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01-22-2009, 05:44 PM   #1
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Help! Lens Buying 101, especially legacy lens

Hi,

I'm in the market to purchase some lenses, especially older Super Tak and other legacies. I'm trying to learn to be an astute buyer and would greatly anyone if they can clarify several issues for me and perhaps offer some guidance.

1. Fungus: How do I look for this? If a lens has fungus does it basically mean that it is a throw away lens?

2. Aperture blades well oiled. What does this mean and how does someone see/test this? Is it possible to have the blades re-oiled?

3. Do scratches on the glass or minor dust inside the elements matter? I see a lot of lens in that category but the seller typically posts pictures and says that it has no affect on IQ.

4. What is all this talk about a "good" copy? People say certain lenses are sharp or soft, can someone elaborate more?

5. Fast lens. What does that mean?

6. Are Pentax Limited lens the highest class lens Pentax has to offer?

7. Finally, what are the differences between lenses? Is it color rendition, sharpness, bokeh, focusing, etc?

Thanks in advance for all the help!

01-22-2009, 06:38 PM   #2
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I'll answer the first 3

QuoteOriginally posted by greenboy Quote
Hi,

I'm in the market to purchase some lenses, especially older Super Tak and other legacies. I'm trying to learn to be an astute buyer and would greatly anyone if they can clarify several issues for me and perhaps offer some guidance.

1. Fungus: How do I look for this? If a lens has fungus does it basically mean that it is a throw away lens?
Fungus often looks like a spiderweb, sometimes radiating from a single spot and sometimes from the edge of a lens. If left too long, fungus will damage the lens coatings, which are important for color, contrast and flare reduction. It's impossible to say how long is too long; the lens must be cleaned and inspected, which often means some disassembly. Most buyers prefer to avoid this entirely, which is the best idea. Most people who try to deal with fungus-infected lenses are doing it to try and salvage something out of a bad deal, not out of choice.

QuoteOriginally posted by greenboy Quote
2. Aperture blades well oiled. What does this mean and how does someone see/test this? Is it possible to have the blades re-oiled?
Aperture blades need to move really fast. On the camera, a K-mount lens will have its blades fully open until the shutter is pressed. Then the blades move to the selected aperture, the shutter opens, the image is recorded and the blades snap back to wide open. They are also very thin pieces of metal or plastic. If any kind of oil or moisture gets on them, they stick together and move very slowly. The oil needs to be cleaned before the lens is useful - more disassembly and work. The test is easy: set the aperture to a high number, the A position, or ignore this step on a lens with no aperture ring. Look at the blades and flick the aperture control lever on the lens mount. The blades should respond instantly. A little bit of oil causes them to return slowly. More oil and they also open slowly. At some point they get stuck.

On a screw-mount lens the oil doesn't matter as much, because the camera can't control the aperture directly. It doesn't need to move as fast. However, Takumar lenses rarely have oil on their blades anyway because of superior design. Some Russian M42 lenses have oiled blades right from the factory.

QuoteOriginally posted by greenboy Quote
3. Do scratches on the glass or minor dust inside the elements matter? I see a lot of lens in that category but the seller typically posts pictures and says that it has no affect on IQ.
It's a matter of degree. Most lenses will have some dust inside because they're not sealed. Focusing and zooming displace air, and the air carries dust. A little dust is OK, a lot of dust is bad. Sellers usually won't certify a lens is entirely dust-free, because they never are. In my experience, dust is an insignificant issue. Scratches are somewhat the same, small ones are not that bad, except they don't just happen. Scratches might indicate careless usage too. Swirly scratches on ther front element mean a bad cleaning job. Sometimes scratches are completely out of the frame.

At first, I would insist on a lens having none of these issues except maybe dust. There are enough good lenses out there to just keep looking. Leave the problems to experts.
01-22-2009, 06:49 PM   #3
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I'll take a few:

QuoteOriginally posted by greenboy Quote
4. What is all this talk about a "good" copy? People say certain lenses are sharp or soft, can someone elaborate more?
The terms mean exactly what you might think: images from a sharp lens have tons of detail; images from a soft lens look a little "fuzzy" in comparison. Usually, this is something people care about when comparing *different* lenses (eg, an FA50/1.4 and an M50/2). But it is possible even when comparing copies of the *same* lens (eg, two FA50/1.4's) for one to be sharper than another. It's not normally something you'd worry about, though.

QuoteQuote:
5. Fast lens. What does that mean?
A fast lens is one with a wide maximum aperture - eg, f/2.8 or larger (and remember, *smaller* f-numbers are larger apertures). These are called "fast" because a larger aperture allows a faster shutter speed. If you want to shoot in low light, a fast lens gives you a better chance at a shutter speed fast enough to avoid blur from camera shake or subject motion.

