(Mis)understanding crop factors - follow up

Written by RedShark News Staff

RedSharkUnderstanding Crop Factors - follow up

Our article about misunderstanding crop factors has had a big response

Phil Rhodes' article which itself was partially a response to Tony Northrup's video has prompted a big response. You can read readers' comments below the article itself, but one was particlualrly informative.

It's from Joe Wellman, who is a RedShark reader with vast industry experience, going back a number of decades.

It's good to read this because it shows that worries around sensor size are nothing new...

You are dealing with the same problem video people dealt with, when we changed from 1 inch imaging tubes to 2/3 inch imaging tubes and later to 1 inch, 2/3 inch and gasp 1/2 inch (why?) CCDs. Lens difference can be a real problem with variable imaging device sizes, never mind the sensitivity of the device. The problem was if you shot sports (outdoors or inside with a ton of overhead lights or night games in stadiums with lighting) you were using a camera with at least a 30 X zoom lens and the biggest imaging device you can get! Why you might ask? Because sports require cameras that you don't turn gain on (more amplification of the signal) because that adds noise!

The 30 X zoom was because you are not 2 feet or 30 feet but at least 300 feet from the game events so you need the ability to close on the action! So we use at least 6 cameras (all ISOs) and you designate cameras that follow the action and other ones for wide shots. Video cameras built for broadcast are supplied with matching lenss (no vignetting allowed during zooming) from the manufacturer and all viewfinder monitors for the cameras have action safe and title safe markings.

There are only two lens manufacturers used in Television in the US, either Canon or Fujinon no, or very little Angenieux (perhaps because they're seen as being a bit expensive).

There is a focal length problem between Tube and CCD because the CCD's are glued to the RGB optical block and the tube units were mounted in a yoke assembly (as we know all tube cameras are obsolete now but in the beginning you could accidently put a tube zoom lens on a CCD camera: oh the pain!). Most indoor studio shots are done with a 12 X lens camera which were not like the big cameras but what we called EFP (Electronic Field Production) cameras. Smaller body and with large viewfinders with action safe and title safe indicators. All cameras in studio production and in sports were color matched and shaded according to a vectorscope and waveform monitor and visually checked on a good, known, monitor to assure the best picture in the production, and set for the F stop that provided the best lit frame picture for the shot (making sure they do not bloom the image).

Film guys are coming in blind! You are used to film emulsion. Forget it! All you need is adequate light to hit the image sensor and a sensor big enough to get you the resolution needed (more is better!). ASA: we don't need any ASA, nor ISO; this is just electrons. Just shoot for the best possible image (yes I know, you want to set a mood) on a monitor you trust. If you open the lens you will get the light you need. Remember - you get to see the image, not develop it! Try a good zoom lens with the proper mount (supplied or recommended by the manufacturer), go in tight and focus, pull all the way back and set the back focus, and try tracking it! Use a grey scale chart to check color and a resolution chart to check focus! Resist using gain: just think of it as a fast emulsion (more grain - read noise - and think, "I'll fix the image in pos"t or "how many F stops can I get?"

Have fun you "new video guys"! Don't worry, be happy. No math, just video image. It's too bad you don't like 16:9 but I know you're stuck on 2.4 to 1 academy, which drives video people bonkers with top and bottom black bars! Talk about crop. Oh well to each his own!


Thanks for that great perspective, Joe!



Tags: Technology


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