Hi Nick,
I second Lowell's comments on vibration - very good post. Of course my setting up on a surface that readily transmits vibration will never help matters (eg. on my wooden deck for backyard birding). I have to remain motionless to ensure the best possible shot because it's on an elevated wooden deck.
Im my mind, therein lies crux of the issue: the personal traits of the photographer may influence or determine what you may need in terms of equipment and accessories for a heavy super telephoto lens. For example, as already mentioned, one person I know who owns the FA* 600/4 has the RRS accessory because he hits the shutter button instead of squeezing it. He has seen a noticeable improvement in "keepers" since installing it. I simply squeeze the shutter and can get clear shots to as low as 1/125 to 1/200 sec. @ 600mm.
Yes, my left hand is normally dampening the lens, as is my face on the back of the camera with lower shutter speeds. It's mainly to counteract the movement caused by the pressing of the shutter button, nothing more.
I am also glad that I asked about your equipment and I believe that I can identify a potential problem here. I don't think you'll find true success in your quest for a solution until you address it - the tripod. Your FA* 600/4 lens weight is nearly 50% heavier than the max. load of the tripod:
Giottos MTL 9351B max. load: 5 kg FA* 600/4: 7.2 kg
Any time you exceed the maximum specs on a material or it's construction, compromise will result. For reference, I owned the Giottos MT 9360 - max. load of 17.5lbs or ~8 kg. It was insufficient support with the Wimberley WH-200 gimbal head and a P50 plate - there was too much vibration for my liking even with long lens technique. I have since moved to the
Gitzo 3541XLS and have no regrets.
My FA* 250-600/5.6 lens weight is actually 5.8kg (12.8 lbs). Both the 2500-600/5.6 and the 600/4 share the same tripod collar design. Add a K10D+grip and gimbal head, the weight now is at 8.5kg (18.75 lbs). I weigh all items and luggage with an Ultimate (now Feedback) Alpine Digital Scale - it's accuracy is to +/- 10 grams. I do this before traveling by air, to ensure I have no surprises!
As an FYI, I've spoken directly with Wimberly (I'm a Professional Services member) on using a Sidekick with heavier super telephotos. I was advised against using it with a heavy lens, unless air travel weight or something similar was a consideration. That doesn't mean you cannot consider other options, including the Mongoose head, which is very light, but the design leaves more than a few serious/professional nature photographers divided on it's long term durability. My understanding is that the entire load of the lens rests on a much smaller surface area - near where the lens platform attaches to the main arm of the head. OTOH, I have no concerns slinging my setup of tripod+gimbal head+lens+camera over my shoulder and have peace of mind.
That being said, I would consider using a high-quality ball head while in a blind/hide too. The tensioning on the ball would be important in addition to proper long lens technique.
I would recommend you seriously consider getting a tripod such as the MTL 927xB series with a max. load of 10kg if your budget limits you. If you are able to afford a higher load tripod, please seriously consider doing so (ie. Gitzo line). Otherwise Feisol makes a slightly higher max. load of around 12-13kg and it's more cost friendly.
If you review some of my image posts, you'll find examples of low shutter speed images. I'll do my best to help where I can.
Regards,
Marc