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05-14-2008, 11:36 AM   #316
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QuoteOriginally posted by palmor Quote
The only way a 2xTC is going to give you better then average results is if the lens your using it with is excellent.. not average but REALLY excellent. I'm shocked that it AF'd at all with a 5.6 lens, making me wonder just how accurate that focus was.

The Sigma 135-400 isn't an "excellent" lens so I'm not surprised by these results at all, especially with an unknown brand TC. For example, if you take a look at some of those Sigma 70-200EX shots in that other thread taken with the Sigma 2xTC you'll see MUCH better results.. like below.

Also don't forget that SR doesn't know about the TC so it still thinks your shooting at 400mm, not the 800mm when including the TC.




Agreed.....

05-15-2008, 12:58 AM   #317
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QuoteOriginally posted by palmor Quote
Also don't forget that SR doesn't know about the TC so it still thinks your shooting at 400mm, not the 800mm when including the TC.
With my Kenko Teleplus MC7 DG though I get the chance to key in the exact focal length for shake reduction. Probably because it won't give me AF with some lenses with smaller maximum apertures.

Paul
05-15-2008, 04:35 AM   #318
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QuoteOriginally posted by channeler Quote
With my Kenko Teleplus MC7 DG though I get the chance to key in the exact focal length for shake reduction. Probably because it won't give me AF with some lenses with smaller maximum apertures.

Paul

That is the first I've heard of that. It sounds more like the TC or lens isn't transmitting the information needed to make the camera believe you have a newer AF lens. If you use those lenses without the TC does the camera ask you?



John
05-15-2008, 08:17 AM   #319
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QuoteOriginally posted by channeler Quote
With my Kenko Teleplus MC7 DG though I get the chance to key in the exact focal length for shake reduction. Probably because it won't give me AF with some lenses with smaller maximum apertures.

Paul
I agree with palmor. I guess you can type in focal length if no focal length is transmitted to the body, either because the TC doesn't transmit it, or because the lens doesn't send it. For instance, an A-only, not AF TC should do exactly this.

I'm wondering if one cannot enforce this by disabling some of the seven contacts on the TC (128 choices...)?

05-15-2008, 08:32 AM   #320
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QuoteOriginally posted by channeler Quote
With my Kenko Teleplus MC7 DG though I get the chance to key in the exact focal length for shake reduction. Probably because it won't give me AF with some lenses with smaller maximum apertures.

Paul
Hmmmm, I too am all ears and eyes. Have not heard this.
05-15-2008, 10:18 AM   #321
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Question? Maybe silly maybe not.
How many stops do we loose with a Pentax 1.7TC?
05-15-2008, 11:32 AM   #322
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QuoteOriginally posted by jgredline Quote
Question? Maybe silly maybe not.
How many stops do we loose with a Pentax 1.7TC?
Answer: 1.5.
05-15-2008, 12:02 PM   #323
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QuoteOriginally posted by Miserere Quote
Answer: 1.5.
Thats what I came up with, yet I have been hearing that it looses 2 full stops....
This would explain why Auto focus and sharpness is still pretty good with this TC. Pentax obviously new what they where doing.

05-15-2008, 01:58 PM   #324
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QuoteOriginally posted by palmor Quote
That is the first I've heard of that. It sounds more like the TC or lens isn't transmitting the information needed to make the camera believe you have a newer AF lens. If you use those lenses without the TC does the camera ask you?

John
QuoteOriginally posted by falconeye Quote
I agree with palmor. I guess you can type in focal length if no focal length is transmitted to the body, either because the TC doesn't transmit it, or because the lens doesn't send it. For instance, an A-only, not AF TC should do exactly this.

