Tips on Choosing an Used Lens

1. Lens should never has mould inside, check whether there is any sign of mould or fungus on the glass. 

~ Mold is a type of fungus that grows on lens. Early sign of mold is a white dot spot on the lens element. It is hard to detect on early stage unless you are experience with it. Heavy growth of mold will form a spider web like on the lens elements, hence is easier for you to notice. Mold grows on lens element is feed by the coating on the lens surfaces, thus having mold on a lens means that the coating is probably has been eaten partly by the mold, hence affecting the photo delivery quality of the lens.

2. Check the coating of the lens, make sure the coating is still on and perfectly laying on the lens. Cleaning process will wash away the coating, thus avoid cleaning lens too often. 

~ besides mold, inexperience user will sometimes scratches or clean away the coating of a lens with poor cleaning technique. Hence, it is advisable to check the coating of the lens at angles (around 45 degrees).

3. Check the lens mount and make sure it is not cracked. If the lens is being used by professional, there should be sign of heavy use on the lens mount. Consumer lens has plastic lens mount, so it is more fragile. For AF lenses especially Nikkor, check the electronic contacts of the lens. I have seen some lenses with cracks on the electronic contacts.

4. Check for dust, or any particle inside the lens. Look into the lens near and far and go to a bright place to check. If the shop is not bright enough, ask the permission to bring the lens outside the shop to check. Always bring a torch light yourself for checking if possible. My personal preference is a yellow light torch light.

~ Almost every lenses that I have seen have dust inside. Minor dust will not affect the picture quality of the lens, but heavy dust or big particle especially in the center of a lens might. Don't mistake fungus with dust...they are very alike in the early stage.

5. Check the aperture ring. Turn the ring to make sure that it clicks perfectly at every aperture. Most AF lenses have loose aperture ring, manual lenses will have a better click. So, if a manual lens has a very loose click, most probably it means it has been used extensively or something not right. Check the aperture blade too when checking the aperture right. Make sure the aperture blades open and close smoothly with NO OIL on it. If you saw some shinny residual on the aperture blade, check closely with a torch light if it is oil.

~ Oil will make the aperture blades sticky and making it not closing/opening up in actual operation, hence resulting in under/over exposed photo. Cleaning/changing aperture blades can be very expensive. Nikon AF 35mm f/2D lens is known to have this problem.  

6. Turn the focusing ring, make sure the ring turns smoothly with no sand or particle in between. If the lens is a zoom lens, check the zoom ring as well. 

~ If you heard the scratching sound when turning the focusing and zooming ring...most probably it means there are some sand in between and the lens has been brought to a sandy environment. Those sand might get into the lens element soon and drop on top of the glasses, hence affecting the picture quality. Worse, it might jam your focusing/zooming ring.

7. Check the filter thread, you wouldn't want a lens that can't fix your filter...you can also use this to bargain down the price if you are not going to use filter on the lens. 

~ Some users when mounting/dismounting a lens in rush might damage the filter ring of a lens. Most lenses nowadays comes with a plastic filter ring, thus it can be easily over-thread by the metal ring of our filter. Also, do take note if there is any uneven round diameter of the filter ring, it might be due to impact damage (drop/knock of the lens). This will make screwing filter impossible or difficult.

8. AFS/VR or USM/IS

~ As the advancement of technology, lenses are getting more and more complicated. When purchasing an used lens with AFS/VR or USM/IS, make sure you test them properly on a camera body. You can't tell the fault of AFS/USM/VR/IS with naked eyes, as these are all electronic parts inside the lens. Do not hesitate to ask the owner questions if you are unsure of the performance/operation of the lens. Do your homework by reading reviews/instruction manual online before meeting up with the seller. Take your time to test/try out the lens. Repairing an AFS/VR or USM/IS motor can be very expensive.

9. Mount the lens on a camera (preferably your own camera, so that you can test all the functions of the lens). Focus from infinity to closest focusing distance. Make sure it can lock into focus confidently and precisely. Point the lens up and down vertically, check for any zoom creep.

~ With the convenient of DSLR, you can test the actual performance of a lens before buying. My standard recommended testing method is "Angle Ruler Test". This test is also important in making sure that the lens is not having back-focus or front-focus with your camera.

~ Zoom creep is referring to a zoom lens that "auto-zoom" when pointing upward or downward. This is due to the heavy front element of the lens or heavy usage that has wear out the resistance in the lens. A fairly new lens should not have zoom creep problem. Most push pull lenses are well-known of this, but if you are fine with it...then it is no big deal.

Last, try to ask for the original box, manual, and warranty card. This gives credit to your lens if you decide to sell it next time.

Nikkor lens has good resale value compare to other brands. In the used market, there are plenty of good quality Nikkor lens. If you are searching for a used lens or want to part your Nikkor lens, this link might help or you can check out ShaShinKi.com Used Products section.

Happy $hopping!