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TEC 140 APO vs Celestron CGEM Pro 1100 HD

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#1 10gauge

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Posted 03 November 2010 - 08:45 PM

Questions regarding refractor vs SCT:

1. For observing planets, deep space, and astrophotography with a DSLR, what is the difference in image quality @250-300X between an TEC 140 APO Refractor and Celestron CGEM Pro 1100 HD SCT?...
-Sharpness/Resolution?
-false color?
-CA?
-Contrast?
-F.O.C.?
-brightness?

2. Can the Celestron 11" SCT @600X limit match the image quality of the TEC 140 refractor @300X limit?

3. Is it true that a SCT needs double the aperture to match the image quality of a refractor? If so, what size SCT could "match" the image quality of the TEC 140 APO in terms of resolution, color, contrast, CA... Before committing serious $$$$, I am deciding whether to go with refractor or SCT...

Thanks,
George

#2 David Pavlich

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Posted 03 November 2010 - 09:34 PM

Welcome! First, you're comparing a low production, premium refractor to a mass produced SC. Other than that, let's assume that all things are equal; collimation is great, scopes are at temp equilibrium and the same quality eyepieces are being used.

The C11 wins for visual. You can't fight the laws of physics. It pulls in WAY more light. Yes, the TEC will be more contrasty (is that a word?), but it can't even come close to the resolving power of the SC.

600X will only be useable under pristine sky conditions. In other words, perfect seeing. I've been using SCs for a long time and find that 300-350X is about it under average conditions.

Now, were I choosing between the two as a pure imaging scope, I'd grab the TEC and wouldn't look back. It's an excellent imaging scope. But if you're doing more visual than imaging, I'd grab the C11, maybe with the Fastar option.

David

#3 gnowellsct

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Posted 03 November 2010 - 11:14 PM

The C11 wins for visual. You can't fight the laws of physics. It pulls in WAY more light. Yes, the TEC will be more contrasty (is that a word?), but it can't even come close to the resolving power of the SC.

David


It won't be more contrasty. It's a 5.5 inch scope vs a scope twice its aperture.

The TEC is an excellent choice, very high manufacturing standards, but if you get an 11 EdgeHD "that meets spec" you will get more contrast and more color saturation to boot.

There are many reasons to get the TEC: Smaller than a C11, easier to keep free of dew, won't need as much of a mount, and wonderful wide field views. Furthermore you'll be able to do that wonderful refractor thing of going from very low power to very high power and keep a sharp image, though of course stars will transform into Airy disks and not look pinpoint the way they do at low powers. The TEC will make it easier to find stuff (a) because of the wide fields and (B) because you will limit yourself to the objects that look great in a five or six inch scope. The C11 will require dew control, will have much smaller field of view, won't show you Airy disks at 200x, will bring in better views of Jupiter and Saturn if well collimated, provided you define "bigger" as better, since, for example, my favorite view of Saturn is in the 4 inch refractor at 40x, luminescent in a field of stars, which I prefer to up in front of my nose at 450x, though this can be mesmerizing too.

If it were 9.25 vs. TEC 140 I'd say you'd be at approximate parity on planet contrast.

Greg N

Incidentally the optimal solution:

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#4 Eddgie

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Posted 03 November 2010 - 11:15 PM

I don't know where you heard that you need an SCT that is twice as big to match a refractor.

Maybe you need one twice as big if the quality is poor, but if the quality is excellent, the SCT only needs to be about 35% larger.

I have a really superb Celestron EdgeHD. About the best optics I have ever seen in a commercial SCT. The difference between the SCT and my 6" APO is far less than most people would believe.

As for using 300x vs 600x, I have a C14 and as I mentioned, a 6" APO.

It is rare to use EITHER of these scopes at even 300x. On most nights, there really isn't any point going higher than about 250x in either of them.

On nights of EXCELLENT seeing, I can use the 6" APO at 300x, but I really don't see anything that isn't arleady visible at 200x. The scale is a bit larger, but there is no new detail to be seen.

