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102ED for Sure -- but F7 or F11?

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#26 Astrojensen

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Posted 16 November 2019 - 05:15 PM

For the things a 4 inch F/11 does better than a 4 inch F/7, there's a vast spectrum of telescopes that are better than either.

Certainly, but sometimes, or indeed perhaps always, it's not about what is the best in any absolute terms, it's about finding the scope that you are happy with. 

 

A 4" f/11 ED may seem a somewhat strange telescope to pick as an allround instrument, but I've found it remarkably pleasing and satisfying to use.

 

 

Clear skies!
Thomas, Denmark 


Edited by Astrojensen, 16 November 2019 - 05:18 PM.

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#27 Jon Isaacs

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Posted 16 November 2019 - 07:35 PM

Certainly, but sometimes, or indeed perhaps always, it's not about what is the best in any absolute terms, it's about finding the scope that you are happy with. 

 

A 4" f/11 ED may seem a somewhat strange telescope to pick as an allround instrument, but I've found it remarkably pleasing and satisfying to use.

 

 

Clear skies!
Thomas, Denmark 

 

I don't think one chooses a 4 inch F/11 as an all around instrument or as the most capable at a certain task, I think one chooses it because, well, just because...

 

I find Bob's decision to buy a 4 inch ED without knowing whether to go F/7 or F/11 rather odd. They're quite different scopes, Bob's got a lot of experience, he knows the advantages and disadvantages of each. In this situation, I'd know because I'd know what I wanted to do with the scope, where it fit with my other scopes.

 

In this situation, I'd be asking myself, what do I want to use this scope for?  For me, this comes first, then comes the scope but either way, it's the important question here, "what's Bob's plan for this scope?"

 

I follow Bob in his meanderings around Cloudy Nights and amateur astronomy as I do many of the members of Cloudy Nights. The Bob I think I know, enjoys smaller scopes, enjoys classic scopes, doesn't seem to be a deep space fanatic as much as he's as a lunar-planetary-double star enthusiast.

 

I don't think he travels with his scopes to dark sky locations, I think he stays at home and enjoys what his home ground has to offer.

 

So, based on what I know of Bob and just extending a guess, I'd think he'd probably find the 4 inch F/11 more fun. 

 

In this context, the things an 4 inch F/7 does better than an 4 inch F/11 aren't that important to Bob.

 

But maybe I don't know Bob the way I think I do. 

 

Very often, we recommend the scope that fits our own style of observing and present the reasons why that might be the best choice... that's helpful to Bob because he can see why i would pick the F/7 and you would pick the F/11 and then decide for himself.

 

But beyond that is knowing Bob and thinking about him and what he likes and what's a better fit..

 

And all the while keeping in mind the goal is to help Bob choose the right scope for him.. just because the F/7 is my preference, I score no points if Bob chooses the F/7. This is about Bob.. not Jon or Thomas or...

 

Jon


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#28 Bomber Bob

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Posted 16 November 2019 - 08:39 PM

But maybe I don't know Bob the way I think I do.

 

Nobody knows Bob -- his secrets have secrets.  Bob's been at The Swamp for 26 years, but in 2021 Bob & Mrs. Bob will be relocating to The Gulf.  House?  Condo?  Who knows.  But Bob anticipates down-sizing, and knowing Mrs. Bob, they won't be living too far from the city lights, so odds are, more backyard observing.  Bob could go Dob, but Dobs ain't Bob.  Bob's already tried the Big Dob in the backyard, and.... nope.  More trouble than they're worth.  Anyway, between here & now and there & then, there'll be some flux.  I have no problem storing the larger mounts until we're settled & sorted out, but that will put the affected scopes on ice, too.

 

A light yet capable 4" ED makes sense as an interim solution, and they're at a price where loss / damage during the move won't be 911 time (that would be Debra calling Me an ambulance).  And if I get it Now, I can enjoy it a bit before the first wave of chaos hits (we haven't moved in a long time)...


