led ring light

[DeSwitch]

wow, i see CS not only got photographers but there are electronic experts too. Thanks guys for giving so much tips, info and guide into this project. My electronic knowledge had been mostly given back to the lecturers.:bsmilie:

 

[unseen]

If you are calculating the resistor value for a single LED, the denominator should just be IacrossLED, no need to multiply by number of LEDs.
Even if you connect a few LEDs in series, the denominator will still be IacrossLED only.

Yups.. but I was referring to his parallel circuit..
his circuit of 8 LEDs in parallel, where each needs 1 resistor.

lol connect just 2 LEDs in series you'll need more batteries just to make it work..

 

[SnapON]

Usually LED drivers are just some of power regulator. And they still need a resistor as a current regulating device.
Therefore, save some money and use a resistor.

There are "voltage" regulating driver & "current" regulating driver, of course not forgetting LEDs are solid-state semicon, they are better to be current driven (@ rated current). Direct resistor connection is just "current limiting", so the rest of the power will be still "wasted" in the resistor. Ideally, proper driver design into the circuit helps to "maintain" the brightness of the LED(s) thru-out battery life (if u are using battery). Of course I agree with u that connecting a resistor inbetween is the easier way (& cheaper also) but make sure u get a clear picture what's the "wattage" taken up by the resistor, i.e. there is a diff "power rating" for the same resistor value. Under-rated calculation will kills the resistor also.

 

[thomas_lkt]

Yes. The points are valid. However, this is about diy a LED light and most, if not all, white LED drivers are surface mount devices (SMD). Being SMD devices, they have tiny connection pads which breaks easily. That is why a resistor is recommended; simple to use.
Typically, the resistor value chosen is low (<300 ohm) because the resistor waste power. And leaded resistors of 1/4w rating are widely available from Sim Lim.

 

[DeSwitch]

ok guys. latest update. I chanced upon a cheaper solution to this ring light. I manage to get hold of 4 mini LED reading light @2.90 each. It consists of 3 Led grouped together, like a mini torchlight with a plastic lens in front. It runs on 3x button type cells but I'm going to modify and convert to AA batteries.

I tested it yesterday and it works better than my 20 Leds. I will post some pictures tomorrow.

The good thing is that it comes with a clip so I clip them on my lens hood and adjust the angle (yes it is adjustable with a sort of ball socket)

Testing at Av at F4, ISO1600 I get the following shutter speed.
With one light ON, I obtained 1/80s, 2 lights 1/125s, 3 lights 1/160 and all 4 lights ON, I get 1/200.


Can anyone help me to calculate how many of these lights do I need to work at ISO400, f8 and shutter speed of >1/100s ?

 

[vince123123]

Not sure on the calculations, but would sure be waiting eagerly to see photos of your new setup.

ok guys. latest update. I chanced upon a cheaper solution to this ring light. I manage to get hold of 4 mini LED reading light @2.90 each. It consists of 3 Led grouped together, like a mini torchlight with a plastic lens in front. It runs on 3x button type cells but I'm going to modify and convert to AA batteries.

I tested it yesterday and it works better than my 20 Leds. I will post some pictures tomorrow.

The good thing is that it comes with a clip so I clip them on my lens hood and adjust the angle (yes it is adjustable with a sort of ball socket)

Testing at Av at F4, ISO1600 I get the following shutter speed.
With one light ON, I obtained 1/80s, 2 lights 1/125s, 3 lights 1/160 and all 4 lights ON, I get 1/200.


Can anyone help me to calculate how many of these lights do I need to work at ISO400, f8 and shutter speed of >1/100s ?

 

[Artosoft]

ok guys. latest update. I chanced upon a cheaper solution to this ring light. I manage to get hold of 4 mini LED reading light @2.90 each. It consists of 3 Led grouped together, like a mini torchlight with a plastic lens in front. It runs on 3x button type cells but I'm going to modify and convert to AA batteries.

I tested it yesterday and it works better than my 20 Leds. I will post some pictures tomorrow.

The good thing is that it comes with a clip so I clip them on my lens hood and adjust the angle (yes it is adjustable with a sort of ball socket)

Testing at Av at F4, ISO1600 I get the following shutter speed.
With one light ON, I obtained 1/80s, 2 lights 1/125s, 3 lights 1/160 and all 4 lights ON, I get 1/200.


Can anyone help me to calculate how many of these lights do I need to work at ISO400, f8 and shutter speed of >1/100s ?

