Tele-Converter Conundrum

[GerryNick2]

Having been experimenting with several tele-converters on my 100-400mm pump a question has arisen of which I am not sure of the answer.

When I attach a Canon 1.4x tc any images taken with the lens wide open will show the focal length as 560mm and aperature as f8 in the exif data within Lightroom, as would be expected.

However, when using a Kenko 1.5x or 1.4x Pro converter at maximum aperture and focal length the aperture shown in the exif data still shows as f5.6 (lens maximum aperature) and the focal length as 400mm.

Whilst I understand that the third party converters do not report back to the camera which in the right conditions allows AF I am intrigued by this.

What I would like to know is when using the Kenko TC's despite still showing an aperture of f5.6 is the actual aperture f8 as would be expected and is the case with the Canon TC.

No doubt someone can put me right on this.

Gerry

[glsammy]

I would assume it's really F8.0. You can't avoid the loss of 1 stop of light it's one of the laws of something or other!
How the camera really meters for this correctly is also a mystery for me.
I have exactly the same effect when I use my 1.4X with the pins taped. It's never bothered me, apart from the fact you cant trust the EXIF information, being wrong on focal length and also aperture. The images look all right though, so even if it's reporting it incorrectly, it's sorting it out in its own unknown way!

[GerryNick2]

Originally Posted by glsammy

I would assume it's really F8.0. You can't avoid the loss of 1 stop of light it's one of the laws of something or other!
How the camera really meters for this correctly is also a mystery for me.
I have exactly the same effect when I use my 1.4X with the pins taped. It's never bothered me, apart from the fact you cant trust the EXIF information, being wrong on focal length and also aperture. The images look all right though, so even if it's reporting it incorrectly, it's sorting it out in its own unknown way!

Certainly is a mystery Graham and as you say the images turn out Ok.

Gerry

[peterjclarke]

It's just some cameras do not have the data for other brand lenses and tele converters. My Nikon 1.7x works with the correct exif data for my nikon lenses but my Sigma 1.4x does not. My D200 recognised a Sigma 50-500 with the sigma 1.4x but the D300 does not work at all with this lens combination. My Bigma has been sold anyway and my Sigma 1.4x is up for sale with the view of getting a Nikon 1.4x anyway.

Peter

[WhiskyBottle]

I'm seeing similar but different results.
Lens - Convertor - Camera
Nikon - Nikon - Nikon, reports correct
Nikon - Kenko - Nikon, reports correct
Sigma - Nikon or Kenko - Nikon, reports lens ap, not resultant ap.
Nikon - Nikon AND Kenko - Nikon, reports ap of lens + one convertor.

Seems the Sigma lenses don't report the corrent apperture with either convertor.
Sigma lenses are 105Macro & 500/4.5, cameras are F80/D70/D300

[Words]

The Kenko 1.4 reports correctly if the pins aren't taped, but you lose auto-focus.

[genuinita]

I've seen a Canon 1.4x taken to pieces & it has a microchip inside

3rd party TCs dont have any chips in AFAIK

this may have something to do with it?

[GerryNick2]

I think the third party TC's have a chip in them as well. The key is what the chip reports back to the camera. It seems that the Kenko pro 1.4x reports the true lens data back to the camera hence on the Canon 100-400mm AF will not work.
Sigma use a smart chip in the bigma 50-500mm Canon fit lens which reports the max.aperture as f5.6 as opposed to f6.3 which is designed to fool the camera and enable AF to work. I believe that there is a similar setup in some third party TC's which is why they will allow AF to work.

Gerry

[WhiskyBottle]

Originally Posted by GerryNick2

...the max.aperture as f5.6 as opposed to f6.3 which is designed to fool the camera and enable AF to work...
Gerry

Nikon camera's don't seem to switch off the AF at a given maximum aperture as Canon do, so the camera will always (attempt to) auto focus. It's just not very good at it above f/5.6

However looking back to my notes above, it's not the telecovertor that seems to have the problem reporting, it's the Sigma lenses. So maybe it's the lenses, not the convertor that's mis-reporting the true aperture to get AF working?

[HowlinWolf]

Originally Posted by WhiskyBottle

Nikon camera's don't seem to switch off the AF at a given maximum aperture as Canon do, so the camera will always (attempt to) auto focus. It's just not very good at it above f/5.6

Nikon cite f/5.6 as a conservative figure. I have read of users having successful AF at f/8, but beyond this hunting does become a problem.

HW