Skywatcher Skyliner 250P or 250PX Flextube Dob?

[paulhereford]

Good evening,

I am looking to upgrade from a Skywatcher Explorer 150P to a Skywatcher Dobsonian and wondered if anyone could tell me what is the difference between the Skywatcher Skyliner 250P Flextube and the Skywatcher Skyliner 250PX Flextube?

Any help would be gratefully received.

Many thanks

Paul Hereford

[tooth_dr]

I understood that the 'x' means pyrex glass? I've a 250px, and it's got pyrex glass mirror, whereas the 200p, for example, is not pyrex. I inferred from this that the x means pyrex!

[Beulah]

Good question, I'd like to know as well.

I was under the impression that all Skywatcher dob primaries were made of pyrex glass.

It's either true of there's a lot of astro-retail websites providing misinformation...

Edited August 31, 2010 by Beulah

[Beulah]

Upon further investigation, it does indeed look like the PX versions stand for Pyrex. I may be wrong though!

[johnkirkpatrick]

Yep I think the "x" means Pyrex as it only the 10" model that has the "x" and advertise's the pyrex mirrors..

[paulhereford]

Thank you all very much for your responses. Think I'm going to go for the 250PX pyrex and all

[Beulah]

There was a 300px solid tube I found advertised on the web...I don't know if they are produced any more in favour of the standard 300p...and why are the 250mm mirrors pyrex, and not the rest?

All the best with the planned increased aperture acquisition, Paul.

Edited August 31, 2010 by Beulah

[johnkirkpatrick]

why are the 250mm mirrors pyrex, and not the rest?

All the best with the planned increased aperture acquisition, Paul.

Good question.....

[Bender]

Enjoy your new scope. I found the step up from a 6" mak to the 250px a hugh one. Couldn't believe how many stars the 10"er pulled out of my light polluted sky

[paulhereford]

Thank you Beulah, John and Bender. I am still deliberating to be honest but I have now managed to sell my Skywatcher Explorer 150P.

I am assuming that pyrex mirrors are superior to standard but can't find any confirmation.

I can't wait to upgrade particularly as the arms of the milky way are spectacular at the moment when clear skies allow.

[Beulah]

Thank you Beulah, John and Bender. I am still deliberating to be honest but I have now managed to sell my Skywatcher Explorer 150P.

I am assuming that pyrex mirrors are superior to standard but can't find any confirmation.

I can't wait to upgrade particularly as the arms of the milky way are spectacular at the moment when clear skies allow.

Pyrex is superior only because of the cool down prior to observing, and perhaps to some mirror grinders during fine polishing (heat transfer from hands can "deform" the plate glass mirror, so one has to wait for the glass to cool before the next stage); once Pyrex and Plate glass have both cooled down to optimum temperatures, there really is no difference to the image. Some say that Pyrex glass cools down 20% faster than plate glass.

I'm quite happy with plate glass, as once I lug the scope out, I usually faff about getting ready anyway, or spend time checking out the sky with a pair of binoculars - I'm in no rush.

In a way, aperture is more important to me...

Edited September 4, 2010 by Beulah

[johninderby]

The Pyrex does cool down faster than plate glass. While it's true to say that there's no performance difference when they're both cooled down there is one very important additional factor to take into consideration. If the temperature is falling the Pyrex tracks the temperature change better than plate glass.

The bigger the mirror the bigger the problem with cooldown, which is why premium scopes with big mirrors use low expansion glass.

John

[hms_furious]

Wrong thread, sorry

Edited June 26, 2020 by hms_furious
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