life expectancy of solar scopes

[Bender]

Hi,

I took advantage of the recent Telescopehouse offer and treated myself to a SM II 60. I would probabely have slightly prefered a Lunt 60 but for the price i could not resist.

I must say the 2 things i was a bit worried about turned out not to be a problem. The scope makes a solid impression, with the 2 nylon screws holding the draw tube firmly. And the helical focuser works fine as well (still tempted to get a Moonlight focuser but after trying the stock foucser with my zoom ep I am not sure if i can justefy it)

I came across a few posts on the other forum talking about limited life expectancy for parts of a solar scope and lenghts some people go to extented it.

They were talking about Baader IR UV filters to protect the blocking filter and even sealing the whole unit and filling it with innert gas.

How much of a problem is aging for the eathalon and blocking filter and what couls be done sensibly to protect them.

[NGC 1502]

Yes, lots of people have wondered about that, including myself. The coating failure on early PSTs adds to that worry.

A couple of years ago, at Astrofest in London, I spoke to Ken Huggett who runs Solarscope on the Isle of Man, and asked this very question. Of course, it could be said that the owner of a company is not going to say anything other than "no problem" or something like that. But Ken is a real nice bloke, I had the privilege of showing him and his wife the night sky when I happened to be staying at Fieldview astronomy B&B at the same time, some years ago. I got to know him, and trust what he says.

He said that his scopes are likely to outlast their owners. Of course he could not vouch for other makers (I didn't ask) so this doesn't exactly answer your concern. But given the nature of the product and that any eye damage that was caused by any issue would collapse the company due to lack of confidence, I bet they try very hard indeed to turn out a good product.

I think it's a good idea to inspect a solar scope every so often for coating failure, just as you would any product for safety reasons.

Regards, Ed.

[Bender]

Ed, i think the safety is a valid point and i havent seen reports that people actually got hurt by a failing coroando scopes.

[Naemeth]

I think the thing to do is test before each use, just like you would with Baader Solar Film. A few minutes out of observing is worth sacrificing for safety, isn't it?

HTH

[spaceboy]

I came across a thread a couple years ago when I was considering buying a PST and from what I gathered there was talk of a 7-10 years life expectancy out of the Corando PST in particular. These figures were being tossed about during the same time of the rust problems so whether this was the general life expectancy of the PST full stop or that of the troubled gold coatings of the time I am unsure. What I do know is it was enough to put me off buying a new one at £450 (at the time) and I am very wary of S/H ones.

[markt]

You will experience no problem with the coatings on the etalon or the blocking filter; the etalon is 2 precisely parallel peices of glass with broadband coatings the same as you would get on optics. The blocking filter is a hard coated filter, and it is highly unlikely to have any issues, ever. In terms of the Coronado scopes, and in some caes the Lunts, the problem with 'failed filters' is the ITF (induced transmission filter) - this is the filter that you can see if you look down the objective side of the blocking filter. The ITF is a 'soft coated' filter and if fails it will have a clouding that gradually ingresses from the perimeter of the filter. This is due to moisture ingressing inbetween the laminate of the soft coats in the filter. If this happens it is perfectly safe to use and the worst that can happen is the image loses contrast somewhat.

What can be done to prevent it? Pay close attention to the length of the warranty and send it back to telescopehouse to have the ITF replaced as soon as it shows any sign of discolouration. If this happens out of warranty it is possible to replace the ITF with Schott KG5 glass (quite cheaply) which has the same blocking characteristics >1500nm - which is what the ITF is there for.

[Merlin66]

In my experience, having modded MANY PST's and using the original SM60 filters I have never see any failures which would compromise the safety of these filters/ telescopes. Never.

As Mark has said, the "mini-erf" is the major element which can and does fail (in both the Coronado and Lunt designs).

[Odd Thomas]

The Daystar Quantum H-alpha filters are reputed to last 20-30 years. One of the reasons I went down that route.

Tom

[Moonshane]

based on the above (excellent) post, given that failure is due to moisture ingress, I wonder if those scopes that 'rusted' were stored in obsy's? Given the periods you can go in the UK between uses, I'd be worried about storing one outside and perhaps you can prevent any moisture ingress by storing indoors?

[JamesF]

Good point, Shane. Worth storing them in a box with a fistful of desiccant if they are to be anywhere that damp air might get at them, perhaps?

James

[Odd Thomas]

An excellent point Moonshane. I don't have an obsy at present (maybe later this year!) but if I had I don't think I would leave my H-alpha scope in there.

[Merlin66]

Tom, et al,

http://www.daystarfilters.com/service.shtml

Note the anticipated life and cost of service.......

[Moonshane]

it depends how you view it. in the worst case (10 years and one day) you get the scope in perfect working order again for <£500 which equates to about £1 per week. if maintained in good conditions possibly a lot longer/less. like eyepieces costing a couple of hundred quid each, if you maintained them in poor conditions and they moulded over destroying the coatings, it would cost almost the value of the eyepiece to repair if not the same cost.

then again, you could buy a new PST every 10 years for less than the cost of this repair. as always, it ain't cheap but at least there's options.

[Odd Thomas]

Hi Merlin66, yes there's a lot of good info on their website, especially about storing them, but a 10 year guarantee speaks volumes, and speaking to them they would expect a well looked after filter to last 20 - 30 years. They also go into great lengths to tell you on no account to open the filter and to send it back to them for service, which makes me wonder, as an ex X-Ray diffractometer Engineer, what I'll do when that time comes for my Quantum?

