SW Evostar 120ED vs Startravel 150?

[superyoche]

Hi,

I have been owning for nearly a year the SW Evostar 120ED, a great all-around scope and portable. I enjoyed some nice views of Jupiter, the moon and some DSOs

I'm having my attention on slightly bigger aperture and still portable refractor these days such as the SW Startravel 150 F/5. I know that this kind of scope is more specific for DSOs observing, and I know that the major issue is the important CA due to the big aperture and short focal length.

Nevertheless, I am still wondering: could such a scope, with a Baader Semi Apo filter or UHC filter for DSOs and maybe a Baader Contrast Booster for planets (to kill all or almost all CA), outperform a 120ED scope in terms of observable details?

Thanks!

[Ricochet]

Not a chance. There is good reason that the 120ED is a defacto standard. 

[dobbie]

I've owned both scopes and if you want detail the 120ed beats it by a long margin. if your wanting more aperture for dso why not try a 150 newt . 

[spaceboy]

I owned and absolutely adored a 6" EVO f/8 for many months. Then I came across an ED120 and after only using it twice I sold the EVO. There is nothing quite like owning a large refractor but you'd be surprised how much good glass can make a difference even in a smaller scope. If you want to up the aperture and see deeper then your best bet is a skyliner 200P. No CA, still manageable even for 8" aperture and a tried and trusted mount. The slower f/6 200p is more forgiving of eyepieces and holds collimation well. Would complement the ED120 and cover most of your needs.

[Paul73]

Good advice.

If you are used to views through the 120ED, you will be easily annoyed by defects. The longer 8" Dob would make a lovely pair

Paul

[paulastro]

Agree strongly with previous comments, it would be a serious error buying a 150 f5 shorty when you already own a 120ED, you'll look though the f5 once and probably never use it again.  The idea of an 8inch f6 dob (or just the tube assembly if you have a suitable mount) as being complimentary is a sound one.

I have a 6inch f8 newt tube assembly, and it's a zillion times better than a 150mm shorty also - in my humble opinion

 

 

[Alkaid]

14 hours ago, superyoche said:

 

could such a scope, with a Baader Semi Apo filter or UHC filter for DSOs and maybe a Baader Contrast Booster for planets (to kill all or almost all CA), outperform a 120ED scope in terms of observable details?

 

No. What you need to aim for is the minimum amount of optical surfaces that are in between your eye and the target.   Every extra lens or mirror that you put in the way, you degrade the image slightly.  The larger aperture of the 150 plus a load of extra lenses to help it would not offset the optical quality of the ED120.

[mikeDnight]

The Evostar ST150 could never match the 120ED for CA even if it had an apo filter. Filters always detract from the purity of the image, and from experience I'd rather put up with the 150's CA than degrade the view. Having used both scopes extensively, I'd say the 150 is well worth having as an RFT and would show a very noticeable advantage over the 120ED on dso's, providing you get a good one. They vary greatly in quality! The CA is of no real concern when studying star fields, nebulae and galaxies. If however you decided to go for a ST150, whatever you do, don't sell your ED. The ST150 will never compete with it on the moon and planets.

[Stu]

I agree with all the comments made above, the 120ED takes some beating. If I were looking for a larger aperture frac for deep sky work I would try one of the 152mm f5.9 TS or Altair scopes, CA is much better controlled and SA much better too. Quite a different budget level to an ST150 though!

8" Newt makes lot of sense to complement the 120ED though as said.

[ollypenrice]

More agreement from me. ED120 every time.

Olly

[rl]

120ED it is....

If you must change you can get a 12" dob secondhand for the price of a 120ED which will show a lot more at the cost of bulk and collimation hassle. A halfway decent newt will beat a short f/l achro.

RL

[Special K]

Id be very happy with the 120ED personally because it seems to strike a great compromise between size, cost, aperture, and quality. 

[superyoche]

Thanks all for your advices!

Yes the 120ED is really a great comprise in terms of aperture, size, cost and quality. I was just wondering if I could replace it for something slightly bigger but not too bulky with a similar visual quality. An 150ED looks amazing but is nearly 4 times the price of a 120ED.. I also heard about the Chromacor lens that converts an achro into apo, but doesn't seem to exist anymore.. Too bad..

Maybe I'll take a big dob one day when I have a bigger place to live. Or I may order a Newt 8" like the SW Explorer 200P-DS additionally to my 120ED as I have a HEQ5 mount.

[Merlin66]

A good UV-IR filter will take most of the UV "blue bloat" away......

[ronin]

The 120ED will outperform the 150.

For all I like and use refractors I would not touch an f/5 achro. At 150mm diameter expect aberrations and no "apo" filter makes and achro into an apo or even close. At best they reduce the effective diameter and so your 150 becomes a 120 or even less. Also they remove the purple/blue simple filtering it out so leaving a colour balance that is towards the yellow.

[spaceboy]

8 hours ago, superyoche said:

Thanks all for your advices!

