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Old Feb 4, 2009, 10:12 AM   #1
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I have a K100D super and have recently got a 75-300mm 35mm telephoto lens so (460 on dslr).

Would a 2x teleconvertor work with this lens I am photography wildlife in daylight.

Any experience out there.

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Old Feb 4, 2009, 11:53 AM   #2
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A 2X teleconverter adds 2 f-stops to the maximum aperture of a lens. If your 75-300mm lens has a maximum aperture of f/4-5.6, it becomes f/8-11, so it won't autofocus. You'll also need to use shutter speeds that are 4 times slower.

Just so you know.
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Old Feb 4, 2009, 7:04 PM   #3
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Gary Smith wrote:
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I have a K100D super and have recently got a 75-300mm 35mm telephoto lens so (460 on dslr).

Would a 2x teleconvertor work with this lens I am photography wildlife in daylight.

Any experience out there.

reasons Cost.!
I'll assume that your lens has a max aperture of f5.6 at 300mm (most lenses of this type do) If you get a 1.4x AF TC, you'll only lose 1 stop of light, so the AF system should still work, but probably only in pretty good light. The Pentax AF system is rated to f8, and I've found this to be pretty accurate. A 1.4x would give you 420mm f8, and though AF will probably work, since you'd be pretty much at the limit, you might not find AF performance that satisfying.

The most common 1.4x AF TCs are the Tamron F AF TC, the Sigma EX1.4x APO AF TC, and the Kenko Teleplus 1.5x AF TC. These are the only Auto Focusing TCs that I would feel comfortable recommending. I've heard that the Tamron was a rebadge of the Kenko despite the different magnification specs, but I'm still not sure of this. The Sigma is definitely built better -- very solid -- but it also costs about 2x what the Tamrons and Kenkos sold for. The Tamrons have gotten scarce lately, and the prices have gone up. I've seen used Kenkos being offered pretty reasonably at KEH.

I have both the Tamron F 1.4x AF TC and the Sigma 1.4x APO AF TC, and they are both optically similar, and pretty good. I don't own any AF 2x TCs, and probably won't. . . The optical performance has not impressed me from the little that I have seen.

Two more TCs are notable. The discontinued Pentax F 1.7x Auto Focusing Adapter is a very unique piece that, in addition to being a very good 1.7x TC, adds a focusing group in the TC, so it effectively makes a manual focus lens a limited auto focus lens -- with longer focal lengths, you need to get the focus point of the lens close, and then the 1.7x AFA will auto focus from there. This sounds complicated, but with some experience, it can actually be faster than a normal AF lens. These AFAs have gotten very expensive on the used market in the last two years, and now command anywhere from $300-600 USD on the used market. The other Pentax TC to look for would be the announced but yet-to-be released 1.4x SDM TC. I expect it to be optically superior to any of the 1.4x AF TCs available currently or in the past, but also expect it to be more expensive.

Scott

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Old Feb 5, 2009, 11:13 AM   #4
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Other than the OEMs, only Sigma and Kenko make teleconverters. And Sigma teleconverters are 'Matched' so they only work with a few lenses. [See http://www.sigma-photo.co.jp/english...ondaitr.htm#05]

Kenko also makes Matched TCs (Pro 300)that Tamron resells (as SP).

All other teleconverters are made by Kenko, and are generic, so they can be used with any lens (mount permitting.)

The Kenko 1.5X TC is their SHQ (Super High Quality) that is also available under other brand names, but the 1.4X is more common.
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Old Feb 16, 2009, 6:21 AM   #5
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My squirrel with a 75 300 vivitar and a 2x convertor through double glazing



any thoughts
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Old Feb 16, 2009, 6:38 AM   #6
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I was concerned about the effect of TC's on image quality, but after using my pentax 1.7 with my DA*300 I'm very happy.

Simon
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Old Feb 16, 2009, 9:31 AM   #7
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I second what Simon and Scott said above about the Pentax 1.7x .

Also use of 2x TC is not recommended at all as I have hardly seen other successful sample images

As it is very confusing to know which TC works with the SDM motors of Pentax (with additional power contacts), I have compiled the following so far:

Tamron 1.4x Pz-AF MC4 AF works. SDM no re Brad (photo.net)

Tamron-F Pz-AF MC4 1.4x both SDM & AF works for DA*300mm re Dave (photo.net)

Tamron-F Pz-AF MC4 1.4x both SDM & AF works for DA*300mm as per Toshi, moderator of Pentaxforums.com.

Kenko DG Pz-AF 1.5x TELEPLUS MC no AF no SDM on DA*300mm re Dave (photo.net)

Kenko DG Pz-AF 1.5x TELEPLUS MC AF works on older AF lens re Dave (photo.net)

Kenko Pz-AF 1.5X TELEPLUS MC only AF works; SDM no as per jgredline of Pentaxforums.com

Kenko Pz-AF 1.5x TELEPLUS SHQ both AF & SDM works for DA*200mm and all older AF lens re Daniel

Kenko Pz-AF 1.5x TELEPLUS SHQ both AF & SDM works for DA*300mm re Borno (Tom) of Pentaxforums.com ….SDM hunts a bit with DA*300mm



Daniel
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Old Feb 16, 2009, 10:37 AM   #8
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Gary Smith wrote:
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My squirrel with a 75 300 vivitar and a 2x convertor through double glazing



any thoughts
That is not a level of detail I would be happy with. Unfortunately you introduced a new variable - "through double glazing". So, it's impossible to tell how much of the results are due to the TC and how much to the window. Both will certainly degrade image quality.
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Old Feb 16, 2009, 6:16 PM   #9
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Gary Smith wrote:
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My squirrel with a 75 300 vivitar and a 2x convertor through double glazing



any thoughts
Remember that digital photography is a process. The better straight from the camera the better the photo will be, but if something happens then post processing can help it out. The double glazed window causes many reflections that can be helped, but do not count on perfection this way. A TC with a good lens can help but a longer focal length with out a TC is better. Just one old man's opinion.

Dawg
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Old Feb 16, 2009, 6:56 PM   #10
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Conversely, here's a sample of a squirrel taken with a sigma 70-200 2.8 and TC (and no window). In general, TCs on top of consumer lenses don't do well. But in the end all that matters is getting results you yourself are satisfied with:


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