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This guide is primarily intended to reduce the number of mistakes by people who do not devote much time for that or those who are new in this fascinating business.
Those who buy used lenses at the "flea market", usually cannot do the normal test because of dirt, dust, means poor lens conditions. Item which does not work will be dropped in to the garbage.
Professional and vintage lenses are bought by people who do not need an advice ... And that kind of things also expensive...
Thus, these recommendations are intended for the purchasing of not expensive lenses, with auto and manual focus produced in period of 1960 to 1990 with a price range of $30 - $300. For example, 95% lenses made in USSR fall into this category.
Autofocus lenses will be observed incompletely, since checking accuracy of auto focus - quite complicated and deserves a separate discussion. Those who still need such information may consult here.
In general, the process of acquisition of the lens can be divided into several steps.
Step One – Information is a key point
At this stage it is necessary to gather as much information as possible which will help to avoid mistakes and errors:
1. Complete and exact name of the lens.
You can get most of this information, having carefully observed the front image of the lens. For example:
Manufacturer - Olympus
Trade mark of the lens - M. Zuiko Digital
Focal length - 14-42mm
Maximum aperture - 1:3.5 - 5.6
Multicoating Availability - different lens manufacturer labels it differently, often "MC"
For USSR lenses - the first two digits of the serial number is the year of production.
Using this information you can find the description of this lens on the internet and it will help to determine the possible price range.
Bonus: a qualitative snapshot of the front of the lens often means serious vendor. Poor or unreadable picture suggests that seller does not know how to sell the lenses and most likely an amateur in this market.
2. Lens to camera interface (Lens mount system).
There are a few dozen lens mount systems used or are still using in the photography equipment. Since this issue is directly related to the flange type, it is important to understand what the lens mount for a particular lens is. In other words, we need to clarify the compatibility of a particular lens with and particular adapter, therefore, with a camera.
Third party manufacturers of lenses, such as Sigma, Tamron, Tokina, Samyang use nearly identical markings for lenses with completely different lens mount system / bayonets. If the lens mount system did not specified, the specialist may be helped by rear picture of the lens, but the rest of the people has only one way - to ask the seller ...
If you have questions about lens mount systems and about the flange - you need to consult here or here. You can also consult with the systems database of Lens-Club.
3. Autofocus and "auto" aperture
Autofocus (AF) by itself should not represent a problem, since AF lenses of 1960-1990 always had possibility to set the focus manually. Modern lenses have typically built in an electric drive and manual focusing is only possible with the "native" connection to the camera. It is enough information on the net about the compatibility of such lenses.
The "auto" aperture issue is a little bit more difficult. It is very important to know whether the lens aperture can be set up manually or not. There are number of lenses where aperture set up available using the "native" system only via body.
A good example is "Jupiter-9 automatic". The lens is specified for cameras Kiev-10 and Keiv-15, where the aperture set up was built in to the camera.
Indirect sign of the possibility or impossibility of the aperture set up is the number of rotating rings on the lens.
Presence of only one ring is almost always indicates that the aperture set up built in to the camera
So, having more or less complete answers and consulting a database of lenses Lens-club you can move on to the next step.
Step two – initial contact to seller
There is a several option how to check seller reputation. Nowadays almost everyone bought staff via internet, so it should not be described here. Anyway, the trial contact with the seller is very important. You should contact the seller with any, even small question or clarification. For example, if the price discussable or not. Answers like, "You an idiot, do not understand ..." speaks in itself, keep away from that seller. Any other response, quick response, etc. help you to understand the qualification and, to some extent, reliability of the seller.
Step Three – ordering.
If all answers are satisfied you - go ahead; order the lens or make an appointment with the seller.
Stage Four – testing.
So you've got the lens in hand. We must remember that during meeting usually not much time assigned to test. I do not believe that anyone would agree to do a test for two or three hours.
So the priority of test – is to identify defects, malfunction of the lens, means distinguish unworkable lens.
1. External visual inspection
First of all - ask to remove the covers and a protective filter. Sometimes, when the lens had not used long time, filter "take a strong liking" and remove it is impossible.
Small dents, minor scratches - all traces of the lens usage should not cause concern - this is normal.You need to pay attention to the strong dents (especially on the edges) although, again, even the presence of such defects does not mean that the lens is defective.
It is also necessary to note the presence of disassembly traces - whipped slots screws. See photos.
Again, this in itself is not terrible, but you can ask the seller, who, and for what purpose disassembled the lens.
You can also shake the lens - any strong knock should alert, inside the lenses all are usually fixed firmly.
2. Check the focusing mechanism
To check the focusing mechanism needs to rotate the focus ring from the minimum focusing distance (MDF) position to the opposite (infinity) position.
Marks on the focusing ring should match the marks to the body. If not - the lens was disassembled and re-assembled improperly.
Or infinity adjustment ring was pulled out.
Focusing ring by itself should rotate smoothly, without hesitation or sticking.
Overly tight focus can cause to improper focus, and loose – focus shift by any slight move.
3. Checking the aperture mechanism
The aperture test depends on the type of set up mechanism.
