Is this a fluorescent light issue?

[doggiedoc]

I've noticed sometimes when I take pictures of patients I get a brownish haze in the middle or bottom of the image. Could this be caused by flicker in the the fluorescent lights of the exam room?


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ISO 400 ƒ1.2 1/500 50mm





[img]/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/24/2068.IMG_5F00_5462.jpg[/img]


ISO 400 ƒ1.2 1/400 50mm





These images were taken within 1 second of each other, no other ambient light besides exam room fluorescents.


Thanks for any help,


Paul

[HDNitehawk]

Metering issue maybe. The pictures are not framed the same maybe it was just the spot you picked on the dog to focus that caused it. Notice one is 1/500 and the other is 1/400. You using AV setting?


Do your lights flicker now?





Edit: looking again I think it is metering. It would have hit on about the dogs chest on the lower picture (dark area). And on its nose (white area) on the top pic.

[Sean Setters]

My instinct says "yes." Fluorescent bulbs can be finicky things. Even though our eyes don't perceive it, flourescent bulbs vary significantly in color and intensity from one split second to the next. I've often gotten very different results after a small shutter speed change. It's quite odd. Maybe one of our resident light experts can chime in and explain this more fully.

[doggiedoc]

Thanks for the quick response.





I had it set to evaluative metering. I could see spot metering do that but why the band of yellow/brown? Yes, using AV mode. I have not noticed the lights flickering but will look tomorrow. Here is another with the stripe in the middle.





[img]/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/24/3872.IMG_5F00_5464.jpg[/img]


ISO 400 ƒ1.2 1/500 50mm Aperture Priority

[HDNitehawk]

Do you have some other light source there? Or a lot of lighting. Looking at some of the pics I have taken in the office (which is all flouresent bulbs) I never got anywhere close to 1/400 in AV mode.

[neuroanatomist]

I'm no lighting expert, but I think it could be the fluorescent lights. If you're at that shutter speed, you're faster than the max flash sync speed. Can't remember what body you have, but for a Rebel/5DII that's 1/200 s, for an xxD/7D/1Ds it's 1/250 s, and for a 1D it's 1/300 s. The reason those are the max shutter sync speeds for those bodies is that's the fastest shutter speed where the first curtain fully opens before the second curtain starts to close, i.e. the entire surface of the sensor is exposed to the light from a flash, which has a duration measured in thousandths of a second. So, with a speed faster than the max sync speed, the sensor is exposed to a 'rolling window' between the first and second curtains. I'd expect that could result in an unexpected interaction with the flicker of fluorescent lights. Typical fluorescent lights flicker at 100-120 Hz (which is above the 'flicker fusion frequency' meaning we perceive them as continuous lighting, just like computer monitors and TVs - to see this effect, take a picture of your television, and depending on the refresh rate you'll see a dark horizontal band at speeds higher than that, which for my TV is 1/60 s).

Do you have some other light source there? Or a lot of lighting.

Or a really wide aperture. [:P] Those were at f/1.2 - I can get shutter speeds that fast with pretty dim lighting using my 85L.

[doggiedoc]

These were close to midday so I don

[doggiedoc]

I have a 7D and I've seen it with my 40D at similar apertures.

exposed to a 'rolling window' between the first and second curtains.

This would explain why some times the stripe is at the bottom others in the middle of the frame. I bet if I looked back at other sessions I could find one at the top!


Any way to avoid this besides using a flash?

[HDNitehawk]

Neuro


I was comparing my 35mm and 24mm at 1.4 at the office. But then maybe I work in a cave []





Doggiedoc


I was doing some research about this on the web after I read your post. What some say is that shutter speeds faster than the lights cycle can cause discolorations. The lights cycle at about 1/100 to 1/120 second and if, the sources say, you keep your shutter speed below that it helps.


Edit...oops typo again

[lculpin]

Not metering, it is a fluorescent light issue. As mentioned above fluorescents