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cambert
sage


Reged: 07/21/04
Posts: 243
Loc: Chartres, France
PST disease explained ?
      #1260915 - 11/20/06 03:03 PM

Its may be a stupid idea but what if the PST disease comes simply because the lens is at the front ?
The Maxscope system put the lens after the etalon, so it get only a tiny fraction of the heat.
But the PST lens get 100% of the sun heat.
And since the light rejected by the internal etalon is reflected back to the lens, its receive another 100% of the heat.
The lens is heated twice !
Do you know another telescope where the lens is pointed directly to the sun without any protection ?
Maybe the coating (standard, gold, blue) are ok but just can't stand that heat...

--------------------
Cambert
Coronado Maxscope 40 telescope
10" Meade SCT
16" Meade Lightbridge


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LarryAlvarez
Post Laureate


Reged: 08/12/05
Posts: 3298
Loc: Texas
Re: PST disease explained ? new [Re: cambert]
      #1260951 - 11/20/06 03:26 PM

Cam - any scope using a Herschel Wedge would recieve 100% of the light. I had an 80ED that I used in this configuration with no issues up until the time I sold it, not quite apples to apples but similar in respect to the light passing through. Clear Skyz, LA

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cambert
sage


Reged: 07/21/04
Posts: 243
Loc: Chartres, France
Re: PST disease explained ? new [Re: LarryAlvarez]
      #1260964 - 11/20/06 03:34 PM

so it was a stupid idea after all

--------------------
Cambert
Coronado Maxscope 40 telescope
10" Meade SCT
16" Meade Lightbridge


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Richard B. Drumm
Pooh-Bah


Reged: 07/14/05
Posts: 1486
Loc: Albemarle Co. Virginia
Re: PST disease explained ? new [Re: cambert]
      #1260984 - 11/20/06 03:43 PM

Pas de probleme, mon ami! Pas de probleme.
It was a good idea, just not the right one...
If the coatings on the lenses has gotten contaminated by exposure to air, then they are oxidized.
Then the heat could have triggered the oxidation to proceed further somehow... I'm no chemist, though...
Rich

--------------------
AKA Richard Drumm The Astronomy Bum
Orion Atlas 10 (10" Newt on an equatorial mount)
Celestron 15x70 SkyMaster Binocs
Coronado Ha PST
President, Charlottesville Astronomical Society
IOTA member

38 10' 57"N, 78 23' 09"W


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cambert
sage


Reged: 07/21/04
Posts: 243
Loc: Chartres, France
Re: PST disease explained ? new [Re: Richard B. Drumm]
      #1261019 - 11/20/06 04:11 PM

Thanks for your french !

I just find extremely strange that the same disease concerns three different coatings, regular, gold and blue.
So I wondered if the problem could be elsewhere.

--------------------
Cambert
Coronado Maxscope 40 telescope
10" Meade SCT
16" Meade Lightbridge


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Bucephelus
Vendor


Reged: 04/20/06
Posts: 777
Loc: Northern, CA
Re: PST disease explained ? new [Re: cambert]
      #1261275 - 11/20/06 06:55 PM

I have thought the same thing actually. I think they need an energy rejection system out front. ANYTHING simple might do it. Like a pop on baader filter.

Chris


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Oldfield
Postmaster


Reged: 03/20/02
Posts: 6310
Loc: Hong Kong
Re: PST disease explained ? new [Re: Bucephelus]
      #1261357 - 11/20/06 07:45 PM

I heard that it's coating problem, the coating got oxidized somehow, so it will show problem even stored inside a box without the sun.

--------------------
The Home Astronomer from a city where most people are proud of the light pollution

Toys: Tele Vue Ranger, GOTO Mark-X, Lumenera LU070M, Canon 10x30 IS...

My observation log and ideas My General Blog


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SprintCar Driver
Pooh-Bah


Reged: 03/19/06
Posts: 1402
Loc: SoCal.
Re: PST disease explained ? new [Re: Oldfield]
      #1261371 - 11/20/06 07:51 PM

I heard it was a problem in the coating process tha allowed air contamination during the coating process.

--------------------
Bill

If theres someone you cant understand try walking a mile in their shoes. If you still dont understand them at least you will be a mile away from them and you will have a new pair of shoes.

