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Sky-Watcher Evostar 150ED Doublet?

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#1 Dame Edna

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Posted 07 February 2019 - 12:33 PM

From what I recall, the two versions of the new Evostar 150ED should be in the hands of a substantial number of amateur astronomers worldwide by now.  Does anyone have any experiences with this telescope to relate?  Anyone compare it optically to higher-end 5" or 6" apochromats?  Seems like the last reports about the Evostar 150ED were several months ago.  Maybe the cold weather (in the Northern Hemisphere) has had something to do with the scarcity of recent reports?

 

Thank you!

 

D.E.



#2 hfjacinto

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Posted 07 February 2019 - 12:40 PM

Hi Dame,

 

I looked through the SW 150 ED DX  which is the higher end version, the basic differences are that the DX has:

 

1) A better more robust focuser

2) Losmandy Dovetail

3) And beefier better rings.

 

I was disappointed in the hardware for the base model and would not get that specific one. The inferior focuser and less than optimal rings and dovetail steered me clear of the base model.

 

Visually there was no difference in the view. I think the view will be good (with some false color on bright objects). I didn't test the SW model, but I do own a competitor model. Visually and imaging I am pretty impressed with the crop of 150 ED scopes.


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#3 skyward_eyes

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Posted 07 February 2019 - 03:12 PM

They have been making their way out to owners for a few months now. Not everyone posts of forum sites but they are out in the world. 



#4 AstroRed

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Posted 07 February 2019 - 04:02 PM

I'd be interested to hear how they match up against the 6 inch f8 achromats, that's the price range I'm shopping in. Is it worth stretching the extra for an ED150? The higher end gear is well out of my depth



#5 John Huntley

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Posted 07 February 2019 - 06:03 PM

I found the ED120 quite an improvement over the 6 inch F/8 achromats so the ED150's should be even more so.


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#6 jay.i

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Posted 07 February 2019 - 06:11 PM

I'd think about the use case for a 6" f/8 achromat. I'm guessing most people would want one for deep sky viewing, and maybe lunar if they're OK with the CA. A 6" f/8 ED on the other hand can actually be used for lunar and planetary viewing without distracting CA. The price increase to the ED and the semi-irrelevance of the color correction for a DSO-focused scope means I would only really suggest the ED if one was wanting to do planetary and lunar viewing with it. Otherwise, you're probably better off with the achromat, or even better, one of the 6" f/6 achromats going around, which is more specialized for DSO viewing, which is the only thing the f/8 achromat would be good for anyway (IMO - depends how much CA there really is and what one's tolerance is).


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#7 Bomber Bob

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Posted 07 February 2019 - 06:50 PM

Most of my observing is urban back yard planetary and traditional high F-ratio targets.  My APM 152ED is worth the expense.  But... I also have a vintage 5" F5 triplet for wide-field -- even in town, it's a blast.  Yeah, I imagine a 6" F6 achro would be as much or more fun.



#8 Jond105

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Posted 07 February 2019 - 06:57 PM

You'd have a better shot on Facebook forums where I've seen a couple now. They seem to really enjoy them.

#9 Tyson M

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Posted 07 February 2019 - 08:13 PM

If you're goal is DSO only you can get by with the 6" f8 or f5.9  easily- and love the scope.

 

As Jay said, lunar /planetary get the 150ED. 

Personally, I would go for a scope I can use on any target, simply because do not have a ton of room in the car for 2 big scopes. 

The views were still amazing in a well made 6" achro. 


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#10 AstroRed

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Posted 10 February 2019 - 08:31 AM

I found the ED120 quite an improvement over the 6 inch F/8 achromats so the ED150's should be even more so.

 

I was thinking specifically of the comparative CA levels. The ED150 is going to have a harder time controlling it than the ED120 both in terms of aperture/ focal ratio and  (at the risk of opening a can of worms!) likely glass types used


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#11 bobhen

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Posted 10 February 2019 - 09:27 AM

CA is one thing but for a lunar/planetary refractor, if CA is even reasonably controlled, and the tube mechanics/focuser are doing their jobs and NOT causing issues, it’s the optical quality of the lens that is the most important feature.

 

The optician and telescope maker R F Royce considers a high quality optic to preferably be 1/9 wave P to V or .96 Strehl or higher.

 

If you get one with that spec (does SW even make them to that quality level?) you will have a very good lunar planetary refractor and a bargain, even with some CA and mediocre mechanics. If you get one with less optical quality (even with a better focuser and rings) then the performance will be less than optimal depending on how far away from optimum the lens is figured.

 

I think that is the issue with the SW ED150 offering. The lens really has to have an excellent figure for high power planetary viewing (which is really demanding) to be considered a bargain because if it isn’t really excellent and the scope ends up being used for just deep sky viewing, then there are much less expensive 6” achromats at F8 or F5 etc. that would do just as well and deliver a wider field of view.

