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09-27-2010, 05:19 PM   #1
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Equivalence? 300mm/2.8 plus a 1.7X TC

Would a 300/2.8 lens plus a 1.7X teleconverter give me a 510/4 or f4.5??

JP

09-27-2010, 05:28 PM   #2
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My understanding is that a 1.7 adds a stop and a half, not just a stop (which would be a 1.4x TC).
09-27-2010, 05:49 PM   #3
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A 300/2.8 + 1.7x TC would give you 510mm, and approx. F/4.8. If it's the Pentax AF TC, I can vouch for it with the FA* 300/2.8 - great combination.

Regards,
Marc
09-27-2010, 06:04 PM   #4
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QuoteOriginally posted by twitch Quote
My understanding is that a 1.7 adds a stop and a half, not just a stop (which would be a 1.4x TC).
Got that, Twitch!
Thanks for the reply.

JP

09-27-2010, 06:07 PM   #5
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QuoteOriginally posted by Marc Langille Quote
A 300/2.8 + 1.7x TC would give you 510mm, and approx. F/4.8. If it's the Pentax AF TC, I can vouch for it with the FA* 300/2.8 - great combination.

Regards,
Marc
Hi Marc.
Thanks for the reply!

Yes, that would be the Pentax AF-A 1.7x adapter. (Or it it A-FA ...?)
Also glad to know that this would be a great combo.

Cheers.

JP
09-27-2010, 06:09 PM   #6
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Focusing range will be very very short if you use AF 1.7x, because of the mechanism limitation of AF 1.7x.
09-27-2010, 06:15 PM   #7
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Very true! It's better to set an approx. distance on the focusing scale via MF, then use the AF TC to do the rest. I found it's generally not an issue, since the subjects are often fairly far away...

FWIW, a simple way to estimate the equivalence is lens maximum aperture x multiplier of the TC. Therefore the max. aperture in this case is 2.8 x 1.7 = 4.8 (rounded up from 4.76).

Regards,
Marc
09-27-2010, 06:17 PM   #8
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I personally think that the 300/2.8 is best without any TCs, but if you absolutely want to use one, I'd say that the 2x-L gives you the most bang for the buck.


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09-28-2010, 08:04 AM   #9
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QuoteOriginally posted by arm_jstp Quote
Focusing range will be very very short if you use AF 1.7x, because of the mechanism limitation of AF 1.7x.
That's OK, I am used to use this TC with the DA*300/4 and all is well. Approximating the focusing distance is no big deal once you're use to it.
The TC then does its magic!

JP
09-28-2010, 08:06 AM   #10
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QuoteOriginally posted by Marc Langille Quote
Very true! It's better to set an approx. distance on the focusing scale via MF, then use the AF TC to do the rest. I found it's generally not an issue, since the subjects are often fairly far away...

Yessir! As I mention in the previous post, it's not really hard to do once you've tried it. Amazing how this TC does the trick.

FWIW, a simple way to estimate the equivalence is lens maximum aperture x multiplier of the TC. Therefore the max. aperture in this case is 2.8 x 1.7 = 4.8 (rounded up from 4.76).
So that's how you came with this funny-looking aperture!

Regards,
Marc
Thanks for the help.

JP
09-28-2010, 08:09 AM   #11
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QuoteOriginally posted by Adam Quote
I personally think that the 300/2.8 is best without any TCs, but if you absolutely want to use one, I'd say that the 2x-L gives you the most bang for the buck.
I agree that using the prime on its own, without any TC is the best way to go, but when your bird-subjects look like mosquitoes from far vaway ... without a doubt a good TC is a must if you don't have a super-telephoto lens, i.e.: 400, 500, 600mm.

The L-type TC's are hard to come by. The only TC's I have are:

Pentax A-FA 1.7X
Pentax-S 2X
Tamron MC4 1.4X

I am told that the L-type TC's are more suited for anything over 300mm ... is that a fact?

JP
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