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PostPosted: Thu Sep 02, 2010 5:32 am 
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Anybody use one of these yet? The specs look good, and the reviews of the 127mm bigger brother seem positive. I'm not sure that I can swing the purchase at the moment. But admittedly a 4" apo has been the number one scope on my "must have someday" list, simply from a versatility standpoint. $1300 with rings and a 99% 2" diagonal? Wow.

ES ED102

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PostPosted: Thu Sep 02, 2010 4:06 pm 
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Wow, that does sound like quite a deal! I wonder if these are rebranded scopes that also sell under a different name? That might be the way to get a review on one.

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PostPosted: Thu Sep 02, 2010 6:45 pm 
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Yeah they are rebranded (JOC manufacture?). Meade sells a version, as do others, I think. I did run across a couple reviews, but they seem to deal with AP more than visual. Good idea, Erik. I'll see what I can pull up on other "brands".

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PostPosted: Thu Sep 02, 2010 10:17 pm 
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Although they call these scopes "APO's", I'd be curious to see how good the color correction really is. I looked through an Orion ED 120 a while back and found that the color correction wasn't nearly as good as the Orion ED80. Of course, the ED 120 is f/7.5 which is frankly too fast to offer color free images with FPL53 ED glass. Still a great scope but not quite an "apo"- at least if the definition is "perfectly corrected for color".

Not that it matters unless you're doing serious astrophotography. My little SV 80ED shows a touch of color on Vega and other bright stars, but i'd prefer that over the poorer build quality, larger physical size, and slightly better color correction of the Orion ED 80.

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PostPosted: Fri Sep 03, 2010 8:02 am 
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Erik wrote:
Of course, the ED 120 is f/7.5 which is frankly too fast to offer color free images with FPL53 ED glass.



I disagree. I think a well made FPL-53 triplet can easily be color free at f/7. The 92mm f/7 FPL-53 triplet Stowaway is an example of such a scope.

The Astro-Tech 106mm f/6.5 FPL-53 triplet was reviewed in S&T as being truly color free, "had absolutely first-class color correction. There was no visible chromatic aberration, even on the brightest targets. When defocused, star images presented nary a trace of false color."

So I believe that "true Apo" performance is certainly acheivable with FPL-53 down to at least f/7.

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PostPosted: Fri Sep 03, 2010 8:51 am 
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One other thing, Jason. Remember that an air spaced triplet will have a longer cool down time than a doublet or an oil spaced triplet. Probably wouldn't make much difference for daytime photography but it's something to think about for night time work.

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PostPosted: Fri Sep 03, 2010 9:40 am 
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Square_peg wrote:
The 92mm f/7 FPL-53 triplet Stowaway is an example of such a scope.


This is the version of the Stowaway I have Erik, and the actual focal ratio is f/6.565. I'm not sure why Roland chose to market it at f/7 but the focal length is only 604mm. It is very much color-free. Vega, Sirius, and Venus are pure white both in and out of focus. Also, no color on the lunar limb, terminator, or on crater shadows at any magnification up to 402x, which was the limit of my EPs for that scope at the time I tested it.

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PostPosted: Fri Sep 03, 2010 9:58 am 
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Square_peg wrote:
Erik wrote:
Of course, the ED 120 is f/7.5 which is frankly too fast to offer color free images with FPL53 ED glass.



I disagree. I think a well made FPL-53 triplet can easily be color free at f/7. The 92mm f/7 FPL-53 triplet Stowaway is an example of such a scope.


So I believe that "true Apo" performance is certainly acheivable with FPL-53 down to at least f/7.


I should have worded my comments better- what I was saying is that at that level of aperture (120mm), a scope with FPL53 glass needs to be longer than f/7.5.

As I mentioned, the Orion ED80 at f/7.5 has virtually perfect color correction. The Orion ED100 is f/9 and has perfect color correction. The ED 120 should've been at least f/9 to maintain that level of color correction. It's still an awesome scope- it's just not on par with the 80 or 100 for color free images. With larger aperture refractors, the f/ratio must be increased to maintain good color correction-assuming the same glass is used.

