Q: Why do DSLRs need mirrors and prisms?

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.

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.

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.

Alexander Arnakis wrote:

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.

This would be an enormous step backwards in usability. Why would you want
to be stuck with an LCD when you can have a decent optical viewfinder?

--
Jeremy |

Alexander Arnakis writes:

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.

The main purpose of the mirror is to enable use of the viewfinder.

It would seem a no-brainer to eliminate the mirror and pentaprism
setup, thereby allowing the sensor and LCD to be used for composing

It's not that simple. The sensors used in DSLRs don't support
continuous readout. Instead, they give superior image quality.
Keeping the shutter closed until you press the button also makes for
faster response.

(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.

Yuck.

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.

Another reason is to enable use of a good optical viewfinder.

--
Måns Rullgård

In article ,
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.

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.

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.

The Olympus E-330 has a "live view" LCD that can show what the sensor
sees, as well as using the optical viewfinder.

Check out the setup on the first page of dpreview's review he
http://www.dpreview.com/reviews/olympuse330/
--
-Take out Ron to reply-
My games blog: http://bloggisgames.blogspot.com
GT4 pics slideshow: http://www.flickr.com/photos/dr_bogg...s/162932/show/

On Tue, 23 May 2006 23:45:57 GMT, Alexander Arnakis
wrote:



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.

The main reason to have a DSLR is to allow the use of high quality
interchangeable lenses and to allow you to get the max performance out
of those lenses by using the optical reflex viewfinder which is orders
of magnitude better for composition and focus than a cruddy LCD
display. If you've never looked through one, you'd immediately see the
difference.

On Tue, 23 May 2006 23:49:51 -0000, Jeremy Nixon
wrote:

Alexander Arnakis wrote:

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.

This would be an enormous step backwards in usability. Why would you want
to be stuck with an LCD when you can have a decent optical viewfinder?

Thanks for the reply. I would *like* to have a decent optical
viewfinder, but the one on my Nikon D70 isn't what I would call
"decent" (at least as compared to the viewfinder on my FM2). The D70
viewfinder is dim, and doesn't have any aids for manual focusing. I
think, all in all, that the LCD screen on the back would be more
useful for composing (if only the design allowed for that).

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.

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.

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.

Go to a store. Look in the electronic viewfinder of the best
point-and-shoot they have. Compare what you see to what you see through
the finder of a Digital Rebel XT. Pan rapidly while looking through the
electronic finder.

Someday electronic finders may be able to outperform an optical finder.
They aren't right now.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

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.

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.

Alexander Arnakis writes:

On Tue, 23 May 2006 23:49:51 -0000, Jeremy Nixon
wrote:

Alexander Arnakis wrote:

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.

This would be an enormous step backwards in usability. Why would you want
to be stuck with an LCD when you can have a decent optical viewfinder?

Thanks for the reply. I would *like* to have a decent optical
viewfinder, but the one on my Nikon D70 isn't what I would call
"decent" (at least as compared to the viewfinder on my FM2). The D70
viewfinder is dim, and doesn't have any aids for manual focusing. I

Check if http://katzeyeoptics.com/ has anything that might be an
improvement for you.

think, all in all, that the LCD screen on the back would be more
useful for composing (if only the design allowed for that).

The resolution of the LCD is hardly enough for focusing.

--
Måns Rullgård

Alexander Arnakis wrote:
Jeremy Nixon wrote:
Alexander Arnakis wrote:

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.

This would be an enormous step backwards in usability. Why would you want
to be stuck with an LCD when you can have a decent optical viewfinder?

Thanks for the reply. I would *like* to have a decent optical
viewfinder, but the one on my Nikon D70 isn't what I would call
"decent" (at least as compared to the viewfinder on my FM2). The D70
viewfinder is dim, and doesn't have any aids for manual focusing. I
think, all in all, that the LCD screen on the back would be more
useful for composing (if only the design allowed for that).

The D70 viewfinder is indeed rather dim and small. Supposedly better
than a Rebel XT or D50 though. I'm very impressed with the upgrade to a
D200 from a D70, I can actually focus and evaluate DOF now. It's great!

I used to have a (used, budget) Canon AE1 SLR back in college and one
day a tourist asked me to take his pic with his camera: wow! I don't
know what it was but I remember being amazed at the big bright sharp
viewfinder in that thing! It seemed like a 35mm SLR to me at the time
but I don't know, maybe medium format? A world of diference!

I did use a P&S digicam from 2000-2004 and learned to enjoy live preview
though there are technical compromises (described in other replies). No
doubt though that today's DSLR viewfinders are .66% the size of the old
film SLRs.