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Archive 2008 · Brighten Mirror; Sacrifice AF?

cogitech
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p.1 #1 · Brighten Mirror; Sacrifice AF?

If one was willing to render the AF system in their camera useless, is it possible to modify the mirror in some way to make it 100% reflective (rather than partially translucent)?

Nov 24, 2008 at 02:38 PM

jcolwell
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p.1 #2 · Brighten Mirror; Sacrifice AF?

You could try laying some reflective mylar over the mirror. Its thickness would probably affect manual focus accuracy a bit, but it might let you see how bright it can be.

Nov 24, 2008 at 02:47 PM

cogitech
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p.1 #3 · Brighten Mirror; Sacrifice AF?

Hmmm... mylar...

And the screen could be re-shimmed.... if necessary.

Thanks for the idea!

P.S. I just read that metallized mylar is over 98% reflective.... cool.

Nov 24, 2008 at 02:50 PM

Anden
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p.1 #4 · Brighten Mirror; Sacrifice AF?

Is the mirror easy to change? Then one could have two :-)

Nov 24, 2008 at 03:09 PM

cogitech
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p.1 #5 · Brighten Mirror; Sacrifice AF?

Anden wrote:
Is the mirror easy to change? Then one could have two :-)

No, it isn't, unfortunately.

The plan is to simply have two cameras (at least).

Nov 24, 2008 at 03:12 PM

Ed Sawyer
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p.1 #6 · Brighten Mirror; Sacrifice AF?

Yeah good luck getting mylar to lay flat on the mirror.

Better idea would be get a front-silvered mirror from an older MF cam, and use that if it's the right size. or get a custom front-silvered mirror.

Nov 24, 2008 at 03:42 PM

rgallie
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p.1 #7 · Brighten Mirror; Sacrifice AF?

Subject your 5D to high humidity until the mirror falls off. Then replace with modified mirror.

Make Canon's shortcomings work for you.

Rodney

Nov 24, 2008 at 04:02 PM

cogitech
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p.1 #8 · Brighten Mirror; Sacrifice AF?

It would be sweet if there was a material with the reflectivity of mylar but the properties of that self-adhesive vinyl stuff that adheres to glass and other smooth objects without any form of adhesive. It could easily be cut to size and then pressed onto the mirror, and easily removed with no mess, restoring AF functionality.

Is this another one of my million dollar ideas that I'll do nothing with?

Nov 24, 2008 at 04:05 PM

edwardkaraa
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p.1 #9 · Brighten Mirror; Sacrifice AF?

It shouldn't be difficult for a camera technician to remove the mirror of the 5D, since as Ed mentioned above they tend to fall by themselves, and replace it with a mirror from an old MF camera. I believe older cameras had larger mirrors (and viewfinders) so it will be mostly a job of grinding the mirror to the required size.

Excellent idea by the way! If it works for you, I will be certainly very tempted to do the same on my 1Ds2.

Nov 24, 2008 at 04:36 PM

cogitech
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p.1 #10 · Brighten Mirror; Sacrifice AF?

Hmmm...

I wonder if it would be possible to remove the 5D mirror, take some careful measurements of the mirror frame and then design a mirror "caddy" that could be glued into place where the old mirror was.

The mirror "caddy" would of course be designed with the facility of easily switching out custom mirrors that have been ground to fit inside the caddy. Maybe the mirrors could simply slide into the caddy from the front and then use some clever mechanism to lock the mirror in place...

The wheels are turning. I like that

Nov 24, 2008 at 04:52 PM

asbalyan
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p.1 #11 · Brighten Mirror; Sacrifice AF?

Along with AF, you may loose in-camera metering too... or May be I am wrong...

Nov 24, 2008 at 05:05 PM

cogitech
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p.1 #12 · Brighten Mirror; Sacrifice AF?

asbalyan wrote:
Along with AF, you may loose in-camera metering too... or May be I am wrong...

Since the metering is affected by the type of focusing screen used (well documented) I can only assume that the meter is in the upper part of the chamber, behind the screen, so a 100% reflective mirror would not cause metering to be lost.

You are correct though, that the extra light would likely affect the metering. Hopefully, EC could take care of that.

Nov 24, 2008 at 05:23 PM

asbalyan
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p.1 #13 · Brighten Mirror; Sacrifice AF?

The meeting is effected by bright screen, but reason is very different. Bright screen has different reflective index (both side), so let go more light side the camera body... and so hitting more to the mirror.

If I am not wrong, the metering sensor is below the mirror. I will check, can be easy to find the designs of the DSLRS.

Nov 24, 2008 at 05:29 PM

cogitech
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p.1 #14 · Brighten Mirror; Sacrifice AF?