The easiest option (as for the Jupiter-8) without an auto-aperture mechanism or aperture pre-set mechanism - ring must scroll from fully open position (smallest f-number) to the closed position (heights f-number), thus it is necessary to observe that the diaphragm really opened - closed.
Lenses with aperture pre-set mechanism (Helios 44-3; Mir-1) tested as follow - pre-set ring should be set to the closed position (heights f-number). After that, second ring, which closes the aperture, should be rotated. Must observe that the aperture really opened - closed. It is also recommended to rotate the pre-set ring too - it should be rotated without any excessively effort.
Somehow it is more difficult to test the lens with auto-aperture mechanism. Auto-aperture mechanism - a mechanical device that leaves the lens aperture as open as possible (for easer focusing), and closes the aperture to a set f-stop simultaneously with shooting. Since auto-aperture mechanism should be associated with a camera for each mount system this mechanism is unique. The following are examples of auto-aperture mechanisms for M42 and Olympus OM systems.
In order to check the aperture of the lens, you need to pull a pin of auto-aperture mechanism to the closed position (see example above). Then rotate aperture ring from the open wide (smallest f-number) to closed (heights f-number) value. The diaphragm should opened-closed.
Or make a check in the opposite direction: set the aperture ring to the closed position (heights f-number) and then press the pin several times. Aperture must be closed and opened completely with no interruption.
IMPORTANT: sometimes (especially for Helios 44M-X) aperture mechanism starts to jam. When the ring is rotating from the "closed" to "open" position - diaphragm works. Rotating to the opposite direction – aperture blades stuck around f8 - f11 and fully closes only after a little shake-up. It is necessary to pay attention to that. It is a small but unpleasant defect.
4. Checking zoom.
The requirements are the same as for the focus ring - the rotation should be smooth and not too easy. Pump lenses - by itself should not fall out.
5. Checking the mount.
For this test, you must have the camera or the adapter.
The lens has to be fixed effortlessly and fixating at the end. If not - the lens may be defective.
On the example of the photo shows that the mount petal was bent, then straightened and slightly polished.
The lens also does not have to hang out in the fixture - the work with this lens will be impossible.
6. Lenses visual inspection.
As has been said many times, a small amount of dust on the lens is acceptable. The lens should not have any visible darkening when looking through the lens at a bright light source.
Cleanness of the rear element is much more important than the front element, so it is better to avoid buying a lens with a scratched or not clear rear element.
Minor surface scratches usually found on the front element, often do not affect the picture quality. Especially if appears on the edge of the lens. Deeper scratches should be checked by using the test images; especially it can be a sign of a severe blow. To leave a deep scratch on the glass, you need to make quite a lot of effort. The example below shows that a fairly strong scratch leaves no mark on the image. An enlarged zone approximates the defect area.
Here you can see an example of how truly scratched front element affects the picture quality.
When you are buying an older lens please take special care to look for fungus. When it visible it might looks like spider web. It is better to avoid buying such a lens either.
Actually there is impossible to determine the actual lens cleanness with no real shooting. For example, a layer of oil is invisible, but the picture will be blurred.
So, all was tested and looks good. It is time to make test pictures.
7. Test pictures shooting.
Since the time pictures shooting is limited, you should be prepared in advance.
Test number 1 – take a shoot of a contrast object (e.g., printed materials - newspapers, magazines, books – all that have large letters) from a distance of about two - three times longer than the minimum focus distance. It must be done in a good light condition, with short enough shutter speed. Or, for reliability, tripod and two second delay after shutter release can be used. At least two shots must be taken - at the fully open aperture and stopped down (one or two stops).
Because the test is for lens usability, pay attention to, above all, obvious defects such as double vision at open aperture in the photo below.
Usually sharpness increases from wide open aperture to stopped down. See the example below.
If it is not - this behavior should raise concern.
Naturally, if you have some experience, test shots can be taken accordingly to the lens specialization. Portrait lens should be testing buy taken the pictures of the human face. Small object to be photographed with macro lenses etc... In any case, it is good to have a plan in advance.
Test number 2 is for advanced users - shooting a pointed source of light.
Shooting conditions: set the lens focus to the minimum focus distance, open wide aperture and shoot a point source of light (the best - LED) from a distance of approximately ten times greater than the minimum focal distance.
The picture should represent perfect circles in the center of the frame, and possibly reduced (kind of ovals) in the edge.
Any irregularity in illumination of these circles or deformed circle may indicate a lens defect. Here is an example, as a scratch on the front element, which in principle, does not impact the overall picture quality, can be easily detected by this test.
You have to understand that these tests are not applicable for all kind of lenses. For example, shooting of a point source of light by "fish-eye" lens is almost impossible. Therefore, it is good to be prepared. If you know which type of lens you will need to test - you can try to simulate it on existing lenses.
So, if all goes well and the lens work, we can move to the fifth step.
Step Five - lens is yours, go ahead, take pictures and create masterpieces!!!
P.S. I hope that dear sellers will take from this article useful information.
Here is a Russian version of the article