 

Bob


Edited by bobhen, 10 February 2019 - 03:46 PM.

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#12 Jeff B

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Posted 10 February 2019 - 11:07 AM

Good advice from Mike and Bob, especially regarding optical quality. 

 

I would speculate that my old school AP pre-ED 6" F9 triplet has overall "CA"  similar to the of the 150 ED.  Roland said about a 4-5X reduction for the same F ratio achromat and I believe it and yes it's there in the blue if I go looking for it at high magnifications on bright objects.   But the lens is very, very well corrected in the heart of the visible spectrum, the yellow/green.  And it give very sharp, high power images.

 

So I would encourage you to pick the sharpest sample you can get and let the "CA" fall where it may.  I too would very much rather have a very sharp optic that falls off a wee bit at the visual extremes and can take high power and remain sharp than an "OK" lens with no visible CA that starts getting soft at medium powers.

 

Be choosy.  You deserve it.

 

Jeff


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#13 Daniel Mounsey

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Posted 10 February 2019 - 01:21 PM

Bob,

You are wise to bring up the subject of optical figure. It's so true.


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#14 SeattleScott

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Posted 10 February 2019 - 01:32 PM

I am with Tyson. For DSO it doesn’t really matter. Planets benefit from the Apo. If you are primarily a DSO observer, do you want to pay 4x as much to see one or two targets an evening better? On the other hand, do you want to get a scope that doesn’t perform well on the most showpiece objects? So it could go either way. It isn’t like the moon and planets aren’t worth looking at in an achro. Just not as impressive as an Apo.

Scott

#15 jay.i

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Posted 10 February 2019 - 03:45 PM

I wouldn't expect most 6" f/8 achros to be any better than 1/4 wave p-v, with anomalies up to 1/8 wave I'm sure. Same for the Evostar 150ED. Jim Barnett estimated his was around 1/4 wave. If both scopes are probably gonna fare no better than 1/4 to 1/6 wave (I'll be generous), the scope with less CA is the better choice for planetary and lunar viewing. I agree, though, that a good figure is significantly more important than good CA correction, but ideally you get both a good figure and good CA correction. And that's where prices really start to go up.


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#16 Daniel Mounsey

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Posted 10 February 2019 - 04:30 PM

I wouldn't expect most 6" f/8 achros to be any better than 1/4 wave p-v, with anomalies up to 1/8 wave I'm sure. Same for the Evostar 150ED. Jim Barnett estimated his was around 1/4 wave. If both scopes are probably gonna fare no better than 1/4 to 1/6 wave (I'll be generous), 

 

What does a 1/4 wave optic look like compared to 1/6 wave in focus? Tell me what I should expect to see. 


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#17 jay.i

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Posted 10 February 2019 - 04:52 PM

What does a 1/4 wave optic look like compared to 1/6 wave in focus? Tell me what I should expect to see. 

I will first say that an improvement in wavefront is an improvement in wavefront, period. 1/6 is 33% less than 1/4 (0.16 / 0.25). Whether one would actually say "the SA is 33% lower" or not is up for debate - the SA p-v variance is 33% lower but you can't generalize it beyond that. 

 

With only a 33% difference, I would not expect the in-focus image variation to be obvious. By obvious, I truly mean obvious. It will not jump out at you. I don't think even 1/4 wave to 1/8 wave would be an immediately obvious difference under most conditions.

 

What is SA? Spherical aberration prevents all wavelengths coming to a precise focus, by an amount measured in the number waves of light (typically below 1 wave length), due to the fast that spherical surfaces lead the center of the field to focus at a longer focal length than the edges. Because the image is not brought to a very precise focus, certain details can be essentially out of focus. Variation of SA by wavelength is called spherochromatism; prioritized correction of SA can leave certain wavelengths very precise, while others are less precise; red/deep red often suffer in doublet designs in favor of green, yellow, and blue, wavelengths to which the human eye is more sensitive. This definition of SA is important because it helps explain why I expect to see the things I do (as you'll see below).

 

We have to talk about seeing conditions when talking about observable differences in wavefront correction because aberrations add up. If seeing is poor, a 1/8 wave optic will display a more detailed image than a 1/4 wave optic, almost guaranteed. Of course, if seeing is poor, I don't think the owners of either scope would spend enough time outside to say "gee, if my optical figure was better, I bet I'd be seeing more detail".

 

Let us assume decent seeing, say, Pickering 7. This is probably the best seeing most people in the US get on average. Mine is maybe around Pickering 5 as I live under the jet stream. Pickering 7 is good enough to allow for some really nice patches of steadiness, but not so good that almost any optic better than 1/2 wave will look great. A lot of optics will look great if seeing is perfect. Seeing is almost never perfect for most people so it makes sense to use a more common (but good) approximation of seeing conditions for this question.

