56 replies to this topic

[Dave D]

10 years ago I owned a 10" LX200 that was definitely NOT in my sweet spot.  Assembly made me nervous, and the overhead of setup, running extension cords, cool down, and tear down time was significant.  Too many times (here in New England) I'd assemble the scope and start cool down and the clouds would roll in and I'd think of all the wasted time.  At the time it was also a budget buster that left me with nothing extra for dew protection or premium eyepieces so I sold it after a few years.

 

Shortly thereafter I discovered something.  I went back to my old 4.5" Tasco Newtonion and upgraded it with some good Plossls & Orthos.  Suddenly, this department store scope was producing surprisingly sharp views and its extreme portability, which allowed me to take it out on a moment's notice, had me out with the scope and enjoying it more than the 10".  Just by upgrading the eyepieces it became my new sweet spot scope.

 

This lesson led me to finally try the SCT route again last year when I bought an 8" EdgeHD on an AVX mount.  But before purchase, my criteria was that it absolutely HAD to be just as fast and easy to setup as my 4.5" Tasco (which had had an accident).  This led me to buy wheely bars, Tempest fans, a Dew Buster, and a good portable power supply.  By going with a smaller scope (8" vs larger) it also gave me the extra budget for some premium eyepieces and advanced accessories.  This scope is now the newest definition of sweet spot for me.  I can roll it out in a moment's notice, there is nothing to assemble, it cools down quick, and between the EdgeHD optics and some great premium eyepieces the views are easily superior to what I recall seeing in the 10". 

 

Someday I'd like to move up to a 14" scope--but if I do it will be an absolute requirement that setup, cool-down, and tear-down time and effort be equal to (or even better than) the 8" today. I'm not sure I have the room in the garage for such a huge scope on wheely bars, so it might take a backyard observatory to do that.

 

So as far as sweet spots go, I still measure it against the convenience and frequency of use of my old Tasco.  If the scope is bigger, but I'm able to use it just as conveniently and frequently as that old scope, then it must be in the sweet spot. If its not, I know now that I probably just won't have the time and patience to use it enough to justify the price.

Edited by Dave D, 23 June 2015 - 07:24 AM.

[Jon Isaacs]

 

So as far as sweet spots go, I still measure it against the convenience and frequency of use of my old Tasco.  If the scope is bigger, but I'm able to use it just as conveniently and frequently as that old scope, then it must be in the sweet spot. If its not, I know now that I probably just won't have the time and patience to use it enough to justify the price.

 

 

From my point of view, a sweet spot a moving target, it is an optimization.. a particularly desirable balance of capabilities and liabilities.  A 10 inch Dob is a sweet spot because it fits easily in a car, it's easy to carry and setup.  It's the biggest tube dob that is practical for most of us.  I do not ask my 16 inch to be as easy to setup as my 4 inch F/5.4 refractor, that is unrealistic, just dealing with the cover represents a significant effort.  Rather, how does the effort required compare to the reward at the eyepiece... Does the view justify the hassle?  

 

 

I think each of my scopes represents some sort of sweet spot, that is why I have several.. 

 

Jon

 

 

[A6Q6]

Hello All,

 

 is 8 inches the point where the detail is more obvious when it comes to reflectors?

 

 what is the appeal of the grab and go scope If say you have a 8 inch reflector and you take your grab and go setup outside " lets say a small refractor" is the ability to have that view less pleasing than in a larger scope really worth the time and effort.

 

As a beginner I am trying to figure out if a more portable scope whatever the size, would, in the end keep my interest as much as a scope that lived in  the "sweet spot".

