ED120 Nexstar 8" comparison

[MartinB]

A rare visual session for me last night. Wanted to have a look at M3 M13 and M92 for the monthly comparative observation and decided to use both my ED120 and NS8. Report here http://stargazerslounge.com/index.php?topic=13549.msg140558#msg140558

The ED120 sits on a Vixen GPDX mount which in turn is on a Berlebach tripod. I can't wax lyrical enough about this tripod - it adjusts so smoothly and each of it's legs has a scale so you can get it level effortlessly (if your surface is level!). It is a vibration sponge - suppressed in less than a second. The mount uses the skysensor 2000 goto system which is accurate and flexible. It makes an annoying clicking sound when tracking which is a known feature but no vibration is transmitted to the scope.

Optically the ED120 seems sound - collimation is spot on and stars remain pin point out to the edge of the FOV using plossls.

The view of the globs was pleasing especially as the stars started to resolve. However, whatever people may think about different scope designs the extra aperture of the NS8 delivered more detailed view. The globs were resolved effortlessly and it was possible to discern details which just weren't possible with the 120mm scope. Both scopes produced bright sharp stars and equally snappy focussing (may be the ED120 had the edge here but I might be imagining it!)

I also had a look at M57. Again the ED120 performed well with the ring showing as a ring rather than a disc at x90. The image started to degrade at higher mags. I was quite impressed until I looked through the NS8 at x135. The extra magnification allowed by the bigger aperture really paid off here with a much clearer impression of the of the rings structure.

The NS8 was sat on a wedge and set up and alignment time was pretty similar to the GEM mounted ED120. Observing is a more relaxed business with the fork mounted scope - no issues crossing the meridian and no awkward angles. Would have been easier still in alt az.

I think the ED120 delivers well for a 5" scope but it is still a near 5" scope and an expensive one at that (but not as expensive as a TMB or AP)

[chuenmanc]

That's good to know Martin, thanks. My dream scope wavers between a 5" apo and a Celestron CPC1100. I've been getting caught up in the refractor forums on Coudynights, and have been hypnotised into thinking the refractor will be inherently better. I guess aperture is still king!

[John]

Thats a very interesting report Martin, thanks. I have been pleasently suprised myself at the capabilities of my C8 SCT compared to the ED100 I used to own - I was expecting it to do better on DSO's of course because of the substantial aperture gain but after reading all the "horror" stories about the impact that the central obstruction would have, I have been suprised at how good the SCT has been at high resolution planetary and double star work with superb detail on Saturn and nice resolving power on doubles such as Epsilon Bootes. You do need to keep the collimation spot on though to get the best out of the SCT wheras the ED100 could be used virtually straight out of the house.

I think you have got the best of both worlds with your current setup !.

John

[moondog]

Martin

I've been going through a similar excercise with the NS8 and the TAL 5ins achro. I would agree with your findings - you can't beat aperture, even with a central obstruction. Mathematically the greatest light grasp with any scope is with the area of the outer part of the object lens and not the central part. The NS8 wins hands down in this respect over a 5ins frac.

I've found more detail with the NS8 in the majority of the objects I've looked at, wether it's the moon, planets, globs or other fuzzies.

The TAL is slightly sharper with a bit more contrast, but much less detail. Doesn't matter how excellent even a 5ins APO lens is, if the detail isn't there to start with you still get a pin sharp blank area!

MD

[John]

...... if the detail isn't there to start with you still get a pin sharp blank area!

Nicely put MD

John

[GordonCopestake]

I think the perfect setup would be a 4" f/5 APO piggybacked on an 8" f/10 SCT.

Although of course if portability isn't a concern then a 6" f/5 APO piggybacked on a 14" f/10 SCT is even better.

[mike bacanin]

I can second the previous comments, having owned the TMB 130 F6 Apo

my £430 C8 Xlt shows planetary detail superior to the refractor which cost me £3500

the contrast is great in such an apo but it will not reveal detail beyond its aperture.

my C8 is critically collimated and my best ever view of saturn was with Meade 4000 14mm UWA.

Simply superb!! ( also use WO 10:1 crayford)

mike

[GordonCopestake]

Mike, you were right about the naglers: I've had to get a job to pay for them hehe

[GazOC]

The NS8 was sat on a wedge and set up and alignment time was pretty similar to the GEM mounted ED120. Observing is a more relaxed business with the fork mounted scope - no issues crossing the meridian and no awkward angles. Would have been easier still in alt az.

:rolleyes:You don't miss a chance do you?

[russ]

Nice comparison Martin. Although I'm not entirely convinced with the SCT design.....the cool down just ruins it for me. I've waited upto 3 hours in the winter for the C8 to perform. Eventually having to pack it up without a proper look because the clouds rolled in. The ED100, as John says, is ready to roll in 30mins or so. Extra detail is great if the scope ever cools to let you see it. Throw in dew problems, image shift, mirror slop and collimation....the whole SCT fun factor where thins pretty quick. The best scope is the scope you use most often.....an SCT wouldn't stand a chance.

Now that's strange thing to say for a man who is about to change over to an SCT setup :? Seem to be ignoring those nagging voices in my head

Russ

[GordonCopestake]

I keep my C6 in my shed and cooldown isn't an issue. For visual use most image shift/mirror slop problems are not an issue and with a crayford imaging isn't too bad. I agree collimation is a pain but it's easier than a newt. I agree that APO's are a better design but 8" APO's are beyond me. As has been mentioned in this thread before, aperture is aperture and APO's are NOT magic. I'm the first to want an APO and they do hit above their weight, but i'm not convinced that aperture can be written off just yet. I'm getting on well with my 6" SCT and I can see a larger one in my future

[MartinB]

The NS8 was sat on a wedge and set up and alignment time was pretty similar to the GEM mounted ED120. Observing is a more relaxed business with the fork mounted scope - no issues crossing the meridian and no awkward angles. Would have been easier still in alt az.