C11 atlas EQ-G DsiI/Neximage
8" Coulter(red)dob.
PST Ha
Edmund Astro Scan
Sears Discoverer refractor/EQ(my 1st scope)


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Erix
Toad Lily


Reged: 12/25/04
Posts: 24022
Loc: Texas, USA
Re: PST disease explained ? new [Re: SprintCar Driver]
      #1261609 - 11/20/06 09:50 PM

Here it is, straight from Russ: thread

--------------------
Erika
Automatic doors make me feel like a Jedi.

Zhumell 16", 10" LX200 Classic,Celestron 102 XLT, ETX70-AT, DS Maxscope 60mm, AT6RC
PCW Memorial Observatory


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Richard B. Drumm
Pooh-Bah


Reged: 07/14/05
Posts: 1486
Loc: Albemarle Co. Virginia
Re: PST disease explained ? new [Re: Erix]
      #1261710 - 11/20/06 10:53 PM

Cambert et al:
Here's a report of a PST (from my list):
99760 sick - (brand new in the box) - Steven Kim "kimsc321"

So if it was in the box all the time it wasn't exposed to the sun. Thus the sun couldn't have caused the problem.
Don't know why I didn't think of that sooner...
Must be all the gray hair...
Rich

--------------------
AKA Richard Drumm The Astronomy Bum
Orion Atlas 10 (10" Newt on an equatorial mount)
Celestron 15x70 SkyMaster Binocs
Coronado Ha PST
President, Charlottesville Astronomical Society
IOTA member

38 10' 57"N, 78 23' 09"W


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Carpe Noctum
Carpal Tunnel


Reged: 05/22/05
Posts: 1500
Loc: Morada, CA
Re: PST disease explained ? new [Re: Erix]
      #1261821 - 11/21/06 12:11 AM

Quote:

Here it is, straight from Russ: thread




FWI, Russ left Meade (Coronado) shortly after that response and-I was told-no longer with the company. Too bad. He was a pleasure to deal with.

Subsequent customer service reps that I spoke to (while ny PST was being repaired, lost and finally replaced) had varying responses regarding the "rust" and the number of PSTs being serviced per month.

--------------------
Bruce

AP 140 7.5 Starfire EDF I love that new scope smell!
Stellarvue SV130
Stellarvue SV80S
Takahashi EM-400 Temma II
DM6 mount w/Sky Commander XP4
ST2000XCM CFW-9 & Astrodons
PST double stacked
Lunt LS100F DS filters
Denk II Binoviewer w/PxS

Project Astro visiting astronomer


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cambert
sage


Reged: 07/21/04
Posts: 243
Loc: Chartres, France
Re: PST disease explained ? new [Re: Erix]
      #1261884 - 11/21/06 01:41 AM

Quote:

Here it is, straight from Russ: thread



Yes I know, but it doesn't explain why new gold and blue coatings get sick too, and why some PST get sick twice (after being repaired).

--------------------
Cambert
Coronado Maxscope 40 telescope
10" Meade SCT
16" Meade Lightbridge


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Richard B. Drumm
Pooh-Bah


Reged: 07/14/05
Posts: 1486
Loc: Albemarle Co. Virginia
Re: PST disease explained ? new [Re: cambert]
      #1262102 - 11/21/06 09:19 AM

I'm not sure that the gold objectives or the new blue objectives get sick.
I know the list has "Davo" in Scotland saying his gold model is sick, but his serial # puts him in the blue objective camp...
He MAY have been referring to the gold color of the OTA...
I'll have to PM him to clear this up...
Rich

--------------------
AKA Richard Drumm The Astronomy Bum
Orion Atlas 10 (10" Newt on an equatorial mount)
Celestron 15x70 SkyMaster Binocs
Coronado Ha PST
President, Charlottesville Astronomical Society
IOTA member

38 10' 57"N, 78 23' 09"W


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NickH
Post Laureate


Reged: 05/09/06
Posts: 3717
Loc: Wiltshire, UK (near StoneHenge...
Re: PST disease explained ? new [Re: Richard B. Drumm]
      #1262143 - 11/21/06 09:46 AM

Wooah...what did I miss here? Gold & blue too...

