Used PST... Need Help

[cshahar]

Hi Everyone:

I just received a used PST which I bought from Astromart. It is a pre-Meade model. I took it to the local club and compared it with a re-furbished non-rusted version. When I shone a flashlight through the front objective mine was quite hazy, to the point where I could barely see the internal etalon. My friend's PST showed no haziness and one can easily see the internal etalon when the flashlight was used. Is my unit suffering from rust, condensation, or something else?

The reason I bought it is that the seller (who seems to have a good reputation) said that the views have not changed significantly since he bought it several years ago. I am now wondering how that could be possible, given this haze.

Please let me know what you think.

Thanks!

-Charles

 

[Peter Drew]

If it is an early PST it is quite likely that the objective coatings have started to "rust". In the event, it is surprising how little effect this has on the performance, usually noticeable as a rise in background glow. The condition should have been reflected in  the price. The long term good news is that the PST can be used as the basis of a much larger PST mod as the original objective will not be needed.

[cshahar]

Peter, do you mean I should send it back to the manufacturer to get it refurbished?

[spaceboy]

You have to decide for yourself depending on what you originally paid out on the scope as to if it is cost effective to do so. As far as I am aware Meade replaced the rusty objective FOC but this has all now stopped so your going to have to cover the cost of return, replacement objective, labour and return postage to yourself while also having the delay associated with any repair. Or you can look into investing the money you will pay out on getting the objective replaced and go about doing a PST stage 1 mod. 

I would go with the PST mod myself but you do have to have a degree of DIY skills to take on such a task. The final option would be to just use the PST and enjoy the views for as long as you can. The rust problem apparently has no effect over the safety of using the scope so the only problem your going to face is yourself accepting the fact the objective is in the early stages of rusting.

[cshahar]

Thanks spaceboy. I appreciate your advice!

[Merlin66]

IMHO it is not viable to repair a rusted PST objective.

You can live with it...... or try to find a new "blue" objective gold tube ex someone who has done a Stage 1 or 2 mod and add an ITF to the eyepiece holder to bring it up to current specifications, or use the black box and etalon for a Stage 1 mod.

 

[gnomus]

On 29 May 2016 at 23:30, Peter Drew said:

If it is an early PST it is quite likely that the objective coatings have started to "rust". In the event, it is surprising how little effect this has on the performance, usually noticeable as a rise in background glow. The condition should have been reflected in  the price. The long term good news is that the PST can be used as the basis of a much larger PST mod as the original objective will not be needed.

So can this be an issue with all solar scopes or is this just a problem with this particular scope?  I ask because I am considering shelling out for a 60mm Lunt.   Do these scopes have a limited shelf-life?

[Peter Drew]

This was a specific problem with early PST's only. The ERF was generated by a special coating on the objective which failed over a period of a few years. Later models had standard coatings and the ERF was provided as a small filter between the etalon and the blocking filter. Apart from the objectives and etalons used in Ha telescopes which appear to be long term serviceable, other components such as the blocking filters and their protective filters do seem to have a limited shelf-life which can be extended by careful storing when not in use. 

[joe1950]

I have an older Coronado PST. Actually my son has it. Reading the post, I'm a bit confused so I've taken some photos to see if anyone notices problem areas.

 

I somewhat understand the ITF filter thing and will check that. From what I see, if the ITF filter is an orange or reddish color on the bottom, it is rusted and must be replaced. My understanding is that the Maier 656 ITF Bandpass Filter will work.

 

 

Serial #:  102606

 

Here are photos:

 

Name Plate

 

 

The Objective. Blue and very clear glass. No signs of rust or spots. It's never been serviced or replaced.

 

 

Taking off eyepiece holder there is a filter glass with a green tint. Looks okay.

 

 

Looking down eyepiece holder from top is ITF Filter. Red tint.

 

 

Looking from underside of eyepiece holder is ITF Filter. Has even density gold appearance.

 

 

If there is anything that appears to need attention, I would appreciate the information. The scope performs as it did when new if memory serves, and is clean.

 

I am not at all familiar with the possible issues others have experienced, so any update will be very helpful.

 

Finally, where might I find information on the Stage 1 or 2 mods?

 

 

 

Thanks very much in advance.

 

joe

 

 

 

 

 

[Merlin66]

Joe,

that looks OK.

Drop me a message or email with your email address and I'll send you the PST mod write-up.

Ken

 

[Peter Drew]

Hello Joe.

As Merlin66 says, all the PST components look ok.

Just a reshuffle on the components, the green tint filter is the ITF, the smaller gold/red filter is the blocking filter. The ITF is the more vulnerable of the two, its gradual failure is exhibited by a pinkish annulus which migrates from the edge, not dangerous but it will reduce the contrast. The later blue objectives have standard coatings and will not "rust".

[joe1950]

Hello Ken and Peter! Thanks for the information. I can't recall when we got the PST, but it seems like a time ago. Maybe they had just started using the standard coatings. I'll ask my son who has it presently if he recalls.

I am going to try to 'borrow it' for a while. Evening observing has been dismal. There hasn't been a good clear night in weeks. Maybe if I observe the sun, which pops in and out, I'll get some time in the books. I do enjoy solar observing with the PST and the Bortel Scale light level isn't a factor! I've yet to see Mars. It is still below the 'tree horizon' but I'd better get a glimpse at my first opportunity since it's surely shrinking.

Years ago, I was never aware of any of the hazards associated with optics, especially lenses. I knew mirrors needed recoating now and then but I thought lenses were virtually free from any harm. Now I find they can have the coatings damaged by oils and moisture, mould can etch the glass and certain ones can rust! Fortunately I've avoided any of that with the few I've had, but it certainly wasn't due to preventative care on my part. Just been lucky. 

Thanks again for the update on the PST. It does a good job for our needs.

Charles, Thank you for allowing me to jump in with my story, I do hope you resolve the issues with your scope.

joe

[cshahar]

Joe, there is a list of serial numbers and their last known status here:

http://www.cloudynights.com/topic/83886-pst-serial-list/page-2#entry1124445

[cshahar]

Who services sick PSTs? Is it Meade or a third party? Is it expensive? What exactly do they do??

Thanks!

[Merlin66]

If you mean an older rusted PST, then I'm not sure you'll appreciate the cost of repair. Meade in Europe I believe can still do repairs, don't know about Meade USA.

Note: that listing from CN is well out of date.....many of the original instruments were improved under the five year warranty.

 

[cshahar]

Thanks Merlin. I appreciate the information!

-Charles