So this scope is all but complete, at the point where it needs to go to the powder coaters and the trim bits to the plater's.
Ever since I 1st started testing the lens I have been somewhat baffled about what I was seeing in the EP. At 90x the moon looks good, but stars had a somewhat bloated appearance. Not being especially experienced in building refractors as in this is the 1st one. I kept thinking, well its not perfectly collimated, its not baffled, its not cooled to equilibrium etc etc.
Well this past weekend we set it up and had fairly decent skies, the baffles were painted and installed, we lined the front of the tube to the 1st baffle and the dew shield with poster paper painted flat black and made sure it had plenty of time to stabilize temp wise. Virtually eliminating all the things that made me unsure what the cause was for what I was seeing and we played with it at 90x 225x and 450x. Moon still looked good at 90x, but horribly soft at anything above that.
We collimated it VERY well.....Star testing revealed really pretty good results inside of focus, outside of focus was another matter. When you could see them it had nice concentric rings also but it was really really nasty, boiling, spiking etc.
Viewing Jupiter at any power it was confusing, at best focus on the moons Jupiter was surrounded by a yellow halo about the width of 1/8 of the planet width. If you went for best focus on Jupiter the moons were out of focus and uniformly spikey looking.
I had been pouring over Harold Suiter's book on star testing for several weeks now trying to find something that would explain what I had been seeing in my testing to no avail.....
Now that I had eliminated all the things I had been excusing the view with I was feeling pretty dejected. Felt as if we had put all this time and effort into what appeared to be a bad lens, we attempted to remove the lens from the cell to check the rotational alignment of the pair, hoping the optician marked them and that they had gotten spun out of alignment when turning the cell down to fit in the tube with collimation clearance. However disassembly was problematic and given my lack of experience I wasn't willing to chance chipping or cracking etc.....
I had seen similar effects on a C11 that a prior owner had taken apart and accidentally reversed the corrector plate. It wasn't a drastic thing and not nearly as pronounced as what we were seeing in this refractor but compared to my other C11 it definitely had an issue. once we discovered the corrector plate was backwards based on the serial # engraved on its edge and corrected it then the two performed pretty much identically. This led us to investigating the lens orientation in the cell......
We shined a laser thru the lens and observed the dots it made on the lens surfaces. Because the lens spacing is only .004 you really only perceive 3 of the 4 surfaces but that is all we needed.
In a fraunhofer design achromat the front lens is convex () and the rear lens is concave )and they reside in this case with a .004" airspace. What we saw was the rear lens (closest to the focuser) was about 1.5 times thicker in the middle than the front lens. As we moved the laser further out on the lens the rear lens got thinner. Conversely the front lens was thinner in the middle and thicker towards the edges. Exactly opposite of the intended design
At some point in the last 35 years the lens pack had been installed in the cell backwards!!
I have to admit my lack of experience in working with lenses left me confused as to how it could possibly work as well as it did with the lens reversed but it was obvious. I have the original ZEMAX design specs by Norman Remer and design data that the lens was figured from and Mike Jones was kind enough to plug the design into the modern ZEMAX and per his comments it was a VERY well done design with very good spot diagrams of the projected performance and he has quite a reputation in optics and designing scopes. Mike was again kind enough to plug the prescription into ZEMAX in reverse and the result matched up with exactly what we were seeing in the EP.....Yellow halo around Jupiter, bloated stars etc.
Problem solved, turn the lens around lol.....However as I mentioned the cell made 35 years ago doesn't appear to follow normal construction and we being inexperienced in such things were hesitant to get too forceful with it.
So it was off to find a professional to deal with it.....Muffoletto Optics went away when Verne died back in 1986 or so but one of the former opticians had given us some info on where those guys ended up in my build thread on Cloudy Nights about 4 years ago. In 1987 9 of the former Muffoletto folks formed Nu-Tek Optics which has grown to a large optics house that does mostly government contracts and professional optics work on large projects. I contacted them via that person who is still there, a Mr Robert Bupp. They were enthusiastic to have a chance to play with this classic lens from back in their early careers at Muffoletto.
I am shipping it off to them today for disassembly, cleaning, optimizing and testing for waveform accuracy etc. I am told one of the guys that will be working on it more than likely had his hands on it 35 years ago......and several of the original 9 from Muffoletto are still there today including Robert Bupp.
I have had this lens about 5 years myself and am the 1st to build a scope with....Having talked with several folks who were familiar with Muffoletto from back in the day they had a world class reputation in the optics world and I now believe once again this lens will prove out to be well worth the time and effort put into building the scope.
Gotta love it when a plan comes together....