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SW 120ED - Expecting too much?

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#26 25585

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Posted 04 January 2021 - 09:37 AM

120 Equinox owner. I do not expect perfection from a Chinese doublet, but "Gomez" performs far better than its price suggested.

 

Compared to my TSA-120 triplet, yes there is some CA, but it depends on brightness mostly. Gomez shows good colour and contrast and light transmission. Great value, you can get more perfection, at a cost.  


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#27 Thomas A Davis

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Posted 04 January 2021 - 02:07 PM

if you are seeing red on one side of the planet and blue on the other, that is mostly an atmospheric effect, at least assuming Mars is near the center of the field of view and there is nothing wrong with the eyepiece. Chromatic aberration in the telescope--longitudinal chromatic aberration--will typically show as a colored halo with the same color all the way around the planet or star. 

 

Try rotating the eyepiece in the diagonal to see if the chromatic aberration moves. I suspect you will find it doesn't. Also, try looking at a bright star near zenith to check for chromatic aberration. 

 

While I suspect you are mostly seeing atmospheric effects, I'm not super confident. the effects you are describing are most common when the planet is close to the horizon, and for mid-latitude northern hemisphere observers Mars is pretty well placed in the evening skies these days. How high up was Mars when you were observing?

No on Mars the fringing is real, due to the brightness at opposition.  As far as FPL53 doublets go, the correction is excellent on the ED120.  Mars was quite high in the sky when I saw this effect, that was more of a red haze than a deep red fringe.  It easily processes out in the images.  When used for long exposure deep sky, red stars will have a halo on stretched images, while bright blue stars will not.  I used to own a Vixen 115ED that also was an FPL53, and it had more of an issue on the red end of the spectrum.  What is going on here is that the designer of the lens can choose which end of the spectrum the color will fall off out of focus.  The 120ED keeps the blue in, but allows a subtle fall-off in the red end.  The Vixen went even further in that direction.  Color correction is not a perfect affair on a doublet, even with FPL53 or fluorite in the objective.  Trade-offs are necessary to get what appears to be excellent color correction to the user.  Most people are sensitive to blue fringing, so tweaking the design in this way provides a more pleasing view to most buyers.  

 

For a doublet, the Synta made 120ED provides excellent trade-offs in color correction, but it is not perfect.  I remember Thomas Back telling me that his AP130 EDT F/8.35 showed some violet to his eye.  I owned that scope, and can tell you it was the best color corrected refractor I've ever seen.  I could see none.  Some people are very sensitive to violet, so manufacturers may favor the blue and violet end by letting the red fall off a small amount.  In the case of the 120ED, the effect is small, but discernable to me on a target as bright as an opposition Mars.  It is clearly discernable in long exposure deep sky images.


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#28 CHASLX200

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Posted 04 January 2021 - 07:31 PM

My last SW120ED was better than my first.  No problem using 450x on the moon.


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#29 russell23

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Posted 04 January 2021 - 08:05 PM

My last SW120ED was better than my first.  No problem using 450x on the moon.

Mine will do the same when seeing allows.



#30 CHASLX200

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Posted 04 January 2021 - 08:08 PM

Mine will do the same when seeing allows.

I should have kept my last 120ED and never got the 6" ED. Setup was 5 times harder with the 6" ED vs the 120ED.


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#31 Reid W

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Posted 04 January 2021 - 08:42 PM

I had asked Stan (op) about the diagonal. 

 

In my experiences, a miss-collimated, or poorly finished diagonal can have negative consequences. Even even a perfectly fine prism can be a poor choice for some refractors.


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#32 teashea

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Posted 04 January 2021 - 08:59 PM

It seems that you are expecting too much, given those viewing conditions.  Those viewing conditions will screw up any telescope.  Do you have any chance to go somewhere where the viewing is better?

 

Make sure that your expectations are not being formed by those fabulous astro photos that we see here on CN and other places.  Remember that seeing something through an eyepiece cannot begin to compare with good astro photography.

 

Take a deep breath.  That scope has a fine reputation.

 

Tom


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#33 Jeff B

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Posted 04 January 2021 - 10:42 PM

Brisguy, any news?  I hope your scope is fine.

