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Celestron refractor omni 102 F1000 question.

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14 replies to this topic

#1 stanislas-jean

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Posted 16 March 2020 - 06:51 AM

Simple question: as mentionned by few vendors, has this OTA equipped with aspherised lens?

Nothing mentionned on the celestron website.

Important question as spherical aberration and spherochromatism can be substantially reduced if so.

Thanks a lot for bringing answers about.

Stanislas-Jean



#2 SeattleScott

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Posted 16 March 2020 - 08:37 AM

I don’t think I have ever heard of that on telescopes. Only eyepieces.

Scott

#3 Hesiod

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Posted 16 March 2020 - 11:14 AM

As far as I remember, only the 150/750 was advertised as hand retouched to address spherical aberration; but it is also true that often such ads were rather misleading (sometimes I saw that MCT was referred to as a refractor).


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#4 SandyHouTex

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Posted 16 March 2020 - 12:32 PM

Yes.  The Omni 150 refractor has an aspherical lens to help with CA.  I own two and plan to make a binoscope out of them.



#5 stanislas-jean

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Posted 17 March 2020 - 07:33 AM

Thanks for your responses.

I know some 150mm has the front lens aspherised like mine the TS 152-990.

This is appearing subtil with the ronchi of 13lp/mm and the operation concerns a fraction of the outer surface say 1/4 to 1/5 of the radius aperture.

The question was raised for this 4" celestrron new edition, omni serie recent.

Question remains.

Stanislas-Jean



#6 SandyHouTex

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Posted 17 March 2020 - 09:53 AM

Thanks for your responses.

I know some 150mm has the front lens aspherised like mine the TS 152-990.

This is appearing subtil with the ronchi of 13lp/mm and the operation concerns a fraction of the outer surface say 1/4 to 1/5 of the radius aperture.

The question was raised for this 4" celestrron new edition, omni serie recent.

Question remains.

Stanislas-Jean

I was responding to Hasiod’s post #3 before me.


Edited by SandyHouTex, 17 March 2020 - 09:53 AM.


#7 SeattleScott

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Posted 17 March 2020 - 01:10 PM

So I believe the answer to your question would be no. For the 4” F10.

Personally it would seem a bit odd to me to go to extra expense to reduce CA on a scope that doesn’t have much to begin with, and has sold for as little as $100 on sale. The TS scope or even the Celestron 6” have much more CA and are more expensive.

Scott

#8 Rutilus

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Posted 17 March 2020 - 02:13 PM

When the Omni XLT series came onto the market the 102, 120,and 150mm were all advertised as having

aspherised lens. At the time, I was looking to buy the 120mm f/8.3 scope, instead I bought the Sky-watcher

version.

Looking at the scope today, on vendors websites, it is still advertised as such. 



#9 BFaucett

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Posted 17 March 2020 - 03:37 PM

Simple question: as mentionned by few vendors, has this OTA equipped with aspherised lens?

Nothing mentionned on the celestron website.

Important question as spherical aberration and spherochromatism can be substantially reduced if so.

Thanks a lot for bringing answers about.

Stanislas-Jean

 

From Celestron's website under product description:

 

"Using aspheric shaping technology in conjunction with hand-figuring the optics the Omni XLT presents an image with virtually no spherical aberration. We also added our famous StarBright XLT coating system to further enhance light transmission."

 

https://www.celestro...t-102-telescope

 

Bob F. smile.gif


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#10 stanislas-jean

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Posted 18 March 2020 - 04:20 AM

Thanks gents, Rutilus and Bob.

This is answered on the celestron website, here in Europe not so clear, probably translation trouble.

This is a good point bringing a plus for the aberrations, the chromatic aberration would be already moderate, probably a little less.

In the mean time even with a doubt I ordered the OTA, now on the way and will report some observations here later.

Good skies to all.

Stanislas-Jean


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#11 Terra Nova

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Posted 18 March 2020 - 12:57 PM

I had one. It was nice and sharp but was clearly (pun intended) an achromat. It had more color than either my previous Unitron or my previous Edmund 4” F15 achomats had and much more than either of my current 4” apos have. However it was more compact than the two achromats, not as compact as the apos. 

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#12 peleuba

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Posted 18 March 2020 - 01:12 PM

Yes.  The Omni 150 refractor has an aspherical lens to help with CA.  I own two and plan to make a binoscope out of them.

 

Aspherization does not help with chromatic aberration.  Color correction is totally dependent on glass type, focal ratio and to a much, much lesser extent the size of the air gap.   But the saying goes and is basically correct:   "...an Achromat is an Achromat is an Achromat..."

