-=FAQ=- Teleconverter/T-Con Tele extender Discussion

Sorry if this has been covered before. I've been 'sitting on" a kenko 1.4 pto 300 DGX for a couple of years now and have only used it with Canon kit lenses a good while ago, that I've now parted with. I finally tried it out today on my 7D with Sigma DC 18-250 HCM and focus was impossible. I tried focusing manually, and although the image in the viewfinder was crisp, the results were terrible.

Any ideas? I'm getting the Canon 70-300L IS at the end of the month and am hoping it doesn't produce the same results.

With just a lens, you can micro-focus-adjust the camera to make sure the AF and lens agrees and the image gets properly projected on the image sensor. With a TC, you must rely on the lens projecting the image exactly where the TC picks it up so the TC will project the magnified image exactly on the image sensor. This means that some lens copies togeter with some TC copies can be notoriously bad while other copies can do much better.

You can AFMA separately for a TC fitted to the lens. The camera sees the TC and considers it to be a different lens.

It's also worth noting that TCs are designed (optimised) to work with lenses which are already "long"(ish). Try it with the lens at 200-250mm, but I wouldn't hold out much hope that a 14X zoom lens with a TC will be much cop. Before going to the trouble of AFMA try the lens/TC combo in Live View at 10X and see if you can get anything close to worthwhile.

Also, at the long end this lens if f/6.3, so with the TC you'll be up to f/9. Even if the AF does (attempt to) work I wouldn't expect much in terms of speed/accuracy/reliabi​lity. Trying to judge focus accuracy of an f/9 lens through the viewfinder is not going to tell the same story as pixel peeping either. It may be Live View only or forget it.

It doesn't fully help that the camera sees TC+lens as a different lens with a different setting - you still have two optical interfaces involved, while the MFA basically adds electronic "shims" for the last step between TC and sensor.

bidkev wrote in post #16182125
Sorry if this has been covered before. I've been 'sitting on" a kenko 1.4 pto 300 DGX for a couple of years now and have only used it with Canon kit lenses a good while ago, that I've now parted with. I finally tried it out today on my 7D with Sigma DC 18-250 HCM and focus was impossible. I tried focusing manually, and although the image in the viewfinder was crisp, the results were terrible.

Any ideas? I'm getting the Canon 70-300L IS at the end of the month and am hoping it doesn't produce the same results.

Ugh. No... superzooms are rarely noted for good image quality, and really aren't something you'd want to consider with a TC. To give you an idea - a Canon 70-200L series with a TC is "OK", but a prime would be better.

As already noted, that Sigma is already f6.3 at the long end, so you can forget AF with a TC on a 7D.

I believe the 70-300L with a 1.4x TC will work (best to check manufacturer's compatibility charts), and should be "OK" - but again that's going to be f8 at the long end, so AF is unlikely to work.

pwm2 wrote in post #16182160
It doesn't fully help that the camera sees TC+lens as a different lens with a different setting - you still have two optical interfaces involved, while the MFA basically adds electronic "shims" for the last step between TC and sensor.

Maybe I don't understand this, but....

If the TC is a reporting type you can MA the lens itself and the lens+TC as a separate entity.

The only zoom lens that is worthwhile (IMHO) using a TC with happens to be the 70-200 f/2.8 Mk2. This is only true for the Canon Mk3 TC's though. In all other cases TC's don't match very well with zooms.


My 70-200 is MA -1, with the 1.4x it is -3 and with the 2.0x it is -2. Quality and AF speed is just where my 100-400 is. IS is actually better than on the 100-400 - thus I will be selling my 100-400 soon.....

Cheers.

RAW-Shooter wrote in post #16184409
The only zoom lens that is worthwhile (IMHO) using a TC with happens to be the 70-200 f/2.8 Mk2. This is only true for the Canon Mk3 TC's though. In all other cases TC's don't match very well with zooms.

My 70-200 is MA -1, with the 1.4x it is -3 and with the 2.0x it is -2. Quality and AF speed is just where my 100-400 is. IS is actually better than on the 100-400 - thus I will be selling my 100-400 soon.....

