Thank you all for your replies!
The dimensions of the lens elements of Ross No.3A in this book are the same as of my Ross lens.
But the difference of the focal length is still strange. I'll try to measure the focal length of my lens using more scientific methods an then we'll see the truth.
But there is another question arised: how to measure the maximum aperture of such lens with different lens elements? As usual, dividing the focal distance on the measured diameter of the front pupil?
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