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Jumping from a 16" to a 20" dob, worth it?

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#1 mantrain

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Posted 21 April 2014 - 12:28 PM

I made my own 16 " dob, and I really love it. But all my tools, and extra wood just sit there now with nothing to be done. There is this 20" primary and secondary for sale, and I am really considering it. But am not sure how much better the viewing will be with a 20." One thing is for sure, the 16" is at the edge of being loaded by one person w/out wheel-barrow handles. So yeah, the 20" would need that.
Just wondering, would a 20" be that much better? 200sq" of glass vs 314 sq ", plus $4000 in parts and lots of labor (of love).

But right now I am not totally convinced it's going to be that much different. I mean, I think they are both sort of in the same visual realm. But I have not really looked too much through a 20." I have looked through an 18" and I couldn't see too much difference.

#2 JustaBoy

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Posted 21 April 2014 - 12:48 PM

It's the same difference as going from an 8" to a 10", only with a lot more weight and size increase.

There are laws of diminishing returns for things that have to be hefted about:-(

How about using the extra wood, tools and know-how to build a slick 10" Travel Scope?

Keep the 16" too, of course.

#3 Pinbout

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Posted 21 April 2014 - 01:13 PM


How about using the extra wood, tools and know-how to build a slick 10" Travel Scope?



Yeah, how about a 10" or 12" slick travel scope. very light and compact...don't forget to build feet into the design. ;)

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#4 craigLambert55

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Posted 21 April 2014 - 01:37 PM

An often mentioned rule of thumb is to increase aperture 1.4 X to get the "wow factor." In your case that would be 22." The 20 would provide 56% more light grasp. I think you would notice a difference in terms brighter DSO's becoming somewhat brighter with more apparent structure in bright galaxy's and better resolve on globular clusters. Having said that, I think the greater difference between the two would occur at the threshold of resolution enabling you to see fainter objects such as more members of galaxy clusters etc.

#5 jzeiders

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Posted 21 April 2014 - 02:18 PM

I would suggest that the 20" would be worth it only if you have pristine sky, dark, transparent, steady. Otherwise you will likely find the atmosphere limiting the performance. The hassle factor, weight, bulk, height all are magnified over the 16". I have seen several guys go from 12" to16" then 20", 22", and 24" scopes and sell them to move back down to something in the 12-16" range due to hassle factor verses performance. Remember bigger scopes are more adversely affected by bad seeing. If you have a site where it can be setup in some permanent location with attendant shelter, then bigger may be the way to go. You may need to go 22-24" to see a big difference over your 16. My 17" set up next to a 20" does not suffer much at all from the difference in aperture at our local observatory site. It has a good smooth mirror, is usually better collimated, and is much less of a hernia factory.

YMMV

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#6 André Heijkoop

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Posted 21 April 2014 - 03:10 PM

You're thinking about a 20". I say do it if you still can handle a big Dobson. If you wait a couple of years longer you might not be able to handle it anymore and regret that you never made the 20".
I made a 24" 2 years ago with that exact reasoning and never regretted for a moment.
At home I take the 24" out for a solar system tour. And at a dark site use it for the dso's.

BTW
I also have a lightweight 14" Dobson which have never seen any photons since the 24".

#7 mantrain

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Posted 21 April 2014 - 03:29 PM

You're thinking about a 20". I say do it if you still can handle a big Dobson. If you wait a couple of years longer you might not be able to handle it anymore and regret that you never made the 20".
I made a 24" 2 years ago with that exact reasoning and never regretted for a moment.
At home I take the 24" out for a solar system tour. And at a dark site use it for the dso's.

BTW
I also have a lightweight 14" Dobson which have never seen any photons since the 24".



Still, It doesn't seem like the jump from a 16" to a 20" justifies the work/cost involved.

Now tell me about the 24..Others here are saying it takes long to cool. hard to move, etc, etc.
I am thinking the wheelbarrow handles will help the move aspect. But what about the cooling?

#8 okieav8r

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Posted 21 April 2014 - 04:45 PM

Still, It doesn't seem like the jump from a 16" to a 20" justifies the work/cost involved.



Judging from your statement above, you may have already answered your own question. If you haven't looked through both 16" and 20" telescopes, it's hard for the rest of us to tell you whether it would be worth your while. Moving from a 16" to a 20" will show you more objects and more detail in the objects you're familiar with viewing through your 16", regardless of what kind of skies you have, though you may find the improvement to be subtle. Enough to make it worth your while? You need to attend a star party or club party and make the comparison for yourself. Until you do, you really aren't going to know.

