Once the pitch lap is on and conformed, there is no such thing as "super smooth polishing" It comes down to technique.
............
That's just a throwaway line IMHO.
Not everyone uses pitch.
There are "super-smooth" polishing techniques.
Teflon laps are used regularly get surfaces down to 1/100th lambda.
P.S. I was flown up to Narrabri some years ago to cover the opening of The Sydney University Stellar Interferometer (SUSI) for Sky & Space magazine.
Talking to some of the research staff and academics at the time I learned scattering was a problem for the instrument, which was solved in the end by using teflon polishing laps to get the mirrors down to 1/75th lambda or so.
P.P.S Sorry Greg....clearly not relevant to your post. Enjoy the new 'scope!
Last edited by Peter Ward; 31-08-2019 at 02:47 PM.
Not sure what people are referring to when they say the lens has a turned down edge.
I have been asking the same Greg, as I am curious where do people see it
Honestly, I am quite surprised by the number of people on IIS who are soooo eager to search for flaws instead of celebrating. If I just bought a house, car, boat, scope and a friend would come around just to point at any imperfections (real or imaginary) or give me a lecture about the brand/maker etc instead of sharing the joy as a normal sensible person would, that would probably end the friendship rather quickly
Anyway all this is hypothetical and the proof of the pudding will be in the imaging. The camera is a known quantity for me.
Greg.
Yeah I don't think you'll have any major suprise and you'll enjoy the scope. CFF seems to have a good track record.
Interesting discussion on tests and certificates. Posts linked to 'Rolando" by Suavi and Peter comments about rms vs. PV make a lot of sense. You can see how you can easily spin the marketing and show the numbers you want.
@Logan, you should email Roland at AP and tell him he's full of it. Sounds like you're ready to take over the business.
Logan,
The Chronograph solar telescope is one of the most optical demanding systems you can think of!
To reduce the light scatter additional attention was give the the edges of the lenses - to reduce diffraction scattering as well as the quality of the lens polish.
To quote from the forthcoming book " Solar Astronomy":
The objectives of professional coronographs, when it comes to refractors, are therefore made from extremely homogeneous glasses (generally fused silica), without inclusions, streaks or bubbles, and with an extremely fine polish, a high quality finish that was called previously "coronograph quality" and now "super polishing". Note that Bernard Lyot had developed with the optician Maurice Françon (discussed in Chapter 5 on instruments) the method of analyzing defects in the polishing and homogeneity of lenses, now known as "phase contrast" testing.
I have been asking the same Greg, as I am curious where do people see it
Honestly, I am quite surprised by the number of people on IIS who are soooo eager to search for flaws instead of celebrating. If I just bought a house, car, boat, scope and a friend would come around just to point at any imperfections (real or imaginary) or give me a lecture about the brand/maker etc instead of sharing the joy as a normal sensible person would, that would probably end the friendship rather quickly
Agree- we need to take each sample as it comes. Make our own assessment of the individual sample. Having enough trust in a brand to confidently buy is what drives me personally, on the basis that poor samples likely would not pass QC. It is to that end I vehemently trust Tak, AP, TEC and CFF.
Sure, CFF did have some initial issues (especially with the mirrored optics) but they worked at it and I have read only perhaps 3 negative user reviews (2 with unremediable blue halo /reflections and another with potentially out of collimation objective). Lessons learned, onwards and upwards.
And Tak won’t even publish their scope results. There is apparently an in-house minimum standard else it is rejected or refigured. Someone once said that figure was 0.985 Polystrehl.
Didn’t Sauvi have issues with the Riccardi? Or am I mixing that up?
Oh the TEC110 - wish I had bought it from you Greg.
Was NOT my intention to bag the scope or manufacturers - i'm sure Greg fill find the scope to be excellent! It's that the numbers don't seem to check out, and the graph surprised me. I thought that a company like AP or CFF would deliver better optics for the price.
Peter, I had not heard of the teflon lap as it is practically never discussed among ATMs, and unfortunately all the results are behind a paywall. I will have to ask on Cloudy Nights - thanks! Thanks Ken as well.
TDE image is linked, see where the edge sharply turns down, in fact it might be more of a rolled down edge as it takes place over a wide area.
From the graph - about 18 nm/550nm = about 1/30 of a wavelength - seems small, to me at least Why not notice a more indicative rms wavefront error of 1/73.4 wavelength - seems very smooth, even for AP standards
And Tak won’t even publish their scope results. There is apparently an in-house minimum standard else it is rejected or refigured. Someone once said that figure was 0.985 Polystrehl.
Didn’t Sauvi have issues with the Riccardi? Or am I mixing that up?
Oh the TEC110 - wish I had bought it from you Greg.
They are a rare scope and it was a beauty. Even the focuser I could live with the flattener handled the 16803 as well. I've only seen 1 come up for sale on Astromart. It was also a very light scope. I used it to take some bird photos sometimes sitting just on a carbon fibre tripod. This new scope is a bit heavier so I wouldn't try that.
And Tak won’t even publish their scope results. There is apparently an in-house minimum standard else it is rejected or refigured. Someone once said that figure was 0.985 Polystrehl.
Didn’t Sauvi have issues with the Riccardi? Or am I mixing that up?
Oh the TEC110 - wish I had bought it from you Greg.
Quote:
Originally Posted by Lognic04
Was NOT my intention to bag the scope or manufacturers - i'm sure Greg fill find the scope to be excellent! It's that the numbers don't seem to check out, and the graph surprised me. I thought that a company like AP or CFF would deliver better optics for the price.
Peter, I had not heard of the teflon lap as it is practically never discussed among ATMs, and unfortunately all the results are behind a paywall. I will have to ask on Cloudy Nights - thanks! Thanks Ken as well.
TDE image is linked, see where the edge sharply turns down, in fact it might be more of a rolled down edge as it takes place over a wide area.
Thanks for clarifying, I thought that was what you were referring to.
Since that part of the lens is inside the aluminium lens cell and is not part of the light stream then I don't see that as a problem. Perhaps all APO lenses are done that way???
Enjoy the scope Greg. Looking forward to seeing what you do with it.
D
Thanks David.
Quote:
Originally Posted by RobF
Yep, sounds like a great scope.
Hope you get the light train sorted soon and suitable skies to enjoy the new beast Greag.
I am hoping the adapters are not a big deal but my 2 cameras the FLI Proline sensor is set back 21mm but the Microline is set back 15mm so it means a screw on small 2nd adapter to pack out the Proline adapter to be at the same length. He's made one like that for me before.
Seems too much obsession with Strehl and P-V anyhow ..sooo many things to take into account measuring that.
You would expect a PREMIUM company like CFF would not let any Lens assemblies pass their scrutiny without being anything less than near Perfect ..their reputation would have been shot by now, and it ISN'T!
MANY happy uses it seems.
I too would choose CFF or Tak if imaging.
It comes down to technique. 
Why not notice a more indicative rms wavefront error of 1/73.4 wavelength - seems very smooth, even for AP standards 
....all expensive...but all impressive performers.
