Skywatcher 120 ED PRO Triplet v Tele Vue NP127is

[25585]

How good is this scope for rich/ flat field and reducing FC & CA?

Much cheaper than Tele Vue equivalent. 

[John]

I'll be interested to read the responses to this. I love my ED120 but the TV 127 has been on my dream list for some time !

The ED120 has a pretty flat field as far as I can tell and it's CA control is excellent for a doublet, just a small splash of CA around the brightest stars. Nothing on the lunar limb / Jupiter / Saturn etc when the scope is at focus and just a touch of CA either side of sharp focus.

I'd imagine that the TV 127 is pretty much 100% flat and colour free but I've never had the pleasure of using one.

[Owmuchonomy]

As John mentions above the ED120 is a doublet not a triplet.  I agree on the almost complete lack of CA but as I mentioned in a recent thread there is some field curvature present with my ES 82' EPs.  I too have no experience of the 127.

[michael.h.f.wilkinson]

The Skywatcher Esprit 120 ED is a triplet, but the TV is a 4-lens Petzval-like design. It should have the flatter field. You can of course add a flattener to the Esprit. Even with flattener, the SW is a lot cheaper. I haven't used either scope, nor have I seen a comparison

[25585]

Review of the doublet http://www.scopeviews.co.uk/SW120ED.htm

But the triplet as can be seen on FLO would hopefully be nearer TV quality. 

However the Equinox is enticing and portable. Extra 1k for a 3 inch focuser

[Doc]

I have the Espirit 120ED and it's pretty amazing, you need to look really hard to see any colour on the moon, there is no CA or colour on any of planets and the only star that has shown it is Sirius. I have looked through a TV101 before, it was many years ago but that was a very good scope.

[John]

Yes, I should have mentioned that my scope is the ED120 Pro , the ED doublet that uses an FPL-53 glass element. Same optics as the Equinox as I understand it.

 

[Stu]

Always fancied a go with an NP127. I love widefield scopes with flat fields, really enjoyed my Genesis. Having fast optics which are well corrected and give a flat field is only really possible with a Petzval design, at least without the faff of separate flatteners.

Not sure if TV's ultimate quality is up to Tak/LZOS standards, but certainly it should be pretty good. Just really expensive!!

[John]

I guess the Vixen NEO 140SS would tick the fast and flat field boxes but is not so good on CA suppression:

https://www.firstlightoptics.com/vixen/vixen-na-140-ss-flat-field-refractor.html

Lightweight too for a 14cm refractor. I bet the deep sky views are lovely

 

[25585]

1 minute ago, John said:

I guess the Vixen NEO 140SS would tick the fast and flat field boxes but is not so good on CA surpression:

https://www.firstlightoptics.com/vixen/vixen-na-140-ss-flat-field-refractor.html

Lightweight too for a 14cm refractor. I bet the deep sky views are lovely

 

When I bought my Genesis, Vixen flourite fracs were the rage & I physically checked one out at Fullerscopes. They were light then, to me their tubes seemed too thin & denting one worried me - also Japanese metal quality generally in the 80s. 

How robust are modern refractor metal tubes? I hope TV are still tough but so much from the far east now. Always buy rubber armoured bins. 

[John]

I have a Vixen ED102SS F/6.5 that dates from around 1999/2000. It's light but seems just as tough as my other refractors. I used to have a Vixen SP102M and that seemed robust as well. I used to lust after the Vixen Fluorites back in the 1980's as well !

I currently have the Vixen (above) a Takahashi FC-100DL, a Skywatcher ED120 and a APM/TMB/LZOS 130 F/9.2 triplet. They all seem pretty well built scopes to me.

I've not owned a TV refractor as yet. Plenty of their eyepieces though

 

[Stu]

Scopes like the TV76 and 85 are built like tanks, lovely engineering but heavy for their aperture. The Genesis felt less 'nuggety', a thinner walled tube I think but the Petzval element cell made it feel quite solid still.

I think the Tak FC100DC is pretty lightweight for a 4" scope, a very different feel to TV but still feels plenty robust enough.

I did try a Vixen NEO 140SS once which someone kindly lent me. Unfortunately I did not get a chance use it under a dark sky for widefield DSO observing as I'm sure it is excellent for that. A bit too much CA for my liking at higher powers.

[Moonshane]

Bear in mind with the petzval designs you cannot use them for solar with a Herschel wedge. The 120ED Skywatcher scopes are really very good.

[Merlin66]

Moonshane,

Sorry mate, you are incorrect.

This urban myth has done the rounds many times.....

