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Skywatcher 120(100) F9 ED dblt vs Stellarvue 110 F7 ED dblt

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#1 JP-Astro

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Posted 28 June 2020 - 07:52 PM

Sorry for another 'VS' thread but specifically talking I haven't found a direct comparison thread with the similar title (I'm a bad searcher BTW.).

 

First of the two is a very popular ED FPL-53 doublet family while the second AFAIK is FK-61 equivalent of FPL51.

Both are out of my budget but I can start scrambling up some money to reach out for at least the Stellarvue 110 F7 (in the European TS version: https://www.teleskop...-Focuser.html).

 

Although I've read some reviews and know of noticeable CA in the 110 F7 My question is: How much of that CA is actually present and how badly will it affect the contrast and sharpness of the image compared to a comparatively "flawless" SW 120/100ED?

 

I'll be using the scope exclusively for visual and almost exclusively on planets. I need a narrow frac tube in the 4" to 5" range set at an angle for my tight balcony framing when the planets approach South (otherwise they are too low at our location while still raising and my larger aperture scope will not fit the framing).

 

Would it be wise to get instead of TS 110 F7 the TS 102 F7 FPL-53 version (https://www.teleskop...-Objective.html) ? They are the same price.

 

Otherwise I could still scramble up (with really hard effort) some more $$$ to reach out for Skywatcher 100 F9 ED.

Unfortunately I doubt I would be able to make one more step up to get the Skywatcher 120 F9 ED.

 

In terms of the aperture: the FK-61 110 mm scope is right in the middle of other two aperture options, 102 mm and 120 mm.

 

My initial logic is the following: since I cannot afford the 120 FPL-53 ED scope I first step down in aperture for a lower grade FK-61 glass in very close 110 mm aperture. That is, while downgrading I first think in terms of aperture (and overall brightness of the image).

 

Does my logic look flawed? - I can admit I feel it is in a way. Maybe it would be wiser to go down 20 mm in size and keep the FPL-53 glass in the equation? In which case I already lose 20 mm of the aperture but retain the better glass in the light path.



#2 Echolight

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Posted 28 June 2020 - 08:21 PM

A 110 f7 sounds like an ideal size if you were to only have one scope and wanted something fairly easy to mount and portable while still offering a respectable amount of light gathering ability.

 

But....I am waiting for a sale on the Evostar Pro ED "Black Diamond" 80 APO as my ultra portable grab and go quick look scope that I could mount on either a phototripod, light alt/az, or AVX mount depending on what day it is...to compliment my much larger 6 inch f/8 C6R fast achro yard cannon that also uses the AVX and I will possibly build a super-duty pipe mount for at a yet undetermined time and date.

 

So, this seems to be an internal dilemma which can only be eventually determined by the individual obsever. But, I guess by the same logic that I would choose the ed80 f7.5 with the high end glass over the short fast StarTravel 102, then the 4" f7 with FPL-53 glass might trump the 110 with cheaper glass.


Edited by Echolight, 28 June 2020 - 08:33 PM.


#3 Brollen

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Posted 28 June 2020 - 09:01 PM

Purely visual and planetary viewing?... Alternatively, why not look at the TS 102mm f/11 ED or a the well corrected TS 102mm f/7 (FPL53 / Lanthanum objective) scope instead? Either would do very well on planets, maybe better while costing the same or less and either would be much lighter! At 6.8KG, the 110 is very heavy for a 110mm doublet and it has a 3" heavy AP-biased focuser which you wouldn't need if doing visual only.


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#4 Eddgie

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Posted 28 June 2020 - 09:12 PM

I have owned the 120ED and the Stellarvue 110ED f/7 Stellarvue.

 

Hands down, the 120ED is a better scope, but it is a much bigger scope as well. The extra aperture and better color correction make better at solar system work.  Much better on the sun in white light where the 110ED color error can absolutely be seen to show some contrast loss.  Now the sun is (in my opinion) the most demanding subject on color correction and on the sun, the 110ED shows distinct softening at high power when viewing the faint penumbral structure around sunspots.

