Home · Register · Search · View Winners · Software · Hosting · Software · Join Upload & Sell

Moderated by: Fred Miranda
Username   Password

  New fredmiranda.com Mobile Site
  New Feature: SMS Notification alert
  New Feature: Buy & Sell Watchlist
  

FM Forums | Photo Critique | Join Upload & Sell

  

Archive 2013 · what phenomenon causes this?
  
 
sonics
Offline

Upload & Sell: Off
p.1 #1 · what phenomenon causes this?


What phenomenon causes this effect?

This part of the photo is taken at f/2.8 1/100 sec during a concert. All fast moving objects I see 4 times instead of one blurry mess between the 1st and the 4th.

What is the reason behind this?

example



Apr 28, 2013 at 06:56 AM
silvawispa
Offline
• • •
Upload & Sell: Off
p.1 #2 · what phenomenon causes this?


lighting strobing at 25 hz.


Apr 28, 2013 at 10:01 AM
Eyeball
Offline
• • • •
Upload & Sell: On
p.1 #3 · what phenomenon causes this?


I agree about the strobing but I think at a significantly higher frequency. 4 strobes during a 1/100 exposure would be approx. 400 hertz. Possibly LED stage lighting something like this:

http://www.lightronics.com/led_fixtures_372c4i.html



Apr 28, 2013 at 01:05 PM
RustyBug
Offline
• • • • • •
Upload & Sell: On
p.1 #4 · what phenomenon causes this?


AI=AR

The light reaching the camera is a byproduct of the angle from the light source, reflected off the subject to the camera.

My hypothesis (read GUESS, if you will) is that they are using "4 light" banks for lighting. The notability of it as 4 distinct strands is the light reflecting from each of the different lights off of the specular (round) subjects iaw AI=AR as it changes with subject position variance. Contrast this with the "blurry mess" of the letter "G" in the name Gibson which shows the typical blurry mess that we are more accustomed to seeing.

I'm guessing that while the flat surfaces reveal a "continuous" reflection/blurry mess as their motion changes the AI=AR, the "point" reflections of the specular components "skip" from one light to the next in the light bank as their positions change relative to the camer/light source relationship ... if that makes any sense.

If it were due to a stroboscopic light source, we'd see the same multi-position characteristic in all portions of the subject that moved. Here, the rounded surfaces are acting differently than the flat surfaces. Noting the lines in the machine heads/tuning knobs/strings as well, but not in the lettering.

Notice also how the bridge while highly reflective white, it's flat surface doesn't exhibit the same stroboscopic effect as the other round highly reflective surfaces do. Also, note how the "E" string shows the multi-strand effect in purple between the bridge and the tuning pegs, but we don't even really see the "E" string below the bridge. The angle of the "E" string (and two next to it) from the bridge to the tuning pegs is different and is picking up the refection from a bank of purple lights, while on the opposite side, the tuning knobs/pegs are in a position for AI=AR to pick up the reflection from a bank of blue lights.

Anyway, that's my read on it.
Any more examples or shots that include the stage lighting?



BTW, that's why jewelry stores use multi-point lighting, so that no matter which way your turn, you keep getting specular reflections. Better to step out into the mall lighting (outside or some area without the multi-point lighting) to evaluate how "sparkly" you're really gonna be before committing a chunk of change.



Apr 28, 2013 at 02:26 PM
sonics
Offline

Upload & Sell: Off
p.1 #5 · what phenomenon causes this?


Eyeball wrote:
I agree about the strobing but I think at a significantly higher frequency. 4 strobes during a 1/100 exposure would be approx. 400 hertz. Possibly LED stage lighting something like this:

http://www.lightronics.com/led_fixtures_372c4i.html


They do have LED lighting on that stage. It looks like the link you send.
It made the auto WB go crazy on my camera. Luckily I only shoot raw.



Apr 28, 2013 at 08:22 PM
silvawispa
Offline
• • •
Upload & Sell: Off
p.1 #6 · what phenomenon causes this?


I got my maths wrong.
Of course it's 400hz.
Strobing is how LED's are controlled for brightness.
(PWM if you want to read up on it)
The reason for the difference between the headstock and the string is simply the speed of movement, the string is going 'boing' and moving faster.
The other parts of the guitar still show the 4 images, but only the specular highlights are truly clear.

Early types of LED stage lights are a nightmare owing to the narrow wavelength of light produced.
Fortunately they are improving very very rapidly.



Apr 28, 2013 at 08:32 PM
 

Search in Used Dept. 



RustyBug
Offline
• • • • • •
Upload & Sell: On
p.1 #7 · what phenomenon causes this?


The strings might be vibrating faster @ "boing", but the machine heads/tuning pegs/tuning knobs/strings above the bridge are moving at the same speed as the rest of the headstock.

Not sure @ LED frequency impact ... ... does LED lighting actually operate at stroboscopic frequencies? If so, then do LED's present a hazardous condition to use in context with rotating equipment / machinery similar to using fluorescent lighting is a hazard?