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PostPosted: Fri Sep 03, 2010 10:23 am 
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What type of glass is used in the 130mm f6.3 StarFire EDF?

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PostPosted: Fri Sep 03, 2010 3:35 pm 
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I'm not sure- I don't think I've looked through the 5", though I believe I have looked through the 6"- though it was several years ago.

I'd be surprised if AP used the same type of glass as Orion does in their apochromaric scopes.

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PostPosted: Fri Sep 03, 2010 4:19 pm 
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Numerous AP scopes are confirmed to have been made with FPL-53.

http://geogdata.csun.edu/~voltaire/tmb/tmb1.html


I'm not suggesting an ES scope is necessarily built to the standard of an AP scope. Just that a very well corrected scope can be made at f/7 with FPL-53.

And whether AP sources their FPL-53 from the same place as Orion is another question I can't answer.

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PostPosted: Fri Sep 03, 2010 4:26 pm 
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The problem with comparing different scopes under different manufacture, or even by technological changes from year to year, is that there are too many variables. I understand that four major features define the color correction of a refractor: focal ratio per aperture (the inch X 3 or 5 rule), the abbe index of used glass, the number of elements, and the curvature/placement of elements in the objective design. Change any one of those variables and you may end up with a completely different scope.

I read the specs on this ED102 triplet as a solid design with regards to:

a) f7 medium speed
b) Hoya FCD1 glass (abbe number ~81)
c) Three element

It's the way the lenses are designed and ground, and spaced, that I wonder about. Ultimately, an Orion ED100 f9 doublet also interests me, especially considering a slightly lighter weight, and currently very low price. But the single speed focuser is a drawback for bird photography (a forseen secondary use for the scope), as is the slower focal ratio. And of course, I'd still need to add a 2" diagonal, rings, a finder scope, and a dovetail, which no longer makes it such a savings.

There is just something about a 4" triplet with high index glass that seems hard to screw up. Maybe I'll just have to pick one up to check it out. I'm sure there are a few retailers I could buy from with a provision to return if I'm not satisfied.

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PostPosted: Fri Sep 03, 2010 4:35 pm 
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Astronomics just dropped the price of their AT106LE to $1,195.00 for Labor Day Weekend!

I'd jump on that before I bought the ES 102.
Link to sale

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PostPosted: Fri Sep 03, 2010 5:30 pm 
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Erik wrote:
I should have worded my comments better- what I was saying is that at that level of aperture (120mm), a scope with FPL53 glass needs to be longer than f/7.5.........With larger aperture refractors, the f/ratio must be increased to maintain good color correction-assuming the same glass is used.


For anyone interested, here is an article by the late Thomas Back on Astro-Physics lenses.

A Brief History of Astro-Physics Lenses

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PostPosted: Fri Sep 03, 2010 5:33 pm 
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Wow, $300 off?!? Dang, I really wasn't ready to rush this...but that is an awesome deal!

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PostPosted: Fri Sep 03, 2010 5:36 pm 
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Thanks, Kerry. I just read that article a couple hours ago while trying to find an answer for Tom's question regarding the 130mm Starfire glass type. It's a good read. I never did find the answer, BTW.

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PostPosted: Fri Sep 03, 2010 5:38 pm 
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Yep, and it's FPL-53 not Hoya 'FPL-51 equivalent' glass.

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PostPosted: Fri Sep 03, 2010 5:40 pm 
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Tell me about it! Plus f6.5...great for photography!

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PostPosted: Fri Sep 03, 2010 5:46 pm 
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Chopin wrote:
Thanks, Kerry. I just read that article a couple hours ago while trying to find an answer for Tom's question regarding the 130mm Starfire glass type. It's a good read. I never did find the answer, BTW.


I guess Tom already beat me to posting it. Weird, there are several more posts than when I finished posting the link that weren't there. Tom's question was the last post before mine when it went through. Must have a bad cookie.

