Front-Silvered Mirror

CMoore · Sep 4, 2019

I suppose it could be ANY camera, but i chose the 35mm.

Why is the flip up mirror made with Front-Silver.?
Would there be a problem with using a "traditionally" constructed mirror.?
Thank You

mike c · Sep 4, 2019

Back surface mirrors have distortion as the light travels thru the glass and also flare as the light rays enter and leave the glass surface.

ciniframe · Sep 5, 2019

On a back surface mirror there are two reflections, a faint one from the front surface and a strong one from the silvered bottom surface.
These will show a double image offset in an amount proportional to the thickness of the glass.

Hard to focus GG image will be the result.

AgX · Sep 5, 2019

The amount of lateral offset between the two rays is dependant on the thickness of the glass. It thus is a constant per mirror.
However the ratio of this constant off-set to the image width at the film plane varies by the location of the mirror!
That is why in the past at cameras nevertheless thick mirrors were used or even thick and foil mirrors combined.

Ian Grant · Sep 5, 2019

There's no difference in making/coating a front or rear surface mirror, rear surface mirrors usually have a protective layer painted over the coating,

These days most mirrors are Aluminium coated rather than Silver, and a thin Silicone layer isnadded to front coated mirrors for protection, I get mine made in London for restoring early MF/LF SLRs. The company I use will either strip clean an existing mirror (just dip in Nitric acid to remove the Silver, or cut a new one.

This shows clearly why Silver is not the best long term solution, it's the mirror from a Quarter plate Thornton Pickard Ruby Reflex, Most post WWII screens are probably Aluminium coated. Vacuum coating mirrors will be a spin off of optical coatings. Silver coatings were a dip/paste process.

Ian

Helinophoto · Sep 5, 2019

Making a new mirror, with front surface is not a very complicated task.
I tried to use rear surface mirrors in my rolleiflex and the effect is that you will get ghosting due to the internal reflections in the glass. You also move the area of reflection (focus issues) back by the thickness of the glass itself.

Check my blog-entry here, on how to make your own front-surface mirror, it was really an easy job.
http://helino-photo.blogspot.com/2016/04/making-new-mirror-for-rolleiflex.html

CMoore · Sep 5, 2019

Very Interesting...Thanks for the info.
I had no idea that a "normal" mirror would present these types of problems in a camera.
Thanks Again

CMoore · Sep 5, 2019

ciniframe said:
On a back surface mirror there are two reflections, a faint one from the front surface and a strong one from the silvered bottom surface.
These will show a double image offset in an amount proportional to the thickness of the glass.

Hard to focus GG image will be the result.

Sorry, i did a search....... What is a GG Image.?

MattKing · Sep 5, 2019

CMoore said:
Sorry, i did a search....... What is a GG Image.?

That would be Ground Glass image - more often referred to this way by those who use large format cameras, but it applies equally to roll film (and DSLRs for that matter).

AgX · Sep 5, 2019

And it is not only about finder images. For instance in colour seperation beam-splitter cameras mirrors (and their flaws) are part of the exposing ray-cone. (I hinted at that above.)

Arklatexian · Sep 5, 2019

AgX said:
And it is not only about finder images. For instance in colour seperation beam-splitter cameras mirrors (and their flaws) are part of the exposing ray-cone. (I hinted at that above.)

Not to mention astronomical "reflecting" telescopes. Since WW2, most use mirrors that are aluminum coated after the mirror is ground to the desired shape. AS has been mentioned this process is done by vaporizing a piece of aluminum in a vacium, not by chemical means.......Regards!

AgX · Sep 5, 2019

And we use such lenses, typically in shorter focal lengths and with high pitch helicoid, on our cameras too.

Let alone the milions of cameras for Polaroid integral film wich need an image reversal.

Front-Silvered Mirror

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