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New TS cassegrain 154F12

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#1 stanislas-jean

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Posted 14 May 2019 - 04:50 AM

Not a SCT or a mak or a DK, but, there is a new pure cassegrain OTA offered by TS:

https://www.teleskop...848-mm-OTA.html

It is cheap, offered with 2 other sizes 203 and 254mm.

The merit of such system is known, good transmission from UV to IR and fixed focus point on the optical axis.

Alignment and collimation is not a big concern.

Is there somebody here who has some returns about the optical accuracy we could expected on?

Seems to be a GSO source.

Thanks for your returns here about.

Stanislas-jean


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#2 MortonH

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Posted 14 May 2019 - 06:19 AM

Previous threads discussing this scope under AT/GSO/Orion labels:

 

 

https://www.cloudyni...cal-cassegrain/

 

https://www.cloudyni...r/#entry9079770

 

https://www.cloudyni...-3#entry9363153



#3 stanislas-jean

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Posted 14 May 2019 - 09:46 AM

Thanks for all the links you brought.

However none gives answer about the question raised: optical quality.

The interest of CC is in comparison with any other design the absence of spherochomatism on the uv- blue color segment, the same characteristics well kept on IR segment.

SCT, mak, klevstov, any derivated fails, not a little but substantially, including 150mm apo of 15000usd.

I read some qualitative witness from a guy owning a CFF arguing of the better contrast got on the uv segment, but not quantified and depending also on the actual optical accuracy of the optics in hands.

If gents are owning already such gso CC, may be they have used them on planets and could report, or, having practiced star test, interfero.

Points to be reported

-spherical aberration on the ota,

-strehl and rms observed,

-PTV, etc...

CC is the best possible design reaching the aperture limit characteristics on the optical axis and few minuts of arc from.

Enough for planets, CC is not dedicated for dso of extended objects where must reach on all its part the optical limits.

Should be a gun in uv for venus and mars. F12 is enough for imaging.

Stanislas-Jean



#4 SeattleScott

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Posted 14 May 2019 - 11:05 AM

This is a very new model and few people (% wise at least) have the equipment and skills to do the kind of testing you are looking for. Generally people sound happy with the optical performance, but that is about all we know at the moment. I don’t even recall a shootout with a 6” F12 Mak yet, although I think there was some talk about that.

Scott

#5 starman876

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Posted 14 May 2019 - 06:08 PM

for $500 sounds like a good deal with nice optics.



#6 stanislas-jean

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Posted 15 May 2019 - 02:42 AM

Thanks gents, Scott, starman for your posts.

In order to see what the value of this OTA, it is now on the way to home.

We will see what will happen. Looks promising, but, here for 400, could be also a kind of lemon due to optical acuracy lacks.

Will report some results here.

Stanislas-Jean


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#7 GlenM

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Posted 15 May 2019 - 08:11 AM

Looking forward to your review, Stanislas.

 

Glen.


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#8 stanislas-jean

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Posted 16 May 2019 - 05:49 AM

Hi, just received via ups.

In good order at the first look, but seems a little mis collimated (or mis aligned also). As it is declared it is collimated before the expedition, we will have to take care of any schock for keeping the status.

The collimation booklet is missing in the box, but no need for.

Weather is changing a lot to-day, but if we have some apertures I will try with the ota well collimated this afternoon with gmk and cheschire.

Stanislas-Jean


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#9 stanislas-jean

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Posted 16 May 2019 - 01:06 PM

Not exactly, numbers are of high importance. I suggest the post to be read fully.

What is aimed is the good vision for the blue color segment and the red nir segment. For the middle any good scope is enough.

Sothat high numbers are researched for those, the best possible in order to keep a L/4 in uv segment. Right?

Refiguring mirrors, especially the secondary, requests a very good optician. The involved costs also will superseed the price of the TS ota. So stricly no interest to do. The operation is delicate here with giving such to well recognised opticians and most of them refuse to act on such.

If you get 5/10 images collected on a star highly magnified, the scope should support 200-250x on planets for the least with good numbers optically speaking. This is done on the mk67 intes but the deep blue/uv is affected by the spherochromatism not negligeable sothat low contrasted features are therefore mostly washed.

Reason why of the cassegrain, a newtonian can do also but a F12 is monstruous, should be also unstable.

