Why no video or 'live' mode in DSLR?

In the hazy back of my mind I seem to remember the reason for video not being possible in a DSLR is the mirror/pentaprism redirects light from the sensor to the viewfinder.

Can someone please tell me, why can the mirror/pentaprism not be lifted up exposing the CCD, and a 'live' output or even movie output be shown on the screen and/or captured to card. I know that this negates many of the advantages of that a DSLR viewfinder has over a P&S digicam, but three things that would be nice is

Sound
movie mode - even if it is not spot on with focussing
A flippable screen for getting the camera into those tricky positions.

Any thoughts?
Thanks
Dave

dgwynne said:

Sound
movie mode - even if it is not spot on with focussing
A flippable screen for getting the camera into those tricky positions.

Any thoughts?

Click to expand...

Yeah. Two.

Firstly, personally I think that'd rock. I'd happily give up the D70 viewfinder for a big, fast, flippable screen. I really, really, don't see why people are so enamored in viewfinders.

Secondly, you're going to get flamed for suggesting this. And so am I.

--

All I write, no matter how silly, are my personal views, and in no way reflect those of my employer or the voices in my head. Honest.

Cameras are for pictures, camcorders are for movies. Its like trying to make a swiss army knife that does everything, it just gets too big and clumsy. You can't create a video mode without compromising something else related to the photography portion of the camera. Not to mention the risk of dust to the sensor, no thank you.
--
http://www.camhabib.smugmug.com

I honestly don't understand what you're suggesting. You know that there's a mirror in there that reflects light to the finder via the pentaprism/pentamirror except when the mirror flips up so the picture can be taken. That's where the Reflex in Single Lens Reflex comes in.

So you want to remove the mirror and finder assembly so that you can put another sensor in there which can feed output to the LCD monitor in real time and record movies? Or you'd like to use a pellicle mirror (partialy silvered) so that light could go to both the sensor and the viewfinder all the time for a movie mode? (That's been done - at least the pellicle mirror part - but it really cuts down on the birghtness of the finder.)

People complain now about dust that gets on the sensor and in the viewfinder. Having a replaceable finder assembly (if that's what you're suggesting) would allow a lot more dust to get in.

The sound recording part is easy. I think there are some SLRs that can do that, for note taking.
--
--Bob

Mike Noren said:

I'd happily give up the
D70 viewfinder for a big, fast, flippable screen. I really, really,
don't see why people are so enamored in viewfinders.

Click to expand...

The reason I see an actual through the lens viewfinder (or actual rangefinder not just viewfinder window) to be 100% crucial for good photographer is that in placing focus or just seeing what's in focus if using autofocus it is much easier with a reflex finder than with an LCD screen. The resolution is too low to judge focus in any sort of critical manner.

Secondly, holding the camera away from your face to view the LCD screen is not nearly as stable a platform as holding it right against the eye. You can shoot with much low shutter speeds when the camera is stable. There are surely sometimes when it might be nice to have the flip-out to see above people's heads at a show or something, but how many good images are really created that way?

Thirdly, and this is admittedly only a personal preference rather than a technical or even quasi-technical reason, when I am looking through the camera I feel as though I am in the scene I am photographing. When I use a flip out screen I feel as though I am viewing it from afar.

I used to really like using the flip-out screen on video cameras, but now prefer to look through the eyepiece--even though I'm still looking at another LCD screen and not truly through the lens.

As far as a reason why video isn't possible with a reflex mirror: it technically isn't, but still won't work with a DSLR. To do it you need a different shape shutter/mirror combination than is used in still cameras. Motion picture cameras use a rotating disk that acts both as shutter and reflex mirror. Half the time it's rotating you are creating an exposure and the other half you see the image. This works with film because discreet exposure are made on a piece of film. On consumer video formats there is no "frame" recorded, only interlaced fields of video. On a video camera there is only an approximation of shutter speed, no actual mechanical shutter.

Also, keep in mind that a 6 mp chip is gigantic for video work. The new Panavision and Arri hi-def cameras have chips approximately this size. The video file would be huge. You might get 10 seconds out of a 2GB CF card. And I doubt the card could handle the transfer rate required to record the information in real time.

I certainly wouldn't want to swap the viewfinder for an LCD, horrible idea as LCD's are less clear, and almost useless for critical manual focus.