 

Jeff



#34 Thomas A Davis

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Posted 05 January 2021 - 12:30 AM

It seems that you are expecting too much, given those viewing conditions.  Those viewing conditions will screw up any telescope.  Do you have any chance to go somewhere where the viewing is better?

 

Make sure that your expectations are not being formed by those fabulous astro photos that we see here on CN and other places.  Remember that seeing something through an eyepiece cannot begin to compare with good astro photography.

 

Take a deep breath.  That scope has a fine reputation.

 

Tom

This is a common problem.  Expecting too much from a scope on the night you first observe.  If it is a bad night, no scope, even a perfect one, will deliver a good image.  I bought a C102F Celestron that I later found out was perfectly corrected.   On the night I used it, Jupiter looked as if it was underwater.  Horrible view, under horrible seeing.  I took it back to the dealer as defective.  Later , that same scope displayed an incredible view on the planet under good seeing at 500X, well beyond Dawes limit. Unfortunately, the dealer then owned it, and I could not get it back,  I learned an important lesson in that experience.  If the seeing is questionable, try again on another night where it is better.  Then, it it is still an issue, take it back to the dealer.  Getting back to the 120ED, I find the Skywatcher to be at least as good on spherical and color correction.  The last C102F I looked through had obvious blue fringing in focus to my eye.  The improvements in optical fabrication machines  today, make the current scopes capable of excellent performance compared to the scopes of decades ago. nostalgia aside.  The lesson is, wait until the seeing is good enough to tell you the optics are bad before declaring them defective.  I'm sure I would have gotten some great views through that C102F if I had  done so.

 

I've gotten some great views through my Skywatcher 120ED.

 

Tom


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#35 skyward_eyes

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Posted 05 January 2021 - 06:01 AM

Getting to know a scope takes time. You need to spend a handful of nights with a telescope before you can really make a definitive conclusion about it.

There are so many variables that will affect the outcome of the view in a scope. This time of year we get a lot of new scope owners with expectations that were not met. Upon speaking with them you find out the level they were looking for was beyond what was reasonable.

For this post I would really recommend taking the scope out on multiple nights. I know there this big race for people to check out equipment within a return window. But you’re going to need multiple nights and an understanding of the site and observing targets to make sure you’re giving it a fair go.

Observing Mars, Jupiter and Saturn is not an ideal situation right now as none of them are in a good position at the moment. This has nothing to do with a scope and likely anything you use will show similar results.

So take the scope back out a few more nights. Really let it cool down and adapt to the environment. Pick some key targets like the moon and some of the brighter deep sky targets. If you still have issues contact us directly.

Edited by skyward_eyes, 05 January 2021 - 06:02 AM.

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#36 CHASLX200

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Posted 05 January 2021 - 06:31 AM

Seeing this time of year is bad for most and even down my way in FL it has been bad.


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#37 25585

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Posted 05 January 2021 - 09:24 AM

Has there ever been an optical shootout between the ED120 & Esprit 120? That would be interesting to read!



#38 Jeff B

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Posted 05 January 2021 - 02:14 PM

I had mine out last night to see how well it mated up with a 35 year old Vixen SP mount as a system (very well actually) and the skies were actually rather calm.  I had it up to ~200X with my Denk II viewer and the image of Mars, though small, was first rate and very sharp.  I specifically looked for AD but did not really see anything overt (though there is always speculation as to what the prisms in the viewer are doing to the light cone).  I had to focus carefully but there was no ambiguity when focus was found.  An excellent view.  A quick star test showed no visible coma or astigmatism.

 

My older, "gold tube", unit does indeed have excellent and smooth optics.  I just completed making another DPAC Ronchi screen and LED holder with a smaller diameter LED (which lets me get the centers of the source and return beams closer together) and decided to shoot new DPAC images of my sample 120ED while I was messing with it.   Attached are the results for inside, outside and at focus with white, blue, green and red colors, left to right in each image.

 

This is a very good lens, with an excellent edge, functionally a little overall under-corrected in green, with best correction falling somewhere between the green and blue (blue lines are almost straight). You can see mild spherochromatism at work by looking at how the lines bend in opposite directions between the red and blue lines in each image set, except, of course, the at focus images.  Speaking of the at focus image set, you can clearly see that, with this sample lens, the red and green focus positions fall very close to each other while the blue focus position is slightly removed from that of the red and green.  You can also see that in the inside/outside of focus images but not as dramatically (visually, the blue focus "error" is not "dramatic" at all, being invisible to me except on bright stars and Venus at high power).  

