Exposure and practical shooting at DVinfo.net

Bjorn Moren · May 6th, 2005, 05:11 AM

The FX1 does a fair job with the auto exposure, but to me it is obvious that it is not quite enough if you want that really good results. I've been trying to find a practical way to handle exposure, a way that is useable in the field.

First there is the obvious locking of all exposure params: I lock the shutter and gain, get an auto-setting for iris and lock it too, check the zebra and if the overall lightness is what I want for the shot, and then tweak the iris. The downside of this: if I want to keep an overall recorded lightness level but the natural lighting changes, I constantly have to tweak the iris while recording. This would only be an option for well planned shots, or the fiddling with the iris will ruin the shot (or I have to improve my real-time iris handling!). So this is my preferred way so far, because constant exposure works good for most shots I do, and I can handle planned basic iris tweaks. I havn't used the shot transition functions yet, but I guess it would be a way if you can time and and plan the shots well enough. Not very practical for the bulk of my shots though.

The second way would be to use the "AE shift" (exposure compensation) in a picture profile to set the overall lightness of the shot to a level I like. Now I get automatic exposure for the whole shot. Downside: "AE shift" is not very accessible, since it it hidden in a menu. It would have been great to have an additional button close to the other exposure buttons for this. Also I find this method to give kind of unnatural results. I may go from a very light shot to a medium light shot, but I want just a slight lightness drop in the recording. Since the light shot gets very overexposed in the auto-setting I use AE shift to bring it down, which in turn brings the medium shot down too much.

Do you have any tips? How do you usually go about with the exposure when you are out in the field shooting?

Andrew J Hall · May 6th, 2005, 05:21 AM

Hi Bjorn

I am very much at the learning stage with this but have you used the AE override approach (pg 88 of the manual) attached to an ASSIGN button (that may be what you already described above, if so sorry). I find it very easy to switch on and off and also to use via the iris dial. As the light changes it is not hard to follow it with a steady adjustment of the dial, especially if you can anticipate the change.

Andrew

Dominic Jones · May 6th, 2005, 05:53 AM

Full manual is the only way to go, for a number of reasons.

Firstly it's the best way of getting a decent exposure. With a little practice you should find it easy to adjust the exposure for changing light, assuming you're not in a nightclub or anything! This way you can get the shot you want, precisely, all the time.

Secondly (and this is linked to the first part, really) all professional cameras have what you might call "real" lenses that will not set an auto exposure for you (because pros would not and do not use auto modes) - they'll probably allow for an auto iris, but that is not the best way to control the exposure as it drastically changes the motion characteristics of the footage. As you start to use these cameras you will find having trained yourself to shoot manually invaluable.

Think about it this way: If you're learning to drive you don't learn in an automatic, do you? You learn in a manual, and then if you decide you want to drive an automatic it's a piece of cake...

It may seem a bit of a challenge at first, but it's really not that bad once you get the hang of it - come on, you're dying to play with your new camera 24/7 anyway, aren't you??! Get stuck in!

George Griswold · May 6th, 2005, 05:57 AM

I am having the best results with locking all parameters except iris, just like a large broadcast camera. The iris control is well placed and responsive.

You may want to try that approach, if everything is changing it becomes a goose chase.

George

Bjorn Moren · May 6th, 2005, 08:01 AM

Thanks for the replies guys!

Yes I will stay with the iris-adjustment method and improve my real-time skills with this. As you say Dominic, I just have to practise and get used to it.

A side note: I understand why iris is the preferred way of controlling the exposure, shutter would mess up the image flow and gain would mess up the dynamics/latitude. But when CCDs will become better in the future, I suspect that a fine tuned gain control would be the preferred way. Since iris also controls focus depth you would ultimately want to leave that dial alone, and just amplify/dampen the digital signal. But I guess those super CCDs are in a far away future.

Andrew J Hall · May 6th, 2005, 05:15 PM

I did some experiments with iris / DOF yesterday (Z1P) and was very surprised by the results - in that changing from F1.4 to F11 I could see a negligable effect in terms of DOF but a lot of effect in terms of image noise (the latter is not surprising, the former is very surprising to me). I can't help wondering if I had some other setting wrong. I will do some further tests with it today.

Andrew

Barry Green · May 6th, 2005, 05:22 PM

If you were at full wide-angle, then yes, you'll likely see very minimal changes in DOF (unless you were very close to the subject).

Try re-running the test at full telephoto, you should see much more noticeable changes.