However, if my Nikon DSLR could record video at DV camcorder (or better still HD TV quality) to the CF card and provide a user option to record in either AVI or MPEG2 (DVD) format, I would happily pay at least $1000 for the feature on top of the regular DSLR price, as then I could dump a similarly priced camcorder, and use just the one camera to do it all. Of course I'd want the hot shoe to also be an intelligent hot shoe like my Canon Optura Xi, where I plug in a shotgun mic to the hot shoe and it both powers the mic, and also connects the audio signal to the camera without any additional wires.

There are some critical technical hurdles, not least of which is the LCD preview with a mirror reflex, or the darker viewfinder with a half silvered mirror (unacceptable). I think the CCD power and heat could be a major issue, I don't think it's powered as much (or at all?) when not in use, but to run it for an hour for video may take huge amounts of power or overheat - but then again, given that blub exposures can be done this may actually not be an issue. Probably a bunch of other issues around the data path, the bandwidth to the CF card may not be sufficient for AVI level video, especially at HD TV quality, and if you wanted to compress from AVI to MPEG2 that takes some significant CPU power, and thus battery life.

Roland.

dgwynne said:

In the hazy back of my mind I seem to remember the reason for video
not being possible in a DSLR is the mirror/pentaprism redirects
light from the sensor to the viewfinder.

Can someone please tell me, why can the mirror/pentaprism not be
lifted up exposing the CCD, and a 'live' output or even movie
output be shown on the screen and/or captured to card.

Click to expand...

What I've heard is that the electronics don't permit this because the image
buffer is implemented as a supergiant shift register. You've got one agent
feeding the pipeline at one end, and another one grabbing data out by
pulling it from the other end. This is really very clever, because you
don't have wait for contended access to clear. I bet that the D70's great
buffering performance owes its fame to this mechanism. Logically, it's not
hard algothimically to implement this in software (SMOP); it's that it's in
hardware that makes all the difference in speed.

--tom

Roland Wooster said:

Probably a bunch of other issues around the data path, the
bandwidth to the CF card may not be sufficient for AVI level video,
especially at HD TV quality, and if you wanted to compress from AVI
to MPEG2 that takes some significant CPU power, and thus battery
life.

Click to expand...

This is the major hurdle. The file size generated by a 6mp sensor recording 24fps is gigantic and would seriously tax both the capacity and transfer rate of a CF card. You could crop a portion of the center of the chip to record a normal video frame size but all your lenses instantly become telephoto--and I don't think anyone's going to make a 5mm lens in a Nikon mount...

Even if it could be done, it would likely cost much more than $1000 more. A Panasonic DVX100 goes for $3500. The new Sony HDV camera (the prosumer one, not the consumer one) goes for $5000. It only goes up from there. Fancy paying $65000 for a HD camera body and a zoom lens costing anywhere from $15000 for the low end ENG end and $50,000 for a Cooke?

Matthew McDermott said:

Also, keep in mind that a 6 mp chip is gigantic for video work. The
new Panavision and Arri hi-def cameras have chips approximately
this size. The video file would be huge. You might get 10 seconds
out of a 2GB CF card. And I doubt the card could handle the
transfer rate required to record the information in real time.

Click to expand...

You're thinking of getting 6mp @ 30fps. That's not how it would work.

Think about the video produced by the point-and-wait cameras. You only
get VGA or half-VGA frames. That doesn't mean they're not using the
whole sensor; I'm pretty sure they are. I think what's happening is
that many photosites are contributing to a single pixel in the VGA
output. Otherwise you'd never be able to shoot without ambient light
equal to daylight or continuous flash. But you certainly can, and
although the image quality is nothing to put in a picture frame on your
wall, it's still a great deal better than if you shot a still photo
without auxiliarly lighting of some sort.

Mind you, I don't know that this is how it works, but it stands to reason.
Informed corrections welcome.

Since full VGA is 640 * 480 == 307,200 pixels, each resulting frame is
much smaller; commonly used half-VGA is 320 * 480 == 153,600 pixels. At
3 bytes per pixel, half-VGA would be 450k, so at 30/fps second, so it
seems to me that you'd need to be able to support a camera-to-card
transfer rate of 13 megabytes per second of unencoded data. That's not
that rough.

