EISCO Concave Mirror - 4" Dia, 150mm Focal Length - 3mm Thick - Glass Labs

It's great, I actually use it for a spin station, it's that perfect. That's actually why I bought it...LOL.

This mirror provides accurate reflections (considering its concavity).

I purchased to use as a beam spreader from a point source It works in that appication but certainly is not "defraction limited optics'. Took off one star as there is some form of de lamination in the outer edge.

The focal length was not to specification

Not worth it. Spend a few more dollars rather than waste your time.

Reflection is very uniform. I used this in class to demonstrate the kind of mirror used in reflector telescopes.

My friend has been complaining for years about how they don't make compact make-up mirrors big enough to do her whole face. When I saw this I got an idea so I ordered this mirror. This is a good quality mirror for this purpose though I would not recommend it say for a telescope mirror. But one would not expect it to be used for that I don't think. The edges are kind of sharpish as one might expect so I took some emery cloth and sanded the edges smooth so my friend does not cut herself. But then I thought it might be nice to add a frame so I put my wood working skills to work and made a backing and cover for this along with a hinge. I covered the cover in satin to make it match her things which are basically all pink. This will be a Christmas gift and I almost can't wait to see the look on her face when she sees what this is now. I am so happy that the seller has offered this for sale. I had no idea these existed until I saw it. I highly recommend this for any occasion when you need a mirror that will magnify and you don't need more than a 4 inch diameter.

Reviewing this mirror became a science experiment. My child and I tried to find a way to test the focal length without looking anything up. We placed the mirror face up on the floor. Turned on phone camera and flashlight function. We aimed the phone to keep the light centered in the image as best we could as we raised the camera further and further from the mirror. The light grew larger and larger till it filled the entire mirror. Kept pulling back and the light image got progressively smaller, revealing more of the camera phone body. The image had flipped. We tried to estimate the distance above the floor using common objects. The flip occurred slightly above the long edge of a notebook. Roughly 11" or 280mm. Much more than the 150mm in the description. So we removed one star from the review. As I said, we didn't look anything up and just went by intuition. We could have easily thought through the problem incorrectly. That is in fact pretty likely since our estimated result is very nearly double the expected result. Answering that question, "are we wrong?" is our next science task. Followed by "what is the best accuracy and precision with which we can measure focal length with the equipment we have at home?"