Jump to content


Photo

Receipt of a 152mm F8 sky-wacher achromat OTA

  • Please log in to reply
10 replies to this topic

#1 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 26 July 2014 - 06:34 AM

I was researching again a new >152mm achromat, having sold my Istar 150mmF10, very good, with regrets.
I bought the 152-1200 sky- watcher at TS Germany, no TS 152-900 available at the time.
I was reluctant to accept the OTA when seeing the absence of collimation on the lens cell.
TS was agreeing to re-take it on this fact, but in the meantime I did tests on OTA:
- lens spacing with a monochromatic light, young fringes well centered,
- cheschire test: seems well aligned,
- artificial star: observed at 10m, collimation until 300x slightly mis collimated from 325 until 480x. Ronchi test exhibit slightly curved bars (<1/8 interfrange).
- on sky on a m3.0 star airy disk was circular with a 1st ring also circular at 200x-300x slightly miscollimated from 325 until 373x.
I was anxious about the absence of collimation possibility on the lens cell.
Force to see this is delivered aligned and collimated as the design is.
325 and 375x get me the banding system on Uranus recently.
This not excellent but good to very good.
No need to go to better scopes as, apo we have one here with resolution ability, mine.
Weight is 9kgs, not 13 kgs given on the advice.
Stanislas-Jean

#2 sonny.barile

sonny.barile

    Viking 1

  • -----
  • Posts: 648
  • Joined: 19 Oct 2010
  • Loc: In the glow.....somewhere between the city and the stadiums.

Posted 26 July 2014 - 07:33 AM

So are you keeping it? What did you mount it on? How hard/easy is it to lug around? :question:

#3 BillP

BillP

    Voyager 1

  • *****
  • Posts: 11382
  • Joined: 26 Nov 2006
  • Loc: Vienna, VA

Posted 26 July 2014 - 10:26 AM

325 and 375x get me the banding system on Uranus recently.
This not excellent but good to very good.
No need to go to better scopes ...


I find that refractors seem to be more tolerant of mis-collimation than other designs. I've gotten some really good performance from refractors that are out of collimation, particularly achormats. If you are getting a good view at 375x from a 6" scope (that's a 0.4mm exit pupil), I'd say that is just fine as that is a practical limit for 99.9% of needs as view getting quite dim by then.

Also, how is the focuser attached? If attached with side screws, then you could probably shim it a little to get the collimation spot on.

#4 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 27 July 2014 - 04:36 AM

375x on a star with a diffraction pattern very clean, means a good scope (airy disk and 1st ring).
The 100ED at 250 doesnot give such.
Be aware of the alignment and collimation which are 2 different operations.
The scope is aligned (the laser inserted in the eyepiece holder get a trace spot on the lens centered at more or less 1mm. The lens cell needs to be retouched very slighly to get a perfect star pattern at 375x, very slightly.
Here is a photo of the lens cell with so many markings, the chineese operators performed a good job: lens perfectly spaced and collimated. For 100 more I pay for a collimatable lens cell.
The rack and pinion is decent, not enough for focusing at 375x but when installing the orion motor it makes a good device and focusing is easy to do for few euros.
Not final bad results for 10 times less than the cheap cn apo.
Reason why of this forum for showing the global good quality of the OTA with an actual potential.
Stanislas-Jean

Attached Files


  • Astronewb likes this

#5 saemark30

saemark30

    Apollo

  • -----
  • Posts: 1111
  • Joined: 21 Feb 2012

Posted 27 July 2014 - 04:01 PM

Interesting your tube looks to be white. My Synta has no collimatable cell and is dark blue. Do you know how to remove the cell so I can change lens spacing and do an element rotation?
What eyepiece/barlow did you get to 375x?

#6 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 28 July 2014 - 12:53 AM

Normally the end cell on synta is screwed as all refractor including their ED apo.
The end is white cream and the tube black nacred.
For an operation on the doublet you need a monochromatic light (5$ at electronic store radio shack for a neon light) and see the spacing correct or not. The Young fringes needs to be centered. After element rotation this is an other story, dismount rotate re-assemble test on sky or an artificial star etc... until finding the best result.
Spacing will involve more results on images at final.
But don't undertake this if you never did. Try in first on a 60mm for training.
I never use Barlow, the 375x is got from a 3.2mm eyepiece, the TMB serie is suitable. For testing, have 2 different kinds because some eyepiece introduce astigmatism, light but present. More often than you can imagine, even on costy eyepieces.
Stanislas-Jean

#7 Astrojensen

Astrojensen

    Fly Me to the Moon

  • *****
  • Posts: 5082
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 28 July 2014 - 02:12 AM

I never use Barlow, the 375x is got from a 3.2mm eyepiece, the TMB serie is suitable.



The 3.2mm TMB has a built in barlow... :grin:


Clear skies!
Thomas, Denmark

#8 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 28 July 2014 - 03:37 AM

any has.
Stanislas-Jean

#9 John Huntley

John Huntley

    Viking 1

  • *****
  • Posts: 926
  • Joined: 16 Jul 2006
  • Loc: South West England

Posted 28 July 2014 - 07:12 PM

Normally the end cell on synta is screwed as all refractor including their ED apo....


The latest versions of the 150mm F/8 achromats have the collimatable objective lens cell again, as the blue tube ones did.

Through the life of this design they seem to have fluctuated between a non-collimatable lens cell and the collimatable type.

The latter affects the tube balance more as it's a heavier cell at the top end of the tube.

#10 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 29 July 2014 - 12:43 AM

Better in fact, but TS germany said that this is the last design since years now.
It may change on new last items as you report.
Stanislas-Jean

#11 stanislas-jean

stanislas-jean

    Surveyor 1

  • -----
  • Posts: 1991
  • Joined: 22 Oct 2008

Posted 20 August 2014 - 01:28 AM

 

325 and 375x get me the banding system on Uranus recently.
This not excellent but good to very good.
No need to go to better scopes ...


I find that refractors seem to be more tolerant of mis-collimation than other designs. I've gotten some really good performance from refractors that are out of collimation, particularly achormats. If you are getting a good view at 375x from a 6" scope (that's a 0.4mm exit pupil), I'd say that is just fine as that is a practical limit for 99.9% of needs as view getting quite dim by then.

Also, how is the focuser attached? If attached with side screws, then you could probably shim it a little to get the collimation spot on.

 

At final I got the collimation.

Thanks Bill, retouching the focucer by shiming, the collimation is good enough now.

The improvement on the images is sensitive on the moon and tiny size details, there was a misadjustment at the origin with the 1st ring not equally bright around and now almost equal.

The way for setting was a good compromise.

Stanislas-Jean








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics