>>3516143>the focal point was always INSIDE the lens.The the cheap Opteka mirror lenses are actually made so that you can twist their focus well past infinity. There's no hard stop at infinity that is. This allows you to use a ton of extension tubes or adapters and still be able to focus to infinity. It also allows use of various mount adapters to be used across various company's camera models. If the lens you speak of has a hard stop at infinity then that would be why you had the focal point inside the lens.
However, sometimes when you stack on tons of extension like that, the DOF can be extremely hard to find. There's a chance that was the case when you tried it. You may need to use a tripod, start a couple feet from the lens then very very slowly move it along the ground outside to see if the DOF is outside the lens. The DOF is already pretty narrow with mirror lenses and the extension makes it far worse making it much more difficult to spot at first. When I first tried extensions on my mirror lens, I also thought it couldn't be used and couldn't find the DOF.
My biggest gripe with mirror lenses is the fact that they are very difficult to focus perfectly. The focus indicator doesn't work with them and they are already so dim that seeing focus in the dim penta-mirror OVF is absurdly difficult. Using the LCD and zooming in a good bit helps, but isn't ideal. I don't have any LCD focus peaking/highlighting on the D3400 so that's out too.
Regardless, I like mine and almost exclusively use it for abstract stuff and getting to know local wildlife.