Maybe I'll take a big dob one day when I have a bigger place to live. Or I may order a Newt 8" like the SW Explorer 200P-DS additionally to my 120ED as I have a HEQ5 mount.

I don't think you'd be disappointed. I have the ED120 and 200P f/5 and feel they complement each other well. I have a giro ercole so if I choose can use both at the same time. If all your used to are refractor views it is worth noting that the edges in an f/5 may be a tad distracting due to coma. You could always get a coma corrector but this is why I originally recommended the slower f/6 dobsonian. It will still show coma but not quite so predominantly. Getting the dob also gives you the option of using both scopes at the same time and if you wanted you could just get ota rings for the newt and use it on the HEQ5. Obviously if your short on space it is easier to hide an ota in the back of a closet than it is a whole dobsonian.

[paulastro]

On ‎12‎/‎09‎/‎2017 at 20:02, Stu said:

 If I were looking for a larger aperture frac for deep sky work I would try one of the 152mm f5.9 TS or Altair scopes, CA is much better controlled and SA much better too. Quite a different budget level to an ST150 though

 

I totally agree with this Stu.  I had a 152mm f5.9 badged as an Ostara (I think this may have been the first version available in the UK) and it made a fabulous rich field /deep sky  telescope.  The Ostara version I had came with a lovely 3 or 3.5 inch focuser and a tank-like hard case.  This scope was outstandingly well built, though this did make it around the 20 lbs weight category.  It was surprisingly good on the Moon and planets too, much less CA than any f5 I've seen of this aperture.  I did like this scope, and do miss it sometimes - good old 'Spud'  (don't ask! )

[John]

I've owned a few Chromacor's and used them with a variety of 6" F/8 chinese achromats. When the Chromacor is well matched with the achromatic objective the resulting scope is very close to a 6" ED doublet in performance but Chromacor's are very hard to source, expensive, fussy to match and install and don't work so well with wide field eypeices.

I'm another strong advocate of the ED120

I'd like to try one of the above mentioned 152mm F/5.9 achromats though. Most of the reports I've read indicate CA correction levels at least as good as an F/8 6" (non-chromacorred) and better SA correction as well.

 

[Ben the Ignorant]

If you want a larger refractor APM makes a 140mm f/7 doublet with FPL-53 glass (same as your 120) that's a real semi-apo scope. The 150mm (or 152mm?) f/8 FPL-51 doublet is just an improved achromat, and only for the dark-adapted eye. The 140 costs twice the price of the 120, though, but less than the 6-incher with inferior glass.

The improvement in tightness of focus is sure to offset the very small reduction of diameter. 

[John]

23 minutes ago, Ben the Ignorant said:

If you want a larger refractor APM makes a 140mm f/7 doublet with FPL-53 glass (same as your 120) that's a real semi-apo scope. The 150mm (or 152mm?) f/8 FPL-51 doublet is just an improved achromat, and only for the dark-adapted eye. The 140 costs twice the price of the 120, though, but less than the 6-incher with inferior glass...

Are your comments based on actual experience with these scopes ?

I have an FPL-51 doublet which at F/6.5 performs superbly - far, far better than an achromat of the same specification would.

 

[Ben the Ignorant]

http://r2.astro-foren.com/index.php/de/10-beitraege/02-ed-optiken-halb-apos-und-frauenhofer-systeme/719-b044a-apm-dublet-ed-152-1-200-in-der-nacht-ein-apo

The 152/1200 is diffraction-limited only between 495nm and 610nm (0.80 Strehl), or 505nm and 600nm if you prefer 0.90 Strehl as your personal norm. Another way to look at it is expressed in the black screen at the end of the article: really apo in blue (0.07 coeff), semi-apo in yellow (1.63 coeff), and just achromatic in red by a broad margin (5.24 coeff). The overal coeff is 2.65, above the 2.0 norm for a semi-apo.

The chromatic spread is 356µ, in the range of good achromats but not in the range of semi-apos and apos (my little triplet has 23µ chromatic spread). However it was smartly designed with night vision in mind, so the numbers are much improved for that narrower strip of the spectrum: 0.85 coeff, under the 1.0 norm for an apo. It is a very good performer but only for those who know and accept its limitations, otherwise they have to double the expense and get a triplet.

 https://www.cloudynights.com/topic/514293-apm-140mm-f7-doublet-test-data/

Not having been tested by Rohr makes the comparo less detailed, but FPL-53 instead of FPL-51. Smaller diameter but f/7 instead of f/7.9, so these differences cancel each other out. Shorter and lighter tube. The switch to 53 glass alone makes a big improvement in refractors, so if I was after one of these (I am not), I would pick the 140.

[John]

So not your own personal experience then ?

 

[spaceboy]

This is interesting. Is the ES127 FPL51 or similar spec as I have seen reviews suggest this also shows false colour which I found odd as it's a triplet and only has 7mm over the ED120 which tend to only show fringing in defocused stars.

 

[spaceboy]

Not terrible false colour in the ES ED127 I might add !!!!!!!!! but fringing none the less.

[TSRobot]

Do folk really need ed apo to enjoy the heavens?