Author Topic: Tele Converter  (Read 432 times)

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Offline BrianNZ

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Tele Converter
« on: August 08, 2017, 01:53:18 AM »
Hi guys, am considering getting a 2 X teleconverter, but have a few doubts as to how good they will be.    My main concern is  i have a sony SAL70400G lens which is what i am looking to use the teleconverter with,  however if i understand the website information, it says the two are compatible but only in manual mode. I guess this means i cant auto focus on BIF pics.  Does anyone use a converter, and how do they find it.
Sony A700, Sony A77, CZ 2.8/24-70, Sony 4.5-5.6/11-18, Sony G 4-5.6/70-400SSM, HVL-F56AM

Offline AScot

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Re: Tele Converter
« Reply #1 on: August 08, 2017, 05:25:14 AM »
I have both the Minolta white converters, x1.4 and x2. They are only compatible with the white lenses as the rear element sticks out too far for all other lenses. However they are rated the best TCs for these lenses. The x1.4 Is great and I seldom use my x2 as the quality impact, although quite small, bugs me.

Here is some information I copied from a website (years ago) that is no longer in existence. It covers all types of convertors.

Tele-converter Guide:

Tele-convertors can be an excellent way to increase the range of a telephoto or zoom lens, at relatively little financial cost. There is however a price to be paid for using them. That price is a reduction in image quality. This is a guide that tries to help you to minimize that loss in IQ.

Tele-converters come mostly in 1.4x and 2x versions, with a few 1.5x, 1.7x and 3x. I will ignore the 3x TCs as they are not very practical. Any user of a TC or potential user of a TC will want to know how good or bad a particular TC is when used with a particular lens, Prior to making a purchasing decision. In other words, how much quality loss can one get by adding a particular TC to a lens.

The short answer is from 5-10% loss to 20-30% quality lost depending on the following factors:

1) OEM Matched or Dedicated TC (between 5-10%)
Minolta APO, KM APO or Sony APO or Sigma EX

2) Pro series TC (Kenko Pro 300, Pro 300 DG or Tamron SP) (5-15%)
Image quality will always be better than generic TCs

3) 1.4X  = 5-10%,  2X =  10-20%
1.4X TC will always give better image quality than 2X

4) F stop being used (Wide open vs. Stop down)
    Shooting stopped down will always yield better image quality than shooting wide open. This is especially critical for a lens that has better performance when stopped down.

5) MC7 (7 Elements) vs. MC4 (4 Elements)
     7 Element TCs in most cases will give better image quality than 4 Element versions.

6) Prime vs. Zoom.
     Using a prime lens will in most cases yield a better image quality than a zoom lens.

7) AF vs. MF
     The TC and lens combination may not be able to AF if the lenses maximum aperture at it’s longest focal length is greater than F4.5 when using a 1.4x TC or F5.6 for a 2x TC.

In practice a 1.4x TC will add 1 stop to a lens. An f2.8 lens will become f4 and will AF. An f4 lens will become f5.6 and should AF. An f5.6 lens will become an f 8 lens and may not AF although it often does in good light. It will certainly hunt a lot and may not lock in poor light.

A 2x TC will add 2 stop to a lens. An f2.8 lens will become f5.6 and should AF. An f4 lens will become f8 and in theory should not AF although it often does in good light. It will certainly Hunt in poor light and may not lock focus. Much will depend on the quality of the lens.

The above factors or combination of factors will directly affect the image quality.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.

Offline Faldrax

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Re: Tele Converter
« Reply #2 on: August 08, 2017, 09:48:54 AM »
I would advise against combining a 2x TC with a zoom, even a very good one like the 70-400G.

The loss of IQ, loss of AF, and loss of 2 stops mean you will very likely be better off simply cropping instead.

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Offline AScot

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Re: Tele Converter
« Reply #3 on: August 08, 2017, 05:44:35 PM »
I did say it was from years ago. :D It is just basic information that is generally still true.

In my opinion the 70-400G is a very good lens but no better at 300mm than my 300G prime and I am not fully happy using the x2 TC with it due to a mild loss of IQ and sometimes, although not always, loss of AF at f8. That said you should know that using any TC has a price to pay in quality and it is up to the individual to decide what they can tolerate. The biggest factor, in all of this, is what TC you buy. I would say that for the 70-400G you should get a matched x2 from Sony, although I'm not sure if they make one for your lens. If not then the Kenko Pro were the next best x2 back when I last checked. I had a Tamron 7 Element x2 and took it back. A x1.4 is not anywhere near as problematic.
Sony A7, A850, A77, A700 || Sony>> 70-300G, 28-75 f2.8 SAM, 16-80CZ, 50 f1.4, FE 28-70 OSS, FE 24-70CZ f4 OSS, LA-EA4 || Minolta>> 300 f4 G HS, 200 f2.8 G HS, 100 f2.8 (D) Macro, 50 f1.7, 28 f2.8, 28-135 f4-4.5, 70-210 f4, 500 f8 Reflex, TC x 1.4 HS, TC x 2 HS. || Sigma 21-35 f3.5-4.2. || Tamron SP 24-135.

Offline BrianNZ

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Re: Tele Converter
« Reply #4 on: August 09, 2017, 01:09:27 AM »
hi guys - the sony 2 x is listed as being compatible with the 70400 lens - but only in manual mode.  perhaps the reason why is explained in A Scots post.   From what i am hearing and reading it could be i would be better off with the 1.4X  and cropping,  both for the reasons lens would still work in autofocus (although how much slower it would be is a bit of a guess) and less loss of quality (hope im correct in my thinking there)
Sony A700, Sony A77, CZ 2.8/24-70, Sony 4.5-5.6/11-18, Sony G 4-5.6/70-400SSM, HVL-F56AM

Offline chappo1

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Re: Tele Converter
« Reply #5 on: August 09, 2017, 04:11:28 AM »
I have the 1.4 Kenko teleplus pro 300.  I tried it for a while but decided the gain was minor.  I have pretty much given up chasing birds in the wild as the weight of the gear was too much for my shoulders.....john
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