Wow... Rolling shutter

Martin Duffy · January 2nd, 2009, 02:56 PM

I also found in a recent dance concert that if the FX is set to auto focus and a scene goes from all black to all lights on, the camera really hunts for focus.

I also found this on the Z1. Its like it took a good 3-4 secs to auto focus!

I never noticed it on the VX2000 or TRV900 to this degree.

It didnt do this on all the scenes and maybe it was in relation to where my last framed shot was if you get my gist.

But as I said in an earlier post once it in focus it is no problem & I certainly haven't noticed any slipping in and out of focus issues.

I am about to edit the dance concert and so will report back on this one.

Ken Ross · January 2nd, 2009, 08:13 PM

Martin, it would seem to mandate manual focus in that case.

Greg Laves · January 2nd, 2009, 08:52 PM

I don't have a Z5 or FX1000 but I do have a V1 and a VX2100. IMHO, because of the much higher resolution, I think focus is more critical in HD cameras than it is in SD. So focus mistakes/problems/issues become much more glaring when shooting HD. I think my VX2100 is pretty typical. I have noticed the focus hunts occasionally. I just seems like the hunting winds up being a little less obvious when shooting SD video.

Jeff Harper · January 3rd, 2009, 08:26 AM

The hunting for focus is occasionally poor with the FX1000. Most of the time it performs satisfactorily, on some occasions it is downright scary. I've had to go full wide or zoom a bit and find something the camera could focus on before I could resume shooting. It is really startling when it happens. Thankfully it doesn't happen often.

This thread's title refers to rolling shutter, etc. As far as I am concerned, forget rolling shutter. No biggie.

Instead, I'd like to share the joy I have found since I became familiar with the phenomenon of F-drop, AKA lens ramping. If you have an FX7 you are familiar with it. I didn't know what F-Drop was when I owned the FX7, and it was one of the reasons I disliked the camera. It is all becoming clearer now that I understand this phenomenon a bit better and know there is a name for it.

The FX1000 suffers from f-drop and apparently with a 20x zoom it is just the way it has to be. In case you are not familiar, when you zoom in on a subject, running the iris manually(in my case I do extreme closeups of faces in my work) the Iris has to compensate and it closes up automatically and underexposes the image. In other words you cannot get a usable image in full zoom when focusing on a face, or anything else, for that matter when running the iris in manual mode.

Apparently if I knew what the specs meant before I purchased the cam I would've know about this beforehand.

Having bought my second FX1000 with the presumption I would figure out the exposure issue, I just today, the day after opening the box for the new cam, found out what lens ramping is.

I have grown to really love the FX1000 othewise and it shoots phenomenal images. However I would have likely at least considered a Z1 for a second cam had I known about this.

Ken Ross · January 3rd, 2009, 09:05 AM

Jeff, why not let the cam control the iris until you're fully zoomed and then lock it down? Even if you feel the cam is overexposing a bit in automatic (as so many seem to do), you can always exposure bias toward the negative a stop or two.

Jeff Harper · January 3rd, 2009, 09:24 AM

I hear what you're saying Ken. That is what I have usually done in the past. That doesn't work when you have lens ramping involved.

That's what was driving me crazy until I learned what it is and that the FX1000 has it.

When you zoom in, almost immediately the iris starts to close up. By the time you get to full zoom you are at f3.4 and cannot change it. You can close it down further, but you cannot open it further.

Hans in another thread helpfully pointed out that I "should have known about this" beforehand. But I didn't. Now I do.

Greg Laves · January 3rd, 2009, 09:38 AM

Quote:

Originally Posted by Jeff Harper

The FX1000 suffers from f-drop and apparently with a 20x zoom it is just the way it has to be.

A 20x zoom lens doesn't necessarily have to have f-drop, Jeff. But the lenses that do have consistant F-stops thoughout the zoom range can get to be pretty darned expensive. Most professional broadcast lenses can zoom without changing the f-stop. The lens in the Z5/FX1000 is an amazing lens at it's price point.

Ken Ross · January 3rd, 2009, 09:57 AM

Jeff, maybe I'm missing something, but I still don't see why leaving it on automatic and then locking it down wouldn't work (assuming you're staying at that same focal length). As long as there is sufficient lighting, the camera should be compensating for the reduction in lens speed as you zoom.

Jeff Harper · January 3rd, 2009, 10:12 AM

You are correct Greg, I meant that the f-drop was ineveitable in this price range of camera, but was trying to keep my post brief. In my world 20x zoom means fdrop. In the broadcast world I have been reading it is a whole 'nuther deal.

Video Lenses: How They All Work

Jeff Harper · January 3rd, 2009, 10:26 AM

Ken, I'm sorry, I didn't explain myself well. I want to be able to open the iris to 1.8 at full zoom. The camera won't do that.

