Yipee!!!!!!!This is better than lottery

ivanong · Post by **ivanong** » Fri Jun 20, 2008 7:45 pm

I saw the new AP 130 f/6 at NEAF this year and was quite surprised by how small it looked. I've owned the previous AP 130 f/6 EDFS and this one seems even more compact. This would be a great scope for Singapore due to its portability and size. Would be great with a Tak EM-200. A GP-DX might be too unstable for imaging and high power visual.

WT · Post by WT » Fri Jun 20, 2008 8:06 pm

11years.... let me calculate.. if save $50 one month, 1 year $600, 11 years.. wow.. must be $7000+++ scope [smilie=evil-smile.gif]

Canopus Lim · Post by **Canopus Lim** » Sat Jun 21, 2008 12:40 am

ariefm71 wrote:Vin, can test the 127 head-to-head with my 115? let me know time and location
Liu Ming tested it against an NP127 and he couldn't detect any difference in resolution.

I would not expect the NP127 to beat another 127 apo on-axis resolution..if they are about equal quality (about the same Strehl). Off axis is another story and field flatness and maximum FOV achievable and colour correction. There are many tests that can be done.. no one side story in any equipment. Also resolution will be about the same since both are 127mm. Contrast wise...different and that depends on the optics design and execution of the design.

ariefm71 · Post by **ariefm71** » Sat Jun 21, 2008 12:59 am

I was referring to 115 vs NP127, I would expect the 12mm extra aperture of the NP gives a slight advantage in resolving finer details, which was not the case in the test conducted by Liu Ming.

Post by **rcj** » Sat Jun 21, 2008 1:49 am

not surprised with the test. with all respect to Nagler et al, their refractors are somewhat less than what one would think Televue would produce. Nice to have, but execution in design, is still a tad less up in pace with the fore runners in apochromat productions. Been there, seen it, decided otherwise.

denebman · Post by **denebman** » Sat Jun 21, 2008 11:13 am

ariefm71 wrote:I was referring to 115 vs NP127, I would expect the 12mm extra aperture of the NP gives a slight advantage in resolving finer details, which was not the case in the test conducted by Liu Ming.

I saw through NP101(2nd hand) and NP127 (brand new), both got noticeable spherical aberration to my surprise.

The good thing about TMB is that each individual lens comes with third party test report. Although the data varies from one to another, they make it for sure that the ptv is better than 1/5 lambda, and strehl higher than 95% (EER(Encircled Energy Ratio > 0.88), which corresponds to "excellent to perfect" in terms of optical quality. (Ref. Star Testing Astronomical Telescopes, H. R. Suiter, page 196-199).

Canopus Lim · Post by **Canopus Lim** » Sat Jun 21, 2008 10:59 pm

Well probably they may not be too good for high power in that regard as it requires better execution for a 4 element design than a doublet/triplet to achieve the same amount of spherical aberration correction especially for doublets/triplets with long F/#. However, for being a 'true' apo (having the smallest chromatic focus shift) if there is such a thing, I would think that it will be better than a doublet or a triplet, and IT SHOULD BE for that kind of price.

Having some knowledge in optical design (I do some in my job..), one can design a scope with SUPERB on-axis performance, but the off-axis performance can be 'crap'... no joke. Also optics design is such that the optical designer has to balance all the 'optical errors' (real name is optical aberrations). Multielement designs will always produce a better off-axis performance if designed well as there are more Degrees of Freedom (DOF) that can be used in the design but sometimes they do sacrifice on-axis in order to achieve a better off-axis. Since most tests are done at high power (and small FOV thus small off-axis aberrations), it just only tell one side of the story. It is just like saying a car has a top speed of 200km/h but it doesn't give the full details of its performance like the torque, 0-100km/h timing etc.

That is why if one wants to really compare a scope/ eyepiece especially of different design and different design objectives, he has to take account all the optical characteristics. Well the NP101 and NP127 could have lousy execution...but I do not doubt the design and what it can possibly achieve in terms of field flatness, off-axis aberration correction and colour correction.

And one last note..it is MUCH EASIER TO DESIGN AND EXECUTE A LONG FOCAL RATIO 'APO'...and I have did some rough designs during my free time at work. It is many orders easier in just about everything. So..if a long focus APO beats a short focus APO on-axis, it DOES NOT MEAN that the designer or that brand of telescope has a better design or better execution. It has to be compared apples to apples and oranges to oranges.