Best 40mm M Mount Lens
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Related Faq
Q
What kind of aa batteries can be used? there are rechargeable nickel-zinc that are 1.6v but hold their charge longer. if not these, what's recommended
A
The camea can take 1.6v rechargeable batteries, but in general rechargeable battery might drop its voltage quick depend on its physical performance. In the cold weather, recommend using Energize lithium batteries to get longer lifetime. 
Q
What lens hood will work for this filter?
A
I have the 77mm version of this and I am NOT able to use a lens hood on my Canon 17-40mm wide angle once the filter is on. I haven't tried putting on the hood first and then trying to screw on the filter yet. That's not to say that all lens hoods won't work but for me it does not under the scenario described above. 
Q
Will this work on my sony a6000 and tokina minolta 100-300mm macro zoom?
A
Yes 
Q
Too loose/there is gap between lens and adapter ring
A
  1. If there is ever any more than a slight amount of rotational play, you may want to try tightening the lens mount adapter so it will hold the lens tighter to the mount. There are 3 flanges in the middle of the adapter (what the lens locks onto) that are split open slightly, this gap is what gives the tension that holds the lens tight to the body. Over time and with use these gaps decrease in size, no longer pulling the lens tight to the adapter, which allows the lens to move inside the mount more than it should.
  2. To tighten the fit, get a slim metal object (a #1.5 or #2.0 small flat eyeglass screwdriver is ideal) and insert it into the slit to open it up just a little bit (see images below, make sure to do it to all 3 evenly). The more you open the gap, the tighter the lens will be to the adapter; too much and the lens will have a hard time mounting so make sure to do it just a little bit at a time to all 3 flanges evenly, it doesn’t take much at all to get a tight fit.Note: please do not use too much strength, or the shrapnel will be damaged.
 
Q
Is this suitable for sky gazing/ astronomy? Thank you.
A
I would say...a qualified "yes." You are going to have a nice wide field-of-view and sharp focus. The 40mm objectives are not going to allow a huge amount of light gathering but you will have portability and that counts for a lot - a light, sharp and accurate optic is more useful than a large and bulky choice. Even if that means giving up some "reach." 
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