In the C14, it is rare to be able to use over 440x. The seeing has to be PERFECT to use more to any advantage. With the C14, about 400x seems to me to be the point where all available detail is presented. Going higher has never shown me a NEW detail that I could not see at this magnification.

The problem though is that sadly, not all SCTs are optically excellent, and if you do have one that is a bit soft, then yes, it helps to have twice the aperture.

If properly cooled though, and if the optical quality is decent, the C11 should do no worse than the TEC, and perhaps a bit better.

#5 gnowellsct

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Posted 03 November 2010 - 11:34 PM

I don't know where you heard that you need an SCT that is twice as big to match a refractor.

Maybe you need one twice as big if the quality is poor, but if the quality is excellent, the SCT only needs to be about 35% larger.

I have a really superb Celestron EdgeHD. About the best optics I have ever seen in a commercial SCT. The difference between the SCT and my 6" APO is far less than most people would believe.


After talking to half a dozen people who've taken the color test I'm beginning to wonder about this (the color test was recently posted here). On the one hand, I think even a four inch scope shows most of what amateur astronomy has to see, logical because the jump from naked eye to four inches, were it to be repeated from four inches to another aperture, requires an 80 inch scope. So everything else we do is just messin' around IMHO.

On the other hand, even though the view of Jupiter in my FS128 (not the one on the c14, which is a Vixen) is exquisite, I think that

(a) to me the difference between it and the C14 is obvious; the C14 blows it away;

(B) but I'm not sure it would be obvious to everyone who does amateur astronomy

© and I'm especially dubious, after the color tests, that people even modest degrees of blue or green impairment would "see" some of the extra detail that a C11 or C14 would bring in. This is particularly true of colors and particularly true of the blue festoons that I consider obvious on Jupiter but which I've had people tell me "they couldn't see". If you *can* see colors readily, then it is *very hard* to say that five and six inch apertures are "almost as good" as 11 to 14 apertures. Because color gets better with size, and color is an element of contrast.

(d) the truth is we are talking about incremental levels of detail: imagine looking at Earth and seeing the general outline of N. America in your four inch scope on Mars, and then looking through a 14" and seeing the same outline but with more of the Aleutian islands and maybe a few more of the islands between Washington State and Vancouver.

Such a difference would not "jump out" at many people and it would be accurate to say that the smaller scope is pretty much doing the trick.

Refractors are excellent and in spite of the C14 and 10" right here where I can use 'em I've never regretted a night with the FS128. About all I can say is that it's a different aesthetic and a different way to enjoy the skies.

Although the TEC will be lighter, and in that sense more portable, I should point out that as a practical matter people treat refractors differently. By the time I have my refractor in its travel case and stashed, it takes up more space than my C14. I used to think that it was easier to hoist up to the mount, too, but that was before I learned the "side mounting technique" for GEMs.

regards
Greg N

#6 Mike Clemens

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Posted 04 November 2010 - 12:57 AM

Having seen crowds of people use SCTs and APOs right next to them, I'd say the average person is instantly drawn to the views in the refractors.

#7 Midnight Dan

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Posted 04 November 2010 - 06:02 AM

Comparing the C11 to a 140 refractor, and accounting for the central obstruction, the C11 will have:

3.5 times the light gathering capability
2 times the resolution
32% more contrast

In my opinion, on a night that allows high magnification, visually the C11 will blow away the 140. On the other hand, the nights when that can happen will be few. I find that pretty much any night I view, I can get to 150x on Jupiter. About half the nights I can get to about 200-250x. On a few nights a year, the seeing will allow me to get to the rated 400x maximum for my scope.

For planetary, the C11 will excel due to it's long focal length. For dim, smaller DSOs the C11 will also do well because of it's large aperture and much greater light gathering capability. The place where the C11 will fall short of the TEC is in wide field imaging. If larger DSOs are your target, the C11's narrow field of view will be a problem.

-Dan

#8 t.r.

