Originally posted by wildman My calculations may be way off but this is more the direction I want to go.
I'm thinking more along the lines of a telescope. There is no telling what will work, but in theory, compared to what you would see in a camera , it could go as far as 57,600mm f16 (theoretical maximum with that parts I have or will have and you could go further). Yes that reads 57,600mm. The only unknown is if a barlow lens as I have no idea if they cause light loss. Of course I do not need anywhere near that magnification, even for looking at stars and faster might be better. From what I gather (mentioned in a forum anyway) f7 and faster is considered a fast telescope (the range they can use is a bit higher that a camera).
Here is where that is coming form. I noticed that the 500mm lens I have with a 12.5mm eye piece, and no other parts was right about the same magnification as the 500mm on my camera in live view, zoomed in 4x, or about 2000mm equivalent on a camera. I was rather shocked, but this is where I think its coming form (again, I could be way off, I'm half guessing). and apsc sensor is what, 24mm diagonal? The most the human eye can get is 9mm? I'm not sure if its a crop factor thing or if the image is being compressed down to a smaller area, or both, but just a 4mm eye piece and the 500mm lens and nothing else should give the same as a 6000mm lens on a camera. Put a 1.6x telconverter in front of the 500mm lens and that is now the same as 9600mm on a camera. Ad a 3x barlow lens (made for use with telscopes) and you have 28,000.
I have no idea if the Barlow causes light loss but the 1.6x front mount telconverter won't (it has a huge 105mm objective lens and I have done the math, it will not lose any light on the 500mm lens). Honestly all I need are a few thousand mm or less which should be quite easy (I think, I'm new to telescopes which is what I'm basically trying to do, for the kids to look at stars or whatever). Just the 500mm lens, the 1.6x, and a 12mm eye piece gives about the same view as a 3200mm lens on a camera. I'm actually thinking of trying/using some of my 300mm lenses as I don think I'll need all that magnification and they are much better quality than the cheapo 500mm.
Fyi, I know you lose image quality with a front mount teleconverter but not as much as you might think in this case. The telconverter I have is a century optics which is top of the line (the exact one I have is currently $649.00 at adorama).
Just the 500mm lens as pictured in post 18, last picture which is finished and working (with an upsidown image which might not matter for stars) is compatible to 2000mm on a camera, could go to 3200mm f8 with the 1.6x converter. Comparing it to a under 100$ telescope from walmart with plastic lenses, I think it will be better.
I'm only waiting on 1 step ring and I can use the 1.6x lens.
This hopefully will also be very versatile (I may wind up in the end having built a couple of different adapters and have many different lenses I could use it with).
On a side note, this can all be done with some simple telescope parts, using them in the manner and configuration they were intended to be used (and I'll have those parts soon). The only reason for experimenting with the mirror boxes from the cameras I I figured they may have better optics (as in the mirror and prism), and I enjoy modding/hacking mechanical things. I have read up a little more since I first posted, and I am far from the first to do this (the most common way is to just drill a hole in a lens cap and glue an eye piece in, its that simple but I like over complicating things). Also from what I gather, camera lenses work very, very well from a collimation perspective (alignment of the elements).
Sorry for the long disorganized ramble but that is about how organized my thoughts and ideas on this are right now, lol. Things will be a little more clear when I get a few parts and tinker a little more. I also have more time than money.