ED80 Vs ST80 for visual

[mark81]

So, the other day I came across a guy who I work for and he also has a SW ST80.  We got to talking about possible upgrades - mainly the focuser - which I know a few people here have done.  Then of course to make the most out of that upgrade you need a 2" diagonal and some good EPs...and a sturdier mount (if you have the standard az3) and then maybe the viewfinder...then you realise that for a little more money you could get an ED80.  Forgive my ignorance, but for visual only, what would be the main benefits of an ED over the ST?  I realise false colour is going to come up, but considering the st80mm short tube doesn't perform well on bright planets and moon it's never something that really seems to be an issue. ...

Thanks

Mark

[Knighty2112]

You should find with an ED scope that you get a much sharper image, which is especially more noticible on the moon and the planets. Better contrast too. 

[Ags]

I use my ST80 a lot for deep sky; I never use it for solar system objects - I have a small Mak for that. On deep sky objects I use magnifications up to about 60x, and it provides sharp and pleasing views. I wouldn't expect an ED80 to provide better views (not that I have looked through one). At any rate the images hold up against those offered by my mak.

Another thing I don't use the ST80 for is doubles; the scope is terrible at reflecting the true color of stars. Basically, if the target's not bright and it doesn't need a lot of magnification, then the ST80 performs perfectly well. But it is not a general purpose scope and the only way to make it good at high magnifications or on bright stars would be to upgrade the lenses at the front!

With an ES 24/68 1.25" eyepiece, I get a 4 degree field of view. That's pretty huge - why spend money on upgrading the focuser, which takes away from the cheap and cheerful nature of the telescope? To get the same field of view in the ED80 would require a massive 36/68 2" eyepiece. So basically by getting the ED80, you are "downgrading" your 2" EPs to 1.25"! Only by getting the widest of widefield 2" EPs could you get a little bit more true field with the ED80.

As for the other upgrades (mount, finder, diagonal) - those aren't specific to the scope and you would need then in any case with the ED80...

[Ben the Ignorant]

Adding upgrades to the 80mm f/5 achro is really a waste of money, these words are not too strong. A 2" focuser would only allow more of the blur the achro produces at its focal plane, and the better diagonal and eyepieces would only permit viewing more of that blur.

Achro glass + very short focal length = lots of uncorrected field.

Upgrading to the ED 80 is a sensible choice, the 2" diagonal and better eyepieces will show sharper stars across a larger area. On top of their poor overall theoretical ability, the super-short achro doublet lenses are often decentered in their oversize plastic cell, reducing their role to very low power scope or mega finder only.

The ED has none of these problems. The false color is not just a ring of spurious light around everything, it's a halo of red and blue/violet on top of everything. Say you watch Jupiter and see the purple halo (mix of violet/blue and red) around it, remember the halo starts at the center of Jupiter, so it is a blurry image permanently superimposed on the sharp (green, yellow-green and orange) image.

Which has to  degrade contrast and definition. There is no cure but to switch to a better scope if you want to spend money for an improvement.

[ollypenrice]

Yes, the ED80 will be sharper and more contrasty and will support high magnifications and widefield eyepieces without coma. It's a much better telescope. I've two ST80s as guidescopes and had one as a finder on a big Dob. It's cheap, cheerful it's a telescope - but you can't say it's a good one. You can certainly say the ED80 is a good one, though. It's downright outstanding at the price.

Olly

[Ags]

Don't be too hard on the ST80. Under dark skies with a good 1.25" widefield eyepiece it can give unforgettable views.