The 1.4X Kenko Teleconverter scam

[David Kilpatrick]

Looks to me as if the 100mm f/2 is a better lens anyway, and the converter does not seem to go well with the 85mm - even with extra stopping down. Thanks for these tests Frank, they also show 100mm f/2 lenses sell for such high prices.

David

[01af]

Because tele converters don't transmit lens speeds greater than 1:1.7. Any extra speed beyond this limit will get lost ...

That depends on the teleconverter design.

Yes---in theory. But so far I never came across a tele converter that was able to transmit lenses speeds greater than 1:1.7 in real life.

The Kenko 300 series have really large bits of glass - the 1.4X has a 25 mm unit, compared to the MC7 2X with a 20 mm unit.

Yes, I know. The diameters of 1.4× TCs' elements usually are wider than 2× TCs'. Still, 1.4× TCs don't transmit more lens speed than 2× TCs.

Actually, the diameter of the average 2× TC's elements is clearly narrower than a 50/1.7 lens' rear element, and still it does transmit the full speed. Don't ask me how that works; I have no idea. And furthermore, the lens elements of the Minolta/Sony 1.4× TCs are significantly wider still than those of the Kenko 1.4× Teleplus even though they are not designed for use with any lenses faster than 1:2.8 ... go figure.

But if this effect exists, it must also be related to focal length.

I think it's not. But I don't know for sure because I don't own any lenses faster than 1:2 other than 50 mm so I can't try.

Is this a T-stop calculation ...?

Definitely not.

It is impossible to tell with the 1.4X as it allows 'f/1.4' to be set.

Just take three test shots with the shutter speed fixed at a reasonable setting and the nominal aperture set to f/1.4, f/1.7, and f/2, respectively. I predict this: The images shot at f/1.4 and f/1.7 will be the same brightness (because both will be exposed at f/2.4 effectively) while the image taken at f/2 (= f/2.8 effectively) will be darker by half an f-stop.

By the way, when shooting in auto-exposure mode this will lead to under-exposure at full aperture ... because the camera will think the aperture was f/1.4 (and will set the shutter speed accordingly) while it really is only f/1.7. At all other apertures, exposure will be accurate. This effect is absent with TCs which communicate their presence to the camera properly. Also see the original owner's manual of the Minolta tele converters MD 300-S and MD 300-L.

-- Olaf

[Vidgamer]

Did I mention that my 1.7 TC had 8 pins? It didn't transmit any info, it was just a pass-through. So, you can't count on the number of pins being an indicator.

Today, against my better judgment, I bought a 2x TC, only because it was $40 new. It's a Quantaray (Ritz/Wolf Camera store house brand) with 4 elements. It actually transmits focal length and f-stop data! I tried it in the store, and sure enough, my f5.6 lens reported f11 in the camera! Nice. I was amazed to make a decent shot through the store window, across the parking lot, and onto distant subjects. AF didn't work, which I didn't expect it to. Detail seemed pretty good, although I was at ISO 800 out of paranoia or maybe because I left it that way from yesterday (whoops).

With rain showers today, I had to wait until later to try it out some more, but it was pretty dim for f11. The 2x shots weren't noticeably better than just enlarging the normal shot, although, with some persistence, I finally found some areas where the 2x showed more detail. Pretty subtle, although these were pretty much worst-case working conditions. I wouldn't expect to get good results in this light. Even so, it seems to do a little better than my 1.7, not just in magnification, but the color and look. Well, it's subjective.

The bottom line is, I feel that when the TC correctly reports the data, that the SSS works better and can help compensate for the inevitable shake that you have at these focal lengths. Also, it's nice to review photos and easily spot which ones were taken with the TC. This is not something I'd often use; but there are times when you can just never have enough zoom, so in those cases, I'll give this a shot.

As for David's problem, I guess the bottom line there is that if you want data reported from your TC to test it in the store (or read comments from others) first, and 2x is more likely to do this than the other ones.

[caporip]

I'm looking for a converter which works with HSM/SSM. The Sigma does not - it is due for replacement right now with a new model which does. Even the old Kenko works with SSM.

Maybe the problem is that a chip to convert the lens data will also cause problems with SSM, but that seems unlikely as my Kenko 2X MC-7 DG works with SSM.

I may just sell the two 1.4X converters I have now got, and only use the 2X - or I may try to find out whether a third party chip could be fitted.

David

David do you find that with the 2x 300 dg you get overexposed shots. I have to adjust to -1 when using the 2x and the 70-300ssm. Maybe its just me?

[David Kilpatrick]

I'm sure you won't get overexposed shots against the sky etc. Normally if the subject is wildlife or landscape with no sky, you always need -1 and it's even more vital with a converter as they lower the contrast.

David

[kysham]

David, hope to read about your review of the Sigma 70-200 F2.8 EX DG II HSM on Sony Alpha mount that you mentioned you are going to use with the teleconverter. I have this lens myself and thought it was quite nice to use. I'm by no means a good lens evaluator and is not technically capable of pinpointing (or even guessing wildly) about the pros and cons of this lens. Yes, you can say I bought the lens blindly!

A little bit off topic, I guess. My apologies.

[braeside]

I'm looking for a converter which works with HSM/SSM. The Sigma does not - it is due for replacement right now with a new model which does. Even the old Kenko works with SSM.

Maybe the problem is that a chip to convert the lens data will also cause problems with SSM, but that seems unlikely as my Kenko 2X MC-7 DG works with SSM.

I may just sell the two 1.4X converters I have now got, and only use the 2X - or I may try to find out whether a third party chip could be fitted.

David

Do you still have one of those Kenko 1.4 dumb TCs for sale David?

[David Kilpatrick]

Yes, I guess I do. I sold the older pre-digital one on eBay and it fetched rather more than I imagined it could. I still have the other one - the newer modern black one, boxed and new. I have the Sigma 1.4X here and it will not fit anything except Sigma apo lenses. PM if interested in the Teleplus.

David