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06-03-2012, 10:10 AM   #1
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Pentax K/M 49mm Adapter

I have this adapter I got in my grandfather's goodie bag...but I don't know what lenses it adapts to.
It reads Pentax K/M 49mm. Is that M-mount 49mm? Any good lenses that I can feed my LBA with using this adapter?
Thanks




06-03-2012, 10:36 AM   #2
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That looks like a mount-reversal ring. You would screw it only any lens (hopefully possessing an aperture ring) with a 49mm front thread, then mount it reversed for close work, like for shooting stuff about 45mm / <2in from the lens. This is a standard tool for macro shooting. Many lenses project images much better when reversed -- but only very close. The reversal itself doesn't gain magnification. Shall I tell you more about using it?
06-03-2012, 11:04 AM   #3
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QuoteOriginally posted by RioRico Quote
That looks like a mount-reversal ring. You would screw it only any lens (hopefully possessing an aperture ring) with a 49mm front thread, then mount it reversed for close work, like for shooting stuff about 45mm / <2in from the lens. This is a standard tool for macro shooting. Many lenses project images much better when reversed -- but only very close. The reversal itself doesn't gain magnification. Shall I tell you more about using it?
Oooh, thanks for the explanation
I am willing to listen to whatever you want to tell me thanks in advance
06-03-2012, 12:18 PM   #4
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First, some macro stuff: https://www.pentaxforums.com/forums/pentax-lens-articles/152336-cheap-macro-b...lose-work.html

Think of how a lens works, unreversed. You point it out at subjects. What it sees is the subject field. It projects that image onto the camera frame (film or sensor). What it projects is the image field. With SLR prime lenses, the image field is always a fixed distance from the back of the lens. That is the register, or flange-focal-distance. That frame is flat, and for it to see a usable image, the lens must project an image that is edge-to-edge flatfield sharp..

So what happens when a lens is reversed? The subject field is now seen by flatfield-sharp optics. The lens projects a not-quite-so-flat flat image to the frame -- but at so close a distance that field roundness is negligible. Result: very sharp image capture. But ONLY at the lens' register distance, which for Pentax PK/M42/M39 is 45.46mm.

So with a prime lens reversed (zooms work a little different -- see below) we get very sharp images taken very close. But magnification depends on extension, on moving the lens further from the frame. Suppose I have two 50mm lenses with nearly identical optics, one with a deep front inset (like my Meyer Primotar-E 50/3.5) and the other with a shallow inset (like my Industar 50-2 f/3.5). The Primotar's deep inset is like built-in extension; it magnifies more than the reversed Industar.

Reversed zooms can work at various distances depending on the focal length used. I'll reverse my A35-80, arguably the worst zoom Pentax ever made. Reversed, it's sharp. At 35mm its working distance is about 4-5cm. At 80mm, close-focus is about 15cm, and far-focus is past infinity. A true macro-zoom!

What this boils down to: To work close, reverse the lens. (It's best if the lens has an aperture ring, to make adjusting the aperture easier.) For more magnification, add extension. Simple PK macro tubes are real cheap, like under US$10 per set. This is about the cheapest way to bet into macro shooting. Have fun!


Last edited by RioRico; 06-03-2012 at 12:29 PM.
06-03-2012, 12:59 PM   #5
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QuoteOriginally posted by RioRico Quote
First, some macro stuff: https://www.pentaxforums.com/forums/pentax-lens-articles/152336-cheap-macro-b...lose-work.html

Think of how a lens works, unreversed. You point it out at subjects. What it sees is the subject field. It projects that image onto the camera frame (film or sensor). What it projects is the image field. With SLR prime lenses, the image field is always a fixed distance from the back of the lens. That is the register, or flange-focal-distance. That frame is flat, and for it to see a usable image, the lens must project an image that is edge-to-edge flatfield sharp..

So what happens when a lens is reversed? The subject field is now seen by flatfield-sharp optics. The lens projects a not-quite-so-flat flat image to the frame -- but at so close a distance that field roundness is negligible. Result: very sharp image capture. But ONLY at the lens' register distance, which for Pentax PK/M42/M39 is 45.46mm.

So with a prime lens reversed (zooms work a little different -- see below) we get very sharp images taken very close. But magnification depends on extension, on moving the lens further from the frame. Suppose I have two 50mm lenses with nearly identical optics, one with a deep front inset (like my Meyer Primotar-E 50/3.5) and the other with a shallow inset (like my Industar 50-2 f/3.5). The Primotar's deep inset is like built-in extension; it magnifies more than the reversed Industar.

Reversed zooms can work at various distances depending on the focal length used. I'll reverse my A35-80, arguably the worst zoom Pentax ever made. Reversed, it's sharp. At 35mm its working distance is about 4-5cm. At 80mm, close-focus is about 15cm, and far-focus is past infinity. A true macro-zoom!

What this boils down to: To work close, reverse the lens. (It's best if the lens has an aperture ring, to make adjusting the aperture easier.) For more magnification, add extension. Simple PK macro tubes are real cheap, like under US$10 per set. This is about the cheapest way to bet into macro shooting. Have fun!
Wow, awesome Great write up, next time I'm in NorCal drinks are on me!
06-03-2012, 02:56 PM   #6
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Here are some quick snaps I did with the reversing ring and some macro tubes










Here is my high dollar macro studio (cell phone pic)


06-03-2012, 03:38 PM   #7
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Ah, my blathering has not been in vain!
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