EOS 500n Flash Synchro Speed

[krisheylen]

Hi,

 

Acording to the manual, the EOS-500's flash synchro speed is 1/90.

Using my Metz Mecablitz 34 CS-2 flash (on the shoe) I always

respected this as maximum shutter speed. A few days ago I forgot to

change the speed so I made a few shots with flash at 1/125 (in a very

dark room). When I got the film developed I was surprised that those

pictures were perfectly exposed on the entire frame !! Anyone knows

what is the REAL synchro speed for this setup ? I know some

dedicated speedlights (TTL) can go up higher, but my flash is just a

cheap auto-flash. Thanks in advance.

Kris.

[bill_goldman]

Canon EOS cameras will automatically restrict the shutter speed to the fastest sync speed for the particular EOS model in use when a flash is mounted and turned on, except for Type A models which have the capability for high speed sync (FP flash) and it is enabled on the appropriate Speedlite.

 

To test this, set a high shutter speed on your camera and mount the flash. When it is turned on the shutter speed should drop to 1/125 or 1/90 or ? What you will see displayed is the true max sync speed.

[krisheylen]

Bill,

Thanks for the answer ! Exactly as you said, the camera drops down the speed when using the build-in flash. However with the external flash mounted, and the camera set in manual mode, I can choose whatever shutter speed I want to. The camera doesn't seem to detect the flash. I was just curious why I didn´t get half of the frame underexposed.

Thanks again,

Kris.

[NK Guy]

It appears from anecdotal evidence that most if not all low-end EOS cameras have

been pre-programmed at the factory to have a maximum sync speed of 1/90 sec, but

that the actual physical shutter hardware is capable of higher sync speeds - perhaps

the 1/125 sec of midrange EOS cameras. This is done for marketing reasons -

separate out the low and midrange cameras.

 

So perhaps you could run a series of simple tests at different shutter speeds to see

what the actual maximum flash sync speed is for your particular camera.

[NK Guy]

To clarify my previous point - the camera's computer automatically sets 1/90 as the

maximum shutter speed when it detects the presence of a powered-up flash unit.

Either the internal flash or a shoe-mounted dedicated flash.

 

If you're using a hotshoe adapter then the camera has no way of knowing that you've

got a flash attached and so its internal program does not restrict the shutter speed,

so you can set any shutter speed you like.

[jimstrutz]

I have tested several low end Canon EOS cameras (EOS 100/Rebel, 500/Rebel X, 500n/Rebel G) with a generic (non-dedicated) flash just to see how fast the shutter really was. They all sync fine to 1/125. Perhaps a studio strobe with a very long flash duration would need a sinc speed of 1/90, but the shoe mount versions I tried this with all work fine to 1/125. In fact, other than clipping the very bottom sliver of the image, they work at 1/180 second. At 1/250, too much of the image was missing to be easily usable.

 

And I agree that Canon probably did this for marketing purposes. They have done nearly the same thing by not providing access to a spot meter with the Elan 7. If Canon wanted to they could have simply used *ONE* of the 35 metering segments for the partial meter, instead of the several that they chose to use. It wouldn't cost any more to do it, but that would have cut into EOS 3 sales. Can't have that I guess.

 

I'm hoping the competition from the spot meters of the N80, and Maxxum 5 will change their minds.

[vlad_soare]

No, this has nothing to do with marketing. It's about the velocity of the shutter curtains. 1/90 is the fastest setting at which the shutter is <b>fully</b> open by the time the second curtain starts moving. At shorter exposure times the second curtain starts moving <b>before</b> the first one ends its journey, which means that in those cases the shutter is never fully open. That's why you can't use flash at speeds faster than 1/90.

<br><br>

The curtains of professional cameras move faster than those of cheap cameras. Because the first curtain moves faster, it takes less time for the shutter to get completely open, so that the second curtain can be allowed to start moving a little later. This means that such a high-velocity shutter can be fully open for a moment at 1/125 s, or even at 1/250 s.

<br><br>

However, increasing the velocity of the curtains does have its price. You need more precision and better build quality. The curtains must withstand higher accelerations and decelerations, the braking mechanism must be more powerful and robust, the induced vibration level is higher so you need more powerful dampers, etc. In other words, a high velocity shutter is very expensive.

<br><br>

With a dedicated external flash, some EOS cameras are able to synchronize at all speeds. This is not a true synchronization however, it's just a trick (a very neat one): instead of firing suddenly, the flash gets discharged slowly from the time the first curtain starts moving until the time the second curtain ends moving. This only works with so-called "type A" cameras (500N is a type A camera, but 500 isn't). Not even the EOS 5 can use this feature (because it's a type B camera).

[NK Guy]

>No, this has nothing to do with marketing. It's about the velocity of the shutter

curtains. 1/90 is the fastest setting at which the shutter is fully open by the time the

second curtain starts moving.

 

Are you sure about this? Jim's empirical testing seems to suggest that the 1/90 sec

flash sync limit on at least some low-end Canons is not required by the physical

shutter hardware.

[vlad_soare]

The limit is not very strictly defined. It's not like at 1/90 the picture is perfect and then suddenly at 1/125 the picture is completely ruined. No, there is a slight gradation. Between 1/90 and 1/125 there is only half a stop, so even if the shutter is not fully open at the time the second curtain starts moving, it is still <b>almost</b> fully open. Maybe the true synchronization speed is not 1/90, maybe it's somewhere between 1/90 and 1/125. This means that at 1/125 it is still possible to obtain a good flash illumination in certain conditions, because the blackout only affects a very small part of the frame. In <b>some</b> cases this can go almost unnoticed.<br>

However, a camera manufacturer must make sure that the illumination is perfect every time; Canon can't allow their cameras to take flash pictures below the true synchronization speed, hoping that the blacked-out area would be very small. They must make sure that you <b>never</b> get a blacked-out area, no matter how small it might be. Jim's picture taken at 1/125 may look fine, he may have got away with it this time, but I'm sure there are situations when a picture taken with flash at 1/125 wouldn't be OK. <br>

Anyway, at 1/180 (only half a stop further) even Jim admits that clipping becomes visible.

<br><br>

Not implementing spot metering in Elan 7 is another matter though. That, in my opinion, is truely a marketing trick. The Elan 7 has 35 metering cells, and for partial metering it uses five of them. Why five? Why not just one? The Elan 7 has the technical ability to spot meter, but it's disabled by software.