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#29 AstroKerr

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Posted 16 November 2019 - 11:06 PM

JayDubyah,

 

  I have the f/11 (wonderful performance, zero complaints), and now want the f/7 (same one) as well - each for it's purpose. So, I vote get both, or f/7 for now - sounds like it would work best during the move phase. I like the longer f/s but am finding it gratifying to shorten things up, explore that territory more. I may even break below f/7 in a serious way someday (other than 'flectors).

 

  Be SAFE during the move - hand trucks, carts, so on and so forth - lighter boxes, smaller boxes when you can. Get help with larger items - I just moved a recliner chair on my head for TLJ, heard a pop, annoying "Ow" right between and just below shoulder blades - maybe that's the last stupid move I make this year and I sincerely hope you don't make any; I believe we all like you 'style uncramped'.

 

That Gulf assigment sounds peachy, hope you two truly enjoy it =)

 

Peace, Light Loads, Clear Skies!  Comes to me that you oughta have a Basset - don't know why, just did. Mine did everything with me.


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#30 Tyson M

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Posted 16 November 2019 - 11:54 PM

Everyone who has the TS102ED f11 loves it, sooooo perhaps that's the one you should choose after all. 

You can always sell your scopes in the same size range. 

Just playing devil's advocate lol. 


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#31 Peter_D

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Posted 17 November 2019 - 09:24 AM

Has anyone any experience of mounting the F/11 on an unpowered Vixen GPE mount? Potential settling time issues? Would the F/7 (barlowed) be a smoother lunar/planetary observing experience?

#32 Jon Isaacs

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Posted 17 November 2019 - 10:08 AM

Everyone who has the TS102ED f11 loves it, sooooo perhaps that's the one you should choose after all. 

You can always sell your scopes in the same size range. 

Just playing devil's advocate lol. 

 

Of course, it seems that everyone who has the AT-102ED also loves it.  

 

People tend to buy scopes that fit their needs. If I were to buy a 102mm F/11, it's unlikely that I would love it. I would have nothing to do with the optics or the mechanicals.. Its just that a 4 inch scope that won't easily fit through my backdoor on it's mount wouldn't get used when inhave a 120ED that will..

 

Jon


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#33 Astrojensen

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Posted 17 November 2019 - 10:11 AM

I don't think one chooses a 4 inch F/11 as an all around instrument or as the most capable at a certain task, I think one chooses it because, well, just because...

But the fact remains that I use it as an all around instrument... 

 

 

Clear skies!

Thomas, Denmark


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#34 Bomber Bob

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Posted 17 November 2019 - 10:17 AM

... and I use my Dakin 4" F10 as a multi-purpose refractor.  The Dakin minus the false color + modern coatings in a lighter OTA could be near-perfect for my use.

 

But... so could a low CA F7 version of my Jaegers F5.

 

Best I can tell from owner posts / reviews, these two EDs are made to roughly the same quality level, and each runs about $600.  I just have to think about my routine use; and, preferences, which are definitely subjective.


Edited by Bomber Bob, 17 November 2019 - 10:21 AM.

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#35 makeitso

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Posted 17 November 2019 - 11:55 AM

Here’s my take on this.

 

I’ll start by saying, I have little experience with telescopes.

 

I have the AT102ED, it’s a great scope with excellent build quality. I got this for grab and go. I had no decent mount when I got it so I purchased a porta ii mount from eBay. The porta barely is adequate for this scope. With the AT102ED and porta, it’s almost not a grab and go, with an f11 of equal build quality, it would be to much and it would require an heavier mount I’m sure.

 

I do see a little false color on Vega, maybe some on the limb of the moon but it doesn’t bother me. I didn’t get for that purpose anyway. It still works for that fine though for me. It gives me great views of the double cluster, the andromeda galaxy and other similar objects. I can split the double double easily when seeing permits (not last night). Jupiter and Saturn look great, I have better scopes to use for planetary observing though.

