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08-13-2010, 06:12 AM   #1
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Telecoverter compatibility & telephoto zoom help

Hi
Im not *majorly* into telephoto photography (i think my wallet is happy with that aspect of the LBA) but want some capabilities for longer zoom shots, beyond the 18-250 travel lens.

Ive just got an FA 100-300 on its way to me for fairly cheap, and was even toying with the idea of the Sigma 150-500 which surprisingly, my local camera shop has in stock for Pentax, and at a decent price, but had read things about some Teleconverter incompatibility issues with some longer lenses.

Can someone give any tips or point me to some resource for help?

I realised that on my recent holiday, i definitely couldve done with a longer FL lens - the crocodiles and moon rise werent enough with only the 100mm Macro.

Thanks in advance!

08-13-2010, 06:48 AM   #2
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All Pentax teleconverters should be compatible with your teles. The old converters specifically designed for a small number of lenses are the 1.4x-L and 2.0x-L.

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08-13-2010, 06:58 AM   #3
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OK thanks.

I had read somewhere that I wouldnt be able to use TCs with the sigma 150-500 specificially.
08-13-2010, 07:32 AM   #4
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Note also

SIGMA teleconverters are slimiar to the pentax ones that adam mentioned.

SIgma TCs require a 35mm diameter 12mm deep recess of the rear element in the lens because the front element of the TC protrudes from the TC.

the pentax ones are worse, but the issue is the same.

As a result, sigma TCs only work on a small number of long and fast sigma and pentax lenses.

the current production lenses the TCs will work with are listed on sigma's site.

I have posted in the past somewhere the list of compatible lenses that came as a printed sheet with each of my sigma TCs, the two lists (sigma site) and my list, are different

08-13-2010, 06:58 PM   #5
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QuoteOriginally posted by Lowell Goudge Quote
Note also
As a result, sigma TCs only work on a small number of long and fast sigma and pentax lenses.
ok, now im really confused

and what specifically is a 'rear converter' TC? if anyone can help!
(you can see i never bothered with TCs in the past!)
08-13-2010, 09:02 PM   #6
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QuoteOriginally posted by JayR Quote
ok, now im really confused

and what specifically is a 'rear converter' TC? if anyone can help!
(you can see i never bothered with TCs in the past!)
Rear converter = Tele converter. It is a set of optics that attach to the rear (camera end) of the lens, as opposed to those attachments that go on the front of the lens. The front converters are less than satisfactory when used on DSLR bodies.

Some rear converters will not physically fit to a given lens, which is what Lowell was pointing out. For example, the Pentax 1.4X-S and 2X-S converters are intended for lenses shorter than about 300 mm focal length. The Pentax 1.4X-L and 2X-L are for use with lenses over 300mm. The catch is, that both the -L converters protrude past the lens mount. I cannot use them with my M 400 because the throat of the lens is not wide enough to allow the protrusion to enter the lens, and must make do with the 1.4X-S, and that is not optically ideal.

There are other lenses that have a throat that is large enough, but the length of the protrusion will cause the converter to bump into the rear lens element, which is close to the lens mount.

I hope this clears up some of the fog for you.
08-14-2010, 07:55 PM   #7
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Thanks for all the info

I guess its just a case of trying to work out which lenses will/wont work with certain TCs, or more importantly trying to find the info on incompatible combinations!
08-14-2010, 11:41 PM   #8
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Since you mentioned the Sigma 150-500....

I don't know about the FA 100-300, but the Sigma 150-500 does NOT autofocus with any of the TCs.

In addition, the Sigma 150-500, at least the version I have, is only so-so IQ-wise at 500mm (there's no reason to use a TC at any other focal length), adding a TC will make its IQ even worse. I'd rather use the lens by itself and crop during post-processing.

08-15-2010, 05:15 AM   #9
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As I posted above the sigma site has a compatibility list of lenses and it's tcs

With respect to AF note that any combination of lens and TC that takes the maximum aperture below F7 will not AF there is just not enough light
08-24-2010, 07:37 AM   #10
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Is there any resource to work out what pentax or non-pentax converters work with whichever lenses? that sigma site seems mostly sigma related as you'd expect, and the pentax TCs here only seem to be compatible with primes.

any recommendations for specific models? ive heard something good about tamrom TC 1.4 ??? and kenko?

apologies, i dont know a TC from Adam.
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