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LarryAlvarez
Post Laureate


Reged: 08/12/05
Posts: 3298
Loc: Texas
Re: PST disease explained ? new [Re: NickH]
      #1262189 - 11/21/06 10:11 AM

Nick there are so many "My pst is sick" posts that its hard to say which one has the info, but I do remember seeing a blue one that had a small concentration of spec's in the center portion from the picture they posted. It was sort of opposite of how the "Classic" haze looked as far as where it was on the lens. I believe the owner was in the process of sending it back. This is the first I've heard of a gold one hazing. Clear Skyz, LA

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NickH
Post Laureate


Reged: 05/09/06
Posts: 3717
Loc: Wiltshire, UK (near StoneHenge...
Re: PST disease explained ? new [Re: NickH]
      #1262195 - 11/21/06 10:14 AM

For info, mine went rusty after a prolonged session in the Sun, tracking on the C8 mount. It is now so bad that I just don't use it, as the images have stripes (at higher magnifications) across the FOV

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NickH
Post Laureate


Reged: 05/09/06
Posts: 3717
Loc: Wiltshire, UK (near StoneHenge...
Re: PST disease explained ? new [Re: LarryAlvarez]
      #1262197 - 11/21/06 10:15 AM

Quote:

Nick there are so many "My pst is sick" posts ...Clear Skyz, LA




You said it..

Thanks Larry, that helps (no pun intended) clear it up a bit..


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Richard B. Drumm
Pooh-Bah


Reged: 07/14/05
Posts: 1486
Loc: Albemarle Co. Virginia
Re: PST disease explained ? new [Re: LarryAlvarez]
      #1262213 - 11/21/06 10:22 AM

Larry:
Here's the speck-led lens:
Steven Kim's "new in box" sick scope.
This "bubbles" scope is his second one, the one from Adorama in NYC.
Both his scopes had issues right out of the box.
You're right, it's getting confusing.
I hope my serial number list helps folks.
If you and Nick want to add your serial numbers, feel free!
Rich


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DAVIDG
Post Laureate


Reged: 12/02/04
Posts: 3663
Loc: Hockessin, De
Re: PST disease explained ? new [Re: cambert]
      #1262217 - 11/21/06 10:26 AM

I am a chemist/research engineer and I have done thin film work. What most likely is happening is what is a very common failure mode in interference filters. When one makes an interference filter, the coatings are applied to a glass substrait. Another glass cover is then applied over the coating to protect them both mechanically and chemically. The edges of the filter is then seals with an epoxy to stop 02 and water from reacting with the coatings. The seal is never prefect and after some amount of time, the coatings go bad, starting from the edge and working inward.
In a PST the coatings were applied to the two inner radii of the objective. The two halves of the lens are cemented together. The is the same process used in filter manufacturing.
I'll add that from an engineering stand point that the lens is made of two different type of glass that have different rates of thermal expansion. Also the 'scope is pointed at the Sun were the objective sees a good amount of thermal energy that causes the elements in the lens to expand at different rates. This can lead to the diffusion of 02 and water in the area were the coatings are applied and cause the failure that many are seeing.
I find it interesting that the serial numbers of the PST's with a problem span a range that is much larger then the 200+ lenses that were stated to have a QC problem. I also find it interesting the design has been changed. To me, this points to a design problem. If it was just a QC problem then the design would have stayed the same to keep the cost of production down.

- Dave

--------------------
Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schiefspiegler,60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4" f/12, 4.5" f/16 & 6" f/12 Schupmann Medial refractors, 4" Celestar, 19 Stellafane awards 9 in optics

Engineering = Taking what you have and making what you need.

Edited by DAVIDG (11/21/06 02:17 PM)


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NickH
Post Laureate


Reged: 05/09/06
Posts: 3717
Loc: Wiltshire, UK (near StoneHenge...
Re: PST disease explained ? new [Re: DAVIDG]
      #1262233 - 11/21/06 10:32 AM

Very nice explanation, and I agree, this is more than your 200 unit QC issue...

Just nobody will admit it, and the one guy who did post something is now gone!

My serial number...for reasons which I cannot discuss due to CN policy, I would rather keep that my myself, just in case I ever do decide to send it back stateside for a fix.


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