 

It all boils down to what you want it to do. I have never looked through any 4” f11 refractor so I have nothing to compare it to. I do know that, in my situation now I would have no use for one. An f11 would not be grab and go, plus, I have better scopes to use for what it would be good for.

 

Jack


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#36 russell23

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Posted 17 November 2019 - 12:04 PM

... and I use my Dakin 4" F10 as a multi-purpose refractor.  The Dakin minus the false color + modern coatings in a lighter OTA could be near-perfect for my use.

 

But... so could a low CA F7 version of my Jaegers F5.

 

Best I can tell from owner posts / reviews, these two EDs are made to roughly the same quality level, and each runs about $600.  I just have to think about my routine use; and, preferences, which are definitely subjective.

Hi Bob,

 

The AT102ED is a really nice scope.  I bought mine and I was considering getting a 2nd sample when the SV102 Access clearance sale happened.    There is less CA with the SV102 because of the difference in glass types, but for deep sky I don't see any difference.    The 102mm f/7's ride nicely on my Vixen SuperPolaris mounts set to alt-azimuth mode on wooden legs.  Anything longer would start to stress that mount.  The 120mm f/7.5 is too much scope for the mount on windy winter nights.

 

Personally I love f/10 and longer refractors with Brandon eyepieces. 

 

Dave


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#37 Bomber Bob

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Posted 17 November 2019 - 07:32 PM

But the fact remains that I use it as an all around instrument... 

 

 

Clear skies!

Thomas, Denmark

Think of all the Vixen Japan-made 100mm F10 achromatics sold by (first?) Orion & Celestron with alt/az, Super Polaris, & Great Polaris mounts -- and all the fans they've garnered over 30 years or so.  No, they're not grab & go, but they're a fine solution for backyard observing in the city.

 

But...  A 100mm F7 is much closer to a grab & go.  Could be packed up & driven away from the lights with room to spare for the mount & accessory cases -- even in my Mustang.

 

But...  Assuming equivalent lens quality between the AT & the TS, I have to think the F11 will control CA better, and suffer fewer hits to resolution than the F7; otherwise, why would I want to go ED at all?  My Dakin already delivers fine views of every object I turn it to.

 

(Rhetorical, of course.  I've already seen the ED advantages with my APM 152 F8 -- while shorter & lighter than my old D&G 5" F10.)


Edited by Bomber Bob, 17 November 2019 - 07:37 PM.

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#38 Jon Isaacs

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Posted 18 November 2019 - 05:55 AM

But the fact remains that I use it as an all around instrument... 

 

 

Clear skies!

Thomas, Denmark

Thomas:

 

Did you buy it because it was the best all-around instrument?  That's not what I remember...

 

The AT-102ED can also be used as planetary instrument and it does a good job. But a 4 inch refractor can be more than just an astronomical instrument, it's also an excellent scope for stationary terrestrial and birding as well as various types of photography, both astronomical and otherwise. 

 

I am not saying that a 4 inch F/11 cannot be used as an all-around instrument, i am saying the AT-102ED is the better all-around performer. 

 

As I said in an earlier post, my gut feeling is that Bob would be happier with the 4 inch F/11, but that's not because it's the better all around scope, it's because it's the better high magnification scope. 

 

But if he wants to get a taste of the versatility of a 4 inch, the compact size, the quality of the wide field views, the does everything quite well, the 4 inch F/7 I think is a better choice. 

 

Jon


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#39 Nippon

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Posted 18 November 2019 - 07:09 AM

There is a Vixen ED103s in the classifieds if it is not sold already. These scopes are f/7.7 and I can tell you from my own experience are really excellent optically and are quite at home on GP class mounts. The asking price is quite reasonable.


