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Archive 2010 · 100% Silver Mirror
  
 
Daniel Heineck
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p.5 #1 · p.5 #1 · 100% Silver Mirror


Bobster2 wrote:
I'm not sure. The dielectric is supposed to be more efficient and lasts longer than silver. But I guess you're right, it's only for beam splitters.


Dielectric mirrors are capable of more selective bandwidths and higher reflectivity, but they're certainly not *just* for beam splitters. That said it's expensive putting 100's of layers down so typically we don't see big optical parts using dielectric mirrors. Those get aluminized instead.




Dec 04, 2010 at 05:57 AM
RustyBug
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p.5 #2 · p.5 #2 · 100% Silver Mirror


Bobster2 wrote:
Note that Canon does not specify the reflectance of the 5D mirror. All they give is the ratio of transmission to reflection which is NOT the same thing because they are not specifying how much of the light is lost (neither transmitted nor reflected). So all we can do is guess. My guess for reflectance is only 50% but it would be nice to have actual data.



Good point, but even assuming no additional losses ... does this make sense / hold true?


60:40 mirror scenario:
10 Lumens hits the mirrror, then @ 60:40 ratio, 6 Lumens hits the VF (and the meter compensates correctly) while 10 Lumens hits the sensor when the mirror flips out of the way.

100:0 mirror scenario:
10 Lumens hits the mirrror, then @ 100:0 ratio, 10 Lumens hits the VF (and the meter does not compensate correctly) while 10 Lumens hits the sensor when the mirror flips out of the way.



Dec 04, 2010 at 06:06 AM
carstenw
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p.5 #3 · p.5 #3 · 100% Silver Mirror


I haven't seen this mentioned so far, but wouldn't it be very important to find a replacement mirror of very close to the same weight? I presume that the mechanism is no stronger than necessary, and that the periods of any bounces in the travel path are very carefully tuned not to interfere with the photo taking or the visual experience.


Dec 04, 2010 at 12:31 PM
AhamB
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p.5 #4 · p.5 #4 · 100% Silver Mirror


Bobster2 wrote:
The SLR mirror is not silvered. It's made with many layers of dielectric material, to cause constructive and destructive interference of the light waves.


That's called Bragg reflection.



Dec 04, 2010 at 12:53 PM
cogitech
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p.5 #5 · p.5 #5 · 100% Silver Mirror


carstenw wrote:
I haven't seen this mentioned so far, but wouldn't it be very important to find a replacement mirror of very close to the same weight? I presume that the mechanism is no stronger than necessary, and that the periods of any bounces in the travel path are very carefully tuned not to interfere with the photo taking or the visual experience.


I've considered this, and I have not been able to come to any conclusion because I do not know much about the design of the mechanism. What I do know is that my mirror mechanism has withstood countless collisions with various lenses over the years with no ill effects, not to mention the shaving process that I subjected it to.

I suspect, if the replacement mirror is say 50% heavier, that the mirror lag might be affected and this may lead to extra mechanism wear over the long term and possible impact to the photos and the viewer's experience.

It is possible, however, that the mirror mechanism design is able to carry thrice its weight with no ill effects.

It is also very unlikely that the replacement mirror would be 50% heavier than the stock mirror (but this is an important measure to consider when selecting the replacement).

One option would be to remove the submirror, which would reduce drag and compensate for some of the added drag/weight in the new mirror.



Dec 04, 2010 at 01:30 PM
theSuede
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p.5 #6 · p.5 #6 · 100% Silver Mirror


Returning to practical, optical matters and the viewfinder picture - I see only good things with replacing the mirror with something of higher reflectivity. If you don't mind loosing AF of course.

version "A", with the standard screen
1) VF brightness increases with about 0.7Ev
2) Base camera exposure compensation (is there such a thing in the 5D classic?) will have to be lowered
3) otherwise NO CHANGES from original.

version "B" - with an Ee-S - compared to standard mirror/screen
1) F/1.4 to F/2.8 will be BOTH brighter and with better (more realistic) DoF, making it easier to focus
2) In stead of losing a full Ev of VF brightness at F/5.6 with the Ee-S, you loose almost nothing. The VF will be almost exactly as bright now as with the standard/standard solution
3) Manual lenses without electronic aperture information will behave more linearly in AE, ie - they will not change their aperture-dependent plus/minus AE correction nearly as much as with the standard screen. F/1.4 will still underexpose (by a tiny bit probably), and stopped down metering at F/11 will still overexpose in A-mode, but not nearly as much.



Dec 04, 2010 at 11:26 PM
Ed Sawyer
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p.5 #7 · p.5 #7 · 100% Silver Mirror


It's time for less armchair engineering and more practical DIY. Someone should order up a mirror from Edmund or elsewhere and give it a whirl.

I suspect the canon mirrors are not coated on glass, but more likely polycarbonate of some type. Replacing that with a glass one would definitely affect weight the mechanism has to handle, I'd think. Could be wrong on the plastic vs. glass though - for those like Paul who ground them, they could tell for sure.

overall though I still think it's way more trouble than it's worth.

If you want bright, try out an aerial image screen. ;-) (like an Olympus OM 1-12 screen) now *that's* bright. A bit tough to focus in non-macro situations though.

-Ed



Dec 05, 2010 at 04:55 AM
Daniel Heineck
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p.5 #8 · p.5 #8 · 100% Silver Mirror


Ed--it's definitely glass not polycarbonate. Plenty of folks sell 1mm thick 25mm or 48mm square enhanced aluminum or silver (enhanced meaning they put other coating on for higher quality) mirrors. Should work fine.