 

Mike

Depending on your eyes (and that's another story that is never told) an 8" reflector like a dob or SCT is a "Sweet Spot". I have had fun with a 6" Mak for 35+ yrs.  An 8" Mak will be really heavy and so would an eq mounted 8" reflector.    8" is where you (start getting the ease in brightness)  for DSO and lunar and planetary and that's were the Sweet Spot part comes in. Bigger is better but you have to start somewhere.   For many of us Its a balance in capability and portability. Telescope design and storage is the key.  If you can't roll , carry,  or uncover your telescope in (one) smooth operation to observe, you will have a problem and there will be times when you will waste time (thinking) about taking out your scope and you will actually be happy if its cloudy, raining or snowing.  Accessibility is the name of the game for a telescope that gets used. You living arrangement will determine how big a telescope you will end up using/enjoying. Is it safe for you leave your scope outside unattended to acclimate to the temperature?  When you (for whatever reason) can't setup the big scope, the grab and go is there to help you out.  Less is more when using a small scope, you don't think about using it, you use it. With a grab and go there is hardly any "time and effort".  http://www.cloudynig...dpost&p=6639751

Edited by A6Q6, 23 June 2015 - 02:14 PM.

[gene 4181]

 my thought on it is, I have seen it mentioned here on CN many times that the planets really start to show good detail, it gets interesting at 200 power.  and 200 power is a 1 mm exit pupil in the 8in scope. and I probably use my 150 f5 quite a bit more than my 8in, but even in my 6in. its does get more interesting at 200 in the 6in too.

[photiost]

For backyard observing the 8in is easy to setup and offers excellent views.

 

When I go out to a dark site the 12" and 15" are the ones I usually take along.

[Adun]

My experience is that the bigger a scope is, the more you will see.
 
If I could only have one telescope it would have to be bigger than 8".
 
For most of us though, we have a big telescope and a little telescope.
 
My big telescope is a 12" dob, and my little telescope is a 5" Apo.

Eddgie, after 2 years, and your experience with Night Vision, ¿has your opinion changed?
 
If you were to advise someone on a roadmap for a convenient dobsonian that can work well now and be used for NV in the future for "going deep", ¿what aperture would you recommend?

[Richard Whalen]

8" makes a good grab an go as the mirror cools quickly to outside temps, around 15 min.

 

However you need at least 10" to see Pluto.  These are my 2 scopes of choice 8 & 10" both f/5.

Really? Seen Pluto in a 5.7" MNT. You must have crappy conditions if it takes a 10".

[Richard Whalen]

In your area I would want something that cools down quick like a 115mm to 140mm APO.

[GeneT]

In my opinion, a 12 inch truss Dob is the sweet spot. It gathers twice the light of an 8, is reasonable portable, gives outstanding views of the planets, numerous star clusters, numerous double stars, and performs fairly well on other deep sky objects such as galaxies and nebula. Of course, to max any telescope, get out to a truly dark sky site. 

[Eddgie]

 

My experience is that the bigger a scope is, the more you will see.
 
If I could only have one telescope it would have to be bigger than 8".
 
For most of us though, we have a big telescope and a little telescope.
 
My big telescope is a 12" dob, and my little telescope is a 5" Apo.

Eddgie, after 2 years, and your experience with Night Vision, ¿has your opinion changed?
 
If you were to advise someone on a roadmap for a convenient dobsonian that can work well now and be used for NV in the future for "going deep", ¿what aperture would you recommend?

 

 

As far as having two scopes go, not really.   My little scope now is a 6" f/2.8 reflector and the stuff I can see is amazing.   With a 6" reflector at f/2.8 though, while I an see galaxies like crazy even from my light polluted yard, they are often so small that I can't seem much detail in them simply because they are so small. I can see to many Globulars to count, but the very small scale means that they don't resolve well because the centers are so dense with stars that they just run together.

 

When I use the 12" dob, because it is f/4.9, nebula and galaxies do not look as bright, but larger nebula like the Veil show considerable structure and using Barlows, it is possible to resolve a huge number of Globulars.

 

 

 

If you made me choose an off the shelf scope today for NV I would probably go with a 10" dob for all of the reasons that makes the 10" dob the "C8" of the Newtonian world. 