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#40 clearwaterdave

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Posted 18 November 2019 - 07:14 AM

Well Bob.,You sure got yourself in a pickle here.,lol.,They are both nice scopes.,you don't NEED either.,but you want a peek through both!!.,Boy do I know the feeling.,lol.,When Thomas first posted about the TS,f/11,I was very very tempted.,but I had just gotten the AT102.,Hind sight I'm glad I resisted temptation.,cause I found a 120/f8 achro for cheap.,and it showed me that it was as long of a frac as I want to mount/drive.,Good luck with your choice.,I bet either or both will make Bob smile.,cool.gif,.


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#41 jag767

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Posted 18 November 2019 - 07:38 AM

Think of all the Vixen Japan-made 100mm F10 achromatics sold by (first?) Orion & Celestron with alt/az, Super Polaris, & Great Polaris mounts -- and all the fans they've garnered over 30 years or so. No, they're not grab & go, but they're a fine solution for backyard observing in the city.

But... A 100mm F7 is much closer to a grab & go. Could be packed up & driven away from the lights with room to spare for the mount & accessory cases -- even in my Mustang.

But... Assuming equivalent lens quality between the AT & the TS, I have to think the F11 will control CA better, and suffer fewer hits to resolution than the F7; otherwise, why would I want to go ED at all? My Dakin already delivers fine views of every object I turn it to.

(Rhetorical, of course. I've already seen the ED advantages with my APM 152 F8 -- while shorter & lighter than my old D&G 5" F10.)


Maybe this is helpful. Before my F11 I only used 4" apos in the f6-7 range. This was my comfort zone, and suited me well (or so i thought). I was very hung up on keeping a wide field of view, never stopped to consider anything else. I then sold my At106 for a sw120ed, which I ended up returning (long story, nothing was wrong with it, just amazon playing games), then purchasing this F11. My immediate reason for buying it was because of the reactions of users on here, as well as the very attractive price tag. I was hoping it was in the ball park of my 106.

After spending some time with it, I honestly felt I gave up nothing in terms of quality viewing, and although I am not one to star test for fear of going nuts evaluting optics, I eventually did. The star test is simply put, outstanding. Inside and outside of focus nearly identical rings with no noticeable imperfections. I feel comfortable saying its the best star test I have seen. I wish i had the 106 here to directly compare, however I feel confident saying the view is every bit as good in the F11. To this point, I'm not the only one to get this impression from this scope. Some have compared the views to much more premium optics. I see no CA in mine (I'm not particularly sensitive to it fyi), but I do see a very sharp, very flat field.

Owning this has changed what I look for in my viewing, and has been an eye opener into why long focus ED refractors have a place. I can honestly say its one of the best astro purchases i have made, and is a long term keeper.
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#42 Eddgie

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Posted 18 November 2019 - 10:32 AM

F/7 Is (in my opinion) too fast for a 4" scope with the glasses being used.  If it were at triplet I might be more inclined to say it would be an equal choice to the f/11 ED doublet, but to beat the 4" f/11 ED doublet, it would have to be an FPL-53 triplet.

 

I owned an 80mm ED f/7 ED doublet and even that scope was borderline for high contrast observing (as compared to a super Stellarvue f/6 FPL-53 triplet).  I was a bit surprised because I had owned an 80mm ED f/7.5 Orion doublet and it was as I recall FPL 53, and it was crisper than the 80mm f/7ED.  Now the 80 f/7 was a fine "all around" telescope, but if you made me pick one of these for planets, I would say that based on my experience with these other scopes, for highest resolution observing, the f/11 is almost surely a better choice.   F/7 is too fast for the glass used. Again, I am sure the f/7 is a great all around scope, but the goal of high resolution observing is to squeeze every bit of performance from a given aperture, and the f/11 is going to be Apo vs ED. 

 

(As a note, I had been considering the AT-102 but my experience with the 80mm f/7 ED doublet while good, eventually made me believe that as inexpensive as the AT was, I would be better served with a triplet Apo with FPL-53 glass.  I found a like new AT 106LE FPL-53 triplet, and as I expected, the performance was quite fantastic. After looking through it, I did feel like I absolutely made the right decision.  I have now owned two FPL-53 Triplets and both have been fantastic.    At f/11 though, an ED doublet is going to be very close, but f/7 is not going to be close enough that that the difference would be undetectable.  I also owned the Orion 100ED FPL-53 and and it too was Apo like.)


