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On 7D flash synch speed

Started Nov 7, 2004 | Discussions thread
PerOP Regular Member • Posts: 247
Re: On 7D flash sync speed

The actual duration of the strobe (full output) is probably a bit shorter than 1/250sec. I have not been able to find the figures for the 5600HS(D), but the 5400HS has duration times from 1/50000 to 1/600, and the 5600 should not be far off.

In an earlier interveiw (sorry can't find the link) a KM engineer explained that they had to design a completely new shutter for the 7D, and as a consequence of the integration with AS had to limit the sync speed.

So I guess the answer to your question is:

a) Technical limitations in the cameras design

Rgds PerOP

Geir Ove wrote:

Hello,

There was a thread covering this subject some time back. I have
been contemplating the subject for a while, and thought I would
share my insights:

The 7D has a synch speed of 1/160 sec if I am not wrong. From the
tables in the Minolta 5600 HS(D) manual, we can read (indirectly)
on page 76 that the max flash duration of the 5600 must be less
than (or equal) to 1/250 sec.

A flash will deliver its power (guide number) through its
brightness and flash duration. For a camera to fully utuilize this
light its shutter speed must NOT be faster than that flash
duration. So for the 7D, we could have had a flash synch speed of
1/250 sec. to fully utilize the power of the 5600.

( The HSS mode allows us to use faster shutter speeds, but at the
cost of reduced guide number. The effective guide number will be
G / Sqrt(S/250) where S the selected shutter speed larger than 250.)

So why doesn't the 7D synch at 1/250 sec? That one I am not sure
of, but I see 2 possibiities:

a) Technical limitations in the cameras design
b) Maybe KM wanted us to be able to utilize Flashes that are slower
than 1/250 sec at their max Guide Number: Studio flashes or 3.
party flashes?

Geir Ove
--
My album at: http://objective.bitfikler.com/geirove/web/

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