K-Tec

I'm just about to start.

More
18 years 1 month ago #27937 by pmgisme
Replied by pmgisme on topic Small scope
Its probably the Bushnell telescope reviewed here.

www.mav-magazine.com/Dec1999/Contents/bushnell/index.htm

Spherical optics!
Dont touch if you want to magnify above 25!

Please Log in or Create an account to join the conversation.

More
18 years 1 month ago #27943 by jeyjey
Replied by jeyjey on topic Re: I'm just about to start.
It's worth noting that there's nothing wrong with a spherical mirror as long as the spot diagram fits within the Airy disk. For an 8" Newt, this is true at f/12 and slower. I'm not exactly sure how this scales, but I think a 4" Newt with a spherical mirror is fine down to about f/9.

-- Jeff.

Nikon 18x70s / UA Millennium                              Colorado:
Solarscope SF70 / TV Pronto / AP400QMD             Coronado SolarMax40 DS / Bogen 055+3130
APM MC1610 / Tak FC-125 / AP1200GTO               Tak Mewlon 250 / AP600EGTO

Please Log in or Create an account to join the conversation.

More
18 years 1 month ago #27979 by Jared Macphester
Replied by Jared Macphester on topic Re: I'm just about to start.

It's worth noting that there's nothing wrong with a spherical mirror as long as the spot diagram fits within the Airy disk. For an 8" Newt, this is true at f/12 and slower. I'm not exactly sure how this scales, but I think a 4" Newt with a spherical mirror is fine down to about f/9.

-- Jeff.


Is it not the case that the mirror in an SCT is spherical and that the huge variety of variations on the theme come from the use of different corrector/secondary treatment? It's only in Newts that the mirror needs to be strictly parabolic.

I know, I know. I'm only asking!

JMP

Please Log in or Create an account to join the conversation.

More
18 years 1 month ago #27980 by TrevorDurity
Replied by TrevorDurity on topic Re: I'm just about to start.
That's true. Maksutov's and Schmidts use spherical mirrors. Newts should use parabaloidal ones so that all wavelengths get focused to a single point.

As mentioned above spherical mirrors are serious nono on newtonians. They are much easier to make, hence the price difference.

I would go for a 6 inch dob or a 80mm refractor as a starter scope. Don't make my mistake and start with something with a huge focal ratio (skywatcher mak). It is much much easier to find your way around the sky with a faster scope, say f6 or so, because you get a larger field of view.

Skywatcher make some great starter scopes.

Trev

Please Log in or Create an account to join the conversation.

More
18 years 1 month ago #27986 by Matthew C
Replied by Matthew C on topic Re: I'm just about to start.
In my opinion, i think the skylux is well suited to you! Its aperture is 70mm. its a great scope! i have one! great optics, every christmas there in lidl for €69! cheap as chips! but im sure you wouldnt want to wait that long! also there is an etx 70 for €170 which is also cheap for this scope! this scope is motorised! well hope i helped somewhat!

Good luck with your scope search!
Matthew

We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time. . . .
T. S. Eliot
A wise man....

Please Log in or Create an account to join the conversation.

More
18 years 1 month ago #27996 by jeyjey
Replied by jeyjey on topic Re: I'm just about to start.

It's worth noting that there's nothing wrong with a spherical mirror as long as the spot diagram fits within the Airy disk. For an 8" Newt, this is true at f/12 and slower. I'm not exactly sure how this scales, but I think a 4" Newt with a spherical mirror is fine down to about f/9.

-- Jeff.


Is it not the case that the mirror in an SCT is spherical and that the huge variety of variations on the theme come from the use of different corrector/secondary treatment? It's only in Newts that the mirror needs to be strictly parabolic.

I know, I know. I'm only asking!

JMP

Yes, that's correct. Spherical mirrors are much cheaper to make, so the various CAT designs use various correctors to allow a spherical primary to function as if it were a paraboloid.

(As a really minor nit, a "parabolic" curve is 2D (similar to a circle, not a sphere) -- a "paraboloid" is the 3D shape.)

If anyone's interested in all this nonsense, I highly reccommend Rutten & van Venrooij's "Telescope Optics". You can't beat it.

-- Jeff.

Nikon 18x70s / UA Millennium                              Colorado:
Solarscope SF70 / TV Pronto / AP400QMD             Coronado SolarMax40 DS / Bogen 055+3130
APM MC1610 / Tak FC-125 / AP1200GTO               Tak Mewlon 250 / AP600EGTO

Please Log in or Create an account to join the conversation.

Time to create page: 0.113 seconds
Powered by Kunena Forum