Edited by Eddgie, 18 November 2019 - 10:43 AM.

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#43 Jon Isaacs

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Posted 18 November 2019 - 11:13 AM

I owned an 80mm ED f/7 ED doublet and even that scope was borderline for high contrast observing (as compared to a super Stellarvue f/6 FPL-53 triplet).  I was a bit surprised because I had owned an 80mm ED f/7.5 Orion doublet and it was as I recall FPL 53, and it was crisper than the 80mm f/7ED.  Now the 80 f/7 was a fine "all around" telescope, but if you made me pick one of these for planets, I would say that based on my experience with these other scopes, for highest resolution observing, the f/11 is almost surely a better choice.

 

 

If higher resolution, higher contrast planetary observing is the goal, of the two, the F/11 is the obvious choice.

 

But for highest contrast, highest resolution observing, a 4 inch telescope is not in the running.. 

 

Jon



#44 daquad

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Posted 18 November 2019 - 12:09 PM

I see the choice between f/7 and f/11 as dependent upon color correction, portability and widest possible field.  Both scopes use equivalent ED elements and, I believe, are from the same manufacturer.  

 

Using the formula from Rutten & Van Vanrooij, and assuming the ED element dispersion to be 1/6000, the f/7 has a color blur of 1.8 X Airy disc, while the f/11 is 1.13. 

 

The f/11 is essentially perfect for VISUAL observing, as present owners have attested.  But:

 

The f/7 is similar in CA suppression to the APM 152 ED doublet, which meets the Conrady criterion.  So if Bob is happy with the CA in his APM, then he should also be happy with the performance of the F/7 and its greater portability.  As for wider field, keep reading.

 

I sold my AT 72 f/7 ED, because I wanted a bit more aperture for wide field sweeping and I now have a nice Unitron Alt-az mount in search of a telescope.  (Kind of like a title in search of an author.)

 

I am seriously considering the AT 102 f/7 ED.  With my 32 mm UO Konig MK80 I would get a reasonably wide field of 3.8 degrees and color correction for high power, should I choose to use it, equivalent to my APM 152 ED, with which I am as happy as Bob.

 

BTW TS also sells the 102 f/7 ED with fixed dew shield, but with a 2.5" R&P focuser, and is a bit less expensive than the Astronomics version even with the shipping and currency conversion taken into account.  Nevertheless, I would spring for the Astronomics version as I prefer to support our sponsor and I have no need for the larger focuser.

 

Dom Q.


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#45 Astrojensen

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Posted 18 November 2019 - 12:44 PM

Thomas:

 

Did you buy it because it was the best all-around instrument?  That's not what I remember...

What is "the best all-around instrument" anyway? What is "best" and by what parameters? I may not initially have believed it would be an excellent all-around performer and not bought it as such, but it turned out to be one in practice and I've used it as such many times. There are some things it's not good at and there are some things it's extremely good at, just like you'd expect from any all-around instrument. 

 

It actually has several very nice points over many other telescopes that are commonly used as all-around instruments. Let's remember that the very definition of this type of instrument is that it ideally can do *everything* reasonably well and that you can look at and photograph all kinds of objects.  

 

Compared to a shorter focal length ED/apo refractor of the same or smaller aperture, it obviously loses true field of view, but it does everything else equally good or better, except deep-sky photography. Simpler eyepieces work well on it, also at low magnifications. 

 

Compared to a 6" f/8 or an 8" f/6 newtonian/dobsonian, it obviously loses resolution and brightness, which is a disadvantage on visual deep-sky and planetary alike, but on the other hand it's a far superior solar telescope, especially for H-alpha. It will also be far superior for daytime landscape viewing. Field of view is basically the same. If one chooses a faster newtonian, one can get a wider field of view than the 4" f/11 ED. The newtonians will in theory win in deep-sky photography, if you add a coma corrector to them, but it's also possible to add a 0.79x corrector-reducer to the 4" f/11 ED, which will make it slightly faster at f/8.7 and highly corrected. 