This is something that apparently many of the people on this forum understand, but I didn't, and honestly still don't, but I accept it is a limitation of 20x lens in my price range.

There is a lot to learn with this camera for someone like me who came into the business with no technical know-how and who had the luxury of learning to shoot with the idiot-proof VX2100.

Setting exposure was so easy, there was no F-Drop, and even I captured stunning images with it. This camera operates very similarly in many ways, but is requiring much more effort and study.

Ken Ross · January 3rd, 2009, 10:29 AM

Ah, OK, now I've got it.

It shouldn't be too bad once you've adjusted to the reduction in your aperture. If your primary concern knowing this drop is inevitable now is the exposure, then I would just let the camera adjust for it and then lock everything down or adjust as necessary from that point.

Greg Laves · January 3rd, 2009, 12:04 PM

Besides potentially changing the exposure throughout the zoom range because of f-drop, it also changes the dof slightly. Which might not be ideal for artistic purposes.

Jeff Harper · January 3rd, 2009, 01:40 PM

Outstanding feedback, thanks guys. I'm off to the races.

Tom Hardwick · January 3rd, 2009, 02:11 PM

Quote:

Originally Posted by Jeff Harper

The FX1000 suffers from f-drop and apparently with a 20x zoom it is just the way it has to be. In case you are not familiar, when you zoom in on a subject, running the iris manually(in my case I do extreme closeups of faces in my work) the Iris has to compensate and it closes up automatically and underexposes the image. In other words you cannot get a usable image in full zoom when focusing on a face, or anything else, for that matter when running the iris in manual mode.

Lots of assumptions and misinterpretations in your post Jeff.
Firstly ramping is a manufacturing design intent to limit the size, weight, bulk and cost of the zoom. It's perfectly possible to have non ramping zooms, as the 10x f/1.4 fitted to my 1974 canon 1014E proves.

So to keep the spec looking good ("20x f/1.6 zoom using a 72 mm filter thread'') the maximum aperture is allowed to diminish the more you zoom to telephoto. If you had a constant f/1.6 max aperture the lens would be physically huge and as I say - very costly indeed.

You say, ''when you zoom in on a subject, running the iris manually the Iris has to compensate and it closes up automatically and underexposes the image''

This again is only true under very specific circumstances, and these are that you're forced to use max (f/1.6) aperture and that the shutter speed and gain settings are locked down. Then - yes - you'll get under exposure the more you zoom in. But if you were shooting at a locked f/5.6 (say) then the exposure would remain fine throughout your entire zoom range.

So your sentence that says, ''In other words you cannot get a usable image in full zoom when focusing on a face, or anything else, for that matter when running the iris in manual mode'' is silly nonsense, as I'm sure you'll agree.

BTW, the 'idiot proof' VX2100 most certainly has a ramping zoom. It loses a stop (f/1.6 to f/2.4) whereas the FX1000 loses two stops.

tom.

Greg Boston · January 3rd, 2009, 03:27 PM

Quote:

Originally Posted by Jeff Harper

This thread's title refers to rolling shutter, etc. As far as I am concerned, forget rolling shutter. No biggie.

Instead, I'd like to share the joy I have found since I became familiar with the phenomenon of F-drop, AKA lens ramping.

Jeff, please keep threads on topic.

Thanks in advance,

-gb-

January 2nd, 2009, 02:56 PM	#46
Martin Duffy Regular Crew Join Date: Jan 2006 Posts: 156	Auto focus I also found in a recent dance concert that if the FX is set to auto focus and a scene goes from all black to all lights on, the camera really hunts for focus. I also found this on the Z1. Its like it took a good 3-4 secs to auto focus! I never noticed it on the VX2000 or TRV900 to this degree. It didnt do this on all the scenes and maybe it was in relation to where my last framed shot was if you get my gist. But as I said in an earlier post once it in focus it is no problem & I certainly haven't noticed any slipping in and out of focus issues. I am about to edit the dance concert and so will report back on this one.

