580EX II Zoom Range

[taygull]

Originally Posted by grsphoto

A 35 is wider then the 50. The spread from a flash at 35 should be wider then the flash at 50.

That is exactly the point the OP is making. The E-TTL does not compensate for the crop.

Sorry guys the discussion is not about Canon and does it underexpose, start a new thread so this one does not get hi-jacked.

[Jose]

Originally Posted by jfrancho

You are confused. Cropping magnifies nothing, and is nothing similar to a teleconverter. The reason the image is underexposed in the first example has nothing to do with the zoom range selected, but is a byproduct of ETTL metering. It is well known that Canon's flash system underexposes consistently by about 2/3 stop. If you look closer at the second image, the center is slightly brighter, due to the narrower beam produced by selecting a longer zoom setting. The image is still underexposed.

Maybe cropping is the wrong word to use. When I select a section of an image and crop it with Photoshop, the area selected is magnified. When I take an image with a full size sensor (35 mm) and crop the center of it to obtain an image the size of a 1.6X sensor, the resulting image is magnified. If there would be a 1.6X teleconverter available and if used with a full size sensor and the same lenght focal lenght, the resulting image size should be the same as the one taken with a 1.6X sensor camera without the 1.6X teleconverter. In this case, the image obtained with the full sensor camera is magnified but the one taken with the 1.6X sensor is not.

When I posted the sample images I mentioned in parenthesis that the images also showed underexposure and a hot spot (brighter area) in the center. If both images are carefully examined, one can see that both shows a slight brighter area in the center and both are underexposed.

This brings me to the my original observation of Canon's claims in page 21 of the 580EX II manual regarding Auto Zoom for Image Size: "The Speedlite automatically recognizes the EOS DIGITAL camera's image size and automatically sets the flash coverage for lens focal lenghts 24 mm to 105." Does it? I see no change in the functioning of the 580EX II in this respect when I compare it to my old 550EX when both are used with the 40D camera.

[swampler]

Again, I reference you to the statement "lens focal length." NOT, 35mm equivalent focal length. Perhaps you choose not to read "lens" in the statement?

[taygull]

Originally Posted by swampler

Again, I reference you to the statement "lens focal length." NOT, 35mm equivalent focal length. Perhaps you choose not to read "lens" in the statement?

Again, the focal length is really not the issue.

a 35mm lens on a 1.6 crop does not take a true 35mm shot, we all know this. The 580EX emits a different amount of light for the same exact lens on a 40D as it does a 5D.

The OP is trying to make the point that the 580EX should be smart enough to adjust for the crop factor and it is not.

[swampler]

Originally Posted by taygull

Again, the focal length is really not the issue.

a 35mm lens on a 1.6 crop does not take a true 35mm shot, we all know this.

The OP is trying to make the point that the 580EX should be smart enough to adjust for the crop factor and it is not.

I know the point the OP is making and he's wrong. The quote from the manual he included says it adjusts for the "lens focal length" but thinks it should adjust to the 35mm equivalent focal length and is complaining that it doesn't. I don't see the problem...it does what it says it does.

The 580EX emits a different amount of light for the same exact lens on a 40D as it does a 5D.

Huh? How do you figure this? If this is the case, then wouldn't it be behaving as the OP wants it to?

[taygull]

Originally Posted by swampler

I know the point the OP is making and he's wrong. The quote from the manual he included says it adjusts for the "lens focal length" but thinks it should adjust to the 35mm equivalent focal length and is complaining that it doesn't. I don't see the problem...it does what it says it does.

Huh? How do you figure this? If this is the case, then wouldn't it be behaving as the OP wants it to?

Sorry, I should have said when adjusted for the same subject.

Just because something does what it says it does doesn't mean it is right or that it is what is best.

I'd never thought about it but I do think it would be very simple for the 580EX to adjust for a crop body.

Tell me why the flash (which is celebrated as being automatic) should not recognize that I am closer to my subject when I'm using a 1.6 crop then I am when using a full frame yet I'm using the same focal length. How really difficult would it be for Canon to realize that you need a different setting on a different crop body and make the adjustment.

[swampler]

I wasn't debating what it should do. I was debating that it performed to specification (as advertised).