Dominic Jones · May 7th, 2005, 08:17 AM

There is something of a quirk with Sony cameras that you need to specifically lock all the modes to manual - Gain, Iris, Shutter - or the camera will automatically compensate for changes.

So, if you were on manual iris but did not lock off the gain, I would imagine that what happened is the camera increased the gain to compensate for the narrower iris and that is what caused the grain/noise to increase in the image.

As Barry says, I imagine the DOF issue was primarily due to lens length.

Andrew J Hall · May 7th, 2005, 05:07 PM

I did another set of test shots yesterday which showed a bit more variation but still not as much as I would have expected. Yes, any variation in noise will come down to the camera boosting light with gain, but what I find interesting is that, except for close-up, there appears limited and uncertain benefit obtained by adjusting iris and sometimes the better overall DOF (image clarity over a range of subject distances) comes with the lower iris setting due to the higher light level. These test shots were outdoors on a pretty gloomy day so that will be impacting on what is being seen.

http://www.andrew-hall-artist.com/jo...ndex.php?p=148

[btw my comments, here and in other similar threads, should be read as exploratory, I am very much a learner with this camera, and with video in general, so I like to run tests as part of familiarising myself]

Andrew

Dominic Jones · May 8th, 2005, 01:44 PM

OK, just had a look at that set of images and everything looks about as I'd expect.

Once you've hit f6 you've got everything pretty much inside the DOF, so no, you're not going to see any major difference between that and f11.

I think the problem with your tests is that you're not shooting anything with enough depth - the scene is really running across the lens, rather than away from it - try conducting the test pretty much along the wall, with some objects very close to the lens and other a *long* way away. You should see more DOF effect then.

May 6th, 2005, 05:11 AM	#1
Bjorn Moren Regular Crew Join Date: Apr 2005 Location: Stockholm, Sweden Posts: 65	Exposure and practical shooting The FX1 does a fair job with the auto exposure, but to me it is obvious that it is not quite enough if you want that really good results. I've been trying to find a practical way to handle exposure, a way that is useable in the field. First there is the obvious locking of all exposure params: I lock the shutter and gain, get an auto-setting for iris and lock it too, check the zebra and if the overall lightness is what I want for the shot, and then tweak the iris. The downside of this: if I want to keep an overall recorded lightness level but the natural lighting changes, I constantly have to tweak the iris while recording. This would only be an option for well planned shots, or the fiddling with the iris will ruin the shot (or I have to improve my real-time iris handling!). So this is my preferred way so far, because constant exposure works good for most shots I do, and I can handle planned basic iris tweaks. I havn't used the shot transition functions yet, but I guess it would be a way if you can time and and plan the shots well enough. Not very practical for the bulk of my shots though. The second way would be to use the "AE shift" (exposure compensation) in a picture profile to set the overall lightness of the shot to a level I like. Now I get automatic exposure for the whole shot. Downside: "AE shift" is not very accessible, since it it hidden in a menu. It would have been great to have an additional button close to the other exposure buttons for this. Also I find this method to give kind of unnatural results. I may go from a very light shot to a medium light shot, but I want just a slight lightness drop in the recording. Since the light shot gets very overexposed in the auto-setting I use AE shift to bring it down, which in turn brings the medium shot down too much. Do you have any tips? How do you usually go about with the exposure when you are out in the field shooting?

May 6th, 2005, 05:21 AM	#2
Andrew J Hall Regular Crew Join Date: Feb 2005 Location: Wellington, New Zealand Posts: 80	Hi Bjorn I am very much at the learning stage with this but have you used the AE override approach (pg 88 of the manual) attached to an ASSIGN button (that may be what you already described above, if so sorry). I find it very easy to switch on and off and also to use via the iris dial. As the light changes it is not hard to follow it with a steady adjustment of the dial, especially if you can anticipate the change. Andrew __________________ http://www.ps-scripts.com/ Intel Core2 Quad Q6600 2.4GHz, 2x 2Gb Ram, ATI Radeon HD 3850

May 6th, 2005, 05:57 AM	#4
George Griswold Major Player Join Date: Apr 2005 Location: New Orleans, LA Posts: 218	I am having the best results with locking all parameters except iris, just like a large broadcast camera. The iris control is well placed and responsive. You may want to try that approach, if everything is changing it becomes a goose chase. George __________________ George T. Griswold, Jr. www.videonow.info New Orleans

