Focus on very far away objects at DVinfo.net

Steve Lewis · June 18th, 2008, 03:58 AM

Was recently at the Port of Los Angeles, photographing the massive cranes in San Pedro that load/unload shipping containers from the ships. I had my xha1 set at IAF and when i looked at the footage on my mac, the cranes (which must have been about a quarter mile away from me) looked out of focus: is this because IAF simply cant focus on objects that far away?... is my only option to use manual focus?
-Steve

PS: Is there ever a time when I wouldn't want to use IAF vs normal AF (obviously if a lens is blocking the IR sensor!)

Annie Haycock · June 18th, 2008, 04:09 AM

I've just looked at some stuff I shot last week of birds on the coast and a lot of it looks out of focus. But a closer look shows that the problem is really from haze and the movement of air up the cliffs. Almost everything is shimmering. The auto-focus had a hard time on distant objects because of it. This wasn't the fault of the auto-focus on the A1, just the limitations of any auto-focus system under such conditions.

Chris Soucy · June 18th, 2008, 05:16 AM

Steve,

The simple truth is, 1/4 mile isn't all that far away.

My A1 will pick out objects in stark clear focus up to 950 metres away, that's about 2/3 of a mile.

Leaving your lens in IAF in those circumstances faces it with an impossible job - what, exactly, to focus on?

The cranes, which aren't "in it's face"? The huge background, which is everything else?

My guess? It went to Infinity, when it should have been set (manually) to 500 odd metres (600 - 700 yards).

Sorry Steve, don't do that sort of thing with a lens as sharp as the A1's, and certainly don't expect it to "think for itself" and do a better job than the operator.

Annie,

Don't use IAF in those circumstances, the camera doesn't have the brains for it. It's good, quite often better than the human operators who use it, but it simply cannot make those sort of decissions with any hope of accuracy.

CS

Annie Haycock · June 18th, 2008, 06:45 AM

Chris - I shot only about 15 seconds with the autofocus on to demonstrate the problem it had focussing on a cliff in the sea mist. The other stuff only looked out of focus at first (I was using manual focus) because of the heat haze. I'm having a problem finding enough material that looks sharp enough to use in the UWOL video.

June 18th, 2008, 03:58 AM	#1
Steve Lewis Major Player Join Date: Apr 2008 Location: Goleta, CA Posts: 233	Focus on very far away objects Was recently at the Port of Los Angeles, photographing the massive cranes in San Pedro that load/unload shipping containers from the ships. I had my xha1 set at IAF and when i looked at the footage on my mac, the cranes (which must have been about a quarter mile away from me) looked out of focus: is this because IAF simply cant focus on objects that far away?... is my only option to use manual focus? -Steve PS: Is there ever a time when I wouldn't want to use IAF vs normal AF (obviously if a lens is blocking the IR sensor!) __________________ www.spreefilms.com - Give me a museum and I'll fill it!

June 18th, 2008, 04:09 AM	#2
Annie Haycock Major Player Join Date: Dec 2007 Location: Pembrokeshire, Wales Posts: 734	I've just looked at some stuff I shot last week of birds on the coast and a lot of it looks out of focus. But a closer look shows that the problem is really from haze and the movement of air up the cliffs. Almost everything is shimmering. The auto-focus had a hard time on distant objects because of it. This wasn't the fault of the auto-focus on the A1, just the limitations of any auto-focus system under such conditions. __________________ Canon XH A1; Canon XF100; Nikon D800

June 18th, 2008, 05:16 AM	#3
Chris Soucy Inner Circle Join Date: Feb 2007 Location: Fairfield, Dunedin, New Zealand Posts: 3,691 Images: 18	Hi guy's........... Steve, The simple truth is, 1/4 mile isn't all that far away. My A1 will pick out objects in stark clear focus up to 950 metres away, that's about 2/3 of a mile. Leaving your lens in IAF in those circumstances faces it with an impossible job - what, exactly, to focus on? The cranes, which aren't "in it's face"? The huge background, which is everything else? My guess? It went to Infinity, when it should have been set (manually) to 500 odd metres (600 - 700 yards). Sorry Steve, don't do that sort of thing with a lens as sharp as the A1's, and certainly don't expect it to "think for itself" and do a better job than the operator. Annie, Don't use IAF in those circumstances, the camera doesn't have the brains for it. It's good, quite often better than the human operators who use it, but it simply cannot make those sort of decissions with any hope of accuracy. CS

June 18th, 2008, 06:45 AM	#4
Annie Haycock Major Player Join Date: Dec 2007 Location: Pembrokeshire, Wales Posts: 734	Chris - I shot only about 15 seconds with the autofocus on to demonstrate the problem it had focussing on a cliff in the sea mist. The other stuff only looked out of focus at first (I was using manual focus) because of the heat haze. I'm having a problem finding enough material that looks sharp enough to use in the UWOL video. __________________ Canon XH A1; Canon XF100; Nikon D800