A limitation of modern cameras?

Brian G

Brian G

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I'm not a great fan of electronic viewfinders, but when using one I'm often surprised by the number of light sources that "pulse" or are not constant.
Because the cameras electronic viewfinder has a constant refresh, you are presented with a strobing effect between the viewfinder and the light source.
This seems particularly apparent on the London Underground, where not only do the electronic destination displays on the trains strobe, but so do a lot of the lights on the station platforms.
I'm not a railway photographer, but I'm interested in the challenge of taking a shot in which both the moving train and the electronic destination display are sharp.
The obvious way to get the train sharp is to use a faster shutter speed, but his is at odds with getting a sharp electronic display.
This is an example:
TubeTrainExample_01 by Brian Gibson, on Flickr

This was taken at a shutter speed of 1/320 and the train is not sharp, but as you can see the electronic destination display has not been captured cleanly.
The trian is travelling about 30mph, but to get it sharper I need to use a faster shutter speed, but this will render the electronic display even more blurred.
It seems the only way I can get a sharp display is to wait until the train is stationary and use a longer shutter speed, but I want a shot of a moving train.
Anyone experienced this problem or has any suggestions?
 
Indeed, I've just trawled through my motorsport photos where similar lights are used, no issues whatsoever at slower shutter speeds (1/15th in this example):

Silverstone 24hr by Chris Harrison, on Flickr

You'll also see flickering on programmes such as Top Gear with modern car LED headlights.
 
That's correct - modern LED light sources are rapidly switched off and on, but because the eye averages to peaks and troughs it appears to be a constant source.
 
ancient_mariner said:
That's correct - modern LED light sources are rapidly switched off and on, but because the eye averages to peaks and troughs it appears to be a constant source.
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Technically every light source powered by AC switches on and off 100 times a second, which causes it to flicker.
 
You see a lot of things doing it in video bus route numbers, petrol station prices, and car rear lights are good examples.
 
But incandescent lamps retain their heat so don't appear to dim appreciably (and the moment where there's absolutely zero current is immeasurably short.)
 
Nod said:
But incandescent lamps retain their heat so don't appear to dim appreciably (and the moment where there's absolutely zero current is immeasurably short.)
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This, which is why I didn't describe it as all light sources. It's a bit obvious with fluorescent tubes, but LEDs really show up strongly in photos because of the very rapid output switching. I failed to mention some lights are also driven by DC i.e. car incandescent headlights, therefore continuous, but LEDs ALWAYS seem to be switched because of the voltage drivers used.
 
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Nod said:
But incandescent lamps retain their heat so don't appear to dim appreciably (and the moment where there's absolutely zero current is immeasurably short.)
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Yes, thats right, which is why I said technically :)

The biggest culprit, in tradition lighting, are fluorescents which is why when installing on a three phase system using different phases helps reduce a possible stroboscopic effect.
 
ukaskew said:
Indeed, I've just trawled through my motorsport photos where similar lights are used, no issues whatsoever at slower shutter speeds (1/15th in this example): <snip image>

You'll also see flickering on programmes such as Top Gear with modern car LED headlights.
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And for much the same reason, car wheels can appear to be rotating backwards. It's unavoidable at faster shutter speeds (not to mention 'rolling-shutter' effects).

Fluorescent lights add another difficulty by sometimes changing colour mid-scan, producing a different colour cast at the top and bottom of the same frame.
 
The school started using projectors to project background images for a play - well they just came out as a mess of RGB in the photos.
 
I have had few led torches over the years (fishing, shooting, dog walking etc) and most of the cheaper ones have had PWM (pulse width modulation) to run at a lower brightness.

The first time I noticed it was in the rain. At 50% brightness (or power) the raindrops streaked, like my eyes had a slower shutter speed! Basically the led is strobed and 'off' for 50% of the time, so half brightness and half battery consumption.

On full brightness it does not happen (or happens so quickly that it is noticeable). Is it possible that the led display is auto dimmed and brightened depending on the light? It seems like a sunny day but the led is in shadow so may be running dimmed via PWM. If this is the case then at night time the effect would be even worse and in direct sunshine better.

I now have a more expensive nitecore torch that does not seem to suffer at any brightness.

T
 
ecoleman said:
That’s not a camera limitation. This is caused by the refresh rate of the display on the train.

You’d get the same result with any camera at a high enough shutter speed.
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Yes, you are quite right.
I didn't mean to imply that it was an effect solely caused by digital cameras.
What I was trying to say was that the strobing of an electronic viewfinder enabled you to see the effect in real time.
When using an electronic viewfinder I was quite surprised how many light sources displayed this characteristic.
As for using a slower shutter speed to capture the train destination display, in the example I posted above, a slower shutter speed will simply make the train more blurred, since I do not have the option of panning to cope with the trains movement.
It's pretty much a "no win" situation, you can either use a high shutter speed and have a sharp train with a scrambled display, or you can use a slow shutter speed and get a legible display on a blurred train.
I guess the answer is to combine the best of both into a composite image.
 
dancook said:
The school started using projectors to project background images for a play - well they just came out as a mess of RGB in the photos.
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You have to experiment with slower shutter speeds, and hope the cast aren’t moving too much!
 
