[dwssas]

The focus ring on the 18-250 works silky smooth on its own. When I attach the telecon to the 18-250 the focus ring becomes quite stiff to operate, enough so that it makes manual focusing quite difficult but not impossible. I would certainly appreciate any suggestions.

[infosyn]

...when I attach the telecon to the 18-250 the focus ring becomes quite stiff to operate

I don't have a Tamron 18-250, but if it works similar to my Tamron 90, you have to switch it from Manual to Automatic focusing -- it does not have Pentax's very handy Quick Shift focus. So I'm thinking that maybe in the process of adding the TC you accidentally pushed in the 18-250's focus ring, putting the lens into manual focus mode. Since the camera is probably still in AF, you are quite possibly doing damage to the camera's AF drive mechanism by forcing it to move.

[Fl_Gulfer]

I have them both and have no problems at all. It works fine in full auto and manual.

[jgredline]

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/19694-tamron-t...rter-pics.html

[dwssas]

Thank you to all for your replies. Gulfer--are you saying that the AF works accross the entire zoom range of the 18-250 with the 1.4 tele attached?

[Lowell Goudge]

Thank you to all for your replies. Gulfer--are you saying that the AF works accross the entire zoom range of the 18-250 with the 1.4 tele attached?

I would be surprised at maximum focal length if the AF works except in very bright sunlight.

the combination of the 18-250 (which I believe is f6.3) plus the loss of a stop with the 11.4x will be a combined F9 at 250mm

Not sure the AF is up to it.

[dwssas]

Thanks Lowell. I contacted Tamron and here is their reply. --------"t is not recommended to use a teleconverter with that lens because of the high gear ration in the lens and when you add a converter, it produces more drag on the gears. And that is the cause of the stiff feeling which even in manual focus will not disengage the converter from the lens. Also the converter is not designed for digital cameras and will degrade the quality of the len's image." This is the first time I have heard the 1.4 tele was not meant to be used on a digital camera! Also the extra weight of the tele making the gears hard to operate makes me wonder because with a Oly 1.7 tele mounted on the 18-250 everything works perfectly even though the Oly is several times heavier.

[Lowell Goudge]

Thanks Lowell. I contacted Tamron and here is their reply. --------"t is not recommended to use a teleconverter with that lens because of the high gear ration in the lens and when you add a converter, it produces more drag on the gears. And that is the cause of the stiff feeling which even in manual focus will not disengage the converter from the lens. Also the converter is not designed for digital cameras and will degrade the quality of the len's image." This is the first time I have heard the 1.4 tele was not meant to be used on a digital camera! Also the extra weight of the tele making the gears hard to operate makes me wonder because with a Oly 1.7 tele mounted on the 18-250 everything works perfectly even though the Oly is several times heavier.

Interesting comment. I had not thought through the focusing drive train, as I generally (but not always) do not attempt to manual focus my AF lenses.

My concern was more over the fact that the lens with a TC would not pass enough light through to let the AF work.

My 1.7x AF TC works well on lenses up to F4, (resulting maximum apature with TC of F6.7) I have heard reports of it working with F4.5 lenses (resulting apature F8), but it does not work with F5.6 lenses (resulting apature F9 due to lack of light)

[John Kovarik]

Interesting comments. I use my Tamron TC 1.4 with the Tamron 18-250 extensively on my K100D and have not noticed any noise or image problems save those resulting from low-light conditions. I have not tried them on the K20D yet. When I was looking for the TC a sales rep (B&H, I think) did tell me essentially what the Tamron company line is but not the possible effect on the lens................

[Fl_Gulfer]

I think the guy at Tamron is nuts, the only thing I have read about the TC is that the Max. Aperature of Lens To Ensure AF operation : F4.5 or Faster, I use it on all my lenses and they focus fast and no different without it.
I mean I'm not going to tell you to use it on the lens, but you do have a 6 year warranty.

[dwssas]

I think I may have found the problem. With both lens coupled I cycled the focus ring on the 18-250 at least one hundred times. This loosened up the stiffness and I believe broke it in. It is now easier to turn. This 1.4 tele is a brand new unit. I then put the 1.4 and the 18-250 and an Olympus 1.7 tele on my K100D and used auto focus. It is a reasonably bright day here. Here are two examples resized and sharpened only.[IMG][/IMG]

[dwssas]

Second pic

[dwssas]

Second pic

Both of these were hand held.

[geoffox23]

[QUOTE=dwssas;189853]I think I may have found the problem. With both lens coupled I cycled the focus ring on the 18-250 at least one hundred times. This loosened up the stiffness and I believe broke it in. It is now easier to turn. This 1.4 tele is a brand new unit.

I am glad to hear of your success, but sadly, this cycling did not produce any result for me.

My near new Tamron TC 1.4 allows me to smoothly manual focus my AF Pentax and Tamron lenses, but does not work well with any of my AF Sigma lenses, and is particularly stiff with the 135-400, which is the lens I most wanted to match with the TC.

I am also concerned that if manual focus is stiff, then there will be a strain on the K100D focus motor, shaft and gears when I auto focus using the Sigmas.

There are a few people here using the 135-400 Sigmas with the Tamron 1.4 TC, and wonder if any have problems manually focusing this lens.

Any help appreciated.

Geoff

[dwssas]

Geoffox---I know that it looks terrible on the cam but results are what count. an inexpensive,debatable, Olympus 1.7 telecon always gave me excellent results. However the 135-400 is proabably too large to adapt to it.