This blog is mostly about manual lenses which are usually 30 to 50 years old. And while most of them are surprisingly reliable the are a few things you should check before or after buying a lens.
This checklist is based on the experience I gained from buying more than a hundred lenses since I discovered how much fun it is to use them on Sony’s Alpha cameras.
If you have additional info about a defect not listed or disagree with my assessment please leave a comment!
Scratches on the lenses
Use a large light source like a window and place the lens between you and the light so that you can see the colorful coating of the lens.
Scratches are seldom a problem in the real world but they lower the resale value of a lens. In theory they could reduce the contrast of a lens or cause some flare but I have never seen that happen.
You can’t really do anything to restore coatings but it sometimes makes sense to fill larger scratches with black paint to avoid light scattering.
Oil on the aperture
Quite a few older lenses suffer from oil on the aperture blades. Close you aperture as far as possible and have a look at the aperture blades. They should be dry and free from oil. If they look like in the image above it is likely that they will open and close slowly.
Using a lens with an oily aperture on a mirrorless camera is not a problem because you meter and focus with the aperture already closed. I use the lens in the picture regularly.
On a classic SLR it will be a problem because the camera will meter and focus with the aperture opened and the aperture will be stopped down the moment you press the shutter button. But because the aperture is slow to close your images will be overexposed and and not stopped down as far as you wanted
It depends a lot on the lens but in general cleaning the aperture requires less skill than other repairs. Apertures are often quite easiy to access and you can clean them with Isopropyl alcohol (affiliate link). Optimally you clean the whole aperture assembly because that’s were the oil is coming from, just cleaning the visible part will only do in light cases.
But be careful to document every step of the dis-assembly and be warned that it is often hard to reassemble an aperture assembly once the aperture blades have been scattered over your carpet (I am speaking from experience 😉 ).
You will find dust in about any lens and unless there are huge amounts of it dust won’t affect your image quality.
You or a technican can open a lens, clean all the elements and reassemble it but I wouldn’t bother unless there are some defects like sticky lubricants.
Fungus isn’t always easy to see because it is inside the lens. You can easily spot it if you shine a flashlight trough the lens.
Fungus looks like many little roots which grow on the lens surfaces.
Here is an image I took with the same lens:
In my experience you still can use many lenses which are not too badly affected. They have a little less contrast but you wouldn’t notice it if you didn’t look for it.
Often fungus can be removed without any traces with a hydrogen peroxide solution but this requires quite a bit of skill and special tool because the lens has to be disassembled. Many repair centers don’t accept infected lenses.
There are certain fungi which damage the coatings or the lenses themselves so that a lens can’t be fully repaired.
According to Zeiss fungus will grow under these conditions:
- Relative humidity of at least 70% (more than 3 days)
- No or little airflow
- Nutrients (textile lint, traces of grease, varnish, dust and dirt)
- Temperatures between 10 and 35°C
So it is a very bad idea to store your lenses in your damp cellar. I store my lenses in a bright cabinet without front lens caps and while I have a few lenses with fungus it hasn’t grown in those or infected other lenses. If you live in a climate with very high humidity it could make sense to buy a climate-controlled cabinet.
The easiest way to detect de-centering is the church tower test (German site but I think it is self-explanatory. No lens is centered perfectly so if you look close enough any lens is decentered. But if you can see the difference between the corners at first sight this is a reason to return the lens.
I think de-centering in a wide-angle lens is more of a problem than with tele lenses but I would always try to return a decentered lens.
Re-calibrating a lens requires special tools and special equipment and not every lens can be re-calibrated (Samyang lenses for example). I think this operation is beyond the ability of almost any hobbyists and not many repair technicians do such repairs. If you know a good repair shop please leave a link in the comments.
The focusing ring does not turn smoothly
The focus ring is very hard to turn or doesn’t turn at all
This usually results from unstable lubricants and it can be fixed by a skilled technician who can remove the old and replace it with new lubricant.
The focus ring has some play
This can have different reasons, but it is often caused by dissolved bearings. Many Canon FD lenses are affected by this problem, for an incomplete list have a look at this thread from a German forum.
The focusing ring turns unevenly
This can happen if the lens fell to the ground or got knocked against something. I think it is quite hard to fix but most older lenses are surprisingly robust and this is unlikely to happen.
Some Lens Buying Advice
These are all the defects I have come across so far, there are a few others like lens separation or yellowing from radioactivity. The vast majority of the 100 or so manual lenses I have bought in the last 4 years were without issue and the last thing I want is to keep you from buying used lenses. Check out my Manual lenses on the Sony a7 beginners guide for more information.
If you are a first time buyer it might be a good idea to either buy locally and check the lens carefully or to pay a little more and buy online at a commercial seller who offers returns.
I buy most of my lenses at ebay from private selles. This is a bit more risky but the cheaper price outweights the risk for me and so far my experience has been a positive one with two exceptions which cost me about $60 together. I had to return a few lenses but this usually worked well.
- If the seller knows something about lenses he should mention that there are no scratches, a smooth focusing ring, no fungus and he should tell me how much the lens has been used.
- I get very catious if an item is sold “as is” and I don’t rely on the images too much. I can make a lens with many scratches on the lens look good and you won’t see fungus or a stiff focusing ring in an image
- Many sellers don’t know much about lenses when they sell grandpa’s old SLR, here I ask about scratches and a smooth focusing ring. It could also make sense to ask were the gear was stored, you wouldn’t want to buy a lens which has been stored in a dark and damp cellar because it is very likely that it has developed some fungus.
- Markus Keinaht’s DIY page with many many guides on fixing and modifying phot gear
- Matt Bierner lenss disassembly videos (thanks Jai)
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