[Michael Piziak]

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Just curious. I seen this Vivitar 2x teleconverter on Evilbay. Can that be used on the Pentax 55-300mm digital lens. Any limitations ?

link: Pentax PKA Mount Vivitar 2X Teleconverter for Digital or Film | eBay

[jatrax]

It CAN be used, the question is whether you should. And my answer is no. You would lose autofocus and 2 stops of light. With the already slow 55-300 I think it would be difficult at best to even see well enough to focus manually. And the image quality would be, well, lets just say 'poor' to be polite. I have used a 1.4x TC with the 55-300 and though it worked it was a struggle. This is a 2x TC which IMHO goes beyond what the 55-300 can handle. If you want to get it for $20 and try, let us know the results but I think I can guess.

[Michael Piziak]

It CAN be used, the question is whether you should. And my answer is no. You would lose autofocus and 2 stops of light. With the already slow 55-300 I think it would be difficult at best to even see well enough to focus manually. And the image quality would be, well, lets just say 'poor' to be polite. I have used a 1.4x TC with the 55-300 and though it worked it was a struggle. This is a 2x TC which IMHO goes beyond what the 55-300 can handle. If you want to get it for $20 and try, let us know the results but I think I can guess.

Thanks. Don't think I'll bother then. 600mm too good to be true with that teleconverter.

[boriscleto]

The 55-300 works well with the Vivitar Series 1 1.4x TC. I spent an entire day shooting with that combo, and I didn't even run into much purple fringing...

https://www.flickr.com/photos/benmcgann/sets/72157644957637352/

Many of my sets from last year use that combo as well. I just wish it transmitted the focal length to the camera correctly like the Pentax TC does...

https://www.flickr.com/photos/benmcgann/sets/72157635545936012/

[clackers]

Just curious. I seen this Vivitar 2x teleconverter on Evilbay. Can that be used on the Pentax 55-300mm digital lens. Any limitations ?

link: Pentax PKA Mount Vivitar 2X Teleconverter for Digital or Film | eBay

Probably doesn't have coatings on its glass. A good way to make your images soft and lose contrast.

[lesmore49]

I have an old Takumar-A 2X Tele-converter. I've tried it with my old 55-300....and K10D and K-5 and the pictures are good.

[goubejp]

The 55-300 is not fast enough for the converter. You must consider that the 2X converter will transform it to a f11.4 lens wide open. Good luck if you are able to focus it properly.

[boriscleto]

The 55-300 is not fast enough for the converter. You must consider that the 2X converter will transform it to a f11.4 lens wide open. Good luck if you are able to focus it properly.

The TC to OP linked to is a manual focus converter.

[lesmore49]

The 55-300 is not fast enough for the converter. You must consider that the 2X converter will transform it to a f11.4 lens wide open. Good luck if you are able to focus it properly.

I have a Sigma 150 - 500. At 500 mm I usually set the aperture to F 10....F 11. I'm usually taking pictures outdoors during the daylight hours. Using my 2X on a 55-300 would make it a 600mm equivalent. F stops of F 10 F 16 for outdoor photos are not an issue...for me...or many other photographers I would think.

F stops of say...F 6.3 to F 8....on my Sigma @ 500mm I find really limit the depth of field. I like good DOF . With my K-5, using my Bigma @ 500mmI find F 10 + at 800 -1600 ISO....gives me very good shutter speed and the lens is still hand hold able.

Good pictures at higher ISO's that modern cameras can provide, takes away a lot of the disadvantages of F stops of F 10 +....IMO.

[jatrax]

At 500 mm I usually set the aperture to F 10....F 11

Yes but the camera is focusing (or if you are manually focusing, then you are focusing) at wide open so much brighter during focusing. It only stops down when the picture is taken. With a 2x TC on 'wide open' is two stops darker in the viewfinder. Just like adding a 2 stop ND filter. Much harder to see well enough to focus.

It CAN be done, it's just not easy and I doubt the results will be satisfactory.

[lesmore49]

Yes but the camera is focusing (or if you are manually focusing, then you are focusing) at wide open so much brighter during focusing. It only stops down when the picture is taken. With a 2x TC on 'wide open' is two stops darker in the viewfinder. Just like adding a 2 stop ND filter. Much harder to see well enough to focus.

It CAN be done, it's just not easy and I doubt the results will be satisfactory.

I often times go to F 16 on my Sigma. Yes , I usually go for bright sunlit days.

[jatrax]

I often times go to F 16 on my Sigma. Yes , I usually go for bright sunlit days.

Which still does not matter. Set it at f/32 if you want, you are still focusing wide open, which is f/5.6 on that lens. The lens only stops down when you press the shutter button. To see what I mean put an ND filter on your Sigma, a 10 stop if you have it or as many stops as you have, you can not see to focus because you are reducing the light available to the view finder. Setting the aperture on a k-mount lens does not do the same thing because it remains wide open until the camera takes an exposure.