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Deciding on a Bigger Mirror

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#1 LateViewer

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Posted 27 April 2013 - 10:39 AM

I am thinking of stepping up from my 12.5" Dob to something bigger. 20" would be the limit but I am thinking of something more like a 16 or an 18. I am looking for the sweet spot in getting something bigger.

What does the tribe think?

Al

#2 Markovich

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Posted 27 April 2013 - 10:57 AM

I have a 15" Obsession and love the size. Do I ever wish for more,? Absolutely! I always thought an 18-20 would be great. But bigger scopes have different logistics that give me pause when I start getting aperture fever. Fortunate for you, there are many choices of scopes in that range and you really cant go wrong with any of the major brands.

#3 DJCalma

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Posted 27 April 2013 - 11:06 AM

Moving up in aperture, I have found that doubling your light gathering power will allow one to see significant differences so as to justify the step up. This would bring the aperture to roughly 18".
Other considerations should include portability issues, the quality of your observing sites, and ultimately, what your goals are in making the jump in aperture.
For me the "sweet spot" would be the largest diameter mirror I could get while observing near the zenith without a ladder.

#4 JMW

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Posted 27 April 2013 - 11:51 AM

I would suggest going to a regional star party and look through a lot of large scopes and speak with the owners about how they handle the size. I think you need to seriously consider the total logistics of owning a large dob. It appears you are from Manhattan. Do you have some property at a more rural location where you would keep the scope, or would you haul it out of the city each time?

I am looking to purchase an faster 18 inch after using a 20 inch F5 for several years. Since it belongs to our club I didn't have to make the financial commitment of a large purchase. I know think I now what I want to use for the next 20-25 years so I am getting ready to buy exactly what I want. Lighter, shorter and a bit wider true field of view all are considerations for me.

Unless money is no issue, it is wise to choice well the first time. I have an inexpensive Z12 dob. It does fine optically but there is a decent leap in what can be seen in the larger dobs. The stability and quality of motion of a large truss dob is a pleasure compared to my water heater style Z12.

#5 Jeff Porter

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Posted 27 April 2013 - 01:17 PM

Once your on a ladder, your on a ladder. I made the jump from 12" to 17.5", and thought I could get away with a stepstool.

I was wrong. While I have found that using a 6' ladder is no big deal, I wished that I had just gone with a 20" scope since I am using a ladder anyway.

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#6 Mike B

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Posted 27 April 2013 - 01:29 PM

For me the "sweet spot" would be the largest diameter mirror I could get while observing near the zenith without a ladder.

This was precisely my thinking, leading me to the 15" F4.55 in my sigline... and very happily so. It maximizes my scoping on several levels- flat-footed use (i'm ~6'2), storage, yard-deployment, & car-transport.


I wished that I had just gone with a 20" scope since I am using a ladder anyway.


This is actually pretty insightful! Why stop at 18" when the use of a stepstool becomes involved? May as well BUY the stepstool for all it's worth, and go a bit more in aperture. I like it!
:grin:

#7 Mirzam

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Posted 27 April 2013 - 04:08 PM

In terms of portability I think the 18" is in a sweet spot. My 20" Starmaster is portable, but the mirror weight is pushing the limit for one person setup. An 18" will show nearly as much and be easier to manage.

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#8 LateViewer

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Posted 27 April 2013 - 04:27 PM

I like the idea of standing on the ground. I am 5'10" and 67" is my maximum ep height. On the Teeter web page the 20" F/3.5 is just that height.

#9 Mike B

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Posted 27 April 2013 - 04:33 PM

Yeah- plus the obvious advantage an F3.5 mirror affords is, if it's cloudy at your viewing location, you can always yank the mirror from the scope & use it as a soup bowl during dinner!
:whistle:

#10 GeneT

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Posted 27 April 2013 - 07:11 PM

Moving up in aperture, I have found that doubling your light gathering power will allow one to see significant differences so as to justify the step up. This would bring the aperture to roughly 18". Other considerations should include portability issues, the quality of your observing sites, and ultimately, what your goals are in making the jump in aperture.
For me the "sweet spot" would be the largest diameter mirror I could get while observing near the zenith without a ladder.


This is good advice. Years ago, Peter Smitka left me with the idea to double the light gathering if I moved up to a larger telescope. That would mean going to about an 18 inch for you. I own a 12.5 inch Portaball and it is just right for me. An 18 inch is too much hassle. The answer is to move/live in a Mag 6 place and have an observatory in the back yard. The next best option is to have an observatory away from home, with all the equipment in place, and just drive to it for viewing. It is the loading up, setting up, taking down, and storing between viewings that gets in the way of this hobby.

#11 careysub

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Posted 28 April 2013 - 01:48 PM

Once your on a ladder, your on a ladder.


Perhaps true, but I find observing near the zenith with a 110" FL telescope much more of a hassle that one rung up at a lower elevation.

I think there is though a difference between a low step-up platform and a multi-rung ladder. A few inches above "flat foot" is different from climbing up to a FL 110" scope.

#12 estwing

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Posted 28 April 2013 - 04:03 PM

i've just gone from a 12.5"starfinder to a 18"F3.9 john nichol mirror..but my dob aint built yet..first light around august..fingers crossed!!

#13 UmaDog

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Posted 28 April 2013 - 04:33 PM

LateViewer, what exactly is your question? Perhaps you just want general discussion? It sounds like you already know that you're looking for something in the 16" to 20" range, so that (by definition) is your sweet spot.

