What does this lever do in the EOS mount?

sandermarijn · Jun 16, 2012

Anybody know what this lever does?

I thought that the EOS system is fully Electro-Optical, but obviously this lever must be useful for something.

I have noticed that if you push the lever upwards and simultaneously press the shutter release that the mirror will flip up while the shutter remains closed. Holding the lever in the upwards position and pressing the shutter release once more makes the mirror go down (but the shutter still does not fire).

Could it be that this feature is there for technicians wanting to get to the front side of the shutter? Or is there a more obvious, picture-taking-related explanation? I've searched the web but nothing's shown up to explain.

Thanks for any help,
Sander

ath · Jun 16, 2012

I think it just drives a switch and is activated when a lens is mounted.

sandermarijn · Jun 16, 2012

And what would the function of that switch be? To let the camera know when a chip-less lens is attached?

But then why the funny mirror up/shutter closed behaviour?

flatulent1 · Jun 16, 2012

With no lens mounted at all, the camera operates normally.
With a Zeiss C/Y lens mounted via an adapter, my camera operates normally.
With a Mamiya 645 lens mounted via an adapter, my camera shuts down and refuses to play along.

This switch doesn't exist on digital EOS that I'm aware of. Folks selling Mamiya lens adapters on ebay generally say they are compatible with EOS digital, and say nothing about film bodies. One seller linked to a series of photos showing this switch pushed up and a wad of paper placed in the slot as the way to get adapter compatibility with film cameras. I couldn't get it to work for me. And I have no idea what this little switch does.

sandermarijn · Jun 16, 2012

Ah, interesting. The thing is, I purchased a Leitax adapter for my favourite Leica lens (I have only one anyway), the 35-70/4. All my EOS bodies (I have no digital EOS) refuse to fire (the mirror goes up, no shutter release) with the adapted lens mounted.

At first I thought of mirror jam against the adapter or the rear element, or the electrical contacts of the camera shorting against the adapter, but then I noticed how the flange of the adapter pushed up this funny little lever. I filed off some of the adapter's flange so that the lever stays put, and all seems well now.

The question remains though, what is this lever for?

sandermarijn · Jun 16, 2012

There is one slightly cryptic remark on the leitax site (http://leitax.com/Leica-lens-for-Canon-cameras.html):

"Our Leitax mount will trigger the AF switch in 1D series bodies."

Indeed, the lever/switch is present on the 1Ds also (Dead Link Removed), although not on e.g. the 5DmkIII (http://www.dpreview.com/reviews/canon-eos-5d-mark-iii/images/sensor.jpg).

So, sticking to the Leitax vocabulary, this is an "AF switch". Isn't such a thing on the lenses already? Puzzling.

ambaker · Jun 16, 2012

It was on the earlier EOS bodies. You can stick a bit of paper in there to trigger it. The older bodies want to see it activated. I forget where I found this info, it's been a year or two. But that is the gist of it. The early EF lenses had a lobe on the mount that would press the switch.

ambaker · Jun 16, 2012

Found part of the discussion here....

http://photography-on-the.net/forum/showthread.php?p=12443702&highlight=Switch#post12443702

It's on page 628, if the link does not take you right to it. It turns on the auto focus when an EF lens is mounted.

sandermarijn · Jun 16, 2012

Thanks ambaker, that's very useful information. I tried to google for more on this but the search terms I can think of are too generic to yield relevant results.

My take is that the camera gets confused when the "AF micro switch" (or what you call it) is activated by a lens or mount that doesn't autofocus. The camera decides to lock up, not knowing what to do with the conflicting information. Maybe the camera is waiting for some sort of AF confirmation or feedback that never comes, and thus gets caught in a perpetual loop.

Advice to self and others: on cameras with the "AF micro switch", do not use non-CPU lenses/adapters that trigger the switch.

Dennis S · Jun 16, 2012

I do know the tab that engages that lever on the adapter must be filed down on M-42-EOS for it to work. I use an EOS 3 with a Helios 44-2/58 lens

sandermarijn · Jun 17, 2012

Yeah, retrospectively I may have had this same problem before with at least one other adapter (OM-EOS), but I simply did not recognize the issue at the time.

