rjlittlefield wrote: ↑Sun Mar 14, 2021 11:44 am
I cannot explain what you're seeing. I agree with Lou Jost about how the system should work.
Although I have not used teleconverters with normal lenses I know how they are supposed to behave but I do not know why I getting this behaviour, with two different TC (Both the Vivitar 1.5X and the M42x).
To summarize these are the steps I take, I can not see anything wrong other than maybe a 1mm off because of the NEX-52 male adapter I use with the bellows and other mm with the adapter that connects teleconverter to bellows ( The TC to bellows mm can be corrected reducing extension by 1mm)
This is with infinity system:
- Focus the raynox mounted on bellows to infinity
- Remove camera
- Add teleconverter and NEX adapter; both the M42 and the Nikkon are the kind of adapter that allows focusing to infinity manual lenses
- Infinity focus is lost on the raynox; to get it back I have to reduce the bellows extension by 27-30mm (with both TC)
With the BHT finite microscope:
- Magnification I get with NEX adapters is 1.8X with 1.5X teleconverter and 2.4X with the 2X Teleconverter is. There is a overall drop in performance with both TC, worse in the corners.
- Next thing I tried is removing the nikon-NEX adapter and place the camera as close to the TC as possible; I would rate extension as 1-2mm
Now on the microscope the 1.5X TC works at 1.51X, overall performance still drops compared to direct projection but image is more balanced (center vs corners) and the 1.5X TC does not produce hot spot in the middle of the frame.
On the bellows I just need to remove is 15mm instead of 30mm to get infinity focus
With the infinity lenses I can just refocus the raynox to infinity (should be enough, right?), problem is the microscope with finite lenses.
I did run other test because this thing puzzles me; with Nikon BD Plan 40/0.65 (Higher NA than the 10 I tested before). 50mm extension added to the BHT phototube to get to those 210mm needed. TC with no adapter as discussed here. Subject is a printed piece of paper
100% Crops, just levels adjusted. Both images aligned in Photoshop.
Pmax files
without TC and
with TC