#9 lpn678

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Posted 21 April 2014 - 04:46 PM

You're thinking about a 20". I say do it if you still can handle a big Dobson. If you wait a couple of years longer you might not be able to handle it anymore and regret that you never made the 20".
I made a 24" 2 years ago with that exact reasoning and never regretted for a moment.
At home I take the 24" out for a solar system tour. And at a dark site use it for the dso's.

BTW
I also have a lightweight 14" Dobson which have never seen any photons since the 24".



I can send you my address if this needs a new home :jump:

#10 Jon Isaacs

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Posted 21 April 2014 - 05:00 PM

My question/thinking:

How long have you had your 16 inch? How many hours of eyepiece time have you spent together, how many nights?

What are you hoping to gain with the larger scope?

My thinking is that the time to move up in aperture is when you (me or whomever) have becomed skilled enough with your present scope that more aperture and not more experience is needed to see more.

Jon

#11 mantrain

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Posted 21 April 2014 - 05:19 PM

My question/thinking:

How long have you had your 16 inch? How many hours of eyepiece time have you spent together, how many nights?

What are you hoping to gain with the larger scope?

My thinking is that the time to move up in aperture is when you (me or whomever) have becomed skilled enough with your present scope that more aperture and not more experience is needed to see more.

Jon


Jon with your logic I should exchange my 16" for a 4."
naturally an amateur astronomer (weekend warrior at best)
will take a life-time to exhaust what can be found in a 16."

We are talking about a labor of love here, a recreational activity.

you all read the article about the truck driver who built his 70" ?? IT was his labor of love.

The desire for a larger scope is purely, well almost purely, an emotional one. Something about a large piece of glass that excited me. Plus I enjoyed putting together my 16"
I am not sure there is a logical explanation though. I think they are within the same observing realm. no object will be that much different ( I do not think). But, yeah, some subtle differences will be there.
My brain tells me "no". My heart tells me "maybe."

#12 GeneT

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Posted 21 April 2014 - 05:20 PM

I offer the advice Peter Smitka (R.I.P.) gave me about 20 years ago. I had purchased a 12.5 inch Portaball from him. He was offering a 14 incher. He said that one should double the light gathering before moving up. That would mean going from a 12.5 inch to an 18.

Yes, going from a 16 to a 20 inch would give you a boost. However, as others have said, that boost will also give you a boost in hassle. If you can handle a 16 incher, are you sure you can handle a 20?

I settled on a 12.5 inch Portaball. It is very portable, yet large enough to give me some great views on moderate to brighter galaxies, nebula, globulars, and planets.

#13 mantrain

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Posted 21 April 2014 - 05:24 PM

I offer the advice Peter Smitka (R.I.P.) gave me about 20 years ago. I had purchased a 12.5 inch Portaball from him. He was offering a 14 incher. He said that one should double the light gathering before moving up. That would mean going from a 12.5 inch to an 18.

Yes, going from a 16 to a 20 inch would give you a boost. However, as others have said, that boost will also give you a boost in hassle. If you can handle a 16 incher, are you sure you can handle a 20?

I settled on a 12.5 inch Portaball. It is very portable, yet large enough to give me some great views on moderate to brighter galaxies, nebula, globulars, and planets.


well a 22" would be just under the 2X light gathering.
While a 24 would be way over.

#14 JimMo

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Posted 21 April 2014 - 05:26 PM

I made a jump from a 10" to the 14.5" in my signature below. I had viewed through many 18" reflectors mostly Obsession and Webster before I decided on the 14.5". I was 47 when I built it knowing I didn't care for ladders and the size and weight would become a factor in the future, I'm 57 now and I'm thinking about rebuilding it to save some weight and bulk. Another reason I chose this size is because I'm short. If I was 6' tall that would have factored in and I probably would have gone with an 18".

As far as comparisons go and like it was said up thread and in my experience the 14.5" f4.3 keeps up very well against 18 and 20" telescopes, losing a bit of resolution and overall brightness but still seeing most DSO's, just not the threshold faint fuzzies. If I ever come into gobs of money for sure I'd go bigger AND faster with a nice piece of dark sky real estate under it. Since I have to haul my dob wherever I roam this is as big as I'll ever go.

