[jgredline]

avier's remark when comparing Sigma and Tamron TC mounted on Tamron 70-200

Actually, if I ever said I tried my Sigma 1.4tc on my Tamron 70-200F/2.8, I would have been mistaken because I have never tried this before. I have used it with my Tamron TC and worked well, but that was a while back.

[Ben_Edict]

If this is not the case, then Ben must be correct that most compatible Sigma lenses have a universal rear element which the Sigma TC compensates aberrations for. A fascinating possibility.

I would not go as far to say, that the Sigma tcs would compensate the lens' abberrations. But at least they do not add any visible abberrations as other tcs do, with these lenses. I know, this is all guesswork to some degree, but the long distance between the groups in the Sigma tc, is there for a reason. Also, we should not forget, that the idea of a "matched multiplier" is not Sigma's invention. Vivitar had a dedicated tc for the 70-210/3.8 and 70-150/3.8 back in the 80s.

I think, these dedicated tcs, though visibly superior in performance, never were loved by the photog community, because at the end of the day, they are seen as being too expensive, useable only with one lens or a select few (just look through the discussions in this and other forums). The universal tcs, on the other hand, were/are seen as good value.

Of course an tc could indeed be a compensating element. You know that from the classical Barlow lens, used for telescopes, which sometimes improve image quality considerably, compared to the "naked" telescope.

Ben

[falconeye]

Actually, if I ever said I tried my Sigma 1.4tc on my Tamron 70-200F/2.8, I would have been mistaken because I have never tried this before. I have used it with my Tamron TC and worked well, but that was a while back.

In post #534, you made this remark relating to shane33 doing the comparison. It wasn't about "your" Tamron, just about "your" comment.

You implied that a Sigma TC may not perform ideally if not used with a Sigma lens.

This is something I have trouble to understand provided the Sigma TC fits mechanically. A magnifier is a magnifier is a magnifier

I am still tempted to challenge either shane33's claim that the Tamron TC beats the Sigma TC on the Tamron 70-200/2.8 (to my eyes, they are equal anyway), or your "night and day" claim that the Sigma TC beats the Tamron TC on the Sigma 100-300 F/4.0. :ugh: Better test images would be great too.

[jgredline]

In post #534, you made this remark relating to shane33 doing the comparison. It wasn't about "your" Tamron, just about "your" comment.

You implied that a Sigma TC may not perform ideally if not used with a Sigma lens.

Ok, but this is not what you said earlier. You added content to what I said regarding the Tamron 70-200 lens.

This is something I have trouble to understand provided the Sigma TC fits mechanically. A magnifier is a magnifier is a magnifier

Perhaps, but I only know what I see. As I said, your the tech guy, not me.

I am still tempted to challenge either shane33's claim that the Tamron TC beats the Sigma TC on the Tamron 70-200/2.8 (to my eyes, they are equal anyway), or your "night and day" claim that the Sigma TC beats the Tamron TC on the Sigma 100-300 F/4.0. :ugh: Better test images would be great too.

This type of test should be performed by you since you are the one who needs convincing. Me, weather I am right or wrong does not matter to me, because I know the results I get and that is what matters to me.

[Ben_Edict]

A magnifier is a magnifier is a magnifier

I understand your hesitations to simply accept (without hard proof), that tcs differ. But if your sentence was true, there wouldn't be those wide differences in tc performance (and pricing!) evereybody using more than 1 modell can testify to.

All in all I have 10 tcs at hand (in my lens cupboard), all of the Pentax tcs, the 2 Sigmas, an older 7-lens Kenko, the new 1,5 DG something Kenko, an old Tamron adaptall, if I recount correctly. There are very visible differences not only between these tcs, but also between performance on different lenses.

Take for example the Old Pentax K6T 2x-tc. It is a mediocre tc with most lenses. Almost always the Kenko MC7 provides better sharpness. But on the old Pentax K 300/4, the Pentax K6T performs surprisingly good, better than on any other lens I have tried it with.

