[Blue]

As far as I am aware there are no extension tubes that are capable of autofocus (no doubt someone will now prove me wrong) but they are compatible with the "A" setting so will be a lot more useful than the ones without.
I actually only want the tubes, it was worth the price for them alone .. the F 1.7 is just a bonus

Kenko made some in the past that were AF compatible, but they are out of production and very hard to find used.

Edit: surprisingly, there is one listed in the marketplace: https://www.pentaxforums.com/forums/photographers-marketplace/41255-kenko-uni...brand-new.html

[ChrisPlatt]

The Spot F requires an adapter to use silver batteries or a Wein cell because the Silver batteries provide too high of a voltage.

Not true. The Spotmatic F meter has a bridge circuit and is relatively immune to voltage variations.

Though originally equipped with the now-banned 1.3V mercury 625 battery,
the Spotmatic-F will work perfectly with the modern 1.5V silver (or alkaline) 625 replacement.

Chris

[Blue]

Not true. The Spotmatic F meter has a bridge circuit and is relatively immune to voltage variations.

Though originally equipped with the now-banned 1.3V mercury 625 battery,
the Spotmatic-F will work perfectly with the modern 1.5V silver (or alkaline) 625 replacement.

Chris

Are you sure the F doesn't have a dual coil meter? The F had a revised meter design to take advantage of the "new" open-aperture metering, using the updated Super-Multi-Coated (S-M-C) Takumar lenses. The meter had higher power demands as a result. The ES was further revised to take a silver oxide battery and the ES II took 4.

Edit: I guess this is a question for Eric.

[jsherman999]

Are you sure the F doesn't have a dual coil meter? The F had a revised meter design to take advantage of the "new" open-aperture metering, using the updated Super-Multi-Coated (S-M-C) Takumar lenses. The meter had higher power demands as a result. The ES was further revised to take a silver oxide battery and the ES II took 4.

Edit: I guess this is a question for Eric.

Why don't we consult The Manual:

[Mike.P®]

Kenko made some in the past that were AF compatible, but they are out of production and very hard to find used.

See, I said someone would prove me wrong
I'm not sure how useful AF would be with tubes, I only use manual focus with macro lenses as AF is virtually useless that close so with tubes I would have thought it would be even more difficult to get a decent lock.

Cheers for the info though.

[ChrisPlatt]

Are you sure the F doesn't have a dual coil meter? The F had a revised meter design to take advantage of the "new" open-aperture metering, using the updated Super-Multi-Coated (S-M-C) Takumar lenses. The meter had higher power demands as a result. The ES was further revised to take a silver oxide battery and the ES II took 4.

The ES and ESII have greater power requirements, mainly for their electronic shutters.
The SP-F has a mechanical shutter.

No additional electrical power is required for full-aperture metering with SMC Takumar lenses.
An additional mechanical coupling is used to transmit set aperture to the camera's meter.

The SP-F meter turns on automatically whenever lens cap is removed.
Of course if left off for long periods battery will run down...

Chris

[Blue]

Wow. The manual calls it a 1.5 volt mercury battery when in fact it is a 1.35 volt battery. I don't see anything in the manual about the F having a bridge circuit or dual coil circuit, but it implies that the metering system is more like that of the ES and ES II than previous Spotmatics. I've been using zinc air batteries in my F to be on the safe side and a little more accuracy if nothing else.