[Ron617]

My apologies if I have chosen the wrong section for posting this request. I have the Pentax 1.4 teleconverter which I use successfully with my DA 300mm lens. However, I am considering getting a 2x converter and the only one that can find available for Pentax is the Kenko Teleplus DG 2.0X MC4 Teleconverter - Pentax AF. Reviews of its performance are in short supply, although it appears to sell well. My man concern is that it is a 4 element converter instead of a 7 element one.

Does anyone have any experience on this converter? Any feedback would be most welcome.

[UncleVanya]

The general consensus is that 2x convertors have lower image quality than cropping, but that particular one isn't over I've seen images from.

[Bob 256]

I shot the solar eclipse with my Sigma 55-500mm and the MC4 2X using the Sigma at 300mm, and had pretty satisfactory results. It does multiply the f-stop of the lens by 2X as well so there's quite a bit of light loss, but I was quite surprised with the image quality. The main lens was stopped down a bit and I was using a higher ISO to compensate but small details resolved well. Not the best of tests and not recommended when you don't need it, but I would say in a pinch, this teleconverter will deliver a fair portion of the main lens's cropped resolution.

Here's a cropped example of a shot (not that good an example of a print from the original file).

[LensBeginner]

The general consensus is that 2x convertors have lower image quality than cropping, but that particular one isn't over I've seen images from.

I beg to differ.
If one knows what he's doing, quality from 2X converters (I have an MC7, which is reportedly better than the 4-elements version, but I've never tried the other one, so...) exceeds cropping by a good margin.

Problems are: 1. it exacerbates the defects of the lens you mount on it, 2. you need a lens with a huge resolving power and 3. the sweetspot is often a sort of very narrow "coffin corner" between diffraction limit, good apertures, light gathering.

You can see some examples and tests here:
Pentaxiani ? Leggi argomento - Moltiplicatore? decisamente SÌ! :-P
and here:
Pentaxiani ? Leggi argomento - Aironi

[UncleVanya]

I beg to differ.
If one knows what he's doing, quality from 2X converters (I have an MC7, which is reportedly better than the 4-elements version, but I've never tried the other one, so...) exceeds cropping by a good margin.

Problems are: 1. it exacerbates the defects of the lens you mount on it, 2. you need a lens with a huge resolving power and 3. the sweetspot is often a sort of very narrow "coffin corner" between diffraction limit, good apertures, light gathering.

You can see some examples and tests here:
Pentaxiani ? Leggi argomento - Moltiplicatore? decisamente SÌ! :-P
and here:
Pentaxiani ? Leggi argomento - Aironi

I stand by what I said. Consensus is that the 2x don't generally help over cropping. However exceptions to this are out there. I also think the very best 2x are dedicated models. A very nice pentax 2x-L used with a compatible lens does a fine job, but those are the corner case examples.

[LensBeginner]

I stand by what I said. Consensus is that the 2x don't generally help over cropping. However exceptions to this are out there. I also think the very best 2x are dedicated models. A very nice pentax 2x-L used with a compatible lens does a fine job, but those are the corner case examples.

I don't think using a 40 y.o. converter (just imagine what you could do with the good ones...) with at least 4 different lenses, including one zoom, one both in the tele and macro range, one in the macro range both straight and reversed, at apertures ranging from f/5.6 up to f/11 can be accurately described as a "corner case".

In my experience, if the lens is at least passable, and has an aperture ring (just because my TC is of the dumb kind), then it works, and in some cases it has even worked better than the resulting prime (SMC-M 100/2.8 X2 better than SMC-M 200/4).

[UncleVanya]

In my experience, if the lens is at least passable, and has an aperture ring (just because my TC is of the dumb kind), then it works, and in some cases it has even worked better than the resulting prime (SMC-M 100/2.8 X2 better than SMC-M 200/4).

Consensus doesn't mean that people are right or wrong, it is what prevailing opinion is. I am willing to admit the prevailing opinion is potentially wrong but I don't think a few posted examples is sufficient for me to conclude that. Now that said, I will also point out that my past tests of several TC's (all are older) like the 2x-A TC used on a number of lenses like the FA* 300 f/4.5, the DA* 60-250 f/2.8 and the DA* 50-135 did not seem to be better than cropping. This was not true for tests involving the HD DA 1.4x. However my tests were very low key and not rigorous. Moreover a comparison of the M100 f/2.8 with a 2x vs. the M 200 f/4 without one would need to be compared to simple cropping of the M100 f/2.8. Final output may need to be up or downsampled or printed since we are dealing with differences in pixel density. Lastly the sensor density will make a difference, the same tests made on 16mp vs. 24mp vs. 36mp may not yield the same results.

