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Should I jump from 10 inches to 15 or 18?

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#76 WyattDavis

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Posted 29 May 2019 - 03:26 AM

An update:

1 magnitude jumps:

6">>10">>16">>25">>40"

8">>12.5">>20">>32">>50"

See any popular sizes there?

For 0.5 magnitude jumps, combine the rows.

But I recommend 1 magnitude jumps whenever possible.

It does make me wonder why there are 11", 14.5", 15", 17.5", 18", 22", 24" and 28" sizes.

My guess is that each person has a maximum tolerable size and that sometimes the 1 magnitude jumps are too much to handle.

 

Well, 1 magnitude makes a profound difference.  Any size larger than that will be >1 magnitude, so even more impressive.

8 to 16" is about a magnitude and a half, and a 16" can be moderately portable.

 

I have adopted the 1-magnitude jump as a good guide rule for getting significant differences - you could argue for .75 or whatever but 1 is hard to deny. I'm still holding at 10" and wouldn't do anything less than 16" if I ever went larger. For sure:  going from 4" or 6" up to a 10" scope is a completely different viewing experience and can be easily justified IMO in terms of increase-in-wow-factor while still maintaining relative ease of use and transportability. Beyond that, the size/weight/cost start to become more formidable. 

 

I do think it is a fact that larger scopes can be easy to use. If you don't plan to/need to transport the scope in the first place, that is one case. And, even if you do transport the scope it can be done with the right setup. My benchmark for this is havasman and his 16" dob. He transports and fields it by himself often (ok, he does have a dog with him, too...), but he has the right equipment and physical setup at home:  garage, driveway, mini-van-style vehicle with low, long, wide cargo deck, etc. And, yes, that jump up to 16" is a clear next-level of viewing experience over a 10" scope. And, an f/4 16" would even keep both of my feet on the ground for viewing, but...

 

I have a small shed and don't have enough room to have what I would consider to be a transportable scope (my 10" dob) AND a larger scope that doesn't travel. And, I have garden paths between my shed and my driveway (uneven, not good for rolling/hauling heavy equipment) and a truck with a tall bed that would not allow me to easily load/unload a 16"+ mirror box solo. All that - plus the cost - is keeping me comfortably seated and viewing through my 10" for now. NV aside, it still seems that the biggest gain to be had is still darker sky, which for me means the scope has to be easy to transport.


Edited by WyattDavis, 29 May 2019 - 03:28 AM.


#77 TareqPhoto

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Posted 29 May 2019 - 08:09 AM

And that one i am planning to get will be in my house or yard only, i have no plan of moving it around, planets from my yard are clear enough so i won't do long transportation, not yet with observatory or permanent pier, but i can always have hands/helpers if i have to haul this large scope around my house.



#78 25585

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Posted 29 May 2019 - 08:44 AM

An update:

1 magnitude jumps:

6">>10">>16">>25">>40"

8">>12.5">>20">>32">>50"

See any popular sizes there?

For 0.5 magnitude jumps, combine the rows.

But I recommend 1 magnitude jumps whenever possible.

It does make me wonder why there are 11", 14.5", 15", 17.5", 18", 22", 24" and 28" sizes.

My guess is that each person has a maximum tolerable size and that sometimes the 1 magnitude jumps are too much to handle.

My largest is 12.....so a 20 next?! drinkspit.gif scared.gif tonofbricks.gif



#79 Achernar

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Posted 29 May 2019 - 03:56 PM

Going from 10 to 15-inches usually made an obvious difference in how objects looked under the same sky conditions, so yes if you want a larger telescope going to a 15 or 16-inch will allow you to see objects one full magnitude fainter. An 18-inch will do even better, but the difference between a 15 and an 18-inch is much harder to see.

 

Taras


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#80 WyattDavis

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Posted 30 May 2019 - 06:09 AM

My largest is 12.....so a 20 next?! drinkspit.gif scared.gif tonofbricks.gif

Yes, it is written.


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#81 macdonjh

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Posted 30 May 2019 - 06:55 AM

Disclaimer: I have not read this thread, other than the original post.  That said, I'm going to post anyway...

 

My last bout with aperture fever was cured by jumping from a 10" to a 14".  That increase in aperture proved to be worthwhile for me.  With my 10" (and the C11 that preceded it) I ignored objects fainter than m11 at my club's dark site (green zone).  With my 14", I regularly see largish m11 objects and compact objects of m12.5 or even m13 on really good nights.  Show piece objects are noticeably brighter, resolution is a bit better, etc.