January 3rd, 2009, 08:26 AM	#49
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	The hunting for focus is occasionally poor with the FX1000. Most of the time it performs satisfactorily, on some occasions it is downright scary. I've had to go full wide or zoom a bit and find something the camera could focus on before I could resume shooting. It is really startling when it happens. Thankfully it doesn't happen often. This thread's title refers to rolling shutter, etc. As far as I am concerned, forget rolling shutter. No biggie. Instead, I'd like to share the joy I have found since I became familiar with the phenomenon of F-drop, AKA lens ramping. If you have an FX7 you are familiar with it. I didn't know what F-Drop was when I owned the FX7, and it was one of the reasons I disliked the camera. It is all becoming clearer now that I understand this phenomenon a bit better and know there is a name for it. The FX1000 suffers from f-drop and apparently with a 20x zoom it is just the way it has to be. In case you are not familiar, when you zoom in on a subject, running the iris manually(in my case I do extreme closeups of faces in my work) the Iris has to compensate and it closes up automatically and underexposes the image. In other words you cannot get a usable image in full zoom when focusing on a face, or anything else, for that matter when running the iris in manual mode. Apparently if I knew what the specs meant before I purchased the cam I would've know about this beforehand. Having bought my second FX1000 with the presumption I would figure out the exposure issue, I just today, the day after opening the box for the new cam, found out what lens ramping is. I have grown to really love the FX1000 othewise and it shoots phenomenal images. However I would have likely at least considered a Z1 for a second cam had I known about this. Last edited by Jeff Harper; January 3rd, 2009 at 10:02 AM.

January 2nd, 2009, 08:13 PM	#47
Ken Ross Trustee Join Date: Jan 2005 Location: New York Posts: 1,945	Martin, it would seem to mandate manual focus in that case.

January 2nd, 2009, 08:52 PM	#48
Greg Laves Major Player Join Date: Nov 2007 Location: Corpus Christi, TX Posts: 640	I don't have a Z5 or FX1000 but I do have a V1 and a VX2100. IMHO, because of the much higher resolution, I think focus is more critical in HD cameras than it is in SD. So focus mistakes/problems/issues become much more glaring when shooting HD. I think my VX2100 is pretty typical. I have noticed the focus hunts occasionally. I just seems like the hunting winds up being a little less obvious when shooting SD video.

January 3rd, 2009, 09:05 AM	#50
Ken Ross Trustee Join Date: Jan 2005 Location: New York Posts: 1,945	Jeff, why not let the cam control the iris until you're fully zoomed and then lock it down? Even if you feel the cam is overexposing a bit in automatic (as so many seem to do), you can always exposure bias toward the negative a stop or two.

January 3rd, 2009, 09:24 AM	#51
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	I hear what you're saying Ken. That is what I have usually done in the past. That doesn't work when you have lens ramping involved. That's what was driving me crazy until I learned what it is and that the FX1000 has it. When you zoom in, almost immediately the iris starts to close up. By the time you get to full zoom you are at f3.4 and cannot change it. You can close it down further, but you cannot open it further. Hans in another thread helpfully pointed out that I "should have known about this" beforehand. But I didn't. Now I do.

January 3rd, 2009, 09:57 AM	#53
Ken Ross Trustee Join Date: Jan 2005 Location: New York Posts: 1,945	Jeff, maybe I'm missing something, but I still don't see why leaving it on automatic and then locking it down wouldn't work (assuming you're staying at that same focal length). As long as there is sufficient lighting, the camera should be compensating for the reduction in lens speed as you zoom.

January 3rd, 2009, 10:12 AM	#54
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	You are correct Greg, I meant that the f-drop was ineveitable in this price range of camera, but was trying to keep my post brief. In my world 20x zoom means fdrop. In the broadcast world I have been reading it is a whole 'nuther deal. Video Lenses: How They All Work

January 3rd, 2009, 10:26 AM	#55
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	Ken, I'm sorry, I didn't explain myself well. I want to be able to open the iris to 1.8 at full zoom. The camera won't do that. This is something that apparently many of the people on this forum understand, but I didn't, and honestly still don't, but I accept it is a limitation of 20x lens in my price range. There is a lot to learn with this camera for someone like me who came into the business with no technical know-how and who had the luxury of learning to shoot with the idiot-proof VX2100. Setting exposure was so easy, there was no F-Drop, and even I captured stunning images with it. This camera operates very similarly in many ways, but is requiring much more effort and study.

January 3rd, 2009, 10:29 AM	#56
Ken Ross Trustee Join Date: Jan 2005 Location: New York Posts: 1,945	Ah, OK, now I've got it. It shouldn't be too bad once you've adjusted to the reduction in your aperture. If your primary concern knowing this drop is inevitable now is the exposure, then I would just let the camera adjust for it and then lock everything down or adjust as necessary from that point.

January 3rd, 2009, 12:04 PM	#57
Greg Laves Major Player Join Date: Nov 2007 Location: Corpus Christi, TX Posts: 640	Besides potentially changing the exposure throughout the zoom range because of f-drop, it also changes the dof slightly. Which might not be ideal for artistic purposes.

January 3rd, 2009, 01:40 PM	#58
Jeff Harper Inner Circle Join Date: Jun 2005 Location: Cincinnati, OH Posts: 8,425	Outstanding feedback, thanks guys. I'm off to the races.