Focus oddity while zooming at DVinfo.net

Boyd Ostroff · October 18th, 2003, 10:50 AM

Here's another "interesting" thing I've noticed recently while filming our stage productions with the PDX-10. I'm using manual focus, manual exposure and 1/60 sec shutter with a Varizoom Pro-L controller set to the minimum speed. When I do a slow zoom in all the way to the max, right at the end I often see the image go out of focus briefly, as though I was using autofocus and it was "hunting". But when I release the zoom button the image snaps back into sharp focus (assuming that it was properly manually focussed to start off with).

I never really noticed this before, but haven't been doing this slow zooms much either in the past. So I'm wondering if this has something to do with the little ND filters dropping into place maybe? Or maybe it's a quirk of the LANC zoom controller? Anybody else notice this?

BTW, I like the Varizoom Pro-L. The zoom button on the PDX-10 is really horrible IMO. I could never get a smooth, slow, continuous zoom with it. The varizoom, set to the lowest speed, does this very nicely. Of course, like just about all of the prosumer cameras, there is still a bit of a jump when you start the zoom.

Also, regarding manual exposure, I wish you could vary it continuously so that you didn't get discrete "bumps" as you turn the dial. But considering everything that we now know is happening with both the iris and ND filters, I guess it isn't too bad. The effect looks exactly the same to me as what I see when turning the manual exposure dial on my VX-2000.

Shawn Mielke · October 19th, 2003, 12:48 AM

You don't like the PDX10 zoom, Boyd? I've had some success with it, but you really have to hold the cam in a way that lets you bear a thumb down in a way that is unmistakably square in pressure, so that you just know where you're at, and where you are not. But then I have found this to be true with all on cam zoom rockers and levers. I find the PDX10's pleasingly responsive, though.
I'm not sure I know the unfocus zoom effect you spoke of, but I know that when relatively close to a subject, the zoom does not focus at the end, and I either have to get closer to get closer, or else back off to not have blur at zoom's end. But I don't think this is what you're referring to.

Wayne Orr · October 19th, 2003, 10:24 AM

It sounds as though there is some sort of "cross-talk" going on between the zoom control and the focus control. I would think the way to test this, Boyd, would be with other quality zoom controllers, such as the Bogen or the Zoe, and see if they duplicate the problem. Since focus on these cameras is the result of "look-up tables" rather than physical lens focus, they are subject to interference.

Wayne Orr, SOC

Tom Hardwick · October 19th, 2003, 11:27 PM

The bottom line is this: if you film outdoors with the PDX10 in auto or manual, all that's happening is the camera chooses the sweet spot (f4 to f4.8) and plays around with the three NDs to smoothly vary the exposure. If this is so, how come the exposure wheel (actually an ND wheel for most of its life) puts unacceptable half-stop visible jumps into our footage? This is a crazy state of affairs, and is something that the new PD170 has made an attempt to correct.

tom.

Boyd Ostroff · October 20th, 2003, 04:05 PM

I'm going to have to look into the focus issue a bit deeper. After posting that message I realized there was another variable in the equation: I have steadyshot turned on. Yes, I know the "conventional wisdom" is NOT to use steadyshot while tripod mounted. However I am shooting from the back of the theatre, over 100' from the stage. There's a lot of vibration and movement in our creaky 150 year old theatre! I did a bunch of tests and didn't notice any steadyshot problems while slowly panning and zooming, and the overall effect was better than the shakiness I got without steadyshot.

However, maybe there's something about zooming all the way to the limit that interacts with steadyshot and causes the lack of focus. Or maybe Wayne is right about crosstalk with the LANC zoom controller? It doesn't happen every time, but the phenomenon is definitely there. Will try shooting some footage with steadyshot turned off and see what happens.

Regarding the PDX-10's built-in zoom rocker, yes I dislike it. Shawn, you're probably right that it isn't any worse than other cameras, it's pretty much the same as my VX-2000. But at least the VX-2000 also has a zoom ring. It's a servo-controlled spinning wheel, but it lets me have a little better control over the zoom. With the rocker switch, if I'm trying to do a very slow zoom I find it virtually impossible. Either I end up pushing too hard and the zoom speeds up, or I don't push hard enough and the zoom stops dead. Either way I get ugly results. The Varizoom Pro-L lets me set the zoom speed with a dial, then press a button to activate. This gives me a slow, steady zoom which is something I have never been able to do consistently with the built-in rocker.

Shawn Mielke · October 20th, 2003, 05:05 PM

Indeed, the rocker proves to be more challenge than is necessary during a shoot, if one can help it. Plenty of other things to think about!

Chris Long · October 20th, 2003, 08:43 PM

I agree completely with your points about the zoom rocker, Boyd. I have disliked it from the first time I played with it, a despite much practice, cannot consistently produce a slow, smooth zoom.

Fast and jerky, I can do.

I really wish the engineers had seen fit to include a slow/medium/fast setting selector in the menu (and an "Ultra Slow" setting, while we're at it). It would be nice to have, in place of the hair trigger variable speed thing. Being variable doesn't mean it's all things to all people, unfortunately!

I may eventually want to look into a zoom controller. Seems to me that it might be fairly simple to put one together, if I knew where to start.

Anyone know of any homebuilt zoom controllers?

By the way--I have used the controller on the Remote Commander occasionally, to fairly nice effect. Just has to be the right situation.

