Kenko 800mm& 500mm F8 DX

[bkj]

Kenko 800mm F8 DX

http://dc.watch.impress.co.jp/cda/parts/image_for_link/140130-8578-3-1.html
http://dc.watch.impress.co.jp/cda/parts/image_for_link/140132-8578-3-2.html

Kenko 500mm F8 DX

http://dc.watch.impress.co.jp/cda/parts/image_for_link/140134-8578-6-1.html
http://dc.watch.impress.co.jp/cda/parts/image_for_link/140136-8578-6-2.html

Too bad F8 could be too slow for most cameras to AF.

Cheers

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Nikon AF-S 18-200/3.5-5.6G VR
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Nikon AF 50/1.4D
Sigma AF 150/2.8 Macro

 

[nickleback]

Too bad F8 could be too slow for most cameras to AF.

The 800mm mirror should be able to, assuming it's an AF lens (which I doubt it is). However it should do fine with focus confirmation.

Mirror lenses use a larger physical aperture than than the focal length and aperture ratio would suggest. The reason for this is that there's a big black spot in the middle which reduces the effective exposure. If they just sized the diameter for f/8, exposure wise it would be 2/3 of a stop under. Not a problem with auto exposure camerasSo they add 2/3 of a stop in diamter. That means the light is coming in at up to f/6.3. That's close enough to f/5.6 to light up the AF sensor (third party lens makers do this all the time).

Minolta/Sony has an AF 500mm f/8 mirror lens.

http://en.wikipedia.org/wiki/Minolta_AF_500mm_Reflex_lens

And in case you don't believe me, 500/6.3 = 79mm. According to the specs on the linked page, the front filter size is 82mm.

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Fear is the darkroom where negatives are developed

 

[JanneM]

Neither support AF - manual focus only.

Also, Kenko offers dedicated 2x teleconverters for both lenses, making them 1000mm and 1600mm respectively.

The 500mm should be somewhat interesting for backpackers; at 600 grams it is probably the lightest non-mirror lens you could find with that kind of reach.

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Blog: http://janneinosaka.blogspot.com

 

[John W Peterson]

is this a kenko branded version of lens's already produced by third parties ?

The lens's look similar to some of the ebay and back-of-popphoto adds that I have seen over the years.

 

[JanneM]

is this a kenko branded version of lens's already produced by third
parties ?
The lens's look similar to some of the ebay and back-of-popphoto adds
that I have seen over the years.

AFAIK, both the 800mm mirror and the 500mm fixed aperture lens are new designs. They're stated to be specifically for APS-format cameras too, not 35mm.

As an aside, the design constraints on a mirror lens means they all tend to look pretty much the same. There's only so many ways you can style a fat can with a large opening and a small mirror in the middle.

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Pics: http://www.flickr.com/photos/jannem/
Blog: http://janneinosaka.blogspot.com

 

[luxor2]

This was an alternative way of making a 500 mm mirror lens. Very sharp, good for macro, no central mirror to reduce contrast, and no glass in the optic path, so UV and IR correction were superb. I had one, buy it was too slow for my film cameras. With a D300, etc, it would be a lot of fun.

http://www.macrolenses.de/ml_detail_sl.php?ObjektiveNr=293

 

[JanneM]

Now that was an interesting design. How was the blur characteristics? The major drawback of mirror lenses is usually the rather distracting donut-shaped out of focus highlights. I guess the patent is the reason nobody else has bothered with the design.

Not that the box design is a major improvement from an esthetic standpoint...

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Pics: http://www.flickr.com/photos/jannem/
Blog: http://janneinosaka.blogspot.com

 

[nickleback]

I guess the patent is the
reason nobody else has bothered with the design.

Looking at the lens and guessing it was made in the '70s, the patent must have expired.

--
Seen in a fortune cookie:
Fear is the darkroom where negatives are developed

 

[Ken Phillips]

Even if the central obstruction (astro term) is 1/3 the diameter, the obstruction occults just over 11% of the light!
KP

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I don't believe in fate, but I do believe in f/8!

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