Pentax-F SMC AF 1.7 Converter

*tlfaust* · 04-29-2007, 09:06 AM

Hi
I attached my 1.7TC to my M* 300 last night for some moon pictures. I found that I could not focus to infinity. Do I need a different TC? Does anyone have any experience with the vivitar mc a? Will it allow focus to infinity?

Thanks!
Ted

carpents · 04-29-2007, 10:07 AM

Your 1.7x will focus to infinity, it is just fickle. I sometimes try to pre-focus on something nearby and turn the main lens until I'm sure the teleconverter is focused at its farthest distance. I find it has a particularly hard time with f/4 lenses (as opposed to f/2.8 ones.)

You can also try turning portrait (or even skewed) and centering the moon to see if it just wasn't getting enough contrast.

FWIW, other teleconverters are fixed in their focus, meaning that when the main lens is at infinity, so is the lens + teleconverter.

clm · 04-29-2007, 11:05 AM

The Pentax website used to have a manual for the 1.7x adapter available for download. In the support section somewhere.

The adapter has a limited focusing range. To get infinity focus, you have to manually focus the lens to near infinity.

rfortson · 04-29-2007, 10:06 PM

Also, I believe the AF converter is only supposed to work with f/2.8 and faster, though it will usually work with my 300 f/4.0. That may have also played a part in it's performance, or lack thereof.

Lowell Goudge · 05-01-2007, 04:30 PM

I am not sure if it is focus to infinity or just incorrect focus on distant objects. depth of field is so small I wonder if slight focusing error is the issue. in close (birds etc) it does just fine

I use the 1.7x on my 300mm F4 K mount lens and both my *istD and K10D. and have had some disappointments on very distant objects in low contrast settings.

I initially bought it to use on my series 1 70-210 F3.5, after trying it and learning that my PZ-1 (yes I have had the 1.7x a very long time) and all subsequent cameras simply can't read. Manual clearly states f2.8 or brighter. The limit is reached at an F5.6 prime (my 400 F5.6 just does not work)

Khukri · 05-04-2007, 04:30 AM

Hullo!
I am in the process of organising a 1.7x for myself. Will be happy to get whatever inputs you can give when it comes to practical shooting.

I am curious to know: How efficiently does it work on the 100mm macro? Is it possible to do the followng:
1. Put lens on manual and focus approximately at object at say magnification 1:2; 2. Next, depress shutter half way to get the 1.7x to auto focus accurately.
3. And now, use the manual focus ring on the lens to fine-tune focus even further. (Will the shutter trip even though the focus as per the 1.7x is now 'off' its mark?
Thanks,
Bharat.

Gimbal · 05-04-2007, 04:54 AM

I recently got my sticky fingers on an old 2xconverter and promptly connected it with an equally old tokina 100-300. Everything is manual, no electric contacts or auto focus coupling. Yet, for some reason, I can’t use focus trap with the converter attached. The green focus lamp still lights up when in focus so that part still works, the shutter however doesn’t wait for the focus lamp. Without the converter it works though, strange…..

Lowell Goudge · 05-04-2007, 10:49 AM

Originally Posted by Khukri

Hullo!
I am in the process of organising a 1.7x for myself. Will be happy to get whatever inputs you can give when it comes to practical shooting.

I am curious to know: How efficiently does it work on the 100mm macro? Is it possible to do the followng:
1. Put lens on manual and focus approximately at object at say magnification 1:2; 2. Next, depress shutter half way to get the 1.7x to auto focus accurately.
3. And now, use the manual focus ring on the lens to fine-tune focus even further. (Will the shutter trip even though the focus as per the 1.7x is now 'off' its mark?
Thanks,
Bharat.

I have tried it on my SMCM 100mm F4.0 lens just to see if it would focus. I have not done any detailed work yet, but the way I would do things is as follows

1) mount on a tripod if possible
2) set lens to close (approximate focus manually
3) hit the green button to set exposure (assuming manual lens)
4) press shutter 1/2 way to focus using what ever focusing sensor position you select (on K10D)
5) take the picture

Unless you have a desire to focus on something that is away from a focusing center I would not readjust afterwards, this is especially true if you do not have a tripod, as you will move and depth of field on macro is very limited, the auto focusing would keep you correctiing for changes in lens to object distance

clm · 05-04-2007, 01:28 PM

Originally Posted by Khukri

Hullo!
I am in the process of organising a 1.7x for myself. Will be happy to get whatever inputs you can give when it comes to practical shooting.

I am curious to know: How efficiently does it work on the 100mm macro? Is it possible to do the followng:
1. Put lens on manual and focus approximately at object at say magnification 1:2; 2. Next, depress shutter half way to get the 1.7x to auto focus accurately.
3. And now, use the manual focus ring on the lens to fine-tune focus even further. (Will the shutter trip even though the focus as per the 1.7x is now 'off' its mark?
Thanks,
Bharat.

I think you would need to set camera to AF-C to get the camera to fire without focus confirmed.