 

So brisguy, your lens has a fine pedigree and should perform very well indeed if it was properly made.

 

Jeff

Attached Thumbnails

  • SW120ED, Redo Montage, Inside Focus.jpg
  • SW120ED, Redo Montage, Outside Focus.jpg
  • SW120ED, Redo Montage, At Focus.jpg

Edited by Jeff B, 05 January 2021 - 02:22 PM.

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#39 brisguy

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Posted 05 January 2021 - 02:43 PM

It looks like many missed my follow-up post on January 2nd, so I will reiterate: I no longer think there is a problem with my 'scope.

 

I have read up on atmospheric dispersion and even found a filter that is supposed to correct it. Watching the setup video, I can confirm that this is the type of discoloration I was seeing.  Also, I should mention that the last time I tried viewing Mars, there could have been a high haze that night which could have caused the effect, even though Mars was nearly straight overhead. I live in the SF bay area (about 38 deg. long.) so, near the coast, and there is often some marine layer here. That is why I mentioned it is hard to tell when seeing will be good. To the naked eye, the sky looks clear, but the results I get from the 'scope vary wildly. 

 

Also to reiterate, I was basing my expectations on a review I read where the reviewer was talking about seeing canals and ice caps on mars. I've never been able to see any detail over multiple nights over a period of months. Again, only using the stock EPs which provide 180X max, but I would think that is what the reviewer used as well.

 

Unfortunately, it has been cloudy since I my original post and will continue that way for what looks like another week or so, so I won't be able to report on the star test, but as I said, having read about the effects of AD, I am sure that is what I mistook for CA. Thanks to all for your feedback!


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#40 chaoscosmos

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Posted 05 January 2021 - 08:07 PM

Difference between this Skywatcher and the discontinued Orion 120 EON is what? Build quality and aesthetics of the scope?



#41 Kutno

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Posted 05 January 2021 - 10:05 PM

I should have kept my last 120ED and never got the 6" ED. Setup was 5 times harder with the 6" ED vs the 120ED.

 

Due to unwieldiness  -  tube and/or mount  -  or some other issue(s)?



#42 Jeff B

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Posted 05 January 2021 - 10:11 PM

Difference between this Skywatcher and the discontinued Orion 120 EON is what? Build quality and aesthetics of the scope?

That seems to be basically the case.  However, the build of my early SW sample, while a bit spartan compared to an Eon, was of high quality.  The collimations of both the objective and the focuser were both dead on and, when adjusted, the focuser was quite smooth.  I did however, replace the stock focuser for a nice ML 2.5" jobbie, which was a very nice upgrade IMO as I use bino-viewers.

 

Jeff

Attached Thumbnails

  • 120ED with Moonlite 2.5 focuser B.jpg

Edited by Jeff B, 05 January 2021 - 10:17 PM.

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#43 Thomas A Davis

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Posted 05 January 2021 - 11:09 PM

It looks like many missed my follow-up post on January 2nd, so I will reiterate: I no longer think there is a problem with my 'scope.

 

I have read up on atmospheric dispersion and even found a filter that is supposed to correct it. Watching the setup video, I can confirm that this is the type of discoloration I was seeing.  Also, I should mention that the last time I tried viewing Mars, there could have been a high haze that night which could have caused the effect, even though Mars was nearly straight overhead. I live in the SF bay area (about 38 deg. long.) so, near the coast, and there is often some marine layer here. That is why I mentioned it is hard to tell when seeing will be good. To the naked eye, the sky looks clear, but the results I get from the 'scope vary wildly. 

 

Also to reiterate, I was basing my expectations on a review I read where the reviewer was talking about seeing canals and ice caps on mars. I've never been able to see any detail over multiple nights over a period of months. Again, only using the stock EPs which provide 180X max, but I would think that is what the reviewer used as well.

 

Unfortunately, it has been cloudy since I my original post and will continue that way for what looks like another week or so, so I won't be able to report on the star test, but as I said, having read about the effects of AD, I am sure that is what I mistook for CA. Thanks to all for your feedback!