QuoteQuote:
6. Are Pentax Limited lens the highest class lens Pentax has to offer?
There is also the "*" series. Both are very high quality, but the Limited lenses emphasize small size and craftsmanship in the build of the lens along with high image quality perhaps at the expense of speed; the "* series lenses emphasize image quality and speed perhaps at the expense of size/weight. The modern "*" lenses are also weather sealed.

QuoteQuote:
7. Finally, what are the differences between lenses? Is it color rendition, sharpness, bokeh, focusing, etc?
All of the above. The only one that one can be somewhat objective about is sharpness - there are tests that can put a number on this, and some review sites will publish the results of such tests. But for the most part, lens evaluation is pretty subjective.
01-22-2009, 07:32 PM   #4
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.


Some thoughts in red.


QuoteOriginally posted by greenboy Quote
Hi,

I'm in the market to purchase some lenses, especially older Super Tak and other legacies. I'm trying to learn to be an astute buyer and would greatly anyone if they can clarify several issues for me and perhaps offer some guidance.

1. Fungus: How do I look for this? If a lens has fungus does it basically mean that it is a throw away lens?

It means that the resale value of the lens has dropped about 70% if the fungus is noticeable, but generally, the lens is still usable - just make sure you don't pay a lot for it. Take a look at This Thread, if it's a quality lens to start with, fungus doesn't kill the IQ.


2. Aperture blades well oiled. What does this mean and how does someone see/test this? Is it possible to have the blades re-oiled?

If they snap back & forth without any delay, they're sufficiently oiled. And yes, they can be re-oiled, but it's tricky - very easy to put too much oil on.


3. Do scratches on the glass or minor dust inside the elements matter? I see a lot of lens in that category but the seller typically posts pictures and says that it has no affect on IQ.

As Dave said, swirly cleaning marks are the worst. Little nicks often don't make any difference to the image, but affect the resale value of the lens.

4. What is all this talk about a "good" copy? People say certain lenses are sharp or soft, can someone elaborate more?

Sometimes QC (Quality Control) issues with the manufacturer can result in lenses having back or front focus issues. The K20D mitigates this a huge amount with focus adjustment, and the K10D has a debug procedure that can be used.


5. Fast lens. What does that mean?

Generally, any zoom that has a constant f/2.8 is very fast, constant f/4 is pretty fast. A prime lens (fixed focal length) with an f/2 max aperture is considered fast, and f/1.4 is very fast. f/1.2 is esoteric and expensive (and hard to focus wide-open.)

6. Are Pentax Limited lens the highest class lens Pentax has to offer?

Pretty much - they're smaller, have all-metal construction and the IQ is usually exceptional. Here's how I rate them: FA 77ltd, FA 31ltd, FA 43ltd, DA 70ltd, DA 40 & DA 21ltd (tied). (I have not owned the DA 70 & DA 21, judging by pics, reviews and reps.) But even the lowest-rated limited is wonderful. The reason I rate all the FA's higher is because they're faster and have better bokeh - the DA's are just as sharp and probably have just as good if not better color/contrast.

The DA* (and F*, FA* and M*) lines are top quality also, but are larger and include zooms.


7. Finally, what are the differences between lenses? Is it color rendition, sharpness, bokeh, focusing, etc?

This is what you will find out on your journey into the depths of LBA. It's why you're here. Have fun, and stay on the trail as much as possible.


Thanks in advance for all the help!





.


Last edited by jsherman999; 01-22-2009 at 07:44 PM.
01-23-2009, 11:44 PM   #5
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Thanks to everyone for their responses.

"7. Finally, what are the differences between lenses? Is it color rendition, sharpness, bokeh, focusing, etc?

This is what you will find out on your journey into the depths of LBA. It's why you're here. Have fun, and stay on the trail as much as possible. "

I guess that is what I really have to learn jsherman999. I saw your "dead lens" thread and the pictures you took with your fungus ridden lens look amazing. Sometimes I wonder what more can an expensive lens do? Do you know of any threads that have side by side comparisons of cheap lens vs expensive ones? Sometimes I just feel like it comes down to the skill of the photographer......
01-24-2009, 12:20 AM   #6
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A few more notes about fungus...It does not go away on its own and it is "contagious" and can spread to your other lenses. It is more prevalent in equipment from humid climates or where stored in a damp space. Fungus is particularly significant if present on the rear elements. In general, it can degrade sharpness and significantly reduce contrast.

Fungus may look like filaments with a fine "branching" pattern or like a radiating fuzzy "puff". The best way to see it is in a dimly-lit room with a narrow beam flashlight shown into the lens from the other side at an oblique angle. Pretty much everything inside the lens will jump out at you with this technique.

