LED Ringlight

[canonian]

This is the DIY LED Ringlight I used in this post .
8 powerleds are surrounding a plastic cup, giving a nice omnidirectional and dimmable diffused light on the subject.

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It is bolted on a BHMJ microscope focusblock and has full travel of 3cm in 1µm increments.
_________________
Fred
Canonian@Flickr

[BugEZ]

Wow! That is one powerful ring light! How long are your exposures?

Keith

[ChrisR]

Indeed! And what's the output spec for the LEDs?

[canonian]

[ChrisR]

I have four 300Lumen head torches waiting for batteries. I think, Fred, you've saved me the trouble of a test!

I've been drooling slightly over these
http://www.luxeonstar.com/Neutral-White-4100K-7-LED-40mm-Round-Assembly-p/sr-02-wn300.htm
which are 2000 Lumen ( for short periods).
Eight of those would be a significant investment though.

Thinking on the keyboard here:
On the face of it (probably naively) the exposure time could go from 200ms to 10ms.
Looking at Fred's arrangement, I can't recognise anything inside the "cup", so there may be potential to move the lights closer, or focus them more. Perhaps 1ms is achievable?

Is this a Good Thing?
It could certainly help with reducing vibration movement for some situations but I do see mirror/shutter induced movement with 1ms (flash). That goes with shorter durations (eg 1/32nd power is 0.031ms).
So we're perhaps an order of magnitude too long still, to be rid of those.

Mirror/shutter induced movements become insignificant if the exposure is much longer, say 2000ms (2 seconds), because they're strong in the first 50ms or so. *

With my particular situation - (wooden floor, table with isolation under a heavy slab, copy stand on that) I see vibrations going on forever, at low frequency. I think I still have to use flash.


*"Citation required"! I vaguely remember that from some German tests.

[BugEZ]

Canonian

FYI...

The much less luminant ring lights I have built use approximately 24-36 5mm LEDs (http://www.ledshoppe.com/Product/led/LE1019.htm). I don't drive them to the full continuous current as my power regulation circuit is quite simple and I don't individually regulate the flow of power to each bank of 3 LED's. Each LED is rated for 13000 mcd. An online calculator estimates that each can produce approximately .3 lumins. I probably drive them to 2/3 of this.

A better estimate for comparison to your brightness may be to compare the power dissipated . With approximately .020 A and 3.2 V, the power is .06W per 5mm LED. Thus I probably have .06 W/LED X 36 LED = 2.3 W total electrical power consumed by the LEDs. If each of your lights uses 2.3W (edit) then you have 8X more light.

I adjust the intensity to keep the exposure around 1-2 seconds (ISO 200) to help "de bounce" my rather rickety rig. My home built controller allows me to sequence the LEDs to turn on about 100 ms after the shutter opens to help reduce the shutter bounce. I have done comparisons with and without this delay (10X microscope objective lens), and it is difficult to detect any change in image quality, so I usually don't bother to cycle the lights.

On the ring lights I use with microscope objectives, I have shifted the plane where the lights are located to be on the camera side of the objective lens opening. The skirt of my diffuser extends perhaps an inch beyond the objective lens. My goal is to reduce how much light shines directly onto the objective lens face. This has helped a lot with "fogging" of the images, similar to taking a photo toward the sun with no lens hood. I am presently experimenting with some microscope objective lens hoods I taped together using black construction paper. My goal is to pull the illumination a bit closer to the subject to provide more natural side lighting yet to avoid the "fog".

Your setup looks very clean and neat. Once again many thanks for sharing.

Keith

[canonian]

[canonian]

[AndrewC]

[BugEZ]

Canonian wrote

[Andrew®]

[ChrisR]

Yeah, I'd noted is as a key thing to watch.
With an exposure time of say 10ms the duty cycle would be low, but I'd start with short pulses at low voltages while watching the resistance of the thermistor, or it could get expensive!