You say you want a 67" eyepiece height. Keep in mind that if you have a good adjustable seat (more or less a necessity for comfy viewing) then you can can push that maximum height upwards by at least 2 or 3 inches depending on which seat you buy. I view at the Zenith whilst seated and find it more comfortable. On my scope the zenith height is 68.5".

So the question really becomes one of price and bulk. If you can afford the Teeter then this would work. Alternatively an 18" f/4 (or, better yet, estwing's f/3.9) would give you the same eyepiece height for less money and less bulk and weight. Finally a 16" f/4.2 (I'm guessing) would do the job too. Just depends how much scope you want to haul about and how much money you want to spend.

You're in Manhattan, do you get out to Custer at all or do you observe upstate?

#14 LateViewer

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Posted 28 April 2013 - 05:52 PM

So here is the deal; I had not been able to set my 12.5" up in two years plus but I did just that two weeks ago. JUST LOVED IT! I have tried to love my TMB 92L and my C9.25" and they are wonderful in their own way but, there is no substitute for aperture!

Now my 12.5" is f/6 and I have been thinking of going f/5. But then that has me thinking about bigger. And that has me thinking and so this posting.

I am also now in a position to buy a country home and can more access to dark skies and my telescopes.

Just thinking and dreaming.

#15 Mike B

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Posted 28 April 2013 - 06:59 PM

I am also now in a position to buy a country home and can more access to dark skies and my telescopes.


Well, good on you! An enviable situation, indeed! :waytogo:

Noticed this in your sigline:
Chance favors the prepared astronomer

That wouldn't have anything to do with this "dreaming" of yours, now would it?
;)

#16 LateViewer

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Posted 28 April 2013 - 07:26 PM

"Chance favors the prepared astronomer" is a variation of a Louis Pasteur quote, " chance favors the prepared mind."

A change in life circumstances and a very heavy 18 months of work had me reworking my observing life. Hence the quote.

But now I am reworking it again.

I think there is a new larger telescope in that reworking.

#17 GeneT

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Posted 28 April 2013 - 07:47 PM

I am also now in a position to buy a country home and can more access to dark skies and my telescopes.


If your country home would allow you to do most of your viewing there, then I recommend building an observatory (or roll off roof building) for your telescope. If you did that, you could go as large as 25 inches, maybe an F4 or faster mirror, and be set.

That is a dream--but a dream that could be made to come true. :whee:

#18 Vic Menard

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Posted 28 April 2013 - 07:47 PM

Depends on what you can afford and what you want to observe.

I would go with the best possible optics, ServoCAT/SkyFi/Sky Safari integration, and a robust/transportable(?) mounting (not necessarily in that order).

FWIW, 16- or 18-inches of quality aperture is a definite "sweet spot". At f/4 (or shorter), I also feel a Paracorr 2 is an important accessory. And be sure to budget some eyepiece upgrades too.

#19 JMW

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Posted 28 April 2013 - 08:30 PM

Since you wouldn't need to travel with your scope it changes the decision. If you put down a pad and build an observatory or a roll-away shelter or just roll out your dob, go as big as you want to deal with. Ladder or not would be the next factor. With f/3.3 scopes you can go pretty large without a ladder.

I was thinking with a roll away shelter you could build a deck around a concrete pad in the middle for the dob. The deck could be 12-16 inches higher than the concrete pad for the dob and this would allow you to keep your feet on the ground. Has anyone tried this before? I guess the tricky part would be having the mirror box clear the deck and keeping the deck close enough that you could work the scope near the zenith

#20 lionel

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Posted 29 April 2013 - 07:42 PM

I went through similar thinking to size my "ultimate" new scope. I wanted an aperture of 16 to 18 inches with my feet firmly planted on the ground while viewing at the zenith. It also had to be easy to load and unload in a small wagon or SUV.

I'm 5'9 1/2" tall and the zenith ep height on my new 16" F/4.2 Teeter is about 65", which lets me use a Stardust chair for all viewing. The scope has a thin (1.4") 20 lb mirror which, if necessary, allows me to lift the mirror box with the mirror in place. I can push the lower assembly into the back of my Prius v and Honda CRV using short (6') collapsible ramps and then fold the wheelbarrow handles in half to store on the floor behind my front seat. In fact, all long items including truss poles, wheelbarrow handles, ramps, table and Stardust chair will fit crossways in my vehicles, greatly increasing loading flexibility.

Lionel

#21 JMW

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Posted 29 April 2013 - 11:56 PM

Do you have a picture of the folding wheelbarrow handles?

#22 LateViewer

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Posted 30 April 2013 - 04:50 AM

Lionel,

How do you like the views from your 16? What did you have before?

#23 lionel

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Posted 30 April 2013 - 11:37 AM

Do you have a picture of the folding wheelbarrow handles?


Here you go Jeff. Rob Teeter makes the folding handles as an option. There's a heavy duty hinge on one side to take the weight, and a brass hook and loop latch on the other side to lock the handle in the extended position.

Lionel

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#24 lionel

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Posted 30 April 2013 - 11:41 AM

When folded the handles are 37" long including the wheels.

Lionel

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#25 JMW

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Posted 30 April 2013 - 01:34 PM

Thanks. It looks like a modification that I could do on my own.






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