50-500mm "bigma" focus

[eeyore]

Originally Posted by Roy C

Surely if you are in av mode, you dial in the required apature and the camera will automatically select the shutter speed I cannot see how you can change this Unless you dial in some ev compensation.

you are completely correct roy - to do as true nature suggests you need to be in full manual (M) mode - but putting it in AV and selecting f8 (or in fact i would sugest f5.6) and leaving the camera to pick the speed is much more likely to get good results as the exposure will vary considerably depending on where you are poiinting the camera (and if you are tracking a moving subject you wont have time to keep altering the speed manually)

[true nature]

av mode f8 and use the av -/+ button and dial in -1/3 or + 2/3 depending on the b/g its the sharpest method ive found that works for me . beside if id have known that the bigma is not sharp wide open iwould'nt let the camera set it for me 5.6/6.3. no thanks.
if im walking about 90% of my subject are going to be in folage differant shaids of green and browns so ill set the camera to -1/3 or 2/3 and if im trying to get flights shots ill quickly dial in +2/3 simple.
thanks

[eeyore]

Originally Posted by true nature

av mode f8 and use the av -/+ button and dial in -1/3 or + 2/3 depending on the b/g its the sharpest method ive found that works for me . beside if id have known that the bigma is not sharp wide open iwould'nt let the camera set it for me 5.6/6.3. no thanks.
if im walking about 90% of my subject are going to be in folage differant shaids of green and browns so ill set the camera to -1/3 or 2/3 and if im trying to get flights shots ill quickly dial in +2/3 simple.
thanks

simple but franky inaccurate - the bigma isnt sharp at the edges wide open but the cropped sensor in 90% of our dslrs doesnt see the edges anyway so this is irrelevant, unless of course you are one of the lucky few who can afford a 5d or a 1DS (or their other brand equivalents) but if you have that degree on dosh i'd reccomend teaming it with some better glass anyway such as a 400mm f2.8 IS.

as regards using the exposure compensation to manipulate the speed

a) it doesnt give true control over the speed anyway - it simply slightly alters whatever setting the camera picks , but the speed selected will still vary depending on the ammount of light coming into the camera

and

b) if you set +ve compensation for shots against the sky there is a good chance of burning out any white on your subject - such as the pale wing bars on a red kite , similarly if you set -ve compensation for shots against folliage you stand a good chance of under exposing (particularly as mid green equates to 18% grey anyway)

a better approach is to only set the compensation if you know that the meter will read high or low (such as with snow scenes) or if you know that your meter consistently reads slightly out (for instance my 20D always reads high so it is permanently set to 1/2 -ve)

the way to get your subjects well exposed is to take the metering off the evaluative setting and instead set it to partial or spot so that it is actually taking exposure readings from your subject

putting my pictures where my mouth is these two were taken wide open on the little bigma at 500mm with the exposure set 1/2 -ve as above, and the metering set to spot ( by the way the softness on the wings on the first image is not due to the lens being unsharp - it is due to the shallow depth of field which was deliberate to focus attn on the head - also the slight jaggies under the right hand wing are a product of the rapid resizing for wab - they arent there on the original)

[glsammy]

There's no hard and fast rule you can apply to any type of shot, exposure compensation has to take the light levels and the subject matter into consideration.
Take this shot:



Bright sky, so set compensation to +2EV? No, quite the opposite. It's at -1EV. As Pete said, you've got to allow for any white in the subject, as here.

Here's another one:


That's at -1.33EV.

[geordie1970]

I think someones up to no good or desperate eBay.co.uk: Sigma 50-500mm f/4-6.3 EX APO DG HSM - *Mint Con* (item 260129091127 end time 20-Jun-07 12:02:39 BST)

[glsammy]

Originally Posted by geordie1970

I think someones up to no good or desperate eBay.co.uk: Sigma 50-500mm f/4-6.3 EX APO DG HSM - *Mint Con* (item 260129091127 end time 20-Jun-07 12:02:39 BST)

Just look at the feedback ratings for the top two bidders, one at £750 and one at £760.. One of them is zero, and the other less than zero! This sellers needs to learn to block these types of bids, no one in their right minds would pay that for a second hand Bigma.