[jfrancho]

Tell me why the flash (which is celebrated as being automatic) should not recognize that I am closer to my subject when I'm using a 1.6 crop then I am when using a full frame yet I'm using the same focal length. How really difficult would it be for Canon to realize that you need a different setting on a different crop body and make the adjustment.

It does this by reporting subject distance data gained from the AF system. You can see this clearly on the flash's display. Again, I see no relevance sensor size has in this.

[grsphoto]

I suspect that Canon doesn't do something like adjust for sensor size in the flash zoom feature because it would hurt sales.

I know I won't buy it.

I want a flash that is going to cover the FOV of the lens ( plus more) instead of purposely darkening the edges. I want my lens to gather as much light as possible.

Seriously I can not understand why you want this feature? The only benefit I can see is you may save a bit of power...maybe enough for 2 flashes per battery set?

Glenn

[jfrancho]

I want a flash that is going to cover the FOV of the lens ( plus more) instead of purposely darkening the edges. I want my lens to gather as much light as possible.

You're right on the money there Glenn.

[taygull]

Originally Posted by grsphoto

I suspect that Canon doesn't do something like adjust for sensor size in the flash zoom feature because it would hurt sales.

I know I won't buy it.

I want a flash that is going to cover the FOV of the lens ( plus more) instead of purposely darkening the edges. I want my lens to gather as much light as possible.

Seriously I can not understand why you want this feature? The only benefit I can see is you may save a bit of power...maybe enough for 2 flashes per battery set?

Glenn

I disagree;

If the flash is reading the focal length and you're at 50mm and the effective focal length is 80mm on a 1.6 crop then you are going to be further away from your subject thus you will have less light.

If the flash only has a reach that is sufficient at 105mm then what happens when you put that 100mm lens on and your effective focal length is now 160mm you are not going to have the same light as if your 100mm was on a full frame censor.

[jfrancho]

Originally Posted by taygull

I disagree;

If the flash is reading the focal length and you're at 50mm and the effective focal length is 80mm on a 1.6 crop then you are going to be further away from your subject thus you will have less light.

If the flash only has a reach that is sufficient at 105mm then what happens when you put that 100mm lens on and your effective focal length is now 160mm you are not going to have the same light as if your 100mm was on a full frame censor.

Again, the camera communicates AF data, specifically subject distance, to the flash to determine output. FOV has nothing to do with it, if there is total coverage for full frame sensor and below. Zoom range and subject distance are two completely different functions.

[grsphoto]

There seems to be a misunderstanding about how the flash & E-TTL works.

The flash doesn't know or care about distance.

When your shutter fires, the flash fires. It continues to fire until the light hits the subject, bounces back, travels down the lens, and the sensors in the the camera say "there is enough light, now shut off".

Or the flash becomes fully discharged and it runs out of juice.

Sensor size doesn't matter to the flash! It puts out light until the camera tells it to stop! ( when working in E-TTL mode)

If the subject is closer or further away by the 2 feet difference caused by the change in sensors size... it doesn't matter! The flash will just fire for a small fraction of time longer.

Glenn

[jfrancho]

That contradicts this, from Flash Photography with Canon EOS Cameras - Part I.

Distance data incorporated into some calculations.

Second, E-TTL II can use distance data when it’s available. Many EF lenses (see list in next section) contain rotary encoders that can detect the current focus distance. For example, if your camera is focussed on an object 4 metres away then the lens will send this approximate focus distance data to the camera body.

Under certain conditions the distance data is factored into the calculations for determining proper flash output. This is particularly useful if you use the focus and recompose method without setting FEL - the new system can help minimize flash metering errors under these conditions. Canon describe the new system as essentially metering flash data across a flat plane rather than a point.

Up until now distance data hasn’t really been used much by EOS cameras. Some PIC (icon modes) apparently incorporate distance data into their exposure calculations, but that’s really been about it. E-TTL II is the first really useful application of this information that Canon have implemented, and is obviously very similar to the fashion in which Nikon have long relied on distance data for their flash metering system.

[grsphoto]

The flash doesn't care about distance. It has two states, on or off.

E-TTL metering ( Electronic Through The Lens) metering can take into account distance data to "metering flash data across a flat plane rather than a point".

The metering is done in the camera.

The Camera tells the flash to turn off when it has enough light.

Glenn

[jfrancho]

I think we're speaking of the flash and the camera as a "system." ETTL-II can't happen without both, so I don't see the relevance of limiting the discussion to what just the flash can do. ETTL-II uses distance data. Surely the distance meter shown on the flash's dislay is not just raccoon bait.

