How to carry OM-D E-M5 to be accessible when backpacking?

Yep, I understand - but will stay away from replying about a specific gear or pouch recommendations and speak to "where" to put it - and "size / shape / bulk" - and weather resistance - having hiked and backpacked a bunch...

First, figure out what body and lens you think you "have" to have - go small and light if possible - then pick a thinner, smaller, low-bulk pouch to fit.

In general, I've avoided bags and pouches that are "overbuilt" - but to each their own.

As to "shape" - well, the less it protrudes from a harness or waist belt (or wherever) in any one direction the better, as you will not like it being in the way as you move through your hike.

I've had good success with my solutions - use trekking poles - and often forget I even have a camera pouch on - especially once I enter the Zen of moving miles down the trail - and THAT is nice.

Worried about protection and weatherproofing?  Find something with thinner padding - or add your own (like foam packing sheets) - and take along a zip-lock bag - or such - for when the weather turns.

In-pack, on-the-back solutions haven't worked well for me - as I like a cam to be in very quick easy reach - without having to stop a remove a backpack or CamelBak...

So:

I have found that for a small P&S or small-bodied m43s cam - since I am right-handed - a left upper harness small pouch works best - enabling me to quickly retrieve the cam without removing a pack.  If the pouch isn't especially weatherproof, I slip a zip-lock bag over it (friends sometimes use a sil-nylon ditty bag or shower cap) and have found one of those simple solutions faster and quieter to use than zippers or velcro; especially for capturing wildlife shots quickly.

If I'm using a larger m43s body and lens, a larger but adequately thin pouch or small fanny pack mounted on the left front backpack waist belt works well too.  If the pouch is mounted on the waist belt too far around toward the side - it is in the way of arm / trekking pole movement.  If it hangs too low while more around to the front - it gets in the way of leg movement.  So, a more horizontal pouch toward the front works best.

The key, for me, is quick accessibility without the cam / pouch being fiddly, loud, or in the way.

In good weather - and when I am in an area I know wildlife is abundant - I'll leave the top-zip pouch partially or wholly open - being mindful all the time.  Think:  top loading pouch here.

Either of the pouch positions described is out of the way of almost all my arm and leg movement - and works for about everything but more extreme rock scrambling in tight places.  Then, its a choice of being uber-careful - or placing the cam temporarily inside the backpack or CamelBak.

In general, on longer trips I carry a smaller cam, on shorter ones a larger one; but it depends on what I am after.  Weight, bulk, capability, situation, and weather are always tradeoffs.

Pouch size and position on a harness or waist belt are key.

Less may be more.

Cheers,

Scott