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Posted 04 November 2010 - 07:13 AM

I've had both a C-11XLT and TEC 140 side-by-side...no contest, the C-11 showed more planetary detail with better color saturation and better dso detail on average nights. The C11 also has an advantage in binary viewing. But pure stellar views goes to the refractor of course.In less than average, the TEC held the steadier view, but it has been argued that no less detail is seen in the C11, just a more aesthetically pleasing view in the refractor.

I will say this, if you chose the TEC over the C11, you WILL be missing detail thats available on an average night for the reasons cited in posts above. An average SCT, diffraction limited will do this. It doesn't take pristine seeing conditions or an exceptional fluke of an SCT to do it.

Without doubt, refractors, especially apos, do give a fantastic, wide, clean image. The BEST for their aperature...but to beat double the size sct, not often. YMMV. ;)

#9 j3ffr0

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Posted 04 November 2010 - 08:10 AM

The C11 wins easily if it's properly cooled and collimated. Cooling the C11 is really important and takes 2 hours without a cooler. I've had much better views of Jupiter with the C11 than the 120ED. I've also had much worse on nights when it couldn't reach thermal equilibrium and I was fighting dew and seeing too. I suppose I should buy a Lymax.

Tough choice. The TEC might be a more consistent performer, but you will get more resolution and the best shots with the C11. One other thing in the TEC's favor is the ability to do wider field work.

#10 10gauge

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Posted 04 November 2010 - 10:22 PM

Fantastic responses David, Greg, Eddgie, Mike, Dan, t.r.! Initially, about a year ago, I was contemplating on Celestron 9.25" SCT. However, as I began to read more on refractors this past week, I learned that they put out a better image for the same aperture. I just wasn't sure how much better the resolution/contrast was better on the refractor. So I decided to look into the 11" SCT to see if 2X the aperture can overwhelm the refractor in terms of sharpness, contrast, brightness, color, etc. for a given magnification.

I am at the early stages of this new hobby. I wish I could spend time in the field among peers to test several setups.

I also wish there was a way to see images from a TEC 140 and 11" SCT at the same magnification of let's say 200-250X and see what the differences are in image quality of the same target in space. Are there any images of "test targets" in space between a 5-5.5" refractor and SCT? That would really be interesting to see how big or small the visual differences are.

... Perhaps getting both a refractor and SCT in the future may be the way to go, especially if one telescope can't do everything well. But, it seems that sacrificing a little of the upper echelon of image quality, an 11" SCT is the "Do Everything Telescope" for viewing. But the wide angle views must truly be majestic in refractors...

Early on, I just want to do viewing. Image brightness will is going to be important. As time goes on, I'd like to add imaging to the hobby. I just don't know of too many top tier 11" SCTs that can be mounted on a EQ mount?...

Thanks everyone! You all made consistently great suggestions and offered keen wisdom. Great food for thought here...

#11 Jon Isaacs

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Posted 05 November 2010 - 06:24 AM

.. Perhaps getting both a refractor and SCT in the future may be the way to go, especially if one telescope can't do everything well. But, it seems that sacrificing a little of the upper echelon of image quality, an 11" SCT is the "Do Everything Telescope" for viewing. But the wide angle views must truly be majestic in refractors...



A couple of quick thoughts;

- As a do everything visually scope, Newtonians have their virtues... Shorter focal lengths, smaller central obstructions, faster cooling optics, larger practical apertures.

- A larger scope and and smaller refractor make a good combo. I think a faster 4 inch refractor is a good companion for a larger scope. A TEC 140 would provide more detailed views but requires a mount that makes it about as manageable and portable as the 11 inch SCT. A scope that is easy to setup up is more likely to be used...

Jon Isaacs

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#12 t.r.

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Posted 05 November 2010 - 06:53 AM


I also wish there was a way to see images from a TEC 140 and 11" SCT at the same magnification of let's say 200-250X and see what the differences are in image quality of the same target in space. Are there any images of "test targets" in space between a 5-5.5" refractor and SCT? That would really be interesting to see how big or small the visual differences are.


