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01-07-2010, 02:50 PM   #1
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teleconverter advice please

what brands are reliable and what brands should i stay away from?
tia

01-07-2010, 03:03 PM   #2
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What lens(es) do you plan to use the TC with?
01-07-2010, 03:06 PM   #3
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Forget about using a TC for SDM lenses or any lens slower than f/4.
Other than that, any of the AF TCs for Pentax are good, particularly the Pentax genuine TCs.
I have the Tamron 1.4x TC and it is very good quality, and relatively inexpensive.
01-08-2010, 04:00 AM   #4
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Try to avoid them altogether. You'll probably get a better picture.

01-08-2010, 05:08 AM   #5
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QuoteOriginally posted by Ash Quote
Forget about using a TC for SDM lenses
Why do you say that, Ash? I use TCs with my DA*300mm and have gotten decent results.
01-08-2010, 08:11 AM   #6
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QuoteOriginally posted by dadipentak Quote
Why do you say that, Ash? I use TCs with my DA*300mm and have gotten decent results.
Same here. My 1.4x works pretty well with both the DA*50-135 and DA*300.
01-08-2010, 08:15 AM   #7
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there are some issues you need to consider.

first of all, if the combination of TC and lens result in a maximum aperture more than F6.7 then AF will either not function or hunt very badly.

Second, there are not many TCs made for the pentax KAF2 mount which include power contacts for SDM motors, and some of these may not work because they do not recognize the SDM communications. these need to be tested case by case

third, Sigma teleconverters do not support SDM yet, and sigma teleconverter design has the TC front element extending into the rear of the lens, and therefore only fit on a select few lenses, not even all sigma lenses. To use this TC requires the lens have a clearance of 35mm diameter, 10-12mm deep between the flange of the lens and the rear element. Note some pentax rear converters are similar and require even more clearance. Sigma TCs also do not modify the aperture or focal length reported.

finally, there is the pentax SMC-F 1.7X Auto Focusing TC. This TC has screw drive moveable elements that provide a range of auto focus once a lens is manually focused close to the focus point. This TC also has electronics to modify the reading of aperture to correct for the addition of the TC
01-08-2010, 08:44 AM   #8
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Thanks for the explanation, Lowell. I have the Tamron 1.4x which works with SDM and the AF 1.7x. In both cases, I shoot MF a lot anyway since the situation often requires it. I'm pretty pleased with the IQ though.

01-08-2010, 08:52 AM   #9
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QuoteOriginally posted by dadipentak Quote
Thanks for the explanation, Lowell. I have the Tamron 1.4x which works with SDM and the AF 1.7x. In both cases, I shoot MF a lot anyway since the situation often requires it. I'm pretty pleased with the IQ though.
I chose not to comment on IQ because there are lots of different opinions on this point when using TCs.

I have found the SMC-F 1.7x AF TC to be excellent, as well, I have the same view of the sigma TCs, I only use my Sigma TCs on one lens, an origonal APO 70-200 F2,8 ED (Non DG Non Macro)

In my opinion, this is the best sigma 70-200 produced, but not all people share that opinion.
01-08-2010, 08:53 AM   #10
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I just picked up a $10 2x teleconverter at a local antique store, threw it on my 50mm f2 lens, and got these ice crystals on my windshield the other morning:


bigger version
01-08-2010, 11:17 AM   #11
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QuoteOriginally posted by eclipsed450 Quote
I just picked up a $10 2x teleconverter at a local antique store, threw it on my 50mm f2 lens, and got these ice crystals on my windshield the other morning: ]
That strikes me as an odd application but I can't argue with the results--very nice!
01-08-2010, 11:31 AM   #12
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QuoteOriginally posted by dadipentak Quote
That strikes me as an odd application but I can't argue with the results--very nice!
why an odd application?? thanks
01-08-2010, 12:14 PM   #13
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QuoteOriginally posted by eclipsed450 Quote
why an odd application?? thanks
Why use a TC r/t shoot with the 50mm alone?
01-08-2010, 12:21 PM   #14
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QuoteOriginally posted by dadipentak Quote
Why do you say that, Ash? I use TCs with my DA*300mm and have gotten decent results.
QuoteOriginally posted by dgaies Quote
Same here. My 1.4x works pretty well with both the DA*50-135 and DA*300.
Yes, I've seen a few as yourselves confirming TCs with 300s work fine. Point taken.
The OP is asking this question not to put on a 300, he has an 18-250, which the TC would struggle with also.

But as a general rule for a newbie I wouldn't recommend it on any other SDM/HSM zooms given their disappointing AF hunt and lack of focus locking at the long ends of zooms (50-135 and 70-200 comes to mind - both f/2.8). The long ends of the zooms is where it really matters.

I'm yet to hear someone testing out a TC with the 60-250... interested to hear how it fares at the long end...
01-08-2010, 12:24 PM   #15
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QuoteOriginally posted by dadipentak Quote
Why use a TC r/t shoot with the 50mm alone?
because i couldn't have focused that close with just the 50mm, the TC brought the lens closer without me having to move, giving a macro look...that picture i posted is uncropped...
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