at the same distance/angle. Verified that the grey area was showing as a even fuzzy line in the center of the chart in the WFM.
Paolo,

Just curious, are you using a spot (reflective) meter on the 18% gray, or an incident meter at the chart position?
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Old June 13th, 2006, 05:02 PM   #55
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Quote:
Originally Posted by Enzo Giobbé
In setting my exposure curve on a grad GS chart, I come up with a 320 ISO equivalent (wide open at 16mm zoom). FYI, the stock lens works out to be a T1.5 on the wide end, and a T2 on the far end.

I have found that using a "400 slide" meter setting gives a good exposure compromise for the HD100 on Caucasian faces.
1) When you say "400 slide" meter -- do you mean set an ASA of 400?

2) When one sets a CAMERA/FILM ASA and a Shutter-speed and the reads-out the Aperature, I assume that the reading is assuming the T-stop and F-stop are the same -- a ratio of 1:1. With Primes, this is a reasonable assumption. But with zooms it is not -- as you have measured.

So, in theory, one should set the Aperature slightly more OPEN than the meter reading. Correct? For example, 10% more open.

If that's true, shouldn't the ASA you dial into the meter be 10% LOWER. Thus, if you knew the TRUE ASA sensitivity of the camera, without lens, you would lower this value by an amount suitable for each zoom lens you installed.

HOWEVER, since you obtained the sensitivity with the stock lens using the Aperature indicated on this lens -- and the shutter-speed -- the ASA you got is already lower. So, the camera ASA can be computerd by:

Camera ASA = [ [ WIDE (F-stop/T-stop) + TELE (F-stop/T-stop) ] /2] X Meter ASA

So when you say ASA 320 -- have you already taken into account the AVERAGE difference (ratio) between F-stop and T-stop at Wide through Tele?

I ask, because as more lenses come to market -- we need the Camera's ASA. Then, each lens will have its own average F-stop/T-stop ratio.


Paolo -- why get as at the 40%-45% marker? What's wrong with shooting an AVERAGE brightly lit scene and getting the ASA there?


Last, I'm getting a bit confused because I think this discussion includes ASA values from two different lenses. Correct?
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Old June 13th, 2006, 06:26 PM   #56
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Quote:
Originally Posted by Steve Mullen
Paolo -- why get as at the 40%-45% marker? What's wrong with shooting an AVERAGE brightly lit scene and getting the ASA there?
I adapted the procedure from Scott Billup's "Digital Moviemaking" where Sean Fairburn describes how to do it. Specifically I placed the 18% gray of the DSC chart in that range because the line is rather thick and so it covers a range instead of just one value in the WFM. Fairburn says that that's where it should be and it actually makes sense when you look at the monitor. BTW, the camera's reading agreed with that too. The display on the LCD rated the scene as perfectly exposed. Not terribly important but a verification that the exposure was OK. It could be wrong but now I now that the reading from the camera is aligned.

Quote:
Last, I'm getting a bit confused because I think this discussion includes ASA values from two different lenses. Correct?
I don't think so, I believe that we are talking about the stock lens. It's just that Enzo, like any self-respecing crazy Italian, can't stop making jokes ;)
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Old June 17th, 2006, 11:02 AM   #57
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Quote:
Originally Posted by Steve Mullen
1) When you say "400 slide" meter -- do you mean set an ASA of 400?
Yes.

Quote:
2) When one sets a CAMERA/FILM ASA and a Shutter-speed and the reads-out the Aperature, I assume that the reading is assuming the T-stop and F-stop are the same -- a ratio of 1:1. With Primes, this is a reasonable assumption. But with zooms it is not -- as you have measured.

So, in theory, one should set the Aperature slightly more OPEN than the meter reading. Correct? For example, 10% more open.
No. Too confusing. Since all two current lenses "officially" available for the HD100 are only calibrated in f stops, it's best to do the conversion on the meter and then transfer the setting to the camera as an f stop value.

Out of respect to Paolo, I just did a more comprehensive test using just a 18% gray card instead of a grad. The following are absolute values that can then be modified by the user to their own personal exposure preferences. These settings are based on the factory presets for HD/24/108% and HD/30/100%. I could not come up with any other method to arrive at the actual ISO sensitivity of the camera that would not be biased or affected by personal user settings.