 

 

For someone interested in NV, I would say that a medium sized reflector f/5 or faster is about the best way to go (and larger if you can handle it).    NV allows you to do things like use a 55mm Plossl, something that would not benefit you with brighter images using a standard eyepiece.  In my 12" dob, a 41mm eyepeice will give me an effective focal ratio of about f/3.2, and for smaller objects, I can go to prime focus or use Barlows. 

 

This then would be my recommendation for a scope that would eventually be used for NV:   A mid sized reflector with a focal ratio of around f/4 to f/5 (and faster if possible, but this is typical in the 10" range and it is not until you get to 16" where f/4 is common in a dob).  I will leave it to each individual to determine what "Mid sized" means because that will differ by individual. 

 

NV is crazy good and it does things that are impossible to do with conventional eyepieces, but just as with everything else in astronomy, there are always compromises and just like with regular eyepieces an telescopes, the best approach is to usually have one smaller and one larger scope.

 

I dumped the 5" Apo. Just not my thing.  To big and heavy for the aperture.  The 6" f/2.8 is far more exciting to use.

 

(If I were to build a telescope today for NV, it would be a "Travel Dob"  style truss scope made with the optics from a 12" f/4 imaging Newtonian. This is because this is about the largest telescope I could see myself taking out to dark skies. If the truss assembly did not fit in the back of my Prius all assembled, I would go smaller.  If I have to put it together in the field, I am no longer interested. If I could pull the base out, set it on the ground, pull the truss tube out and dump it in, I would be on board to move it. No more assembly for me. I know what I don't want to do anymore and on that list is putting a telescope together and taking it apart to be able to use it).

Edited by Eddgie, 06 October 2017 - 08:28 PM.

[Adun]

This then would be my recommendation for a scope that would eventually be used for NV:   A mid sized reflector with a focal ratio of around f/4 to f/5 (and faster if possible, but this is typical in the 10" range and it is not until you get to 16" where f/4 is common in a dob).  I will leave it to each individual to determine what "Mid sized" means because that will differ by individual. 

 

Thank you.

 

I think there is probably an aperture at which an NVD is a better value per dollar addition than an aperture upgrade. I don't have the experience to even try to guess where that point is, but one thing I learned from EAA is that raw aperture is too much of a "brute force" approach at solving the "need to see more" problem.

[fcathell]

I think the answer to your question (based on doing amateur astronomy for 40+ years) is that yes, all things considered, an 8" scope is probably the best size for decent aperture and portability. Having many variations of 8" SCTs in the past, I would say that it is an ideal general purpose scope. The same could probably be said for an 8" F/5 or F/6 Newt if it has a good mirror.  A large scope won't buy you much in poor skies, however, a small scope will surprise you in a dark, transparent sky venue.  As I've gotten older, the size/weight of my scopes have diminished to the point where now my largest aperture is 6".  I have always believed in this axiom: Generally, the amount of observing you do is inversely proportional to the size/weight of the scope! (Well, unless you have an observatory).

 

Frank

Tucson

[Eddgie]

If there is thinking that a future goal will be for NV use I would absolutely go with  mid sized Dob f/5 or faster. 

 

Of course if you asked me what scope would be the one I would recommend to someone looking to buy a scope for use with regular eyepieces, my answer would be the same.

[Richard Whalen]

I think for a Newtonian, a 8" mounted on a GEM was a sweet spot 30 years ago. Today with the dobs being massed produced I would say 12.5" with a f4 to f5 mirror of good quality. A good friend still has his Meade 826 he bought new in the early 1980s also has a Starmaster 12.5" EL. The EL is easier to set up, takes up less space and shows a whole lot more. Back when we had heavy GEMs an 8" was about all most wanted to deal with night after night . Anything larger and you needed a station wagon, van or truck.

[Jared]

An 8" reflector or catadioptric is, indeed, a "sweet spot" for a telescope.  It is just large enough that you are seeing limited on the planets and moon from the average location on an average to above average night (look up Fried parameters if you are interested--the typical diameter of a seeing cell is 100mm to 200mm).  Yet it is small enough to be easily transportable and affordable.  I think it's really as simple as that.  You get diminishing returns above eight inches or so in a reflector when used for the planets.  Not zero returns, just diminishing.  And you've got enough aperture to generate a lifetime of observations, especially from a dark location with a 200mm diameter objective.  