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PostPosted: Mon Sep 06, 2010 10:24 am 
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Jason, if you have not seen it, there's a thread on CN about theses two scopes here.

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PostPosted: Mon Sep 06, 2010 3:26 pm 
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Hey thanks, Kerry. I have been incredibly tempted to jump on that AT106 sale, but I'm still trying to figure out what I really want to do with the scope (is this going to be used more for bird photography, or night time astro viewing?). That, and I'd need to bend the plastic to buy right now, and I've improved my purchasing habits over the past few years so I'd rather not fall back into that hole.

Ultimately the 4" range is certainly where I want to be. But I'm also factoring in the best compromise of size/weight (less is better), price (less is better), and violet fringing (you guessed it...less is better). I'm starting to lean to the Orion ED100. It's 3 lbs less than any of the other three I'm looking at, being the ES102, the Orion 110 ?7, and thanks to Tom, the AT106. Actually, I believe the ES102 is more than 10 lbs. I'm sure the ED100 is better color corrected than the 110 ?7, simply based on design, and especially based on reviews. I'd bet the ED100 is on par with the ES102, and probably close to the AT106. After pricing the ED100 with rings, dovetail and dielectric diagonal, I'm at $840. Seems like a deal, and it feels like a low risk investment with solid optics. I'm pretty wishy washy about purchases like this, and I'll probably go back and forth another 20 times before making the plunge. I do fear, though, that the ED100 is destined for history if I don't buy soon.

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PostPosted: Mon Sep 06, 2010 7:36 pm 
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The ED100 is a nice scope but it's loooooong! At f/9, it's physically larger looking than its aperture would suggest- at least that was my take on it when they first came out. It is very well color corrected though. If you've got a mount that doesn't mind the long tube that might be the way to go.

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PostPosted: Tue Sep 07, 2010 3:39 am 
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Erik wrote:
The ED100 is a nice scope but it's loooooong! At f/9, it's physically larger looking than its aperture would suggest- at least that was my take on it when they first came out. It is very well color corrected though. If you've got a mount that doesn't mind the long tube that might be the way to go.


Erik,that is an issue, for sure, and the one thing holding me back. I have a newt that is about the same dimension as the ED100, but comparing the two designs (refractor vs reflector) is misleading since the eyepiece is so low on a refractor. :mrgreen: There is no question I would prefer a shorter tube, say 750mm or less. But in the end, regarding mount sturdiness, will a tube that is six inches shorter really make much of a cantilever difference if it adds 3 lbs of weight in the process? I wish I could just compare these side by side, but I don't have that luxury.

As for having a mount strong enough, I'm playing guess work here. I will start off with my Bogen 393 gimbal head for mounting, which is easily as strong as the Televue Gibraltar. The only problem is it's vertical design , rather than 45?, limits how high in altitue I will be able to swing the scope. Here is an image of the mount with my lens:

Image

The saddle can sit above or below the lens (scope) offering some flexibility. I'm looking at the Stellarvue M2 mount a a possible alternative, so that I can achieve full zenith movement. Are there any other readily available mounts similar to the M2 with relative handling and price?


As for the tripod, I have a set of Bogen 3246 legs which have a load capacity of 27 lbs. They handle a pair of 10 lb. binos now with aplomb. Although I have two GEMs (one with a 10 lb limit, the other with a 25 lb limit) I expect to use this scope in alt-az configuration more often for grab and go work.


Lastly, does anyone have experience with the Orion ED102 or ED110 (or similar ED doublets from other manufacturers)? I've read mixed "reviews" with regards to false color. At what magnification does it become an issue? The only refractor I've owned and used extensively was an Orion 100mm ?6 achromat. It was sharp, but suffered from violet severely beyond 50x, IIRC. Are these doublets only being bagged by people who expect Takashashi performance, or is the violet fairly noticeable on bright objects. If a scope is good up to 150x before a tinge of color is visible, I'd be fine with that. But if 100x is the limit I'd hesitate.

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