LED Photo Flash Power

[popcorn]

Hi All,

I have just started to dabble in Macro Photography.
It didn't take long before I realized that, if I was going to produce reasonable results,  I would need a lens ring light.
Not wanting to spend a lot of money on what might prove to be a passing fancy, I bought the first "reasonably priced' LED constant light I found. a Godex Ring 48.
Like all things done without much research, it has proved to be inadequate.

I found a replacement on line which offered variable light output and 80% more LEDs. It was primarily a flash with constant light capability.
Apparently the light intensity on full power flash is about twice that of the constant light mode.
Before I bought it, I wanted to make sure it had adequate power. The only measure of flash power that I am familiar with, is Guide Number and recycle time.
Unfortunately LED's power is only quoted in Watts. 

I searched the web but could not find any correlation between Watts and Guide Number. I realized that Watts was a measure of power and that Guide Number was a measure of light intensity.
I did find a correlation between Watts and lumens, so there should be a link to Guide No. I think Lux would be a better unit to equate with Guide No. 

The LED light has an advertised power of 5W. I realize that reflector shape has an affect on the intensity of the light emitted but, assuming the same efficiency of reflector, can anyone please tell me what sort of guide Number would a 5W 
LED light source equate to?   

  

[kdcintx]

Hi Popcorn,

A guide number (GN) is the distance from the subject to the flash * the f-stop  and is measured by the flash manufacturer for a specific flash typially at ISO 100.

From dpanswers.com/roztr/content_show.php?id=317   "Measuring the GN of a flash is straightfoward. Just fire the flash and measure its output with an incident flash meter set to ISO 100. Multiply the aperture reading with the distance in meters or feet, and that's the GN of the flash in meters or feet."

I'm not sure there is a simple, direct correlation between a 5W led and a specific GN.

I've done a lot of macro photography using speedlights. The best way I've found to determine the correct exposure/flash setting is by experimenting. It didn't take too many experiments (or should I say errors ) before I could pretty well determine the flash setting for a given photo.

Maybe someone can find additional information regarding a direct correlation between watts of an led and GNs.

[popcorn]

Hi kdcintx

I have always regarded the Guide Number as being the intensity of light emitted by the flash. The higher the Guide Number the smaller the useable aperture for a given distance and a given ISO.
Just like a 100 Watt light bulb is brighter than the same type of 50 Watt bulb. Si it seems logical that there must be some at least rough conversion.
Do you use a LED Ring light for your Macro photography? If you do I would really appreciate your pointing me in the right direction before I buy.
The price range is huge and I don't want to spend my children's inheritance! Do you think a 5 Watt output will suffice. I can't justify the expense if I only use it for macro so it would be nice to be able to use it as fill flash for close up portraits as well, so a Guide Number in the region 30 meters would be OK..

[BuckSkin]

From what I gather, LED is an entirely different animal from anything we all used to know.

5 Watts seems like it would be a lot of power draw for a few tiny LED like what would be in a ring flash.

My best advice would be to read all of the reviews on such sites as Amazon and maybe some of the photography sites like dPreview (which I reckon now is owned by Amazon); that way, you can find out what is and is not working for others.

I have learned this much, more LEDs is not necessarily going to be better/brighter; I have flashlights with a single LED that will set the grass on fire in front of them; and, I have flashlights with lots of LEDs that I have to hold them up to a match to see if they are lit.

There are several good LED ring lights for less than $30; if I were going to pay more than $30, I would have to do a lot of research and investigating to see if I were not just giving the difference to help pay for a big ad campaign.

I am going to follow this with interest as I plan to soon be buying one myself.

[Chris]

I agree with Buckskin, it would be best to read the reviews.

Here are some other points I can think of.

An LED ring light does have some advantages and disadvantages.
Advantages: 1- Cheaper 2- Constant bright light to aid focus. 3- Can use the camera light meter to adjust exposure without worrying about flash compatibility. Should work on any camera.
Disadvantages: 1- Will probably produce less light than a tube flash ring light, so you will probably need to work with larger apertures. 2-Some models could be more bulky.

IMHO a macro flash with a tube is much more powerful and useful. Yongnuo make an affordable macro ring flash with a tube that also has the option to constantly light the subject (weakly) for focussing. The disadvantage is that if you upgrade your camera it might not work properly. I have the Yongnuo YN14EX which worked fine in TTL mode with my previous Canon cameras. But when I upgraded to the Canon 90D it did not work properly and I need to use work-arounds to get the correct exposure. Yongnuo make a newer ring flash and also a twin flash that you might want to look into.

Here are some differences I can think of between macro ring lights and macro twin lights (flash on either side of the lens rather than in a ring). I have also seen an led macro flash with 3 adjustable lights.

A macro ring light is generally cheaper and more portable. It has the advantage that it is more likely to fit into tight spaces when taking pictures. The disadvantage is that you are more likely to get reflections off the subject because the light is head on.

A macro twin light will probably be more expensive and more bulky to carry but will give a better quality of light that will reduce reflections with light coming from either side and will flatter your subject more.

Its also possible to take good macro shots in natural light if the quality of light is good enough.

I hope this helps.

Kind regards
Chris