Chromatic Aberration In Skywatcher's

[gordyb]

Is chromatic abberration in the startravlel and evostar range the same and is it the same or better with different apertures. Thanks

[step_hen]

The Longer focal length of the Evostars has much better control than the short ST series. I have had 102mm and 120mm Evostars and found them excellent scopes. CA is there on bright objects but not bad enough to ever distract me much. I have also had an 80ST, and a 102ST, and currently have a 120ST. They are good scopes if used as designed- low power wide field of view. If you want something for planetary as well as DSO viewing, then the Evostars are a better bet. CA can be reduced with a 'minus-violet' type of filter

Stephen

[Bizibilder]

I have an Evostar 120 and find that the CA is no problem to me when looking at the Moon and planets, excepting of Venus, which is so bright that CA is a real problem! especially in a twilight sky.

[John]

As step_hen says, at F/5 the Startravel range exhibit more CA than their Evostar cousins which range between F/8 and F/10 - but that's what you would expect with achromatic refractors.

CA also increases with aperture so a 120mm F/5 will show more CA than an 80mm of the same focal ratio.

CA bothers some people more than others so it's a personal thing how much you can tolerate without it becoming a distraction. It only really affects brighter objects of course - for low power, deep sky type viewing it's not an issue IMHO.

[gordyb]

Thanks stephen as you have had the 102 and 120 evostar's i have seen reviews that the optics are better on the 102 is this true thanks gordon

[step_hen]

The 120 is suprisingly heavier! i would say an EQ5/ CG5 is the minimum mount for it, whereas the 102 is fine on an eq3. both have the same focal length so the 120 is a faster scope and should give more contrasty views with brighter DSOs, but as a result of the lower focal ratio will have a bit more CA.

[russ]

I agree, i found the 120 Evostar was pushing the EQ5 (but this was back in 2004 and the steel tripod wasn't even an option). Probably a lot better on the CG5 with the 2" steel tripod. At the time i found the CA bothersome but i've used a 120 a few times since and found it excellent. My problem back then was i owned the Skymax 127 as well and it was a notch better than the Evostar.

[gordyb]

I want to keep this on the same thread i have seen the Startravel 102 on the EQ-1 and AZ3 mounts and the Startravel 120 on the AZ3 whereas the Evostar 90 is on the EQ-2 and AZ3 mounts at minimum.Are the Startravel scopes much lighter.

[John]

I want to keep this on the same thread i have seen the Startravel 102 on the EQ-1 and AZ3 mounts and the Startravel 120 on the AZ3 whereas the Evostar 90 is on the EQ-2 and AZ3 mounts at minimum.Are the Startravel scopes much lighter.

The Startravels are a bit lighter but, more importantly from a mounting perspective, much shorter. Short tubes are easier to mount. I've had an F/10 4" refractor on an AZ-3 and it was marginal - OK for a quick look but a bit wobbly for lots of high power use. The AZ-4 (with the steel legs) is much sturdier.

[SiriusB]

Is there a particular area you are interested in or are you after an all round telescope Gordy?

I used to own an Evostar 120, like Russ i thought the eq5 only just adequate for the weight & bulk, but like Russ that was before they upgraded the tripod, which was the weak link, so probably fine now.

As far as the Chromatic aberration goes, it was there but it only bothered me on Venus,Jupiter,moon at high power & bright stars like Sirius & Vega.

I recently bought a Startravel 120 for deep sky on an az3- the az3 again just copes IMO, though i'd expect the eq3 to be dandy with this scope.

Again with the C.A. the same comments apply, there's just more of it(but not as bad as i expected) One thing to be aware of on the startravels is that focusing can be a bit tricky at first, being a "fast" scope, though the focuser seems better than i remember on the Evostar- i'm guessing Q.C. may have improved?

Have you had a look through any refractors? If not try & blag a few views through different scopes to see how the C.A. bothers you.

As stated by someone in a previous post its a rather subjective thing- you may take one look & decide refractors aren't for you or you may wonder what all the fuss is about C.A. You won't know till you've seen it.

I'd recommend either scope, the Evostars a better all round package, the Startravel easier to use, But it depends what you're going to use it for...

Hope that helps.

[gordyb]

I suppose i would use it for all round use but the 102 evostar is around £270 on a EQ3-2 the same price buys you a 8" dobsonian,before i buy anything i will be going up to either the newcastle or sunderland astro to see through various telescopes,the one i favour at the moment may not be the one i eventually get after looking through different ones.

[Moonshane]

if you are just looking for a visual scope the 8" dob will beat the others hands down. try one when you go to the astro meeting.

[gordyb]

I certainly will i wonder if anyone from the newcastle or sunderland astro clubs are on here.

[gordyb]

The 150p skyliner is f7.84 while the 200p skyliner is f5.91 is there much of a collimation problem or cheaper or dearer eyepieces within these 2 specific models Cheers Gordy

[Moonshane]

collimation and eyepiece quality get less critical the higher the f number (i.e. the slower the scope). BUT you will need to learn collimation with any newtonian - I have a f11 newt and always give it a slight tweak before every session. it's not an issue and easily picked up - takes me maybe 30 seconds - 1 minute each session - the scope will need to cool for an hour so no time pressure at all if you plan.

also, better eyepieces are better eyepieces and you generally get more and sharper field of view, contrast and less light scatter etc with more expensive EPs. the two scope you mention are reasonably slow and most people see f6 as the cut off between fast and slow, based on what others say (I have not used them myself) they are both good scopes and excellent value for money.

[gordyb]

i have noticed you get the crayford focusser with the 8" dobsonian but i am not sure if you get one with the 6" dobsonian Thanks again

[Moonshane]

Crayfords are OK but a well adjusted R&P is OK too. the main difference for me was the 10:1 ratio fine focus on the Crayfords. you may not be aware but the most expensive focusers are R&P, albeit out of the reach of most amateurs.