Ad
Ad
Ad
Pages: [1]   Bottom of Page
Print
Author Topic: Why the viewfinder blackout?  (Read 3900 times)
PeteC
Newbie
*
Offline Offline

Posts: 13


« on: December 28, 2005, 08:57:48 PM »
ReplyReply

I bought a KonicaMinolta A2 a while ago largely on Michael's enthusiastic reviews, and I'm very happy with it. The Anti Shake, in particular, is brilliant. I don't regret my purchase one bit.

But my brother came up with a point that hadn't occurred to me: why does the viewfinder black out at the moment of exposure? He's got a Fuji S5000 or similar, and it doesn't black out at all.

I hadn't noticed it until he mentioned it because I'm so used to SLRs. But there's no mirror in these digicams, so why do I lose the viewfinder image momentarily?

It's got me upset now. The one thing I find fault with in this camera is the shutter/AF delay and this is part of it.

Cheers,
Pete
Logged
Jonathan Wienke
Sr. Member
****
Offline Offline

Posts: 5759



WWW
« Reply #1 on: December 28, 2005, 09:19:19 PM »
ReplyReply

Reading the image data off the sensor involves moving about 12MB of data off the chip. This takes time, and on the A2 it's enough time to cause a brief viewfinder blackout. Since the EVF/LCD relies on the constant flow of image data from the sensor, it is inevitable that there is an interruption to this data flow while the 12MB of image data is being read. There's no point being mad about it.
Logged

PeteC
Newbie
*
Offline Offline

Posts: 13


« Reply #2 on: December 28, 2005, 09:58:18 PM »
ReplyReply

Quote
There's no point being mad about it.
[a href=\"index.php?act=findpost&pid=54562\"][{POST_SNAPBACK}][/a]

Yes, I should have put a smiley after my "upset" remark. I'm not mad, I just feel that a major advantage of this type of digital capture is the lack of a mirror and this opportunity has been wasted by Minolta. My field is electronics and I still can't see why a read operation should shut everything else down unless there's just not enough processor horsepower. That's what it must be.

Similarly, it seems to me that  a camera based on the EOS RT should be possible with a digital sensor. Just make the sensor sensitive enough to compensate for the loss of light through the half silvered mirror. Voila - no loss of viewfinder, no mirror slap etc. Please?

Pete
Logged
Jonathan Wienke
Sr. Member
****
Offline Offline

Posts: 5759



WWW
« Reply #3 on: December 29, 2005, 12:08:09 AM »
ReplyReply

It's not processor horsepower necessarily, it's the bandwidth of read bus on the sensor chip. The same bus is used for the LCD preview and the still image data, so reading 12MB or so off the chip temporarily diverts all available bandwidth away from the LCD preview.
Logged

Gary Brown
Full Member
***
Offline Offline

Posts: 211


« Reply #4 on: December 29, 2005, 06:33:18 AM »
ReplyReply

Quote
The same bus is used for the LCD preview and the still image data, so reading 12MB or so off the chip temporarily diverts all available bandwidth away from the LCD preview.
[a href=\"index.php?act=findpost&pid=54573\"][{POST_SNAPBACK}][/a]
And even if it were designed to avoid an EVF/LCD blackout, wouldn't the EVF image nevertheless have to "freeze" for the duration of the "download"? If it continued to "expose" the CCD to a live image, it would wipe out the exposed image you just shot, that it's in the process of reading from the chip.
Logged
Jonathan Wienke
Sr. Member
****
Offline Offline

Posts: 5759



WWW
« Reply #5 on: December 29, 2005, 10:15:25 AM »
ReplyReply

Quote
If it continued to "expose" the CCD to a live image, it would wipe out the exposed image you just shot, that it's in the process of reading from the chip.
Exactly my point. The chip isn't designed to provide 2 simultaneous and independent image outputs; it's an either/or thing.
Logged

