Strange Photo Phenonenon

[John Oh]

I was sitting at my Pc and messing about with my camera I took a picture of the screen, As you do. It was in Manual mode F18 1/60sec and I had the flash on. Below is the picture I got.

Both monitors were on, but appear completely black

Below is the smae picture with no flash, f2.8 and 1/60sec



Anyone any idea why.

[Ian A]

Ooooooooooooooooooooooooooh   :blink:

[Danny Sutton]

it is cos of the speed the flash fires at and the refresh rate of your screens

[mike leahy]

[quote="mad-dan" post=8581] refresh [/quote]

 i thought they where sweets  :lol:  :lol:  :lol:  :lol:

[Ali Wiseman]

[quote="mad-dan" post=8581]it is cos of the speed the flash fires at and the refresh rate of your screens[/quote]

Indeed. Most PC monitors refresh at 60Hz. The timing of the Shutter being open on an LCD will gernerally have a full lit, or unlit screen. On an old CRT, it used progressive scanlines, and You could catch it partway through the scan.

I think... I'm tired, and my brain hurts.

[mick murphy]

this happened to me once johno and i saw 2 black screens when there were on and it was some twat poked me in the eyes with 2 fingers,

[Ian A]

LMAO  :lol:

[Tim Watts]

[quote="NewStuff" post=8587][quote="mad-dan" post=8581]it is cos of the speed the flash fires at and the refresh rate of your screens[/quote]

Indeed. Most PC monitors refresh at 60Hz. The timing of the Shutter being open on an LCD will gernerally have a full lit, or unlit screen. On an old CRT, it used progressive scanlines, and You could catch it partway through the scan.

I think... I'm tired, and my brain hurts.[/quote]

Test the theory - 1/60 second shutter speed - take a load and roughtly half should come out black....i think.....

Hmmmm... whats the duty cycle......

hmm....hang on its not a scan rate like CRT, its a refresh rate.

SO it doesn't go 'off' at all (unlike crt), it just refreshes.....ohh i dunno - its too late!!

One to fall to sleep with!

[John Oh]

It's not shutter speed dependant tried at 1/40, 1/80 & 1/125 - same effect sorry missed that bit of info off before.

[Danny Sutton]

it's not (just) the shutter speed, it's the speed the flash fires at, try it at say F3.5 for 1/20th with the flash, you should get an over exposed picture, but you should see the screen lit.

or just stick the camera in night mode, the flash will fire, but the shutter speed should be long enough to catch the refresh

[John Nicholson]

Why do you have two screens?
Does it do 3D?

[John Oh]

[quote="NewStuff" post=8587]Indeed. Most PC monitors refresh at 60Hz. The timing of the Shutter being open on an LCD will generally have a full lit, or unlit screen.[/quote]

I am not convinced it has anything to do with refresh rates, if it was the results would be unpredictable I.E. sometimes on, sometimes off and sometimes a bit of both but it was as ways the same completely dark and when the screen had a white background I would expect the photo of the screen overexposed but it never was.

Also I don't think LCD pixels actual turn on and off during the refresh (unless they are changing) and both monitors would be refreshing at different times.

John

One of the monitors is a 3d monitor, but I have 2 to give me a extra large desktop, useful when I am doing video editing but more useful at work when I am coding.

[John Nicholson]

It seems that I have the same monitor as you have LG Flatron E2411.  I am told it works in landscape oir portrait mode.  
Some people use two screens on Hauptwerk installations to represent the right and left side of a pipe organ console.  I'n not sure if they are a different type of screen that responds to screen contact (to operate the organ stops).

Am I right that an LCD screen does not emit light as does an old fashioned cathode ray tube?  This means that the picture is only visible if back lit by a light source positioned behind the LCD screen layer.  Your camera may not be able to detect the low level of light used, or the angle may be such that the light is low. - Just an idea as to the reason for your discovery!

[Tim Watts]

Anti relective coating - Tricks exposure metering?

I'm a two screener too , would be lost with one!

[John Oh]

[quote="TimWatts" post=8632]Anti relective coating - Tricks exposure metering? [/quote]

No It can't be that either, as the camera was in manual mode so metering wasn't used to set the exposure.