Pentax K3 ii and back Button Focusing

I am struggling to get sharp images of birds in flight with my recently purchased K3 ii. I know it can focus sharply but my BIF photos dont seem as sharp as what my K5 iis produced with the same Sigma 150-500 lens attached. I thought I would try using the rear focus button but the camera struggles to stay locked on the subject. I had a Little Egret in flight pressed and held the back button, the camera focused on it fine but as soon as I started shooting the focus swapped to the wooded area behind. I held the back button all the time the camera and was shooting and it was set to continuos AFC, Continuos shooting M, AF Select Expanded (M). I've tried other settings with very little luck. I thought if the AF button was held then the shutter release had no effect on focus but am I wrong. I have also tried AF2 in button customizing but I still cant get the camera to maintain focus on a BIF. I seem to get better results with the half press shutter and then shoot AFC, but even then I dont think my images are as sharp as the K5 iis produced. What am I doing wrong? Any suggestions gratefully recieved.

Are you using the camera shake reduction or the lens image stabilisation?

Best to use one or the other. If you use both they start to fight each other!

All the best, bob.

Hi Bob, I've tried both but not at same time, if back button is used the lens shake reduction doesnt work anyway because it needs the shutter half press to trigger it. I've been shooting at 1/1250 second so altough shake reduction may help I dont think it would be critical. The Sigma lens can be set to pan mode but it doenst seem to help either.

Static focusing is pretty good provided I use the half press shutter method. Probably no sharper than the K5 ii but as the detail from the sensor is better it probably makes the final image better. I'm pretty sure the focusing of the lens is pretty well spot on, if I let the camera auto focus on a subject I cant improve it by tweaking the focus ring.
My real gripe is a cant get the back button to work as I think it should with birds in flight.

Hand held Sigma 150-500 at 500mm, 1/500 sec, ISO 100, spot focus.
These are images of Little Egret, before and after cropping. I dont think there is much wrong with the focusing although I did use some sharpening in RAW edit and I applied PSE editor's shake reduction to tweak it a little more, it wasnt bad before.

Dont think I've tried spot focusing with BBF because I struggle to keep birds in the centre. When you use BBF and spot focus do you have to keep the plane in the centre of frame for BBF to stay locked on it?

Dont think I've tried spot focusing with BBF because I struggle to keep birds in the centre. When you use BBF and spot focus do you have to keep the plane in the centre of frame for BBF to stay locked on it?[/quote]

Not generally, but it helps to keep the largest part within the spot focusing area. BIF images with pentax is more difficult imho than perhaps other manufacturers, its a skill that takes honing and the success rate perhaps isn't as many as canikon, but when you do get it right, its worth it !!




The Hawk is a tad noise, shot at 1600 ISO ( K3ii )


[/quote]
Right I'm going to persist with it, we get plenty of aircraft here so will try them first, they are more predicatble. What do you use, "select spot" or "spot"

Thanks Chris,