The REAL scoop on MX!

Started Nov 9, 2008 | Discussions thread
Bernard Languillier Veteran Member • Posts: 4,672
Thanks

Joseph S Wisniewski wrote:

Bernard Languillier wrote:

Joseph S Wisniewski wrote:

3. New lens line but will work with older ff lenses.

Do you think the new camera is going to be a pure EVF (or EVIL:
Electronic Viewfinder, Interchangeable Lens) camera without an SLR
optical viewfinder?

The back focus (minimum distance between rear element and sensor) for
FX is 39mm. That was determined 5 decades ago by the arc the mirror
made when it swings.

For an SLR, making the sensor larger means making the mirror bigger,
which means increasing the back focus.

The only way to make this work is to do like Panasonic did with Micro
Four Thirds, do away with the SLR mirror. Personally, I'm ready for
this, but I don't think the camera buying public is...

  • What if the mirror doesn't move? Canon used to make a super fast

body with a pellicular mirror,

Canon made at least three variations. I have one in my collection.
Nikon made one, also. I do not have one of those.

If you're proposing the pellicle mirror because you believe that pros
will not like the EVF, I'd counter with the pellicle being so much
worse than the EVF it's really not a valid solution.

1) Pellicle mirrors are close to the sensor at the top edge. So they
bring dirt into sharp focus, especially when you stop down (just as
sensor dirt becomes more visible at small apertures).

2) They let light into the camera through the eyepiece. They were
only suitable for applications where you have the camera to your eye,
and you're using large apertures so the ratio of viewfinder light to
lens light remained low. Stop down to f22, and the viewfinder
dominates. You'd need a fast electrically driven eyepiece shutter.

3) They are too thick. The Pellix used a 20 micron film. That was
fine when your concern was shooting sports with pushed Tri-X for
newspaper reproduction. But on digital, 20 microns puts the rear
surface ghost reflection two whole pixel widths away from the main
image. You'll see ghosts...

4) They get dirty easily, and are near impossible to clean. They're
not like a sensor, which is usually vertical, so gravity keeps a lot
of stuff from sticking. They're slanted at 45 degrees, so they pick
up everything.

5) They are fragile. The sensor cover glass is, well, glass: 7 moh
hard, can be cleaned with a spatula covered with a wet pad. I'd say
that most photographers lack the skills to clean a pellicle mirror,
and a good percentage lack the physical dexterity to not poke their
cleaning tool right through it, or press it hard enough to stretch it.

6) They consume a great deal of light. The Canon mix, if I recall,
was 30% reflective, which made the viewfinder two full stops dimmer
than a non-pellicle camera.

7) They rot. It's unusual to find an old Canon Pellix with the mirror
reasonably intact.

8) For an AF camera, you still need a "popup" secondary mirror for
the AF system. On a "conventional" SLR, the secondary mirror is as
large as possible, because it anchors to the main mirror. A pellicle
camera requires a smaller mirror, because it has to keep well clear
of the pellicle.

9) Any lens that moves the rear elements when focusing or zooming
temporarily deforms the pellicle until the camera vents enough to
equalize pressure. That vent will suck in water, making a
weatherproof camera difficult, and making it more vulnerable to water
infiltration than a non-vented camera.

Thanks for the feedback Joseph.

A very similar conversation must have taken place a few years back in a Nikon R&D center office... we might find out on the 20th whether Nikon engineers went this way or not, and whether they found some solutions to the valid issues you list up.

There are other options besides pellicular mirror that reduce the space used by the mirror box also

Cheers,
Bernard

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