I tried to find an image that came close to matching a high power view of Mars in my 120ED under good seeing.  This one fairly closely matches the video I took with a ZWO ZSI224MC camera and a Televue 5X Powermate it was derived from.  The visual view at 375X with a 6mm Delos and 2.5X TV Powermate was really close to this.  The contrast is a bit higher, but the polar cap, surface detail and blue limb atmospheric haze were all seen this well.  I saw no canals, but neither have the Mars orbiters,  Under the right conditions, this is a really fine instrument.

 

Tom

Attached Thumbnails

  • Mars1104.jpg

Edited by Thomas A Davis, 05 January 2021 - 11:14 PM.

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#44 25585

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Posted 06 January 2021 - 04:10 AM

Difference between this Skywatcher and the discontinued Orion 120 EON is what? Build quality and aesthetics of the scope?

S-W Equinox was their deluxe version to rival the Orion. 



#45 sg6

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Posted 06 January 2021 - 05:59 AM

Think expectations are a bit high, Mars is always something people point at and almost always the result doesn't match the expectations. And many times the expectations are of an image from something like a 925 SCT and 2.5x powermate with the video processed for an hour or two, and likely only the single best stacked video (of 5 or more videos obtained) is the posted one.

 

If you are looking at any picture, on the internet or a book, then forget it. By definition that has to be an image and almost 100% certain a stacked and processed image. You do not and never will get the same visual result.

 

I can look at a planets and my thoughts get about as far as: That is Mars/Jupiter/Saturn looks nice, now what else is there.

 

Planets hold little interest to me other then maybe something to have a quick look at. Sort of: That is Saturn done until next year.

 

Does in a way make my life easy. No even sure I have bothered with scope and a planet this past year.



#46 CHASLX200

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Posted 06 January 2021 - 06:35 AM

Due to unwieldiness  -  tube and/or mount  -  or some other issue(s)?

The SW120ED could be used on a much smaller mount. 2 trip scope to set up.  I could carry the whole thing really. The SW150ED was mounted on a AP800 and that was like a 6 or 7 trip scope to set up.  My house is not set up to roll out a big scope all set up.

 

OTA was easy to handle, but the mount and pier was a pain to set up for fast looks.


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#47 Thomas A Davis

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Posted 06 January 2021 - 09:16 AM

The SW120ED could be used on a much smaller mount. 2 trip scope to set up.  I could carry the whole thing really. The SW150ED was mounted on a AP800 and that was like a 6 or 7 trip scope to set up.  My house is not set up to roll out a big scope all set up.

 

OTA was easy to handle, but the mount and pier was a pain to set up for fast looks.

This is one of the reasons I really like the 120ED.  I have it mounted on an AVX mount and carry it all out to my observing spot from the garage as one unit.  The mount works well enough with the ZWO camera as an autoguider with a 50mm finder for imaging.  Simple, easy to use setup that gets a lot of use.

 

Tom


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#48 Jon Isaacs

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Posted 06 January 2021 - 09:42 AM

This is one of the reasons I really like the 120ED.  I have it mounted on an AVX mount and carry it all out to my observing spot from the garage as one unit.  The mount works well enough with the ZWO camera as an autoguider with a 50mm finder for imaging.  Simple, easy to use setup that gets a lot of use.

 

Tom

 

:waytogo:

 

When I was looking for a 5 inch class refractor as a planetary/double star grab and go scope to provide more capability than my NP-101, I looked at full 5 inchers around F/7 and they were just too big to really be grab and go.  

 

The 120mm F/7.5 FPL-53 doublets seemed to be the right balance between aperture and size.

 

Jon


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#49 25585

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Posted 06 January 2021 - 09:49 AM

waytogo.gif

 

When I was looking for a 5 inch class refractor as a planetary/double star grab and go scope to provide more capability than my NP-101, I looked at full 5 inchers around F/7 and they were just too big to really be grab and go.  

 

The 120mm F/7.5 FPL-53 doublets seemed to be the right balance between aperture and size.

 

Jon

I have come to the same conclusion, more or less. An APM 140mm doublet may be a future upsize, but not for awhile.



#50 drd715

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Posted 06 January 2021 - 10:16 AM

I have come to the same conclusion, more or less. An APM 140mm doublet may be a future upsize, but not for awhile.

If you do get the APM 140ED i recommend the 3.7 inch focuser over the 2.5 version as the extra weight on the back end balances the tube better.



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