70-200 F2.8 stange results

wegotitugetit

wegotitugetit

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alex
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GOT A 70-200 F2.8 today so thought i would take it for a quick run at work and see what it was like and got some strange results

now at work we have flurescent lighting and never had a issue when testing lenses before

i used the from door on both photos for focus points and both metered to the same area the

and just realised i left on a high iso setting too and had filter off and had smae result as when it was on

the focus is on the red sticker on the door


IMG_9571 by wegotitugetit, on Flickr


focus point is on the bottom half of the door


IMG_9570 by wegotitugetit, on Flickr
 
Not sure I follow what you are asking, Alex. Is it the apparent difference in white balance between the 2 pics. If you are using auto white balance I could see that happening.
 
Strange results indeed! Were you shooting JPG? What was your shutter speed?

White balance would be the obvious culprit, but to my eye it seems consistent through the window across the two images. The only other thing I can think of is a high shutter speed and a frequency/flicker difference in the fluorescent lighting between the two shots.
 
What's your shutter speed? Flourecsent lighting flickers which causes this effect if your shutter speed is too high
 
I don't think there's anything unusual about the shots when there's a good dose of flourescent lighting playing its part.

Bob
 
Working this out on my fingers, fluorescent flicker is at 50Hz, so any shutter speed different from a multiple of 1/50th is going to capture a fractional portion of the flicker's phase rather than a precise cycle/number of cycles.

So 1/50, 1/100, 1/150, 1/200 etc should capture multiples of the fluorescent bulb cycle. Any speeds outside of multiples of 1/50th will result in inconsistent results over multiple shots.
 
SimonH said:
Strange results indeed! Were you shooting JPG? What was your shutter speed?

White balance would be the obvious culprit, but to my eye it seems consistent through the window across the two images. The only other thing I can think of is a high shutter speed and a frequency/flicker difference in the fluorescent lighting between the two shots.
Click to expand...

This^

You were using a higher ISO than you normally pick for lens testing and so you got a faster shutter speed - you've captured the colour cycling of the lights. Look at the colour of outside - they're close to identical, but the inside is showing as actually lit with different colour lights.
 
SimonH hasn't got it quite right. If the lights are cycling at 50hz, you need a shutter speed of 1/50th or slower to ensure that you capture a full cycle that the lights go through. Anything faster and you are only capturing part of the cycle which can lead to strange colour casts.
 
You're quite right, of course! This is why I got into computers in the first place.. They do the basic maths I can't do! :D
 
I took some photos of a friends birthday party in a village hall a year or so ago and they had some ancient florescent tubes which gave me the weirdest results.

One frame would have a pinkish cast, the next green. It was actually really hard to correct for in post so I think I ended up processing them in mono - there was no other source of light to help balance the effect because it was dark outside.

I shoot raw and I always set my white balance with a preset. Auto white balance does a fantastic job on modern cameras, but it can still be thrown off course by mixed lighting or colour combinations in the frame, at least if you stick with a preset you'll get consistent results.

But yes, florescent lighting pulses horribly and you might not notice it with new tubes, but with older ones you can kind of see it, a horrible dull flicker.
 
wegotitugetit said:
in other words its like looking into a secrity camera that is looking over more pc's it shows the screen flickering and this what i have captured

cheers bob
Click to expand...
Flickering on it's own would simply change the exposure but the colour temperature also changes as the flouresent light goes through its cycle.
If you used a shutter speed of 1/100th second then your exposure would be based on all the component parts of a complete cycle. Once you increase the shutter speed beyond 1/100th then you effectively catch only a part of the cycle and consequently miss some of the component parts.

Aim for 1/100, 1/50, 1/25

Bob
 
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