 

I currently use a 106mm f/6.5 FPL-53  LED triplet and this is a much better scope for my own needs.  Color correction is amazing and the scope is half the length of the 120ED.

 

These days, the only kind of refractor I recommend is an FPL-53 triplet.  It can be more compact and outperform modestly larger ED scopes.   

 

 

While the 100ED f/9 is wonderful, it is also very long for its small aperture (and I have owned two of these) and does not have much of a wide field capablity.  

 

One negative of these fast Apos is that they have bad field curvature.  If you are younger and can accommodate the curvature, fast Apo is an amazing instrument.


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#5 JP-Astro

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Posted 28 June 2020 - 09:14 PM

Purely visual and planetary viewing?... Alternatively, why not look at the TS 102mm f/11 ED or a the well corrected TS 102mm f/7 (FPL53 / Lanthanum objective) scope instead? Either would do very well on planets, maybe better while costing the same or less and either would be much lighter! At 6.8KG, the 110 is very heavy for a 110mm doublet and it has a 3" heavy AP-biased focuser which you wouldn't need if doing visual only.

Good point on the focuser.

Yes, if you read my very complicated original post I was also throwing in the TS 102 F7 FPL-53 version but I was too much concerned with the analysis of what to drop first - the glass grade or the aperture.

I often see people mentioning that 20 mm or aperture difference is significant like in for instance Skywatcher 120 ED vs 100 ED discussions.

For me the 120 ED is out of question so I'm focused on the remaining options.



#6 JP-Astro

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Posted 28 June 2020 - 09:25 PM

I own a Skywatcher 72ED (FPL-51). Three days ago when we had a pretty steady atmosphere (extremely rare event at our location) we watched Ganimed shadow transit on Jupiter that is at 8° this year.

When I saw it for the first time over past 2 years I was almost screaming! This is first time I realized how sharp/clear/contrasty these simple EDs can be.

Immediately I got a bug for a larger ED glass. You can read my rationale in the original post.

I would be happy to skip all other options and get to the SW 120 ED (which I recently briefly borrowed for 1 night of not so good seeing session) but I'm already over my (non-existing) budget for other scopes in the list including my first choice TS 110 F7.



#7 SteveG

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Posted 28 June 2020 - 09:41 PM

Try to find the money to get a used ED120 for the best planetary views.

 

I agree with Eddgie that you want an FPL53 refractor, but I think you want a longer focus doublet which cools faster and doesn't cost as much as a triplet. I would skip the shorter focal length refractors, especially if they don't have the FPL53 or equal glass.

 

If you can't get the ED120, then get an f9 ED100. I've had my 120 and 100 side by side. They have the exact same focal length, and on planets they are very close. The 100 is of course very easy to mount. It weight almost nothing!!


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#8 JP-Astro

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Posted 28 June 2020 - 09:51 PM

I hear you Steve. For me the SW 100ED is significantly less costly than the 120 ED version. I can still reach for the 100ED if I try.

These SW 100/120 EDs are extremely rare second hand over here and if someone sell one - it's of a great suspect.

Most of the time in this country if someone sells such an expensive (per our standards) piece of astro equipment it's because it's flawed in one or another way.


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#9 SteveG

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Posted 28 June 2020 - 10:24 PM

I hear you Steve. For me the SW 100ED is significantly less costly than the 120 ED version. I can still reach for the 100ED if I try.

These SW 100/120 EDs are extremely rare second hand over here and if someone sell one - it's of a great suspect.

Most of the time in this country if someone sells such an expensive (per our standards) piece of astro equipment it's because it's flawed in one or another way.

I love how light weight the 100 ED is, and yes, it's optically excellent. That's too bad they're rare over there. I had mine for sale a while back, for $650 US on a Vixen Polaris mount with RA drive. There were zero bites! I'm glad I didn't sell it.

 

I just ordered a new GSO focuser for mine, and I'm going to repaint the tube. I'm also going to move it to a Vixen Super Polaris mount that I have. It will be my "Super lightweight Grab n Go Refractor".


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#10 MortonH

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Posted 28 June 2020 - 10:30 PM

Since you have restricted space on your balcony have you considered a Mak-Cass or SCT?



