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12-24-2018, 05:17 PM   #1
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K3II + M 200 f4 + T6-2x Math Question

I just picked up one of these for cheap. I'm understanding on Full Frame the Rear Converter K T6-2X permits the doubling of the focal length AND f stop.

If using together with K3II + M 200 f4 am I tripling the focal length to 600mm @ f11?

Thanks in advance

12-24-2018, 05:41 PM - 1 Like   #2
dms
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Only as regards the field of view.

---------- Post added 12-24-18 at 05:43 PM ----------

As regards the f-stop, the effective f stop for exposure is two stops more closed down--so f/5.6 would become f/11.
12-24-2018, 06:03 PM - 1 Like   #3
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Crop factor makes the field of view look like it is a lens that is 1.5x longer, but the actual focal length isn't changed. The f stop also is 2 stops changed, but that isn't different for crop vs full frame, but some will argue about effective f stops for depth of field.

So an f4/200mm becomes a 400mm/f8. The crop makes this appear like a 600mm f/8. Focusing this may be difficult except in great light.
12-25-2018, 05:56 AM - 3 Likes   #4
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Vanya gave you all the correct info, but some advice. The lens rig you describe would be seductively light and easy to hold, but don't do it. Put it on a sturdy tripod if you want to get any idea of the best the combo can deliver. DOF will be razor thin @ 600mm, so the chances of missing the focus on your subject are very high. Vibration, even on a sturdy tripod, will make focusing a challenge as well, Finally, the 200mm f4 is a middling performer, not at all outstanding for a prime lens, and the TC will not, cannot improve that mediocre IQ. So stop it down to f5.6~f8, which in terms of light transmission will be f11~16. Overall, do not set your expectations for IQ too high, but also, don't give up after a handful of exposures. Working with 600mm at apertures of f11~16 there are numerous ways that IQ can be degraded other than the quality of the optical system.

12-25-2018, 08:51 AM   #5
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QuoteOriginally posted by WPRESTO Quote
Vanya gave you all the correct info, but some advice. The lens rig you describe would be seductively light and easy to hold, but don't do it. Put it on a sturdy tripod if you want to get any idea of the best the combo can deliver. DOF will be razor thin @ 600mm, so the chances of missing the focus on your subject are very high. Vibration, even on a sturdy tripod, will make focusing a challenge as well, Finally, the 200mm f4 is a middling performer, not at all outstanding for a prime lens, and the TC will not, cannot improve that mediocre IQ. So stop it down to f5.6~f8, which in terms of light transmission will be f11~16. Overall, do not set your expectations for IQ too high, but also, don't give up after a handful of exposures. Working with 600mm at apertures of f11~16 there are numerous ways that IQ can be degraded other than the quality of the optical system.

What he said!
12-25-2018, 06:52 PM   #6
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QuoteOriginally posted by WPRESTO Quote
do not set your expectations too high
I have zero expectations so if I get anything even remotely decent I'll be happy; just killing time. Thanks for the info.
12-26-2018, 06:50 AM   #7
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QuoteOriginally posted by WPRESTO Quote
don't give up after a handful of exposures
OK I see what you mean. I gave up already....
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