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Today I received a red dot finder wich I intent to use with 500-1000mm lenses.

It turned out that it has a metal cold shoe, may I mount this on my Sony A7 or would I risk some damage by shorting circuits?

EDIT: I already thought about protecting the contacts with tape to avoid shorts.

I made a macro of the actual situation:

It seems there is a gap between the contacts in question (indicated by the green arrow). The cold shoe should be shifted along the yellow line and pulled up by a mouting screw, so the finder mount must be stoped at the red arrow which should be possible to verfiy by meausring with a caliper?

enter image description here

This shoe of a TTL-flash looks trustworthy:

trustworthy

The contacts were designed to match.

But now this guy seems questionable: enter image description here

The red zone looks dangerous to me, probably it can be mounted other way around and gets blocked at the red arrow from the 1st image. Otherwise there is a lot accessories offered with metal cold shoes and other people don't seem to worry as I do. It 'could' also be that it is safe to mount it because it would take place above the contacs (following the yellow line in 1st image) but I don't dare to risk damgage because of 'could'.

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    Does the cold shoe have a channel in the bottom so that it won't actually contact the pins of the flash interface? A quick search on Amazon shows models that do, but of course I don't know exactly which one you have... – twalberg Nov 18 at 21:21
  • @twalberg Thanks for your quick response, I could not find the same 'svbony' model at amazon.com it seems to be modified by the vendor, but it is made of metal with a flat bottom. – stacker Nov 18 at 21:32
  • Can the portion of the cold shoe that comes near the Sony hotshoe contacts be removed with a grinder or saw? – scottbb Nov 20 at 0:14
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    @scottbb Yes the cold shoe can be removed and cut by an angle grinder. But I already mounted it the otherway around so that the flat edge points to the contacts. – stacker Nov 20 at 7:45
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The hot shoes I am familiar with are designed to accept metal cold shoes. You can tell by looking closely at the shoe on the camera, the contacts will be slightly recessed and only have contact when connecting a device that has contacts meant to push into these recesses.

Also, hot shoes should have a protection circuit in them as well. Cameras can get tossed into some nasty situations.

You should be fine.

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Maybe. To be absolutely sure not to damage your camera, you can place a piece of self-adhesive plastic tape over the bottom plate of the accesory shoe to prevent any electrical contact between the metal plate and the camera contacts.

  • This might not work well with the Sony MIS that OP's A7 has -- there, the contacts are along the front row instead of the bottom. – Nate S - Reinstate Monica Nov 19 at 19:50
  • @NateS-ReinstateMonica I just checked my A7 and the pins you refer to are so deep inside the socket, that unless the utility 'foot' is much longer than standard, something I see no reason to asume, it will not reach these contacts. It is of course possible to wrap the tape around the edge of the foot to make 100% sure that there is also no contact with these pins either. – jarnbjo Nov 19 at 20:47
  • @jambjo, true, if there's no contact, there's no problem, but OP would definitely want to double check that. Tape might work if the connector will still fit, but probably not all tapes would work well for this. Standard electrical tape I'd think would be too thick; kapton tape might work. – Nate S - Reinstate Monica Nov 19 at 20:51
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If it shorts the front contacts, there may be damage.

Your camera uses the Sony Multi-Interface Shoe (MIS), which has a whole lot more contacts than the hot shoes found on other brands.

Sony Multi-Interface Shoe

One pin in particular brings the full, unregulated battery power, with a 1.6A fuse (Pin 17 in the Wikipedia link above). If this pin is shorted to ground (such as the metal shell of the hot shoe), it would certainly blow the fuse, and anything that needs power from this pin would no longer function. It's not clear if this fuse is self-resetting, replaceable by Sony (likely expensive), or not replaceable at all. Other pins may or may not also have problems, but this one we can be sure about -- it's called out in the spec as an unregulated connection straight to the battery.

Of course, if your metal cold shoe doesn't reach far enough back into the mount to make contact with the pins, then there's no problem. But if I were you I'd double check this very carefully before trying it -- perhaps do a test fit with the camera's battery removed.

  • Pin 17 is according to the Wikipedia page you are linking to (and other available documentation on the net) 'switched'. I would understand that as in 'enabled by software command'. The fuse is also most likely a self-reset circuit breaker as commonly used in power supplying computer interfaces like e.g. USB. Otherwise, you could very much risk to fry your camera simply by placing it in a bag next to something conducting, like e.g. a chocolate wrapped in aluminum foil or similar. The slit is wide enough for many unwanted objects to intrude. – jarnbjo Nov 19 at 20:53
  • @jarnbjo, usually 'switched' in this context means that it's only (but always) powered when the camera is switched on -- I'm not aware of any software controls for it. And it could be a self-resetting polyfuse, but I'd think they'd call it that if it were the case. And since it's switched, things getting in there while it's in a bag are not a major concern, assuming you don't turn the camera on with junk stuffed in the hot shoe. – Nate S - Reinstate Monica Nov 19 at 20:59
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    Trying is of course easier than guessing. When I turn on the camera without inserting any device in the shoe, there is no voltage on pin 17. – jarnbjo Nov 19 at 21:22
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Sch*matics of the A*7 exist online, enough said.

Pin 17 is switched from the UNREG_ACC bus via a power MOSFET Q6502 controlled by the IRIS0 pin of the main SOC.

UNREG_ACC is switched by another power MOSFET Q6501 controlled by power controller IC6501 straight off the battery. There is an 1.6 amp fuse F0006 protecting that bus. This fuse does not appear to be self resetting. This fuse does not appear to be replaceable unless you have good SMD soldering skills. There is no evidence of UNREG_ACC powering anything else besides pin 17.

It is likely that a short of Pin 17 while powered would destroy the fuse. It is not likely this would do any further damage to the camera.

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