TAL Differences

Still hunting for an ideal scope, its a minefield- anyway, I have found
Beacon Hill offering reasonable prices on the TAL range which sound okay,
but I'm a little unsure as to the differences between the 2M and the
150PM... one is f/8 and the other f/5 I believe, and from my photography
knowledge this would suggest the f/5 would give a brighter image? I'm sure
it cant be that simple, would the image be brighter but the quality worse?
Is one going to be better for some types of viewing than others? I found a
review of the 2M that said the image quality is very good, can't find much
on the other though....
Thanks
James

"James" wrote in message
...
Still hunting for an ideal scope, its a minefield- anyway, I have found
Beacon Hill offering reasonable prices on the TAL range which sound okay,
but I'm a little unsure as to the differences between the 2M and the
150PM... one is f/8 and the other f/5 I believe, and from my photography
knowledge this would suggest the f/5 would give a brighter image? I'm sure
it cant be that simple, would the image be brighter but the quality worse?
Is one going to be better for some types of viewing than others? I found a
review of the 2M that said the image quality is very good, can't find much
on the other though....
Thanks
James



Hi James

In my limited experience it is that simple. A 10" F5 (my current config)
gives
a far brighter image than a 10" F10.

I cant say much but i do now know from experience that my little 4.5" mirror
@ F8 gives a brighter and more contrasty image than the 10" stopped down
to 4.5 @ F10.

Rob

On Thu, 9 Oct 2003 09:35:54 +0100, "James"
wrote:

Still hunting for an ideal scope, its a minefield- anyway, I have found
Beacon Hill offering reasonable prices on the TAL range which sound okay,
but I'm a little unsure as to the differences between the 2M and the
150PM... one is f/8 and the other f/5 I believe, and from my photography
knowledge this would suggest the f/5 would give a brighter image?

The F8 'scope will give you more magnification from a given eyepiece
but the F5 will give you a wider field of view. The 'P' in 150PM is
parabolic, the shape that the mirror is ground to. There is also a
parabolic version of the 2M but I've never seen it advertised in this
country and it's arguable that the mirror doesn't need to be parabolic
at that focal length. The 2M comes on a much better (steadier) mount
than the 150PM (it was designed for a much bigger refracter that Tal
never produced) but the 2M is much longer and much heavier despite
being the same aperture.

I'm sure it cant be that simple, would the image be brighter but the
quality worse? Is one going to be better for some types of viewing
than others?

The 2M would be preferable to the 150PM for planetary use and the
150PM is a better choice for deep sky work.

When I was into Tal 'scopes I heard that the image quality was very
good on the 150PM but, if I were looking for a reasonable quality
reflector now, I would rather spend my money on an Orion (UK) Europa
or possibly a Synta 127 Maksutov, if portability is important to you.

Cheers

- Mike