Apr 28, 2013 at 10:18 PM
Eyeball
Offline
• • • •
Upload & Sell: On
p.1 #8 · what phenomenon causes this?


Google "led stage 400 hz" and you will get quite a few hits. You will also see references to this as "flicker-free", which I guess it is under normal conditions and compared to something at a more traditional 60 hz.

In this case though the movement was fast enough and the shutter-speed long enough to catch 4 blips. Pretty much everything on the headstock shows the 4 blips except the Gibson logo and the colors in the middle of the headstock.

I think the reason it doesn't show in the Gibson logo is because the logo does not have as fine and as bright of detail and the 4 images overlap.

The color in the middle of the headstock might be reflections of neon signage or something. The pictures of Gibson SG-X's that I saw just had black in that area.



Apr 29, 2013 at 12:26 AM
sonics
Offline

Upload & Sell: Off
p.1 #9 · what phenomenon causes this?


The links contain 1 100% crop example of the 400hz flickering.
You see clearly that the non / slow moving drummer is "sharp" (well not really sharp since the foreground (the singer) was in focus) and the fast moving drumssticks contain 5 blips... err this one has 5 blips. Could it be a combination of the red LED flickering and the blue LED flickering?

I don't know if I like this effect or not. Is it normal that the auto wb goes weird with this type of lighting?

example 2


Eyeball wrote:
Google "led stage 400 hz" and you will get quite a few hits. You will also see references to this as "flicker-free", which I guess it is under normal conditions and compared to something at a more traditional 60 hz.

In this case though the movement was fast enough and the shutter-speed long enough to catch 4 blips. Pretty much everything on the headstock shows the 4 blips except the Gibson logo and the colors in the middle of the headstock.

I think the reason it doesn't show in the Gibson logo is because the logo does not have as fine and
...Show more



Apr 29, 2013 at 09:05 AM
cgardner
Offline
• • • • •
Upload & Sell: Off
p.1 #10 · what phenomenon causes this?


AWB is never a good choice if shooting RAW because it bases the "guess" about WB on scene content in each shot and over a series of shots where content of lighting changes there will be no consistency between frames. That makes adjusting color when editing more difficult.

In a situation like a concert set the camera to the nearest reset, "tungsten" and it will provide a consistent "spotlights are neutral" baseline and will render the colored stage lighting similar to how it is perceived by eye.

A huge advantage of RAW is batch correction of things like WB, but that only works when all shots are taken from the same consistent WB pre-set. For example if using tungsten and it wasn't a perfect match to the stage lighting you could correct the first RAW file with eye dropper on something neutral then copy / paste that WB adjustment into all the other files to reflect the same adjustment. You can't do that if shooting AWB because there's no consistent capture WB across all the files.

Something the brain does in person but camera WB can't is mentally tune out color casts. For example in person if a performer is seen on stage with the face in red stage lighting it doesn't seem odd because a second later the lighting is different. But if you happen to capture a photo of the face in the red light it will look odd and unnatural. That's because in person the brain mentally "tunes out" the color being more focused on the music / action and overall context of the lighting in the venue.

What I do when use of flash is allowed / feasible (such as shooting dress rehearsals of stage performances for promotional materials) is to put 1/2 CTO orange gel on my flash to match the baseline tungsten balance of the stage lighting, then I set Custom WB off a gray card with the gelled flash. That creates an effect similar to having a white spotlight in the actors in the foreground within range of the flash because the face and costume in the Custom WB balanced flash lighting will be rendered neutral. Because the flash gel is 1/2 CTO not Full CTO the background lit with the stage lighting gets rendered slightly warmer than neutral which winds up looking similar to what is typically seen on stage when the lead actors are in a white spotlight. The net outcome in the photo reproduction are faces in the foreground which seem more "normal" than if spot with just the ambient stage lighting.




Apr 29, 2013 at 12:20 PM
RustyBug
Offline
• • • • • •
Upload & Sell: On
p.1 #11 · what phenomenon causes this?


Eyeball wrote:
Google "led stage 400 hz" and you will get quite a few hits. You will also see references to this as "flicker-free", which I guess it is under normal conditions and compared to something at a more traditional 60 hz.


Always good to learn something new.

I didn't realize the LED was actually cycling like fluorescent. I'm a bit surprised to learn that, because around rotating equipment lights that cycle can produce a scenario when the equipment is rotating at a cycle that is a multiple of the light's cycle the equipment will appear stopped, when it fact it is actually moving. DANGEROUS potential ... yet, I'd not ever heard mention of the cycling in LED's.


http://www.osha.gov/Publications/woodworking_hazards/osha3157.html

An employee may be injured if he or she reaches in to clean a saw or remove a piece of wood after the saw has been turned off, but is still coasting or idling. Also, saw blades often move so fast that it can be difficult to determine whether they are moving. This is especially a problem under fluorescent lighting



Apr 29, 2013 at 12:25 PM





FM Forums | Photo Critique | Join Upload & Sell

    
 

You are not logged in. Login or Register

Username   Password    Retrive password