I confess not to have made a scientific test with all the possible combinations. That would be far too much time investment for me - and I only use tcs either with the longest prime lenses at hand or the Sigma tcs with the Sigma 70-200/2.8 - which is an extraordinary combination.

Nevertheless I have a clear order of quality/performance:
1. Pentax 1.4x-L (and Sigma 1.4x Apo on the matching Sigma 70-200/2.8)
2. Pentax 1.4x-S
3. Pentax 2x-L
4. Pentax 2x-S (and the Sigma 2x Apo on the matching Sigma 70-200(2.8)

5. Kenko 1.5 DG
6. Kenko Mc7 (A-version)
7. Pentax K6T (except on the K 300/4, where it performs much better)

I cannot comment on the Tamron adpatall, as I find it to slow to use - I use the Pentax L tcs with my Tamron 300/2.8 - which is an excellent combination.


What stands out for me, is that tcs with a longer built, e.g. the protruding front elements, seem to gerenally perform best. So the internal distance of the lens groups is a way to optimize performance. That is a well-known factor in optimizing lenses, quite as the air space between achromatic lens elements.

Ben

[falconeye]

This type of test should be performed by you since you are the one who needs convincing.

No problem. Javier, it wasn't to ask you to do another test anyway
I am a curious person but not obsessed to the point that I need to run every possible test I'd rather go out and have some fun with the grass hoppers.

What stands out for me, is that tcs with a longer built, e.g. the protruding front elements, seem to gerenally perform best.

I have no trouble to understand this. Just makes a TC closer to a perfect magnifier.
I have problems to understand that all of a sudden, a TC with protruding front element performs worse if the other lens isn't called Sigma anymore. Where I trust Javier that this is a fact. But on the other hand, I don't have to understand everything Let's just assume that Sigma TC are women

[jgredline]

Let's just assume that Sigma TC are women

Now this is a profoundly true statement!

[pcarfan]

I had my sigma 100-300 F4 DG (?) with the Sigma 1.4 TC DG (?,both lens and the TC the latest version), and I was able to get hold of a Tamron 1.4 TC Pz MC?, and I took a couple of shots, liked the Tamron and sold the sigma....mostly for the IQ, partly for me possibly getting an SDM lens later...

[Class A]

I have problems to understand that all of a sudden, a TC with protruding front element performs worse if the other lens isn't called Sigma anymore.

Could it be possible that some TC weaknesses can cancel out certain lens weaknesses?

If every TC were constructed according to the same "interface" then there shouldn't be any odd combinations that suddenly make a generally weaker TC produce the best performance with a certain lens. However, if some TCs are built in a way to correct for certain problems of specific lenses, they could work well with them and less well with others.

[falconeye]

Could it be possible that some TC weaknesses can cancel out certain lens weaknesses?

I thought about this possibility in post #535: "The only other option I see is making an imperfect TC correcting known aberrations from a particular lens."

But with 35 "dedicated" lenses?

The "women" theory explains it much better: The "better" woman not always performs better

[Ben_Edict]

I thought about this possibility in post #535: "The only other option I see is making an imperfect TC correcting known aberrations from a particular lens."

But with 35 "dedicated" lenses?

The "women" theory explains it much better: The "better" woman not always performs better

I just stumbled across an interesting post in the German Digitalfotonetz : DigitalFotoNetz.de :: Thema anzeigen - AF Telekonverter für Pentax

Go to the third post. The poster complains about the poor quality of his Sigma Apo tc on his FA 300/2.8 and FA 77mm - wheras the tc is excellent with the Sigma 70-200/2.8

That is at least an indication of the optimization the Sigma engineers may have aimed at. By the way, the lens count is just under 20, as the list contains different builds of the same lens (with and without HSM for instance) - and (apart from some old out of production lenses) it only contains EX lenses.

But I am sure, that you are correct, that the tcs are not properly matched to the whole bunch of lenses in the list. It is probably more the result of an cross-selling effort...
Ben

[falconeye]

Go to the third post. The poster complains about the poor quality of his Sigma Apo tc on his FA 300/2.8 and FA 77mm - wheras the tc is excellent with the Sigma 70-200/2.8

Thanks for the quote. Yes, he says "fair" with Sigma 2.8/70-200 but "poor" with FA* 2.8/300 fully open. And "not tested" with FA77. And it is about the Sigma 2x TC.

