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**jpzk** · 09-27-2010, 05:19 PM

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

JP

twitch · 09-27-2010, 05:28 PM

My understanding is that a 1.7 adds a stop and a half, not just a stop (which would be a 1.4x TC).

**Marc Langille** · 09-27-2010, 05:49 PM

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

**jpzk** · 09-27-2010, 06:04 PM

Originally posted by twitch

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

**jpzk** · 09-27-2010, 06:07 PM

Originally posted by Marc Langille

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

arm_jstp · 09-27-2010, 06:09 PM

Focusing range will be very very short if you use AF 1.7x, because of the mechanism limitation of AF 1.7x.

**Marc Langille** · 09-27-2010, 06:15 PM

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

Adam · 09-27-2010, 06:17 PM

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.

**jpzk** · 09-28-2010, 08:04 AM

Originally posted by arm_jstp

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

**jpzk** · 09-28-2010, 08:06 AM

Originally posted by Marc Langille

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

**jpzk** · 09-28-2010, 08:09 AM

Originally posted by Adam

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

09-27-2010, 05:19 PM	#1
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251	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, 06:17 PM	#8
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,609	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. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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09-27-2010, 05:28 PM	#2
twitch Veteran Member Join Date: Nov 2009 Posts: 4,571	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
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,710	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
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251 Original Poster	Originally posted by twitch 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
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251 Original Poster	Originally posted by Marc Langille 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
arm_jstp Veteran Member Join Date: Apr 2009 Location: Blacksburg, VA Posts: 485	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
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,710	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

09-28-2010, 08:04 AM	#9
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251 Original Poster	Originally posted by arm_jstp 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
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251 Original Poster	Originally posted by Marc Langille 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
jpzk Site Supporter Join Date: Jan 2009 Location: Québec Photos: Gallery \| Albums Posts: 8,251 Original Poster	Originally posted by Adam 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

Equivalence? 300mm/2.8 plus a 1.7X TC

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