 

As to jumping to 15" or 18", assuming equal optical quality, there is no reason not to buy an 18" scope.  It will do everything a 15" scope will do but a bit "more".  Living with and transporting an 18" scope; however, will be different than a 15".  Some questions to ask yourself (I have no doubt that the following is a repeat of previous posts):

  • can you afford the 18" scope?
  • do you have room to store an 18" scope?
  • is it too heavy for you to manage by yourself?
  • is it too bulky for you to manage by yourself?
  • can you get all the components into your vehicle so you can get it to dark skies?
  • will the extra height of the 18" scope mean the difference between not needing a ladder and needing a ladder?
  • when your new scope is at home (you know, most of the time), will it be so much hassle that you won't want to use it?  I know, that's another reason to keep your 10" scope.

Before I bought my C11 years ago, the other option I considered was a 15" Dobsonian.  I chose 15" because the mirror/ rocker box would fit in the back seat of my car, the truss poles would fit (stretching front seat to back seat) and I figured the majority of the time I could observe standing on the ground.  If I needed a step up, it would be just that, a two-step step stool.  Nat that this is relevant, but I chose the C11 because I could use it on my equatorial mount; with the Dobsonian scope I'd have wanted a Servo-Cat so I could have go-to.  That proved too much expense at that time.

 


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#82 pyrasanth

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Posted 30 May 2019 - 07:04 AM

An important consideration for me with larger aperture is image scale. The same objects appear bigger in the larger telescope and if the F ratio is the same you get a bigger image with the same brightness and that alone is worth the jump. One of the considerations is how large an image appears at the focal plane and for me short focal length big optics are the holy grail especially if you move into astrophotography- the Dream range of telescopes are just that- big aperture- short focal length at a price to make you cry!



#83 vdog

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Posted 30 May 2019 - 09:48 AM

My last bout with aperture fever was cured by jumping from a 10" to a 14".  That increase in aperture proved to be worthwhile for me.

I think this is the jump that I'll look at in a few years as well.  It's still nearly twice the aperture of a 10".



#84 macdonjh

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Posted 30 May 2019 - 09:45 PM

I think this is the jump that I'll look at in a few years as well.  It's still nearly twice the aperture of a 10".

Nearly twice the area...



#85 vdog

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Posted 30 May 2019 - 09:56 PM

Nearly twice the area...

I stand corrected.



#86 TareqPhoto

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Posted 31 May 2019 - 08:45 AM

So the jump or the increase in aperture do matter after all, thanks all.



#87 Richard Whalen

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Posted 31 May 2019 - 10:30 AM

The OP? mentioned planetary observing? If this is his primary interest that changes the equation somewhat. If this is the case I would go with a 12.5" or 14" at f5 to f6 for the smaller CO. I noticed a real jump visual going from 10" to 12.5", though for dso work 15" to 16" is a sweet spot. Right now on CN classified there is a 14" Parks on a Bigfoot mount for sale. If he does not need or want goto it might float his boat.



#88 jtrezzo

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Posted 31 May 2019 - 10:51 AM

I just went from a 14" to an 18" and the difference was HUGE to me. Even though it's only 66% more light gathering and only a half mag deeper. I observe in Bortle 5 skies. All of a sudden I'm seeing objects I've only glimpsed hints of before. I don't know how much of this could just be a difference in individual mirrors, that's also something to consider.

 

Anyone going from a 10" to either a 15" or 18" would be an insane difference.


Edited by jtrezzo, 31 May 2019 - 10:57 AM.

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#89 REC

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Posted 31 May 2019 - 11:15 AM

Keep your 10" and get a PVS14 Night Vision monocular.  It will beat the 18 and you'll have a much more portable set up with plenty of wow. 

Here's a "night vision workshop" video I did on the subject:  https://www.youtube....h?v=6usKtqpVMi8

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#90 JDFlood

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Posted 01 June 2019 - 06:34 PM

i Will admit the NV comments have me thinking. I am definitely going to investigate further. If I can bring a lot of DSOs to my porch instead of waiting for a weekend, this may be worth the next move on my part.


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#91 Rick150

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Posted 22 June 2019 - 03:42 AM

Somewhat ambiguous argument, my wife who is no expert wanted to go to the local astronomy club to see Jupiter, she looked through their 16" & 18" dob and so did I but not really taking much time. We got home and she wanted to look through our 14", well her first comment was that Jupiter looked so much clearer and she was right. So a lot comes down to the quality and setup of the unit. A good 14" can be better than a medium 18". Find an 18" that will be as good as an average 20".



#92 TareqPhoto

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Posted 22 June 2019 - 10:24 PM

Somewhat ambiguous argument, my wife who is no expert wanted to go to the local astronomy club to see Jupiter, she looked through their 16" & 18" dob and so did I but not really taking much time. We got home and she wanted to look through our 14", well her first comment was that Jupiter looked so much clearer and she was right. So a lot comes down to the quality and setup of the unit. A good 14" can be better than a medium 18". Find an 18" that will be as good as an average 20".

And how can you make sure that 16" or 18" is that good then?

 

I am getting 20", and trying to find the primary mirror that i gonna use which i can afford and being great enough, i may think about something for lifetime if i have to pay/spend more, but i can't tell which one and how good and what if.


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