This is a link to a well known site that has a program you can download for free. It will show you what various scope types and sizes do to a planetary image. It should help you with what your looking for...

http://aberrator.astronomy.net/

#13 gnowellsct

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Posted 05 November 2010 - 03:56 PM

Early on, I just want to do viewing. Image brightness will is going to be important. As time goes on, I'd like to add imaging to the hobby. I just don't know of too many top tier 11" SCTs that can be mounted on a EQ mount?...


I don't understand the question about the mount. Any C11 can be mounted on an EQ mount. The real issue though is to throw some money at the mount. A junky EQ mount isn't worth the bother, much better to get a CPC type fork arrangement than a poor quality EQ mount. A good EQ mount however is a wonderful thing.

The world works in many ways. One stock approach is that you should start with low magnification instruments such as binoculars and then diversify after experience. My learning curve was 180 degrees opposite. It was only after many years of in-my-face views of M27 that I finally grew to appreciate it as a luminescent chip in a binocular field. A C11 a jolt of cosmic bourbon, and all told one of the better bourbons I'd say, whereas the Tec 140 is a vintage Burgundy. You have to know, in each case, what it is you want.

Greg N

#14 Miguel Lopes

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Posted 05 November 2010 - 05:16 PM

My opinion:
If you want to own a single, all purpose scope, the best option is a C9.25 or a C11.
If you can afford 2 expensive scopes, get a 18" dob for visual and a refractor for imaging.

#15 10gauge

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Posted 06 November 2010 - 08:50 PM

Thanks Jon, t.r., Greg, and Miguel. Very good suggestions and amazing setup photos! I looked at the Celestron C1100 HD more closely, and mechanically, the focuser, diagonal, and eyepiece assembly looks rather cheap compared to the Meade LX200.

It looks like the Meade LX200 12" SCT can't fit onto a German EQ mount? It only comes with the fork attachment. It would be nice if I could mount it to a CGE type mount...

I tried to compare images/videos of Jupiter taken with a few 4" apochromatic refractors and C11 SCT and 10" Newtonians. Wow! no comparison, the reflector had much more detail at similar magnifications. There also was an image taken with the TEC 140. It fared better than the Chinese 4" ED refractors, but not enough to match the 11" SCT or Newtonians.


C11 SCT:
http://www.youtube.c...h?v=L73UTz4BNlg

Tak 130 TOA Refractor:
http://www.youtube.c...h?v=6xM9VVfCwLI
http://www.youtube.c...feature=related

Thanks guys for the advice! I just inquired about Amateur Telescope Makers of Boston, which meets only 15 minutes away...


#16 jrcrilly

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Posted 06 November 2010 - 09:10 PM

It looks like the Meade LX200 12" SCT can't fit onto a German EQ mount?


It can be done (I use mine on a GEM) but it's pretty heavy. Marginal on a G-11 or CGE, good on a CGE Pro, Titan, NJP, or AP-900.

#17 SteveC

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Posted 07 November 2010 - 01:37 PM

.. Perhaps getting both a refractor and SCT in the future may be the way to go, especially if one telescope can't do everything well. But, it seems that sacrificing a little of the upper echelon of image quality, an 11" SCT is the "Do Everything Telescope" for viewing. But the wide angle views must truly be majestic in refractors...



A couple of quick thoughts;

- As a do everything visually scope, Newtonians have their virtues... Shorter focal lengths, smaller central obstructions, faster cooling optics, larger practical apertures.

- A larger scope and and smaller refractor make a good combo. I think a faster 4 inch refractor is a good companion for a larger scope. A TEC 140 would provide more detailed views but requires a mount that makes it about as manageable and portable as the 11 inch SCT. A scope that is easy to setup up is more likely to be used...

Jon Isaacs


Good advice Jon,

That describes my situation exactly. I had a Meade Starfinder reflector for many years. Between the collimation and its weight, it was a pain to set up outside, I hardly used it. Enter my 7" Mak. It's a great late spring to early fall scope, but once the cold weather approaches it became a 6 month scope, I still have it. Now, I'm in the final phase, with the TEC140. I roll it out from the garage on my Scopebuggy, and I'm viewing in 2 minutes and it's at ambient temp, regardless of the season. I roll it back into the garage with little effort when I'm done. The scopebuggy and the TEC140 made astronomy easy and enjoyable. I knew exactly what I was missing visually when I passed up buying a larger Mak, SCT, and reflector, - nothing. I can't see anything if I'm not using a telescope.

