Fast f/5 and telecentric for a f/10 PST mod?

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Pedro

Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Pedro » Thu Dec 01, 2011 11:54 pm

Very interesting mod. You still will have to deal with the BF5 of the PST (limited field of view)

I am certain it will reach focus. Please keep us posted

best regards

Bill E.

Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Bill E. » Fri Dec 02, 2011 12:42 am

Interesting reading.Need more posts like this. :idea:

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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by alex » Fri Dec 02, 2011 10:33 am

Common barlows don't have a constant 2x factor when you move further away, so I guess it must be the telecentric type.

Check the Powermate ones .
They are the only one that provide info on their real focal length and there is a a chart with the mag. factor according to the distance .

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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by marktownley » Sat Dec 03, 2011 3:52 pm

Don't know the answer to your question Neo, but I will certainly follow this with interest...
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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Roel » Sun Dec 04, 2011 7:46 pm

Hello Neo! Thanks for your link to this great forum!

I was thinking: I see your PST etalon is behind the focuser. Therefore changing focus means moving the etalon away from the ideal position of 200mm inside focus. Your current setup may keep the etalon pretty much at a right position, but mounting a Barlow directly in front of the etalon might cause a "etalon ideal position" issue, resulting in a low detail image. You might check if everything works out ok by adding a barlow in front of the setup you already have, before cutting up a new refractor.
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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Merlin66 » Tue Dec 13, 2011 1:35 pm

Hi guys,
I've done and assist with my fair share of PST mods, over forty successes at the last count....
The reason for the "majic number" 200mm is very straight forward.
The front of the PST etalon has a barlow lens which is....you guessed it -200mm focal length; this means to present a collimated parallel beam through the etalon it MUST be placed 200mm inside the prime focus.
On the rear of the etalon...there's a positive lens (yes you guessed correctly!) which is 200mm focal length.
So, if the final focus is 200mm behind the etalon you'll be pretty much assured that the etalon is in the correct position.
(I have a PST Mod write up available (6.5Mb) just drop me an email address and I'll send a copy)
If you do want a challenge try a double stacked PST etalon design!!
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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by swisswalter » Tue Dec 13, 2011 3:31 pm

Hi Ken

thank you very much. I would like to have your essai.

You just have no email adress listed in your profile, you will see mine in my the profile
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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Merlin66 » Tue Dec 13, 2011 3:49 pm

I thought my email was in the profile data???
Anyway here it is:
kenm(dot)harrison(at)gmail(dot)com
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Re: Fast f/5 and telecentric for a f/10 PST mod?

Post by Merlin66 » Wed Dec 14, 2011 10:16 am

based on the mods done to date, there seems to be about a 3-5mm tolerance band before you get collimation problems with the etalon.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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"Astronomical Spectroscopy for Amateurs" and
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