Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

After a quarter of a century...

  • This topic is locked This topic is locked
266 replies to this topic

#201 Mirzam

Mirzam

    Aurora

  • *****
  • Posts: 4799
  • Joined: 01 Apr 2008
  • Loc: Lovettsville, VA

Posted 09 November 2019 - 12:09 PM

What makes a refractor's optics sensitive to collimation? Refractors' strongpoint should be that none is needed, hopefully ever.

 

If APM 152s are uncertain of quality, might as well chance going for a Sky-Watcher ED150 & upgrade bits if necessary.

Poor lens cell design and a triplet lens that is extremely sensitive to decentering of a lens element will do it.

 

JimC


 

#202 BillP

BillP

    Hubble

  • *****
  • Posts: 18795
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 09 November 2019 - 03:07 PM

What makes a refractor's optics sensitive to collimation? Refractors' strongpoint should be that none is needed, hopefully ever.

 

The unique optical prescription of the particular refractor's main objective I would posit as being one important contributor.  I would posit that the focal ratio also comes into play as well, like with Newtonians.  But since refractors typically have small apertures, taking them to 50x/inch (~.5mm exit pupil) or more is usually a routine activity since their magnifications at that level can generally be well within seeing conditions.  So for that fact alone they need more precise collimation as we typically push the refractive optic to extreme limits more often.  So collimation needs to be more precise when you push your optic like that if you want excellent results.  With larger aperture instruments like Dobs and the such, routinely getting to 50x/inch is a relatively rarer thing.  E.g, for a 12" Dob that would be 600x, not something most of us can get to except on rarest evenings of seeing. 

 

As Thomas already mentioned, he brought it up to 255x with the 130mm mask installed for a double star, which is 49.8x/inch.  So refractor users more routinely IMO push their optics, so very precise collimation is a must under those circumstances.


Edited by BillP, 09 November 2019 - 03:13 PM.

 

#203 Traveler

Traveler

    Gemini

  • *****
  • Posts: 3224
  • Joined: 19 Aug 2007
  • Loc: The Netherlands

Posted 10 November 2019 - 02:52 AM

Hi BillP,

May i ask you a question?

 

Why didn't you mentioned the following: 

 

" When I got my 152 from Markus it was well out of collimation." 

 

not in your review from 2014?


 

#204 Steve Allison

Steve Allison

    Apollo

  • *****
  • Posts: 1015
  • Joined: 25 Nov 2016
  • Loc: Olympia, Wash. 98502

Posted 10 November 2019 - 03:39 AM

If it is just a collimation issue, why is APM sending a replacement objective? If the original lens cell is not square to the tube, why would the replacement cell and objective be? 

 

Sounds like APM recognizes that Thomas got a poor lens, in spite of its claim that each telescope is star tested before shipping.

 

Again I ask, how could this happen?


 

#205 Kunama

Kunama

    Aussie at large

  • *****
  • Posts: 4878
  • Joined: 22 Oct 2012
  • Loc: Australia

Posted 10 November 2019 - 03:54 AM

Lot of guessing here.... at least Markus is going to fix the problem.....


 

#206 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • topic starter
  • Posts: 12297
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 10 November 2019 - 04:13 AM

In the case of objective #252 (mine, soon going back to APM), it's definitely NOT a collimation issue. All tests showed a very well collimated lens. 

 

 

Clear skies!
Thomas, Denmark


 

#207 Erik Bakker

Erik Bakker

    Cosmos

  • *****
  • Moderators
  • Posts: 8082
  • Joined: 10 Aug 2006
  • Loc: Netherlands, Europe

Posted 10 November 2019 - 05:19 AM

Quality and consistency have their price. 

Hope this is resolved soon.


 

#208 Steve Allison

Steve Allison

    Apollo

  • *****
  • Posts: 1015
  • Joined: 25 Nov 2016
  • Loc: Olympia, Wash. 98502

Posted 10 November 2019 - 05:55 AM

Me, too.


 

#209 drd715

drd715

    Vostok 1

  • -----
  • Posts: 140
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 10 November 2019 - 10:46 AM

If it is just a collimation issue, why is APM sending a replacement objective? If the original lens cell is not square to the tube, why would the replacement cell and objective be?

Sounds like APM recognizes that Thomas got a poor lens, in spite of its claim that each telescope is star tested before shipping.

Again I ask, how could this happen?

