Why is it the screen goes darker or lighter when shutter speeds are changed? On my old Super 8 camera I could choose shutter speeds without affecting exposure. Why don't they put F stops on Video cameras? Does anyone use the shutter control on the NV-DX100? If so, can they pass on some tips? rmaytum@mistral.co.uk
Your questions in order, Roger.
1) The screen goes darker/lighter because you're in the manual mode most probably (which enabled the shutter speed alteration in the first place). The aperture isn't compensating as it assumes you want to be in control. On some cameras you choose hi shutter speeds by turning to the "golfer" pictogram - in this case the screen goes darker (even though you're in an auto prog mode) simply because there isn't enough light around and the camera has reached maximum aperture.
It's worth remembering that most modern cameras are at least 1,5 stops faster at their wide angle end of the zoom, so use w/a in darker conditions. Super 8 was never so.
2) Yes, my Super 8 camera allowed shutter speed changes, but all of the above still holds true. It would only give correct exposure if there was enough light around. Also, my Super 8's top shutter speed was 1/250th sec (in slo-mo and smallest sector angle) wheras my video cam happily shoots at 1/10000th sec - a huge difference.
3) They do put f stops on video cameras - my TRV900 is excellent in this respect.
4) I don't have a DX100 but as to using the shutter speeds, I'd say beware. In the late 80s camera designers found they could switch off the output from the CCD, thus giving very short exposure times per frame. This was seized upon by the advertisers and paraded as a must-have, but in movie-making reality it simply serves to make every frame sharper. That's fine as far as it goes, but the illusion of movement within the frame relies upon the fact that each frame shows a small blurr (of the moving subject) and this blur makes the object appear to move smoothly around the frame.
You can test it - shoot the kids charging about at hi and lo shutter speeds - the lo (1/50th) will look a lot better on screen. But if you're into using your camcorder as a still camera, then do go ahead and shoot at 1/250th (say).
I auto, my TRV900 ups the shutter speed when it gets too bright for the smallest (F11) aperture. This is Not Good, and so the camera includes an inbuilt ND filter. The ND filter is still not strong enough, as the camera is much sharper at 5,6 than 11.
tom
Is a video camera's exposure controlled mechanicaly with an iris, like in SLRs or are they digital (i.e. just cutting or amplifying the signal)? If there's an iris within the lens array, the depth of field should increase as it gets smaller and decrease as it gets bigger.
I know the TRV900 shows f-stops but are these a real indication of the apature or just approximations? I'd prefer it if they were real because it would give me more control as I have been considering changing my TRV9 for the 900 soon.
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Christian J. Lett
clett@nationalexpress.co.uk
Roger,
Presumably you know that you can also change the f stops on the DX100. If I remember rightly you press the selector wheel again after the shutter speed has been set. You can also change the gain by pressing again after the f stop is set. Any change in exposure is reflected in the viewfinder because, as Tom said, the camera is now in manual mode. Sounds like your previous Super 8 camera was in shutter priority mode which automatically changed the f stop to compensate for changed shutter speed.
Tom - Christian - Gladders
Thanks guys for some excellent responses. I've printed your replies and once I've had an opportunity to try them out - I may come back to you. Your kindness is very much appreciated. Roger
A video camera's lens contains a real set of diaphragm blades, Christian, just like in your SLR. And as you surmise, the depth of field decreases the more telephoto you pile on. And yes, they can be relied upon up to a point - you cannot set a flash gun up using them as you don't know the "film speed" of the CCD, but you can take it that each stop you close down will halve the amount of light reaching the chip(s).
But we're talking very short focal lengths here. The TRV900 has a 4,3 to 51,6mm focal length zoom, and at its 51mm focal length it's only f2,8. Now if you had a 51mm f2,8 prime lens on your 35mm SLR, even at max aperture you'd hardly be delighted with the differential focus effects you could produce.
So too with your video cam - the differential focus effect is governed by the focal length & aperture, and will look EXACTLY the same as the still camera, no more, no less. What WILL look different though is the telephoto "compression" effect, as the tiny 1/4" chip is like blowing up a tiny part of the 35mm frame.
At wide angle (4mm say) and f8, the depth of field is phenominal. It's pretty good on an SLR with a 28mm widie at f8, so realise that you must keep your video camera's front element absolutely spotless, as most of the time the dust is being recorded in sharp focus.
Tom.