focus problem at DVinfo.net

Warren Cook · January 10th, 2011, 10:58 AM

I am shooting with the XL2 with the 20X lens. Mostly of eagles setting in trees. I'm shooting in manual mode with manual focus. Bright sun light using ND set at max, 30 fps and shutter at 1/60th.

The problem is the focus keeps going in and out slightly, just enough to make the footage useless.

In auto focus I could understand but in manual focus, even when I set the focus it will go in and out of focus slightly.

Thanks for any help.

Warren

Piotr Zubik · January 10th, 2011, 02:02 PM

Do you mean that providing the subject you are filming remains in the same place all the time, the focus drifts out in manual mode? If so, there must be definitely something wrong with your camera.

Is it possible you are hitting the focus ring by accident? With hand or piece of equipment?

Colin McDonald · January 10th, 2011, 03:06 PM

Are you absolutely sure it's not an atmospheric effect? You did mention bright sunlight.

Chris Soucy · January 10th, 2011, 03:10 PM

With the shutter tacked to 1/60, my guess, and that's entirely what it is, is that the apeture is wandering around based on subject matter, changes in light levels etc (and with the ND's maxed out as well, the changes could be quite significant).

With the change in apeture, there will be a significant change in DOF, so that something that was apparently tack sharp at f8 goes soft at f3.5, say.

[That 20X lens is incredibly sensitive to DOF even at 700 metres, which is one heck of a long way].

This would give the effect you're describing.

For such pinpoint shooting where the DOF MUST stay where it's put, I can't see any way around it but to switch to 60i, tack the apeture to say, 5.6 and let the shutter speed do the walking.

That's my standard shooting mode with my A1, and I don't get the problem you have described.

Make any sense?

CS

Rainer Listing · January 10th, 2011, 05:35 PM

Trees do sway, enough to affect critical focus at long lengths and wide apertures, and you get atmospheric distortion as Colin suggested. If you need the wide apertures not much you can do, it's a compromise, but otherwise stopping down helps. I do have some suspicions that the inbuilt NDs tend to soften things, as does any extra glass in front of your lens. Why shoot at 1/60 in bright sunlight? If this is an attempt to get a film look, you might need to know that higher end film cameras (and lower end like the Bolex H16 which was the wildlife staple) had (and have) variable shutters and it wasn't (and isn't) unusual to shoot equivalent to around 1/120 in daylight. No-one complained that it looked unnatural or didn't look like film. You do want locked exposures and shutter and unless you want to do half res slo-mo 60i is a really bad idea.

Warren Cook · January 12th, 2011, 02:39 PM

Thanks guys for the replys.

I'm going to try your suggestions. Shooting with a higher shutter speed and also try setting the Av

at 5.6 or 6.3 and letting the shutter done what it needs to do.

After looking at my clips again I now believe this may be atmospheric effect. I'm shooting over a wide stream at these birds. I also shoot them setting on ice at the edge of the water and I think it's mostly
atmospheric effect.

I'll be back out again tomorrow and give it another try.

Thanks again,

Warren

Don Palomaki · January 16th, 2011, 08:16 AM

Let us know how it worked out.

January 10th, 2011, 10:58 AM	#1
Warren Cook Regular Crew Join Date: May 2007 Location: Yulan, New York Posts: 61	focus problem I am shooting with the XL2 with the 20X lens. Mostly of eagles setting in trees. I'm shooting in manual mode with manual focus. Bright sun light using ND set at max, 30 fps and shutter at 1/60th. The problem is the focus keeps going in and out slightly, just enough to make the footage useless. In auto focus I could understand but in manual focus, even when I set the focus it will go in and out of focus slightly. Thanks for any help. Warren

January 10th, 2011, 03:10 PM	#4
Chris Soucy Inner Circle Join Date: Feb 2007 Location: Fairfield, Dunedin, New Zealand Posts: 3,691 Images: 18	Hi, Warren........... With the shutter tacked to 1/60, my guess, and that's entirely what it is, is that the apeture is wandering around based on subject matter, changes in light levels etc (and with the ND's maxed out as well, the changes could be quite significant). With the change in apeture, there will be a significant change in DOF, so that something that was apparently tack sharp at f8 goes soft at f3.5, say. [That 20X lens is incredibly sensitive to DOF even at 700 metres, which is one heck of a long way]. This would give the effect you're describing. For such pinpoint shooting where the DOF MUST stay where it's put, I can't see any way around it but to switch to 60i, tack the apeture to say, 5.6 and let the shutter speed do the walking. That's my standard shooting mode with my A1, and I don't get the problem you have described. Make any sense? CS

January 12th, 2011, 02:39 PM	#6
Warren Cook Regular Crew Join Date: May 2007 Location: Yulan, New York Posts: 61	Focus Problem Thanks guys for the replys. I'm going to try your suggestions. Shooting with a higher shutter speed and also try setting the Av at 5.6 or 6.3 and letting the shutter done what it needs to do. After looking at my clips again I now believe this may be atmospheric effect. I'm shooting over a wide stream at these birds. I also shoot them setting on ice at the edge of the water and I think it's mostly atmospheric effect. I'll be back out again tomorrow and give it another try. Thanks again, Warren

January 16th, 2011, 08:16 AM	#7
Don Palomaki Wrangler Join Date: Sep 2001 Location: Northern VA Posts: 4,488	Let us know how it worked out. __________________ dpalomaki@dspalomaki.com

January 10th, 2011, 02:02 PM	#2
Piotr Zubik Regular Crew Join Date: Jan 2008 Location: Miedzyrzec Podlaski, POLAND Posts: 30	Do you mean that providing the subject you are filming remains in the same place all the time, the focus drifts out in manual mode? If so, there must be definitely something wrong with your camera. Is it possible you are hitting the focus ring by accident? With hand or piece of equipment?

January 10th, 2011, 03:06 PM	#3
Colin McDonald Trustee Join Date: Dec 2007 Location: Glasgow, Scotland Posts: 1,546	Are you absolutely sure it's not an atmospheric effect? You did mention bright sunlight.

January 10th, 2011, 05:35 PM	#5
Rainer Listing Major Player Join Date: Jun 2008 Location: Nowra, Australia Posts: 440	Trees do sway, enough to affect critical focus at long lengths and wide apertures, and you get atmospheric distortion as Colin suggested. If you need the wide apertures not much you can do, it's a compromise, but otherwise stopping down helps. I do have some suspicions that the inbuilt NDs tend to soften things, as does any extra glass in front of your lens. Why shoot at 1/60 in bright sunlight? If this is an attempt to get a film look, you might need to know that higher end film cameras (and lower end like the Bolex H16 which was the wildlife staple) had (and have) variable shutters and it wasn't (and isn't) unusual to shoot equivalent to around 1/120 in daylight. No-one complained that it looked unnatural or didn't look like film. You do want locked exposures and shutter and unless you want to do half res slo-mo 60i is a really bad idea.