Re: Q: Why do DSLRs need mirrors and prisms?
- From: "John Falstaff" <not@xxxxxxxxxx>
- Date: Thu, 25 May 2006 18:36:15 -0400
"cjcampbell" <christophercampbell@xxxxxxxxxxx> wrote in message
news:1148430342.117336.70710@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Alexander Arnakis wrote:
Maybe this question has been discussed here before, but I'll ask
again:
Other than being a holdover from the film SLR design, what is the
reason that DSLRs still have mirror boxes and pentaprisms? It seems
that the main thing a mirror (on a DSLR) does is block the sensor so
that the LCD screen can't be used for composing.
If it did not have a pentaprism, it would not be a reflex camera, would
it? You would have to call it something else.
Well, not exactly. The "reflex" implies a mirror, but not necessarily a
pentaprism. There were single- and twin-lens reflexes for many years before
the first pentaprism came along.
It would seem a no-brainer to eliminate the mirror and pentaprism
setup, thereby allowing the sensor and LCD to be used for composing
(like on a point-and-shoot). If an eye-level viewfinder is necessary,
then a second electronic display can be incorporated, like on a video
camera.
That would be a no-brainer, all right. Just as jumping off a cliff is a
no-brainer.... :-)
Of course, having the LCD on all the time would greatly reduce battery
life and it would introduce a lag between what is happening in front of
the lens and what you see in the LCD. If you don't believe it, just
wave your hand in front of the lens on a point and shoot. You will see
that there is a very noticeable delay between the movement of your hand
and its display on the LCD. That time delay represents the difference
between getting a picture of a deer and a picture of a deer's tail. The
whole point of the DSLR is speed and flexibility. You lose that the
moment you start composing with the LCD.
It would seem that the main reason to have a DSLR is to enable the use
of high-quality interchangeable lenses. Having interior mechanics that
emulate film SLRs is irrelevant.
Not so. The main reason for the DSLR is speed. Interchangeable lenses
are secondary.
The *main reason* for any SLR, historically, is absence of parallax --
seeing the image in the viewfinder (or focusing screen) as formed by the
lens, so just as the film (or sensor) will see it. Since the LCD monitor of
almost any non-SLR digital camera does that reasonably well (if relatively
coarsely, and as you say with some slight delay), the dSLR's advantage in
this characteristic is much diminished, and the advantages of lens
interchangeability, speed, and lower noise become more important.
Any of these things may be "the main reason" for any particular user, and
only he can define it. I don't buy a dSLR primarily for speed, so that's not
"the main reason" for me. Lens interchangeability is much more important to
me.
.
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