Lou Jost wrote:Mike, the EL should be stopped down one or two stops to be really sharp, but it's hard to say whether the best place to do that is in the lens or behind it. When the tube lens is much longer than the front lens, then the front lens' aperture is often usable. When the two lenses are similar in focal length, the paper aperture is almost always best. This is an intermediate case, so an empirical test would be worthwhile.
Rik has pointed out elsewhere that the default should be to stop down a combination somewhere between the two lenses.
Theoretically the combination can be made telecentric with the right choice of aperture position.
Thanks Lou, I am still trying to cut an aperture for it as you mentioned in previous post, to be positioned in between.
Lou, Mike : I stopped it down to f/4, at f/2.8, I saw some CA on another subject, stopping down reduces it to almost nothing. Also, I used a segment of M42 tube (via a M42-to-M39 step down ring) as hood, else, for my light setup, the images are washed out.