SMC Pentax-F 1.7x AF Adapter questions & observations

[14mm 2.8l]

I decided to buy a 1.7X AF Adapter to see whats up with it. I see now how it

aides in autofocus when using either a manual focus and autofocus lens:

 

The 1.7x element moves in and out, driven by the cameras AF drive screw.

 

It does seem to work with my slow aperture zooms on my overcast day.

 

In the next few days as time permits I'll post digital images taken with it

and my 2 slower zooms:

 

135-600mm/6.7 & 80-320mm/5.6

 

I am also experimenting with a manual focus Vivitar 100mm f2.8 macro, 1977

vintage. I'm pretty impressed with all 3 lenses I've tried so far. The

instructions say use with 15mm/3.5 SMC will damage the 15mm, so I won't try it.

 

So far as I can see, if you manually focus into the general place you should

be, the AF 1.7x then moves its inner element in or out to precisely dial the

focus in and give me the green light.

 

Any insight, and opinions using the 1.7x AF adapter are appreciated. I am new

to the pentax system, I know alot of the rest of you are long time pentax

experts&photographers

 

Thanks, Lindy

[stemked]

"It does seem to work with my slow aperture zooms on my overcast day."

 

That's a little surprising. I find it doesn't perform all that well with slow zooms. I haven't tried it for a while myself though. However, if you max aperature if f5.6 and effective aperature at ~f9.5 is awfully slow and likely rather impracticle for most but rather brigth days IMHO.

 

The autofocus works, but it is slow and that may drive some people crazy. No, its not like the ME-F autofocus (which is slower than molassis in January) but it is not a super fast autofocus experience. I recall it didn't autofocus with my screw mount lenses. Also since it is a teleconvertor and because of where the elements are located I personally wouldn't use it with really large lenses with recessed real elements (like fast 300mm + Pentax lenses). I have heared of it used with long fast Tokina lenses (it was either a 300mm or 400mm f2.8, don't recall) but these lenses are EXTREMELY rare.

 

You got a good piece of equipment. Pretty rare too. Have fun!

[14mm 2.8l]

Douglas, The instructions say it cannot be used with screw mount adapters and teleconverters. They also list 3 lenses it will break, as of 1987.

 

Pentax instructions archive site is down right now. I'll post its link when its up again.

 

I agree my zoom glass is incredibly slow at 5.6 and 6.7. But I have had success already with pentax 2x & 1.4x on dslr inspite of this insanely slow combined speed. Its cloudy again today, you're right it'll likley be a sunny day only assessory.

 

When I shoot my comparision images I'll include all my pentax brand adapters:

 

AF 1.7x

 

1.4X-S

 

2X-S

 

2X-L

 

So far, I am pretty darn happy with this odd little adapter. I didn't notice it was slow to focus with my A aperture vivitar 100mm 2.8 macro, both with and without onboard flash shooting coins and outside shooting various distances to infinity.

 

Lindy

[hanh]

Hi Lindy,

 

I have the SMC Pentax-F 1.7x AF Adapter. It worked wonderfullỵ

 

It work with screw mount lenses ALSO.

 

The trick for the SMC Pentax-F 1.7x AF Adapter to work with screw mount lenses is the short out the contact pins on the adapter. I use a thin strip of foil paper across all the pins.

 

If you have the Pentax istD, this trick of shorting out the contact pins on the camera mount will allow the Focus confirmation to work with screw mount lenses (the ist-DS and beyond does not need this trick for the focus confirmation).

 

I am using the 1.7F AF with the screw mount 85-210mm F/4.5, 35mm F/2 and the images are amazingly sharp wide open. I was surprised of how good the IQ is.

 

Let me know if this works for you.

 

Hanh

[14mm 2.8l]

Hanh, Very helpful observation. I cannot try the short out technique as I own no screw mount lenses. Maybe Douglas S. can try this with his 500mm f4.5 screw mount with your info.

 

It is quite surprising it works well with slow zooms. Its a very underrated assessory with more usefulness than the instructions sheet says 1.7x AF offers.

 

Lindy