Sigma 50-500 and K10D STRANGE!

Just had a wierd experience with the above combo, I was out shooting birds and had the aperture wide open (f6.3), I was getting a shutter speed of 1/180th (in Av). as I was using a tripod and using the SR I thought I would try a smaller aperture, Now this is the strange bit, I went through f8 and f9.5 but the shutter speed remained at 1/180th, (no it wasn't the light level changing) the shutter speed didn't change till I stopped down to f11, then it dropped to 1/125th.

I put the camera into P and it came up with a combo of 1/180th f9.5, switching back to Av gave me 1/180th again at f6.3

I also tried changing the exposure comp, again it didnt shift the shutter speed untill I got over +2 stops.

The lens was at max 500mm.

Has anyone else experienced similar problems.

Do you have your ISO set to Auto?

It caught me out a couple of times until I switched it off and moved ISO to a control dial

If you were using a tripod, then SR should be switched off.

Depends on how good your tripod is with that monster on it!

Can someone explain to me why this is? is it just that it does you no good 'cause you're allready on a tripod, or does SR actually cause bad things to happen if you are tripod mounted?

This is my understanding:

SR is designed to deal with the relatively large and slow vibrations caused by delirium tremens (in my case!) or simple hand trembling.

The vibrations experienced by a camera on a tripod are of a completely different order; much smaller and faster.

The AS is unable to keep up with such vibrations, but (being stupid) will nonetheless attempt to do so. It will fail, and may actually cause greater instability.

G

DOH!!!!!

Hang on, i'll be back in a minute, just going to bang my head on the wall........


.......OK I'm back, feel much better now, even checked the exifs on the shots, ISO was up and down like a YoYo. Thanks!


Everybody else, thanks, will also try it without the SR, but as gwyn said, this lens is a beast, even my shiny new Velbon CF630 trembles under its weight and as I am still using the shutter button I will probably still get a little movement.

I suggest that you use the 2 secind self timer setting. This locks up the mirror and releases the shutter with virtually no vibration at all.

John, you didn't thoroughly read my OP did you

I was shooting birds, y'know, the feathered variety, they dont hang around for a 2sec delay.

I have tried it with the IR remote but that flashing light makes it look like I'm showing off , especially when I've prefocused on a particular spot and I'm just hanging around waiting for something to perch, plus I have no idea what that light does to the battery life (minimal I would think) but in cold weather with no backup I need every ounce of power I can get.

I strongly recommend the remote release and remote control drive mode, not the 3 second delay remote release. Even if you are looking through the viewfinder at the time the picture is taken, there will be no torquing of the camera, unless you bash it with your face ...

Well I did, but not the second time I came to the thread!

In those circumstances I would use the highest shutter speed possible and probably (in the absence of a faster lens) up the ISO value to achieve that. Even on a tripod shake can occur, so maybe an even sturdier tripod as well?

To follow up on SR, in the absence of the sort of shake it expects the system tries to find it and compensate for it, causing a loop of spurious movement instead. SR is for hand held shots. It also does nothing for subject movement....

thanks for the explanation George and John, very interesting