300mm f/4 AF-S with Kenko 1.4x TC: incorrect focal length? (1 Viewer)

I have a question of negligible importance. I received the Kenko Teleplus PRO 300 1.4x teleconverter today. Works surprisingly well with all of my lenses, and somehow even manages to AF in low light with my Tamron 18-270 at the 270mm end (with an effective aperture of f/9).

So here's the only strange quirk I've noticed: when it's attached to my Nikon 300mm f/4 AF-S, the camera (a D90) still reads it as having a 300mm focal length and an f/4 max aperture (vs. the 420mm f/5.6 that it should read). What's curious is this only happens with this specific lens; with the 35mm f/1.8, for example, the D90 correctly recognizes the 48mm f/2.5 with the TC attached. I wonder if this has to do with the fact that the 300mm f/4 is an older lens than my other two. Aside from this issue, everything else works great with the 300mm f/4; autofocus works great, and I don't really perceive any real drop in image quality.

Overall, this is a very minor issue; left to its own devices, the D90 will slightly underexpose shots with the 300/Kenko TC setup, but all I really need to do is compensate + 1EV to deal with this. So I think the Kenko TC is a keeper; the Nikon TC-14E II I previously rented didn't have this issue, but then, it doesn't work with any of my other lenses, so it's less useful to me. But I was wondering: is there anything that I can do to get the correct focal length/aperture reported when using the 300mm f/4? I get the feeling this is a software glitch that can't be worked around, but any insight would be greatly appreciated!

if you google for Nikon Compatibility Chart, you should find a spreadsheet that lists all these quirks, its a common issue with Nikon lenses and other vendor equipment.

My Tamron 1.4x tc (which I think is the same as the Kenko) has the same focal length issue with my D90 and both Nikon 300 f/4 AF and 28-105 AF, though I have not noticed any significant underexposure. Haven't tried it on other CPU lenses. Sorry, but I don't know of any workaround.

Thanks everyone. I figured there wasn't much to be done about it. Fortunately, after taking some more shots, I've determined that the lens does in fact meter correctly with the TC, so I can live with it having the wrong EXIF data, given that image quality is excellent.

This is a common problem with the kenkos and various brands of lens

Discovered a new twist in the story: it looks like the issue is in my 300mm f/4 AF-S lens and not the teleconverter. I borrowed a Nikon TC-14E II teleconverter, and I get the same incorrect EXIF data. I also noticed the AF tends to oscillate a bit (that's my best description of what it does) before settling on the correct focal point, but only with the TC attached. None of my other lenses exhibit this kind of AF activity. Also, a different 300 f/4 and TC-14 combo I'd borrowed previously did in fact register the correct EXIF data, and exhibited relatively more normal AF behavior. Thus, I'm pretty sure it's the lens itself that has the issue.

I don't know if this is a fixable problem; I doubt it is, but let me know if anyone happens to have any ideas. Otherwise, as before, I don't think this is a deal-breaker, and I'll probably keep both the lens and the TC!

Worthwhile checking the screws on the lens and teleconverter. I find that they come a bit loose on my 1.4x teles but not the 1.7x or 2x. If everythink is tight there should be no play.
Neil.