Last but not least - I'm very glad for your input. I am interested in the results you have posted.

---------- Post added 04-17-18 at 02:12 PM ----------

I will assume you have results and defer to your example since I have had trouble with the translation - but my own testing doesn't mimic what you are reporting. @normhead has done some extensive testing and his tests seem to indicate the initial quality of the lens is very important as is the speed. He and I both have used the stacked 1.4x and 1.7x on occasion but only for very high quality initial lenses like the DA* 200 (in my case) or for moon shots with the FA* 300 f/4.5.

[Ron617]

Many thanks all for your comments. They are all very much appreciated. I already have a Pentax DA 1.4 converter which for me works excellently with my DA 300mm lens, hence my interest in obtaining longer reach. I remain cautious about the Kenko 2x 4 element lens. However, if you want a modern 2x converter for your Pentax camera you have very little choice and the Kenko, going by current availability, is about all there is? Reviews on this converter are few and far between. I am reluctant to step out and buy a Kenko 2x, especially since it's a 4 element piece. However, it sells well. Perhaps I'll hang off and see if I can track down some user reviews?>

[UncleVanya]

Many thanks all for your comments. They are all very much appreciated. I already have a Pentax DA 1.4 converter which for me works excellently with my DA 300mm lens, hence my interest in obtaining longer reach. I remain cautious about the Kenko 2x 4 element lens. However, if you want a modern 2x converter for your Pentax camera you have very little choice and the Kenko, going by current availability, is about all there is? Reviews on this converter are few and far between. I am reluctant to step out and buy a Kenko 2x, especially since it's a 4 element piece. However, it sells well. Perhaps I'll hang off and see if I can track down some user reviews?>

Is it something you could advertise about? Maybe someone near you would let you try it? I agree that a 7 element in the film era was considered quite a bit better than a 4 element 2x TC so I would likely agree with your thinking. The F 1.7x TC is pretty good but it is a semi-autofocus not a full autofocus TC. It does give you slightly longer reach than the 1.4x and has been tested a bit more extensively by others on the site.

[LensBeginner]

Consensus doesn't mean that people are right or wrong, it is what prevailing opinion is. I am willing to admit the prevailing opinion is potentially wrong but I don't think a few posted examples is sufficient for me to conclude that. Now that said, I will also point out that my past tests of several TC's (all are older) like the 2x-A TC used on a number of lenses like the FA* 300 f/4.5, the DA* 60-250 f/2.8 and the DA* 50-135 did not seem to be better than cropping. This was not true for tests involving the HD DA 1.4x. However my tests were very low key and not rigorous. Moreover a comparison of the M100 f/2.8 with a 2x vs. the M 200 f/4 without one would need to be compared to simple cropping of the M100 f/2.8. Final output may need to be up or downsampled or printed since we are dealing with differences in pixel density. Lastly the sensor density will make a difference, the same tests made on 16mp vs. 24mp vs. 36mp may not yield the same results.

Last but not least - I'm very glad for your input. I am interested in the results you have posted.

---------- Post added 04-17-18 at 02:12 PM ----------

I will assume you have results and defer to your example since I have had trouble with the translation - but my own testing doesn't mimic what you are reporting. @normhead has done some extensive testing and his tests seem to indicate the initial quality of the lens is very important as is the speed. He and I both have used the stacked 1.4x and 1.7x on occasion but only for very high quality initial lenses like the DA* 200 (in my case) or for moon shots with the FA* 300 f/4.5.

1. You talk about the 60-250mm. I don't have it, but in the second link (second post) it is said that it doesn't perform well when multiplied (we call it the incompreso, i.e. the "underappreciated", see: Pentaxiani ? Leggi argomento - Glossario nomignoli obiettivi ). I was implicitly referring to that when I was talking about resolving power. The M 80-200mm is no slouch in that respect.

2. regarding the objections you make, please see first link, scroll down to post 7 (a couple below the chimneys): there are some test chart shots.
Same aperture (the 100mm is at f/5.6 which becomes f/11 when multiplied), same camera, same session. First one is the 200mm@f/11, second one is the 100@f/5.6 X2, third one the 100m@f/11 upsampled with the "preserve details" algorithm. Best one is the second (100mm multiplied) by a long margin.
As you can see I had already though of this Even though, to be super-thorough and super fair I could have also shot the plain 100mm at all (good) apertures - but I don't think it would have made much difference.