Stanislas-Jean.



#10 stanislas-jean

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Posted 17 May 2019 - 03:20 AM

Weather was not cooperating yesterday to practice tests on sky.

Yesterday afternoon, cheschire, laser were performed on the received ota.

 

- Cheschire: font tube obturated, the secondary was out slightly and moved to get concentric circles through the cheschire.

Easy to do, but this could be ok only if the optical axis, primary and secondary are perfectly the same. Also with the eyepiece holder axis.

- laser: when inserting the laser at the eyepiece holder the beam should set the red point at the center, this was at the 1/2mm more or less. The reflected beam set a red point almost on the laser device almost at its center, say 2mm from the center. This means the presence of a slight misalignment between secondary and eyepiece holder. I didn't re-touch this slight defect because the mechanical quality would not keep the proper settlement (due to the crayford in place, play of components and tension into the crayford).

- gmk: the figure got into the gmk with a 12-15mm eyepice confirmed the above evaluation. The four light dots were not centered together, but the mis centering was slight also.

 

This was solved globally with the slight modification of the tilt of the eyepiece holder, acting on the push pull screws of the crayford holder (2x3 screws). A tenth of turn screw on a side was enough with using using the laser beam. Confirmation with the gmk and the cheschire after recollimation acting slightly on the secondary. Enough.

 

The misalignment of the axis of each component, secondary, primary, eyepiece holder, should be slight now, not null.

Was happy to get a tube with this misalignment rather slight otherwise I had to modify the centering of the secondary with acting on the spider, an other game and long to do.

Now remains the test on sky with 300x magnification to see donuts in and out focus, diffraction rings and airy disk, that must be clear at focus point, well centered and uniformly lighted.

Centering between secondary and primary are of high importance because influencing significantly the contrast image.

This is compromise here because primary is fixed position, no possibility for a settlement, because it is pre-supposed we have alignment between the eyepiece holder and the primary axis (not perfect perfect surely indeed).

It is considered to be into settlement tolerance of the considered design, but if we gain some contrast % more this is full benefit. 

In order to see the quality of the settlement, I shocked the tube at the front normally and re-settlement was to be re-achieved (fortunately only a collimation), so be aware of the handling.

I did on a 305 meade sct considered by the 1st owner only average, becoming average good, getting views on uranus and venus afterwards. Same on a vmc-vc 200mm getting substantially more than a good c8, on c11ultima misaligned.

Waiting weather now for testing, for few days.

Good skies.

Stanislas-Jean


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#11 GlenM

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Posted 17 May 2019 - 08:21 AM

Thanks, Stanislas.

 

Glen.



#12 stanislas-jean

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Posted 17 May 2019 - 09:42 AM

Just a preliminary Glen.

S-J



#13 stanislas-jean

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Posted 18 May 2019 - 02:57 AM

At final I tried yesterday evening between clouds and holes in cloud layer on arcturus to what at a first look.

After only half an hour of cooling time (not enough), I examined the diffraction patern of the star at focus point, in and out but fugitively.

 

First, to get focusing simply a 25mm spacer needs to be installed for using eyepieces from 32 to 5mm, all designs.

I inserted the only I had, a 2" dia of 2" long, that was enough for use with eyepieces from 15 to 6mm, crayford pipe fully out.

 

Collimation was to be retouched a little and this was quick to achieve (in and out focus get to the focus point concentricly. Means not bad alignment and collimation.

 

I commenced with the 123x to see the donut pattern (in-out of focus point), after retouching the secondary I got a perfect donut that focused concentricly to the focus point, then checked with 264 and 308x to see the diffraction pattern of a star close to arcturus.

 

The airy disk was there with an hazze surrounding its, moving with seeing, sometimes becoming stable with the vision of 4 spikes, 3 equally set around at 120° angle and the fourth placed between 2 spikes.

This network may be correlated to the spider conformation. The fourth spike is typically what we see on the cassegrain design when the tube is cooling having not reached its temperature equilibrium.

 

Sometimes on 1s moment appeared the 1st diffraction ring, almost concentric, but very slightly miscollimated.

The said spikes pattern commenced to fade with the time.

Weather was calm, no wind, but cloudy, 14°C on the time.

 

I didn't have some more time for evaluation with the ronchi eyepiece of 10lp/mm. This should get an idea about the residual spherical aberration of the present optics.