#11 drd715

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Posted 29 June 2020 - 01:59 AM

If planets are your primary visual goal you can use the longer F-9 FPL-53 to advantage over a shorter fl scope. Also the higher F number will have the least CA and ease of finding the sweet spot in focusing. The 120 ED would be better for resolution,  but you have to keep with in your financial limits.  Not that you can find a similar price,  but B&H had the Skywatcher 100ED on sale last Christmas for $626. I  see the regular price is a couple of hundred dollars higher. I was torn between the  Skywatcher F-9 100ed and a TS-F-11ED and ended up getting the F-11 ED  - no regrets. Either would have made me happy. 



#12 JP-Astro

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Posted 29 June 2020 - 05:40 AM

Since you have restricted space on your balcony have you considered a Mak-Cass or SCT?

In fact I've got a SW Mak 127 but somehow I can tell comparing it to a smaller SW 72ED that Mak is a whole different instrument optically from a closely sized (after accounting for the CO and mirror surfaces) ED refractor.

 

ED72 gave me a rough idea of what I would experience with up scaling the ED glass so I'm hooked.

Mind you, my Mak is a great compact scope but I need to get the larger ED frac to intelligently get rid of this fixed idea. If I find in the end that in the same (rare over here) great seeing conditions Mak keeps up with the larger ED on par I will prove myself wrong.

At the moment I'm obsessed with the idea and only the real thing can cure this obsession :)



#13 Hesiod

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Posted 29 June 2020 - 07:06 AM

If yor balcony is narrow, mind that using a 900-ish focal refractor may be very nasty.
We have a narrow balcony and there is an obvious difference in ergonomics between the 100/900 and 100/740.
As for planetary work, I dare to suggest to think also to a 7-8" MCT or SCT (the latter should be easy to find used at good price).
As for the refractors, there is more than just CA, and even a good achro may be used for excellent planetary observations (I use more often my TAL 100 for WL Sun instead of the FC100DL...).
A last observation: very small telescopes lack resolution and therefore look very often "sharper" than larger ones unless the sky is steady enough to allow the latter to "muscle" out their advantage.
It is therefore "risky" infer the performances of scaled up versions
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#14 JP-Astro

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Posted 29 June 2020 - 07:29 AM

Good points, Alberto.

>>> "...very small telescopes lack resolution and therefore look very often "sharper" than larger ones unless the sky is steady enough to allow the latter to "muscle" out their advantage..."

 

I suspect I may exaggerate my expectations when thinking that SW 100ED would give me substantially more in the same viewing conditions than a smaller 72 ED and by the way...

 

... I've read a lot about 5" Mak vs 4" ED and in most cases people would call that competition a "tough call".

Maybe I need to cool down? It's a bad thing I didn't have my Mak 127 out at that steady nigh that impressed me with the Jupiter view in the 72 ED. Maybe I'd see the same clear picture with a little bit more resolution? I confess I'm sometimes prone to strong impressions beyond good sense.



#15 Hesiod

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Posted 29 June 2020 - 10:16 AM

A good 5" MCT does not lag much behind a good 4" refractor: I have tested several times my 5" MCT against the 4" refractor and usually was a very tough call to make the decision.

The refractor looks more "vibrant" and it is easier to spot the lowest-contrast features, and of course is thermally more stable, but all that features I see in it are visible in the 5" MCT as well.

The refractor's greatest asset is the ability to frame much larger fovs, but it is totally inconsequential for planetary observing, and not very useful unless at a decently dark site.

 

In my opinion a decisive leap is from the 5" MCT to a 8" aperture: managing the larger telescope may be harder but, when the sky is steady enough, there is a very obvious difference on the Moon* and Mars, while personally found that Jupiter rewards more optical accuracy due to many low contrast, but quite large, features (I see more easily the "white spots" with my 100/900 than with the C8).

However a  5" is IMHO already very enjoyable so, in your boots, would start thinking to an upgrade once get the feel you have reached its limit and want more

 

 

*except when observing the full Moon, or very far from the terminator


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