[speagles2]

Hi all

Forgive me, as I know this issue has been discussed before, but I've been trying out the Sigma EX DG APO 1.4x teleconverter with the Sigma EX DG APO 100-300/F4 on the new K3 iii. Seems like a great combo, AF is fast and precise and the image quality is impressive. However, the one issue is that the camera doesn't know that the teleconverter is there, so it thinks the lens is 300mm at full telephoto, not 420mm.

I was pondering the impact on SR, and it seems to me that so long as the lens is longer than the camera thinks it is, SR should still work fine and give some advantage, albeit it won't quite work as effectively as it could if it knew the correct focal length, as it will tend to 'under move' the sensor. If the focal length of the lens was shorter than the camera thought it was, on the other hand, I assume SR could potentially introduce motion blur by over-compensating (moving the sensor too much).

This seems to be borne out in practice - I took a few test shots today and was able to shoot down to 1/30 at 420mm (!) with SR on and still get sharp images, whereas with SR off there was plenty of motion blur.

So... interested to know if anyone else has experience with this combo and has found the same, and also if there's any way around the issue - I assume not since I'm using the latest Pentax body with the latest firmware :-(

[Fogel70]

I might be wrong, but I believe the only K-mount TC that transfer correct focal length to camera is Pentax HD DA 1.4x.
Most other TCs were released before Pentax had DSLR with SR, so it was not that important back then.

[othar]

I have never tested it, but I assumed as much (concerning under/over-compensation of the sensor movement), therefore I always set the focal length of my MF Vivitar 70-210mm lens to 70mm (it's also more easy to recognize the lens via exif data, when you always pick the same value)

[speagles2]

I might be wrong, but I believe the only K-mount TC that transfer correct focal length to camera is Pentax HD DA 1.4x.
Most other TCs were released before Pentax had DSLR with SR, so it was not that important back then.

Hmmm, it looks like the Sigma 1.4 one only came out in 2013, which was 3 years after the K5, so SR was definitely the norm on Pentax DSLRs by then - but I suspect you're right and it's only the Pentax TC that gets this right, which is a shame.

---------- Post added 07-31-21 at 04:39 AM ----------

I have never tested it, but I assumed as much (concerning under/over-compensation of the sensor movement), therefore I always set the focal length of my MF Vivitar 70-210mm lens to 70mm (it's also more easy to recognize the lens via exif data, when you always pick the same value)

Sounds like a good plan. I did think of setting the focal length manually, but that's not possible with a lens that can communicate focal length (short of taping over one of the contacts in the lens mount) - the option to manually set the focal length is greyed out unless you have mounted an old manual lens that isn't able to tell the camera its focal length.

[vonBaloney]

Yes, that as always seemed to be the case -- if the focal length value is set lower than reality, it won't hurt you, just won't help as much. (Doesn't always hurt you to be a higher value than reality either with a long lens.) And focal lengths are not nearly as precise as we think of them, especially on a zoom, there is some leeway there anyway. Just experiment to see what you can get away with in terms of minimum shutter speed.

[Bob 256]

Perhaps tape over a contact on the X1.4 converter and then your camera should prompt for focal length whenever you use it?

[vonBaloney]

Perhaps tape over a contact on the X1.4 converter and then your camera should prompt for focal length whenever you use it?

Don't think that works with an AF lens -- not without losing AF anyway.

[Fogel70]

Hmmm, it looks like the Sigma 1.4 one only came out in 2013, which was 3 years after the K5, so SR was definitely the norm on Pentax DSLRs by then - but I suspect you're right and it's only the Pentax TC that gets this right, which is a shame.

I believe that is a later version of Sigmas TC that has never been available in Pentax K-mount. The Sigma APO EX DG 1.4x TC is older than that. Probably from early 2000s when many of the Sigmas EX APO DG lenses came.

[vonBaloney]

Does the Sigma TC at least compensate for the aperture (or at least give you the original correctly) ? You can get weird aperture readings with Sigma lenses and some TCs.

[kypfer]

Hi all
Forgive me, as I know this issue has been discussed before, but I've been trying out the Sigma EX DG APO 1.4x teleconverter with the Sigma EX DG APO 100-300/F4 on the new K3 iii. Seems like a great combo, AF is fast and precise and the image quality is impressive. However, the one issue is that the camera doesn't know that the teleconverter is there, so it thinks the lens is 300mm at full telephoto, not 420mm.
I was pondering the impact on SR, and it seems to me that so long as the lens is longer than the camera thinks it is, SR should still work fine and give some advantage, albeit it won't quite work as effectively as it could if it knew the correct focal length, as it will tend to 'under move' the sensor. If the focal length of the lens was shorter than the camera thought it was, on the other hand, I assume SR could potentially introduce motion blur by over-compensating (moving the sensor too much).
This seems to be borne out in practice - I took a few test shots today and was able to shoot down to 1/30 at 420mm (!) with SR on and still get sharp images, whereas with SR off there was plenty of motion blur.
So... interested to know if anyone else has experience with this combo and has found the same, and also if there's any way around the issue - I assume not since I'm using the latest Pentax body with the latest firmware :-(

You're correct, the camera will under-compensate, which has got to be better than the other way around … 1/30 @ 420mm is good going, what ISO were you getting? Probably plenty of room for adjustment!

