>>3499141Those are dirt cheap. It will start to fail around 2 years. The slider where knob tightens down on the rail will be the first thing to go. Piece of its internals will slip out between the slider and the rail. If you don't put them back in "because they fell out in grass and were lost" then the slider will eventually start making a grove where the knob tightens directly onto the rail then. It isn't a huge issue, but it will make quick adjustments clunkier, that is all. Only get bellows that have metal mounting rings. Same goes for extension tubes. The cheap ones have a type of plastic, for the mounting ring that likes to snap off rather easily. That issue will only happen if you are really using it a lot. Like nearly every day or 3 times a week. Otherwise, it may last you many more years if you don't move it much.
Also, both bellows and extension tubes sometimes use a tiny screw to stop a lens when you twist it onto the mount. Often times, that screw will fall out. If that happens, they the lens can turn and turn instead of stopping. A drop of loctite for screws fixes that issue.
I've had no other issues with those. With my dirt cheap 4-way rail the assembly inside the slider fell apart and made it useless. I had to JB Weld things back into correct order for it to work right.
>>3499150>>3499167It depends on the lens. You can calculate it here with one of these calculators:
http://extreme-macro.co.uk/calculators/>>3499146>>3499148You can get bellows with contacts, they are just expensive. They are easy enough to diy, if the aperture is also electronic on the lens.