Collimation in the general sense of the term is external to the lens cell. First the objective light cone is centered to the tube, then the focuser is squared to the light cone. Next the diagonal is adjusted (quality diagonals are adjustable ) to center the reflected cone to the center of the eyepiece. And the eyepiece mut be square to the diagonal. All this is owner field adjustment do-able.

But the lens cell has internal alignments between its elements that are best left to the optics shop or advanced amateurs that are into the minutiae of the parameters. De-centering is most likely here baring a defect in the individual lens elements. On an ED doublet especially as the F ratio gets relatively shorter the curves at 2 and 3 are somewhat aggressive. This makes the alignment of exact center between each element very critical to have the two lenses optically interact for the perfect image. Depending upon the internal holding and spacing mechanical mechanism for each lens it is easy enough to knock the internal alignment off center. This will certainly take the sharp crispness out of the image. This is why the cell should go back for evaluation and correct adjustment.

The very early on versions (Lunt) of this scope had some issues with the internal lens cell mechanisms and the cells were redesigned.

As long as the cell adjustments, especially centering (and no tilt between lenses) are tightly tolerance adjusted then this scope will provide extremely good images. It is more critical to adjust lens elements with steeper curves than mild curves, the tolerances are just in a narrower band.

Sent from my SM-N950U using Tapatalk
 

#210 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • topic starter
  • Posts: 12297
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 10 November 2019 - 11:04 AM

 

Depending upon the internal holding and spacing mechanical mechanism for each lens it is easy enough to knock the internal alignment off center. This will certainly take the sharp crispness out of the image.

Yes, but this kind of misalignment is very easy to identify. It will, in severe cases, cause comatic stars on axis. In less severe cases, it gives bright stars a blue fringe on one side and a red fringe on the other, IE it actually shows them as a short spectrum. In the latter case, if the misalignment is slight, but not perfect, the lens can actually give very satisfying performance, but just seems to fall a bit short in terms of color correction (hint to owners of ED objectives that seem to have slightly worse color correction than they should have!). If the lenses have radial adjustment screws, it's actually not very difficult to align them in the field. It's a bit of fiddling and careful work with a tiny screwdriver, but it's not hard. I've done it multiple times on my 72mm f/6 ED. 

 

My APM ED lens shows none of this, so it's well collimated.

 

 

Clear skies!
Thomas, Denmark 


Edited by Astrojensen, 10 November 2019 - 11:05 AM.

 

#211 garret

garret

    Apollo

  • ****-
  • Posts: 1474
  • Joined: 26 Jul 2009
  • Loc: Netherlands

Posted 10 November 2019 - 11:06 AM

Hi BillP,

May i ask you a question?

 

Why didn't you mentioned the following: 

 

" When I got my 152 from Markus it was well out of collimation."

 

not in your review from 2014?

I'm not Bill.P... but the issue with collimation has been solved (see post #209), if this problem is still mentioned in the review, then that problem starts to take on a very negative course for this telescope of its own on the internet.

(Google translation)


Edited by garret, 10 November 2019 - 11:09 AM.

 

#212 Bomber Bob

Bomber Bob

    Hubble

  • *****
  • Posts: 15888
  • Joined: 09 Jul 2013
  • Loc: The Swamp, USA

Posted 10 November 2019 - 11:16 AM

Quality and consistency have their price. 

Hope this is resolved soon.

I had misgivings about this when Thomas didn't get an AtmosFringe Analysis Report like I got with mine (#207).  Yes, it's a gamble buying a 6" ED for under 3 grand, and the missing report is a "tell" -- as it turns out.  APM will make it right, but this scope should never have shipped.


 

#213 donadani

donadani

    Viking 1

  • -----
  • Posts: 886
  • Joined: 20 Jul 2015
  • Loc: Germany

Posted 10 November 2019 - 01:40 PM

I had misgivings about this when Thomas didn't get an AtmosFringe Analysis Report like I got with mine (#207).  Yes, it's a gamble buying a 6" ED for under 3 grand, and the missing report is a "tell" -- as it turns out.  APM will make it right, but this scope should never have shipped.

 

Strange is, that Thomas wrote it was mentioned a startest was done and everything was ok before shipping.

