The lens is over corrected by about 1/4 to 1/6 wave like you stated but you also have to understand that spherical aberration in an achromat also affects chromatic aberration as well so they add .
Hi Dave - thanks for the feedback! Very glad you responded as I know you have a TON of experience and have tested some Jaegers lenses previously. I think based on your previous comments in other messages, this one is probably represents the median - not the best, but neither is it the worst you've seen.
Yes, I ultimately used a laser to fine tune the alignment.
Regarding astigmatism, Your point is well taken. Though, I'm not sure the lens has any appreciable astig. The grating was placed in an eyepiece I had 3D printed that also contained the LED. The eyepiece was placed in a series of extension tubes so that it could be placed in a v-block on my lab jack. Its quite likely that I slightly rotated the eyepiece/grating combo in the extension tube. So, I would not read too much into the orientation/tilt of the bands within the posted photos. I did test for astig but saw none of the tell-tale signs such as the "chocking" of the bands as I transitioned slowly from inside of focus through best focus and finally to outside of focus. I am pretty confident in this.
Regarding spherical correction at differing wavelengths - you're right and the point is not lost on me regarding correction at the various wavelengths. These errors are additive. Even so, I think this lens will provide reasonable images. I don't often test longer focus achromats - mostly shorter ED doublets - but I was surprised at the color error especially noticeable in the white light image. I thought it would be more subtle/suppressed. This preconceived notion is directly related to my lack of experience with these long focus lenses.
Also, it took a bit of time for the lens to thermally settle on my bench. I started the alignment procedure when I took the lens out of the shipping box after it had been sitting in my den. There is a only a minor delta in temp between the den and where my test bench is. But it took ahwile for the lens to settle. So I finally let it sit overnight on the test stand/lab jack.
Interestingly, this lens is spaced with metal rings. I'm used to seeing rubber rings, or thin foil spacers and not metal rings. Are all Jaegers lenses spaced using metal rings that fit inside the cell separating each glass element?
Below are photos of my tester eyepiece. For this test, it was placed into a set of extension tubes so that assembly could be placed on a v-block on top of a lab jack.
Edited by peleuba, 22 June 2022 - 12:03 PM.