I learned how to calculate the f-stop of a lens then measured and calculated it for this lens using this page, among others,
http://www.steves-digicams.com/knowledge-center/how-tos/digital-camera-operation/how-is-an-f-stop-calculated.htmlI'm not sure I did this correctly but here's the specs:
>Step 1 - Determine Your Lens Diameter62mm Lens Diameter.
>Step 2 - Determine the Lens Focal Length127.5875mm focal length at infinity.
132.35mm focal length at closest focus.
>Step 3 - Divide the Diameter by the Focal Length>a camera with a with a 10 mm and a focal length of 2 mm. The f-stop would be f/5 because the ration is 10/2.Seems it may be f/0.46 to f/0.48, but that seems absurd. Regardless, it is super bright/fast. I need to get ND filters for it.
I found this nice calculator for DoF, AoV, and related,
https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/Here's a list of super fast, super expensive lenses I compiled while researching. The image quality of mine isn't comparable obviously, but I thought it was neat,
Canon 50mm f0.95 Dream Lens (I even named mine "Dream Lens" before I read about this one)
Leica Noctilux-M 50mm f/0.95 ASPH
Voigtländer Nokton 10.5mm f/0.95
Mitakon Zhongyi Speedster 25mm f/0.95
Mitakon Zhongyi 50mm f/0.95
Navitron 50mm F0.95
Voigtlander 25mm F0.95
Angenieux 25mm f0.95
Leitz 150mm f/0.85
Handevision IBELUX 40mm f0.85
Canon 65mm F0.75
Rayxar 50mm F0.75
Zeiss 50mm F0.7
Signal Corps Engineering 33mm f0.6
GOI CV 20mm f0.5 Mirror lens
Carl Zeiss Super-Q-Gigantar 40mm f/0.33
And, this image was nearly white. It is a 30min exposure of the darkest part of the night sky I could find. I was going to do a star swirl, but when I saw the screen whited out, on the camera when I came back, I decided not to. Though, I might try again, pointed at Polaris, on a moonless night.
