If you had to choose: DA 55-300 plus Pentax 1.4 TC, or Sigma 150-500??

Started Aug 10, 2014 | Discussions thread
brandrx Forum Pro • Posts: 28,337
Re: Jeff...

JeffAHayes wrote:

brandrx wrote:

JeffAHayes wrote:

I'm unsure about how well the TC would work with the 55-300, but this is as much of a question as it is an answer...

Its specs state that it will work with "any lens with a minimum aperture of F 4 or less." Well, we all know the 55-300 is rated at F 4-5.8, so my question/concern is that although it IS minimum F 4 all the way to about 180 mm (according to my own measurements), once you pass that point, the minimum aperture creeps all the way up to F 5.8. So my question/concern is whether or not the TC will work with that lens at its longer lengths, or not?

Has anyone tried using it with the 55-300 and discerned this one way or the other?

Hi Jeff,

Yes, I have tried it. I have also tried other 1.4X (1.5X) teleconverters.






Thanks, Ron. That's good to know. So I guess as long as a lens has a STARTING aperture of F 4 or lower, the Pentax 1.4 TC will work and AF with it then, huh?

The recommendations for 1.4X teleconverters is a lens of F/4 or faster. However, they will work with slower lenses with some lilitations. For instance I just now checked out the Sigma 120-400mm f/4.5~5.6 at 400mm with the Pentax 1.4X HD AW. It works and I will soon give it a try against some real subjects. I have also used a 1.4X teleconverter with the old screwdrive Sigma 50-500mm which is f6.3 (actually f/6.9) at the long end. It doesn't work so well with the new OS HSM version of the Sig 50-500mm.

Another example is the Pentax-F 1.7X AF Adapter. The recommendation for use is with an f/2.8 or faster lens. However, long ago many of us found that it works great with no problem on f/4.5 or faster lenses. Works OK with f/5.6 lenses. Will sometimes work with f/8 lenses.

As for that $99 Vivitar 1.4, you seem pretty sold on that, as well -- especially for 1/6 the money.

IMO, the Vivitar 1.4X Series 1 teleconverter is the same as the Tamron-F 1.4X Pz_AF except that it doesn't have the SDM contacts and will not autofocus SDM or HSM lenses.

You said it won't AF with SDM or HSM, so I assume it WILL AF with screw drive lenses, although I don't keep up with that much, so I'm not even sure which, if any of my Pentax lenses ARE screw drive (or that Sigma F 3.5 180 mm Macro I got used from KEH). I guess there's a way to find out, I'm just not quite sure where to look. Is the 55-300 screw drive? From all the noise it makes, I assume the D FA 100 mm Macro MUST be screw drive, but I really have no idea.

Look on the rear of the lens. If you see two gold contacts next to each other then it is SDM (HSM for Sigma). Screwdrive lenses will not have these gold contacts.

Looking at the back of a screwdrive lens arrange it so that the data pin is at the 180 degree position. The data pin is the last pin as you count CCW. While you have it in this position the screwdrive (notice the slot) will be at 225 degrees.

The last thing to note about teleconverters is that the only one that will pass both the cortrected focal length and aperture to the camera is the Pentax 1.4X HD AW. However, with Sigma HSM lenses it will not pass the corrected information. All of the other teleconverters will not pass any corrected information to the camera.

The Pentax-F 1.7X AF Adapter will pass the corrected aperture aperture to the camera. The correct focal length is input via the operator when you have SR enabled. Again, with some (most) Sigma lenses the aperture is not passed correctly when using the Pentax-F 1.7X AF Adapter. For instance if you try to use it with the Sigma 500/4.5 then wide open will read f/2.8 instead of 1.7 times 4.5 (f/8) as it should read.


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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

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