First tests with the Pentax-F 1.7x TC and 60-250

**clackers** · 06-02-2020, 07:37 PM

Will be interesting to see how hit and miss your autofocus is, Bernard.

The 1.7x, while not 2x, still pushes the aperture beyond f5.6, which is what the autofocus systems are traditionally rated for.

Maybe fine while the light's good.

This is the real reason for say, a 300mm f2.8. A 2x TC can go on it.

Last edited by clackers; 06-02-2020 at 07:43 PM.

bdery · 06-03-2020, 05:04 AM - **1 Like**

Originally posted by clackers

Will be interesting to see how hit and miss your autofocus is, Bernard.

The 1.7x, while not 2x, still pushes the aperture beyond f5.6, which is what the autofocus systems are traditionally rated for.

Maybe fine while the light's good.

So far it has not struggled a tall. I have not tested it in very low light, but inside the house, at night, it works as expected, and is pretty fast!

normhead · 06-03-2020, 06:21 AM

SO far with the DA 55-300 PLM ƒ6.3 works fine. I did try it on the A-400 ƒ5.6 once, and over ƒ9 was not so good, but there's a possibility that the lens isn't sharp enough for use with a TC. . There's no problem on ƒ4 lenses, although I do prefer to use it on ƒ2.8 glass if I can.

normhead · 06-03-2020, 08:28 AM

Another big thing is although it can be a pain to get the manual focus part right, once done, it acts as a focus limiter, and as long as you've set the range correctly, you get super fast AF within the range of the Adapter.

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06-02-2020, 07:37 PM	#16
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Will be interesting to see how hit and miss your autofocus is, Bernard. The 1.7x, while not 2x, still pushes the aperture beyond f5.6, which is what the autofocus systems are traditionally rated for. Maybe fine while the light's good. This is the real reason for say, a 300mm f2.8. A 2x TC can go on it. Last edited by clackers; 06-02-2020 at 07:43 PM.

06-03-2020, 05:04 AM - 1 Like	#17
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,357 Original Poster	Originally posted by clackers Will be interesting to see how hit and miss your autofocus is, Bernard. The 1.7x, while not 2x, still pushes the aperture beyond f5.6, which is what the autofocus systems are traditionally rated for. Maybe fine while the light's good. So far it has not struggled a tall. I have not tested it in very low light, but inside the house, at night, it works as expected, and is pretty fast!

06-03-2020, 06:21 AM	#18
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	SO far with the DA 55-300 PLM ƒ6.3 works fine. I did try it on the A-400 ƒ5.6 once, and over ƒ9 was not so good, but there's a possibility that the lens isn't sharp enough for use with a TC. . There's no problem on ƒ4 lenses, although I do prefer to use it on ƒ2.8 glass if I can.

06-03-2020, 08:28 AM	#19
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	Another big thing is although it can be a pain to get the manual focus part right, once done, it acts as a focus limiter, and as long as you've set the range correctly, you get super fast AF within the range of the Adapter.