 

Will you see more with a bigger scope?  Sure.  Will it cost more?  Both in dollars and in effort to transport?  Absolutely.  That's why this size has been popular for so many years.  Not too expensive, generally cools fairly quickly, easy to transport, and generally seeing limited for double stars and planets.  

 

That being said, there is no "perfect" scope for all situations.  If my favorite thing to do was track down faint galaxies, whether from my back hard or from a dark sky site, I would want more than 8" of aperture.  Something like a 12" Dobsonian would be a better choice.  So for this use, an 8" is a little on the small side.  If, however, I liked imaging deep sky objects, the costs to work with an 8" reflector vs. an 80mm refractor might be substantial--sturdier mount requirements, differential flexure concerns, issues with coma and/or readily available flat field adapters, etc. make imaging with an 8" scope much more of a commitment than an 80mm.  For this purpose, an 8" scope is a bit too large to be considered a sweet spot.    So there are lots of specialists who would have a strong preference for something different.  But overall, it's as close to a good general purpose amateur telescope as one can get.

[Jeffmar]

I think 24 inches or bigger is a sweet spot for a reflector. I love looking through huge scopes at star parties. The beauty of these large scopes is how bright and detailed images are. I also don't have to set those big scopes up nor pay for them so I just have go for whatever I can comfortably lift which is my c11. The mount is a bigger pain for me than 28 pounds of optical tube. 

Edited by Jeffmar, 10 October 2017 - 07:04 PM.

[corax]

I think for a Newtonian, a 8" mounted on a GEM was a sweet spot 30 years ago.

I got my C8 30 years ago. The 8-inch SCT was still king, but Dobs were becoming commercially available and generating a lot of interest. Maybe there were still some 8" GEM-mounted Newtonians being sold, but they weren't very popular. And while at one point they may have been about the best an amateur could hope for, was a 4-foot-plus column on a GEM with an impossibly-positioned eyepiece ever "sweet"?

[Scott Beith]

I think as an all around scope an 8" SCT or an 8" reflector is a solid choice.  I think the sweet spot for a reflector is a bit larger though.  The thing a reflector offers over a refractor is aperture.  Since a 5" apo is a sweet spot in the refractor range and the performance is similar to an 8" reflector (yes an 8" will go a bit deeper) I think the sweet spot for a reflector should do what reflectors do - gather more light than a refractor.  Thus the 10"-12" realm is in my opinion the sweet spot for a reflector.  It allows a reflector to best the sweet spot refractors in light gathering by a noticeable amount capitalizing on its strengths.

[Don W]

In my experience, an 8" SCT is about right for most people. The problem with SCT's is not necessarily the weight, but the bulk. At 8" it's manageable, at 10" and up, they get a bit awkward and heavy. I think of it in terms of being portable and transportable, with the 8" being the former and 10" plus the latter.

 

I agree with others here that when it comes to dobsonians, the portable size can be up to around 12" and anything above is transportable. It's all a matter of opinion of course.

 

I think it's interesting to note that prior to the mid 80s or so, an 8" scope was considered to be pretty big. I was in awe of a friend that had a 12.5" dob built using the OTA from a Meade Research Grade Equatorial.

 

Having owned scopes up to 20" has spoiled me and it's hard for me to think in terms of anything less than 10". Although I have a couple of very nice refractors of 80mm and 4" and a C11, I still find myself wanting more. I picked up a 14.25" mirror and hopefully that will be enough for me. I'm getting too old to wrestle with those big ones anymore.

[CrazyPanda]

is 8 inches the point where the detail is more obvious when it comes to reflectors?