Dec 05, 2010 at 05:24 AM
amade1974
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p.5 #9 · p.5 #9 · 100% Silver Mirror


btw, the reflecting surface of the mirror is behind the glass. this would have to be maintained in order not to lose 2mm of the optical path.
if you coat the back of glass with aluminum, the oxide would form on the side exposed to air, and not the glass, therefore your mirror would stay shiny...



Dec 05, 2010 at 07:31 AM
Ed Sawyer
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p.5 #10 · p.5 #10 · 100% Silver Mirror


I think camera mirrors are front-surface, not rear surface...


Dec 05, 2010 at 03:22 PM
 

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cogitech
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p.5 #11 · p.5 #11 · 100% Silver Mirror


If my wife didn't rely on AF sometimes, I'd be ripping into this project right now. I am so eager to put all this theory into practice and clear up some of the debate. I do believe that theSuede's theoretical assessment of the benefits will prove true and, if so, it would be a very worthwhile mod for me personally.

Is anyone with a 5D, sufficiently sized cajones, and nothing better to do going to go for it, or what?



Dec 05, 2010 at 04:38 PM
Ardea
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p.5 #12 · p.5 #12 · 100% Silver Mirror


A front coated Silver mirror would tarnish quite fast. It would be best with a rear coated mirror though. For front coating, Aluminum coating is the way to go. When I ground my 8 inch telescope lens I had it Al coated by a company in California that coats optical lenses and mirrors. Sorry I can't find the link but try googling astronomical mirror coating...

Regards, Richard



Dec 05, 2010 at 05:48 PM
ZoneV
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p.5 #13 · p.5 #13 · 100% Silver Mirror


Thread slept 8 months, but I suppose no one here has done it until now?

My 5D lost its mirror two weeks ago, at the moment it is only taped inside the camera :-)
Some seconds after I saw the mirror has fallen out of its frame, I thought about a ~100% reflective mirror. And about mirror shaving.
Today I found this thread, and read wheter others are thinking its a bad idea - seems not.

Last weekend I salvaged two old SLR cameras, on mirror broke - but that one was too thick.
The other one seems to be good, need to clean the glue from the backside. And I need to do that very carefully, without breaking it, probably I should use a bigger UV filter as a base plate for that work.

Thought about changing the focussing screen as well, to get a split screen EE-S alternative, but those I got are to small, relative to the normal 5D screen. But probably not the whole size is needed, have to analyse the metal frame.



Aug 01, 2011 at 09:51 AM
cogitech
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p.5 #14 · p.5 #14 · 100% Silver Mirror


I look forward to hearing how your mirror replacement goes, ZoneV.

I have been far too busy to even take photos, much less do camera mods, but I will try this mod some day...



Aug 01, 2011 at 09:05 PM
ZoneV
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p.5 #15 · p.5 #15 · 100% Silver Mirror


At the moment I am not sure if I could recommend one to do this with an intact EOS 5D.
The get the mirrors out of their frame on the donor cameras wasn't exactly easy. Or let it say not only with small gentle force. Not sure how good the 5D mirror normaly glued into.


Edited on Aug 01, 2011 at 09:52 PM · View previous versions



Aug 01, 2011 at 09:14 PM
MichaD
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p.5 #16 · p.5 #16 · 100% Silver Mirror


They fall off without even trying on occasion. Yours is definitely not the first, so...


Aug 01, 2011 at 09:17 PM
ZoneV
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p.5 #17 · p.5 #17 · 100% Silver Mirror


Yeah, but if my mirror went off alone, I would have tried to get it away. And with the EOS 5D mirror frame, it seems even a bit harder to get it away than with my donor cameras - there I could get between mirror and frame with a thin knife.

My donor mirror is 0,02mm thinner as the 5D mirror - but that could be measurement tolerance (caliper, not micrometer). But I have to make it 2,5 mm smaller - the EOS 5D mirror has not even 36mm width! Height is some 2 mm smaller on the donor - so I need no shaving on this side (on the glass). At the moment I am not sure if I better grind or break the glass. In my experience with 2 mm thick filter glass, grinding is most time safer, but the edge looks worse. Not sure if this 1 mm filter break, as soon as I have a small angle. Or if I even should think about taking that mirror between two thicker glass sheets, and grind them together. But that is too much effort.
Stop working, its about midnight.



Aug 01, 2011 at 09:40 PM
ZoneV
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p.5 #18 · p.5 #18 · 100% Silver Mirror


By the way, do you have ideas / wishes how to show / measure the brightness difference?
In that camera I have the normal focusing screen inside.

Thought about simple measurement with exposure meter (and a lens attached at camera, infinity setting and definied iris setting. Indoors with long burning illumination, from tripod).

For the first try I will not glue it, but use tape. Has to test how I could perform a measurement without influence of taped area.



Aug 01, 2011 at 09:51 PM
mMontag
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p.5 #19 · p.5 #19 · 100% Silver Mirror


Sounds like a great project - I've been waiting for my 5d mirror to fail so I can exercise my "Alt" options.

ZoneV - you may want to check weight of the second mirror - hard to find an accurate scale for that light of weight - any friends that work in a laboratory? A weight difference may mess with getting the mirror out of the path fast enough.

Good luck!
mM



Aug 03, 2011 at 01:26 AM
ZoneV
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p.5 #20 · p.5 #20 · 100% Silver Mirror


I suppose that the new mirror would have even a bit less weight: Glass should have about the same specific weight, and it is (or getting) some 2x24mm smaller. The new mirror has about the same thickness, probably a bit thinner.

At the moment I think that it is probably useful to do the grinding between other hard material. That mirror is pretty thin.
I think I could do it probably on Friday (because of lout sound)



Aug 03, 2011 at 05:30 AM
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