Re: Tal 2m or Explorer 150/200?
- From: "Roger Hamlett" <rogerspamignored@xxxxxxxxxxxxxxxxxxx>
- Date: Sun, 01 Jan 2006 11:22:28 GMT
"Saxon" <speedbird011@xxxxxxxxxxx> wrote in message
news:4PMtf.14549$r4.12537@xxxxxxxxxxxxxxxxxxxxxxx
> Chaps (Mike especially),
>
> Many many thanks for the comprehensive reply - it's greatly appreciated
> when
> those with experience stop to help those just starting out. I am
> pleased to
> report that I did buy a scope yesterday but it ended up being one that
> wasn't on my shortlist. I went in to Telescope House and they helped me
> choose a Bresser Messier N203 8" Newtonian reflector
> http://www.telescopehouse.co.uk/page.aspx?theLang=001lngdef&pointerid=100227B23A584F13A8144199EC3120C0&action=lnk
> which along with a basic filter pack and the two axis motordrive ended
> up
> coming to £450 with SPA discount. The scope seems to bear some
> resemblance
> to the Meade LXD75 range in terms of both mount and according to
> Telescope
> House the optics too although I believe assembly is of course done in
> China.
> Overall I was extremely impressed with the fit and finish and it
> certainly
> felt like a well engineered product for the price, the tripod for
> example
> not dramatically different from that on the LX90. I spent a very
> enjoyable
> few hours putting the scope together and achieved first light around
> 7.45pm.
> It was such a thrill to see how many stars were visible through the
> scope in
> any patch of sky. I closed in on Mars which by now was starting to
> approach
> my neigbours trees on the South West side of the back garden. I moved
> through the eyepieces - 25mm, 15mm, 10mm and then 10mm with 2x Barlow,
> still
> fumbling for the RA and DEC levers in the dark and trying to get used to
> the
> strange motion of my first equatorially mounted experience! One thing I
> found very tricky was adjusting the height of the tripod with the scope
> attached - I'm presuming this is best accomplished before the scope is
> mounted! I ended up either stooped or kneeling most of the time!
The LXD75, is basically Chinese as well. It depends which OTA it has. The
SCT's have the optics made in the US, but the Newtonians, are Chinese.
> Eventually I got Mars nicely centred although did find that at 180x
> magnification even adjusting focus caused the planet to move around in
> the
> view. I presume this is normal on a lower end telescope -or should I
> tighten the eyepiece screws more? I was rewarded with an obvious orange
> sphere only occasionally exhibiting surface patches. I couldn't see any
> ice
> caps or anything but my goodness it was a thrill!! I wouldn't say the
> image
> was tack sharp either, but it's hard to know if that was related to the
> fact
> I haven't collimated the scope yet, the quality of the bundled eyepieces
> or
> just the general seeing conditions on the fringes of the M25.
The eyepiece screws,should make no difference to the focussing. This is
all down to the mount, and is normal to some extent, even on very
up-market kit. This is where an electric focusser helps. You may also be
able to make, something to help. On several scopes, a flexible 'spring'
extension to the focusser knob, can be fitted, and this decouples the
focusser, so that the effect is much less bad. If you are at all
mechanical, you may be able to produce something like this.
> I was just turning my attention to Orion and the Orion Nebula which was
> prominent in the Southern sky last night when the clouds rolled in and I
> realiseed that by 21.30 my opportunity for observing was done for the
> night.
> Can't wait for tomorrow now!!
Unfortunately, cloud will now follow.... :-(
> I haven't yet connected the motor drive control, I wanted to get a feel
> for
> the manual handling of the scope. I'm really looking forward to seeing
> the
> moon later in the month along with Saturn and Jupiter. I'm chuffed to
> bits
> after having an interest in the subject for 30 years (I still have my
> Hamlyn
> Book of Astronomy 1975!) that I finally own my first telescope.
>
> One final query - I know that my 90mm focal length isn't ideal for
> planetary
> observing but the chaps at Telescope House stillreckoned it would
> produce
> better results than the 6 inch reflector with 1200mm focal length. It's
> tempting to push the magnification beyond the 10mm Plossl and 2x Barlow
> with
> a 5mm Pplossl which would give me around 360x magnification (approaching
> the
> 50x per inch theoretical maximum). The chaps in Telescope House did say
> that getting clear images above 200x magnification depended greatly on
> seeing conditions and was rarely achievable in practice. Would you
> chaps
> agree with this or would a 5mm give me even greater usable
> magnification?
>
> Either way I'm delighted - many many thanks for all advice and a Happy
> New
> Year once again to all of you.
>
> Jon
Not 90mm focal length. 900mm. Their comments are really spot on. The '50*
per inch' rule, is really very 'flexible'. There are some conditions, when
trying to seperate tight doubles, or looking for the finest planetary
detail, when people push way past this. Conversely though, seeing often
makes even 30* per inch, almost worthless. I'd suggest 'staggering' your
eyepiece lengths. A 5mm eyepiece, really duplicates what you can get with
the Barlow and the 10mm. In instead you get (say), something round a
6.7mm, or a 3.6mm, you then get a better possible 'range' of
magnifications. Unfortuately, the very short focal length eyepieces, can
have rather restricted eye-relief, except in more expensive designs, so
I'd perhaps say something round 6.7mm, might be a good choice, giving you
135*, which is likely to be a very useful magnification, and going to
270*, when conditions are good. It is worth also remembering that
something like a 1" extension tube in the top of the Barlow, will increase
it's magnification, to perhaps 2.6*, for a very minimal cost.
Best Wishes
.
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