Of course, you still have the problem of fast, real-time MPEG encoding,
which takes non-trivial processing power but produces smaller files. If
that's too much hassle, you could punt and dump raw video frames, the
way Fuji's Finepix cameras do (did?), but that just makes huge AVI files
that somebody is going to have to encode into MPEG for reasonable
storage and convenient viewing by the technically challenged.

--tom

Matthew McDermott said:

Matthew McDermott said:

Probably a bunch of other issues around the data path, the
bandwidth to the CF card may not be sufficient for AVI level video,
especially at HD TV quality, and if you wanted to compress from AVI
to MPEG2 that takes some significant CPU power, and thus battery
life.

Click to expand...

This is the major hurdle. The file size generated by a 6mp sensor
recording 24fps is gigantic and would seriously tax both the
capacity and transfer rate of a CF card. You could crop a portion
of the center of the chip to record a normal video frame size but
all your lenses instantly become telephoto--and I don't think
anyone's going to make a 5mm lens in a Nikon mount...

Even if it could be done, it would likely cost much more than $1000
more. A Panasonic DVX100 goes for $3500. The new Sony HDV camera
(the prosumer one, not the consumer one) goes for $5000. It only
goes up from there. Fancy paying $65000 for a HD camera body and a
zoom lens costing anywhere from $15000 for the low end ENG end and
$50,000 for a Cooke?

Click to expand...

Major hurdle, no doubt about it. but I'm asking for HD TV, not 6MPix!!! I'm asking for 1080 lines, approx 1600 pixels wide, so around 1.7Mpix, at 29.97 FPS. You may well be right about the prices of those HD cameras you list, but I think there are other HD cameras below $2000 now, like the JVC. Actually given the specs of the cameras, the HD cameras seem to only cost $100-150 more than their equivilent spec'd DV Cam brethren, so I don't think it will be too long before you see sub $1000 HD Camcorders.

Roland.

Cameron Habib said:

Cameras are for pictures, camcorders are for movies. Its like
trying to make a swiss army knife that does everything, it just
gets too big and clumsy.

Click to expand...

Since many DSLRs are sold for uses with high frame rates,
the camera and video functions are really quite similar. The
only major addition would be a decent microphone input,
although that circuitry is substantial. Though, I'd go for
30-60 fps bursts at lower resolutions. CCDs can be
shutoff electronically 30x/second, but I'm not sure about LBCAST.

I would LOVE to have a real-time histogram or real-time
digital zoom to check focus.

I would LOVE to shoot DV or HD quality video with the
huge sensor of the Nikon SLR. I still get my best action
stills from my video frame grabs, although the picture
quality pales in comparison to my D2H.

Roland Wooster said:

Major hurdle, no doubt about it. but I'm asking for HD TV, not
6MPix!!! I'm asking for 1080 lines, approx 1600 pixels wide, so
around 1.7Mpix, at 29.97 FPS. You may well be right about the
prices of those HD cameras you list, but I think there are other HD
cameras below $2000 now, like the JVC. Actually given the specs of
the cameras, the HD cameras seem to only cost $100-150 more than
their equivilent spec'd DV Cam brethren, so I don't think it will
be too long before you see sub $1000 HD Camcorders.

Roland.

Click to expand...

The JVC and Sony HDV cameras do technically record a HDTV image but in a much reduced color space than a full HD camera. The Sony looks much better than your average miniDV camera but compared side by side with their multi-thousand dollar HDCAM camera it doesn't look so nice.

Part of my skepticism is that I'm used to dealing with pro-level gear and a sub-$1000 (or even $3000) camera doesn't look too good when projected unless some serious post-work is done to the image, and even then doesn't look nearly as good as the image from the more expensive gear.

You very well may be right that we'll see a sub-$1000 HDV camera sometime soon.

Robert Cohen said:

So you want to remove the mirror and finder assembly so that you
can put another sensor in there which can feed output to the LCD
monitor in real time and record movies? Or you'd like to use a
pellicle mirror (partialy silvered) so that light could go to both
the sensor and the viewfinder all the time for a movie mode?

Click to expand...

The monitoring can be done from the sensor. When each
picture is taken with an electronic shutter (possible on CCD,
not sure about LBCAST) and updated on the LCD - just
like on the P&S cameras.

Robert Cohen said:

People complain now about dust that gets on the sensor and in the
viewfinder. Having a replaceable finder assembly (if that's what
you're suggesting) would allow a lot more dust to get in.