I keep the question open for myself and withdraw from its discussion. Too difficult to settle

Thank You, Javier and Ben, for your contributions. I learned a lot from them.

[Class A]

I thought about this possibility in post #535: "The only other option I see is making an imperfect TC correcting known aberrations from a particular lens."

Ah, sorry, didn't follow all of the thread.

But with 35 "dedicated" lenses?

As others have said, it isn't quite 35 and then the TC may only work optimally with a further subset.

Regarding your calculations about what lens quality (expressed in sensor MP) is required to even allow a perfect TC to create a benefit over cropping it is useful to have a look at Table 3 of the "Do Sensors “Outresolve” Lenses?" article. As even high-quality long lenses won't be diffraction limited at f/5.6 there might be just a very small sweet spot for a very good TC to actually make a difference around the optimal aperture for the lens, but it appears that range isn't big at all.

[danielchtong]

Somebody has kindly posted the difference between the SDM non-compatible and compatible one (Kenko 1.5x MC and 1.5x SHQ version respectively)

The MC version is on the left . Notice the missing contact on the left side!!









Daniel

[danielchtong]

This thread is about Kenko/Tamron TC. But it is worthwhile to quote this Sigma's notice Sigma - News

+++++++++++++++++++++++++++++++++++++++++++++++++++++
Notice to customers using Sigma Tele Converters for Pentax mount

SIGMA APO TELE CONVERTER 1.4x EX DG for Pentax mount and APO TELE CONVERTER 2x EX DG for Pentax mount are not compatible with lenses epuipped with HSM. Therefore, these Tele Converters cannot be used with the APO 50-150mm F2.8 II EX DC HSM for Pentax mount and APO 70-200mm F2.8 II EX DG MACRO HSM for Pentax mount.

Please refer to the list below for compatibility of Sigma Tele Converters.

APO TELE CONVERTER 1.4x EX DG for Pentax mount

It is possible to use AF
APO 70-200mm F2.8 EX DG, APO 70-200mm F2.8 EX
APO 100-300mm F4 EX DG, APO 100-300mm F4 EX IF
APO 300mm F2.8 EX DG, APO 300mm F2.8 EX

It is only possible to use MF
APO 50-500mm F4-6.3 EX DG, APO 50-500mm F4-6.3 EX RF
APO MACRO 180mm F3.5 EX DG, APO MACRO 180mm F3.5 EX IF
APO TELE MACRO 300mm F4, APO TELE MACRO 400mm F5.6
APO 500mm F4.5 EX DG, APO 500mm F4.5 EX
APO 800mm F5.6 EX DG, APO 800mm F5.6 EX

APO TELE CONVERTER 2x EX DG for Pentax mount

It is possible to use AF
APO 70-200mm F2.8 EX DG, APO 70-200mm F2.8 EX
APO 300mm F2.8 EX DG, APO 300mm F2.8 EX

It is only possible to use MF
APO 50-500mm F4-6.3 EX DG, APO 50-500mm F4-6.3 EX RF
APO 100-300mm F4 EX DG, APO 100-300mm F4 EX IF
APO MACRO 180mm F3.5 EX DG, APO MACRO 180mm F3.5 EX IF
APO TELE MACRO 300mm F4, APO TELE MACRO 400mm F5.6
APO 500mm F4.5 EX DG, APO 500mm F4.5 EX
APO 800mm F5.6 EX DG, APO 800mm F5.6 EX

Sigma lenses, except hose in the above list, cannot be attached to Sigma Tele Converters. Sigma APO Tele Converter 1.4x and 2x are dedicated to Tele Converter lenses, which should only be used with the above lenses.

Please do not use the APO Tele Converter on top of another APO Tele Converter, or any other kind of converters.

AF function of Pentax mounts cannot be used with SFX / SF7 Cameras.