Help - My DP needs to know the ASA of my DVX100b & 35mm adapter???

Lucas Adamson

Lucas Adamson

Well-known member
OK, so my DP (I'm at film school) needs to know the relative ASA of my DVX100b, as we're shooting a scene with very complex lighting, and she wants to use a light meter, which I know is not everybody's cup of tea, but she finds it useful.

I have found threads about the ASA rating of the three DVX100 models, in which there is no absolute agreement, but various suggestions that the DVX100b should probably rated at about 640ASA, one stop more sensitive than the average for a 1/3" chip camera apparently (average is 320ASA, I'm told)

Anyway, that's all well and good, but my 35mm adapter complicates matters enormously, or so it seems to me. I can't work out the maths. How do I calculate the light loss of my adapter? It can only be used with a lens, and it's the lens that really sucks the light out it seems. I have heard manufacturers talk about a "less than one stop" loss, and that seems about right, but how do I account for a prime lens on the top? My fastest is lens f1.4, and my slowest lens opens to f2.8, but we sure as hell don't want to actually shoot our film at these apertures. What shall I tell her.

My adapter, by the way is a SGPro R3 Achromat, Nikon plano-convex condenser lens sitting on a very good wax gg.

My lenses are Zeiss T* Contax badboys (and some Yashica MLs)

Many thanks
Lucas
 
Lucas, unfortunately for your DP, a light meter will not work to check for exposure levels, but rather can be used still to check for contrast ratio's. I.e., knowing the ASA will be of no importance to you.

What has been noticed lately is that 35mm adapters do not react linearly as they do on film. One stop on a 35mm lens on an adapter does not cut the light by one stop. If you take a look at the brevis, or the letus, you will notice that going from 2 to 2.8 cuts maybe 1/5th of a stop at most.

If it helps at all, i am able to set my digital still camera to ASA 200, with my shutter at 1/50th and my lens at F4, this matches what my canon XH A1, on 24F, 1/48th shutter speed, and the letus extreme wit ha lens at F2.0 . Which, if you continue to follow the logic ( if the 35mm lens was the same against GG as it as against film ) then 200 ASA at F4 gives the same light as 100 ASA at F2.8, and then the same as 50 ASA at F2.0

So roughly 50 ASA ?
 
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Lucas, as PaPa is saying, there's simply no way to use a light meter effectively with an adapter. Your DP could maybe use it to rough in lighting a little, but in no way can you use it to actually set exposure. It's just not possible.
 
PaPa said:
Lucas, unfortunately for your DP, a light meter will not work to check for exposure levels, but rather can be used still to check for contrast ratio's. I.e., knowing the ASA will be of no importance to you.

What has been noticed lately is that 35mm adapters do not react linearly as they do on film. One stop on a 35mm lens on an adapter does not cut the light by one stop. If you take a look at the brevis, or the letus, you will notice that going from 2 to 2.8 cuts maybe 1/5th of a stop at most.

If it helps at all, i am able to set my digital still camera to ASA 200, with my shutter at 1/50th and my lens at F4, this matches what my canon XH A1, on 24F, 1/48th shutter speed, and the letus extreme wit ha lens at F2.0 . Which, if you continue to follow the logic ( if the 35mm lens was the same against GG as it as against film ) then 200 ASA at F4 gives the same light as 100 ASA at F2.8, and then the same as 50 ASA at F2.0

So roughly 50 ASA ?
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Very helpful post, Papa. Thanks!
 
Thanks all,

Well that makes a lot of sense - it is not possible to calculate which I had kind of concluded.

I am not sure about the logic of taking the digital stills camera and extrapolating in this way though. For a start, I would assume that the light sensitivity would be much better on the DVX100b than the XH A1, and secondly, as has been discussed, for some reason it seems the whole thing is not linear in the way the 35mm lens aperture reacts. Just from experience of using 50ASA film, I know that my DVX + adapter is way more useful in low light than 50ASA film.

I guess she can still check light levels with the meter and get a sense of relative levels, but it sounds more confusing than helpful if you can't use the meter to directly set aperture etc.

Anyway many thanks to you all.
Lucas
 
Get a Waveform.

Seriously. Rent a Panasonic Monitor with Waveform built in, and ste exposure with that and a properly calibrated monitor with a hood.

If your DP tries to set exposure with a light meter they will feel sore when the exposures are all over the place when you get back to the edit room.
 
I'll second the get a waveform. The Panny gives you a good solid calibrated monitor (assuming you calibrate it) and the waveform makes for some serious confidence in your levels. Being able to show the client the monitor and say "this is what we are getting" and not saying "it'll look better cause the lcd on the camera is crap" is also worth its weight in gold.
 
Lucas, what your DP is looking for is a standard that she can use on the set to make sure that the creative decisions she is making are correct. I know exactly what that means. I came up totally trusting my meter, then they handed me a DV camera, "We can't afford film, let's use this...". It took a while for me to get used to how to light for DV and I totally agree with the above advice that the light meter is almost totally useless when it comes to lighting for DV, except as noted, for roughing in contrast ratios.
As for the use of a waveform monitor, well, it is a wonderful tool, however, if your DP is not experienced with making creative decisions based on using one then she should not be force to try. What I suggest is that she be allowed to make tests, using the camera, lenes and production monitor that you plan to use on this gig, to see how her lighting decision look. You should allow her to take the test footage through your anticipated post process to see how the images end up looking like as an end product. She should do what ever she needs to do coordinate this information into an on-set set of standards she can use for your gig. I know that if she is wanting ASA setting as in your original post, then she is anal enough to get what she wants from such tests.

Oh yeah, once your DP sets the production monitor to her requirements and then she kills anyone that messes with it... that is justifiable homicide... that included Directors!!!
 
Lucas Adamson said:
Thanks everybody. I hope you read this Julia!!
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I just want to add that if you were using a laptop with Adobe Premiere Pro 3 that comes with 'ON LOCATION' all of these issues become academic. This software has all of the fundamental scopes and readouts any DP could want. So much so that they would be embarrassed to even bring a light meter on a set where this software is functioning. This is really a cutting edge software that should be looked into if you demand a really precise look for your production. Good luck with that.
 
SISUMAN said:
I just want to add that if you were using a laptop with Adobe Premiere Pro 3 that comes with 'ON LOCATION' all of these issues become academic. This software has all of the fundamental scopes and readouts any DP could want. So much so that they would be embarrassed to even bring a light meter on a set where this software is functioning. This is really a cutting edge software that should be looked into if you demand a really precise look for your production. Good luck with that.
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Lucas, it is obvious that there are, "Tools a plenty" for your DP to use. If you trust her aesthetic sensibilities, then give them the best tools possible, then work with her to make the best creative decisions possible.

No go out and make a great movie.
 
Oh yeah, once your DP sets the production monitor to her requirements and then she kills anyone that messes with it... that is justifiable homicide... that included Directors!!!
Click to expand...

Could we please post this as a sticky . . . . no - make that a banner . . . in the director's forum. please.
 
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