"The EOS 5D Digital SLR uses the same 35-zone metering
sensor as the EOS 20D, but it has metering functions on
a par with the EOS 1D Series. The sensor and the
metering optics are positioned behind the pentaprism
with the metering lens magnification set to obtain the
optimum correlation between the nine AF points and the
metering sensor zone areas."

Nov 24, 2008 at 05:49 PM

asbalyan
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p.1 #15 · Brighten Mirror; Sacrifice AF?

cogitech wrote:
"The EOS 5D Digital SLR uses the same 35-zone metering
sensor as the EOS 20D, but it has metering functions on
a par with the EOS 1D Series. The sensor and the
metering optics are positioned behind the pentaprism
with the metering lens magnification set to obtain the
optimum correlation between the nine AF points and the
metering sensor zone areas."

Great.. thanks...

(Found the 1-series diagram confirming your text...
http://www.mir.com.my/rb/photography/hardwares/classics/eos/EOS-1n/metering/index.htm )

Nov 24, 2008 at 05:56 PM

robsteve
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p.1 #16 · Brighten Mirror; Sacrifice AF?

Your problem may not be the mirror, but the penta-prism. One of the better SLR viewfinders is the Leicaflex SL and that camera also used a partially silvered meter.

Robert

Nov 24, 2008 at 06:05 PM

Ed Sawyer
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p.1 #17 · Brighten Mirror; Sacrifice AF?

Skip the caddy idea - doesn't the 5D have an existing mirror frame which is why it has clearance issues? Use that - the mirror must be removable somehow. From there, get an existing mirror from an older SLR and grind to 5D size. You can use a diamond wheel on a dremel to do the job, or any type of grinder. I'd use a front-silvered mirror only, since those have the highest reflectivity, but of course are the most fragile to damage.

whatever the attachment method it's going to have to be robust to handle the high-G accel/decel of the mirror slapping up and down 5 times a second or more.

how much is the transmission on the stock mirror? It can't be more than 20% I'd think, probably less. So, not a huge amount to gain here, I'd think...

Consider the EOS-1nRS - that had a 66% transmissive mirror! (Fixed, pellicle) but the viewfinder was still plenty bright (with the screen that came with it, which was brighter than normal screens I think).

-Ed

Nov 24, 2008 at 06:13 PM

cogitech
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p.1 #18 · Brighten Mirror; Sacrifice AF?

robsteve wrote:
Your problem may not be the mirror, but the penta-prism. One of the better SLR viewfinders is the Leicaflex SL and that camera also used a partially silvered meter.

Robert

But nearly doubling the amount of light that reaches the pentaprism would surely help, no?

Nov 24, 2008 at 06:14 PM

cogitech
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p.1 #19 · Brighten Mirror; Sacrifice AF?

Ed Sawyer wrote:

how much is the transmission on the stock mirror? It can't be more than 20% I'd think, probably less. So, not a huge amount to gain here, I'd think...

Isn't it more like 40%?

Nov 24, 2008 at 06:16 PM

cogitech
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p.1 #20 · Brighten Mirror; Sacrifice AF?

Yep, just confirmed it:

"Quick-return half mirror (Transmission:reflection ratio of 40:60, no mirror cut-off with EF600mm f/4 or shorter lenses)"

As seen here:

http://www.canon.com/camera-museum/camera/dslr/data/1995-/2005_eos5d.html?p=2

Nov 24, 2008 at 06:22 PM

cogitech
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p.1 #21 · Brighten Mirror; Sacrifice AF?

Ed Sawyer wrote:
Skip the caddy idea - ....

The benefit of the caddy idea would be to make the mirrors easily swappable. It is a pipe dream, and I'll likely end up with a more permanent method as you describe and then just have a second 5D for AF usage.

Nov 24, 2008 at 06:27 PM

gasrocks
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p.1 #22 · Brighten Mirror; Sacrifice AF?

Why is the mirror not 100% reflective to begin with? What does the amount of light going through it do?

Nov 24, 2008 at 07:42 PM

cogitech
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p.1 #23 · Brighten Mirror; Sacrifice AF?

gasrocks wrote:
Why is the mirror not 100% reflective to begin with? What does the amount of light going through it do?

40% of the light goes through the mirror, hits a 100% reflective sub-mirror (set at an opposite angle) and bounces down to the AF sensors in the bottom of the mirror-box.

Nov 24, 2008 at 07:48 PM

gasrocks
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p.1 #24 · Brighten Mirror; Sacrifice AF?

OK, thanks. I guess I thought AF sensors were up in the viewfinder along with everything else. How is AF done during LiveView with the mirror up? Aren't they working on cameras that will have no mirror at all?

Nov 24, 2008 at 07:55 PM

Daniel Heineck
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p.1 #25 · Brighten Mirror; Sacrifice AF?

they're focusing using the actual sensor and edge contrast (software calculated)

D

Nov 24, 2008 at 07:56 PM


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