40mm (or 50mm) ERF

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Boomshadow
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40mm (or 50mm) ERF

Post by Boomshadow » Wed Sep 23, 2015 5:30 pm

OK - as the old saying goes, 'fools rush in'! My old PST objective was severely rusted giving a very poor image at the eyepiece, so I decided to see if I could separate the two elements and clean things up. As I lowered the lens into boiling water, there was a quite loud 'ting' and I immediately thought 'that's the end of this experiment'. However the lens survived and when it had cooled I gently prised the two sections apart by pressing a knife carefully into the groove on the lens edge. It worked!

The coating cleaned away with gentle use of a thumb nail. What I assume was the adhesive was a bit more resistant but eventually it came away by using a sharpened piece of plastic (acrylic I think) as a scraper. After a thorough clean I found that the two halves fit back together beautifully and stick!

I re-assembled the PST and using the ERF from my 'Frankenscope', a brief gap in the clouds in Buckinghamshire allowed me to see that the image has improved considerably.

This raises a couple of questions -

Is there a safe but cheaper alternative to the 40mm Lunt ERF at €140 (of course it's only $99 in the USA)?

Can anyone suggest whether the lens should be re-assembled with adhesive (and if so which) or will it be OK without (I didn't notice any untoward effects during the brief test).

Any further suggestions gratefully received.

PS I should probably add that if anyone else gives this a go, I will not accept any responsibility for any damage caused by following this process!

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marktownley
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Re: 40mm (or 50mm) ERF

Post by marktownley » Thu Sep 24, 2015 5:58 am

Use a 2" Night time Ha filter screwed onto the front of the objective cell as a belt and braces approach.
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Boomshadow
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Re: 40mm (or 50mm) ERF

Post by Boomshadow » Thu Sep 24, 2015 9:05 am

Many thanks for your reply Mark. Being a newbie on this site (this was my first post), I suspect that I could have chosen a better forum for my questions. Nevertheless, if anyone has a 40 or 50mm ERF or a 2 inch Ha filter that they would like to sell, I would be very interested.

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marktownley
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Re: 40mm (or 50mm) ERF

Post by marktownley » Thu Sep 24, 2015 6:58 pm

ofcourse the other approach is if anyone has a surplus PST objective to sell and just swap them over?
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

Boomshadow
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Re: 40mm (or 50mm) ERF

Post by Boomshadow » Thu Sep 24, 2015 7:27 pm

Thanks again Mark.

As per Mark's suggestion, I would be interested in finding a rust free PST objective lens (or a 2in Ha filter or a 40mm ERF or 50mm ERF).

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