50-500mm goes to 5.6 not 6.3?

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Xarra

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Hi,

I've just been trying out my new bigma (50-500 Sigma) which says 4-6.3 for the f stop.

However I can use it at 500mm at 5.6 according to my camera (Canon 1000D)? Shouldn't it be at 6.3?

Any ideas why this is? (not complaining, just curious!)
 
does it not trick the camera into thinking its f/5.6 so you can still autofocus?
 
Indeed it does report itself to the camera as F5.6 in order to allow the autofocus to work with it.

This can mean you need to dial in exposure compensation of between +1/3 - +1 EV.
 
All Canon bodies except the EOS 1 series do not AF above f/5.6

EDIT: Or rather, they aren't supposed to.
 
Vertigo1 said:
Because only the 1D-series bodies can autofocus above f/5.6.
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trencheel303 said:
All Canon bodies except the EOS 1 series do not AF above f/5.6

EDIT: Or rather, they aren't supposed to.
Click to expand...

Well I never knew that. Seems a strange one, even entry level Sonys AF at whatever aperture you set.
 
Just before I bought my Siggy 150-500mm, I was informed that the AF would not work after f5.6, but I cant remember the reason now. I have a Nikon D5000.
 
fabs said:
Well I never knew that. Seems a strange one, even entry level Sonys AF at whatever aperture you set.
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It's not the aperture that you set that's the issue, rather the lens' maximum aperture.
 
fabs said:
Well I never knew that. Seems a strange one, even entry level Sonys AF at whatever aperture you set.
Click to expand...

Sorry, I'm not being clear.

When you zoom a variable aperture lens such as the Siggy, the further you zoom the more the aperture closes (this is why variable aperture lenses get darker in the viewfinder as you zoom in). If the aperture is physically closed past f/5.6, most bodies can't AF because there just isn't enough light, but you can trick them into trying to AF with teleconverters by taping pins, etc.

If you stop a lens down to f/8, obviously it only goes to f/8 as the shutter fires - but it meters the scene wide open. Obviously the siggy at the long end is f/6.3 wide open, which is why I was wondering about the AF on Canon bodies.
 
How odd, I'd assumed it would depend on the light level ie. less light at f6.3, so on a bright day or high contrast it wouldd still be ok. My 150-500 on a pentax AF is ok at f6.3 as long as it's bright.
 
mr_pants said:
It's not the aperture that you set that's the issue, rather the lens' maximum aperture.
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So the Canons (apart from the 1s) won't focus at f6.3 on the sigma because it's at its widest aperture? Still seems odd, I'm assuming this is purely a sigma thing. I use the Bigma for certain sports and it happily AFs at f6.3 and beyond.
 
Canon xxD and xxxD bodies only supposedely AF up to f5.6
xD bodies AF to f8

Sigma f6.3 lenses trick the camera into AF'ing at f6.3

Until now I thought it was by reporting f5.6 at the longest end but subtracting half a stop

BUT I just tried the 50-500mm OS with the 550D and the Kenko 1.4x DGX

At the long end it reports f9 (as it should) BUT it still autofocuses!!!

So it looks like it does not subtract half a stop it just tells the body that the f value is 5.6 whatever the case!

Very, very interesting

BTW the new 50-500 OS is still perfectly sharp and useable at 700mm f10 to f11 (so stopped down a bit from the min f9)
 
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It will AF at f/22 if thats what you set it to but its only that aperture for a split second as the camera takes the shot. If the lens max aperture is above f/5.6 wide open then non 1 series will not autofocus. 1 series only autofocus up to f/8.0 and thats centre point only.
 
Euan said:
It will AF at f/22 if thats what you set it to but its only that aperture for a split second as the camera takes the shot. If the lens max aperture is above f/5.6 wide open then non 1 series will not autofocus. 1 series only autofocus up to f/8.0 and thats centre point only.
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That is the strange thing. Min aperture with the 1.4x is f9 and it still autofocuses on a canon 550d!
 
i think thats to do with it being a 3rd party lens and tc but might be wrong,

my reply was more aimed at fabs but you beat me to it!

if you take a pic and download it does the camera pick up thats there is a 1.4x and the 50-500?
 
fabs said:
So the Canons (apart from the 1s) won't focus at f6.3 on the sigma because it's at its widest aperture? Still seems odd, I'm assuming this is purely a sigma thing. I use the Bigma for certain sports and it happily AFs at f6.3 and beyond.
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It's basically a 'safety feature' - if you check other manufacturers specs a lot of them say that the camera will only focus reliably up to f/5.6 (maximum), it seems that Canon in their wisdom have simply added a deadlock.

The camera only goes to the aperture that is set at the instant the picture is taken, at all other times it is wide open (and hence the camera can focus properly, unless the maximum aperture is f/6.3 fer example).
 
Euan said:
if you take a pic and download it does the camera pick up thats there is a 1.4x and the 50-500?
Click to expand...

Surprisingly it does! Shot below with intact EXIF data

Exposure Time = 1/30"
F Number = F10
ISO Speed Ratings = 1600
Max Aperture Value = F8.72
Focal Length = 700mm

50-500mmat700mmf10800x600.jpg
 
micloi said:
Canon xxD and xxxD bodies only supposedely AF up to f5.6
xD bodies AF to f8

Sigma f6.3 lenses trick the camera into AF'ing at f6.3

Until now I thought it was by reporting f5.6 at the longest end but subtracting half a stop

BUT I just tried the 50-500mm OS with the 550D and the Kenko 1.4x DGX

At the long end it reports f9 (as it should) BUT it still autofocuses!!!

So it looks like it does not subtract half a stop it just tells the body that the f value is 5.6 whatever the case!

Very, very interesting

BTW the new 50-500 OS is still perfectly sharp and useable at 700mm f10 to f11 (so stopped down a bit from the min f9)
Click to expand...

that's amazing... :eek:
 
scottthehat said:
whats the af speed like.
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The same as when you mask the 3 pins on a reporting TC for other lenses.
Good when the light is good. Hunts a bit before locking if the light is not good.

Advantages in this case (than having to mask the pins):
1. Convenience
2. Reports the correct info in the EXIF data
3. Metering is correct so no need to under-expose (which makes it impossible to use some modes, i.e. the Manual mode with a set aperture and shutter speed and variable ISO)
 
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