4 LED on and you are on ASA1600, f/4, 1/200s...

For ASA400, you need another 2 stops (or 4 times brighter), it is means 4 x 4 = 16 LED.
For f/8, you need another 2 stops from f/4, or you step down the shutter speed from 1/200 to 1/100 for 1 stop gain. Another 16 x 2 = 32 LED.

My calculation is 30-32 LED for working with ASA400, f/8, 1/100s.

Regards,
Arto.

 

[DeSwitch]

Well guys, as promised the photos on the latest update on the project. The result were slightly different than my previous trial but guess it may be my metering patern. The photos here uses center weighted whereas the earlier trial are spot.

Photo#1 is the setup of the LED in OFF status.

Photo#2 is the setup of the LED in ON status.

Photo #3 with 1 LED ON. (ASA 1600, F4)

Photo #4 with 2 LEDs ON. (ASA 1600, F4)

 

[DeSwitch]

Photo#5 with 3 LEDs ON. (ASA 1600, F4)

Photo#6 with 4 LEDs ON. (ASA 1600, F4)

Photo#7 with 4 LEDs ON. (ASA 400, F4)

Photo#8 with 4 LEDs ON. (ASA 400, F2.8)

 

[vince123123]

Looks interesting - where did you get the lights from?

You mentioned that you intend to convert them to AA power source - I assume that hasn't been done yet? Do you intend to have ALL the LEDs run from the same power source? Or does each LED have its own source.

The disadvantage of a separate power source system however is that you need to switch on all the LEDs one by one - imagine if you have more than 10....

 

[DeSwitch]

I forgot to add the shutter speed. (anyway can be found in the exif)

For 1 Led ASA1600, F4, Shutter speed was 1/60s
For 2 Leds ASA1600, F4, Shutter speed was 1/60s
For 3 Leds ASA1600, F4, Shutter speed was 1/125s
For 4 Leds ASA1600, F4, Shutter speed was 1/125s
For 4 Leds ASA400, F4, Shutter speed was 1/30s
For 4 Leds ASA400, F2.8, Shutter speed was 1/60s

I dont know why the shutter speed was the same for 1&2 Leds and 3&4 leds at the same ASA and Aperature. This test was done using Av mode using the same "model" (my daughter's Aerial the mermaid) Tamron 90mm Macro lens and 350D mounted on a tripod. Cable release is used for all shots.

All photo are not edited except resize Colour was set to custom white balance.

Yes, I think I need more than 32 LEDs to work at ASA400, F8 and shutter speed of 1/100s.

 

[DeSwitch]

Looks interesting - where did you get the lights from?

You mentioned that you intend to convert them to AA power source - I assume that hasn't been done yet? Do you intend to have ALL the LEDs run from the same power source? Or does each LED have its own source.

The disadvantage of a separate power source system however is that you need to switch on all the LEDs one by one - imagine if you have more than 10....

My friend got it for me at some budget stores in Bt Batok. Its made in China. I had not seen them anywhere else. He said the store also look like got only a few piece left as I asked him to get 6 pieces more for me.

The battery supply will be link to one source as I dont want to change 30 pieces of button cells. I think 3xAA batt will last me quite some time.

 

[SnapON]

My friend got it for me at some budget stores in Bt Batok. Its made in China. I had not seen them anywhere else. He said the store also look like got only a few piece left as I asked him to get 6 pieces more for me.

The battery supply will be link to one source as I dont want to change 30 pieces of button cells. I think 3xAA batt will last me quite some time.

30pcs of button-cell... if u don't mod it u will be :sweat:

 

[DeSwitch]

30pcs of button-cell... if u don't mod it u will be :sweat:

Yup, sure :sweat: :sweat: :sweat: if change all at once.

My friend still have not get the additional 6 pieces I need yet. Could be already out of stock liao.

 

[DeSwitch]

Finally, my friend got the additional 6 pieces of LED light. I tested last night with a total of 10 LED lights. manage to get quite good shots hand held. Depending on the subject, I can get between 1/20s to 1/125s at ASA800 f8. If subject is dark and non reflective, result in low shutter speed. I tried manual mode at 1/80s f8 ASA400 and still manage to get decent shot of my Digicab label.

Will be spending some time to modify them to use AA batteries and also to make a proper mount for them. I consider this project a success. now I can shoot without flash and get almost shadowless photos.