 

Collimation problems caused by transport can happen to any scope is it Takahashi, AP, TEC, Vixen or other top class brands. But a TDE or strong spherical abberation is not affected by transport - especially if Thomas says collimation is just ok - and I´m sure he knows what he writes as he has some very, very good ones as reference wink.gif

 

For uncritical doublet designs - it´s no problem if such a misscollimation happens via transport - just with older scopes it should be enough - to open the cell completely - take out the lenses, cleaning them and put them carfully back with the two pencil stripes over each other... Did that with my FL-80S, FL-102S, A-102M, A-90M, ED-130SS, Zeiss AS80, AS63 - all had a perfect collimated optic after that - just without any collimation screw in the lenscell.

 

Other designs seems to be much more critical to collimation and problems getting bigger with bigger optics too.So that the descibed "Vixen workaraound" maybe don´t work with an APM 152... And OF COURSE never, ever try that with an triplet!

 

But back to Thomas´s problem that is not a collimation-thing... maybe other guys who don´t have the experience of Thomas and don´t know how a really good startest should look like would never care about what Thomas cares. I´m sure you can use the scope just as it is and have nice nights with it - but if you looked through an Zeiss AS... - hmm - better don´t await too much from a 6" "not so expensive" "apo".

 

Btw. as mentioned before - with my APM scope that was MUCH more expensive it was told me with every delivery "that everything should be ok" too - it was not! and it was A LOT of work to proof it and even more work to send it back two times. The good thing: finally I got what I paid for (at least I hope so wink.gif ). 

 

Just a further point in your statistic of life... 

 

cs

Chris


Edited by donadani, 10 November 2019 - 01:46 PM.

 

#214 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • topic starter
  • Posts: 12297
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 10 November 2019 - 02:46 PM

Had a chance to test the scope on the Moon and Capella (still with lens #252). The problem remains the same. The Moon was awash in a haze of unfocused light, when observed at full aperture at 255x (4.7mm ES82). Stopping down the lens to 140mm improved the situation dramatically, but it needed to be stopped down to 130mm to fully remove the problem. 

 

It was NOT a false color issue, as the scope has almost no false color at all, even at full aperture, when in best focus. At 130mm it has basically none at all. The lunar views were beautifully clean and sharp at 130mm, but the seeing was only fair and I was soon interrupted by clouds. 

 

The star test at full aperture in best focus is pretty psychedelic in mediocre seeing, which breaks the haze surrounding the airy disk up into long, bright, twisting, striped snakes of light, that dances around the airy disk! Never seen anything quite like that before! shocked.gif  

 

This goes away completely at 130mm aperture, leaving only a sharp, white airy disk and a first ring, with faint hints of second rings. 140mm is dramatically improved, but faint "snakes" still dance around the airy disk, again proving that the scope needs to be stopped down to at least 130mm for best performance. 

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 10 November 2019 - 02:48 PM.

 

#215 Tyson M

Tyson M

    Soyuz

  • *****
  • Posts: 3740
  • Joined: 22 Jan 2015
  • Loc: 53 degrees North

Posted 10 November 2019 - 05:55 PM

Striped snakes......just when we thought us refractorholics had enough optical abberations to worry about, now this(!).

 

*adds it to the list


 

#216 Tyson M

Tyson M

    Soyuz

  • *****
  • Posts: 3740
  • Joined: 22 Jan 2015
  • Loc: 53 degrees North

Posted 10 November 2019 - 05:57 PM

In all serious though, all things considered- I think Markus is a class act for letting you exchange the lens.


 

#217 Bomber Bob

Bomber Bob

    Hubble

  • *****
  • Posts: 15888
  • Joined: 09 Jul 2013
  • Loc: The Swamp, USA

Posted 10 November 2019 - 05:58 PM

Haven't used my 152 in MONTHS, so I have it set up now.  Gonna repeat star tests, and test some new uber-cheap 2" eyepieces.  The lens is cleaned & collimated -- so no alibis!

 

What I saw...  I started right after sunset (clouds on the way!) ~ 2330Z

 

First star test was on Altair in 7/10 seeing.  With a UO HD 9mm Ortho, IF showed a round Airy disk with very bright center / bright 1st ring / much fainter 2nd ring, and outer rings were fainter & tougher to distinguish;  OF showed a fainter center, faint 1st ring, very faint 2nd, and outer rings were out-of-round.  To save my neck, I put the Baader prism in, and got the same results as straight through,

 

Second test was on Vega in 8/10 seeing.  I used the UO HD 6mm Ortho.  I got similar results to Altair, EXCEPT at OF, the center had a green tint.  I switched to my spectros PL7.5, and got a cleaner picture both sides of focus, and no green.  At focus, I didn't see the "blue halo" that I've seen before in this scope.

