100% Silver Mirror

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Archive 2010 · 100% Silver Mirror

RustyBug
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p.3 #1 · 100% Silver Mirror

(Alexandre, you've just been caught not reading the whole thread

)

Dec 03, 2010 at 07:18 PM

cogitech
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p.3 #2 · 100% Silver Mirror

RustyBug wrote:
I was wondering about the old MF Canon's AE1, A1 etc. as possible donors

Sure. Any 24x36 format camera should have a mirror pretty darn close in size. It's just if you wanted to avoid having to grind the replacement mirror... some shopping around might be worthwhile.

Ideally, the replacement mirror would be about 3mm shorter than the original, in order to avoid mirror issues with some of the alt lenses.

Dec 03, 2010 at 07:20 PM

theSuede
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p.3 #3 · 100% Silver Mirror

For starters:

50/50 > 100% gives 1.00Ev more light to AE-sensor > 1Ev underexposure
60/40 > 100% gives 0.73Ev more
70/30 > 100% gives 0.51Ev more

Using an Ee-S but still keeping the "normal" Ec-s setting in the menu will normally result in a "tilted" exposure, giving over-exposure with lenses with a small maximum aperture, and underexposure with lenses with large maximum apertures. This has a pivot point (zero) placed at about F/3.5 as far as I have been able to tell, with no formal testing (just a WHOLE lot of modified screens going through my cameras the last few years). This is only valid for lenses WITH an electronic coupling and full EF compatibility aperture.

If you in stead consider using a lens without electronic coupling (no aperture information to the body) you get a reversal effect - counteracting the normal loss-slope of stop-down metering. Using a more reflective mirror together with a more diffusing screen with equalize the differences between lenses used at different apertures, thus making them more "consistent" over the available aperture ranges.

I'd say the experiment would be highly interesting, never thought of it myself. Maybe I should sacrifice the last D90? :-)

The only thing is that I know just how time-consuming a full mirror-box teardown is, so even if the spare parts are cheap and easy to get some serious work is involved if I botch it. I'd also have to take the trip down to the shop to use the specialized collimating tool needed to get mirror & submirror angles right again after rebuilding it.

I'm not too sure about the sticker-thing though, I think the 5D has a first-surface mirror, and the adhesive on the sticker will quite probably jus rip large parts of the "silver" coating off the mirror substrate when you try to remove it...

Dec 03, 2010 at 07:22 PM

RustyBug
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p.3 #4 · 100% Silver Mirror

I think it would be easier to modify h x w than thickness (flatness) if need be ... only guessing that the old Canon mirrors might be the same thickness as the newer ones ... maybe not

Dec 03, 2010 at 07:24 PM

cogitech
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p.3 #5 · 100% Silver Mirror

theSuede wrote:

The only thing is that I know just how time-consuming a full mirror-box teardown is, so even if the spare parts are cheap and easy to get some serious work is involved if I botch it. I'd also have to take the trip down to the shop to use the specialized collimating tool needed to get mirror & submirror angles right again after rebuilding it.

I'm not too sure about the sticker-thing though, I think the 5D has a first-surface mirror, and the adhesive on the sticker will quite probably jus rip large parts of the "silver" coating off the mirror substrate when you try to remove it...

With the 5D, I don't think an entire mirror-box teardown would be necessary. Hell, the mirrors were literally falling of thousands of them

Hopefully, if done carefully, the mirror removal would not result in any serious deviation in the mirror mechanism. However, the risk is very real.

Regarding the sticker, I didn't mean to suggest trying to remove something that has a strong adhesive, but rather something that has no adhesive at all.

I'd love to get the details of Canon's procedure for replacing all those loose mirrors. I am quite sure they did not perform complete mirror-box teardowns and collomation on all of them. It would be prohibitively expensive for them to do so. This is why I consider this operation "entirely doable". It is just a matter of thinking through it.

Dec 03, 2010 at 07:32 PM

cogitech
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p.3 #6 · 100% Silver Mirror

RustyBug wrote:
I think it would be easier to modify h x w than thickness (flatness) if need be ... only guessing that the old Canon mirrors might be the same thickness as the newer ones ... maybe not

As long as it is the same or thinner, it is all good. Adding more shims under the focus screen is a no-brainer. Just don't go thicker, or you are painting yourself into a corner.

Dec 03, 2010 at 07:34 PM

Bobster2
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p.3 #7 · 100% Silver Mirror

Buy a replacement mirror for the 5D from Canon. Send it to somebody who can strip and resilver it. Actually you probably need to have it aluminized.

Dec 03, 2010 at 07:35 PM

U.C.
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p.3 #8 · 100% Silver Mirror

Bobster2 wrote:
Buy a replacement mirror for the 5D from Canon. Send it to somebody who can strip and resilver it. Actually you probably need to have it aluminized.

Aluminium corrodes like hell, so it won't be bright for much longer than a few weeks. Better get it chromed.

Dec 03, 2010 at 07:39 PM

RustyBug
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p.3 #9 · 100% Silver Mirror

Bobster2 wrote:
Buy a replacement mirror for the 5D from Canon. Send it to somebody who can strip and resilver it. Actually you probably need to have it aluminized.

or just send the current mirror ... buying a replacement later only if wanting to restore to OEM.

Sources ...

Dec 03, 2010 at 07:39 PM

cogitech
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p.3 #10 · 100% Silver Mirror

Bobster2 wrote:
Buy a replacement mirror for the 5D from Canon. Send it to somebody who can strip and resilver it.

