Re: What am I doing wrong?


"ELIZABETH KEARNEY" <steveandlizzie@xxxxxxxxxxxxxxxx> wrote in message
news:xI_6g.225895$8Q3.56183@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
I recently bought a Skywatcher Explorer 130P. This is a 5.1inch reflector
with focal ration F5.

I have two eye pieces - 10mm and 25mm and a x3 barlow.

I was observing jupiter last night on maximum mag (10mm and barlow - about
x195 I think) it looked big but I was unable to achieve a good focus.
Using
different combinations I could achieve a sharper focus but without the
magnification to see better! Viewing conditions weren't ideal but I was
wondering - is this lack of focus down to the barlow?

What would be a better set-up with the equipment I've got or what new eye
pieces would anyone recommend. I have seen posts in other forums from
people
with the same scope and they seem to be doing much better!

Thanks for any help you can give

Steve



Your scope has a focal length of 900mm. Your 10mm eyepiece will give you
90X (900mm / 10mm = 90X). Add the 3X Barlow and you get 90X x 3 = 270X.

I Googled your scope and find it listed with 260X as the highest potential
magnification. Thus, with the 10mm eyepiece and the 3X Barlow, you were at
or above max mag for this scope.

Rule of thumb is to multiply 50 times the aperture in inches for max mag.
Thus, your 5 inch scope would yield a maximum magnification of 250X -- which
is about what the manufacturer states.

I have a XT-12 -- 12-inch dob, 1500mm focal length -- 12 inches x 50 ==
600X max mag. I have eyepieces that will get me up to 450X but my best
viewing of the planets is always around 175X - 250X. Anything more and
atmospheric conditions -- seeing conditions -- degrade the view. Also -- at
300X or more, objects move across the field of view pretty quickly.

Your 25mm and 10mm eyepieces are now giving you 36X and 90X, respectively.
With the 3X Barlow you get 108X and 270X -- and as we see, the 270X is not
usable.

A 2X Barlow would be a good investment. With the 10mm and 25mm eyepeices
and the 2X and 3X Barlows, you would have the following magnifications:
-- With the 25mm eyepiece: 36X, 72X, and 108X
-- With the 10mm eyepiece: 90X, 180X, 270X (not usable at 270X)

The 10mm with a 2X Barlow at 180X will give you excellent views of the
planets.


.

Relevant Pages

  • Re: What eyepieces/filter for 10" dob
    ... I could get a 5mm and still use the barlow. ... practcle limit with the 10" scope. ... your eye is probably about 60 seconds of arc. ... manage 1 arc sec or worse much of the time, this mag is probably OK. ...
    (sci.astro.amateur)
  • Re: Advice on eye pieces
    ... find that the 2x Sky watcher Barlow introduces chromatic aberrations to ... I get the impression that the barlow that come with the ... scope are pretty budget and that buying a better set could somewhat ... My brother used to live in Dartmoor, and I know just how dark the skies can ...
    (sci.astro.amateur)
  • Re: Saturn 2005-10-17
    ... > Second - make sure your scope is collimated properly. ... > focuser) move back through focus again. ... I realised I needed the Barlow to get any chance of a decent ... size image of Mars at all. ...
    (uk.sci.astronomy)
  • Re: true magnification of Televue 3x?
    ... do have the JMI installed between the scope and the Televue, ... image scale was smaller than with the 3x barlow. ... Powermate 5x (and thereby get less overall magnification once the filter ... these are effectively complete 'scope' assemblies used to ...
    (sci.astro.amateur)
  • Re: We found Saturn!
    ... be quite pleased with the performance and value of the Orion Skyquest ... so that folks here can recommend a different scope. ... have to follow it as it moves across the sky (actually, ... The first accessory that you will want is a 2X Barlow. ...
    (sci.astro.amateur)