 

Thomas, maybe I missed it, but did you do any straight-through (no diagonal) star tests?

 

Also:  Did APM / Markus say they did a star test on your 152 before shipping it?

 

It's been posted in this thread & others that the APM 152 & S-W 150 push a lot of limits to stay economical:  Cheaper ED glasses, steep curves that must be aligned to tight tolerances, and must stay aligned for shipping globally, etc.  The lab report on mine is toward the bottom of the range, and it is by no means a perfect doublet -- I have 50+ year old Japan-made achromatics with better DPAC patterns -- but it performs better than expected.  It's like a compact 6" F15.

 

I hope the replacement is acceptable.  Maybe APM has come up against that other limit -- profitability -- and is shipping whatever they have on hand.


Edited by Bomber Bob, 10 November 2019 - 10:52 PM.

 

#218 Steve Allison

Steve Allison

    Apollo

  • *****
  • Posts: 1015
  • Joined: 25 Nov 2016
  • Loc: Olympia, Wash. 98502

Posted 10 November 2019 - 06:31 PM

In all serious though, all things considered- I think Markus is a class act for letting you exchange the lens.

Well, maybe. But is it a class act just to exchange a clearly defective lens that was sent out with the assurance that it was star-tested and was good? The lens seems to have been misrepresented to Thomas, which would not be a class act.

 

I don't get why some posters always try to minimize the problem and suggest it is great customer service for a company to merely replace a bad telescope that should never been sent out in the first place.

 

APM has a developed some good products at very attractive prices, but I think lumps must be taken when they are deserved.


Edited by Steve Allison, 10 November 2019 - 06:35 PM.

 

#219 Tyson M

Tyson M

    Soyuz

  • *****
  • Posts: 3740
  • Joined: 22 Jan 2015
  • Loc: 53 degrees North

Posted 10 November 2019 - 06:34 PM

No one is perfect, and problems can happen with anyone, over any sale (including preowned).  Shipping refractors can be problematic too, despite the best packing jobs, sometimes a courier drops a box, ect.

It's how one responds to a problem that is my main concern in this hobby.  They don't deserve lumps if they remeadiate the issue. 


 

#220 Steve Allison

Steve Allison

    Apollo

  • *****
  • Posts: 1015
  • Joined: 25 Nov 2016
  • Loc: Olympia, Wash. 98502

Posted 10 November 2019 - 06:38 PM

Granted. I guess my problem is that the telescope was supposed to have been star tested and good optically. In Thomas' case either it was not star tested or the tester did not know how to conduct the test. Is this okay?


 

#221 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 6874
  • Joined: 04 Jan 2004
  • Loc: ROR Obs. near Pettigrew, AR

Posted 10 November 2019 - 09:12 PM

Thomas,

How long do you think it will take to make the exchange and get back to star testing, providing it's good weather?


 

#222 donadani

donadani

    Viking 1

  • -----
  • Posts: 886
  • Joined: 20 Jul 2015
  • Loc: Germany

Posted 11 November 2019 - 12:50 AM

Look at post #106 - Thomas got even a "certificate" that it was successfully startested... It´s always good to have a paper that ceritficates something :D 


 

#223 Erik Bakker

Erik Bakker

    Cosmos

  • *****
  • Moderators
  • Posts: 8082
  • Joined: 10 Aug 2006
  • Loc: Netherlands, Europe

Posted 11 November 2019 - 05:07 AM

Look at post #106 - Thomas got even a "certificate" that it was successfully startested... It´s always good to have a paper that ceritficates something laugh.gif

The world on certificates can look very bright lol.gif


 

#224 emilslomi

emilslomi

    Messenger

  • -----
  • Posts: 403
  • Joined: 12 Nov 2015
  • Loc: Alps

Posted 11 November 2019 - 05:31 AM

@ Thomas

How does your star test compare to the one that Marcus posted when the scope came out? Is it really much worse?

 

Emil


 

#225 Erik Bakker

Erik Bakker

    Cosmos

  • *****
  • Moderators
  • Posts: 8082
  • Joined: 10 Aug 2006
  • Loc: Netherlands, Europe

Posted 11 November 2019 - 01:42 PM

@ Thomas

How does your star test compare to the one that Marcus posted when the scope came out? Is it really much worse?

 

Emil

I do think that Marcus put some realistic disclaimers there waytogo.gif


 


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics