Light loss with canon 814

[jacob thomas]

The view down the barrel of a Sankyo XL620:

 

 

hopefully someone can provide a definitive answer as to what it is and how it works.

 

Sorry about the huge picture. :unsure:

Edited July 1, 2007 by jacob thomas

[Mark Dunn]

It's difficult to answer someone who sticks to his own theory of optics and image formation.

The term 'pencil of rays' returns 982,000 Google hits, mostly in optics but incidentally in many scientific fields. It's not a layman's term. Likewise 'partially-silvered mirror' returns 80,700 hits. Lots of info there.

 

Jacob, the squarish part is the partially-silvered mirror which takes part of the image-forming light to the viewfinder and meter. That's why you lose half a stop or whatever. The 'V'-shape is the iris. In an interchangeable lens it consists of a number of leaves which open and close to form a more-or-less circular aperture, but in a built-in zoom it's easier to use the wedge shape. In your photograph it is at full aperture, but in brighter light the 'V' slides up to admit less light, driven by a signal from the meter. A camera with auto-exposure AND interchangeable lenses, such as the Beaulieu, has the aperture driven by a motor.

My Sankyo ES-44XL seems to have partially-silvered mirrors both top and bottom, for finder and meter separately. The brand doesn't matter, of course. They're all much the same.

[jacob thomas]

Jacob, the squarish part is the partially-silvered mirror which takes part of the image-forming light to the viewfinder and meter. That's why you lose half a stop or whatever. The 'V'-shape is the iris. In an interchangeable lens it consists of a number of leaves which open and close to form a more-or-less circular aperture, but in a built-in zoom it's easier to use the wedge shape. In your photograph it is at full aperture, but in brighter light the 'V' slides up to admit less light, driven by a signal from the meter. A camera with auto-exposure AND interchangeable lenses, such as the Beaulieu, has the aperture driven by a motor.

My Sankyo ES-44XL seems to have partially-silvered mirrors both top and bottom, for finder and meter separately. The brand doesn't matter, of course. They're all much the same.

 

Thanks Mark, that was my guess.

[Terry Mester]

This thread reached an impasse quite a while ago now. Is there an authority who you would accept being

corrected by, perhaps they would be so kind as to step in and resolve this somewhat surreal difference of

opinion (on a question of fact).

 

As for partially silvered mirror (often also referred to as pellicule mirror) again check wikipedia:

Thank you Jacob for directing me to the Beam Splitter article. It would have been wise for Mark to

note that the "half-silvered (aluminum) mirror" is just another type of Prism. Most people don't have

the time to study up on every type of Prism used in S8 Cameras. Since aluminum has been used

in Mirrors since early last century, the claim to "silver" sounded dubious to me. This half-silvered

mirror is similar in concept to the one-way mirror used in Front Projection. It should result in less

refraction of light than a Cube Prism.

 

As for the Sankyo Camera Model you posted, that looks like a Prism (half-silvered or otherwise).

My Camera has a Mirror (not a Prism) on the bottom, and I will soon post a picture to prove it.

That unbelievably huge picture you posted proves what I've been saying. The Prism in your

Camera is clearly not in the light path which goes through the Aperture to the Film Gate! It is

the same thing for the Mirror in my Sankyo! Shine a Flashlight through the Eyepiece to further prove

it to yourself!

 

Dawkin also explains how only one image is formed in the eye and not an infinite jumble of

images as you seem to believe: it's called a lens.

I never said any such thing! :o What I noted was that the Rods are integral for the Eye to produce one image

from the millions of Light Rays entering through the Lens.

 

 

 

A simpler analogy for the way the Sankyo Viewfinder Mirror or Prism works is the way your two Eyes see

an image. Each Eye receives a Light Image at a few Degrees of Parallax to the other Eye. This is the exact

same difference between the Light Image which goes to the Viewfinder Mirror and the Image which goes to

the Film. It would be roughly similar to the Parallax between your Left and Right Eyes. The only difference

is that the Light Rays which go to the Mirror are always a few Degrees under 90 Degrees -- whereas both

Eyes receive Light at or about 90 Degrees. Sankyo's Viewfinder Mirror is that simple, and is a lot smarter

than having a Prism in front of the Film Gate. As the picture you posted proves, Sankyo's Prism is also

not in front of the Film Gate. Thank you very much for proving what I've been saying.

 

P. S. When did you get this Sankyo?