 

The preliminary conclusion is, comparing with other tube of known characteristics placed in similar conditions, the optical quality rather average (may be average good) than good. This not means average poor. The mk67 is making better under such. Anyway a diffraction limited as said usually on commercial booklets (the 400bucks is on the optics).

 

This has to be retaken on a better night conditions for a firm evaluation/ confirmation under the ota on the temperature.

I inserted one of the spacers furnished with the scope (the 25mm) at this issue, but, everything about the alignment and collimation has to be re-done (it is possible to move the crayford axis laterally because some play is existing at the assembly on the spacer, new additional problem).

This is only a preliminary for the moment.

Good skies.

Stanislas-Jean

 

resized_cass 150F12 test 17.05.19 20H30UT.jpg


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#14 GlenM

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Posted 18 May 2019 - 05:59 AM

Thank you,Stanislas.

 

Glen.



#15 stanislas-jean

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Posted 21 May 2019 - 03:16 AM

Hi,

At final I had a good stable night in order to evaluate more acurately this scope.

 

With 123, 205 264 308 and 450x, the collimation was retouched, just a little, lucky I was.

Seeing was quoted 7-8/10 at 20H20UT, 3 quaters hour after sunset on SAO100949 of m6,0, near arcturus.

The 1st diffraction ring was well centered equally all around and the airy disk well clear and circular.

Elevation was 39° above horizon.

I pointed on arcturus to see in and out focus donuts at 2-3 wavelenght .

Sketches are shown under.

 

Evaluations was conducted with reference to the De Suiter book "star testing astronomical telescopes":

 

-roughness of optics: external ring donuts, in-out showed a figure corresponding between 1/20-1/40th wavelength, rather close to 1/20th,

-astigmatism: not especially marked on that point, say standing at less 1/10th wavelength,

-spherical aberration: say standing at less 1/8th wavelength,

-optical acuracy: say standing between 1/4 and 1/8th wavelength, rather close to 1/4th probably 1/5-6.

 

The ronchi test which is more qualitative had confirmed the above assessments.

The easy tester (6lp/mm) showed on arcturus straight bars with no inflexion especially at the outer diameter of primary.

It seemed that 2 bars, still straight, exhibited some very slight angle, this involves some residual astigmatism (not actually shown with the star test).

The 10lp/mm ronchi eyepiece use didn't confirmed the previous evaluation, bars were straight and parallel. This confirmed narrowly the star test results.

With adding the fact in-out donuts were always circular at the 205-264x magnifications.

 

The test was conducted on a m6.0 star, a little too dim, and on arcturus of m0,0, too bright. This should be performed on a m2-3,0 star in order to observe more subtilities.

 

Anyway the tests involve a scope status being not a melon, not an excellent scope but say an average good to good scope, quoted at L/5 more or less, of no specific aberration raising at a significant distroying amount. The roughness on the optical surfaces is say normal, better than a simple diffraction limit optics of 1/14th wavelength theorical.

At final a good buy for the 400 invested, and roughly a good buy.

A roddier test would be also a good additionnal, if I have the courage for performing.

Also a knife edge placed at the focus plan would be an help.

There was no planet visible, no moon visible at the time so this could be also a confirmation when viewing.

L/5 if well actual would help for performing on the target expected, planets in deep blue color also in near uv.

 

Hope this helps gents for selection of such scope, a CC.

Good skies.

Stanislas-Jean

 

resized_star test 150CC F12 20.05.19.jpg


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#16 memento

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Posted 21 May 2019 - 05:17 AM

Stanislas, great reports so far. I realize you have other better / higher quality scopes but did you ever use a standard SCT? If so how would the TS Cassegrain compare with that?


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#17 stanislas-jean

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Posted 21 May 2019 - 10:15 AM

No question for SCT I owned C8 and C11, to-day the C9 stays still here.

All are and were not bad, an excellent C8, good C11.

However, with regards to the design all these compacts, sct, mak, klevtsov are suffering from the spherochromatism on the blue color segment, so uv worst. Even the apo.

Some limitations also for the NIR segment were transmission light is somewhere lowered.

The only designs that support these absences are the newtonian, the dk, the CC.