October 18th, 2003, 10:50 AM	#1
Boyd Ostroff Wrangler Join Date: Dec 2002 Location: Mays Landing, NJ Posts: 11,802	Focus oddity while zooming Here's another "interesting" thing I've noticed recently while filming our stage productions with the PDX-10. I'm using manual focus, manual exposure and 1/60 sec shutter with a Varizoom Pro-L controller set to the minimum speed. When I do a slow zoom in all the way to the max, right at the end I often see the image go out of focus briefly, as though I was using autofocus and it was "hunting". But when I release the zoom button the image snaps back into sharp focus (assuming that it was properly manually focussed to start off with). I never really noticed this before, but haven't been doing this slow zooms much either in the past. So I'm wondering if this has something to do with the little ND filters dropping into place maybe? Or maybe it's a quirk of the LANC zoom controller? Anybody else notice this? BTW, I like the Varizoom Pro-L. The zoom button on the PDX-10 is really horrible IMO. I could never get a smooth, slow, continuous zoom with it. The varizoom, set to the lowest speed, does this very nicely. Of course, like just about all of the prosumer cameras, there is still a bit of a jump when you start the zoom. Also, regarding manual exposure, I wish you could vary it continuously so that you didn't get discrete "bumps" as you turn the dial. But considering everything that we now know is happening with both the iris and ND filters, I guess it isn't too bad. The effect looks exactly the same to me as what I see when turning the manual exposure dial on my VX-2000.

October 19th, 2003, 12:48 AM	#2
Shawn Mielke Major Player Join Date: Jul 2003 Location: Santa Rosa, California Posts: 745	You don't like the PDX10 zoom, Boyd? I've had some success with it, but you really have to hold the cam in a way that lets you bear a thumb down in a way that is unmistakably square in pressure, so that you just know where you're at, and where you are not. But then I have found this to be true with all on cam zoom rockers and levers. I find the PDX10's pleasingly responsive, though. I'm not sure I know the unfocus zoom effect you spoke of, but I know that when relatively close to a subject, the zoom does not focus at the end, and I either have to get closer to get closer, or else back off to not have blur at zoom's end. But I don't think this is what you're referring to. __________________ Breakthrough In Grey Room

October 20th, 2003, 05:05 PM	#6
Shawn Mielke Major Player Join Date: Jul 2003 Location: Santa Rosa, California Posts: 745	Indeed, the rocker proves to be more challenge than is necessary during a shoot, if one can help it. Plenty of other things to think about! __________________ Breakthrough In Grey Room

October 19th, 2003, 10:24 AM	#3
Wayne Orr Major Player Join Date: Dec 2002 Location: Northridge Ca Posts: 734	It sounds as though there is some sort of "cross-talk" going on between the zoom control and the focus control. I would think the way to test this, Boyd, would be with other quality zoom controllers, such as the Bogen or the Zoe, and see if they duplicate the problem. Since focus on these cameras is the result of "look-up tables" rather than physical lens focus, they are subject to interference. Wayne Orr, SOC

October 19th, 2003, 11:27 PM	#4
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	The bottom line is this: if you film outdoors with the PDX10 in auto or manual, all that's happening is the camera chooses the sweet spot (f4 to f4.8) and plays around with the three NDs to smoothly vary the exposure. If this is so, how come the exposure wheel (actually an ND wheel for most of its life) puts unacceptable half-stop visible jumps into our footage? This is a crazy state of affairs, and is something that the new PD170 has made an attempt to correct. tom.

October 20th, 2003, 04:05 PM	#5
Boyd Ostroff Wrangler Join Date: Dec 2002 Location: Mays Landing, NJ Posts: 11,802	I'm going to have to look into the focus issue a bit deeper. After posting that message I realized there was another variable in the equation: I have steadyshot turned on. Yes, I know the "conventional wisdom" is NOT to use steadyshot while tripod mounted. However I am shooting from the back of the theatre, over 100' from the stage. There's a lot of vibration and movement in our creaky 150 year old theatre! I did a bunch of tests and didn't notice any steadyshot problems while slowly panning and zooming, and the overall effect was better than the shakiness I got without steadyshot. However, maybe there's something about zooming all the way to the limit that interacts with steadyshot and causes the lack of focus. Or maybe Wayne is right about crosstalk with the LANC zoom controller? It doesn't happen every time, but the phenomenon is definitely there. Will try shooting some footage with steadyshot turned off and see what happens. Regarding the PDX-10's built-in zoom rocker, yes I dislike it. Shawn, you're probably right that it isn't any worse than other cameras, it's pretty much the same as my VX-2000. But at least the VX-2000 also has a zoom ring. It's a servo-controlled spinning wheel, but it lets me have a little better control over the zoom. With the rocker switch, if I'm trying to do a very slow zoom I find it virtually impossible. Either I end up pushing too hard and the zoom speeds up, or I don't push hard enough and the zoom stops dead. Either way I get ugly results. The Varizoom Pro-L lets me set the zoom speed with a dial, then press a button to activate. This gives me a slow, steady zoom which is something I have never been able to do consistently with the built-in rocker.

October 20th, 2003, 08:43 PM	#7
Chris Long Regular Crew Join Date: Jul 2003 Location: Middletown, Maryland USA Posts: 177	I agree completely with your points about the zoom rocker, Boyd. I have disliked it from the first time I played with it, a despite much practice, cannot consistently produce a slow, smooth zoom. Fast and jerky, I can do. I really wish the engineers had seen fit to include a slow/medium/fast setting selector in the menu (and an "Ultra Slow" setting, while we're at it). It would be nice to have, in place of the hair trigger variable speed thing. Being variable doesn't mean it's all things to all people, unfortunately! I may eventually want to look into a zoom controller. Seems to me that it might be fairly simple to put one together, if I knew where to start. Anyone know of any homebuilt zoom controllers? By the way--I have used the controller on the Remote Commander occasionally, to fairly nice effect. Just has to be the right situation.