May 6th, 2005, 05:15 PM	#6
Andrew J Hall Regular Crew Join Date: Feb 2005 Location: Wellington, New Zealand Posts: 80	I did some experiments with iris / DOF yesterday (Z1P) and was very surprised by the results - in that changing from F1.4 to F11 I could see a negligable effect in terms of DOF but a lot of effect in terms of image noise (the latter is not surprising, the former is very surprising to me). I can't help wondering if I had some other setting wrong. I will do some further tests with it today. Andrew __________________ http://www.ps-scripts.com/ Intel Core2 Quad Q6600 2.4GHz, 2x 2Gb Ram, ATI Radeon HD 3850

May 7th, 2005, 05:07 PM	#9
Andrew J Hall Regular Crew Join Date: Feb 2005 Location: Wellington, New Zealand Posts: 80	I did another set of test shots yesterday which showed a bit more variation but still not as much as I would have expected. Yes, any variation in noise will come down to the camera boosting light with gain, but what I find interesting is that, except for close-up, there appears limited and uncertain benefit obtained by adjusting iris and sometimes the better overall DOF (image clarity over a range of subject distances) comes with the lower iris setting due to the higher light level. These test shots were outdoors on a pretty gloomy day so that will be impacting on what is being seen. http://www.andrew-hall-artist.com/jo...ndex.php?p=148 [btw my comments, here and in other similar threads, should be read as exploratory, I am very much a learner with this camera, and with video in general, so I like to run tests as part of familiarising myself] Andrew __________________ http://www.ps-scripts.com/ Intel Core2 Quad Q6600 2.4GHz, 2x 2Gb Ram, ATI Radeon HD 3850

May 6th, 2005, 05:53 AM	#3
Dominic Jones Major Player Join Date: Mar 2005 Location: Brighton, England Posts: 225	Full manual is the only way to go, for a number of reasons. Firstly it's the best way of getting a decent exposure. With a little practice you should find it easy to adjust the exposure for changing light, assuming you're not in a nightclub or anything! This way you can get the shot you want, precisely, all the time. Secondly (and this is linked to the first part, really) all professional cameras have what you might call "real" lenses that will not set an auto exposure for you (because pros would not and do not use auto modes) - they'll probably allow for an auto iris, but that is not the best way to control the exposure as it drastically changes the motion characteristics of the footage. As you start to use these cameras you will find having trained yourself to shoot manually invaluable. Think about it this way: If you're learning to drive you don't learn in an automatic, do you? You learn in a manual, and then if you decide you want to drive an automatic it's a piece of cake... It may seem a bit of a challenge at first, but it's really not that bad once you get the hang of it - come on, you're dying to play with your new camera 24/7 anyway, aren't you??! Get stuck in!

May 6th, 2005, 08:01 AM	#5
Bjorn Moren Regular Crew Join Date: Apr 2005 Location: Stockholm, Sweden Posts: 65	Thanks for the replies guys! Yes I will stay with the iris-adjustment method and improve my real-time skills with this. As you say Dominic, I just have to practise and get used to it. A side note: I understand why iris is the preferred way of controlling the exposure, shutter would mess up the image flow and gain would mess up the dynamics/latitude. But when CCDs will become better in the future, I suspect that a fine tuned gain control would be the preferred way. Since iris also controls focus depth you would ultimately want to leave that dial alone, and just amplify/dampen the digital signal. But I guess those super CCDs are in a far away future.

May 6th, 2005, 05:22 PM	#7
Barry Green Barry Wan Kenobi Join Date: Jul 2003 Location: North Carolina Posts: 3,863	If you were at full wide-angle, then yes, you'll likely see very minimal changes in DOF (unless you were very close to the subject). Try re-running the test at full telephoto, you should see much more noticeable changes.

May 7th, 2005, 08:17 AM	#8
Dominic Jones Major Player Join Date: Mar 2005 Location: Brighton, England Posts: 225	There is something of a quirk with Sony cameras that you need to specifically lock all the modes to manual - Gain, Iris, Shutter - or the camera will automatically compensate for changes. So, if you were on manual iris but did not lock off the gain, I would imagine that what happened is the camera increased the gain to compensate for the narrower iris and that is what caused the grain/noise to increase in the image. As Barry says, I imagine the DOF issue was primarily due to lens length.

May 8th, 2005, 01:44 PM	#10
Dominic Jones Major Player Join Date: Mar 2005 Location: Brighton, England Posts: 225	OK, just had a look at that set of images and everything looks about as I'd expect. Once you've hit f6 you've got everything pretty much inside the DOF, so no, you're not going to see any major difference between that and f11. I think the problem with your tests is that you're not shooting anything with enough depth - the scene is really running across the lens, rather than away from it - try conducting the test pretty much along the wall, with some objects very close to the lens and other a long way away. You should see more DOF effect then.