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manual strobe control


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#1 steelhead

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Posted 07 August 2004 - 03:36 PM

I am currently upgrading to a D70 and (I hope) auqatica housing when they come out. I was wondering if you fellas had any genius way to get a manual controller on my sb-105's so that I can have more than just full, 1/4, 1/16 without having to buy a whole new strobe setup. Maybe adapt an ikelite controller to work on this thing?

#2 NickTeasdale

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Posted 05 November 2004 - 11:19 AM

If you get a good answer to this please let me know...
I just got an Aquatica A70 housing and will be trying out my two SB105 with it next weekend. I'm used to TTL shooting and now have to start learning the basics over again...

Cheers
Nick

#3 bobf

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Posted 05 November 2004 - 12:00 PM

the diffuser is equal to -1 stop of light. Put it on, take it off. Every time you do, you're expanding the capabilities of the SB 105.

full dump= no diffuser
1/2 power = full dump with diffuser
1/4 power
1/8 power = 1/4 power with diffuser
1/16 power

True, not as seamless as a 10 step Ikelite Manual Controller, but doable....
oly 4040 and a pair of DS 125's
Inon Macro and an Oly WAL

#4 james

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Posted 05 November 2004 - 12:18 PM

Agreed.

My guess is that for macro you will be shooting the D70 at F16-f22 with the strobes at full power and the diffusers on. Too bright? Go to f27.

For wide, depending on your depth, you will probably be shooting at f8 or f11 with the strobes at full power and the diffusers on.

Pretty simple eh? :-)

Cheers
James
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#5 CeeDave

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Posted 18 February 2005 - 10:44 AM

Warning: If you aren't a nerd, you probably don't want to read this...

My guess is that for macro you will be shooting the D70 at F16-f22 with the strobes at full power and the diffusers on.  Too bright?  Go to f27.


In my admittedly limited experience, these are good guidelines. However, there may be some decreased sharpness due to diffraction error at such high f-stops, especially for magnifications >= 1, as I imagine James knows. However, the ideas are so fascinating to me that I cannot restrain myself...

The diffraction (or Airy) disk size is about D ~ 0.7*N*(m+1), D in microns [wavelength in the middle of the visible band]. Crudely put, this is the size a "point" spreads to due to diffraction of light through the aperture. Thus, it is the minimum size that can be imaged at the sensor, due to diffraction.

We can estimate the maximum f-stop free of diffraction artifacts by setting D equal to the circle of diffusion, C, C~0.7*Nmax*(m+1); Nmax~1.4C/(m+1). Basically, Airy disks smaller than C won't be imaged, those larger than C will be, and should therefore be avoided.

At a magnification of 1 and with a DX sensor (C~20microns), the max f-stop without diffraction is about 14; for the larger circle of confusion on a full-frame sensor C~30microns gives Nmax~21. This limit is one of the motivations for large-format sensors for m>1, as Craig Jones has eloquently written; the larger f-stop gives the larger format more depth of field without diffraction.

At larger distances, m is smaller and larger fstops can be used without diffraction. At infinite distance, m=0 and Nmax~1.4C, or 28 for a DX sensor (42 for full frame). Thus, an f-stop of 27 will probably cause diffraction artifacts on a DX sensor at close-up to macro range.

m depends on focal length and distance to subject, but not on sensor size.

If you are more concerned about depth-of-field than softening due to diffraction, you may choose to shoot at f-stops higher than Nmax and use high strobe power.

If you want to limit softening due to diffraction, use Nmax from the above and lower strobe power.

Besides Sidney Ray's book, there's a nice discussion here.

All the best,
Chris
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#6 bobf

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Posted 18 February 2005 - 11:52 AM

Chris,

Cliff Shade discusses something he calls resolving power and "sweet spots". Same concept ?

http://www.dpfwiw.co...e.htm#resolving

Cliff went on to say:

Chances are, the aperture sweet spot for your lens is also ~2 full stops down from wide open. For the sharpest images your camera can muster, target that aperture when you can and work to avoid f/8 and smaller apertures.............


Not sure if Cliff was referring specifically to Oly P&S camera lenses or all lenses in general ....

regards,
b
oly 4040 and a pair of DS 125's
Inon Macro and an Oly WAL

#7 CeeDave

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Posted 18 February 2005 - 02:04 PM

Bob,

I think he is addressing it, just in a more "reader-friendly" way than I did. While (link to )the images I posted earlier does show significant diffraction at high f-stops (look at it full size), it's not clear to ME that this is all that important for a housed camera in a real-world setting -- there're so many other things I can screw up -- focus, exposure, backscatter, and of course the port itself. All the same, it's interesting that one CAN estimate the "optimal" aperture to maximize depth of field without visible diffraction artifacts. I live for minutiae like that...

Cheers,
Chris
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Subal ND70 + 2X DS125 ... mostly 10.5, 16, and 60

#8 satura

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Posted 18 February 2005 - 04:12 PM

I was wondering if you fellas had any genius way to get a manual controller on my sb-105's so that I can have more than just full, 1/4, 1/16 without having to buy a whole new strobe setup.


Quote from Mathias' website:
" all non-compatible TTL strobes (Old SB-105/SB-104 or other) can be used with 10 camera controlled manual power settings. If the strobe button (FEC or flash pop-up) is supported on your housing you'll be able to switch between manual with 10 power settings and iTTL underwater. iTTL mode requires double-flash compatible strobe, manual mode will work with ALL kind of Nikon-TTL underwater strobes "
:?: :!: