Some testing with my 150mm F5

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John Baars
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Some testing with my 150mm F5

Post by John Baars » Fri Aug 30, 2019 9:55 am

I did some startesting with my newly arrived 150 mm f/5, the 1.25" Zeiss prism and the 1.25" Baader BBHS diagonal mirror. Goal was to establish if the use of the Zeiss prism could improve CA. It did a bit. At higher magnifications I run into another phenomenon, which JG already mentioned in his post on Astronomyforum. http://www.astronomyforum.net/telescope ... ction.html

I performed the tests on Wega and mostly Altair ( more comfortable to observe:-) I used my Leica WW ASPH Zoom 18 mm for lower magnifications (42X), the same Leica with Zeiss barlow for higher magnifications (190x) en my Pentax XO2.5 for highest ones.(290X)

The lenshood has an extra central opening of 110mm. One can choose to observe with the full 150 mm or the 110 mm opening. In the last case it becomes a f/6.8 system. At high magnification the difference becomes obvious: a slightly bigger Airy disc, surrounded by at least one or two calmer diffraction rings. The influence of seeing can be lessened this way. Furthermore I saw a slight improvement in axial coma. No noticeable difference in CA at lower magnifications. But since I was testing a 150 mm instrument, I left the diaphragm out.

Low magnification (42X)

- BBHS mirror.
The colored halo at the size of 11X the Airy disc was blue.
Scattering was present but moderate.

- Zeiss prism.
Halo was not noticeable smaller or intens.
Scattering seemed a tad less.

High magnification (190X)

- BBHS mirror.
Halo was noticeable less then at lower magnification. Less blue, far more moderate, seemed shifted to gray. Same size as at 42X. Slight orange / blue rim around Airy disc depending of eye position
Scattering was bigger than the faint blue colored halo, moderate though and gray.

- Zeiss prism
Halo seemed noticeable less than with 42X. Seemed shifted to gray. Same size as 42X. Slight orange rim / blue rim around Airy disc depending of eye position. Scattering a tad less intens than with mirror, but same size.

Highest magnification ( 290X)

In both accessoires the blue halo had almost turned into gray, except for a slight blue /orange somewhat irregular rim around the Airy disc ( Not the first diffraction ring), depending on eye position. I suppose I described Spherochromatism here. I could not see the difference between a colored halo and the scattering any more. Scattering was a tad less intens in the Zeiss.

We are talking about marginal differences though. Only visible at a direct comparison when accessoires can be changed quickly. The differences in intensity in halo and scattering could only be established with the star outside the field! With the star inside the field its brightness overwhelmed all differences. Edges of in-and out focussed stars could not help me any further.

At what magnification was the transition from blue to gray and at what magnitude?
NGC 457 was a nice testing object for that. I found that the 5th magnitude star SAO 22191 in the cluster at around 100X was more or less the turning point. Its 7-th magnitude neighbor SAO 22187 was not bothered by anything.

Did the presence of the grayish halo have effect on the observation of let's say double stars?
It did not on double star SAO 84572, magn. 7 and 7.8, separation 1,2". At 190X I could see them both with ease, clearly separated, with a small dark split between them. Delta Cygni, magn. 2.9 and 6.3, separation 2,8" was clearly separated, never seen it like that before, but one could see a slight gray halo around the main star. I can imagine that Sirius B would be more difficult....
Telescopes in Schiedam : SW 150mm F/5 Achromat, SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
Eyepieces: Kitakaru, Eudiascopic, Jena, Panoptic, Nagler, Morpheus, Leica ASPH, Brandon, Parks, Fujiyama, Pentax XO.
Binoculars: AusJena 10X50 Jenoptem, Swarovski Habicht 7X42, Celestron Skymaster 15X70, Swift Observation 20X80.

Astronomical Rijswijk observatory telescopes: Astro-Physics Starfire 130 f/8 on NEQ6, 6 inch Newton on GP, C8 on NEQ6, Meade 14 inch SCT on EQ8, Lunt.

Amateur since 1970.
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Re: Some testing with my 150mm F5

Post by Lady Fraktor » Fri Aug 30, 2019 6:04 pm

A nice report and interesting results John.

I know the slight blue/ orange can sometimes be caused by a manufacturer shifting the coatings towards the "blue" end of the spectrum but that would not really explain the change to grey.
If it was a widefield eyepiece I would suspect the grey was caused by edge of field brightening but that cannot be the case with the equipment used.
Perhaps a email to Baader describing this? They may be able to explain it.
Proper Telescopes: Antares 105 f/15, Celestron 150 f/8, Stellarvue NHNGDX 80 f/6.9, TAL 100RS f/10, TS 102 f/11, UR 70 f/10, Vixen ED115s f/7.7
Mounts: Celestron CG-5 w/ Argo Navis & tracking motor, SLT w/ pier & tripod mods, Manfrotto 028b w/ SV M2C, Mantrotto 055Pro w/ 128RC, TAL MT1C, Vixen SXP w/ HAL-130 & half pier
Diagonal: 2" A-P Maxbright, 2" Baader Herschel Wedge (P), 2" Zeiss/ Baader Amici Prism (DX2), 2" Orion Amici Prism, 2" Stellarvue DX, 2" TeleVue EverBrite
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Re: Some testing with my 150mm F5

Post by Bigzmey » Fri Aug 30, 2019 6:40 pm

Interesting results John. I have not done side by side comparison of diagonals, but I did play with barlows and stopped scope to 110mm. Similar to your results this did not have much effect on CA. The blue halo was still pretty bad on Moon and planets.

Well, as we already discussed 150ST was not designed for that. :)
Scopes: Stellarvue: SV102 ED F7; Celestron: 8" SCT F10, Omni 150R Achro F5, Onyx 80ED F6.3, Mak 127mm F12; Meade: ST80 F5. Mounts: ES Twilight I, Bresser EXOS2, SW SkyTee2, AzGTi, UA MicroStar. Binos: Orion 15x70, 10x50, Nikon 8x40. EPs: Pentax: XWs; TeleVue: Delites, Plossls & barlows; ES: 68s; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV; Meade: UWAs & Plossls. Diagonals: Baader: BBHS mirror, Zeiss Spec prism, Clicklock; TeleVue: Evebrite. Filters: Lumicon, Baader, Astronomik. DSO tally: 1490 (Completed: M110, H1, H2. In progress: H3: 168, H2,500: 1087, S110: 77). Doubles: 857, Comets: 13, Asteroids: 62
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Re: Some testing with my 150mm F5

Post by John Baars » Sat Aug 31, 2019 7:27 am

Change to grey
Yesterday evening I spent most of my time experimenting again with the blue/grey question.

It seems that at least half the problem has to do with my own eyes. Caught myself on this...
Imagine:
1. Looking at a star with high magnification with direct vision. Cones in the retina are activated. So I see color. The blue halo. Surrounded by grey scattered light.
2. Looking at the same star with averted vision. Rods in the retina are activated. I won't see color that well any more. Blue halo is mostly overwhelmed by grey scattered light.

What did I do wrong?
I observed the scattered light, which was overwhelming the blue halo, and assumed that the blue halo was almost gone. And forgot to concentrate on the blue. I am commonly used to use averted vision while looking at a faint phenomenom, even with a bright star in the field of view. That's all. How could I deceive myself / how wrong could I be? Well this way :oops:

Of course I repeated the testing. Differences prism/mirror diagonal still stand. Does the blue halo still stand as fierce as visible with lower magnifications? No it doesn't. It weakens all right, but simply as a result of the higher magnification.
I had the key to the solution in my hand but forgot to turn it:
Scattering was bigger than the faint blue colored halo
Telescopes in Schiedam : SW 150mm F/5 Achromat, SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
Eyepieces: Kitakaru, Eudiascopic, Jena, Panoptic, Nagler, Morpheus, Leica ASPH, Brandon, Parks, Fujiyama, Pentax XO.
Binoculars: AusJena 10X50 Jenoptem, Swarovski Habicht 7X42, Celestron Skymaster 15X70, Swift Observation 20X80.

Astronomical Rijswijk observatory telescopes: Astro-Physics Starfire 130 f/8 on NEQ6, 6 inch Newton on GP, C8 on NEQ6, Meade 14 inch SCT on EQ8, Lunt.

Amateur since 1970.
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Re: Some testing with my 150mm F5

Post by John Baars » Sun Sep 08, 2019 9:48 am

Since some questions were asked about the performance of the 6 inch f/5 on another Forum, I posted some pics there which I won't withhold here.
In the first pic you can see a simulated star ( Altair) in the program Aberrator at high magnifications. I used a Pentax XO2.5 for 300X and sometimes even a barlow to reach 600X. I did my best to come as close as possible to the real thing. Collimation errors were set at 0.05 mm for X and Y axis. ( not visible in the display) The influence of coma is noticable at high mags. The in-and-out focus pics are in real a tad better than in the display.
Point Spread Function, you could say Strehl, is 0.83. Contrast function is somewhat lowered in the midrange resolution, as you can see in the MTF diagram. Similar instruments with less spherical aberration (LSA) score better on the contrast-scale.
Aberrator 6 inch F5.png
The same Altair is used in the second schematic pic. The yellow / orange /sepia coloring of Altair is true. The blue interrupted circles stand for the size of the CA Halo. It has roughly 11X times the diameter of the Airy Disc. The grey circles stand for the scattering, roughly 3 times the size of the CA Halo. At high mags the blue halo seems to diminish. With averted vision the scattering seems stronger, as expected. Concentrating on the outer edges of the pic simulates the effect of reducing the blue halo. In highend instruments like a 130mm Astrophysics Starfire, the blue halo dissapears and the scattering is less intens. Less intens scattering is can be reached by the best polishing of the optical surfaces.

At low to medium magnifications the CA halo is visible on brightest stars until magnitude 4. At magnitude 5 you will have to search for it. Scattering is best visible at medium to high magnifications on brightest stars and becomes better visible with averted vision.
Altair with CA and scattering 6 inch F5.jpg
Telescopes in Schiedam : SW 150mm F/5 Achromat, SW Evostar 120ED F/7.5, Vixen 102ED F/9, OMC140 maksutov F/14.3, SW 102MAK F/13 on Vixen GPDX.
Eyepieces: Kitakaru, Eudiascopic, Jena, Panoptic, Nagler, Morpheus, Leica ASPH, Brandon, Parks, Fujiyama, Pentax XO.
Binoculars: AusJena 10X50 Jenoptem, Swarovski Habicht 7X42, Celestron Skymaster 15X70, Swift Observation 20X80.

Astronomical Rijswijk observatory telescopes: Astro-Physics Starfire 130 f/8 on NEQ6, 6 inch Newton on GP, C8 on NEQ6, Meade 14 inch SCT on EQ8, Lunt.

Amateur since 1970.
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