There is another thing that looks a little like fungus. If the cement fails between elements in a cemented group, the separation often takes on a branching appearance. This is an expensive repair if even possible.

In summary: Don't knowingly buy a lens with fungus. Always ask if fungus is present. Always inspect for fungus. Always return if supposedly free from and fungus is found (unless you paid little or nothing for the lens and are willing to risk disassembly to remove and disinfect).

Steve

Last edited by stevebrot; 01-24-2009 at 12:33 AM.
01-24-2009, 12:28 AM   #7
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Regarding oily blades:
  • Oil should never be visible on the iris blades, except as noted below. This is true even for the screw-mount lenses. The mechanism generally requires little or no lubrication.
  • A small amount of oil may be present or even necessary on manual aperture or preset aperture lenses. These include the popular Russian Jupiter-9, many long off-brand telephotos from the late '60s through the '70s, and many other vintage lenses. Even on these lenses, the blades should not appear wet.
  • The rule of thumb is that if the iris is expected to flick closed at exposure time, the blades should be oil free.
  • Oiling the aperture blades is not a part of normal equipment maintenance

Steve
01-24-2009, 12:29 AM   #8
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Big chunks of dust, big bugs, etc. in your lens will affect the rendition of the circles of confusion, in the same way the mirror in a mirror lens does:

Identifying Digital SLR dust location

01-24-2009, 12:31 AM   #9
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I want to add a bit on dust specs...

I may get some argument from the veterans... but from my experience, if it is a macro lens or any lens that you may need to stop way down to f16 and up, then dust on the rear element is not good. I have a macro lens with two dust spots on the back element and from about f16 on they are very obvious in every pic. I have yet to see any real effect from front element dust or scratches really...

With macro I need to stop way down to get more DOF and it is frustrating to have to clone out every time.
01-24-2009, 12:38 AM   #10
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Just can't quit...

A short note regarding scratches...Minor scratches on the front element usually have a minor affect. Any scratches on the rear element are significant. Always take special care to avoid damage to that rear element.

Steve
01-24-2009, 03:29 AM   #11
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QuoteQuote:
7. Finally, what are the differences between lenses? Is it color rendition, sharpness, bokeh, focusing, etc?
Browsing the Pentax lens reviews on this board will help understanding the various features.
01-24-2009, 06:49 AM   #12
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Another forum I was on, a fellow reported he was interested in buying a used lens. His agent in England inspected the glass by shining a flashlight through it and looking for defects that way.
He found a very serious defect that way (possibly a cracked or separated element) using this method. Apparently using a red filtered light can show up things we wouldn't see with a white light as well.
01-24-2009, 08:13 AM   #13
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QuoteOriginally posted by stevebrot Quote
A few more notes about fungus...It does not go away on its own and it is "contagious" and can spread to your other lenses. It is more prevalent in equipment from humid climates or where stored in a damp space.

Steve
2 out of three ain't bad. True, fungus won't go away on it's own. True, fungus happens in sufficiently damp/humid conditions. False, that fungus is "contagious" from lens to lens. Fungus spores are literally everywhere and it's moisture that's the enemy and is required for the spores to grow.

Say I'm in Florida or Hawaii or some other semi tropical location. It would be far worse to leave several lenses stored together without silica packets than it would be to store the same lenses, one with fungus, together with silica packets.

The group that was damp is the group that would "catch" fungus even in the absence of a fungus infected lens .

Regards,
Mike
01-24-2009, 09:14 AM   #14
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QuoteOriginally posted by X Man Quote
2 out of three ain't bad. True, fungus won't go away on it's own. True, fungus happens in sufficiently damp/humid conditions. False, that fungus is "contagious" from lens to lens. Fungus spores are literally everywhere and it's moisture that's the enemy and is required for the spores to grow.

Say I'm in Florida or Hawaii or some other semi tropical location. It would be far worse to leave several lenses stored together without silica packets than it would be to store the same lenses, one with fungus, together with silica packets.

The group that was damp is the group that would "catch" fungus even in the absence of a fungus infected lens .

Regards,
Mike
Not all molds and fungi will grow on the surface of a lens. Some will, some won't. For myself, I wouldn't take the risk. If a lens becomes infected with a spore that will propagate, the chances are that said infection can spread to other lenses, if not directly, then by secondary infection where the spore transfers to the camera body and then to subsequent lenses.
For me, it would have to be a very special and irreplaceable lens for me to keep around if it had a fungal infection, as it would have to be worth the cost of a total disassembly, cleaning and reassembly.
01-24-2009, 10:32 AM   #15
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Thanks for all the tips. They have been very helpful and educational. I have an old Steinheil 135mm on the way to me and hopefully it will be very clean.
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