exif not recording 2x focal length

[DennisT]

Before it was stolen my minolta 2x converter when paired with a700 and sigma bigma would be recorded as focal length 1000mm being 2x 500mm. My replacement sigma 2x converter when coupled with bigma is recorded as 500mm in exif. Any ideas why????

[SmartWombat]

So it's a difference Minolta vs Sigma?
I would say the software in the converter is different and the Sigma converter is not reporting that it's fitted in the same way as the Minolta.

[NoKnees]

Not all converters are created equal. Not just physically, but as noted by Paul, some are "dumb" without an active computer chip installed in it to convert length and aperture info. The dumb ones just forward the lens info to the camera, seeming transparent.

This can be good in some cases as it will fool the camera into allowing auto-focus at some apertures where it normally wouldn't work, but more often than not, they don't do much other than confuse you when checking exif info later.. ;)

Dyxum website has a good section on teleconverters that covers what each one does, what lenses they are compatible with, etc... Teleconverter Guide

To Save you a side trip, relevant info here:

Correct F Stop and Focal Length Information With A Teleconverter

If a teleconverter has an IC chip (ROM) inside, it should display the correct F stop and focal length information to the camera body and EXIF data.
Example:
50mm F1.4 + 1.4X TC = 75mm F2
50mm F1.4 + 2X TC = 100mm F2.8
50mm F1.4 + 3X TC = 150mm F4

Based on my observation, most 2X teleconveters (except Sigma EX and EX DG) report the correct F stop and focal length information.

For 1.4X and 1.7X teleconverter, it depends on the particular make and model. Minolta APO 1.4X, Sony 1.4X and Vivitar 1.4X TC report the correct information while some other 1.4X TC does not. Apparently some manufacturer has decided to design their TC without any IC Chip. This has resulted in incorrect information being displayed in the viewfinder and EXIF data. Other than the incorrect information, there is no issue of using the teleconverter except AS/SSS may not be as effective.

The following 1.4X, 1.7X and 2X teleconverters (partial list) do not have chip inside therefore it will not report the correct F stop or focal length information to the camera.
Kenko Pro 300 1.4X (dedicated)
Kenko Pro 300 DG 1.4X (dedicated)
Promaster Spectrum 7 1.7X (generic)
Soligor 1.4X Pro (Probably a rebadged Kenko Pro 300)
Soligor 1.7X C/D4 AF (generic)
Sakar MC4 1.7X (generic)
Tamron SP 1.4X (dedicated)
Tamron MC4 1.4X (generic)
Sigma APO EX 1.4X (dedicated)
Sigma APO EX DG 1.4X (dedicated)
Sigma APO EX 2X (dedicated)
Sigma APO EX DG 2X (dedicated)

The camera just ignores the presence of the teleconverter although you still have correct exposure since exposure is based on actual amount of light passing through the lens. You'll also notice the viewfinder is dimmer and the focusing is slower because of the reduction of light to the camera.

One side benefit of using non-chip passthrough TC is the camera will attempt to AF with a slower lens previously not possible.

Example:
75-300mm or 100-300mm F4.5-5.6 with a 1.4X TC will normally not AF, but with a non-chip 1.4X or even 1.7X TC, it will try to AF but whether it can lock focus is another story

[DennisT]

Thanks for the really useful info - it is a case of no chip in the converter (Sigma EX DG). Guess I'll just have to make do with "mental" adjustments when invoking the converter.
Really appreciate your help.

[NoKnees]

No problem... The first time I used a TC and it didn't work as expected, I started doing some homework.. Found out they were a bit more complicated than I wanted them to be. The problem is I sold the first one I had when it didn't work with my current lenses, not realizing that it'd work for the better lenses I'd purchase later.

The Sigma EX DG is not a bad quality converter, even if it's "dumb". ;)

Happy shooting!