 

From a color correction standpoint, this scope will perform exactly as any other Achromat of the same aperture and focal ratio.  This no way around this with normal dispersion glasses.

 

Aspherization does help correct spherical aberration and spherochromatic aberration (which is SA as a function of wavelength).

 

This should be a terrific bino scope at low to moderate powers.


Edited by peleuba, 18 March 2020 - 01:13 PM.

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#13 stanislas-jean

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Posted 19 March 2020 - 06:22 AM

Hi,

Teleskop-Service is very quick, 24H chrono!

I received yesterday afternoon and undertake some verifications, the period being clear at the sky.

First: verification of the alignment and the collimation with the GMK collimator.

The net patch of the 4 light spots were at final well at the center of the FOV, the images of the 3 images of the 4 spots well collimated: no need for additional adjustment on the sky.

The focuser is only decent and need to be replaced by a better one with amplification to be more acurate on the focus point. Anyway it does the job.

The OTA was received without a finder, a dovetail plate for mounting, a diagonal mirror (the OTA is designed for receiving a 2" diagonal).

The focuser tube is very long sothat this may diaphragm the aperture, I have to verify that.

 

I could use it on venus in order to apraise the contrast level of the banding patern appearing.

Hereafetr is a report of venus performed last 18th of march with the new 102mm refractor F10.Conspicuous features at the eyepiece with 111x were met, reduced by the seeing.Very more one hour later when the seeing level was at his best, 7/10, anyway this was not modifying the collected data.

AL was not there, bright spot as well.Polar caps were observed with all filters, banding pattern also.

At the focus point the blue halo is not there, commencing to appear with a 7.7mm ortho eyepiece.

The filter use cancelled this color residue.

I was disapointed of the overall results with a blue RG435 filter where the halo was conspiscious (that was not so proheminent in the meade 90F1000 OTA). Anyway the banding pattern appeared as shown.

This mean the lens aspherisation on that deep blue segment is not a significant help.

This mean also, to be verified the thickness spacers betweeen lenses of the doublet are not optimised in this view.

The yellow-green and deep red segments gave perfect results. The edge of the planet moving with the seeing kept sharp ondulations without filter and with the W11 filter, not blured. A good sign.

 

On the dark sky, the observation of stars m2.0 to M4.0 confirmed the very good collimation with 250x (ortho 4mm kasai).

The 1st diffraction ring was observed circular without light condensations, the airy disk was well clear and circular.

The ronchi exhibited  almost straight bars (less than 1/8 curvation).

Intra extra focus images exhibited spikes of moderate amplitudes suggesting some rough lens surfaces, evaluated to be L/20 +/- rms, rather average.

In fact this is here the limiting point that lower the contrast levels. A pitty.

With a 20mm plosl eyepieve, FOV 1°, pinpoint stars were nored on all the FOV.

 

This must be also evaluated on jupiter, mars, saturn, mercury for a clear completion.

For 320€ this is not a bad figure, but smoother optical surfaces would be welcome for improvement, spacing the lenses as well.

Globally for a comparison, a 102F10 vixen or an istar 100F12 are making similar performance (but little better) on the yellow-green and red color segments, but perform superiorly on the deep plus segment.

Even my 150F6.6 refractor with aspherised lens performs better on the blue segment, but is more sensitive to seeing.

To be followed.

Thanks for reading.

Stanislas-Jean

 

resized_venus 18.3.20 16H00UT.jpg

 


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#14 Rutilus

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Posted 19 March 2020 - 04:13 PM

Very nice report. With my 120mm version of this scope, I re-placed the lens spacing.

when using the scope with 102mm aperture mask, I have an extremely good star test,

and good lens surface. It performs as good as my Japanese made Vixen 102mm f/10.



#15 stanislas-jean

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Posted 24 March 2020 - 07:02 AM

At final, after some days on venus with the 102 refractor, some views has to be modified with regards to the blue channel performance.

Not actually bad in fact. The results had been improved with cleaning deeply the filter, the diagonal mirror and the eyepiece with the aceton solvant.

This was done with the isopropyl alchohol, but in fact this solvant doesnot remove the residual fat on the surfaces.

Now it does images with some contrasts on the blue channel, in spite of the seeing duly noted.

The lens aspherisation is not for Nothing. Easy to compare results with the CC154mm regarding the contrast on the same segment, same times.

Good skies.

Stanislas-Jean

 

resized_venus 23.03.20 11H05UT.jpg

 

 


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