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Old March 26th, 2010, 01:18 PM   #1
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how to compare 5D ISO to GAIN (dB) in video cameras

Hello there!

I own 2 cameras...
One is Sony Z-1 HDV camcorder and the other DSLR Canon 5D Mk II

Now, something's been bothering me, espeically when lightning scenes...

If I need to let more LIGHT into my camcorder, except SHUTTER and APERTURE/IRIS (which both of my cameras have) - the 3rd value is DIFFERENT...

Canon lets me do it with changing ISO value (from 64 up to 6400)
AND
Sony lets me do it with building up my GAIN with values from 0 - 18 dB....

Can you COMPARE these two values - are they representing the same thing in the first place, and what GAIN on my Sony Z-1 would equal ISO 100 on my Canon 5D...

I hope there is an answer to my question.. I tired Google it up, but all I got is some Dynamic Range info and very hard to understand charts :(

Hope you guys will be wise and enlighten me!!!

Cheers!
V.
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Old March 26th, 2010, 01:44 PM   #2
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6db of gain doubles the light gathering, giving you one more stop of exposure, so does doubling the ISO on the Canon. So 100 vs 200 ISO is the same as 0 vs 6db.
On a lot of the broadcast cams you can define gain as ISO instead of db.
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Old March 27th, 2010, 05:43 AM   #3
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I tend to keep my camcorders set at -3DB for almost all my shooting, which equates to around 200 ISO on a DSLR.

Take a look at this earlier thread on dvinfo, expecially Floris Van Eck's post and this will give you a good idea of gain versus ISO levels:

Setting a Sekonic lightmeter for the Canon XL-H1

Floris provides these numbers:

-3db is the equilivant of ISO 200
0db is the equilivant of ISO 320
+3db is the equilivant of ISO 400
+6dbis the equilivant of ISO 800
+12db is the equilivant of ISO 1250
+18db is the equilivant of ISO 2500+
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Old March 27th, 2010, 06:26 AM   #4
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Tony, I'm sure you know this already, but at -3db you lose a small amount of dynamic range - 0 is optimal and unless you get a lot of noise so that it's worth using -3 it's better to stick at 0. I used the HPX2700 at -3 because the noise was a little bit of an issue but on HDCam and XDCam I stick with 0. In fact the PDW700 goes to -6db but it's so quiet anyway it's not really neccessary most of the time.
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Old March 27th, 2010, 06:57 AM   #5
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I tend to prefer to push the blacks and boost colours in-camera anyway so although maintaining -3DB in these circumstances may possibly lose a smidgen of dynamic range, it is the end results and 'look' of my footage that means far more to me.

I've always found that the Canon range of camcorders such as XL2 and XL-H1 provided the best image at -3DB, so it is a firm favourite to leave it there and I only tend to nock it to "O" sometimes during dismal rainy or dull weather, and only above that for night filming.
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Old March 28th, 2010, 04:40 PM   #6
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I don't think my Sony Z-1 has "-" gain

Thanx for help!

I'd love to try -3 db, but I am afraid that my Sony Z-1 starts from 0db and has 0,3,6,9,11,18 - not entirely sure, it's not by my side at the moment!

But I definitely didn't even dream that even 0 dB is as high as 320 ISO!?!?!?

And thnx for a link on Lightmetering...

Earlier I let my Sony camcorder measure its own light, but now since I have 5D Mk II as well, I got me Lightmeter... It is "SECONIC Flashmate L-308S" --- But I don't thing it's gonna make any help for my video shooting...

In its manual and specs it says it's for both photography and video shooting...

But what it does, in one setting it just goes to setting which is suppose to be FRAMERATE, and as I change the framerate, it changes THE APERTURE - often so low, that I can't even think of getting it with my best photo lens, and not to mention Camcorder...

So I guess I am either not using it well, or it isn't really meant for videography!!!
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Old March 28th, 2010, 05:09 PM   #7
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Equating 0dB with an ISO value has no absolute meaning - it will vary from camera to camera. It doesn't even provide a very good indication of the cameras sensitivity - unless you define other factors such as the noise level at 0dB. (A good camera may have a good noise figure, such that even at +6dB it's less noisy than a second camera at 0dB. Comparing their ISO ratings at 0dB doesn't really tell you a lot.)

Practically, the best way to compare two cameras in this respect is to take them somewhere dark, open iris fully, then add gain until you get decent exposure and the same on each. Then compare the pictures to see which looks the best.

As far as lightmeters go, the most accurate indicator for exposure setting is normally the camera itself. Lightmeters can be useful for checking lighting without the camera being present, when you need to know the approx ISO value for the camera and gain setting to be used - just be aware that 0dB doesn't correspond to any single ISO value, it will vary with the camera.
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Old April 5th, 2010, 03:20 AM   #8
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David,.. i agree with you.. but.. one question..... GAIN is actually artificially enhancing lights on a standard setting (0 db)...like an extra step in handling the signal. Is ISO working the same way? I mean.. does a DSLR camera have a standard setting that means "cleaner process".. "less steps" . Is 160 or 320 the "default" ? Because ISO comes from film and every film had is own.... then if you wanted you could cranck it... but what ISO is "by default" the CMOS of.. let's say.. Canon 5D?
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Old April 5th, 2010, 07:29 AM   #9
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As David mentioned, each camera is slightly different in that they have differing sensors and pixels per sensor.

An FX (full-frame) DSLR will generally provide cleaner stills images and video footage at higher ISO levels than a DX (crop sensor) DSLR.
For example the Canon 5D Mark II and Nikon D3s tends to be better at higher ISO than the 7D - (The D3s even better than the 5D due to it having less MP for the same size sensor). But at really low ISO levels of 50-400, all the modern DSLRs are fairly equal in how clean the image is and free from 'noise' so it is quite difficult to detect a major difference.

I actually laugh to think that I've been working for decades with stills cameras loaded with 50 ASA fuji Velvia and in latter years the 100 ASA/ISO Velvia for all subjects. I would rarely ever put anything higher than 200 ISO in the film chamber, and a maximum 400 ISO in only extreme circumstances due to washed-out colours and grain with those faster film emulsions.

Now photographers and videographers using DSLRs are moaning about seeing noise (grain) in their images and movie clips at ISO levels we could only dream of using a few years ago!

I guess my stills film photography roots have been so ingrained into my head that I continue to strive to keep my DSLR cameras locked on 100 ISO or 200 ISO for most of my work - both in stills and video.

The nice thing about the D3s and 5D Mark II is that even when you do need to up the ISO levels during dull/dawn/dusk/night filming, the footage quality remains fairly clean, and is a huge improvement over the XL-H1 and similar HDV camcorders when set at high gain to film a similar scene.
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