:rolleyes:You don't miss a chance do you?

aha!!! That hit the target :D

Actually, wasn't trying to make a "what scope is best" thread. Just trying to give as objective a report as possible of a short observing session.

[russ]

These threads always descend into scope bashing....it's natural.

All I wanted to say is it's not clear cut. Yes the SCT will outperm the Frac no problem, it's a fact, can't be argued. But if you store your prized possesion in a nice warm and cosy house and then bring it out on a cold and crisp night, the tables turn. SCT's take hours to cool, it's a fact, can't be argued. And as the British climate on the whole only allows for cloud breaks rather than clear nights. This makes things tricky for the SCT, as there's a very good chance the sky will cloud before it can get upto speed.

But ultimately Martin's findings are spot on. The ED120 doesn't have a chance of beating the C8.

Russ

[GazOC]

But ultimately Martin's findings are spot on. The ED120 doesn't have a chance of beating the C8.

Maybe I've been unlucky with my 2 SCTs (or my memory is playing up!!) but I certainly prefer planetary views through a smaller refractor or Mak to an SCT. Maybe its just an athestic(sp) thing though as a scope can only resolve based on its aperture.....I always found the views very soft when comared to other types of scope though...

For DSOs, aperture def. rules

[MartinB]

I think it is an extremely sensitive topic Rus because some people have invested a lot of money going down a particular route and they will defend it to the hilt. Steve posted a good link some time ago on how this thinking develops. You always post good objective opinions which is what the folk of this forum are interested in. One big advantage of the ED100 over the ED120 for people who keep their scope indoors is the much shorter cool down time. The ED120 is apparently quite slow in this regard (I keep mine in an outbuilding so it isn't so much of an issue).

I like the ED120 but I think some of the stuff writen about the wonders of apos are a little over stated to say the least (at least visually). They certainly fill some speciality niches - high contrast planetary and lunar observing and a number of imaging applications (a Takahashi FSQ is one of my dream scopes) but for general observing people should try before they buy.

Gaz, the ED120 gives lovely views of the moon and saturn. I haven't run the 2 scopes side by side to compare. I know with the SCT, unless the seeing is excellent it doesn't pay to go beyond x150. Well, the ED120 can handle this easily and will probably give better views without the lower resolution being such issue. I think the SCT only comes into it's own when the seeing is very good.

[FLO]

These threads always descend into scope bashing....it's natural.

I don't think we're there yet Russ, fortunately.

Broadly speaking, aperture determines brightness and resolution whilst optical design determines the look/feel of the image. The first is objective, the second is subjective.

Much of astro product marketing, particularly American, concentrates on brands/personalities rather than actual manufacture and performance per £. In the worst cases owners can become brand zealots where they lose the ability to speak objectively.

I believe one of SGL's strengths is that members aren't blinkered by exotic brands and feel able to speak as they find without fear of being jumped on or intimated by others.

This is a good forum 8)

<edit> Ah, Martin beat me to it

[GazOC]

I think the SCT only comes into it's own when the seeing is very good.

That ties in with what I find with my ED100 and 7"Mak. Most nights on Saturn the difference hasn't been massive, but on a couple of great nights the Mak really does show well.

[Grant]

Steve posted a good link some time ago on how this thinking develops.

I don't remember the link but this sort of behaviour and thinking is called cognitive dissonance, a great example from wikipedia:

Without evaluating various blenders, Luke purchases a blender. Luke's decision is consonant for the preferred qualities of his blender and the disadvantages of the rejected blenders. However, it is dissonant with the defects of his new blender and preferred qualities of the rejects.

Unknown defects: If Luke's dissonance is amplified often enough, e.g. by new, authoritative reviews of his blender, reviews which rate his blender poorly, or, if his experience using his friends' blenders has Luke finding his machine lacking, Luke begins to be overwhelmed by the dissonance related to the blender, at which point he starts to second-guess his choice (buyer's remorse).

Known defects: Luke's previously-unavailable first choice had caused him to "settle" for a lesser choice, or "placeholder". Then if his first choice becomes available, Luke will experience an instant increase in the second choice blender's hitherto repressed dissonance.

Under either scenario, Luke experiences full-blown cognitive dissonance when dissonance outweighs consonance.

Tipping point: Luke may act to resolve the imbalance in favor of consonance by exchanging his blender for one that more fully meets his expectations. Or, if no exchange is possible, and Luke is cognitively dissonant enough, he may even outright discard his blender and buy one which is less dissonance-inducing, as consonance should always trump dissonance. It is also possible that Luke will simply reject the negative reviews and his own bad experiences with the blender and convince himself that his blender is actually the best.

Linky: http://en.wikipedia.org/wiki/Cognitive_dissonance

[FLO]

Good stuff Grant.

Needless to say I find the psychology behind our reasons for buying one brand over another fascinating.

This probably isn't the article that Martin is thinking of but it is one of my my favourites: 'Tyranny of Choice' by Barry Schwartz, professor of Social Theory at Swathmore College.

Rather than hijack this thread further, I'll find the original post and 'bump it' (though I don't think it received any responses first time round).

<edit> HERE