I'm wondering if one cannot enforce this by disabling some of the seven contacts on the TC (128 choices...)?
QuoteOriginally posted by jgredline Quote
Hmmmm, I too am all ears and eyes. Have not heard this.
Hi, I don't fully understand what is going on. The Kenko 2x MC7 DG is a TC I bought some years back, though the contacts seem identical to the Kenko 1.5 TC I bought recently. I have used the 2x TC with my Sigma 70-300 DL Macro. If I set the zoom at 70mm, the maximum aperture is then at F4 and I get AF with the TC connected. The camera does not ask for focal length with SR on. If I set the lens to 300mm with SR on and TC attached, the SR menu comes up asking me to select focal length, so I can select 600mm. I presume this occurs because the maximum possible aperture is then F5.6 and the TC instructions say that AF is only possible with lenses of maximum aperture of F4.0 or greater. I have to use manual focusing. With the lens only connected the focal length is transmitted at all zoom settings.

I have also used the 2x TC with a DA*300 and this behaves exactly in the same way as with the Sigma zoomed to 300mm. I can select a focal length of 600mm and use the lens in manual focus mode. As I mentioned on another thread I had hoped that the DA*300 being a constant F4 might give me AF with this TC but this was not to be. Still, it is useful being able (apparently) to get full SR function.

Paul
05-15-2008, 02:04 PM   #325
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Channeler, this is really wierd. I'm wondering if you have a problem with one of the TC contacts that is broken so it doesn't transmit correctly. Although I can't imagine how this is happening...
05-15-2008, 02:42 PM   #326
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QuoteOriginally posted by Miserere Quote
Channeler, this is really wierd. I'm wondering if you have a problem with one of the TC contacts that is broken so it doesn't transmit correctly. Although I can't imagine how this is happening...
But if it was a broken/faulty contact the SR focal length menu would come up with the Sigma at 70mm zoom with the TC attached.

Paul
05-15-2008, 03:33 PM   #327
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QuoteOriginally posted by channeler Quote
But if it was a broken/faulty contact the SR focal length menu would come up with the Sigma at 70mm zoom with the TC attached.

Paul
I'm just going to guess that there is some incompatibility with that TC and Lens combo where the TC doesn't transmit the focal length data to the camera past a certain focal length.

The menu asking your focal length has nothing to do with the camera being able to AF or not, its all about the camera knowing the focal length. That is why we are all so perplexed with your situation


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05-15-2008, 03:46 PM   #328
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QuoteOriginally posted by channeler Quote
If I set the lens to 300mm with SR on and TC attached, the SR menu comes up asking me to select focal length
Ok, now this is interesting!

I can only imagine one logical explaination:
The 2xTC knowing the aperture and the KAF-AF specification decides, in its builtin micro-chip, that it should report "no AF available" and conclusively stops transmitting a focal length as well -- for connected apertures smaller than f/5.6 permitted by the KAF-AF specification, i.e., for apertures smaller than f/2.8 on the lens alone.

So, the TC is able to switch from reporting AF to reporting no AF.

If it can do this, we must wonder why it didn't double the focal length as well. It obviously must report the lens original focal length to make AF work. Bad news for the forthcoming Pentax TC -- hope they pimp up the spec here...

So, if we now can know how to report focal length or AF capability, we may indeed able to disable it by masking out the proper pins. Isn't the KAF specification public? Where is it?
05-15-2008, 03:46 PM   #329
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Well, I have been experimenting a little with my newly arrived Pentax 1.7TC. I had to read the manual for this one. Correct me if I am wrong.

Since it does not have a screw drive, I guessed that the focusing was being done by the TC itself. I set my Camera to auto focus and the lens to Manual focus and set it to infinity...This gave me some pretty good clear shots. I also could not resist so I took the Manual F/2.8 off my K1OOO and it to focused spot on...I can see this opening up a whole new world as far as good old manual lenses go...
05-15-2008, 04:04 PM   #330
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QuoteOriginally posted by jgredline Quote
the focusing was being done by the TC itself.
Yes, from what I read, the Pentax AF-1.7x TC can be autofocussed on its own (within some scope), whatever be the lens. It may even be it transmits the focal length x1.7...

About my previous remark...

From

[Source: Dario Bonazza K-mount variations]

I learn that the only difference between KA and KAF is the 7th contact next to the screw. So, if we mask it... We may loose AF but gain full SR stabilisation. Anybody tried this?

Does apply to the Tamron and Kenko, not the Pentax TC.
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