Hi, I have a Markins Q20 head with the lever clamp on a Gitzo 3 series tripod, and I do like the lever, since it makes me feel like the plate is securely fixed when the lever is tightened.
I have fooled around a little bit with my sister's Kirk ball head, with it's screw clamp, and the screw head is fairly smooth, and would make me worry whether it would be tough to tighten or loosen with gloves on, etc. Also, I have worries whether I might not tighten it enough, and have it accidentally loosen, or whether it would be more difficult with thumb arthritis. I think I worry too much, since those issues don't seem to be discussed, and there are many more screw clamps than lever clamps.
I do think that a screw clamp would probably be easier to use with a monopod, though, so I will probably get that when it come time...
I am using mostly a Kirk L bracket on my D7000, and from the factory, the lever clamp is pretty tight (probably a bit too tight), and my Markins camera plate is perfect. This is somewhat disappointing, because I heard that the Markins and Kirk plates were supposed to be the same size, and wouldn't need adjustment between the two. So far, I have just been using the lever clamp too tight on the Kirk L bracket, and it's been fine, just takes a bit more effort to engage the lever, and it definitely feels like it's fully engaged and won't slip!
I do think that I should probably back off the lever clamp a small bit and will probably do that in the future.
The future is now, so they say, and writing this post has motivated me to actually adjust the lever clamp.
It's easy, and you can do with the Victorinox Classic screwdriver that's in your pocket! ... kind of. It's a bit futzy, but you can do it. I ended up going into the garage and getting the small straight screwdriver with a 3/16" blade ( I just measured it--it would be your pocket screwdriver size), because I didn't want to muck up the threads, but because the screw is recessed, it turns out the blade on the screwdriver isn't a whole lot wider than the pocketknife, but easier to handle.
So I backed off the lever clamp to be perfect for the Kirk, and the Markins clamp was literally sliding back and forth in the lever clamp when it was fully engaged. What?!! Taking a closer look, the widest dimension of the base of the 2 plates is pretty much the same (I don't have a micrometer, so no numbers, you'll have to trust me with the eyeball technique), but the slope of the base as it comes up to the part that attaches to the camera appears to be different. Actually, it's about the same, but the slope starts earlier on the Markins plate. Both Markins baseplate and the Kirk has a slope of about 45 degrees, but the base is thicker before it slopes up, and so in effect, the Kirk is much wider than the Markins.
Dash Art: _ ___ Markins ______ _________
_ ___ Kirk ______ ______
I don't know if you can understand my dash art, or whether it will come out right (I've already tried to adjust it according the the preview), but suffice it to say, on my particular Kirk and Markins plate, there is enough difference in the clamp geometry that I would just stick with one brand. Or, to say it another way, if I were to switch back and forth between the two, I would have to use the screwdriver to adjust the clamp.
...Anyone need a Markins clamp for a D7000, used only for this test?