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06-17-2011, 04:20 AM   #1
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Teleconverters question

I am looking for teleconverters to attach to my 55-300mm AF lens. Are there any teleconverters for AF lenses? If we attach that teleconverter, would AF still work? Would aperture function work? What about other auto settings?

I don't mind any brand at all.


Last edited by 3drives; 06-17-2011 at 04:27 AM.
06-17-2011, 06:05 AM   #2
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I have used a Promaster 1.7x TC with the 55-300mm, I think it is a little better than cropping for the same shot. I don't think it is really a 1.7x, more like 1.6 or 1.5. I don't think this is made anymore, and you would need to buy used. AF works fine with the 55-300 in daylight and all aperture functions work as intended. There is a loss of light (around one stop) that reaches the sensor, compared to the lens alone, but the meter in the camera measures this properly and no special adjustment is required because of the TC. Auto settings like P mode work normally. The Pentax camera does not recognize that a TC is mounted, so EXIF data records that the 55-300mm was used, it does not record the actual focal length, it records what the lens reports. The contacts in the TC just pass the lens data through to the camera. When using this auto TC, it is important to mount this TC to the lens first and then mount to the camera, because the lever inside the TC just flops around and needs the lever in the lens to position the TC lever correctly. I have seen Adorama list a Pro Optic and a Vivitar 1.4x auto focus TC, but I have used neither, so can't comment. TC use is kind of a strange thing, it is hard to predict what lens works with what TC, but if it works, then it works. One needs to try it and see. Good luck on your quest.
06-17-2011, 06:18 AM   #3
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I have the Vivitar 2X and had it attached to my K-x with the 300 mm and took this picture... that I cant find....

Well anyho it worked rather well taking a picture of an Osprey young perched high atop a tree. I was free handing it also with no support.
06-17-2011, 06:31 AM   #4
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Ok I lied...

"I did the "one step" PP in PSP X3. Considering the bird was all the way in the top of the tree and I was a good 40 yards from the tree I think it came out pretty good.

I used a monopod and manual focus. A task I am slowly learning."

I still used:
Lens: 55-300 DA L w/Vivitar 2xMC4 Camera: K-x Photo Location: JULIE J. METZ WETLANDS BANK ISO: 200 Shutter Speed: 1/350s Aperture: F5.8

And here is the picture:


The TeleConverter is AUTOFocus however as was mentioned depending on the target, light, distance(?) etc it is better to go manual on SOME shots.

At least that is the way I understand it.

06-18-2011, 12:38 PM   #5
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gp1806 and aknot, Thanks many.

How do I know, before I buy, if a converter can do AF or not? What indicators to look for?
06-19-2011, 07:42 AM   #6
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QuoteOriginally posted by 3drives Quote
gp1806 and aknot, Thanks many.

How do I know, before I buy, if a converter can do AF or not? What indicators to look for?
The TC should have all the electrical contacts to match the contacts of the camera body lens mount and the screw drive. If it has the extra contacts for the power zoom feature, so much the better. One thing to remember is that there is a loss of light getting to the sensor when using a TC, sorry, no free lunch. The 1.4x and the 1.5x loose less light than a 2x. When using a slow lens like the 55-300mm with a TC, you can get in a situation where the camera won't focus (hunts), not because of the mechanics of the TC, just that there is not enough light getting to the AF sensors. You will need bright daylight for a 2x to work properly with your lens. Because of this, I would suggest getting a shorter TC like a 1.4x or 1.5x. TCs works better with a fast lens, like a 300mm f/2.8, but that costs very much money. Also, I have read that TCs don't work well with SDM lenses. I don't own any SDM lenses, so I have never tried this.
When I said earlier that if the TC/lens combo works, then it works. I meant that the TC image looks better than cropping the non TC image for the same magnification. You should test your TC/lens combo to be sure that it does work well. If you are not happy with the TC images, you can always remove the glass from the TC and you will have a dandy close focus extension tube.
On the other Pentax forum, a member there posted that he ordered a Vivitar 1.4x TC to use with his 55-300mm. He said he will report with his results when he tests the combo. You might want to wait and see what conclusion he posts. I will post back when I see what he says.

Last edited by gp1806; 06-19-2011 at 07:50 AM.
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