apochronaut wrote: ↑Fri Aug 28, 2020 11:09 am
no accessories for BF, no accessories for DF, fluorescence head for fluorescence and only the bertrand lens for phase. This doesn' t alter the infinity space , else the whole system downstream would get thrown out in normal use of those accessories. That is one of the basic benefits of infinity optics.
But this is only true as long as infinity space is actually infinity-focused, right? I brought it up because I have been interpreting some of your other suggestions (see below) as involving moving the objective away from the designed working distance and in that case the space between the objective and telelens is no longer really infinity space and the behavior (in terms of what sort of aberrations appear) could depend on what is in between, I think?
apochronaut wrote: ↑Fri Aug 28, 2020 11:09 am
It's possible that you are over analyzing my numbers.
The numbers are fine and it sound like you have actually measured more carefully than I have. I am also mainly positioning things empirically based on focus. 193.725 mm from the patent I mentioned just out of general interest and I have not been trying to use that number to actually set positions of stuff.
What I am not following, I think, is what exactly you mean when you talk about changing reference length vs. projection length and what that implies about objective working distance:
apochronaut wrote: ↑Tue Aug 04, 2020 1:30 am
...using the optics at the correct reference length. I don't mean the correct projection length, which doesn't matter, except for the sensor size.
apochronaut wrote: ↑Wed Aug 26, 2020 4:44 pm
Here is the thing about that correcting optic. Way back in this thread I suggested that it was the distance or tube length that needed to be adjusted in order to rid the 181 eyepiece of it's ca. You tested that theory by testing at various projection distances not reference lengths.
apochronaut wrote: ↑Fri Aug 28, 2020 11:09 am
... At that point, the eyepiece seems as perfectly corrected as possible and it is visually parfocal and it projects exactly the same field if view as the eyepieces in the head. Parfocality to the sensor is not part of that set up...
If the objective is fixed at its normal working distance then unless I am missing something fundamental there is only one remaining degree of freedom to adjust things while maintaining focus -- the relay optic and sensor must be moved simultaneously and in opposing directions. This sort of adjustment is what I think you mean by projection length? (And it sets relay magnification going from the intermediate image plane to the sensor.)
So then what other adjustment is possible, while maintaining focus, that does not involve moving the objective away from the normal working distance?
And if we are actually talking about moving the objective relative to the specimen plane to maintain focus while "changing reference length", then that is why I brought up accessories in the infinity space as a possible confounding factor if I am going to try to replicate your 145 setup.
I put "changing reference length" in quotes because personally I find that phrasing a bit confusing. As far as I understand, reference length is a fixed property of the design that specifies the condition under which it was optimized to minimize aberrations. That is why I keep using other phrasing like "move the objective away from the designed working distance" and if we want to talk about the effect on the image side, maybe something like "moving the intermediate image away from the reference position" would make more sense? Is that what you mean by changing reference length?