Skywatcher Startravel 80 mag limit

[Inthedark]

OK, I know that I'm not going to get huge magnification from my SkyWatcher 80mm Startravel. I have the 10mm and 25mm EPs and the 2x Barlowas supplied, plus a 6mm Celestron Plossl. So with the 'scope's 400mm focal length I have 16x, 32x, 40x, 66x, 80x and 133x. All well within the theoretical max of 160x.

I'm quite happy with it a low magnification. 16x is great, and up to 40x it's pretty good. The 66x is a bit squinty,smearyand hard to focus, while the 80x and 133x are completely useless.

I'm wondering what's causing this? Does the short tube design limit the mag?Could the 'scope be misaligned somehow?Or are the EPs to blame? Cheap Barlow? Rubbish Diagonal? Is it possible to get a decent 80x or 100x with this scope with the right EP? Or should I just enjoy itswide fieldviews until I can afford an 8" reflector?

[John]

Hi,

The Startravel 80 is a short FL acro refractor which is great as a wide field scope but it's capabilites are much more limited at higher powers. I've found that 80x is about the practical maximum with the scope and even then the views are a bit compromised. Better quality eyepieces won't really help here as the limitation is with the scope design.

My advice would be to enjoy it for what it does best - low to medium power views and extreme portability.

The theoretical capability you mention is only theoretical and assumes perfect viewing conditions, excellent optics - in practice it's very rare to be able to use that whatever scope you are using.

John

[philsail1]

Hello "Inthedark!"

John is correct there. Every scope has it's limitations - if not in magnification, then it will be in some other aspect of performance (field of view, brightness of image, portability, etc).

If you are looking for purely more magnification, then it might be worth considering a small Maksutov?

I have the 90mm version of the Skywatcher "skymax" which because of its long focal length of 1200mm, will easily cope with magnifications of up to 120x and still give very crisp, clear images. But, (and there's always a but!), because of the design of the scope, you do lose a significant area of the field of view.

If you wanted a good "all round" scope, you wold need to consider perhaps a Skywatcher 130PM, or 200mm Explorer (both are reflectors).

If you are quite happy with what you have, then as John says - just enjoy the magnificent wide field views the Startravel gives!

Regards,

philsail1

[Inthedark]

Thanks for your replies.

I suspected that it would be a limitation of the short f/l design. While I love the portability and the fantastic bright and wide field views, I still wonder if I can do a bit better than the 2 shorter EPs I have - the standard issue 10mm and the 6mm Plossl. Would a better quality EP like a Celestron X-cel or Baader Hyperion 8mm give me a good useable 50x? Or would I be better putting that money towards something like an Explorer 150PL as a compliment to the ST80?

[philsail1]

I personally would put your money towards the Explorer 150PL. You will then have a scope for wide field star views, and a scope for high power planet viewing!

I've tried using high quality eyepieces on my 90mm Maksutov and it just doesn't improve matters. i.e. I tried 1 5mm Vixen Lanthanum but it was worse than the basic Skywatcher 10mm Kelner eyepiece which came with the scope.

Best wishes,

philsail1

[John]

I personally would put your money towards the Explorer 150PL. You will then have a scope for wide field star views, and a scope for high power planet viewing!

Thats a great plan I think - the ST80's a great little "grab and go" scope and combined with a 6 inch newt you would have a really versatile combination

John

[Inthedark]

As soon as I typed that I realised it was daft... I've already been considering an upgrade to an EQ3-2 mount at £139, plus £78 on an eyepiece... that's more cash than a 150PL/EQ3 combo!! Thanks guys.

[asteria]

Hi there - I have a version of the ST80 too and I like it a lot, but it is designed for getting the 'bigger picture' i.e. wide field stuff. For this sort of work it is excellent, and it gives a good clear view. Some of the views of the Pleiades etc I have had through it have been great, and I guess I would have to spend a lot more money to get a significant step up in image quality. Portability and quick cool down are also great plus points.

Hang on to it for the time being, and when you have it paired with something that gives higher mags you will have a great combination.

Ed

[Neon]

I wouldn't jump into anything quite yet Inthedark. Although a short tube scope won't give you massive magnification, I'd spend a bit more time getting used to what's up there before splashing out on your next big purchase.

All the suggestions here are as always spot on, but what I planned to do when I got into astronomy has slowly changed over the past year. Initially I wanted to buy a big EQ5 tracking mount, but my viewing habits don't really suit that (as I have learned).

What I would personally recommend at the moment is an Orthoscopic eyepiece. These are fairly cheap (£30 - £70) and although they lack a wide FOV, they're very clear. I recently purchased a 6mm for my 80mm scope and have been impressed with its performance on the moon and planets.

However, I rarely get to barlow it due to poor seeing. If you're looking for clearer views of the moon or planets, then maybe get one around the 7-8mm size. You'd probably get quite a lot of use out of it and if you did eventually upgrade to a bigger scope it'd work fine with that too.

HTH

Mark

[jgs001]

Inthedark, I don't have an ST80, but I have a Konus badged 80mm Achro, it's basically the same thing though. I have a 5mm Ortho and a 5mm Hyperion. Using both of them, and when the seeing has been good, I've barlowed them, and had a great deal of fun observing the moon. I wrote up the reports some time back and they are in the observing reports section. I've also used a x2 barlow with a webcam on this scope and that too has been posted. So whilst it may not be designed for it, mine is certainly achieving it. Would I get better view with a different scope, probably, but that's not going to happen in the short term.

[acey]

Does the short tube design limit the mag?

You ask about limiting magnification, but to get the best out of your scope you should consider another kind of mag - the limiting magnitude.

A scope's limiting mag(nitude) depends on two apertures - its own and your pupil's, and also on the limiting magnitude of the sky you observe under. A scope gives a "magnitude gain", and if the gain is, say, 5, and if you observe under a sky where, with the naked eye, you can see down to, say, mag 4, then the mag(nitude) limit of the scope will be 9.

Let's suppose your eye can dilate to 7mm. Then the magnitude gain of an 80mm scope is

5log(80/7)=5.3

If you take your 80mm scope to a dark-sky site with limiting mag 6 (which is very easy because it's such a small scope) you'll see down to mag 11.3 - enough to view all the Messiers. Because of the short focal length, you'll actually find objects like M33 easier in the 80mm than in a larger instrument with a longer focal length.

I use an 80mm short-tube as a travel scope, and by going to places like the Canaries I've been able to see objects I could never see from England with my 8-inch dob (eg Omega Centauri, the Sculptor galaxy, etc etc). It's a great little scope. Highest power I use in it is 50, but mostly I use a magnification of 20. It's not an instrument for seeing the discs of Jupiter's moons, but there's a whole lot else you can see with it. So carry on enjoying its wide-field views - and even when you get your 8-inch, the 80mm will still have its uses.

Andrew

[Inthedark]

Well, I'm not making any hasty purchases.

Mark - I've been spending a bit of time learning my way around the sky, unaided and with some 10x50 binos. That and I've finally got the EQ1 mount working nicely so I don't feel a desperate need to upgrade at all right now.

John - I've read some of your reports with interest, I'm sure to check out some more now I know you've a similar 'scope.

Andrew - I'd been wondering about limiting magnitude, but couldn't get my head around some of theexplanations. I think I've got it now! Thanks!

David

[gordyb]

What is the EQ1 mount like for the Startravel 80 would it be better on a AZ3 or is fine on the EQ1,and is it worth getting any different eyepieces with this scope.Cheers Gordy