#15 Starman1

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Posted 21 April 2014 - 06:01 PM

I look at it this way: I don't want to move up unless I gain a full magnitude. Why? Because my experience indicates there is a half magnitude of variation in the sky alone, from night to night. I wouldn't want to move up, only to discover the smaller scope on a good night can outperform the larger scope on a night of mediocre transparency.
That means, for me, the jump is from a 12.5" to a 20", or 2.512X by area. That's a serious consideration.
For a 16", it's a jump to a 25". That will wow you with the difference in appearance....of everything, all the time--not just on good nights.
But, think of the weight and size. It's wheelbarrow handles and ramps to put it in your SUV or truck. And it's a fairly tall ladder to use it, unless you get a short f/ratio version and pay really big bucks.

#16 Cames

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Posted 21 April 2014 - 06:46 PM

Have you considered the ergonomics of observing with the 20?
Will you love being perched on the taller ladder? If you can't get or stay comfortable while looking through the eyepiece you may eventually resort to the 'peep-and-run' mode of observing....That's where you miss a lot of the subtle stuff that can be a major factor in your satisfaction of what you and the 20 can accomplish together.

You may also find that it becomes drudgery to change eyepieces or filters after a few hours. The discomfort of the wear and tear on your shins, knees and soles of your feet can entice you to close up shop early for the comfort of your recliner or sleeping bag.

Remember, if you’re not out there looking, you probably won’t see anything.
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C

#17 Jon Isaacs

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Posted 21 April 2014 - 07:19 PM

Jon with your logic I should exchange my 16" for a 4."
naturally an amateur astronomer (weekend warrior at best)
will take a life-time to exhaust what can be found in a 16."

We are talking about a labor of love here, a recreational activity.

you all read the article about the truck driver who built his 70" ?? IT was his labor of love.

The desire for a larger scope is purely, well almost purely, an emotional one. Something about a large piece of glass that excited me. Plus I enjoyed putting together my 16"
I am not sure there is a logical explanation though. I think they are within the same observing realm. no object will be that much different ( I do not think). But, yeah, some subtle differences will be there.
My brain tells me "no". My heart tells me "maybe."


A 4 inch and a 16 inch would probably serve you better than a 20 inch and a 16 inch..

But if the hunk of glass and building the scope are what excites you, that is logic enough... Some people seem to enjoy building scopes more than they enjoy looking through them..

Jon

#18 bvillebob

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Posted 21 April 2014 - 08:20 PM

You didn't say what kind of 16" you have. If it's a commercial scope, like a Meade or Orion, have you considered building a nice unit using the same optics? Or, if it's a commercial mirror, maybe have the mirror refinished by a high-end optics shop? Or, consider a smaller, higher quality scope as an alternative.

I live in the boonies and don't get to use other folks' equipment for comparisons so don't have a lot of experience with different scopes. I also have a 16" and went the other way, I built a 12" for portability and quick cool down. I picked up a used Hubble Optics mirror from the ads here and recently finished the scope and have been blown away at the difference in planetary views with the new mirror, they're so much higher contrast that then GSO mirror in the 16". I now find myself using the 12" for planetary viewing rather than the 16" due to the quality of the mirror, even though it's a lot smaller.

#19 TCW

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Posted 21 April 2014 - 08:39 PM

My question/thinking:

How long have you had your 16 inch? How many hours of eyepiece time have you spent together, how many nights?

What are you hoping to gain with the larger scope?

My thinking is that the time to move up in aperture is when you (me or whomever) have becomed skilled enough with your present scope that more aperture and not more experience is needed to see more.

Jon


Jon with your logic I should exchange my 16" for a 4."
naturally an amateur astronomer (weekend warrior at best)
will take a life-time to exhaust what can be found in a 16."

We are talking about a labor of love here, a recreational activity.

you all read the article about the truck driver who built his 70" ?? IT was his labor of love.

The desire for a larger scope is purely, well almost purely, an emotional one. Something about a large piece of glass that excited me. Plus I enjoyed putting together my 16"
I am not sure there is a logical explanation though. I think they are within the same observing realm. no object will be that much different ( I do not think). But, yeah, some subtle differences will be there.
My brain tells me "no". My heart tells me "maybe."