I use the Sigma EX 2x with my Sigma EX 70-200mm f/2.8 quite regularly (and Kenko a/f t/c's with other lenses) and none of them notify the camera of their existence. I simply let the camera do the best it can with the information supplied and am rarely disappointed

Admittedly, I've usually got the shutter speed fairly wound up to compensate for (wildlife) subject movement, so the in-camera Shake Reduction probably doesn't have a great say in the matter … given the low-light capabilities of the modern Pentax cameras it's rarely an issue for me

[Paul the Sunman]

I might be wrong, but I believe the only K-mount TC that transfer correct focal length to camera is Pentax HD DA 1.4x.

I still can't understand why Pentax doesn't have a modern FF TC.

[speagles2]

I believe that is a later version of Sigmas TC that has never been available in Pentax K-mount. The Sigma APO EX DG 1.4x TC is older than that. Probably from early 2000s when many of the Sigmas EX APO DG lenses came.

Ah, OK.I know there were earlier versions of this one before the 'DG' version (which means 'optimised for digital' as I understand it) but yes, perhaps it's a bit older than I thought :-)

---------- Post added 07-31-21 at 07:56 PM ----------

You're correct, the camera will under-compensate, which has got to be better than the other way around … 1/30 @ 420mm is good going, what ISO were you getting? Probably plenty of room for adjustment!

I use the Sigma EX 2x with my Sigma EX 70-200mm f/2.8 quite regularly (and Kenko a/f t/c's with other lenses) and none of them notify the camera of their existence. I simply let the camera do the best it can with the information supplied and am rarely disappointed

Admittedly, I've usually got the shutter speed fairly wound up to compensate for (wildlife) subject movement, so the in-camera Shake Reduction probably doesn't have a great say in the matter … given the low-light capabilities of the modern Pentax cameras it's rarely an issue for me

Hah, yes, I wouldn't rely on 1/30 at 420mm normally, esp. with the K3 iii's high ISO performance - I was just experimenting with SR :-) I tried a bunch more test shots just now handheld and standing up at 1/30 / 420mm and the results are certainly variable even with SR. My best shot with SR was totally sharp, but my worst one certainly wasn't, even with SR enabled. My best shot without SR was surprisingly good too, but still only as good as the worst of the SR shots. So SR definitely helps, but good technique and a steady hand are clearly still important!

On your other question, no, the TC doesn't correct the aperture either, so the camera still thinks it's F4 wide open - but I don't think that really matters in practice.

Thanks all for your replies and sorry to dig up a question that's probably come up plenty of times in the past...

[speagles2]

Just in case anyone's interested, these were the results of my quick test this morning. I should point out was that this was just after my second cup of coffee!

All Sigma 100-300/F4 + Sigma 1.4x TC at 420mm and 1/30s

[Lowell Goudge]

Perhaps tape over a contact on the X1.4 converter and then your camera should prompt for focal length whenever you use it?

It might work , there is a specific one to cover to convert F4 to F5.6, I did that with my tamron adaptall PKA mount on my 200-500/5.6 because the adaptall mount maximum aperture can only go to F4 with the pins available.

Don't think that works with an AF lens -- not without losing AF anyway.

it’s worth a try

I believe that is a later version of Sigmas TC that has never been available in Pentax K-mount. The Sigma APO EX DG 1.4x TC is older than that. Probably from early 2000s when many of the Sigmas EX APO DG lenses came.

The sigma TCs were available in APO / EX and later APO / EX - DG versions but always screw drive

Does the Sigma TC at least compensate for the aperture (or at least give you the original correctly) ? You can get weird aperture readings with Sigma lenses and some TCs.

no it reports the lens aperture only. On some cameras this introduces an exposure error, the K10 was really bad for this because it’s focusing screen really introduced some non linear Oates so he camera had to know the effective aperture of the combined lens not the native aperture of the lens only

---------- Post added 08-01-21 at 10:11 AM ----------

Snip……

On your other question, no, the TC doesn't correct the aperture either, so the camera still thinks it's F4 wide open - but I don't think that really matters in practice.

Thanks all for your replies and sorry to dig up a question that's probably come up plenty of times in the past...

Wrong aperture does not mean a lot until you want to add flash then it really needs to be correct.