Moonshane, as you indicated, you pays your money and makes your choice... I have never doubted I made the choice that was right for me. The Daystar filters seem to do better on t'other side of the pond, seems a lot of colleges etc buy them. I don't know of anyone near me using one.

Tom

[Mark at Beaufort]

I bought PST in early 2005 to view the Annular Eclipse in Spain. Several years later I notice the front element had the 'rust' problem. I was assured that the PST was still safe to use but in time the viewed image might deteriorate. Well the scope has viewed several partial, annular and total eclipses not to mention the 2012 Venus Transit and the view is still the same. In fact I have been out this morning viewing the Sun.

As for storage the PST has been kept inside the house for the last 8 years.

Mark

[Moonshane]

great post Mark - you cannot beat the personal experiences of someone experienced!

[michael.h.f.wilkinson]

As a precaution I always commandeer every silica-gel bag found in every piece of packaging, and press into service into one of the cases with optics (scopes, EPs). Humidity can wreck good optics. No guarantee against "rust" on the mini-ERF I gather, but at least I will know I have done my bit.

[GlassWalker]

With two "new style" PSTs of different ages, I have seen my older one does have a degraded ERF. I put that down to the design of the PST which concentrates light before it passes the ERF, unlike most other designs with an ERF up front. Less energy density passing through, but far more expensive. Is that the case or does it resemble the degradation shown above which is more environmental?

I have wondered if regular (dichrotic?) deep sky Ha filters would be adequate in the role of an ERF since per-area I think they work out cheaper than the dedicated Baader ERFs.

[Merlin66]

The problem is the design and construction of the filter element. I have seen many old and new PST's as well as Coronado blocking filters (BF10/BF15 etc) and all suffer to a degree......

No easy answer. I'm sure if you kept the scope in a environmentally controlled room and never used it...the filter may last a little longer. But where's the enjoyment in that??

Re "regular" Ha dichromatic filters as a possible alternative - the jury is still out. Would be nice, but at this stage not enough rigorous testing has been done to verify the safety of this filter.

Solar observing is great fun, but seriously, never take any chances with your eyesight. Be safe.

[GlassWalker]

Certainly understand safety is a critical issue when it comes to anything solar. I know this thread is posted in the observation section, but my personal uses will only be for imaging so the worst case is perhaps the loss of a sensor. Actually on that note I think I need to start another related thread...

[Galilean]

I came across a thread a couple years ago when I was considering buying a PST and from what I gathered there was talk of a 7-10 years life expectancy out of the Corando PST in particular. These figures were being tossed about during the same time of the rust problems so whether this was the general life expectancy of the PST full stop or that of the troubled gold coatings of the time I am unsure. What I do know is it was enough to put me off buying a new one at £450 (at the time) and I am very wary of S/H ones.

Does anyone know, has the rust problem been completely cured now? Is there a serial number after which they are OK?

[Peter Drew]

The front objective problem of rust has been resolved, the coating feature has been discontinued, the current coating is a normal AR coating. The current modification is the inclusion of a small filter prior to the blocking filter. At present, the life span of this filter and that of the blocking filter are the subject of debate. When Merlin66 wakes up in OZ he should be able to offer further advice.

[Merlin66]

I'm awake!

I can't quote any cut-off serials any more as many of the earlier models have had the objectives replaced under warranty.

If there are still any of the older "gold" objectives still actively in use then they must be at least 4-5 years old.

I don't know of any "gold" objectives which have not failed or show signs of deterioration.....

Unfortunately the added "mini-erf" filter (in the eyepiece holder at the black box end) - and similar filters in the Lunt Ha solar scopes are also prone to pre-mature failure...The complex interference coatings (ITF) (placed between two pieces of glass) can deteriorate due to moisture and if the edge seal of this filter assembly is compromised it's only a matter of time before the "rust" starts to show at the outer edges and creeps in towards the centre....

Many have been replaced by Coronado/ Lunt under warranty.

As it is very difficult to obtain a replacement PST ITF ( I believe Meade in Germany quote around 150euro) we are actively seeking suitable cost effective (and safe) replacements.

Two candidates are being evaluated (both for the PST and the Coronado SM blocking filter diagonals)

For the PST - a Baader 35nm CCD Ha interference filter - as a replacement ERF combined with

The new UV-IR/KG3 filter from BelOptics which cuts UV and IR through to 2500nm

Early days, but the quest for the Holy Grail continues.....

Hope this helps.

( We have not seen any failure of the actual (small red coloured) blocking filters.

[Andrew*]

Fascinating thread.

I contacted telescope House about my rusty BF10. They said sending to Coronado for repair usually has a turnaround of one year and costs approx $150. They also said TH rarely get allocated any stock of BFs so couldn't even sell me one in the meantime! Importing from US would cost at least £400.

The views are fine, as it happens, but I don't know if they will stay that way...

Ken, just to clarify: there are solutions for the ERF but not the BF (at least readily available and moderately priced)?

Cheers

Andrew

[Merlin66]

Think of the current PST blocking filter assembly as being similar to the Coronado SM blocking filters (ie BF10/Bf15 etc)

The "front" element, the ITF is the one which fails..the "rear" element the actual sort/ blocking filter seems to survive very well.

The discussions ( and searching) is on the replacement ITF element.

Hope this helps.