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Old Jan 21, 2010, 8:42 AM   #21
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Originally Posted by ac.smith View Post
I guess I'll enter the fray.

....
4. .... A used prime telephoto of the same resulting focal length would likely give better results.

A. C.
I've two principal purposes for pursuing this:
  1. To prove a point for myself & demonstrate it to others.
  2. To find a cost & weight effective alternative to lugging a fast long lens.
Otherwise you are likely correct.

Last edited by newarts; Jan 21, 2010 at 8:53 AM.
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Old Jan 21, 2010, 7:43 PM   #22
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I own some excellent teleconverters. They degrade the image.

I've used them with a tripod, and gotten some decent results. The teleconverters I refer to are NOT front mounted. I know of no front mounted teleconverter that can match the quality of mine. My opinion of teleconverters in general, is that they are better than nothing. If you own a SLR camera, and you Need, absolutely need the extra reach, than fork over the money for a decent one.

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Old Jan 21, 2010, 9:12 PM   #23
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The question to keep in mind is "Is the increase in maginification of the image enough to overcome the image degradation of the extra glass?"
IOW, can you get a sufficiently large image with T/C with better quality than you could by resizing?

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Old Jan 22, 2010, 7:44 AM   #24
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The question to keep in mind is "Is the increase in maginification of the image enough to overcome the image degradation of the extra glass?"
IOW, can you get a sufficiently large image with T/C with better quality than you could by resizing?

brian
In fact, that's what I'm testing. Here's a test result comparing a sharpness test of a good Pentax-f 50mm lens bare at f:4 & with nikon TC-15ED and Olympus B-300.

The Nikon gave good results. Unfortunately, the diameter of the Nikon TC-15ED is smaller than required for low light loss use on a longer primary lens. That's why I'm taking a chance on a high quality, large diameter, afocal adapter.

I suspect a Nikon TC-E17ED would be excellent but don't want to spend that much for a single test (they typically sell for about $450 now.)

In other tests I have found that a good behind-the-lens TC (kenko Pz-AF 1.5X SHQ) with a good Pentax-DA 55-300mm @300:5.8 gives results no better than simply enlarging the photo taken without it.

I should receive the Minolta ACT-100 TC soon. I'll test it carefully and let you know the results.

Dave
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Old Jan 22, 2010, 6:22 PM   #25
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In fact, that's what I'm testing. Here's a test result comparing a sharpness test of a good Pentax-f 50mm lens bare at f:4 & with nikon TC-15ED and Olympus B-300.

The Nikon gave good results. Unfortunately, the diameter of the Nikon TC-15ED is smaller than required for low light loss use on a longer primary lens. That's why I'm taking a chance on a high quality, large diameter, afocal adapter.

I suspect a Nikon TC-E17ED would be excellent but don't want to spend that much for a single test (they typically sell for about $450 now.)

In other tests I have found that a good behind-the-lens TC (kenko Pz-AF 1.5X SHQ) with a good Pentax-DA 55-300mm @300:5.8 gives results no better than simply enlarging the photo taken without it.

I should receive the Minolta ACT-100 TC soon. I'll test it carefully and let you know the results.

Dave
An odd choice of test images. This is an optical illusion (at least on my monitor).

However I took hundreds of pictures of a colony of Cormorants from about 1/2 a mile both with and without a good teleconvertert (Nikon TC 201) and without a doubt far more detail was resolved with the teleconverter than without it.

Dave
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Old Jan 30, 2010, 5:44 PM   #26
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I purchased a good Konica-Minolta 1.5x front type teleconverter for testing. It is a large, heavy piece of glass with a front lens about 75mm in diameter. The rear of the adapter has a 49mm filter thread.

I tried it with both a 300mm lens on a Pentax dslr and an 88,8mm (420mm equivalent) lens on a Panasonic bridge camera, FZ30.

Here are the results (all out-of-the-camera jpegs):

These were tripod mounted, mirror up shots, IS off.

The TC helps the Panasonic bridge camera at full zoom but degrades the Pentax dslr at full zoom.

It is very difficult to focus the Pentax Zoom lens I used with the ACT-100 attached because the TC is so heavy, perhaps the results would be better with a strictly internal focus lens (the Panasonic's lens is internal focus.)

It both cases there was little light loss, about 20% as expected; about 1/4 stop.

So this TC is not useful for my non-IF 300mm zoom, but does a good job of extending the effective range of my Panasonic FZ30.

Dave

Last edited by newarts; Jan 30, 2010 at 5:47 PM.
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Old Jan 30, 2010, 6:32 PM   #27
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What does "enlarged to ..." mean? How did you get 450mm out of the K100D and DA 55-300?
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Old Jan 30, 2010, 6:51 PM   #28
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What does "enlarged to ..." mean? How did you get 450mm out of the K100D and DA 55-300?

The photo on the left had a 1.5X TC (ACT-100) on the front of a fully zoomed Pentax DA 55-300, increasing its focal length to 450mm. What you see is a screen grab of the out of the camera shot displayed in about a 9x7 Picasa frame.

The photo to its right is a screen grab (same format) of the same scene taken with the bare 300mm lens & subsequently enlarged (on edit: zoomed using Picasa) so the images are the same size on the display.

Dave

Last edited by newarts; Jan 30, 2010 at 8:05 PM.
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Old Jan 30, 2010, 7:46 PM   #29
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I'd hesitiate to call that a rigorous test. Optically enlarging the image will produce different results than a software enlargement, and cropping from a resized image isn't a very good tool for comparison. (See Why a resized photo is no use in showing camera quality )
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Old Jan 30, 2010, 8:04 PM   #30
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I'd hesitiate to call that a rigorous test. Optically enlarging the image will produce different results than a software enlargement, and cropping from a resized image isn't a very good tool for comparison. (See Why a resized photo is no use in showing camera quality )
Besides this, in the first photo comparison, the image on the left is clearly out of focus...

Can't resolve detail with an image that's out of focus and compare it to an in focus shot.

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