No. There's really no single "inflection point" where the aperture goes from too small to just right. 8" is certainly a very capable aperture, but it's no more magical than 4" or 6" or 12" etc. Just depends on your targets and expectations are. It's just one aperture along a very broad spectrum.
 
What *is* more concrete though, is actual portability. Either you can transport it, or you can't. It's a binary decision. So get the biggest scope you can both afford, and transport. 
 
Also note that a smaller scope in a darker sky will be preferable to a larger scope in a light polluted sky. So if there's a certain size that makes it possible to transport, while the next size up makes it impossible, get the size that's possible to transport, even though it's smaller.
 
Maybe that's 8" for you. Maybe it's just 60mm. That will be up to you to evaluate. 
 
BUT, definitely get the largest possible aperture that fits within your budget and transport requirements. Don't try to aim for a "sweet spot" aperture alone, because no such thing exists.

Edited by CrazyPanda, 11 October 2017 - 11:14 PM.

[Sarkikos]

8" is the sweet spot for SCTs.

 

10"-14" for Dobs.

 

5" for APO/EDs.

 

6" f/5 for achromats.

 

This is considering what the telescope can show you vs how much effort you need to set it up.

 

Mike

Edited by Sarkikos, 12 October 2017 - 10:05 AM.

[RAKing]

Hello All,

 

I have been doing some reading about reflectors with regards to apature vs portability.  There seems to be info that suggest that an 8" reflector: newt, maknewt, sct is a good balance between apature and portability.

 

I guess like most beginners I would like any reason real or otherwise to buy a BIG scope.  While I realize that it is my decision in the end , is 8 inches the point where the detail is more obvious when it comes to reflectors?

Short answer: No, not really.

 

First of all, you listed three different designs and if I had my choice, I would take an 8-inch f/6 Newtonian, or Mak-Newt over any 8-inch SCT -- especially if I wanted to see more detail.  Sorry, but the massive 33 percent CO of the typical f/10 SCT hurts contrast a lot more than the sub-25 percent CO of the Newt or Mak-Newt.  I have set up my "little" 5-inch refractor next to C8 SCTs at a number of star parties and I have been able to show them nice objects in my scope that they could not see in their scopes.  Better contrast was the reason.

 

I don't think there is any "magic" number.  As others have noted above, more aperture shows more. Size wins and it is mostly a matter of what you can afford and what you can manage.

 

BTW - More Experience helps, too.  The more often you go out and look at stuff, the more you will see. 

 

Cheers,

 

Ron

[Eric63]

8" is the sweet spot for SCTs.

 

10"-14" for Dobs.

 

5" for APO/EDs.

 

6" f/5 for achromats.

 

This is considering what the telescope can show you vs how much effort you need to set it up.

 

Mike

And 6"F5 for a mounted reflector

[Sarkikos]

 

8" is the sweet spot for SCTs.

 

10"-14" for Dobs.

 

5" for APO/EDs.

 

6" f/5 for achromats.

 

This is considering what the telescope can show you vs how much effort you need to set it up.

 

Mike

And 6"F5 for a mounted reflector

 

Well, all of the scopes in my list would be mounted.  I'm not holding them in my arms while I'm viewing objects in the sky.  Though I suppose that could be possible for a 6" f/5 Newt.    

 

Mike

Edited by Sarkikos, 12 October 2017 - 11:28 AM.

[Sarkikos]

The sweet spot for grab-n-go scopes (= take everything out the door in one trip and set up near your house):

 

80mm f/7.5 (C80ED) for APO/EDs.

 

90mm f/12.9 (C90) for Maks.  (Maybe a 100mm Mak?  I've never owned one.)

 

4.7" f/5 (ST120) on alt-az mount for achromats.

 

6" f/5 on alt-az mount for Newts.

 

6" f/10 (C6) on alt-az mount for SCTs.

 

Just put them all on alt-az mounts.  I don't do GEMs.  GEMs are not practical if you need to move the scope around to avoid obstructions like trees and buildings.

 

Mike

Edited by Sarkikos, 12 October 2017 - 11:33 AM.