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04-26-2015, 10:40 PM   #1
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Which TC will I need for 300mm FA or DA on K5 iis

Hello Shutterbugs,

I am new to adapters, filters, and tripods...
Since I will have 300mm lens, I also want to extend by using TC. But people use lot of terms, 1.7, 1.4, 2.0 and talk about whihc ones are better in terms of preserving quality as well as some of them don't work on AF? Basically I have no idea which TC to even type into database in B&H or other stores..Of course with 300mm FA or DA(still have yet to decide), I know theye are different types.

Any advice on brand, size and kind would be appreciated. I am not good in troubleshooting so would be good to purchase one that will work smoothly from start...

Thank you,

04-26-2015, 10:57 PM   #2
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Hi Kat,

The number tells you the multiplying factor of the teleconverter (ie. 1.4 multiplies your focal length by... 1.4)

However, there will also be a loss in light, a 1.4x converter looses 1 stop of light a 2.0 converter looses 2 stops of light.
What this means is if you attach a 1.4x teleconverter to a 300mm f4 lens, you effectively get a 420mm f5.6 lens.

if the f number gets too much, there is insufficient light for the AF system to work, the usual advice is to stay at f5.6 or wider.

The Pentax HD 1.4 converter is widely considered the best for use with the DA* 300.
But essentially, you get what you pay for.

I'm sure others will have other advice for you as well. Good luck with your purchases.
04-26-2015, 11:10 PM   #3
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I have HD Pentax-DA AF Rear Converter 1.4x AW
The HD DA 1.4 is the best quality wise and Image quality (IQ) wise. I would go with this one for start, you can not go wrong,
1.4 gives usally the lowest magnification an leads to lowest IQ & light loss.
1.7 gives you already a quite heavy magnification but has dependent on the lens a medium to big influence on IQ & light.
2.0 doubles your focal length but has the biggest influence on the IQ & light.

These are for special occasions, where i need even more reach or where they are specially designt for some lens types like the A 1.4-L (will be used with the A 200 Macro).
I have a Rear Converter-A 2x-S
plus a kenko or what ever
Promaster Spectrum7 AF 1.7x
on order a Rear Converter-A 1.4x-L

Last edited by max_pyne; 04-27-2015 at 03:57 AM.
04-26-2015, 11:18 PM   #4
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I also recommend the Pentax HD 1.4x converter for the DA*300. It works well with the K5IIs.
Pentax 1.4x HD PENTAX-DA AF Rear Converter AW for K-Mount 37962

This combo will have the advantage of a weather resistant kit, which an FA would not be.
(If that is important for you.)

04-27-2015, 11:39 AM   #5
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Original Poster
Thank you so much for all the advice!
Now I understand about loss of light with larger magnification. The 1.4 is now on my shopping list:-) I will try and post my pictures from island vacation once I come back in June. It would have bee taken with new DA 300 and either with or without the TC(if I realize I ran out of money after the DA 300:-)


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