Is there a quick way to test what coverage a lens will give. I read on the net sometime ago that it could be done by shining a torch through the lens whilst holding the lens at its focal distance from a wall. Is this nonsense or is it practical?
Is there a quick way to test what coverage a lens will give. I read on the net sometime ago that it could be done by shining a torch through the lens whilst holding the lens at its focal distance from a wall. Is this nonsense or is it practical?
That's practical for evaluating the illuminated field but not the sharp-covered one. Though when offered a xerox lens at a flee market one day, I just projected the sun onto a wall by it and saw such a ridiculous amount of astigmatism that buying got out of the question at once....
You can actually view the aerial image of the lens by putting a loupe up to your eye and then moving the lens around until the focused image appears on your loupe. Very tricky to do, I learned this trick from someone who was very good at it and could accurately gauge the usable coverage of a lens this way - since you can see detail in the loupe. I've only managed to do it a couple times...
Take a large piece of mount board or cardboard. Draw the film size on it. Turn off the lights in your room, close the drapes. Point your lens out the window at a distant object. Move the board in and out behind the lens till you have a sharp image. That’s your coverage. Do it wide open and then at 22.Originally Posted by GoodOldNorm
I don't give a hoot about any circumference number. I want to know, for example, how high I can raise the front standard. So, I mount the lens and observe the image circle through the cut corners.
My lenses then are categorized as either covering all movements the [field] camera gives, or not.
Lenses that cover all available movement are easier to use, because I don't need to check all corners as I work.
The other lenses require corner checking and centering as we all know.
Posting Permissions
Reply With Quote
Bookmarks