Teleconverter magnification comparison. (5 imgs)

Started Aug 25, 2013 | Photos thread
Greyser Veteran Member • Posts: 6,365
Re: Dave...

brandrx wrote:

DaveJC wrote:

I bought the lens from group member Fleafly who recommended a Sigma over the Kenko. IQ is the main thing for me. Birds are small enough to start with so the better IQ is worth the price for me. Also waiting for a used IIs to come into my price range. Should not be too long after September announcements.--

There is no Sigma teleconverter that I am aware of that will fit the Pentax-F*300mm f4.5 lens. The protruding front element of the Sigma will hit the rear element of the Pentax and cannot even be mounted.

Hi Ron,

I'd like to understand for myself and resolve this issue what we've been clashing over and over again once and for all.

First. The rear element of my FA*300/4.5 (and F*300/4.5 as well I assume) is recessed way deep down in the lens body.

Second. Both Sigma 1.4x TCs: APO EX non-DG and APO EX DG fit well with my FA*300 and do not harm anything. Yes it's true that the EX DG front element protrudes about 0.5mm or 0.020"-0.025" (I'm lazy to measure it exactly) over the the mount edge. However it doesn't interfere with anything in the lens.

From our previous discussions I know that your Sigma TC K-mounts do not lock with your F*FA*300 lenses. Mine do without any trouble. I see no mechanical issue with using the Sigmas with FA*300/4.5.

Long time ago, pairing most of available 1.4x TCs with FA*300, I found the Tamron Pz-AF (and Vivitar Series-1, which is re-branded Tamron with no Pz contacts anyway) to be superior (by small margin) to both Sigmas. However, playing recently with my Sigma 500/4.5 I discovered that both Sigma TCs do require different than for the lens itself AF micro adjustment when they are installed. I did not take it in account when I was testing them with FA*300. Now I believe that for the 500/4.5 Sigma at least 1.4x EX non-DG and EX DG resolve a bit better than my Tamron. However, I did not test this thing with FA*300. Due to inconvenience of constant changing of AF micro adjustment settings I still prefer using the Tamron Pz-AF over sigmas with my FA*300.

it would be nice, if someone else with F*FA300/4.5 and Sigma 1.4x TC, especially EX DG, experience would elaborate on the issue as well. Please do. I'd like to know the ultimate truth.

My warmest regards,


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