Question about the SB 700's zoom read out

[Revet]

I am confused about the zoom read-out on my SB 700. When I am using it on my camera, the zoom read out matches the zoom read out I set on my camera. Thus if I use a larger mm setting, the zoom moves back in the flash as it should to focus the light to match what the camera is doing.

Here is where I am confused. When I put the diffusion dome on the only zoom settings I have (in DX format) are 8, 10 and 11 depending on which illumination pattern I use. What I don't get is if I have it center weighted (illumination pattern), the zoom is on 8 mm. Then when I put it in even lighting position, the zoom goes to 11 mm. I would think it would be opposite (lower mm, wider angle and higher mm, zoom). Can some one help un-befuddle my brain on this.

 

[WayneF]

The illumination patterns (Standard, Center, Even) are themselves zoom positions. Center zooms in a bit to concentrate more light in the center (at expense of covering the corners). Even zooms out a bit to make sure the corners are covered evenly.

The Dome does necessarily change to a preset wide value (a lot of this is about making the reported guide number be correct). But then illumination patterns do adjust that value slightly. Using your numbers, 8mm is zoomed in a bit to concentrate light in the center. 11mm zooms out a bit to insure corners are even.

 

[Revet]

I am still having troubles here. Without the diffusion dome on, when I zoom my lens, the flash also zooms and moves back in the SB-700 housing. I believe this has the effect of concentrating the light in the center matching the zoom lens higher mm. But if shooting wide angle (like 18), the flash moves forward and gives you a wider array of light to match the wider view from your lens. Thus a lower zoom mm on the flash is more even lighting (wider) whereas a higher mm number would be more center weighted. When you put the diffusion dome on, the mm numbers appear to be backwards (center weighted is a lower number (8) than even lighting (11).

I must be missing something here or need more coffee.

 

[WayneF]

Sorry, I was going too fast and missed it before. I see your point now, you would think 8mm was wider than 11mm.

I don't know the reason either. But the SB-700 manual has a page H-21 that mentions these. It shows the 8, 10, 11 mm values, calls 8mm Center, and calls 11mm Even. Does seem backwards. But it says the guide number is the same for any case of the dome (GN 14), which is not the case for longer values.

 

[Revet]

Thanks, I thought i was going crazy. I guess the real message is as soon as you put that diffuser dome on, you want a lower zoom (wide angle) for more light to diffuse. With it on, I doubt the whole center weighted, normal or even illumination patterns really matter that much anymore. Thanks for your help
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[WayneF]

Thanks, I thought i was going crazy. I guess the real message is as soon as you put that diffuser dome on, you want a lower zoom (wide angle) for more light to diffuse. With it on, I doubt the whole center weighted, normal or even illumination patterns really matter that much anymore. Thanks for your help
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I agree, just the Standard pattern seems plenty. The others just zoom a bit more or less, which we can always do manually. DX zoom too actually, but it is obviously handy to be automatic.

The dome switch (to declare wider zoom mm) has two purposes. One is just a number shown to the user in the LCD for their information, to use as they choose. I am puzzled too by the 8mm and 11mm values, seems backwards my expectations, but they are just numbers. I cannot imagine the flash has any use for the 8mm number.

The other purpose is to switch to a different lower guide number (wider but lower light level within that wider coverage). Flash models like SB-700, SB-800, SB-900 have a GN Mode, which is manual flash, but we enter a distance and it computes flash level for that distance using guide number. Pretty accurately too. It has to know the guide numbers, and snapping the dome in place trips a switch to tell it is there, and that the guide number is changed. The manual says the 8mm, 10mm, 11mm patterns all are GN 14 (no change with pattern, which is surprising too), but the GN 14 is much lower than without the dome, which is necessary for GN mode to know.