 

Compared to a 6" - 8" SCT (usually f/10), it loses resolution and brightness, at least in theory!! In practice, I've found it superior in deep-sky performance to a 6" SCT, especially wide-field. It is a far superior solar telescope, especially in H-alpha. It has a wider field of view than both the 6" and 8" SCT, unless a compressor is used on the 6" (and I'm not sure it's possible to use a compressor AND 2" eyepieces on the 6") and it's still wider than the 8", even with a compressor on the latter (unless you can get a very agressive 0.5x compressor, instead of the common 0.63x one). Deep-sky astrophotography is basically a toss-up between them. The 8" SCT has aperture and focal length, but the 4" f/11 ED has a much wider field of view (especially with compressor) and is likely far better corrected over a large field with much less vignetting, thanks to the large focuser. 

 

So, what the best all-around telescope really is, depends on the things you want it to excel at and what things you allow it to be mediocre at. I've chosen my all-around telescope to be an excellent solar telescope, particularly in H-alpha, and allowed lesser performance in terms of brightness and resolution. Deep-sky photography is not a concern. I've used both 6" f/8 newtonians and a C8, as well as smaller refractors, and the 4" f/11 ED really does not seem very compromised in visual performance in comparison to them on most objects, even when it theoretically should be and it's definitely the better solar telescope. 

 

But if you look at an all-around telescope in a more narrow definition, namely purely visual and ONLY nighttime objects, as most people do (but then it's not really all-around, is it?), then the 4" f/11 ED will obviously lose to a 6" - 8" newtonian or SCT, as most of its advantages are suddenly taken from it. And even then, it still puts up an impressive fight.

 

 

Clear skies!
Thomas, Denmark 


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#46 Eddgie

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Posted 18 November 2019 - 01:02 PM

 

 

But for highest contrast, highest resolution observing, a 4 inch telescope is not in the running.. 

 

Jon

I totally agree.  If planetary observing is the primary application, there are far better scopes to use, but given the OPs choice between these two scopes, I would say that the f/11 scope is going to be the better of the two for that specific purpose, which was given a high priority in the OPs post.

 

Me?  I would never use a scope this small if my primary application (or my highest priority) was high contrast planetary viewing. 



#47 Jon Isaacs

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Posted 18 November 2019 - 01:18 PM

So, what the best all-around telescope really is, depends on the things you want it to excel at and what things you allow it to be mediocre at.

 

 

Thomas:

 

I look at it differently.  An "all around" 4 inch telescope does all the various things one wants to with a 4 inch telescope very competently, it does a good job at all the things one can ask of a 4 inch scope. Some of the things:

 

- Low Power, wide field

 

- High magnification planetary double star.

 

- Terrestrial both visual and photographic

 

- Astrophotograpy

 

- Compact, easy to transport

 

These are all things the AT-102ED quite well.  It doesn't offer the wide flat fields of the NP-101 or the high power prowess of a 4 inch Takahashi but whatever you ask of it, it'll do a good if not perfect job.

 

A scope that is more of a specialty scope will probably excel at one aspect but be quite weak in another. 

 

I am not trying to knock the 102mm F/11, I am just trying to provide some perspective. I see it as more of a niche scope, one would not have taken that Osprey photo with it, it's not a rich field scope, it's not a scope I would take with me to the dark skies of the Navajo reservation. 

 

It's a scope that I would choose if higher magnifications were the main interest.

 

Which, I think probably is the best fit for Bob..

 

Jon


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#48 drd715

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Posted 18 November 2019 - 03:49 PM

What this basically comes down to is that for the best image quality at a fixed 100mm objective size then it is going to be had with the longer fl ed or under F 9 you really need a quality triplet to eliminate the aberrations inherent with lower F numbers.

