Used Glass Awareness

With the release of the RED ONE camera, buying used lenses has become a very common practice. I am writing this guide in order to help buyers be more aware of the potential risks and adversity. One of the most frequently investigated sources for used glass is the internet. With the vast collection of lenses on Ebay, Craigslist, Pennysaver, and other sellers, glass has come from every corner of the globe and is now being auctioned for what seems like a great deal.

I receive several phone calls and emails a week asking to review a handful of pictures presenting a lens from any of the said sources and decide if the lens is worth buying. I cannot stress enough, the lack of capacity to judge the quality of a precision optical instrument from a one dimensional photo. Your average online auctioneer uses their brand new Sony Cybershot that takes “amazing photos at a zillion megapixels” (I won’t blather about my detest of the megapixel balderdash) The common and inaccurate method of showing a lens for sale is to photograph the front and rear glass in an attempt to parade the condition of the elements. However, this does not provide any certification that the optics or mechanics are in good working order.

There are two major categories to consider when a purchasing optics for your camera or any motion picture camera for that matter. Neither is more important than the other and both can effect each other equally.

1. Optical
2. Mechanical

-Optical Quality-
Several threads in this forum have been circulated where someone has posted pictures of lenses that they are reviewing for purchase and would like to hear what others have to say. As I said before, this is not a particularly astute method of determining the value of a lens.

Here is an example I have used before on this forum. This is a photo of a LOMO zoom lens, similar in style to those taken by your average auctioneer. From this point of view the lens appears to be completely clear of any defects, dust, or flaws in the optics. The rear of the lens is pointing towards an open door casting bright sunlight all the way through each element…
(****The photo used here was removed from flickr and cannot be recovered, it WAS a lens showing what appeared to be a flawless, clean optical path with no scratches, oil, or blemishes.****)

The next photos were taken immediately after the first photo. No changes were made to the lens at all. I simply adjusted the angle at which the photo was taken and using reflected light to reveal the true nature of this poor piece of optical misfortune. This lens was used up until the time humidity got the best of it. You can clearly see the oil residue that spread from the lubrication in the focus section, onto the inner elements. This lens would not produce an acceptable image at all and should not be sold unless this nasty flaw was disclosed beforehand.

This is just one example. A few other questions to ask about optical quality:

• Axial alignment – Does the lens flare more in one direction that others?
• Tracking – When zooming from tele to wide, does the image float?
• Variation – Are all the elements secured in their proper positions?
• Repetition – When racking focus, do the marks repeat the same from either direction?
• Collimation – Does the image land precisely on the film plane?
• Accuracy – Are the focus marks accurate? (also collimation/mechanical)
• Contamination – Are the optics free of dust, lint, debris, moisture, oil, haze, etc.?
• Defects – Are there any chips or scratches on any of the elements?
• Coating – Are there any blemishes or imperfections in the coating?
• Fungus – Are there any signs of fungus, minor or severe?

All of these aspects are very important and none of them can be assessed by looking at a quick snapshot taken at a deceiving angle. The only way to truly determine the optical quality is by having the lens in your hands, looking at it with an experienced eye.

-Mechanical Quality-
Just as important as optical quality and twice the opportunity for mishap. Motion picture lenses are designed to endure consistent, specific internal movements over and over again for a seemingly endless amount of time. Unfortunately, if something disrupts these actions, a series of distress occurs. Different lens manufacturers use varying methods to achieve movements of internal groups. For example; some lenses use a simple helical to move glass elements back and fourth to obtain accurate focus while some models utilize a cam to execute similar maneuvers. These different methods each have their own potential complications. Helical threads can easily wear over time leaving space between metal that results in unwanted movement and inaccuracy in the focus. Cam followers can become worn out or develop flat spots that give rise to lost motion and inconsistency.

Here is a quick illustration I made showing how focus threads can wear.

My point is, nothing lasts forever. Modern lenses have become more reliable but far more extravagant in their construction. That doesn’t mean that older lenses are less complex, it simply means that they are far more likely to have been dropped, hit, disassembled and serviced improperly, or any number of potential catalysts.
Zoom lenses and prime lenses have many features in common to consider when inspecting for flaws. Basically, anything that applies to a zoom lens applies to a prime lens when it comes to assessment, just disregard any zoom specific features. A few mechanical traits to be aware of:

• Lubrication – Is the viscosity of the zoom, focus, and iris acceptable?
• Lost Motion – Does the zoom/focus scale move without any optical results?
• Barrel end play – Does the zoom/focus barrel shift back and forth, changing focus?
• Gears – Are there any defects in the zoom/focus gear that would interfere with a follow focus?
• Impact – Is there any sign of impact damage that may cause internal jamming or limitations?
• High spots – Are there certain areas of the zoom/focus that are harder to turn than others?
• Zoom creep – Does the zoom move by itself either from spring tension or gravity?
• Security – Are there any rings or parts that seem to be loose or shifted?
• Mount – Is the mount secured and in good, clean condition, free of dings or dents?
• Scale travel – Does the zoom/focus scale stop firmly at the end of travel both ways?
• Threads – (if applicable) Are the helix threads loose causing image shift or focus loss?
• Cam – (if applicable) Is the cam free of dents and is the follower secure and in proper form?
• Contamination – Is the zoom/focus free of grit from sand or other dirt?
• Engravings – Are the markings for the scales clean and legible?

Some of the above issues may not apply to certain models and some are negligible but may segway to far more serious problems. Again, none of these conditions can be determined from photographs or untrained, dishonest sellers who are just trying to make a quick buck. The ONLY way to buy a lens is to physically hold and inspect it. Build a relationship with a lens technician that you can trust and utilize the experience and skill offered by a professional.

Using photos to sell lenses online or in print is not a bad practice. It is extremely useful as an advertising tool and catches the attention of buyers instantly. Photos can be a reasonable means of evaluating the general exterior condition of a lens, but should never be considered whole or revealing. In the end, as a buyer, request a test period when purchasing a lens from any seller. Be it a national chain, specialty shop, or online auction, there is no reason not to provide adequate time for a lens to be properly evaluated. Of course this doesn’t mean you should expect every lens to be exemplary. In a perfect, honest world, lenses would still have flaws and will need servicing, but a seller would make note of any known issues and the established price would reflect such imperfections. I hope this little chaperone helps people avoid shady sellers and disappointing results. Like most of the lenses for sale on ebay, I’m not perfect 😉 So please feel free to add anything I might have left out.