The f4 IS version also works pretty well with a 1.4x TC. I tend to use the 2x with the f2.8 IS II for the occasional "zoo" wildlife shots (or rare BIF shooting) and it's OK if stopped down to f11.

sploo wrote in post #16184999
The f4 IS version also works pretty well with a 1.4x TC. I tend to use the 2x with the f2.8 IS II for the occasional "zoo" wildlife shots (or rare BIF shooting) and it's OK if stopped down to f11.

F11?

Nah...that does not sound right to me....

First with 1.4x: @280mm 1/250 f/4 ISO 500
Second with 2.0x: @400mm 1/400 f/5.6 ISO 200

f/11 seems overkill to me as well. This was with my 5D3 and Sigma 120-300/2.8 OS (non sport) + Sigma 1.4X at 420mm, 1/200, f/5, 100 ISO. 1/4 frame crop before resizing....

HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO

HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO

tdodd wrote in post #16186057
f/11 seems overkill to me as well. This was with my 5D3 and Sigma 120-300/2.8 OS (non sport) + Sigma 1.4X at 420mm, 1/200, f/5, 100 ISO. 1/4 frame crop before resizing....

100% crop....

Hell, yes....I stand corrected, I completely forgot this lens. Maybe because its so darn heavy...:p

This zoom is very good with a TC as well. 1.4x for sure, with a 2.0x I have no idea. I don't recall that I have seen pictures shot @600mm.

Cheers.

RAW-Shooter wrote in post #16186151
Hell, yes....I stand corrected, I completely forgot this lens. Maybe because its so darn heavy...:p

This zoom is very good with a TC as well. 1.4x for sure, with a 2.0x I have no idea. I don't recall that I have seen pictures shot @600mm.

Cheers.

Examples at 600mm...

With 5D3 - https://photography-on-the.net …p=16156136&post​count=3866

With 7D - https://photography-on-the.net …p=16156290&post​count=3868

And another at 420mm with my 7D at 1/50, f/5.6, 100 ISO....

HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO

RAW-Shooter wrote in post #16186003
F11?

Nah...that does not sound right to me....

First with 1.4x: @280mm 1/250 f/4 ISO 500
Second with 2.0x: @400mm 1/400 f/5.6 ISO 200

Not trying to be combative, but two web sized images are a bit small to make a definitive conclusion (though - good shots BTW).

Based (admittedly on a bit of pixel peeping, but mostly prints), I've generally found I need 1 stop down for the 1.4x TC and two for the 2x TC to "bring back" a decent amount of quality vs. the lens without the TC. Certainly shooting the 70-200 with the 2x TC at f5.6 doesn't get me the quality I'd like.

That said, I often find I need to stop down in order to get enough depth of field at 400mm anyway, so even some uber 400mm f2.8 would still end up being shot at f11 (400mm, f11, 4 meter subject distance = 6cm DOF).

tdodd wrote in post #16186057
f/11 seems overkill to me as well. This was with my 5D3 and Sigma 120-300/2.8 OS (non sport) + Sigma 1.4X at 420mm, 1/200, f/5, 100 ISO. 1/4 frame crop before resizing....

Quality looks good - but f2.8 with a 1.4x TC is f4 wide open, so f5 is knocking on for an extra full stop down (so pretty similar to my findings with the 70-200). A 2x TC always seems to have a greater "hit" on the quality too.

You might be surprised how little stopping down is needed.Getting more DOF yeah, but sharpness isn't necessarily an issue within the given DOF when working with a good lens.

I was at f/5 to get the shutter speed I wanted for prop blur. The choice was nothing to do with DOF or lens IQ.

tdodd wrote in post #16195800
I was at f/5 to get the shutter speed I wanted for prop blur. The choice was nothing to do with DOF or lens IQ.

Understood - but my point was that the 70-200 f2.8 with a x1.4TC at f5.6 is also pretty good (regardless of the reason for being af f5.6), but with the x2TC I'm generally not that impressed without stopping it down quite a bit.

As I noted - when at 400mm I find I often want the extra DOF for the subjects I'd shoot anyway, so it's not the end of the world. Plus it's a damn sight cheaper than a 200-400mm f/4L IS USM Extender, so I can't really complain!