I have a 11 1/2 wollensak verito and heard you could use just the rear element and it would be about a 20 inch. I tried it and and looked pretty good on the ground glass. I stopped it down and it got really sharp. My question is how many stops should I compensate. Anyone have any experience doing this?
Rich
I only just saw this, merely some 14 years late... Sorry!
The arithmetic is simple starting with the basic focal length (FL) and f/stop.
aperture = FL/ fstop
which gives us 11 1/2 / 4 = 2.875
thus, 20 / 2.875 = 6.95
The rear group, wide-open, then, is 20-inches focal length at f/6.95 or for practical purposes, call it f/7.
You'll need to make notes for each of the corresponding f/stop markings for the true (effective) f/stop. You can measure the aperture or simply use the theoretical aperture derived from the wide-open aperture of 2.875 inches. For the f/8 marking (which is for the 11 1/2" focal length). That would give you a 1.44" aperture at the f/8 marking. Figure from there as above. And thence for each f/stop marking and calculate for the converted focal length of 20". Keep your notes handy for future use. You'll find that beyond about f/8 effective stop, your image will sharpen quite noticeably. So keep that in mind when planning your shots. Of course, with a 20" focal length, you'll be running into depth of field effects, too.
All of the Veritos are convertible lenses, making them quite versatile. The rear group seems to be the image forming component, while the front element adds power, thus shortening the focal length to the nominal figure. In the converted form (rear element only) the lens appears to exhibit the same image characteristics as with the front element included, the focal length being the only thing changing.
This is from my experience working with a number of Veritos, including the 5-inch, 8 3/4-inch, 11 1/2-inch, 14 1/2-inch and the 18-inch. With proper care in composition and lighting, this is a phenomenal lens which can be very expressive.
As with anything in life, YMMV.