Still wondering what the purpose of the tab/switch/lever is. EOS is all about electronic communication, right? It just seems odd to have a switch when you already have contacts. Historical reasons? Hm, the EOS system was all new from scratch, no legacy issues involved. Strange.

pekelnik · Jun 17, 2012

There might be a relationship between this and my battery draining problem: (there was a url link here which no longer exists)

Peltigera · Jun 17, 2012

Of my three EOS film cameras, it is only present on the 50e but not on the 300 or 500n. All of my lenses (from old to bought this year) work will my three EOS film cameras and with my EOS digital. As do my entirely contactless extension tubes.

As the mirror stays flipped up and the shutter stays closed until the shutter release is pressed again, I can only assume this is for maintenance. There would be no point in turning the AF system on if the mirror is always up and the shutter always closed.

flatulent1 · Jun 17, 2012

Is it possible that triggering this switch is something we DON'T want? I'm going to play with that today, see if I can make a body NOT work with my C/Y adapter.

sandermarijn · Jun 17, 2012

If the switch is for maintenance purposes only, then why did Canon not add some electronic MLU feature instead? The switch is just too clumsy, too mechanical, too not EOS.

Fred, I was actually wondering the exact opposite: will not triggering the switch leaves us out of something we do want?

I am baffled that nobody here knows what this switch is for (or wants to tell us ). Of course it doesn't help much that only the older & higher-end EOS cameras have the switch.

I'll do some more googling if I feel like it (bit tired of getting a zillion results on DSLR AF fine tuning and what else ).

Tony-S · Jun 17, 2012

sandermarijn said:
Anybody know what this lever does?

It connects to the flux capacitor found in all EOS cameras.

sandermarijn · Jun 17, 2012

pekelnik said:
There might be a relationship between this and my battery draining problem: (there was a url link here which no longer exists)

Check if the adapter triggers the switch. If so, maybe you can measure the current draw without the adapter in place but with the switch forced up.

How did you measure the draw? Take the battery out of its housing, connect it to the camera with some wiring, and then measure the current? Did you tape the wiring to the terminals? Fiddly affair.

sandermarijn · Jun 17, 2012

Tony-S said:
It connects to the flux capacitor found in all EOS cameras.

Hm, not sure I understand what that means. Can you describe what the switch and the flux capacitor do in terms of practical functionality?

sandermarijn · Jun 17, 2012

You don't mean this flux capacitor, do you? http://en.wikipedia.org/wiki/DeLorean_time_machine#Flux_capacitor

Tony-S · Jun 17, 2012

sandermarijn said:
You don't mean this flux capacitor, do you? http://en.wikipedia.org/wiki/DeLorean_time_machine#Flux_capacitor

ambaker · Jun 17, 2012

If your adapter has a compatible focus confirm chip, then you would want to activate the switch when it is mounted,

If your adapter does not have a compatible focus confirm chip, the opposite would be true.

In theory, the switch should not be a source of battery drain. If a regular EF lens were mounted, then the same thing should happen. The camera should be shutting down, when not in use, switch on or off. But then I turn my cameras off at the main switch, just to be sure something isn't pressing on the trigger, activating the camera when it is in the bag.

pekelnik · Jun 17, 2012

Yeah, I got a wire between the + and - of the battery somehow. I remember it wasn't pretty. Now I checked all my lenses and adapters. Some chipped adapters (nikon-EOS and M42-EOS) have a short bayonet piece there, that probably doesn't flip the switch (don't know if they do or don't drain the battery). My chipless Samyang has a long one (and doesn't drain battery) and my chipped OM adapter has a long one too and does drain the battery. I'll do some more tests later this week.

flatulent1 · Jun 17, 2012

sandermarijn said:
Still wondering what the purpose of the tab/switch/lever is.

I'm going to ask the local camera tech when they open on Tuesday.

In the mean time, I ground down the piece on my Mamiya adapter that was activating the switch (thanks, DWC, dunno why my brain couldn't sort that one out) and it works on the EOS 3. Next task is to take some actual pictures with a real lens mounted.

Poisson Du Jour · Jun 17, 2012

Lens mount index confirmation. The flange engages here and pulls it up, thus confirming with the body that the is in the correct position and electronic control state is readied.
It's best not to fiddle with it.

Dennis S · Jun 18, 2012

I have been using the M-42-EOS adapter for some time on my EOS 3 HS and have not seen any problems with battery drain . I am using 8x Eneloop batteries since Febuaryish and are still fully charged after 4-6 rls per month. I also have forgotten to shut if off in between times. Why Canon did not install a automatic shut off makes me wonder sometimes.

What does this lever do in the EOS mount?

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