PeteC
Newbie
*
Offline Offline

Posts: 13


« Reply #6 on: December 29, 2005, 09:38:57 PM »
ReplyReply

Quote
Exactly my point. The chip isn't designed to provide 2 simultaneous and independent image outputs; it's an either/or thing.
[a href=\"index.php?act=findpost&pid=54610\"][{POST_SNAPBACK}][/a]

Um, no, wait a sec. A video camera exposes the sensor and simultaneously reads the result at 60 times per second (50 for PAL). In addition, if it has a variable shutter, it exposes the sensor for as little as 1 mS (1/1000 S) or even shorter. Every frame has to be read in 1/60 second, converted to digital, DV compressed and serialised for recording to tape. Then 1/50 sec later, it does it again. It's not a problem, this is well known technology. There are plenty of A/D converters that work in the MHz range and even at GHz rates for test equipment. Expensive, of course.

Granted, a still camera with an 8Mp sensor has a lot more photo sites than a video camera (Even the latest Sony HDV camera = 1920x1080 = ~2Mp).

It's simply a matter of designing the A/D converter to work faster. That takes more power of course, and still camera batteries are a lot smaller and last longer than a video camera battery.

I think it's simply a matter of power consumption vs battery duration (and price, of course).

Pete
Logged
Jonathan Wienke
Sr. Member
****
Offline Offline

Posts: 5759



WWW
« Reply #7 on: December 29, 2005, 10:06:39 PM »
ReplyReply

Quote
Um, no, wait a sec...
A video camera's resolution is typically 720x480, which assuming 12-bit RAW data is 518400 bytes of data per frame, or 29.66MB/s of bandwidth. A 12-bit, 8MP, 3FPS camera has a bandwidth requirement of 34.33MB/s. Even with an ADC fast enough to handle standard video, there still isn't any room for the LCD preview video when shooting stills.

So to keep up with the still frame rate and preview video without missing a beat, you need an ADC that has some pretty impressive bandwidth specs, something more along the lines of the one found in the 1D-MkII, which can transfer 98.67MB/s (8.2MP/12BPP/8FPS). And the cost and power requirements for such a beast are simply not appropriate for a camera in the A2's class. So you get an ADC that can handle ~30MB/s and a small amount of blackout instead.
Logged

PeteC
Newbie
*
Offline Offline

Posts: 13


« Reply #8 on: December 30, 2005, 07:54:32 PM »
ReplyReply

Quote
So to keep up with the still frame rate and preview video without missing a beat, you need an ADC that has some pretty impressive bandwidth specs, something more along the lines of the one found in the 1D-MkII, which can transfer 98.67MB/s (8.2MP/12BPP/8FPS). And the cost and power requirements for such a beast are simply not appropriate for a camera in the A2's class. So you get an ADC that can handle ~30MB/s and a small amount of blackout instead.
[a href=\"index.php?act=findpost&pid=54706\"][{POST_SNAPBACK}][/a]

Yes, we're saying the same thing: it's a bandwidth/cost/power issue. But the Fuji handles it with no viewfinder blackout (but it's only about 4Mp, I think). It's just something I'll pay attention to next time I buy one of this type of camera. If there is a next time!

Pete
Logged
Bobtrips
Sr. Member
****
Offline Offline

Posts: 679


« Reply #9 on: December 30, 2005, 08:07:01 PM »
ReplyReply

Quote
Yes, we're saying the same thing: it's a bandwidth/cost/power issue. But the Fuji handles it with no viewfinder blackout (but it's only about 4Mp, I think). It's just something I'll pay attention to next time I buy one of this type of camera. If there is a next time!

Pete
[a href=\"index.php?act=findpost&pid=54804\"][{POST_SNAPBACK}][/a]

It's not necessarily a function of 8 megs vs. 4.  The same blackout occurs with the 5 meg K-M A1.

I suspect a design choice.

Perhaps to make the A1/2 more "SLR-like".          
Logged
Pages: [1]   Top of Page
Print
Jump to:  

Ad
Ad
Ad