shorter flash sync time

Hello experts,

it seems that the Nikon D70 / D70s remain the only DSLRs with a flash sync time as short as 1/500s. Even considerable higher priced professional DSLRs don't measure up, not even in Nikon's own lineup.

Is there any technical reason that prohibits the use of such a fast shutter in other cameras?

This sync shutter speed translates into considerably higher flash reach under bright ambient light conditions in fill photography. For instance, under a given condition, the faster sync speed gives a flash on the D70 nearly 60% higher reach than a flash of the same guide number on an EOS 350D (which has "only" 1/200s as shortest sync time).

Very curious to hear your expert opinion. Or does anyone really KNOW why this is so?

I don't know the technical reasons for it, but the F5 and F100 film cameras are also 1/250 (ignoring the high speed mode which is pretty complicated). High sync speed is also great for using a wider aperture outside - like fill flash portraits when you want the background out of focus. I usually don't have a problem with 1/250, but even one stop slower (like my Fuji S2) can be a pain. For one thing, hand-holding an 80-200 f2.8 with fill flash is more of a challenge!

I agree it's interesting that the D70/D70s are the only DSLR's (that I know of) that have 1/500 - not even the D2X.

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Originally Posted by wus

Hello experts,

it seems that the Nikon D70 / D70s remain the only DSLRs with a flash sync time as short as 1/500s. Even considerable higher priced professional DSLRs don't measure up, not even in Nikon's own lineup.

Is there any technical reason that prohibits the use of such a fast shutter in other cameras?

This sync shutter speed translates into considerably higher flash reach under bright ambient light conditions in fill photography. For instance, under a given condition, the faster sync speed gives a flash on the D70 nearly 60% higher reach than a flash of the same guide number on an EOS 350D (which has "only" 1/200s as shortest sync time).

Very curious to hear your expert opinion. Or does anyone really KNOW why this is so?

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I think I can describe how it works but not why.

Normally on a SLR flash sync speed is the minimum length of time when the film/sensor is fully uncovered by the shutter. At shorter exposure times the sensor is only partly exposed by the shutter window passing over it.

On point-and-shoots the situation is different - there is no shutter and the exposure time is determined by how long the sensor is read to see what's going on.

The D70 combines these two techniques. The sensor is exposed for a longer time (1/160s?) but it's only read for 1/500s. Finally the effective exposure time is 1/500s.

Perhaps this is why it's rumoured that the D200 will not have a CMOS sensor?

Charles

Thanks Charles!

That means they can gate a CCD as you decribed, but not a CMOS sensor? It would explain why all the point-and-shoots seem to use CCDs - or are there any with CMOS sensors?

Is there any reliable information about the D200, other than just rumours? Pixel count, sensor size, price?

Quote:

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Originally Posted by wus

Thanks Charles!

That means they can gate a CCD as you decribed, but not a CMOS sensor? It would explain why all the point-and-shoots seem to use CCDs - or are there any with CMOS sensors?

Is there any reliable information about the D200, other than just rumours? Pixel count, sensor size, price?

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I have no idea about gating a CCD or a CMOS. It was just an idea that occurred to me as I was writing the reply, following what Chasseurs d'Images said (see below).

There is no reliable information on the D200. Last week I reported what French magazine Chasseurs d'Images said on their web site, saying a load of things it won't be :

- not full-frame
- not the same sensor as the D2X
- why do you assume it will be a CMOS?

Food for thought. Apparently the announcement date is close, however.

Charles

Note... You can increase the D70 flash/shutter speed by taping over the back two (I think) contacts on the SB800. Search this site (it has been discussed)....

I have a question closely related to this post: Why the dslr have a shutter? I assume this is better than powering on and off the sensor, but exactly why?


EDIT: Ok, i found some info:

http://photo.net/bboard/q-and-a-fetch-msg?msg_id=008J5r
http://forums.dpreview.com/forums/re...essage=8635736
http://forums.dpreview.com/forums/re...essage=8635307

It appears that a mechanical shutter is always used to keep light off from the sensor beetwen shots. In the case of the P&S, the iris (aperture shutter) is used for this, but it's too slow, and the image data is dumped while the iris is closing (or before it can do it)... (i don't think that's very good to image quality :eek:). Read the second link for more details.

I think that explains why the P&S has longer shutter lag than the SLRs.

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Originally Posted by Norfindel

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It appears that a mechanical shutter is always used to keep light off from the sensor beetwen shots. In the case of the P&S, the iris (aperture shutter) is used for this, but it's too slow, and the image data is dumped while the iris is closing (or before it can do it)... (i don't think that's very good to image quality :eek:). Read the second link for more details.

I think that explains why the P&S has longer shutter lag than the SLRs.

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The links you provide are very interesting but I think you've got it a bit wrong.

In a P&S you need to have the light on the sensor between shots to give the continuous image on the LCD for framing. When shooting video on a P&S the iris stays at shooting aperture all the time.

If the iris really closes then opens at the start of a still image then there's no reason why this should take a long time - the iris blades are miniscule compared with the mirror and shutter of a DSLR. I think the shutter lag on a P&S is just down to the delay in focussing, determining exposure, etc.

Carles