To arrive at the absolute ISO settings for the HD100, I first had to factor in the difference between the f stop and T stop values. Since I know that the stock lens has a T stop range of 1.5 to 2.0, I set my meter between the 1/8 and 1/15 shutter speed marks for a 24 camera shutter, and at the 1/15 mark for a 30 camera shutter. The indicated f stop would then mirror the correct exposure for the median T stop of the lens.

For practical purposes, the stock lens can be said to have a median T stop of f/1.8.

Now, based on those shutter speed settings, and after doing a white balance using a 5600K light source, I shot a 18% gray card and passed it out to a vectorscope. A 18% gray value is normally said to be between 45 and 55 IRE (I used 55 IRE, as do most broadcast outlets). At 55 IRE on the vector, using my converted shutter speed settings on the meter, I came up with an absolute ISO value of 250 at a 24 shutter/108% clip and 200 for a 30 shutter at 100% clip.

Since my broadcast chain editors (I shoot for several broadcast outlets) all seem to like the HD100 output to be a little on the underexposed side, I would personally use a 320/ 400 ASA @ 1/15 shutter setting on my meter to arrive at the correct ISO / f stop for my uses (at a 30 camera shutter setting 100% white clip, using my personal color and camera settings). Deviating from the factory default settings will most likely result in a change to the exposure curve / ISO rating, that's why I used the factory defaults to arrive at my "absolute" HD100 ISO rating.

Quote:
So when you say ASA 320 -- have you already taken into account the AVERAGE difference (ratio) between F-stop and T-stop at Wide through Tele?
Yes.

Quote:
I ask, because as more lenses come to market -- we need the Camera's ASA. Then, each lens will have its own average F-stop/T-stop ratio.
Agreed.

Steve, I'm posting the manner at which I arrived at the absolute ISO setting for the HD100, because you are obviously a very technical person. For myself and Paolo, who are just simple Italians, a simpler answer would be to set your incident meter at between the 1/8 and 1/15 shutter mark @ 250 ISO for a 24 camera shutter/108% clip and 1/15 shutter@ 200 ISO for a 30 camera shutter/100% clip (using the stock lens), or:

24 camera shutter/108%clip = 1/12 shutter @ 250 ISO on the meter = corrected f stop reading for the stock lens.

30 camera shutter/100%clip = 1/15 shutter @ 200 ISO on the meter = corrected f stop reading for the stock lens.

...and then modify the above values based on your own personal user and exposure preference camera settings.

Two asides, the built in meter appears to be calibrated for a 12% gray card using the factory default settings, and using the factory defaults for the HD/30/108% setting, the ISO works out to be about 225.
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Old June 17th, 2006, 06:58 PM   #58
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You guys are so far ahead of me that I'm going to try to repeat back what I think I understand:

1) "These settings are based on the factory presets for HD/24/108% and HD/30/100%."

I had never noticed that the IRE limit was different between 24p (to film) and 30p (for broadcast video.) It makes complete sense. Thank you!



2) "To arrive at the absolute ISO settings for the HD100, I first had to factor in the difference between the f stop and T stop values."

OK.


3) "I know that the stock lens has a T stop range of 1.5 to 2.0, ... . For practical purposes, the stock lens can be said to have a median T stop of f/1.8."

The stock lenses F stop range is from f/1.4 to f/1.8. Thus, the average F-stop is f/1.6. Correct?


4) Therefore, we know the loss of light is the difference between 1.6 and 1.8. If, for example, based on a meter reading, I were to set an exposure of 1.6 -- the shot will be slightly underexposed. Correct?


5) So I want to bias the meter so that it indicates f/1.6 when the exposure should be f/1.8. That means the bias must be toward slight OVER-exposure. In fact, about 1/4 stop over-exposed. Correct?


6) Which means the meter's ASA setting should be reduced OR the meter's shutter-speed should be INCREASED. Either will cause, for the same amount of light, the iris value to be smaller. Correct?