 

Let us also use Jupiter as an example of a very finely detailed object that stands to benefit from SA improvements.

 

With the 1/6 wave optic, I would expect to see slightly finer detail. For example, on Jupiter, I would expect to see slightly more definition in the belts and the swirls between them. I would expect to see sharper definition of textures especially in low-contrast areas like the tan/beige belts. Better edge definition (which is sort of analogous to contrast) is what I would expect to see. This makes fine details stick out better.

 

With the 1/4 wave optic, after having looked through the 1/6 wave optic, I would expect to see slightly less definition in the Great Red Spot, and in the swirls between belts. I would expect to see what could be described as a smudging effect in the belts, where I may have seen actual texture and hinting at deeper detail and intricate interwoven strings of clouds of slightly varying colors.

 

I have not spent enough time with Saturn under good seeing to say, but I would expect the same principles to apply. Sharper definition within the rings, clearer delineation of colors within the rings and on the planet itself, maybe even some "micro separation" between the rings (like Encke's division, which IIRC is not possible to see with only 6" of aperture) if seeing and magnification are good enough for that.

 

As I said, the differences will likely not be any synonym of obvious, but I am confident the differences would be visible if both scopes had enough time for thermal acclimation and the observer(s) used a single diagonal/eyepiece combination at the same magnification & exit pupil to swap between scopes. I would generally recommend at least 2 people do a comparison like this to challenge confirmation bias and to account for subjective differences due to visual acuity.

 

Dan, I think you know what you should expect to see, but I appreciate the challenge. As I said, an improvement in wavefront is an improvement, period. With a higher quality instrument, the observer can be more sure that if they are not seeing something, it is either due to the sky, or them, and not their instruments; because of this, along with cumulative aberrations, I would always recommend people seek instruments with SA p-v lower than 1/4 wave if at all possible, with 1/4 wave being the bare minimum (maximum?) that I personally would accept for a scope of any size. We have today the tools to make instruments to this specification in a cost-effective manner; there is no reason to accept anything worse.


Edited by jay.i, 10 February 2019 - 05:03 PM.

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#18 jrbarnett

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Posted 10 February 2019 - 06:25 PM

CA is one thing but for a lunar/planetary refractor, if CA is even reasonably controlled, and the tube mechanics/focuser are doing their jobs and NOT causing issues, it’s the optical quality of the lens that is the most important feature.

 

The optician and telescope maker R F Royce considers a high quality optic to preferably be 1/9 wave P to V or .96 Strehl or higher.

 

If you get one with that spec (does SW even make them to that quality level?) you will have a very good lunar planetary refractor and a bargain, even with some CA and mediocre mechanics. If you get one with less optical quality (even with a better focuser and rings) then the performance will be less than optimal depending on how far away from optimum the lens is figured.

 

I think that is the issue with the SW ED150 offering. The lens really has to have an excellent figure for high power planetary viewing (which is really demanding) to be considered a bargain because if it isn’t really excellent and the scope ends up being used for just deep sky viewing, then there are much less expensive 6” achromats at F8 or F5 etc. that would do just as well and deliver a wider field of view.

 

Bob

I dunno about that.

 

Even a middling figured 6" f/8 ED doublet is going to escape the nastiness of central obstruction as well as the nastiness of achromatic false color.  CA is ugly whenever present and visible, including in DSO viewing with a Magnitue 4-ish or brighter star in the FOV.  It's not all that uncommon to have a a bright star or two in many bright DSO fields of view (i.e., DSOs ideal for modest 6" aperture).

 

The beauty of the Skywatcher 150ED to me is actually the base model, not the "Deluxe" model.  I'd never bother imaging with such a scope; I'd rather image with something smaller, similarly priced, faster, and much better color corrected.  But I'd rather have a 1/4 wave 6" f/8 ED doublet than a 1/8 wave 6" f/8 achromat for DSOs suitable for such instruments any day.

 

Don't forget that in the rest of the world the base SW 150ED is a sub-$2000 telescope.  That's 3" Asian triplet price territory.  And they aren't always just 1/4 wave.  Some are likely going to be quite good.  Especially as production ramps up.  Synta tends to invest in QA/QC throughout the lifespan of a model or line.

 

Best,

 

Jim


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#19 John Huntley

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Posted 10 February 2019 - 06:28 PM

I was thinking specifically of the comparative CA levels. The ED150 is going to have a harder time controlling it than the ED120 both in terms of aperture/ focal ratio and  (at the risk of opening a can of worms!) likely glass types used

I actually think that the ED150 will be rather good at CA control. While the 2 that I have used had collimation issues, the CA levels seemed very low. I'm looking forward to trying another ED150 soon, one where the objective lens is in good shape, hopefully smile.gif

 

I'll be able to directly compare it with my ED120 and see how Synta have done with whatever glass they decided to use in the ED150.



