[tduell]

Hello All,
I would like a 1.7x TC, but the only one I see is the Pentax F 1.7x AF which appears to take over the focussing.
Are there any other 1.7x TCs available, that I have missed, that provide all the functionality of the Pentax AF Rear Converter 1.4x, and can be used with the 150-450...and on the K-1?

Cheers,
Terry

[sergysergy]

I am not sure whether it will work or not but the only other 1.7x I am aware of is this (it may come under different names; the one I had was promaster):
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/44676-proma...converter.html

[tduell]

I am not sure whether it will work or not but the only other 1.7x I am aware of is this (it may come under different names; the one I had was promaster):
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/44676-proma...converter.html

OK. Thanks for that, I had missed that one.
Has anyone used this TC with the 150-450 and K-1
Does it all function OK, focus quickly, is there any vignetting?

Cheers,
Terry

[mbukal]

I have used: Ricoh KR-10 Super (FF) with smcPentax-F 1,7xAF (FF) and Pentax DA 55-300 / 4-5.8(APSC), the combination is no autofocus but nor least does not vinjetira, when using these lenses (FF+APSC) on Pentax K30 (APSC) and autofocus works without problems and at all no vignetting

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Last edited by mbukal; 05-25-2016 at 06:33 AM.

[narual]

A teleconverter should prevent vignetting, not introduce it. It's making the beam of light coming into the camera bigger, not smaller.

[Lowell Goudge]

OK. Thanks for that, I had missed that one.
Has anyone used this TC with the 150-450 and K-1
Does it all function OK, focus quickly, is there any vignetting?

Cheers,
Terry

The TC should NOT vignette, but at F5.6 plus 1.5 stops, af may not work. You need a true native aperture of F6.9 to maybe F8 on the newer bodies to get reliable AF. For example, my Pentax Af1.7x converter works just fine on my 300/4 with every bodie I have owned since the PZ1, but even with my K5 and much newer AF engine, it needs really bright light to achieve AF lock on my 200-500/5.6

[tduell]

A teleconverter should prevent vignetting, not introduce it. It's making the beam of light coming into the camera bigger, not smaller.

I think you might have got the wrong end of the stick on this, and maybe I could have explained a bit better.
The 150-450 is fine on the K-1, as it is expected, but adding the Pentax AF Rear Converter 1.4x does introduce vignetting.
My concern was that the available 1.7x TCs may do the same.

Cheers,
Terry

[Lowell Goudge]

I think you might have got the wrong end of the stick on this, and maybe I could have explained a bit better.
The 150-450 is fine on the K-1, as it is expected, but adding the Pentax AF Rear Converter 1.4x does introduce vignetting.
My concern was that the available 1.7x TCs may do the same.

Cheers,
Terry

No a TC should not introduce vignetting because it enlarges the projected image and therefore spreads it out in theory over a larger image circle. Vignetting is only if the TC is not index dead for the format, or perhaps has a rear mask to prevent excess light from getting into the mirror box.

[tduell]

No a TC should not introduce vignetting because it enlarges the projected image and therefore spreads it out in theory over a larger image circle. Vignetting is only if the TC is not index dead for the format, or perhaps has a rear mask to prevent excess light from getting into the mirror box.

Sure, but it's just semantics if the image circle isn't designed for FF, in which case it will vignette on a FF.
There are threads on whether the 1.4x TC is OK on the FF, and I can assure you that it does vignette on the 150-450 on the K-1, and it would be nice to know, from those who have first hand experience, which 1.7x TC, if any, work OK on the K-1 with the 150-450.
There's not a lot of help in repeating the same line when does not address the question.

Cheers,
Terry

[Lowell Goudge]

Sure, but it's just semantics if the image circle isn't designed for FF, in which case it will vignette on a FF.
There are threads on whether the 1.4x TC is OK on the FF, and I can assure you that it does vignette on the 150-450 on the K-1, and it would be nice to know, from those who have first hand experience, which 1.7x TC, if any, work OK on the K-1 with the 150-450.
There's not a lot of help in repeating the same line when does not address the question.

Cheers,
Terry

The SMC -F 1.7x AF adaptor will not vignet on full frame. It came out for film bodies in the early 1990's

As for the Pentax 1.4x can you show examples of the vignetting you experience and alao a view of the rear of the TC. It would be useful in the discussion. Since no photo is presently attached, it would be interesting to know if it is true vignetting, or simply light fall off at the edges. Even the K50/1.4 wide open on APS-C has non uniform exposure falling off by over a stop from centre to edge of frame, it is not the same as vignetting

[tduell]

The SMC -F 1.7x AF adaptor will not vignet on full frame. It came out for film bodies in the early 1990's

As for the Pentax 1.4x can you show examples of the vignetting you experience and alao a view of the rear of the TC. It would be useful in the discussion. Since no photo is presently attached, it would be interesting to know if it is true vignetting, or simply light fall off at the edges. Even the K50/1.4 wide open on APS-C has non uniform exposure falling off by over a stop from centre to edge of frame, it is not the same as vignetting

Thanks for the info on the SMC-F 1.7x AF adaptor, that's helpful.

Here's a shot from K-1 + 150-450 + 1.4x TC