[mgvh]

(There's a thread on this topic in DPR, but maybe someone here might have more knowledge.)

I have the highly regarded Kenko Pz-AF 1.5x Teleconverter. (This is the one that's actually 1.4x) I can shoot in A mode and the autofocus works fine. I'm not expecting Pentax/Ricoh to support this older, non-Pentax gear. What I would like to do is manually input the focal length as I do with other non-AF lenses, but this option is not available in the menu. (bottom option in camera #3 in menu) I.e., I'd like a manual override to input focal length. I'm thinking that wouldn't be a terribly hard firmware update, but what do I know? Or is there some other way to improve my odds besides using a tripod and turning off SR? Thanks.

[JeffB]

What lens are you using? What does your EXIF data show for shots using the TC + lens? My understanding was that the prompt for "input focal length" appeared when the camera could not detect the lens data. So if you are not seeing that prompt the lens data must be getting to the camera.

[photoptimist]

Have you looked at the EXIF data for images taken with this teleconvertor? Is it possible the camera is automatically calculating the correct focal length already?

[mgvh]

E.g., I'm using the DA 18-135 on a K-3 with the Kenko TC, and I'm shooting at full 135mm. The EXIF focal length indicated is 135mm. With the 1.4x TC, I'm really shooting at 189mm. SR at 135mm when it's actually 189mm isn't so bad, but I can use all the help I can get when handholding a shot at that length. And the main reason I'm using the TC is when I'm travelling light and don't want to carry along my DAL 55-300, so tripod isn't the answer.

[JeffB]

Most teleconverters have limited functionality when used with lenses slower then f/2.8. So using that lens at f/5.6 could be causing some trouble. Beyond that, it is likely just a limitation of the off-brand TC. Do you have any documentation on the TC? Is it supposed to transmit "altered" lens data or is it just a pass through allowing the unaltered lens data to get to the camera? I do not have a current Pentax branded TC but I'd be curious to know if those register TC * lens focal length in the EXIF or just the lens focal length.

[mgvh]

Most teleconverters have limited functionality when used with lenses slower then f/2.8. So using that lens at f/5.6 could be causing some trouble. Beyond that, it is likely just a limitation of the off-brand TC. Do you have any documentation on the TC? Is it supposed to transmit "altered" lens data or is it just a pass through allowing the unaltered lens data to get to the camera?

No, it doesn't transmit altered focal length, and that's why I'm hoping that there could be a manual override so that I can input the focal length as I would with other non-autofocus lenses.

[jbondo]

Here is a kind of workaround for screw-drive lenses... (won't work for SDM/DC/PLM lenses)

The menu choice to set this:
Menu->Shooting4->Input Focal Length
Is grayed out whenever a lens is attached that the FL can be read from.

If you press the lens release button and rotate the lens a tiny amount (just a microscopic amount where "F--" appears, the AF and exposure still work pretty much right, and since the camera can no longer read the lens FL, the menu choice becomes available and you and set whatever value you like. However, the lens is no longer locked in place so care must be used. Also, you will want to test and listen and make sure the screw-drive is not binding when used like this.

Alternately, you could tape over the data contact on the lens to achieve the same thing, and more safely and this would also ensure the stop down doesn't get skewed.

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Last edited by jbondo; 12-23-2016 at 12:40 PM.

[tduell]

I do not have a current Pentax branded TC but I'd be curious to know if those register TC * lens focal length in the EXIF or just the lens focal length.

I use the HD Pentax-DA AF Rear converter 1.4x AW, with the D FA 150-450, and it reports the the focal length correctly in the exif, along with the full description in the lens ID.

Cheers,
Terry

[surfar]

I use that Kenko/Vivitar/tamron +++ TC,its good but will always show the normal length of the lens.just add 40% and store it in yr memory!

[noelpolar]

To the OP.... it's like you outlined and there's nothing you can do.... some manual over ride would be handy for such a thing.... as you indicated..... I've not seen any reliable data on how much impact an understated (30% for 1.4x) FL has on SR effectiveness at various FL's.

[goatsNdonkey]

When you really, really need shake reduction, can you switch the camera to manual focus? And if you do that, do you then get the option to input the actual/effective lens+TC focal length? At other times, maybe the automatic reading of the focal length is giving you enough shake reduction, even though it is wrong.

[mgvh]

When you really, really need shake reduction, can you switch the camera to manual focus? And if you do that, do you then get the option to input the actual/effective lens+TC focal length?

Switching to manual focus does not allow for manual setting of focal length.

At other times, maybe the automatic reading of the focal length is giving you enough shake reduction, even though it is wrong.

Yes, shooting at 135mm (which is what the SR will be set to) with the 1.4x TC means an actual length of 190mm, so that's a significant help. But you also lose some light with the TC, so all the SR you can get helps.