I carry a SLR with three lenses but no laptop. I use a photo backpack with a non-photo top compartment. My bike has a front rack with platform, which was bought specifically for that.
My current is a Tamrac Aero 70 that i bought with touring in mind. I like it because the photo compartment opens like a handlebar bag. The shoulder straps are stuffed in the side pockets and the bag is attached to the rack with a single strap with buckle. I pass the top handle over the handlebar for added stability. The front panniers also help with stability. I rode without front panniers and it was ok, just not great. I've found a better way for day riding. I'll post about that tomorrow with pictures. I put warm "emergency" socks under the lenses, but no extra padding for the camera and lens attached. There's a closed-cell foam under the bag which adds padding but it's mostly to make a larger fender. I've also used it to sit. I'll post pic of that later too. Under the rain, I just put a pannier rain cover. You can always line the bag with a plastic bag. The only thing I miss is a small outside zippered pocket for my wallet.
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Before, I had a Lowepro Orion Trekker. It opens by "splitting" the bag in two, which is a bit (very) annoying. The bag was attached with the buckle that closes the bag so every time I opened the bag, it was free to move around. It couldn't fall though. The top compartment was huge and usually carried the camera with lens attached, sometimes an extra lens in the top compartment. I used a fleece to pad a little. Again, since the front panniers stick above the rack's platform, they help suspend and stabilize the photo bag a little. The photo compartment was lined with a plastic bag and I added a layer of closed-cell foam under the bag.
I've also put the photo padding in the top compartment for easier access, which is essentially how the Tamrac bag is set-up for day riding:
My photo gear has around 10 000km and still going strong... sort of. I've dropped the 70-300VR twice on pavement/concrete due to poor carrying setup that I won't mention. It was repaired once and is acting up a little but it's still working.