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SLT-A77 Custom White Balance Problems

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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Topic: SLT-A77 Custom White Balance Problems
    Posted: 10 May 2012 at 01:15
Sony A77 problems when trying to set a studio strobe light custom white balance using the "Expodisc" white balance standard.

Equipment used:
1.     Sony Model SLT-A77 Camera
2.     AlienBees B800 Studio Strobe Light
3.     Expodisc White Balance Standard

Conditions:
1. "Mixed" lighting conditions - florescent room lights & one Alien Bee strobe.
2. Expodisc used in accordance with manufactures instructions.

Results:
1. When the room lights are on, the "grey frame" produced by the expodisc consistently has a blue tint - definitely not a "neutral" grey frame.
2. When the room lights were turned off - the A77 custom white balance worked perfectly.

Apparent cause:
In "M" (manual shutter & aperture) mode, the user has no input on shutter speed when the custom white balance is set.

It does not matter if I set the shutter speed for 30 seconds or if I set it to 1/8000 second, it has no effect upon the manual white balance that the camera firmware sets.

The only input I can change that has any effect upon the manual white balance is the F-Number (aperture).

The Sony A77 firmware is apparently using a fixed, pre-set shutter speed when the manual white balance is set.

This firmware pre-set shutter speed is too slow to exclude ambient (non-studio strobe) light sources.

Has anyone else observed this SLT-A77 studio strobe custom white balance problem?
 



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Post Options Post Options   Quote Frankman Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 10:07

An interesting observation Squid. I guess that this also has implications for venue shoots under mixed lighting without flash. In the studio, I use the XRite colour checker. It gets me close, but I'll often create my own profile in LR or PS to give me a slightly warmer look for portraits.

Frank

Edited by Frankman - 10 May 2012 at 10:14
*** Sony A850 * A700 * Minolta 5D and other stuff ***
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 14:01
Your observation regarding mixed light venues goes right to the heart of the problem.

I've owned two previous Sony cameras (F-828 & DSC-R1) and never had a "studio strobe / mixed light" white balance issue with either of them.

Since the SLT-A77 has an external flash synchronization connection it was clearly designed to accommodate the use of studio strobe lights.

Furthermore, the SLT-A77 instruction manual directs the photographer to shoot in manual mode, specifies a shutter speed of 1/250 second and to set a custom white balance when using an external flash.

It's strange that the SLT-A77 firmware does not allow the photographer to input the shutter speed when setting a manual white balance.

Sony technical support has been made aware of this issue, but thus far has not responded in any meaningful way.

I made this post see if any other SLT-A77 / studio strobe photographers have had a similar "custom white balance" experience.
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 15:39
Thanks for your response.

I tried setting an insanely fast ISO with the idea of "forcing" a faster white balance shutter speed....

- that didn't work.

Any other suggested "work-around"?
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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 16:40
Originally posted by Squid Squid wrote:

In "M" (manual shutter & aperture) mode, the user has no input on shutter speed when the custom white balance is set.

Wait a minute - this part is not true with my cameras (KM5D, KM7D, and A55). In M/S/A/P modes the displayed shutter speed and aperture are both being honored when setting custom WB... well, as far as I can tell with humanly observable shutter speeds.

Whether or not the varying shutter speeds do in fact have the expected effect under mixed lighting, I haven't tested that. What has happened to me is that sometimes the camera cannot obtain a WB reading at all, so I have been forced to change something to get it to work.
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 16:55
Just for the sake of clarity, where you trying to set a custom white balance under mixed "ambient" and strobe lighting conditions?
 



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Post Options Post Options   Quote sybersitizen Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 17:40
Originally posted by Squid Squid wrote:

Just for the sake of clarity, where you trying to set a custom white balance under mixed "ambient" and strobe lighting conditions?

Not specifically. I was just pointing out that the indicated shutter speed is in fact honored in my cameras, and that remains true even when flash is in the mix.

And in quick testing just now under mixed lighting, my A55 does vary the Kelvin number and change the visible WB results over a wide range depending on shutter speed. But trying to go beyond normal sync speed (above 1/200s) produces images with shutter shadows and eventually results in a WB error. I assume that you can't get correct results that way with your rig either.

Sounds like the best one can do is to use the camera's fastest sync speed, or maybe a little faster.

Edited by sybersitizen - 10 May 2012 at 17:43
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Post Options Post Options   Quote igogosh Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 17:57
I've never used the expo disc. I did all the tests in a controlled environment and simply bring in desired WB setting when I'm using a specific light. Kelvin Scale works for me and you can fine tune it as well. Shooting RAW, I only need to be close enough.
Doesn't a77 memorize the Custom WB settings for you to use later?
I suggest you test all you lights in studio to figure out their correct Kelvin temperature and be done with it.
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Post Options Post Options   Quote igogosh Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 18:03
dial WB settings on the kelvin scale as you shoot and compare the results in Lightroom. Studio strobes work in the 5000 K - 5500 K range, and 3300 - 3800 when gelled with a CTO or 1/2 CTO filter, adjust to your desired look, it will only take once to learn and never worry about it later. I may be missing something, nut it works for me.
http://www.KeeperExpert.com/ is my website, it has lots of examples of such work in "commercial" http://www.KeeperExpert.com/
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 10 May 2012 at 19:11
To summarize...

The SLT-A77 custom white balance works perfectly well in a pure "ambient" (no strobe) light environment.

It works perfectly well in a pure "strobe" (blacked-out studio) environment.

The problem occurs when I find myself in a mixed light environment: e.g. a gymnasium, wedding reception hall, outdoors, or anyplace I work with strobes and can't eliminate or control the ambient light.

