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Old Jun 7, 2009, 10:40 AM   #1
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Default Old Screw Mount used with 50D

Years ago I bought many Takumar screw mount lenses for my Pentax cameras. It would be great to use them on a 50D I am considering. I know that auto functions will go away and image size might be a bit off but they are still fine lenses. Does someone currently manufacture a viable adaptor? Thanks - - Bill
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Old Jun 7, 2009, 7:09 PM   #2
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OK - I found reference to a "Bower" EOS to screw mount adaptor. Given its low cost I will certainly try it but does anyone know how such an adapter will affect performance. For example, will focus track with a zoom lens?
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Old Jun 7, 2009, 9:49 PM   #3
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Quote:
Originally Posted by 1080pla View Post
...will focus track with a zoom lens
With such an adapter there will be absolutely no automation of any kind.

1. There will be no autofocus of any kind
2. The camera can't set the aperture
3. The camera can't close the aperture when the shutter is fired

This last issue means that when you set f/8 you view at f/8. You, not the camera, has to manually open the lens to maximum aperture to view and focus and then manually stop down to the working aperture before taking the picture. With Takumars you generally have an A/M switch that makes this easy. With some lenses, you may not be able to stop down at all and will be forced to shoot only at maximum aperture unless this adapter is one that has a plate to push, and hold, the stopdown pin in when the lens is mounted. This would override the A/M switch on those lenses that have one and force you to use the f/stop ring to open and close the aperture.

I'm not sure what you mean by "focus track with zoom lenses". The camera can do nothing for you as far as focusing. If you are refering to refocusing when you zoom to correct for lenses that are really varifocals (focus shifts when zoomed) rather than true zooms (focus remains constant when zoomed) then no the camera can no longer "track" for you. Classic MF zooms will almost always hold focus when zoomed. The few that didn't were marketed as "varifocals" rather than zooms. Today, many so called zooms are actually varifocals that shift focus when the FL is changed and rely on the AF system to correct for the shift.
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Old Jun 8, 2009, 11:12 PM   #4
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I use a 500mm manual lens on my DSLR for mostly for wildlife. It is a bit of a pain, but the images are worth it. There are quite a few M42 adapters made for various cameras, Canon being one of them. Some have "chips" built in to tell the camera that a lens is mounted. There are also adapters for other lens types available. I have an adapter that allows me to use my old Minolta MD extension tubes, bellows and lenses on EOS bodies.

You won't find much difference than the old "match the needle" metering of the Spotmatic except for the lack of automatic "Stop Down". I forget that at times and end up with real off exposures .

Phil
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Old Jun 11, 2009, 12:00 PM   #5
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Regarding the focus issue, I was looking for assurance that the adaptor would preserve the original ability of the lens, mounted to the Pentax, to hold or track focus over the entire zoom range. The concern was that the adapter might not be able to hold the lens at the correct position relative to the sensor. Based on responses, I expect no problems. Thank you.
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Old Jun 11, 2009, 12:14 PM   #6
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Phil,

So far I haven't seen an adaptor with "chips" but I'll be looking. I expect to find that using manual lenses will be a pain but I hate not to use the old favorites. Also, I would bet they're still pretty good by todays standards. Thanks for your input. - - Bill
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