Using an f6.5 152 Refractor for Stage One Mod

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Starry Jack
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Using an f6.5 152 Refractor for Stage One Mod

Post by Starry Jack » Mon Apr 20, 2015 2:19 am

I'm having greater and greater success with my PST 100 mm. So now I'm looking at my 152mm F6.5 achromat.

What are the mechanics to use f6.5 rather than f10? I'll stay with the Stage One Mod still.

Thanks,
Jack

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marktownley
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Re: Using an f6.5 152 Refractor for Stage One Mod

Post by marktownley » Mon Apr 20, 2015 5:40 am

You need to look at replacing the collimating lens. Also you need to consider the ERF, 152mm generates some energy that must be dealt with.
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Re: Using an f6.5 152 Refractor for Stage One Mod

Post by Merlin66 » Mon Apr 20, 2015 11:12 am

If you don't change the front collimating lens to match the scope, the etalon will act as an f10 aperture stop and you'll end up with a 99mm f10 system....no improvement there....
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Re: Using an f6.5 152 Refractor for Stage One Mod

Post by Starry Jack » Mon Apr 20, 2015 3:10 pm

Thanks to you both.

What about adding a 3rd lens to correct to F10?

And which lens is the collimating lens in a doublet?

Lastly, my ERF is 100mm so I am hoping there is not too much heat that far up in the optical path.

Thanks,
Jack

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Re: Using an f6.5 152 Refractor for Stage One Mod

Post by Merlin66 » Fri Apr 24, 2015 1:01 am

Jack,
It is possible to use a Telecentric type barlow to give the amplification, but it's not easy to set-up.
I'm not sure I understand your comment re "collimating lens in doublet".....
The PST etalon assembly has a single element -200mm focal length lens at the front, then the etalon and a +200mm focal length lens at the rear to re-image.
Some modders have replaced the front negative lens with one to better suit the donor fratio.
For a f6.5 system you'd be looking for a 25mm diameter x -163mm lens.
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Re: Using an f6.5 152 Refractor for Stage One Mod

Post by Merlin66 » Fri Apr 24, 2015 10:38 pm

Good point!
For an open aperture of 20mm then the focal length would be 130mm.
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