I am not a professional photographer. I do not have a dedicated studio. I always shoot "on-location".

To see examples of my photos (THERE IS NO "ADULT" OR "MATURE" CONTENT ON THIS LINK!):

http://bardulf.deviantart.com/

I have taken a series of "canned" strobe white balance profiles at full power, 2/3 power, & 1/3 power in a blacked-out basement & saved them in the SLT-A77 memory.

At best, this is a "kludge" & doesn't give the best white balance results.

Depending upon the relative strength of the ambient light vs. the strobes, the color balance can be critical. I'd prefer to have a white balance that is valid for the light that is present during the exposure - (1/250 sec. & whatever F/stop that is used).

In terms of custom "real-time" white balance performance, I'm disappointed that my $2000 SLT-A77 is being outperformed by my old DSC-R1.

I may in fact have a defective camera. In all other respects, it performs very well.

I was just wondering if my experience trying to set a custom white balance is unique or if this problem has been observed in other SLT-A77 cameras.

Edited by stiuskr - 11 May 2012 at 00:01
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 11 June 2012 at 17:52
Update:
I recently had the opportunity to test another SLT-A77 alongside my own. Both SLT-A77 cameras were using firmware version 1.05.

Both cameras were tested in a mixed (ambient & off-camera flash), a "flash only", and a ambient (no flash) lighting environment. Both cameras were tested in manual mode at a shutter speed of 1/250 second and a variety of F-numbers.

Both cameras produced virtually identical results. Neither camera can set a neutral custom white balance in a mixed (ambient & off-camera flash) lighting environment.

The conclusion:
The SLT-A77 firmware in itís current version (1.05) has a defect. Sony technical support has been made aware of my findings.
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Post Options Post Options   Quote Bob Maddison Quote  Post ReplyReply Direct Link To This Post Posted: 11 June 2012 at 18:54
In any digital camera, both auto WB and custom WB are designed to cope with light that has a colour characteristic consistent with a "Black Body" source at a given temperature (the "colour temperature"). Mixed light sources such a flash with tungsten lighting can no longer be represented by a single "colour temperature". As an extreme example, imagine a uniformly lit scene using three lights, but one of the three lights is red, one is blue and one is white. The camera can only do its best to record the scene, but whatever it does, the lighting will be distorted. If WB is set to be compatible with the white light, then the red area will record as red and the blue area as blue. If either auto WB or custome WB are used, the camera will attempt to correct and the result will be unpredictable, probably an overall neutral colour with the red lit area showing a washed out pink and the blue area a washed out blue - far from satisfactory.

With mixed lighting, don't expect the camera to do the impossible. It will be far better to set the WB for the dominant light which in your case is probably daylight or tungsten, then accept that the limited area where the flash dominates will be a little colder. If you set the WB to flash, then the ambient lit area will look a little warm. You must make the choice.

On a separate issue, Firmware updates have a limited application. The camera functions that can be updated must be designed into the camera from the beginning. This implies that the maker must have some idea of what might be needed in future. That is why all camera makers regularly produce upgraded models because those upgrades go beyond what any firmware update can do.
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Post Options Post Options   Quote Squid Quote  Post ReplyReply Direct Link To This Post Posted: 11 June 2012 at 20:15
Your points are well taken. However there are salient differences between "ambient" light and strobe light besides their respective color temperatures.

The first difference is intensity. In most situations where a studio strobe is used it is by far the more dominant light that illuminates the subject. Thus studio strobe use allows a much higher F-number than an ambient lighting scenario would. The 1/250 second shutter speed and a high F-number greatly diminish (but do not completely eliminate) the contribution of the ambient light.

The second difference is the duration of the light. The duration of a typical studio strobe is between 1/1000 and 1/3000 second. This very brief duration allows it to function as the "effective" shutter speed.

If a custom white balance is set at shutter speed that is slower than the recommended synchronization speed the ambient light will proportionally "contaminate" the custom white balance. I suspect this is the situation with the A-77 firmware 1.05.

Sony clearly designed the SLT-A77 for use with an external flash. The SLT-A77 has a synchronization port for use with an external flash. The A-77 Instruction Manual directs the photographer to set a custom white balance when using an external flash. Therefore, it is odd that the custom white balance firmware does not support the use of this camera with an external flash.

Other camera manufacturers do not seem to have any problem setting a neutral custom white balance in a external flash & ambient light scenario.

I have used two old Sony digital cameras (F-828 & DSC-R1) for years. Both of these cameras have performed flawlessly when setting a neutral custom white balance under mixed lighting conditions. In my experience, a custom white balance that is set under the "as shot" conditions is invariably superior to any of the "canned" presets.

I don't wish to sound like I am "bashing" the SLT-A77. I honestly like the camera & enjoy using it. However, at present I am forced to rely upon photo-editing software to compensate for a firmware defect.

This link explains the general characteristics of studio strobes far better than I can.

http://www.paulcbuff.com/lightingforstillphotography.php

I apologize for being a bit long-winded. Thank you for your patience.

Edited by Squid - 11 June 2012 at 22:43
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 12 June 2012 at 09:35
Rather than an expodisc, would it be feasible for you to shoot a grey card at the start of the session then use the eyedropper tool in Lightroom (or other raw converter) to correct the white balance later on?

That's what I tend to do, using the whitebalance part of my colorchecker passport. Of course, this won't work too well unless you shoot raw.

For what it is worth, all my previous Sony DSLR/DSLT cameras also honoured the settings in M mode when taking WB readings. It's just the a77 that differs.
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