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Old Oct 11, 2002, 7:51 PM   #1
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Default What limits Light Sensitivty fo Digicams?

I own a Nikon 995 and an Olympus C4040, I have been intrigued by the observation that the light sensitivity of both of these cameras is remarkably similar to a film camera.

Is this just a coincidence, a law of physics or have the camera manufacturers designed it that way? It seems very surprising that two completely different technologies would happen to have exactly the same light responsiveness. This is even more surprising when you consider that Modern CamCorders can record at almost 0 Lux and yet modern DigiCams start to need flash fill at early dusk?

Can anyone explain?
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Old Oct 12, 2002, 5:13 AM   #2
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This is a useful post to discuss, there is no single answer. Start with the lens, the bigger the glass (lower the f No.) the more light the greater the sensitivity.

Next the ccd sensor. The efficiency of collecting light and converting to electricity. The higher the pixel density, the larger the area, the more light can be collected. BUT there is a physical limits to how small they can be made and how many on the silicon for given size/cost.

Now if there are say 6M pixels on the chip, but their outputs are combined to give say a 2Mpix image there may be 3X more light sensitivity BUT lower res pics.

Also we should remind ourselves that our still cams are SINGLE SENSOR. Pro video uses 3 or 4 large ccd chips for Red Green Blue or Luminance - but they cost a lot more and are bigger and heavier!.

Next the electronic processing. How good the cam circuit amplifies the small signals without adding visible noise. Different cams will use different methods. Don't assume there is one best way, there are often trade-offs.

Back to your camcorder question, have you tried taking still pics with one yet and printing say 13X9? Since they output pics to TV's which you view from afar, you don't need hi res (unless its HD).

So take your 2 still cams (which I don't know). I'll bet they have good lenses, probably reduce res. for higher sensitivity, and have good noise processing?

Hope this helps.
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Old Oct 12, 2002, 6:52 AM   #3
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Digicams sample light electronically through it's CCD (ie there's no shutter per say). The faster the sample, the faster the shutter speed. In low light the electronics in the camera command the CCD to sample the light for longer period, or multiple times, to get an aggregate correponding exposure. With camcorders theses samples are almost continuous hence there's more light to work with and they can manage to go down to 0 lux... However if one does a freeze frame upon playback clearly those shots are not sharp! (and that's what one get in a digicam)
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Old Oct 12, 2002, 1:01 PM   #4
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Thanks to Voxmagna and NHL for your thoughtful replies. I understand the limits to light reception and electronic processing, and it is now clear on reflection why Camcorders work at much lowere light levels. Thanks.

I still remain a little puzzled that the relative sensitivities of such different technologies as CCD's and Chemical Emulsion are so very close. I contrasted my Contax TVs with 200 ASA at 50 mm and my Olympus C4040 set at '200 ASA- 50mm' and found they called for flash at almost identical light levels. With advances in CCD's this might all change and we might finally get the equivalent of 16,000 ASA grain free, color true 'film'. That would be most useful.
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Old Oct 12, 2002, 8:27 PM   #5
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I'm pretty sure the ASA scale is artificial, ie the manufacturer calibrate their CCD/camera sensitivities to match that of film so a photographer can relate to.

They can also use 'lux', or other unit of measurement, but then they'll have to educate the consumers all over again...
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Old Oct 13, 2002, 4:04 AM   #6
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I think NHL is right. Serious photographers using film and new digicams will have an experienced film speed/exposure mindset when shooting for both media. Many will be using manual exposure and exposure meters to get best creative pics.

So I think compatible ASA makes sense - this is young technology with a way to go though. The big difference of film v digi still lies with resolution and latitude, that's film grain (size/random distribution) versus pixel blocks(size/structured) and noise. Latitude is V. important. Digicams must work very close to their peak white clip limits for lowest noise. Here the film man must understand and be careful to work within the digicams' limitations.

I could over/under expose most scenes on film by a couple of stops, which when corrected in processing, would still get good pics. Not so yet with a digicam.
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Old Oct 13, 2002, 7:41 AM   #7
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Quote:
I could over/under expose most scenes on film by a couple of stops, which when corrected in processing, would still get good pics. Not so yet with a digicam.
I believe it varies with each camera's CCD and the photo editing tools used. In my experience I can easily correct underexposed shots by several f-stops, but find it a litttle more difficult on overexposed shots! With the magic of Photoshop one can push this process even more than film by creating a new color layer increase the saturation>gaussian blur>blend/opacity back to the original underexposed background shot with exceptional result...

On overexposed shots some textures are lost, but then there's the raw mode on the camera specifically for this purpose. During critical shooting (where one only get one chance) in this mode, the camera's capture raw data from its CCD along with the aperture/shutter, white balance, and any other compensation values pertaining to the shot in the same raw file. The resulting pictures are now computed by PC computer intead of the camera where one can undo most of the mistakes made initially while the pictures were taken (ie the data are still intact and not rounded off by the in-camera processing and worse jpeg away!) .

:P :P :P
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Old Oct 15, 2002, 8:18 AM   #8
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I'd tend to agree with NHL. I'm gradually reducing the amount of automatic options I use on my CP4500. One of the key goals for me remains avoiding over-exposure and I now tend to shoot on manual exposure, spot metering. By preference I go for up to one stop under exposed as I think the final colours are richer.
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Old Oct 15, 2002, 8:34 AM   #9
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Default This trick seems to work for me:

http://www.stevesforums.com/phpBB2/v...?p=14814#14814

One can also record this sequence as an Action...
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Old Oct 15, 2002, 8:50 AM   #10
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Does your posted link also work for misty conditions ? I took a photo last weekend of a Mediterranean Gull and I'd like to be able to "cut through" the mist
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