#20 Illinois

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Posted 11 February 2019 - 11:31 AM

I was thinking specifically of the comparative CA levels. The ED150 is going to have a harder time controlling it than the ED120 both in terms of aperture/ focal ratio and  (at the risk of opening a can of worms!) likely glass types used


I found out about SW 150ED come out and I was think to buy it because I heard that SW120 is so good until no one know what 150ED glass, high power is soft and packing problem so I step back for now!
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#21 SeattleScott

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Posted 11 February 2019 - 12:11 PM

They are completely different scopes. You can try and make generalizations based on the brand reputation but the design and materials are different. Also the 150 is new whereas the 120 is a very mature product.

Scott

#22 SeattleScott

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Posted 11 February 2019 - 12:24 PM

The optical quality versus CA debate is a valid one, at least in certain circumstances. An excellent figure may allow one to see details that a middling ED might not show. Recently someone posted about a premium 80mm F11 besting a Chinese ED80 on planets, despite showing more CA. But on the other hand I never bothered requesting the optics test report for my AR102 because, well, what does it matter? At F6.5 CA will be the limiting factor. So there is a point where achros can control CA well enough to compete and prevail against a mass produced Apo, like an ultra premium 6” triplet achro or a Vixen 80mm F11. Someday I would like to pit my Vixen 4” F9.5 against a Chinese Apo. But having a very good 6” F8 achro, I wouldn’t expect it to show more planetary details than a 1/4th wave 6” ED. 150x is quite sharp albeit a bit colorful on bright objects but you lose some crispness going higher. I would like to think a 1/4th wave ED could deliver crisp views at 200-300x. I will have to experiment with CA filters in the coming year to see how much difference they make. At least with an achro you can sort of filter out the CA. There isn’t a SA or astigmatism filter for Chinese Apos.

Scott

Edited by SeattleScott, 11 February 2019 - 12:27 PM.

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#23 25585

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Posted 11 February 2019 - 03:15 PM

I dunno about that.

 

Even a middling figured 6" f/8 ED doublet is going to escape the nastiness of central obstruction as well as the nastiness of achromatic false color.  CA is ugly whenever present and visible, including in DSO viewing with a Magnitue 4-ish or brighter star in the FOV.  It's not all that uncommon to have a a bright star or two in many bright DSO fields of view (i.e., DSOs ideal for modest 6" aperture).

 

The beauty of the Skywatcher 150ED to me is actually the base model, not the "Deluxe" model.  I'd never bother imaging with such a scope; I'd rather image with something smaller, similarly priced, faster, and much better color corrected.  But I'd rather have a 1/4 wave 6" f/8 ED doublet than a 1/8 wave 6" f/8 achromat for DSOs suitable for such instruments any day.

 

Don't forget that in the rest of the world the base SW 150ED is a sub-$2000 telescope.  That's 3" Asian triplet price territory.  And they aren't always just 1/4 wave.  Some are likely going to be quite good.  Especially as production ramps up.  Synta tends to invest in QA/QC throughout the lifespan of a model or line.

 

Best,

 

Jim

The DX version has a better focuser, beefier tube rings, and a Losmandy dovetail bar. The budget focuser may be OK to start, but thin rings and Vixen dovetail are for any 6 inch refractor, IMO inadequate. Why not sell just the OTA, for less, and let the new or prospective owner choose mounting hardware separately? 



#24 CHASLX200

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Posted 11 February 2019 - 06:35 PM

The DX version has a better focuser, beefier tube rings, and a Losmandy dovetail bar. The budget focuser may be OK to start, but thin rings and Vixen dovetail are for any 6 inch refractor, IMO inadequate. Why not sell just the OTA, for less, and let the new or prospective owner choose mounting hardware separately? 

Thin rings and a Vixen dovetail seemed to work fine with a heavy CR6 i had.


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#25 John Huntley

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Posted 11 February 2019 - 09:41 PM

The DX version has a better focuser, beefier tube rings, and a Losmandy dovetail bar. The budget focuser may be OK to start, but thin rings and Vixen dovetail are for any 6 inch refractor, IMO inadequate. Why not sell just the OTA, for less, and let the new or prospective owner choose mounting hardware separately? 

I've actually used a couple of Skywatcher ED150's in their basic trim (as I think you know) and they seemed fine to me in terms of practicality. The tube rings, dovetail bar and focuser did their job pretty well. Don't judge them as inadequate until you have personally tried them I suggest.


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