7) "I set my meter between the 1/8 and 1/15 shutter speed marks for a 24 camera shutter, and at the 1/15 mark for a 30 camera shutter. The indicated f stop would then mirror the correct exposure for the median T stop of the lens."

Here's where I'm doubly lost!!!!


8)(A) You DECREASED rather than INCREASED the shutter-speed which would bias toward under-sposure. This ie reverse of what I think needs to be done get the correct exposure. (B) You mention a 1/30th shutter-speed. But, 30p uses a 1/60th shuttter-speed. (24p uses a 1/48th shutter-speed).


9) "Now, based on those shutter speed settings, and after doing a white balance using a 5600K light source, I shot a 18% gray card and passed it out to a vectorscope. A 18% gray value is normally said to be between 45 and 55 IRE (I used 55 IRE, as do most broadcast outlets)."

OK


10) "Since my broadcast chain editors (I shoot for several broadcast outlets) all seem to like the HD100 output to be a little on the underexposed side, I would personally use a 320/ 400 ASA rather than 200/250."

By increasing the ASA you do indeed reduce the exposure for a given amount of light.


11) "That's why I used the factory defaults to arrive at my "absolute" HD100 ISO rating."

I agree fully.


12) A simpler answer would be to set your incident meter ... .

Would it be any different for a reflective meter?
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Old June 17th, 2006, 07:31 PM   #59
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Ouch... there is a lot of bad math & procedure going on here.

1. to calibrate the camera's ISO, you should be using a standard B&W chip chart with the 10 steps of black/white. the reason is that if you set an iris based on a single value, you may well be clipping highlights and shadows, or not making a full signal in the real world.

2.the cameras black level, white clip, gamma and knee all come into play. The most important are black level and knee, since they can significantly change the correct exposure in the real world. In any attempt to derive an ISO rating, you should be using your normal shooting settings. You could also try the factory plain settings for a worst case ISO setting.

3. Shutter - the proper shutter for 24P is 1/48th, or 24FPS on you light meter. For 30P, I prefer to shoot @30th, but techincally you should be using 1/60th. For me 1/60th is just regular video looking, so I opt for the slower shutter speed, which is a one stop gain. very usefull in low light. Again effective ISO is in big part based your shooting habits/settings.

4. the change of T stop in the lens is close to a stop. averaging to F1.8 or F1.7 means you will be a 1/2 stop over at the long end, and 1/2stop under at the long end, and thats a big deal with video. The effective exposure is at the particular focal length the lens is at *not* the theoretical average because its not the averaged setting thats hitting the sensors, its the actual shooting iris. FWIW, most of the fall off *should* be happening at the very last 20% of the lens, most of it before should be pretty close.

to measure the cameras ISO you should point the camera at the chip chart and frame it up, *white balance* the camera because that does make a difference, and then look at a *waveform* monitor, not a vectorscope which is used to measure color levels/vectors, not overall video levels.If you are using a vectorscope to set levels, you are off by about 20% if there is color in the image. on a pure gray scale, it might be close provided the camera was white balanced.

Looking at the waveform, you should have 100/108IRE for white, and black at 7.5 or 0 depending on your video standard and delivery format. at that point, you can now take out your light meter, and read the light at the chart. Your shutter should match the camera. Now adjust the ISO until the lightmeter's F value matches the camera's. That ISO is what the camera is shooting at. You can now take the light meter and use it for prelighting and know it will be very close to what the camera will be happy with.


I have used this technique for years - I've worked as a LD ( and engineer) in a couple of TV stations where I did not have camera's around when lighting, yet had to get lit. Once I had my meter calibrated to the camera's, I would consistanly light sets, and find the cameras irised with +-1/2 stop of my meter reading. The main difference for the reading is based on if the set was high-key, shadowdy, or average ( typical interior ) and the camera was adjusted a little for the best look. 1/3 a stop is a visible difference in light to a video camera, so when I lit sets, my keys were always dead on to +- .1 stops, more than that and you had a problem.


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Old June 17th, 2006, 07:51 PM   #60
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Didn't Adam Wilt and the boys figure the ISO at just under 320?
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