I read these posts and I ask myself, why didn't I buy a 11" SCT or a 14" Dob, I'm missing out on a lot of stuff. I begin to make plans, because I forget that there is a reason why I bought the TEC140. I need an avid viewing neighbor, who own a large SCT or Dob, so that I can walk over and start viewing when it's convenient for me.

Note to self: find real estate agent who tracks telescope demographics.

Item #2 Check our San Diego - good prospect

#18 RAKing

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Posted 07 November 2010 - 01:52 PM

I read these posts and I ask myself, why didn't I buy a 11" SCT or a 14" Dob, I'm missing out on a lot of stuff. I begin to make plans, because I forget that there is a reason why I bought the TEC140. I need an avid viewing neighbor, who own a large SCT or Dob, so that I can walk over and start viewing when it's convenient for me.


Steve,

I have owned two C11, one C925, and one Meade 10 inch. The only thing you are missing is the brighter view the extra aperture can collect.

My TEC 140 is sharper than all of those scopes and much easier to use and manage - less cool down time, no collimation hassle, no worries about dew, MUCH better focuser, no mirror shift, and lighter (except for the C925).

It's all about personal choice. I tried to go for more aperture, but in the end I keep coming back to the better quality view.

Ron's Rule - The best scope for anyone is the scope they WANT to use, can't wait to use, and feel they have wasted a night if they don't use. :cool:

Cheers,

Ron

#19 Midnight Dan

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Posted 07 November 2010 - 03:01 PM

Hi Ron:

I have an 8" SCT and a SV110 ED. Probably a similar comparison to the 140 vs C11. Interestingly I find myself always reaching for the SCT.

For me, the SCT cool down is not a big deal. I just set it on the back porch when I get home from work. When I go out to view, it's ready. Dew? I just plug in the heaters and forget about it. I check the collimation from time to time but find I only have to adjust it once a year. And I find the viewing positions are much more comfortable with the SCT since the eyepiece height doesn't vary much from horizon to zenith. That, and the brighter, more detailed views keep me coming back to the SCT.

BUT ... that's a purely visual-observing statement. If I was doing AP, I'm pretty sure I'd be using the SV110 more due to some of the issues you bring up like mirror shift and focuser quality, plus the wider field of view.

Like you point out, it's about personal choice. Each type of scope has it's pros and cons and it depends which are important to the particular user, and the intended use.

-Dan

#20 10gauge

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Posted 08 November 2010 - 12:05 AM

Great discussion. At the same magnification, just how much wider is the view in a refractor, like the TEC 140, compared to a SCT, like the C11?...

A wide field of view associated with refractors has a unique grandeur that sounds appealing to my style of viewing. It's analogous to panoramic photography. Do any of you use the Televue Ethos eyepieces with refractors?... a 100+ degree view at the same magnification seems amazing...

Thanks

#21 SteveC

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Posted 08 November 2010 - 12:20 AM

I read these posts and I ask myself, why didn't I buy a 11" SCT or a 14" Dob, I'm missing out on a lot of stuff. I begin to make plans, because I forget that there is a reason why I bought the TEC140. I need an avid viewing neighbor, who own a large SCT or Dob, so that I can walk over and start viewing when it's convenient for me.


Steve,

I have owned two C11, one C925, and one Meade 10 inch. The only thing you are missing is the brighter view the extra aperture can collect.

My TEC 140 is sharper than all of those scopes and much easier to use and manage - less cool down time, no collimation hassle, no worries about dew, MUCH better focuser, no mirror shift, and lighter (except for the C925).

It's all about personal choice. I tried to go for more aperture, but in the end I keep coming back to the better quality view.

