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07-23-2009, 02:05 AM   #16
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QuoteOriginally posted by imtheguy Quote
As long as you show me yours I'll show you mine right now. Mine is a Tammy 1.4x TC, the SDM compatible version and the EXIF does not change regardless of whether I have the TC mounted or not. I used PhotoME and looked everywhere that made sense.

Reading through this interesting stuff got me thinking that we are possibly looking at it too complex when there is a simple answer. Consider the case of a 2x TC used in Ap Priority mode. It passes only 1/4 the light of the lens its attached to. Since the camera meter is on the other side of the TC it is aware only of the reduced light and can go blissfully about its business of calculating the shutter speed requirement for the focal length the lens is set for and the ISO the camera is set for.

So my question now is does the camera actually USE more than the ABSOLUTE amount of light to calculate the metering in this case? If the lens is a constant f/4 and we want to shoot at f/8, it will calculate without knowing what is lost in the middle. I am suggesting that it washes in the calculation such that the TC does not transmit any information about itself to alter the results.

Fire away boys....
You are right.
I've just tested this with my Kenko.
What a disappointment, what may be more important, it also does not change the focal length info.
Meaning that the shake reduction mechanism is under compensating for camera movement....
Are Pentax TC's any better?

- Bert

07-23-2009, 02:50 PM   #17
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Well, you can use a manual TC so you can input the FL on the camera for the SR compensation..but then you have to stop down too.
07-24-2009, 06:14 AM   #18
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QuoteOriginally posted by bymy141 Quote
...Meaning that the shake reduction mechanism is under compensating for camera movement...
They certainly are under compensating.

QuoteOriginally posted by GerryL Quote
Well, you can use a manual TC so you can input the FL on the camera for the SR compensation..but then you have to stop down too...
If you use TC with A lenses, you get to enter the modified focal length and you don't need to stop down.


QuoteOriginally posted by bymy141 Quote
...Are Pentax TC's any better?
Not that I know.
07-24-2009, 06:34 AM   #19
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I am not sure about all TCs.

Sigma TC's don't modify any information being passed through from the lens.

With my Sigma 70-200 F2.8 the focal length and aperture reported are the actual values set on the lens, not the resultant focal length and aperture when using the TC.

THis causes 2 problems on a K10D, first of all the camera does not know the effective aperture and as a result, the metering is impacted. This is tied to the LL-80 screen. Secondly the focal length for SR is wrong.

I know the SMC-F 1,7X AF TC modifies the corrected aperture to the body, hence has circuitry that corrects this.

I have not checked the Takumar-A 2x TC yet.

07-24-2009, 07:04 AM   #20
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QuoteOriginally posted by Lowell Goudge Quote
...I know the SMC-F 1,7X AF TC modifies the corrected aperture to the body, hence has circuitry that corrects this...
One more reason why this one is quite a piece of equipment. Comes at a price, though. Such is live, isn't it .
07-24-2009, 07:09 AM   #21
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QuoteOriginally posted by imtheguy Quote
As long as you show me yours I'll show you mine right now. Mine is a Tammy 1.4x TC, the SDM compatible version and the EXIF does not change regardless of whether I have the TC mounted or not. I used PhotoME and looked everywhere that made sense.

Reading through this interesting stuff got me thinking that we are possibly looking at it too complex when there is a simple answer. Consider the case of a 2x TC used in Ap Priority mode. It passes only 1/4 the light of the lens its attached to. Since the camera meter is on the other side of the TC it is aware only of the reduced light and can go blissfully about its business of calculating the shutter speed requirement for the focal length the lens is set for and the ISO the camera is set for.

So my question now is does the camera actually USE more than the ABSOLUTE amount of light to calculate the metering in this case? If the lens is a constant f/4 and we want to shoot at f/8, it will calculate without knowing what is lost in the middle. I am suggesting that it washes in the calculation such that the TC does not transmit any information about itself to alter the results.

Fire away boys....
Well, the 2x Kenko converters contains an integrated circuit and a small circuit board through which the seven A-contacts go. Presumably it modifies the signals.


So if you all take your converters appart we can compare...
I've shown mine!
07-24-2009, 10:08 AM   #22
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Interesting discussion.

I have a related question that I've never seen asked. Let's say you mount a 2X TC on an F2.8 lens which normally reaches maximum resolution at F5.6. Will an Av setting of F2.8 result in maximum resolution for the combination of lens + TC?
07-24-2009, 11:05 AM   #23
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QuoteOriginally posted by audiobomber Quote
Let's say you mount a 2X TC on an F2.8 lens which normally reaches maximum resolution at F5.6. Will an Av setting of F2.8 result in maximum resolution for the combination of lens + TC?
Nope. The lens resolution has nothing to do with the TC. To reach max. resolution, the lens itself still has to be at F/5.6.

If the TC does not modify the data between the lens and the body, you'll have to set the Av at 5.6.

If the TC modifies the data, you'll have to set the Av at 11.

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