Al Nagler for TV petzval telescope designs has gone on record (S&T last year) to say their scopes are 100% OK to use with the Herschel wedge.

I have also received similar written replies from Takahashi and Williams Optics who also confirm their scopes are 100% OK to use with a Herschel wedge.

Maybe we should make this a sticky....

 

[Moonshane]

I stand corrected. I suppose it would be best to continue thus off this thread. Would you be willing to pm me links or copies of correspondence ? I'll See what I can do.

 

[Merlin66]

No problem.

I'll bring the correspondence together and send you a copy.

(Copy sent)

 

 

[cletrac1922]

What is the advantage of ED120 over ED80 which I have on a EQ5 external drive mount

Cheers

John

[Merlin66]

Similar performance, only 225% more light and better resolution.

(Edit - Ahhh I see they're talking about the 120ED triplet - colour correction will be better)

 

[John]

5 hours ago, Merlin66 said:

 

(Edit - Ahhh I see they're talking about the 120ED triplet - colour correction will be better)

 

Some of these posts are about the triplet (the Esprit) and some about the doublet (the Pro and the Equinox).

I've owned an ED80 (doublet) and currently an ED120 Pro and confirm that the ED120 Pro (doublet) is very much like a larger aperture version of the ED80 in performance terms and CA control. You might think that, with the larger aperture and the same focal ratio (F/7.5), the 120 would have lesser CA correction but thats not my experience. I understand that Synta (who make the scopes) went to considerable lengths to get the 4.7" version of the ED doublet objective "right".

The EQ5 will cope with an ED120 fine for visual observing but a heavier duty mount would be needed to image with it.

If you search around the internet there are many favourable reports on the ED120 Pro and Equinox 120 doublets and on the other side of the Atlantic, the Orion badged versions of the same scopes.

[25585]

Refractor (and eye piece) optics features make reflectors seem sooo easy by comparison!

For me as the OP, my quest is to find a refractor that will be a (smaller aperture) instrument which copes very well with no CA, allows wide-ish field, can split double stars showing different colours, good enough for push-to magnifications for the above & planets, and which has the magnitude pick-up of (say) an 8 inch SCT. A focal length allowing use of longer fl/eye relief eye pieces & which would be easy to use with barlow, diagonal & bino viewer. 

Not much to hope for really  but what are available apart from my title scopes?

[Stu]

19 minutes ago, 25585 said:

Refractor (and eye piece) optics features make reflectors seem sooo easy by comparison!

For me as the OP, my quest is to find a refractor that will be a (smaller aperture) instrument which copes very well with no CA, allows wide-ish field, can split double stars showing different colours, good enough for push-to magnifications for the above & planets, and which has the magnitude pick-up of (say) an 8 inch SCT. A focal length allowing use of longer fl/eye relief eye pieces & which would be easy to use with barlow, diagonal & bino viewer. 

Not much to hope for really  but what are available apart from my title scopes?

Isn't that the mythical scope we are all looking for?  

[25585]

7 minutes ago, Stu said:

Isn't that the mythical scope we are all looking for?  

Sooo anyway how close does the triplet or TV get to all that, or are there better?

[Moonshane]

I doubt you'll ever get a 5" scope to gain the same resolution/star magnitude as an 8" scope

That said there are other reasons people (myself included a lot of the time) use smaller refractors over bigger instruments of different design.

[Stu]

I think the challenge is the combination of a widefield scope with one capable of higher resolution and powers. For me, widefield is probably around 650mm focal length and below. The ultimate really is the Genesis in that it combines 4" aperture with a 500mm focal length with that flat field capability which a non Petzval scope would struggle with. It doesn't have the CA control of the later scopes though.

The NP127 is a great option as it does combine a great aperture in terms of being able to cut through seeing well and still having good resolution, whilst also having a flat field and a short enough focal length to give widefield performance e.g. Around 3.6 degrees with a 31mm Nagler which is enough for the Veil or NA nebulae to be framed nicely.

As I understand it, it gives lovely high power views too, but I think it is probably just a step below Tak/LZOS territory in terms of ultimate optical figure and performance. Certainly a scope I would enjoy trying and possibly owning in future. Very pricey new though!

I have no idea how compatible they are with binoviewers though.

[ollypenrice]

6 hours ago, Moonshane said:

I doubt you'll ever get a 5" scope to gain the same resolution/star magnitude as an 8" scope

That said there are other reasons people (myself included a lot of the time) use smaller refractors over bigger instruments of different design.

...all things being equal! But are they equal? Aaaarrrggghhh, the million dollar question!

Olly