[taygull]

If distance does not matter then why does the 580EX make an audible adjustment when you zoom with a lens? Why even show focal length data on the back of the flash unit, or heck even have it availabe when in E-TTL mode then?

[Jose]

I assumed that those discussing the 580EX II would have one and accesibility to the manual; I was shortsighted in not quoting the whole paragraph so here it is: "EOS DIGITAL cameras have one of three image sizes. The lens' effective focal lens will differ depending on the camera's image size. The Speedlite automatically recognizes the EOS DIGITAL camera's image size and automatically sets the flash coverage for lens focal lenghts from 24mm to 105 mm."

Therefore if I use a 35 mm focal lens, based in Canon's description above, this lens would become approximately 50 mm focal lens when used in a camera with a 1.6 sensor and the Speedlite should automatically recognize it and set the flash head zoom to the effective focal lens of 50 mm since it is within the 24 mm to 105 mm coverage. It does not; perhaps I have a defective unit.

I do appreciate the patience of those that have responded to this thread; the greatness of PhotoCamel. Hope that we all can reach a concensus as to the true meaning of Canon's description in the 580 EX II manual. I will ask Canon and if I get an answer will let you know.

[jfrancho]

Please do.

[Max@Home]

...my, are we confused...

OK then, the answer to the zoom/coverage-question:

Canon Manual with explanatory add-on :

EOS DIGITAL cameras have one of three image sizes. The lens' effective focal lens will differ depending on the camera's image size. The Speedlite automatically recognizes the EOS DIGITAL camera's image size - and shows this ONLY with a symbol in the upper right corner of the LCD - and automatically sets the flash coverage for lens focal lengths from 24mm to 105 mm.

The confusion lies in the fact that when you use a lens within that 24mm-105mm range, on a 1.3x or 1.6x crop body, the zoomposition-display will still show the lens' actual (FF-FoV) focal length, and NOT the 'FoV' focal length, but it does (RE)CALCULATES and ADJUSTS the zoomposition for the sensorsize!

How can you tell/proof this works?

Mount an EF-S 10mm-22mm lens on a xxD/xxxD body and put the 580exII on it: this lens has a FoV of 16mm-35mm on a 1.6x crop body. The zoomcoverage of the flash is 24-105mm, below 24mm you have to pull out the 'widescreen' giving maximal 14mm wide coverage.

Now zoom the 10-22 lens from wide to tele, you will notice that from 10mm to 14-and-a-bit mm the '24' zoomposition indication flashes/blinks, indicating you are below zoomcoverage range, and that you have to pull out the widescreen. The flashing/blinking stops at 14-and-a-bit (actually 15mm, but 15mm is not indicated on the lens ) mm, as 14-and-a-bit mm is equal to the FoV of a 24mm lens and thus falls within the range, no need to pull out the 'widescreen' although the lens actually is a 14-and-a-bit mm.

The Tele-end does not have a 'warning' sign, but if you use a lens that covers below and above 'FoV' 105mm, say a 24mm-105mm , on a 1.6x crop body, then you might notice that above the ~65.625mm position (=FoV 105mm) the zoomposition indicator still changes, but not the flashes actual zoom position (you do not hear it zooming/changing position any more): as the zoomhead has reached his limit at ~66mm (=105mm+)

*my* conclusion:

Does the 580exII adjust the zoomposition for the sensor size ?? Yes !

Does it show that on-screen ?? Yes !

But not by changing the actual focal zoomposition of lenses used, but by showing a little 'sensor is smaller than FF coverage' symbol.

Does that confuse a lot of users ??

YOU BET!

...*my* €0.02 worth...

Kindest regards!

Max@Home

PS 1: on a sidenote: the 580EX(II) does use the distance-to-subject measurement the camera and lens do to calculate it's output, but it does not show that distance on the LCD: the distance marks shown on the LCD indicate the flash's working ('covered') range at MaxSyncSpeed and depends on aperture and ISO used.

PS 2 : further on that: the better you place your subject (take distance) to the middle of the available flashrange, the more 'harmonious'/'balanced' the image will look.

PS 3 : why not post Canon-equipment questions in the Canon forum, would have saved a lot of people a lot of typing