Focal Length

[thommo10]

Hi all

I have a old 6inch Astro-Systems Newt bought back in the eighties, after many days and nearly throwing it up the garden I have managed to almost collomate it I think, with the help of astrobabys collomation notes, and many thanks by the way to Moonshane for offering to break his journey and have a look at it for me, unfortunatly I couldn't make it. I was wondering if anybody could tell me what the focal Length is of this scope.

[NGC 1502]

Hi Keith. I've just pulled out the December 1987 edition of Astronomy Now, and found

an advert from Astro Systems with details of your scope. It shows a focal length of

900mm, F6. It was called the FG 1. Two models of this scope are mentioned. The

FG 1 has a rack & pinion focuser and 6 x 30 finder and was £195. The FG 1 'clubman'

was the same scope, but had a sliding focuser and the finder was an optional extra,

price was £149.

You have a lovely classic scope, glad you didn't "throw it up the garden" !! The

optical quality of these scopes are great, and the alt-az mount is bomb proof.

Best regards, Ed.

Edit - also in that mag is another Astro Systems advert with the same optical tube

on a Super Polaris EQ mount, model V 13, price was much more at £495.

[thommo10]

Thanks Ed, I have the one on the SP mount, and the Rack and pinion focuser I wonder if I can replace it with a Crayford? Thanks again for the info.

[NGC 1502]

Thanks Ed, I have the one on the SP mount, and the Rack and pinion focuser I wonder if I can replace it with a Crayford? Thanks again for the info.

Hi Keith, yes I'm sure you could replace the focuser. You would

need to ensure the focus range would be adjustable to the same

as the original one, to achieve focus. And it's very unlikely that

the tube holes would match, so you would need to drill new ones.

Great scope you have, quite sought after, especially to those who

recall Astro Systems of Luton.

Best regards, Ed.

[thommo10]

Hi Ed.

By focuser range do you mean the length of the focuser tube and travel in and out ?

[NGC 1502]

Hi Keith. Yes, if you put an eyepiece the focuser, and focus up on a distant object,

a star is best of course, then measure the distance from the end of the focuser tube

to the tube wall. A new focuser would need to put an eyepiece at the same position.

It's probably best if focus is achieved with the focuser in mid travel, as

some eyepieces need more in or out movement to find focus.

Best regards, Ed.

[thommo10]

Ok, thanks Ed for the info.

[Peter Drew]

Before anyone asks, FG1 stood for FLOGGLE GROPER 1, not quite sure how it came about, it might have been a suggestion from one of the staff. Whacky sense of humour in those days, just look at the photo on the back cover of their catalogue!

[NGC 1502]

Before anyone asks, FG1 stood for FLOGGLE GROPER 1, not quite sure how it came about, it might have been a suggestion from one of the staff. Whacky sense of humour in those days, just look at the photo on the back cover of their catalogue!

FLOGGLE GROPER 1 ? How odd is that !! I always thought that

was a serious model number. It would have taken me to the end

of the Universe to guess ...........Ed.

[Moonshane]

hi Keith

Glad you seem sorted. Focal length of any scope is basically aperture x focal ratio so f6 x 150mm = 900mm.

It works the other way too for magnification so magnification = focal length divided by eyepiece in mm so a 9mm eyepiece would give 900mm / 9mm = 100x.

On the focuser front, as long as you are the same as or closer to the tube than before, you can usually get an extension tube if required to bring it out a bit. Being too far out is more tricky to deal with. If drilling etc, always take your optics out (more collimation practice! ).

[thommo10]

Thanks Moonshane really looking forward to that (not) you would think though that beings I can only move the secondry it would be easier to collomate ?

[FLOGGLE GROPER 1]

Before anyone asks, FG1 stood for FLOGGLE GROPER 1, not quite sure how it came about, it might have been a suggestion from one of the staff. Whacky sense of humour in those days, just look at the photo on the back cover of their catalogue!

just had to make an account with that name!

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