Compromises will have to be made in accordance to the highest priority usage intended.

Add in mount requirements, maximum field of views needed (what objects do you want to view, what size are they),CA correction, flat field, contrast, and many more considerations.

Individually one must make a list with top priorities first, then pick a scope that meets your needs.

I think the image produced by the F7 is going to be noticeably of lesser sharpness and have more unwanted color than the F-11 .

If one needs a shorter 100mm scope for use on a lighter mount for grab and go then the best option for color reduction and sharp image is most likely a triplet (triplets have some issues too, nose heavier, cooldown time) , but they will provide the better image; at a price.

Dollar for dollar that F-11 is a real bargain. I would get one like it if such a bargain could be had in the 127/130mm ED size package. I'm still tempted by the 100mm F-11 as the price is very good for the quality of the image.

Such a quandary

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#49 Bomber Bob

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Posted 18 November 2019 - 04:12 PM

First, I want to thank all y'all for your opinions / experiences.  Second, I will place my order for one of these 4" EDs on WEDS, but I won't say which one until it's delivered.  Third, rather than do a mini-review here, I'll add my testing to an existing thread -- unless I see something that hasn't been reported & needs to be.

 

Lots of stuff to consider between now & then.  Pretty sure that I could be happy with either ED, and that says a lot about the huge impact of China on our hobby.  Their scopes keep getting better & better, and they're branching out in the hobby.  As I've posted before, so many choices that it's becoming too much of a good thing!

 

As a review...

 

BB's Objective Criteria:

 

- 100mm minimum clear aperture ED doublet

- Retractable dew shield

- 2" rack & pinion focuser

- Felt-lined hinged tube rings

- Vixen-style dovetail bar  [OTA must be SAFE on the dovetail -- not too long or heavy / no break-aways!]

- Bare OTA weight less than 14 lbs

 

BB's Subjective Criteria:

 

- The Views!!  It MUST focus to a sharp lunar / planetary limb at a minimum of 200x (50x / inch).  Field stars at 40x MUST be pinpoints / micro-dots (same as my APM 152ED).  It MUST show at least as much lunar / planetary detail at ~ 150x as my Dakin and/or Edmund 4" achromatic refractors.  Its color correction MUST exceed that of my Dakin 4" F10 at similar magnifications.  Ditto for contrast, resolution, & background field darkness.  IOW:  Its performance on all targets MUST exceed that of my Dakin 4.  [The Dakin uses an F10 Baker-type achromatic doublet, and its views & planetary images are outstanding for its aperture.]  So...  AT F7 / TS F11 owners:  How does your ED compare with these samples (Dakin 4 / Edmund 4)?

 

Dakin 4 - Jupiter (Io Transit) 20170609V04AS21.jpg / Edmund 4 - Saturn 20170707V06AS12.jpg

 

Stuff like a rotating focuser, 50mm RACI finder (with its base NOT on the stinkin' focuser!), would be nice but aren't required.  Fit & finish should be at least as good as my APM 152ED.


Edited by Bomber Bob, 18 November 2019 - 07:07 PM.

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#50 gwlee

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Posted 18 November 2019 - 05:10 PM

If higher resolution, higher contrast planetary observing is the goal, of the two, the F/11 is the obvious choice.

 

But for highest contrast, highest resolution observing, a 4 inch telescope is not in the running.. 

 

Jon

No 4-inch scope is capable of providing enough magnification (150-200x minimum) with enough exit pupil (1mm minimum) to be entirely satisfy to me for planetary observations. It takes at least a 6-inch scope to approach these requirements and an 8-inch scope to meet them.
 

If forced to make a choice between f7 or f11 for a dedicated 4-inch planetary scope, I think an f11 scope would give marginally better planetary views, but be more difficult to mount and harder to handle, which might partially explain why so few 4-inch f11 scopes are marketed. 
 


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