Has anyone used Bower lenses?

I saw some Bower lenses on B&H. Has anyone used them? Is there any issues with them except the fact that they are manual focus? Does anyone find manual focus hard with the present line of Canon cameras?


Thanks

Many of their designs lack any sort of diaphragm control--that is to say, the lens has a fixed aperture, because they are catadioptric (mirror lenses), which means they will also exhibit significantly lower contrast. They are also less sharp because they use low-cost optics.


So right there, you have a few major drawbacks:

1. Loss of variable f-number, meaning you lose one dimension of adjusting exposure and cannot control DOF
   
2. Loss of contrast due to mirror design
3. Loss of sharpness due to cheap optics.

Additionally, there are a few minor drawbacks:

1. Annular (donut) bokeh.
2. Low light-gathering ability, making focusing difficult.

There are a few advantages, though:

1. Extremely long focal lengths possible
   
2. Light weight
3. Low cost.

The result of all of the above? Think of mirror lenses as Lensbabies for the birding crowd. They can be useful, but are best when purchased with expectations appropriate to this type and quality of lens.