The prices here:

CC 150F12: 400, from GSO,

DK 180F11-12: 2200, from Takahashi,

newtonian 150F8: 500, from Orion UK. F/D is not enough but the barlow needed may be an handicap,

not the same optical acuracy, the CC on the ota tested say L/5, the dk targeted to be L/10, the newtonian of L/8 500.

Zen optics sell a CC mirrors set of 150F16 for 660, hardware to be created, of L/6 probably (global not more but with very soft surfaces).

Make your deal.

I feel the CC gso can be sufficient for imaging with the astrodon uv filter and the RG 435 baader for venus and mars at the focus point, no barlow. F16 would be better but we have what we have for getting a completed ota.

Reason why of the buy.

Good sky.

Stanislas-Jean


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#18 stanislas-jean

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Posted 23 May 2019 - 06:01 AM

An other night yesterday evening maked some other observations with this scope.

Nothing more to say on the diffraction pattern of a star at high power.

But regarding the low magnification results especially at 58x, this is the flat field observed at the 32mm eyepice I got (0,9° AFOV), a basic plossl. Pinpoint stars on 100% of the field, no coma seen also with 123x, 15mm TV plossl.

For a CC this is somewhere exceptionnal, I think at final this is a RC of F12, instead of their F8 RC, and moderate CO with quartz mirrors.

Why not ! Results are there, rather good enough.

Good skies.

Stanislas-Jean.


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#19 dweller25

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Posted 26 May 2019 - 02:00 PM

Great reports so far S-J, thanks for sharing.



#20 Mert

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Posted 26 May 2019 - 02:13 PM

At least the scope looks like the RC!

Thanks for your extensive testing, very interesting!



#21 stanislas-jean

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Posted 27 May 2019 - 03:09 AM

Thanks David, Mert for your kind words.

Yes this scope at final is looking a F12 RC rather than a pure CC.

Doesn't matter for the issue.

With such I would have to buy the 8" also available on the moment.

However, this is for mine, if some other owners could test also simililarly we could have a good figure of the ota quality produced by GSO.

So a call for these performances (even with a roddier test).

Good skies.

Stanislas-Jean



#22 dweller25

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Posted 27 May 2019 - 04:08 AM

Hello Stanislas-Jean

What is your best guess for how the 154mm TS Cassegrain would compare visually on planetary performance to a C6 or a good 4” APO ?



#23 stanislas-jean

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Posted 27 May 2019 - 11:16 AM

None of them David.

The 4" even apo remains with a resolution of the 4", substantially less in UV, also in deep red.

the 6" sct, with 37%CO (C6) will have the resolution of the 6" but with lower contrasts (D-d 96mm) substantially less in UV.

the GSO with 33%CO will have the resolution of the 6" but with lower contrast (D-d 103mm).

The strehl will be the best in the CC/RC for UV, good for YG and good for deep red. The apo and the sct will be affected for deep red to NIR, said already for UV.

Now for very fine details, the high strehl will prevails, met on the apo but only a 4", the vision of such in the 6" sct will be affected by its actual strehl (say 90% which involve a L/4-5 and about rms L/20), similar to the GSO in the yellow-green but improved in UV and deep red.

Now, in the seeing, closed tube may be under certain conditions an advantage regarding the instrumental seeing, one light way into the apo, the more stable, 3 light ways into the compact tubes. I know conditions when open tube get better and more stable, especially under warm weather.

Now if you make interfering the strehl of the optics, the CO, the seeing of the sky, the color of observation what is sure:

the greater CO doesnot help to keep the contrasts, the moderate strehl too. The combination between these parameters can be evaluated using ftm curves.

What is sure on action with each tubes, this is well verified, considering the quotation of each parameters this involves logically the vision of known features more or less, sothat watching at a sketch, can be expected some pertinence and the evaluation of the visual acuity of the observer.

At the results got with the GSO, on mine, this is representing a good compromise for observing in UV, yellow-green, deep red/NIR.  Without  hesitation the best for making many things with flat field on bonus with only 2 optical surfaces.

Hope GSO may consider the fact for producing L/6 and better optic levels.



#24 dweller25

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Posted 27 May 2019 - 03:34 PM

Thanks S-J

Looking forward to more reports.......



#25 Peter Besenbruch

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Posted 29 May 2019 - 01:59 PM

stanislas-jean's comments regarding breadth of response in the deep red into the ultra-violet are interesting.




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