Sounds far more expensive that simply using the mirror from a $10 camera.

Dec 03, 2010 at 07:42 PM

cogitech
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p.3 #11 · 100% Silver Mirror

RustyBug wrote:
Bobster2 wrote:
Buy a replacement mirror for the 5D from Canon. Send it to somebody who can strip and resilver it. Actually you probably need to have it aluminized.

or just send the current mirror ... buying a replacement later only if wanting to restore to OEM.

Sources ...

But the current mirror is too big

Dec 03, 2010 at 07:42 PM

Bobster2
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p.3 #12 · 100% Silver Mirror

Silver tarnishes. Aluminum is used for optics.

Dec 03, 2010 at 07:44 PM

cogitech
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p.3 #13 · 100% Silver Mirror

Bobster2 wrote:
Silver tarnishes. Aluminum is used for optics.

Really? I thought chrome was the answer.

Anyway, if you use a mirror from a cheap (or free) camera, then it is a moot point.

Dec 03, 2010 at 07:47 PM

Bobster2
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p.3 #14 · 100% Silver Mirror

Not all mirrors have the same reflectivity. No mirror reflects 100%. Some are more than others. If you find a mirror from an old camera that used to reflect 90% when it was brand new, it's not going to reflect 90% now. A cheap mirror from an old camera is not likely to be better than what you have in a stock 5D.

If you want better, you have to spend money, and have it done by somebody who makes top quality optical equipment.

Dec 03, 2010 at 07:50 PM

U.C.
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p.3 #15 · 100% Silver Mirror

Bobster2 wrote:
Silver tarnishes. Aluminum is used for optics.

Aluminium with a coating (like the foil used in the kitchen) to keep it shiny.

Dec 03, 2010 at 08:24 PM

Ed Sawyer
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p.3 #16 · 100% Silver Mirror

Bobster2 wrote:
Not all mirrors have the same reflectivity. No mirror reflects 100%. Some are more than others. If you find a mirror from an old camera that used to reflect 90% when it was brand new, it's not going to reflect 90% now. A cheap mirror from an old camera is not likely to be better than what you have in a stock 5D.

If you want better, you have to spend money, and have it done by somebody who makes top quality optical equipment.

+1 on this (above).

Silver has the highest reflectivity of various metal (optical wavelengths) first-surface mirrors. Aluminum is a close 2nd. Gold is right up there too. Chrome (WTF!?) is not even in the picture.

All of these have a molecular coating (think transparent anodyzing, essentially) that prevents tarnishing, when used in this way.

Edmund Optics offers custom mirrors in any size, with any of a variety of coatings. Silver or aluminum would be the obvious choices.

If I was going this route, that's where I'd start. They (Edmund) have an amazing catalog, one can learn a lot by just reading it. And there's other providers too.

Ultimately I think this quest is not worth the trouble though. It's based on the (false?) premise that more light reflected from the mirror will increase brightness in the finder. Although that might seem logical it's probably likely that it won't have a big effect, if any. My guess is that the light is throttled from the other things in the system - the focusing screen and the prism itself. Shoving more light through it is not necessarily going to result in a brighter image. (to wit: The effective "aperture" for the focus screen is about f/2.8 or so. Brighter lenses than that don't appear brighter in the finder, and stopping down doesn't darken the finder much if at all between f/1.0 and f/2.8. )

If you really want a bright finder, hack off the prism and build a little hood to use the screen as a waist-level finder, ala medium format SLRs. Probably not any more work than the above idea of replacing the mirror. Of course, a bit more permanant perhaps. ;-)

-Ed

Dec 03, 2010 at 08:25 PM

cogitech
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p.3 #17 · 100% Silver Mirror

Ed Sawyer wrote:

Ultimately I think this quest is not worth the trouble though. It's based on the (false?) premise that more light reflected from the mirror will increase brightness in the finder. Although that might seem logical it's probably likely that it won't have a big effect, if any. My guess is that the light is throttled from the other things in the system - the focusing screen and the prism itself. Shoving more light through it is not necessarily going to result in a brighter image. (to wit: The effective "aperture" for the focus screen is about f/2.8 or so. Brighter lenses than that don't appear brighter in the finder, and stopping down doesn't darken the finder much if at all between f/1.0 and f/2.8. )

I can't agree with this. There is no device in the light path that can "throttle" the input in the way you described. If the focus screen or pentaprism had some sort of photochromic action, then yes. But they don't.

Dec 03, 2010 at 08:32 PM

Bobster2
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p.3 #18 · 100% Silver Mirror

Aluminum foil does not have a coating to make it shiny. It's shiny because it's pressed against polished rollers. It doesn't corrode because there is aluminum oxide that always forms on the surface of aluminum when exposed to air.

Dec 03, 2010 at 09:00 PM

U.C.
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p.3 #19 · 100% Silver Mirror

Bobster2 wrote:
Aluminum foil does not have a coating to make it shiny. It's shiny because it's pressed against polished rollers. It doesn't corrode because there is aluminum oxide that always forms on the surface of aluminum when exposed to air.

Aluminiunoxide ain't shiny.

Dec 03, 2010 at 09:09 PM

Bobster2
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p.3 #20 · 100% Silver Mirror

So?

I didn't say aluminum oxide is shiny. I said aluminum is shiny when it's polished. And the shine is protected by a 4 nm layer of aluminum oxide that keeps it from tarnishing.

Dec 03, 2010 at 09:51 PM

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