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Old Aug 10, 2006, 1:09 PM   #1
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I was thinking we should discuss buying used lenses. There are lots of new people around here who don't have a 35mm background, or others like me who up until last weekend never really thought about the mechanics of lenses.

As I found out last weekend, there is more to evaluating a used lens than just seeing if there are scratches on the lens, and if the twisty things move.

Here's what I've come up with as far as how to evaluate a lens, and also have a couple of questions. I'd love to have others here chime in and say what they look at/do to lenses when they are buying.
  1. Look at both front and back glass for scratches. [/*]
  2. Work the aperture ring to see if it twists easily. [/*]
  3. Look through the lens and watch to make sure the lens is capable of stopping down (problem with my father's old Kiron lens!). [/*]
  4. See if the lever will stop down the lens and release it. [/*]
  5. While you are doing that, check to see if the light going through the lens is clear, not obscured in any way. [/*]
  6. Make sure that zoom functions correctly (either push-pull or twist type - my dead F70-210 zoom mechanism broke so it would only twist a bit). [/*]
  7. Look at the outside for any signs of dings, wear, fungus or???[/*]
Now my questions:

How do you evaluate focus? Is the only way to put it on a camera?

What is the best way to see/evaluate the leaves (is that what you call them?) of the aperture mechanism? Should you use a pen light to shine on the elements?

I don't know that I've ever seen fungus on a lens, and unless it was blocking the glass, not sure I'd know how to spot it. What else do you look for?

What difference does "brassing" (I think that's the term I saw on KEH's website) make as far as the operation of the lens- if it means what I think it means, that the black on the outside of the lens has been rubbed off in places. I can understand being concerned about scrapes and bumps on the outside because that could mean something inside is not working. But is there some other reason to be concerned about the outside condition?
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Old Aug 10, 2006, 1:57 PM   #2
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mtngal wrote:
How do you evaluate focus? Is the only way to put it on a camera?
Yes, I think so.

I don't know that I've ever seen fungus on a lens, and unless it was blocking the glass, not sure I'd know how to spot it. What else do you look for?
Fungus will be obvious (I have an old Tokina 80-200mm with some fungus in it. it will be white-ish spots with a diameter of about 1-3mm inside the lens glass. Sometimes it will interfere with your images, sometimes it wont. I make it a rule: it's ok if you get the lens for free, otherwise find a better one.
Problem with fungus is that it will probably expand...so when I see "minor fungus marks" in an auction, that's an instant "no deal" for me.

Also look for Dust inside the lens...very hard to get out and might interfere with your images.
As a general rule: if there's something inside the lens (behind the glass), don't bother and look for another one.

Something else you can look for is zoom creep. This happens often with a push-pull zoom. Hold the lens vertically up or down, and see if the zoom ring slides on its own.
While zoom creep won't affect the image quality at all, it can be annoying when walking around...

Great idea starting this topic

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Old Aug 10, 2006, 2:37 PM   #3
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Agree, Very useful thread particularly for those of us without much experience....

Apologies if these sites are already well known but I found this ebay site a good starting point.


This one was had some interesting opinions on old lens'

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Old Aug 10, 2006, 5:08 PM   #4
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Hi mtngal,

A very good thread idea indeed.

A couple of additional points :

Aperture blades movement must be both smooth and fast -- if the blades move even a bit sluggishly, this will cause exposure problems, as the mechanism in the body will not be able to stop the lens down in the very short amount of time needed for an exposure.
This isn't an insurmountable problem, most likely caused by thickened lubricant on the blades, and can be cured by a CLA (clean, lubricate & adjust) by a good lens tech, but the cost of this ($100 or less) must be considered in the purchase price.

Some site-specific advice -- KEH is usually 1-2 grades conservative in their grading (the lenses are usually 1-2 grades BETTER than stated). For my purposes (shooting as opposed to collecting), BGN and above have been very satisfactory. I stay away from the UGLY graded lenses, as they probably have some significant issues, but YMMV. This is a great source with ultimately fair pricing IMO, but for the premium lenses, you have to be very fast -- any hesitation at all and it'll be gone.

B&H used lenses -- I'd stick with lenses graded 9 and above -- I bought an 8+ FA80-320, and the zoom ring action was beyond what I'd consider just annoying.

Other sites which might help in deciding optical quality of older lenses are:

Photodo: MTF tests of some Pentax and 3rd party lenses -- a little dated, but recently changed with new owners -- seems a little harder to use than before, but they're updating regularly, and there are user reviews being included.

Photozone: User supplied reviews of Pentax and 3rd party lenses. A little hard to evaluate sometimes, but you can get a good idea of how the particular lens has been regarded.
http://www.photozone.de/active/survey/surveyform.jsp?filter=%22brand='Pentax'%20OR%20bra nd='Sigma%20AF'%20OR%20brand='Tamron%20AF'%20or%20 brand='Tokina%20AF'%20or%20brand='Vivitar%20AF'%22 &title='Pentax%20mount'

SPLOSdb: Site compiled by J Cowell. A bit dated, but great info on older Pentax and 3rd party lenses for Pentaxes. You can download the DB and view it, alter it, or add to it with your own spreadsheet program. The rating system he uses has been accurate for me, and is generally well regarded.

Fred Miranda: I use this site to check out 3rd party lenses only -- user reviews can be a little haughty, but I think that you can get a good idea of the relative quality of Tokina, Sigma, and Tamron lenses from them.

I use any and all of these sites to get an idea of whic lenses I'd like to try to obtain, and which ones I'd rather stay away from.

Hope this helps someone


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Old Aug 10, 2006, 8:19 PM   #5
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Given my recent experience with having to go through three (3) different 80-320mm lenses to get one I could use:

Does it communicate correctly with your camera body. (Of course, this requires actually mounting it on said body.)

Larry in Dallas
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Old Aug 10, 2006, 8:40 PM   #6
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Hi Larry,

I assume your post referred to nime -- It actually is a problem with the zoom ring -- at the short end it's fine, but "sticktion" (it gets really hard to turn, and rotates in little jerks instead of smoothly) is a real problem at the long end, where I tend to use it the most. I have heard of more than one case of this happening with this lens (though probably not as severe as mine). Otherwise, the lens functions as it should, and I still use it on occasion when I want that range of FLs in one lens, but don't anticipate using the zoom that much.

The point is that it came that way as an 8+ rated lens from B&H, and I thought that their rating was a little high, IMO.
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Old Aug 10, 2006, 9:38 PM   #7
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mild amounts of fungus posses little fault to quality images. if you hold the lens up to the a light, ck the perimeter of both front and rear lens. it will be apparent. most of my older lenses from new orleans have a small amount of fungal damage. if you find it , it's easy to kill any that's active by setting the lens on aluminum foil around noon time for the sun to shine thru it for 3-4 hours. the UV will kill any that is still active. i sold a lens to ira, an A70-210, with a bit of fungal damage in it, actually with more than any of mine had. i had ckecked the lens out comparing it to images of my 70-210 and found no difference at any aperture.i told him about it and told him i'd refund his shipping back to me if he was not 100% happy with the lens.. how about it ira??? was the lens worth 45usd???

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