testing flicker with a digi cam...

J

JustinT

Active member
Hey guys,

I just came across an 18" fluro light that only required me to add light and cable.

only problem is that the only lights I found for it were 15W 5600K(ish) lights. Lit ok, but will probably never be a keyer...

The main reason for this post is because I current't don't have my dvx with me and wanted to test for flicker (so if there is none i can go get a few more before they run out - these were $20AU all up which i think is quite good).

I used my sony DSC-V1 which has manual flicker from less than a sec to 1000. I scrolled down from 1000 down to less than a second and didn't notice any flicker through the lcd (when doing this on a tv set i do notice flicker). Is this a good guide?

That aside, would there be an easy way to link up more than one light to one power point - as oppose to using double plug adapters.

I'm also looking to mod some barndoors and foil for to reflect the light forward (finding it hard to find highly reflective tape in AU). Any other suggestions would be great - still looking at a way to mount them

Pics here ('scuse the mess)-o ya, main point of this setup is for portability and interviews
light1.jpg

light2.jpg
 
Actually, all fluorescent lights have a flicker rate based upon the driving frequency. In the case of lights with magnetic supplies (ballasts) it is twice the mains frequency (either 50 Hz or 60 Hz). Lights with "electronic" supplies can have a flicker rate (frequency) as high as they choose to design it too (can be as high as 100 kHz in some cases). What makes a difference in the applicability for use as a light source in film/video is the relative shutter speed versus the flicker rate. In the case of a 50 Hz magnetic light (which from your picture is what it appears that you have) the flicker rate is 100 Hz, for a 60 Hz mains situation the flicker occurs at 120 Hz. In most cases, except for extremely slow shutter speeds, this will almost certainly guarantee flicker in the image. I would recommend that you look for a similar fixture but with an electronic ballast system. A factor of 100x the shutter speed would be a good criteria to assure good results.
 
wow khmuse you can see flicker in that picture? - i've just noticed that if i have the light just off to the left of my vision - i do notice a very slight flicker - like when u look at a CRT monitor that has a low refresh rate.

However looking at the surroundings, I didn't notice flicker (naked eye and through lcd of my digi cam).

But in your opinion, the light aint good?

EDIT - looking at the info of the pic, there is shutter speed - but it does state an iso speed of 1/13 sec
 
Actually, no, I can't "see" flicker in a still image (no one can as it won't show up). Your testing methodology is invalid as it won't reveal flicker no matter how bad. My reason for stating the "nature" of this light is based upon its construction (your first image). This is how that I established that this is a low frequency (mains driven) light.
 
hehe yeah, i see where you're coming from now...

might try to get my dvx back asap to shoot some stuff to see if the lights are usable or not, been to a couple stores, and the sales peopel didn't know what i meant when i asked about ballasts and cri etc...
 
It is no surprise that the retailers wouldn't know these aspects of the lights. Look for wording like "high efficiency" as this might indicate an electronic ballast. Also, the pure mass of the lamp can be a good clue if you can't look inside before you purchase, magnetic ones will typically be heavier as they have mains (low) frequency magnetics.
 
thx KHmuse: you've been a GREAT help. I might still go ahead and get a couple more of these lights for testing purposes until i can find/afford better ones..

I just realised how silly I've been pondering over this, when it would have just cost me an extra 40$ (nothing considering the friging fines i get heeh)
 
Happy to assist.

By the way, If you want to use mains frequency lights (like the one you have already purchased) and minimize the flicker effect, you can use the "SYNCRO SCAN" feature to find a non coincident shutter speed. You will need to use an external monitor (preferably a CRT based one) to look for the minimum interaction between your shutter speed and the flicker rate of the lights.
 
khmuse - the flicker is generally pretty noticable right - like u really can't miss it?

Also would me connecting the camera to my PC via firewire as I shoot be a good way of monitoring (real time monitor so to speak on my dell LCD)?

thx again.
 
Flicker can be very annoying and not easily missed. I would still recommend that you use the video output of the camera to a standard CRT monitor. The problem with a lot of LCDs is that they are slow enough that they can mask this type of problem.
 
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