[UncleVanya]

1. You talk about the 60-250mm. I don't have it, but in the second link (second post) it is said that it doesn't perform well when multiplied (we call it the incompreso, i.e. the "underappreciated", see: Pentaxiani ? Leggi argomento - Glossario nomignoli obiettivi ). I was implicitly referring to that when I was talking about resolving power. The M 80-200mm is no slouch in that respect.

2. regarding the objections you make, please see first link, scroll down to post 7 (a couple below the chimneys): there are some test chart shots.
Same aperture (the 100mm is at f/5.6 which becomes f/11 when multiplied), same camera, same session. First one is the 200mm@f/11, second one is the 100@f/5.6 X2, third one the 100m@f/11 upsampled with the "preserve details" algorithm. Best one is the second (100mm multiplied) by a long margin.
As you can see I had already though of this Even though, to be super-thorough and super fair I could have also shot the plain 100mm at all (good) apertures - but I don't think it would have made much difference.

Honestly I looked at your examples and I can't say I see much difference in the test charts - not "by a long shot" like you say. But that doesn't mean the difference isn't there - the screen I'm looking on isn't large and I don't have a lot of time to scrutinize. I will take your word. As for the 60-250 - I have found it to work quite well at least with the 1.4x HD TC. And while I have used the 70-210 A series I don't know if I have ever used the 80-200 f/4.5, but that's an interesting thing to hear. Thank you for taking the time to engage on this. I think the discussion is useful.

---------- Post added 04-17-18 at 02:33 PM ----------

I shot the solar eclipse with my Sigma 55-500mm and the MC4 2X using the Sigma at 300mm, and had pretty satisfactory results. It does multiply the f-stop of the lens by 2X as well so there's quite a bit of light loss, but I was quite surprised with the image quality. The main lens was stopped down a bit and I was using a higher ISO to compensate but small details resolved well. Not the best of tests and not recommended when you don't need it, but I would say in a pinch, this teleconverter will deliver a fair portion of the main lens's cropped resolution.

Here's a cropped example of a shot (not that good an example of a print from the original file).

Nice shot!

[LensBeginner]

Honestly I looked at your examples and I can't say I see much difference in the test charts - not "by a long shot" like you say. But that doesn't mean the difference isn't there - the screen I'm looking on isn't large and I don't have a lot of time to scrutinize. I will take your word. As for the 60-250 - I have found it to work quite well at least with the 1.4x HD TC. And while I have used the 70-210 A series I don't know if I have ever used the 80-200 f/4.5, but that's an interesting thing to hear. Thank you for taking the time to engage on this. I think the discussion is useful.

If you click on them you can see them at 100%, thumbnails don't help much.
When you have time and if you feel like it, of course. Have a nice evening.

The 80-200mm/4.5 was said to be more resolving than the 70-210mm (which had more contrast), so I've heard.

[UncleVanya]

If you click on them you can see them at 100%, thumbnails don't help much.
When you have time and if you feel like it, of course. Have a nice evening.

The 80-200mm/4.5 was said to be more resolving than the 70-210mm (which had more contrast), so I've heard.

Oh dang - I did not do that! Like I said the lack of translation threw me off a bit. I'll look later and thanks.

EDIT:
I was wrong I had done that. But I did it more deliberately this time. I can see slight differences but they are subtle between the 2x 100mm and the enlarged upsampled 100mm. The 200 is clearly inferior to both, mainly due to what looks like some aberrations perhaps CA?

[LensBeginner]

Oh dang - I did not do that! Like I said the lack of translation threw me off a bit. I'll look later and thanks.

Yeah... Italian... not the most widespread language in the world, let alone the WWWeb
I should write the posts I use as a reference in English, but then most of my friends would have troubles reading them...

I wouldn't define them "subtle"... in one you can make out the single lines on the center-right, in the others you can't.
don't know... red/green usually points to LoCA, but I did more than one shot (this was the best one), and focused in magnified LV.

That lens is not my favorite M, its infinity falls a bit short, has some fringing... not the sharpest weapon in my arsenal...

[UncleVanya]

Yeah... Italian... not the most widespread language in the world, let alone the WWWeb
I should write the posts I use as a reference in English, but then most of my friends would have troubles reading them...

I wouldn't define them "subtle"... in one you can make out the single lines on the center-right, in the others you can't.
don't know... red/green usually points to LoCA, but I did more than one shot (this was the best one), and focused in magnified LV.

Don't laugh - I missed that. I was looking everywhere else. I never looked to the right side. LOL. Yes I see the astounding differences FINALLY. Thanks for being patient.