Slavesetting

I have just purchased an used Ike Ss 300, which I want to use as a slave flash for WA in combination with my Ike ss 100.

(GN SS300= 42; GN SS100= 28 )

I want to know what a good startsetting is for this combination in clear waters, since I go on a trip to Egypt in two weeks and the waters in Holland are too dark to do a good test.

With both strobes to Full, I should have a combined guidenumber of around 45 at ISO 100 (Is this correct?), so f8 with subject at 6 feet and f16 at 3 feet.

The shutterspeed should be set according to the midwaterreading.

Is my thinking correct or do you have experience with other settings?

How exactlly do you calculate the combined guide number with two strobes and with the strobes at 1/2 or 1/4?

YES, I am still shooting slides, NO I don't have a LCD-display, YES I am still happy with my rig, NO you don't have to feel sorry for me.

Most likely the second strobe is used to fill in shadows created by the main strobe in macro ( therefore no actual increase in illumination, just a balancing sort of). In wide angle, there should be little if any meaningful overlapping of beam angles in order to avoid illuminating the water column between the lens and subject to minimize backscatter.

So considering that we most likely will be aiming the strobes at different angles as opposed to layering one strobe output directly on top of the other, it has been my understanding that we only use the larger of the two dissimilar strobe outputs when determining guide numbers. Therefore, I would assume that the GN in your case should remain at 42 maximum. This will also keep you on the underexposed side of light capture, which I've been taught is more desirable than to overexpose.

The guide number for half power is determined by dividing the previous GN by the square root of two, which is 1.4. Half power GN of 42 would therefore be:

42/1.4= GN 30

Quarter power ( from full )= 30/1.4= GN 21

GN=A*D

hth,

b

Thanks Bob,

This is info I can work with.

Greetings,

Kees

Double post

Kees, when shooting Ektachrome Pro 100G wide angle, I generally use an Ikelite SS300 as the main light, and an Ikelite 50MS as fill in the opposite corner.

Although the 300 certainly has the punch to get up to f11+, I find I am rarely there unless in very shallow water.

On wall dives in very clear, warm water, a "grey card" exposure is roughly 1/60 f 4.0 when at 60' to 80' depth. I prefer to underexpose the water a bit to saturate the blues, so my base exposure is f 5.6 .

So, I spend a lot of time with the strobe set to half power. For me, this has given good tones with the subject about 4 to 5 feet from the camera, with the SS300, at the above conditions. EK 100G, 1/60 at f 5.6 .

As I get shallower (or if shooting over white sand), I'll kick up to full power and/or bring the subject closer to match the metering for the background.

FWIW, as cheese whiz as the little sliding exposure guide is (the one on the back of the strobe), it sure is accurate.

All the best, James

Thanks James,

I have tried the settings yesterday in our murky waters, the macroshots were great, but the WA shots were a disaster. I know that WA-shots with visibility below 4 feet won't work, but I just wanted to test the slavesetting of the SS300.

It didn't work that well because the slave didn't fire when the strobes were pointed directly ahead or outward. I had to point de strobes slightly inwards, which resulted in overillumintion of the subject and backscatter.

When this is happening in murky waters, I think the problem will be worse in clear waters (I am going to Egypt this week) or will it work just fine then?

I thinking of making a little reflector on the top of the slavestrobe to "catch" more light.

Does anyone have experience of solutions?

Thanks.

I had to dig a bit to find this photo of my strobes (how many shots do we have of ourselves?). It gives a good idea of the angles, see attached.

However, I'm using the Ike SS300 to trigger the smaller fill (MS50). Since the SS 100 has a narrower field of illumination, and less horsepower than the 300, your setup might be less reliable in triggering the slave.

My SS 300 illuminates about 2/3rds of a 20mm frame. Usually I have the fill strobe aimed at the "back side" of the illuminated subject, to give a bit more pleasing 3-D coverage of the light.

My setup (300 triggering the 50) seems to trigger the slave fairly reliably. When the 300 is at 1/2 power or less, I do make sure the slave eye can see the strobe tube of the master. Full power shots seem to trigger the slave reliably via reflected light from the subject.

Hope this helps!

All the best, James

I Have just completed a number of test shots with the housed camera and with my 2 strobes SB-105 on land (angled straight 90 degrees towards the front) -on land, not UW however- and came to the conclusion that using 2 strobes does not increase the guide number at all. The theoretical (from several books, sources etc) combined guide number would be the square root of 2 times the squared single guide number (for two identical strobes). But my test series do not support this but show identical guide numbers as the manual indicates for one strobe only. Test were made with Full power, 1/4 and 1/16 and the shot in each serie with the correct exposure was compared to the indicated guide number (on land) from the manual. Any other experience or did I miss/mess something?