Ironically, some of the worst effects I've seen on an EVF have been in camera shops where (e.g.) the display cabinet lighting caused very distracting banding when I was trying out a Fuji. In real use it has only quite rarely been a problem, fortunately.
 
Pound Coin said:
You have to experiment with slower shutter speeds, and hope the cast aren’t moving too much!
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I have and It's not an option, 1/50th second isn't good enough to get the shots I need. So had to ignore the backgrounds
 
ecoleman said:
That’s not a camera limitation. This is caused by the refresh rate of the display on the train. You’d get the same result with any camera at a high enough shutter speed.
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You seem to be saying the fault lies with train so how do you feel about a bird photo with blurry wings — refresh rate too high :) ? I thought the OP was making a valid point.
 
The type of displays are a “matrix” which means that the controller is constantly strobing each and every channel looking for changes, it’s not a frequency or driver issue, it’s the way the displays are updated consistently, stand alone high quality led lamps tend not strobe, cheaper ones do, our studio ceiling lights stobe due to the frequency of the driver, the ones that don’t are usually called flicker free.
 
dancook said:
I have and It's not an option, 1/50th second isn't good enough to get the shots I need. So had to ignore the backgrounds
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that a real pain, I know exactly the issue (not at a play) and was luckily able to get some shots.
 
Pound Coin said:
that a real pain, I know exactly the issue (not at a play) and was luckily able to get some shots.
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I just made the school aware of the issue and continued to use 1/250th during the active part of the performance.
 
Caerus said:
Small problem compared to the real limitation of digital cameras. Highlights
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Every technique or tool has a set of performance characteristics that require you to work within their limitations. Film cameras had a limitation with shadows. Both systems would struggle with LED based lights in the context of this thread, because you need continuous lighting to allow variable exposure time with good results.

Out of interest, are you a Canon user? - Just checked, yes. Highlights are a problem, but less so with modern sensors, although Canon seem to be lagging a bit in that area as I understand it. With my D610 I can underexpose to keep the highlights and pull up the shadows by 3+ stops and the image retains detail without becoming horribly noise or going purple. It's not ideal, but much easier to be forced to under-expose than to have to over-expose, which then starts requiring larger apertures or longer exposure times & needs a tripod & remote release.
 
droj said:
Blimey, did you never use slide film?

We're quite spoilt these days!

Highlights are just something that we have to pay attention to but as Toni has explained that's no huge deal. Or are you wedded to default fully-auto without intervention?
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I don't know what slide film is but I was under the impression that highlight were much easier to recover in the dark room with film than it is to recover blown out highlights with digital ?
 
Caerus said:
I don't know what slide film is but I was under the impression that highlight were much easier to recover in the dark room with film than it is to recover blown out highlights with digital ?
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Negative film has a much greater exposure latitude than digital for overexposure. The two things aren't really comparable, as overexposing colour negative film will cause changes to things like saturation, contrast etc rather than blowing out part of the image. Many people who shoot colour negative film will intentionally overexpose the film by one or two stops depending on the effect they're going for.

Film tends to fall apart quite quickly when underexposed, whereas a digital file handles this much better as you can bring the exposure / shadows up in post processing, up to a point.

Slide film is positive film, so instead of seeing a reverse colour negative image it's like a little colour photograph on the film. Slide film has barely any exposure latitude at all, you have to get things right when you take the shot.
 
Caerus said:
I don't know what slide film is but I was under the impression that highlight were much easier to recover in the dark room with film than it is to recover blown out highlights with digital ?
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As richard said, you have to get slide film RIGHT in camera - perhaps +/- 1/3 a stop. Too bright and the slide becomes very thin, without detail. Too dark and you couldn't shine a light through it.
 
ancient_mariner said:
It's not a fault - simply physics. :)
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Umm ... perhaps I should have said responsibility? BTW everything’s simply physics, though I never found physics simple :( — maybe that’s what SMOP should really stand for.
 
ancient_mariner said:
you have to get slide film RIGHT in camera - perhaps +/- 1/3 a stop.
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With slide film I routinely underexpose by about half a stop. But this has to also relate to how you take an exposure reading in the first place - or more exactly, where you take it from.

Which brings us to the method of gauging exposure, interpreting readings, etc. So no change there into the digital era, but an increase in latitude.

The crux is to pay attention to such things. Done on the fly, a bit of guesswork might be involved, mistakes might be made, and you might have to throw some images away. But if you use experience as a teacher and improve your procedures, they'll be be fewer than before.
 
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sphexx said:
You seem to be saying the fault lies with train so how do you feel about a bird photo with blurry wings — refresh rate too high :) ? I thought the OP was making a valid point.
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You can just pick a fast enough shutter speed to freeze the wings - I suggest you haven’t understood the problem.
 
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