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12-06-2009, 06:01 AM   #1
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advice needed from lens gurus

ok, i walk into a pawn shop while on a business trip 1000 miles from home without my k7. on the shelf i see a clearly labeled pentax lens with da, al, af, k, u2 and r2d2, etc. on the lens. i think i would know how to check for scratches but have never been instructed on how to check for fungus, oil on blades, snappy performance, etc. how would i be reasonably be sure that this lens is a good buy?
right beside this lens is an unmarked lens except for the label, 50mm f/1.2, with a serial number and "made in japan" on it. with the advice that you have previously given me i determine that this is a bargain lens but don't know if that little "thingy" is a bayonet mount or not or if this is a k mount lens that will work on my k7. is there a way to tell? i am a true newbie on this so please hold the flaming to a reasonable level. tia

12-06-2009, 06:11 AM   #2
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you need to look at the lens

there are not that many F1.2 50mmlenses around.

obviously if it says pentax or SMC on the front it is pentax.

but there are chinon and a few other K mounts.

the easiest way to tell is to ask for a known pentax lens and compare the mounts.
12-06-2009, 06:16 AM   #3
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If you're not sure how to look for fungus/haze/cleaning marks/oily blades, then have the lens held for you and get someone who does know what to look for. These things do matter significantly.

This more knowledgeable friend should also tell you what mount it is - or you can simply bring your camera in to try and mount it - be careful of how this is done to avoid the lens getting stuck on the camera's mount.

All the best.
12-06-2009, 11:10 AM   #4
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Shops like this will often have a Pentax K1000 film camera around. With a handful of exceptions, if a lens attaches nicely to a K1000, it is a K-mount. The exceptions are some third-party lenses with extended light shields, easily modified to fit if you accidentally get one of those.

An LED flashlight is good for looking inside a lens. If there is an aperture ring, set the aperture to its highest number, probably f22 or f32. You should be able to see the blades closed up to leave a small regular shape. The blades should be an even color, probably gray, with no splotches on them. You can move the aperture lever and the blades should respond. Move the lever so the blades disappear, then release it, and the blades should snap back instantly. Anything else and you'll probably have to take the lens apart to fix it. The aperture ring should click at each number and the blades should move about the same amount each time.

Fungus, element separation, haze, marks and scratches are all visible stuff on the glass. It's not necessary to determine which problem it is; you probably don't want that lens. A few dust particles are no big deal. Ask the shop guy to remove dust on the outer elements. The focus and zoom rings should turn smoothly through their ranges with even effort.

Next, you want to know what the lens will function like on your camera. Pentax-brand lenses are simpler - fewer variations and exceptions. Lenses labeled just "SMC Pentax" or "SMC Pentax-M" are manual focus, and the camera body can't control the aperture or read focal length. "SMC Pentax-A" lenses have an "A" on the aperture ring, electrical contacts on the mount and are manual focus. The camera body can control the aperture. "SMC Pentax-F", "SMC Pentax-FA" or "SMC Pentax D-FA" lenses have those features, a screw-drive slot on the mount and are auto-focus. "SMC Pentax FA-J" or "SMC Pentax DA" lenses won't have an aperture ring. All of the autofocus lenses are at least 99% compatible with Pentax DSLRs, close enough not to worry about. The Pentax-A lenses can't autofocus and can't tell the camera their focal length, otherwise they're compatible.

If you're not sure what a lens is, you can check here or this site:

Pentax K-Mount Lenses and Lens Accessories

Look at the lens photos to get an idea of the typicallook for each series of lenses. A phone that can access the internet would be handy. Value depends a bit on what country you're in, the condition of the lens, caps, accessories, etc.

My general rules: I don't buy it if I don't know what it is. If it's broken, I need to know how to fix it before I can determine if it's worth buying.

12-06-2009, 11:23 AM   #5
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QuoteOriginally posted by Just1MoreDave Quote

Fungus, element separation, haze, marks and scratches are all visible stuff on the glass. It's not necessary to determine which problem it is; you probably don't want that lens. A few dust particles are no big deal.
Fungus is not always so readily apparent without close inspection of the inner elements. With the widest aperture engaged, look through the lens from rear to front at a strong light source, like a light bulb. If you see markings that look like spider web strands inside the lens, that is fungus.
12-06-2009, 01:40 PM   #6
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Original Poster
thanks for the replies and especially to just1moredave!

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