Summary: I have had this lens for a couple of days now and I like it a lot. Very smooth operation and build quality at a great price. If you use this in low light conditions you will need a tripod. The lens has no auto-focus or image stabilization, of course at this price I can't image anyone would expect it to. On a sunny day with a quick exposer you can ditch the tripod if you are quick at adjusting your focus.
Summary: I purchased this lens mainly for birding. It's built very well and I love the fast 6.3 focal ratio. The color and contrast is excellent. I've also used it for astrophotography with good results; very similar to an APO lens. It can be hand-held but you need a fast ISO and shutter speed. The depth of field is razor thin so it's going to be difficult to snap moving targets that are coming or going away from you while keeping them in focus.
Summary: I recently picked this lens up. It does have some issues as mentioned in other reviews. You pretty much have to shoot in full sun because it is fixed at f/6.3, but if you don't mind manual focus (I kind of like it actually) and you know how to use your gear with a reasonable level of proficiency then this is a VERY affordable alternative to name-brand lenses. You can see a shot I took with the Opteka 500 and compare it to one with the Canon 50mm f/1.8 here [...].
Summary: This is a simple lens. It has no auto-focus, variable zoom, or image stabilizer. You will need a good tripod most likely to accompany this lens. The picture quality is pretty good considering the price. I started taking pictures of birds after installing a bird feeder in my backyard. So most of the time it's predictable where the birds will end up (bird feeder).
Summary: I've used this twice in the month that I've had it, once to get some amazing pictures of the moon and again to get pictures of the space station going by. The space station is a little tricky but this lens will get a good shot if you know what you're doing. For the price, you can't beat it.
Summary: I am very pleased with this lens... it is better than I expected for the money I spent... it is not for action... you have to be pretty good at manual focus... Depth Of Field is very shallow... I have taken lots of pictures of birds on over cast days and they have come out really clear... Havent had a sunny day yet but I'm sure it will improve the already good quality of the pictures...
Summary: I just got this lens last week, for the money, or even at twice the cost you could not find a better 500mm lens (1000MM W/2x adapter). Very good quality mechanically. I'm using it on a Canon EOS T3, and the photos are very sharp with good color and almost zero chromatic aberration, even when using the 2x adapter at a 1000 MM.