A problem with HA Coronado PST

[NickH]

Alex, one word of advice is if you can, check the PST first hand, and pick it up first hand. The pentaprism's on them can be easily misaligned, by over excitable couriers.

[AlexG]

Thanks Kai

Just spotted that a moment ago, but I think I have another iron in the fire...

Not too much has changed on them in the last nine months, has it? And is it obvious when their pentaprism is misaligned?

AG

[FLO]

Not too much has changed on them in the last nine months, has it?

Oops, sorry Alex, I hadn't spotted this thread otherwise I'd have let you know about the clearance PST.

I remember Lee buying his PST so can confirm that it has the latest spec and coatings.

And is it obvious when their pentaprism is misaligned?

It isn't so much the pentaprism but the filter itself that can be put out by a knock. My understanding is that the filter depends in part on a a very thin gap that when knocked can become thinner at one end causing a lack of 'bite' and definition.

HTH

[AlexG]

Thanks Steve

Just what I needed to know.

Hope to see you and the rest on Saturday for the Astrofest!

Regards

AG

[NickH]

Not too much has changed on them in the last nine months, has it?

Oops, sorry Alex, I hadn't spotted this thread otherwise I'd have let you know about the clearance PST.

I remember Lee buying his PST so can confirm that it has the latest spec and coatings.

And is it obvious when their pentaprism is misaligned?

It isn't so much the pentaprism but the filter itself that can be put out by a knock. My understanding is that the filter depends in part on a a very thin gap that when knocked can become thinner at one end causing a lack of 'bite' and definition.

HTH

Correct Steve, that the etalon can indeed be put out by a knock, and the likes of Parcelfarce, I would personally not trust to deliver a pair of socks.(from many many experiences...)..but the prism, is held in place by glue, which can easily come away when bashed, and even a fractional misalignment will make imaging at anything over F10 problematic.

On saying that I have just sent a scope via Royal Mail to be looked at, which has a rust issue...so I should really heed my own advice more often :-)

[FLO]

Correct Steve, that the etalon can indeed be put out by a knock...

Thanks Nick, I guess we should also mention that if the 'etalon' is disturbed then it is uneconomical to repair.

[beamish]

These PST's sound fragile ! Perhaps too fragile ?

Karlo

[NickH]

Not at all, it's a problem with all solar scopes, not just the PST range (the etalon part that is). When you effectively have a very tiny gap between the two filters, which has by its very nature to be increibly precise, then the act of sticking it in the post, is a risk.

However, they are great scopes

[FLO]

To be fair, I haven't yet come across a PST with either of the faults we are discussing; its just something to be aware of when buying secondhand.

[NickH]

I've come across 12 out of the 14 I know. (the only two Cak's I have seen non astigmatic until I got my new one, were Pete Lawrences and our club chairmans). but perhaps I'm just unlucky (and so are most of the people I know!).. The PST's used to write the Coronado book were all rusty and astigmatic to varying degrees..

But...and this is important, if you get one from the UK, the quality of support and service is excellent, and second hand..just be aware of the possible issues, and check the scope if you can...

If you get a good one, they are simply stunning instruments for the money

[FLO]

I've come across 12 out of the 14 I know.

:shock:

Were they all the early models?

[GazOC]

I'm a big fan of picking out S/H bargains but used PSTs hold their price so well (along with the 'issues' they used to have) its hard to justify not buying from a reputable dealer.

[NickH]

I've come across 12 out of the 14 I know.

:shock:

Were they all the early models?

There is a rather large serial number list of ones with the problems on the CN forums..the serial numbers cover several hundred units, in fact , over a few thousand if memory serves me well...not all early ones at all. The rust issue is now largely gone with the new optical assembly setup *blue front glass rather than the old gold/red ERF/ITF system, but the astigmatism is still showing up on all serial numbers, it's simply a design flaw in the way they are built..like I say, and seems to be agreed on, getting a new one from a UK dealer is a good option, mostly at shows like Astrofest you can pick them up sub £400, s/h they hold out at about £340-£350...for the extra £50, it's worth the peace of mind.

[AlexG]

Now they tell me..

AG

[FLO]

I wouldn't worry Alex, if you have just bought yourself a secondhand current-model PST then the most likely outcome is that you will be blown away by your first view of the Sun in HA

[daz]

Our society has two, one of which needed the rust problem sorting, and ours survive the trips to members houses very well.

They are borrowed more than any other scope we have!!!

[NickH]

Visually not many people see the astigmatism problem...when you start imaging with them...then you notice...big styleee (F20 and higher!)