Click to expand...

That's a valid complaint, but it's a risk I'm willing to take.

Robert Cohen said:

The sound recording part is easy. I think there are some SLRs that
can do that, for note taking.

Click to expand...

I'd go for silent video, although I'd prefer a microphone jack.
Audio could also be aquired via the USB input using existing audio
input devices for desktop computers.

So would I, although I'd only pay $1000 for a minimum of medium JPEG
resolution. I would LOVE to do sports shooting at higher frame rates.

Tom Christiansen said:

Think about the video produced by the point-and-wait cameras. You
only
get VGA or half-VGA frames. That doesn't mean they're not using the
whole sensor; I'm pretty sure they are. I think what's happening is
that many photosites are contributing to a single pixel in the VGA
output.

Click to expand...

I guess I've never really considered how a P&S records video. I prefer to keep the two activities (still and motion picture) separate.

Tom Christiansen said:

Otherwise you'd never be able to shoot without ambient light
equal to daylight or continuous flash. But you certainly can, and
although the image quality is nothing to put in a picture frame on
your
wall, it's still a great deal better than if you shot a still photo
without auxiliarly lighting of some sort.

Click to expand...

What's the sensitivity of a P&S shooting video? 320? 500? In either case you can probably get an image down to 10 footcandles or so if you open up the lens all the way--which is a good deal less than full daylight. Maybe the gain gets automatically turned up when shooting video to compensate for the reduced number of photosites being used? I've never considered this one, so I'll crawl back off the limb I'm out on.

Matthew McDermott said:

Matthew McDermott said:

Probably a bunch of other issues around the data path, the
bandwidth to the CF card may not be sufficient for AVI level video,
especially at HD TV quality, and if you wanted to compress from AVI
to MPEG2 that takes some significant CPU power, and thus battery
life.

Click to expand...

This is the major hurdle. The file size generated by a 6mp sensor
recording 24fps is gigantic and would seriously tax both the
capacity and transfer rate of a CF card.

Click to expand...

I'd take the Medium, lowest quality JPG resolution from my D2h.
Most of those pictures are about 300K bytes, so 30 fps would need
a flash card that does about 9 MBytes/second. Though,

you're right about battery life. I'd still pay extra money for a few bursts of 15-30 fps and buy an extra battery or power pack.
Also, I would LOVE to avoid sounding like an UZI, be it a D2h or D70.

How long do you think your batteries would last in your D70 with a LCD viewfinder? One of the reasons DSLR have much better battery life is cause your viewning with mirrors or pentaprism which uses absolutely no power.

Call me crazy but I'd prefer 3 full days of picture taking with one battery using a viewfinder and 3 batteries in one day with a LCD screen and a few movies.

I have both my D70 and Coolpix 3500 which a 3.2 MP and makes videos and trust me batteries die fast!!!

----------------------------------------------------------------------------
Nick M

I think you miss the point. The viewfinder is better than a flip lcd in 99 out of 100 scenarios, but in the last one you don't get a picture at all with the viewfinder, because you're in a crowd and you need a ladder to see what you're shooting, but with a flip lcd, you can watch the lcd, while holding the camera over your head. No one would really use it all the time! The battery drain issue is irrelevant, because 99% of the time you'd still use the viewfinder.

It's a matter of time, we'll see a interchangable lens camera without mirror, but with live preview. Current DSLR line is built on film camera patents, so companies simply need to project totally new body (which costs).

BTW. Next question should be: Why current DSLR do not cover sensor during lens change? To give companies profits from cleaning? I completely do not understand this

hopeless,poor,weak,fairly good,quite nice,spiffy,good,excellent,Nikon



http://www.pbase.com/arra

The sensor is covered during lens change, it is the mirror that is exposed ;-).

arra said:

It's a matter of time, we'll see a interchangable lens camera
without mirror, but with live preview. Current DSLR line is built
on film camera patents, so companies simply need to project totally
new body (which costs).

BTW. Next question should be: Why current DSLR do not cover sensor
during lens change? To give companies profits from cleaning? I
completely do not understand this

hopeless,poor,weak,fairly good,quite
nice,spiffy,good,excellent,Nikon



http://www.pbase.com/arra

Click to expand...

--
ShutterBugin
http://www.exposureproductions.smugmug.com