Someone needs to send a 60mm scope to Palomar and tell them they have it all wrong! ;)

#20 davidmcgo

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Posted 21 April 2014 - 09:00 PM

I can see a pretty pronounced difference between my 15" and a friend's 18" when we set up together, especially on galaxies. Planets are pretty equivalent where cool down, collimation, and tracking matter more, but under dark skies, the 18" seems to reach almost twice as deep.

I have a 15" instead of an 18" because my little house, detached garage, and steps between mean I hand carry everything to the car and can't use the wheelbarrow handles. The 15" mirror box is my max to carry. But if that wasn't a constraint, you can bet I would have an 18" instead.

So I think there is a big jump from 16" to 20" and would certainly entertain the idea if I could handle the physical aspects of it. I would still want something in the 4" to 8" range for home use, and would not have a 16" and a 20" at the same time. But for the dark sky trips, a 20" would be awesome.

Dave

#21 Achernar

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Posted 21 April 2014 - 09:31 PM

The best way to answer this question is to attend a regional or national star party where folks bring these very large Dobs. Bring yours along too, then compare what you see through yours and the larger scopes. Then you can decide if a bigger telescope is worth the greater bulk, height, weight and expense. One reason why I settled on a 15-inch was that if I went much bigger, it would be impossible to get it through the door. Another was the fact the optics would be nearly twice the price, and there's no way I can get it into my car.

Taras

#22 rocco13

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Posted 21 April 2014 - 09:34 PM

On a slightly smaller scale, I went from a 12 to a 15 and honestly was not wow'ed like I expected. Perhaps my expectations were too high, although I don't really think so. Sure, the 15 showed a little more, and went a bit deeper, but after two years of handling the bigger & heavier scope, I noticed I was taking it out less and less. So, I sold it and went back to a 12.

Unfortunately I was forced to sell off that 12 and currently have a 10, but I discovered through trial and error that the 12 is my personal 'sweet spot'.

#23 mantrain

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Posted 21 April 2014 - 09:52 PM

Oh, and how to I spend the $$ on the glass and not have the wife find out??

#24 Peter Natscher

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Posted 21 April 2014 - 10:00 PM

Once you've decided that your area you observe from has decent seeing and darkness to support a +15" Dob, I think the next issue is transporting it. Build it so that it can be rolled into your vehicle so that you don't have to struggle lifting anything. Choose a thin primary mirror for less scope weight and a faster cooling time. That's what I'v egot in my 24" 3.3 StarStructure Dob. A fast and thin primary on a great cell with small boxes and rigid frame. I've observed with Dobs of 14.5", 18", 20" and two 24's and have enjoyed all of them. I had great views with my past 20" Starmasters -- completed both Herschel Object lists (I & II) with them. My current 24" f/3.3 StarStructure LE with a Kennedy primary, is fantastic on everything from DSO's to Lunar and planets. Just last week, I bino'd Mars at 450X and it was awesome -- fine detail and lot's of planetary color. It shows much more galaxy halo and arms than my past smaller Dobs. Side by side with another observer's 15" f/4.5 Obsession, the Hickson galaxy clusters were much brighter. The brighter images of larger aperture provides a better view of DSO's when using narrow-band filters. I say go for a 20" or even a 24" if you can transport it. You'll build up the physical strength needed to comfortably manage a larger scope just by using it. You only live once. Managing my 24" SST helps motivate me to keep myself in good physical condition.

I made my own 16 " dob, and I really love it. But all my tools, and extra wood just sit there now with nothing to be done. There is this 20" primary and secondary for sale, and I am really considering it. But am not sure how much better the viewing will be with a 20." One thing is for sure, the 16" is at the edge of being loaded by one person w/out wheel-barrow handles. So yeah, the 20" would need that.
Just wondering, would a 20" be that much better? 200sq" of glass vs 314 sq ", plus $4000 in parts and lots of labor (of love).

But right now I am not totally convinced it's going to be that much different. I mean, I think they are both sort of in the same visual realm. But I have not really looked too much through a 20." I have looked through an 18" and I couldn't see too much difference.



#25 Pinbout

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Posted 21 April 2014 - 10:11 PM

Oh, and how to I spend the $$ on the glass and not have the wife find out??


that's not for us to tell you.

I'd spend the money on a better mirror than a bigger mirror. :grin:

if you go bigger, better chances not as good a figure, rolled edge.

from .707 zone to the edge is the most important part of the mirror cause it delivers more than 1/2 the light to the airy disc.

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