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AndrewJ
18-11-2017, 11:51 AM
Gday All
I have a new model PST ( with the blue objective bought 2007 ) but on using it today after a while in storage,
a) the rubber tuning ring fell off :-(
b) It seemed a lot duller than i remember
On googling around, i found several posts that indicate Meade merely moved the ITF coatings from the front objective to a small unit in the base of the EP barrel, and that this can also rust, but you cant see it :mad2:.
On looking in mine at a lowish angle, best i can see is my unit looks like it has several concentric circular rings, vs complete crud or a single dark region coming in from the edges.
Not sure if this is an interference effect or real as i can only get a grazing angle sideways.
Soooo i tried to remove the EP barrel but it wont budge, even with a rubber strap wrench
Is there a trick to getting it loose without damage???
Secondly, i tried to remove the prism to get a better view but on screwing it up till it almost touches, it is still engaged.
I couldnt see anywhere ( yet ) that explains how it comes off, as if i can do that, i may get a better look at the lower ITF without having to remove the barrel.

Andrew

Wavytone
18-11-2017, 12:05 PM
Let’s try that without the acronyms, then we might understand WTF you are talking about ;)

AndrewJ
18-11-2017, 12:12 PM
Gday Wavytone

Whats WTF?????:lol:

Andrew

If i had typed "Induced Transmission Filter" it probably wouldnt have helped

Merlin66
18-11-2017, 12:38 PM
Andrew,
Definitely sounds like the ITF filter element has failed.
I recently had a similar experience and even with all the practise I've had over the years pulling PST's apart, I couldn't budge the eyepiece holder. The Mexican loctite is something else!
The filter is held by a retaining ring (with the usual two diametric small holes), this can (just!) be accessed from the inside of the black box - the focuser and Pentaprism may need to be removed.
A small wrench was made from a suitable nut and pins which allowed the retaining ring to be removed using a side spanner.....
The replacement ITF is available from Maier Photonics in the US and is a drop in fit.
http://maierphotonics.com/

(I assume you are out of the five year warranty period?)

Re pentaprism removal - If you look carefully at the threaded focuser rod you'll see a circlip - this needs to be removed to allow the focuser rod to move out of the body away from the pentaprism.)

AndrewJ
18-11-2017, 01:03 PM
Gday Ken

Go on, cheer me up some more :-)


Yep, seen some of the threads on this on CN and a few blogs, but also that there were several variants. The disassy seems straight forward, just didnt want to apply force if there was some hidden trick to it.


The best info i found on this was a CN user called DavidG
https://www.cloudynights.com/topic/530890-newbie-trouble-with-coronado-pst/page-2
and he linked to
http://maierphotonics.com/656bandpassfilter.aspx
so that looks like the same beastie.


Yep, bought in 2007. I mainly use my Lunt80 but tried the PST in this mornings sucker holes, and noticed how dim it was.


Will get out my magnified headset and tweezers :-)
I might even machine up a barrel clamp so i can get the whole assy out in one piece.

Many thanks
Andrew

AndrewJ
18-11-2017, 01:55 PM
Gday Ken
Got the prism out but still cant get a good piccy of the rust.
Have attached best shot i can get, but when viewed with a MKI eyeball, the concentric growth rings are clear as a bell
Andrew

Merlin66
18-11-2017, 02:14 PM
Andrew,
Yeah.....it's a gonner.
The good news(!) is that I'm aware of many Maier replacement ITF's and none have failed ...... so far.
If you can rig up a large nut and a couple of pins into those holes it will unscrew easily.
(We have a nut "tool" down here in Geelong I could probably get it for you if you get stuck)

Re the failed rubber tuning ring. Unfortunately these are currently out of stock in the US. The Meade part number is C311380 - "Rubber Tuning Ring for PST"

AndrewJ
18-11-2017, 02:37 PM
Gday Ken

Yep. Once i got the prism out safely, i thought i would apply some BFI ( brute force and Ignorance ) techniques using an oil filter removal tool with masking tape on the barrel so it would grip.:D
With that and me using my free hand to turn the upper barrel as hard as i could at the same time.... it moved .
Much better piccy attached.:sadeyes:

Is that the old Mayor????
I have a workshop with lathe/mill/drillpress and lots of other toys, so making a pin wrench wont be too hard now its out.
Just gotta buy a filter now.

Andrew

Merlin66
18-11-2017, 02:54 PM
Andrew,
Well done mate!

I got my pin wrench set of eBay - pretty cheap and works on all "normal" lens problems.

I'm currently using a Maier ITF on my BF15, no issues, no drama.
Ken

AndrewJ
18-11-2017, 03:21 PM
Gday Ken

Just gotta find a way to get one now
The MAIER site doesnt give much hints on how to pay.
Ive never owned a credit card or Paypal, so was going to grab one of those AusPost Debit card type thingys, but need to see if Maier wil accept em.
All good fun and not urgent as i will just use the Lunt meantimes.

Andrew

PS when resetting the circlip, what means do you use to compress the spring????
Im finding that to be really fiddly, so was going to resort to my old trick of tying up the compressed spring with some cotton first, then cutting it after the circlip is on.

Merlin66
18-11-2017, 03:33 PM
Andrew,
It may be worthwhile setting up a Paypal using the limited debit card as the source of funds. That way you get the flexibility of Paypal with minimal risk.

Fiddle and swear words was all I used....your cotton thread sounds more sophisicated.

Atmos
18-11-2017, 04:10 PM
I've read about the PST Rust issue over the years but never actually been sure where the rust was. I always thought it was an issue that plagued the front aperture or something.

I just pulled the back of my PST apart which surprisingly happened with very little effort. There is dobs of goo (feels like silicone) in spots where it probably shouldn't be, not damaging or anything but still.

Mine is circa 2011 from Bintel. Appears to be fine.

Merlin66
18-11-2017, 04:26 PM
The original PST objective had an energy reduction filter (ERF) coating within the lenses. This subsequently was found to fail and the coating took on a “Rust” like appearance.
This was not directly a safely issue but did significantly reduce contrast and definition.
Meade replaced this design with one based on a non-ERF objective and placed a “mini-ERF” in the eyepiece holder. This is an ITF construction like all the ITF used by Meade. We have found the filter can fail due to moisture ingress aggravated by thermal loading and shock. The filter can last from months to years...but will eventually fail.

Atmos
18-11-2017, 04:51 PM
So what you’re saying is that although it’s okay now, it will, eventually, die :)

Merlin66
18-11-2017, 05:05 PM
Yes......
It will fail.

AndrewJ
12-12-2017, 07:55 AM
Well, my new filter has arrived but i cant use it at present :-(
That said, it has an oring inside the pack as well, and "appears" to have different coloured faces ( i havent fully opened the packaging yet )
Sooooo
is the oring used on reassy to hold it steady
what way round does the filter go, ie can it go in either way round or must one side face the incoming light cone.

Andrew

Merlin66
12-12-2017, 08:24 AM
Andrew,
I didn't get an O ring with my last Maier filter....
The brighter mirrored face faces the incoming light.
Should be as simple as dropping into the existing cell.......

AndrewJ
12-12-2017, 09:37 AM
Thanks Ken
Will see what happens when i can get back into my shed to make a pin wrench.

Andrew