Ron's Rule - The best scope for anyone is the scope they WANT to use, can't wait to use, and feel they have wasted a night if they don't use. :cool:

Cheers,

Ron


I know exactly what you mean. Whenever I'm at a star party, I'll do the obligatory walk around, and I'm always happy to come back to the TEC. Almost everything I enjoy looking at, I can find in the TEC. Many DSOs are worthy only for their crossing off the list value.

#22 gnowellsct

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Posted 08 November 2010 - 12:50 AM

This must be understood:

=>Everywhere and always, at the same magnification, the fields of view are identical, and dependent only up on the eyepiece (eyepiece focal length, and eyepiece size, as in 1.25" or 2").<=

The nuanced commentary would say some telescopes vignette or do not achieve full field illumination etc.

One of the reasons why refractors excel at low power wide fields of view is that they do so with *full illumination* of the wide field eyepiece. For Newtonians, this presents a number of design complications, especially at shorter focal ratios. These problems tend to go away at intermediate magnifications (because one is centering on the field of view) and in SCTs you're at such a long focal length that illumination is not a huge performance issue (there is some drop off, but in any event, you don't get to pick your secondary size, as you may with Newts).

Anyhow field of view is strictly a function of magnification and eyepiece size.

There is a general thought out and about that SCTs are not wide field scopes. This is true, because SCTs typically can't go as low as 17 to 35x like refractors, or 35 to 50x like Newts. But once you get your Newtonian up to 75x, which is about where you'll be with your EdgeHD 11, the field of view will be identical with any other design, assuming equivalent apparent field of view in the eyepiece design.

regards
Greg N

#23 Midnight Dan

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Posted 08 November 2010 - 07:21 AM

Hi 10guage:

Like Greg points out, field of view at a given magnification will be the same for both scopes. It is dependent on the eyepiece apparent field of view and current magnification.

When we talk about a refractor having a wider FOV, we really mean wider *maximum* FOV. You can always use an EP with a longer focal length or wider AFOV to get to a wider field of view ... until you bump into the physical restriction of the focuser barrel size or some other restriction. For an SCT, this tends to be the baffle tube inside the OTA.

In my 8" SCT, the absolute widest true field of view I can get is about 1.9°. If I go wider, the view is clipped. But, in addition to that, SCTs experience off-axis dimming of the image. This becomes noticeable outside of 1.2° to 1.5° depending on your tolerance for the effect. It is MUCH more noticeable when you're imaging.

So, this is one place where a refractor wins. The maximum field of view will be substantially wider than an SCT's maximum ... AND it will be evenly illuminated across the field.

-Dan

#24 RAKing

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Posted 08 November 2010 - 08:02 AM

Great discussion. At the same magnification, just how much wider is the view in a refractor, like the TEC 140, compared to a SCT, like the C11?...

A wide field of view associated with refractors has a unique grandeur that sounds appealing to my style of viewing. It's analogous to panoramic photography. Do any of you use the Televue Ethos eyepieces with refractors?... a 100+ degree view at the same magnification seems amazing...

Thanks


We can't really do an "apples to apples" comparison in these scopes. As mentioned above, the FOV would be the same at the same magnification. The problem is finding comparable eyepieces to give the same magnification. The TEC has a focal length of 980mm, my old C11 was 2700mm - quite a difference and trying to adjust for the same magnification would be unfair to one scope or the other.

With the C11, you can go for much higher magnification and think you are closer to the object. With the TEC, you can soak in the whole picture. M27 can be spectacular in either scope. It's bigger and brighter in the C11, but it has a lot more context with the TEC.

To answer your second question - I use Ethos eyepieces a lot. They are magnificent in the TEC because the refractor's FOV opens your peripheral vision and you do have that feeling of floating above the object in a spaceship.

It's all a personal choice and YMMV. :cool:

Ron

#25 Patrick

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Posted 08 November 2010 - 09:11 AM

Having seen crowds of people use SCTs and APOs right next to them, I'd say the average person is instantly drawn to the views in the refractors.



My experience has been the reverse... :confused:

:smirk:

Patrick






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