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Old Apr 8, 2007, 9:36 PM   #1
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I have been lookingat 50mm prime lenses on eBay, but there seems to be quite a few different ones available.

Auto -It appears that there are some that have auto focus and auto aperature, then some lack auto focus and some lack both. Can I tell by the model number or something on the lens if a particular lens has any auto features or not?

Mount - How can I identiify whether or not the lens will fit on my camera? I believe that anything with a K mount will fit. BTW, what is a screw mount? I assume that this type will work with the help of an adapter, but even if this is true, are these types even worth looking at?

Is there anything else I should be aware of?
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Old Apr 9, 2007, 12:35 AM   #2
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There have been a number of posts on this so I'd suggest you do a bit of searching. There are also web pages full of information on this topic.

If you're only talking about Pentax brand lenses it's usually not to difficult to determine what it'll do if you have the right information, but it can get tricky with off brand lenses. Here are some basics:

Any screw mount lens can be used with an adapter, but no matter what kind of lens it is it will only operate as a fully manual lens, doing nothing automatically.

All K-mount lenses will fit the camera. This is also sometimes referred to as PK mount and is a bayonet type mount (though not all bayonet mounts will fit). If the lens is Pentax brand, it should work fine with any features it was designed with. Most off brand K mount lenses will work fine, but there are a few to look out for where the lens could get stuck on the camera body and be very difficult to remove. That's something you might want to research. Not all off brand lenses will work as they were intended either. I have a Sears "auto" lens that doesn't do anything automatically.

With Pentax brand lenses, M lenses are manual, A lenses are fully automatic except for the focus, and F and FA lenses do everything automatically. Asahi and Takumar lenses are also Pentax brand lenses and will work fine, but as far as I know all will be fully manual. Many of them will be screw mount though.
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Old Apr 9, 2007, 12:36 AM   #3
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Contriver wrote:
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Auto -It appears that there are some that have auto focus and auto aperature, then some lack auto focus and some lack both. Can I tell by the model number or something on the lens if a particular lens has any auto features or not?
You can tell if a lens has the auto apperature by looking at the apperature ring. If it has an "A" setting, then it can be used in Auto apperature mode.

You can tell if the lens can be used in autofocus mode by looking at the mount end of the lens. It will have what looks like a flathead screw on one side of the lens.

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Mount - How can I identiify whether or not the lens will fit on my camera? I believe that anything with a K mount will fit.
Yes, this is correct.

Quote:
BTW, what is a screw mount? I assume that this type will work with the help of an adapter, but even if this is true, are these types even worth looking at?
These are older lenses, and you may or may not want to look at them. I don't have any in my collection, so I can't comment on how they function.

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Is there anything else I should be aware of?
I would suggest looking at the mount information here:

http://www.bdimitrov.de/kmp/technolo...unt/index.html

If you look at the pages for each of the variations of the K-mount, you'll get an idea of what the contacts and mechanical devices on the mount end of the lense actually do. This can be helpful in figuring out what a lens can do.

Paul
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Old Apr 9, 2007, 1:28 AM   #4
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Did you happen to miss this very recent... post/thread
http://www.stevesforums.com/forums/v...mp;forum_id=94
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Old Apr 9, 2007, 8:50 AM   #5
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Thats for your replies guys, thats a big help!

Also, what about shutter speed...does the cameraalways set this automatically no matter which lens I use?
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Old Apr 9, 2007, 9:03 AM   #6
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Is this lens fully manual? (Its a smc Pentax-A 50mm)

http://cgi.ebay.com/Pentax-A-SMC-1-1...QQcmdZViewItem
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Old Apr 9, 2007, 10:16 AM   #7
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Contriver wrote:
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Thats for your replies guys, thats a big help!

Also, what about shutter speed...does the cameraalways set this automatically no matter which lens I use?
Yes, shutter speed is controlled through the body. It is not a function of the lens.

Paul
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Old Apr 9, 2007, 10:19 AM   #8
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Contriver wrote:
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Is this lens fully manual? (Its a smc Pentax-A 50mm)

http://cgi.ebay.com/Pentax-A-SMC-1-1...QQcmdZViewItem
The setting isn't shown in the picture, but it should have an "A" setting on the apperature ring, so it can be used in auto-apperature mode.

It is a manual focus lens.

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Old Apr 9, 2007, 3:33 PM   #9
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Contriver wrote:
Quote:
Thats for your replies guys, thats a big help!

Also, what about shutter speed...does the cameraalways set this automatically no matter which lens I use?
With a screw mount lens, you can set the camera to aperture priority and while you set the aperture on the lens, the camera will automatically adjust the shutter speed. The drawback is having to look through the lens already stopped down which can get pretty dim.

With a K-mount lens, if it's not an A, F, or FA lens, it's not quite automatic. You set the aperture on the lens but it won't stop down. This allows you to look through the lens at it's brightest. Because it doesn't stop down, the camera doesn't know what shutter speed to use. You have to press the AE-L button and the camera will stop down the lens and then set the shutter speed. You have to do that every time the lighting condition changes. Unfortunately, there's no way to get it to operate like a screw mount lens which can sometimes be easier or quicker.

That A lens you mentioned will operate the same way until you turn the aperture ring to "A", then it will be fully automatic except for focusing. I have that lens and highly recommend it, if you don't mind manually focusing. The camera does help you out a bit. When you focus the lens with the shutter button half pressed, the camera will beep and flash focus points in the viewfinder to let you know if something's in focus. Just be sure the camera is set to MF. In AF, the camera will not let you take any photos unles it thinks the focus is good, but I don't think the focus assist will be active.
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Old Apr 9, 2007, 4:49 PM   #10
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Corpsy wrote:
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With a K-mount lens, if it's not an A, F, or FA lens, it's not quite automatic. You set the aperture on the lens but it won't stop down. This allows you to look through the lens at it's brightest. Because it doesn't stop down, the camera doesn't know what shutter speed to use. You have to press the AE-L button and the camera will stop down the lens and then set the shutter speed. You have to do that every time the lighting condition changes. Unfortunately, there's no way to get it to operate like a screw mount lens which can sometimes be easier or quicker.
At least on the K10D, the camera will ONLY stop down a manual apperature K-mount lens, or an auto apperature one not set to the A setting, in M mode. In M (manual exposure mode) you can meter the exposure yourself using the DOF switch (the third setting on the on/off switch). In apperature priority mode, the camera uses these lenses wide open.

I thought the other Pentax DSLRs work in the same fashion with respect to lenses with the apperature ring set to something other than A, but I could be mistaken.

Paul
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