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PST Stage 1 Modification


The_PSY3NTIST

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Hi all

I'm planning to do a pst stage 1 mod with my Evostar 102mm f/10 and I'm trying to source all the parts. I have found a 90mm d-erf for just over 300 pound and just need to get hold of the adaptor to fit in the etalon that goes to 2" nose piece. Can anyone shed light on where to source one? I believe is it m50 x 1mm pitch to 2" nose piece. Not 100% on the measurements but I'm sure you know which adaptor I mean :)

Any advice greatly appreciated :)

Thanks

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Hi David,

Yes, Have a look here:-

http://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=/search%3Fq%3DAOK%2Bswiss%252Btelescope%26biw%3D1680%26bih%3D911&rurl=translate.google.co.uk&sl=de&u=http://www.aokswiss.ch/index_sonne.html&usg=ALkJrhgFJRRu6tSOh7zAQXzTgiNtkG8MnA

Scroll to the bottom of the page.

Beat Kohler is a really helpful guy who speaks very good English and is pleasure to deal with. I dealt purely via e-mail. Lots of people have availed of his services /products

Ian

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David,

Have a look here at the pricelist. Scroll about 3/4 of the way down the page and look under Eyepiece and camera adaptors. or you could just do a Control  + F to find it.

Price is 48 swiss francs. No need to use the 2" IR filter, you have all the filters you need.

Ian

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I have seen that done on quite a few mods but how do you determine the correct distance as not to cut into the light cone or not to waste the erf by only using say 75mm instead of the 85mm after it's fitted into a cell. I need to have a look at the baffles inside for a start. The first baffle may be a good place to fit it but it's a very unscientific guess :p

Ian - thanks for the website link. Been in touch with that guy and he has sent me details of price and shipping :) just need to send the pennies off to him now.

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Right David,

To find out where to mount an internal ERF is quite simple. Your know what the focal length of the scope is, you know what the diameter of the scope is so just apply some trigonometry. From my school days SOHCAHTOA (sine =opposite over adjacent, cosine=opposite over hypotenuse, Tan=opposite over adjacent. Your scope is 102mm diameter, divide this by 2 to get 51mm, this is your opposite. The focal length of your scope is 1000mm that is your adjacent. from this you can calculate your hypotenuse length from this. It will also enable you to calculate the angle of the triangle. If you know the angle of the triangle and the dimension of the opposite i.e the diameter of your ERF, you can calculate the length of the adjacent. So let say you are wanting to use a 75mm dia. ERF, to take account of any variations in you calcs that may cause vignetting lets use a dia of 72mm. So the angle of the triangle is tan=o/a ~ 51/1000=0.051 the inverse tan is 2.9195 deg. From this you can calculate what the length of the adjacent will need to be to make the opposite equale to 70mm or rather 35mm since we are working with a right angle triangle.

So tan 2.91950=35/adjacent   ~ a=35/tan2.91950 which equals 35/0.050999 = 686.288mm from the objective or 313.712 from the focal point.

To find the focal point of your scope point it at the sun with no EP or diagonal. Hold a piece of white card behind the focuser until you get the image of the sun in focus. Measure this point - that is the focal point.

Have a look at this thread as it shows how i interanlly mounted my 75mm ERF:-

http://solarchat.natca.net/index.php/en/this-is-solar-chat/12-solar-scope-modifications/61211-tal-100rs-pst-stage-2-mod#61211

I got the lens mount from here:

http://www.thorlabs.de/thorproduct.cfm?partnumber=LMR75/M

The D-ERF from TS Germany fits perfectly into this metric lense mount.

Hope this is some info to be going on with and i hope you understand it. If not PM me for more info

Ian

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That's great info Ian. I've done a quick run through assuming I use a 90mm erf and once mounted in a lens cell I figure I'll have 85mm actual usable lens so allowing 3mm for vignetting 82mm.

I've come up with 196mm from the objective or 804mm from the focal point. With a question mark :p

Is a 75mm ok for long use on a 102mm aperture? Could save a few quid there!

Thanks

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I've got a diagonal that the pst bf/ep fits into :) just need the sct focuser and adaptor that fits the etalon.

Will see how it evolves :) be good if I can get rid of the pentaprism focuser but on the downside it makes putting the pst back together a little bit more of a task if I want to take it anywhere.

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