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6" F/8

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#26 LDW47

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Posted 23 October 2020 - 03:22 PM

I'm a much bigger fan of tension springs than I am of tension clutches.

I also wonder how well a 1.5" secondary would illuminate a 2" eyepiece.

True though about the price and equipment.

It illuminates it perfectly, I have had a SW 6” for years and 2 SW 8”ers, the both 8’s are long gone but not the 6 ! A wonderful, great performing scope, I have at least 6 2” low power eps I use with it and my various refractors.  PS:  And the tension clutch system works great, very positive in retaining the scope elevation.  What problem were you envisioning with the clutches ? You have had a bad experience with a SW ?


Edited by LDW47, 23 October 2020 - 03:27 PM.

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#27 LDW47

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Posted 23 October 2020 - 03:23 PM

I do recommend a 13% transmission moon filter to get started, because the moon can definitely be uncomfortably bright in a scope this size.


 

Thanks! I was thinking about that. I didn't know which would be better, 25% or 13%.

~Robin

I would go with a Variable Polarizing Moon Filter instead of a fixed ! With a variable you can have it all, lol !


Edited by LDW47, 23 October 2020 - 03:29 PM.


#28 SteveG

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Posted 23 October 2020 - 03:26 PM

I do recommend a 13% transmission moon filter to get started, because the moon can definitely be uncomfortably bright in a scope this size.


 

Thanks! I was thinking about that. I didn't know which would be better, 25% or 13%.

~Robin

25% has always been my preference.



#29 ShaulaB

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Posted 23 October 2020 - 10:30 PM

A 6 inch f8 Dobsonian is the perfect beginner telescope. Does your nephew drive yet? Going to dark enough viewing sites, he can observe all 110 Messier objects with this scope. A scope this size fits into almost any vehicle. You are a super aunt for thinking if this!❤

Edited by ShaulaB, 23 October 2020 - 10:31 PM.

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#30 stargazer32864

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Posted 23 October 2020 - 10:37 PM

Congratulations on a very excellent telescope choice.

 

I would be in absolutely no hurry to "upgrade" to a larger aperture if I were you.

 

Just get out there and explore the skies --Have fun!

 

BTW:

 

That junk refractor you mention: please, do not sell it nor give it away nor donate it to charity.

 

Rather, please use proper eye protection, and take the thing outside and whack the side of the tube over the objective cell with a hammer a few times to shatter the crap doublet before pitching the remains into the trash.

 

Those atrocious little cheap 50-60mm monsters can kill a young person's curiosity with one frustrating stargazing attempt.

 

One fewer of them in circulation is a good thing.

My nephew is an adult but he knows nothing about telescopes. So I'm going to get him a decent scope to see the planets and moon that he wants to see. It brings joy to me to buy things for family and friends that they enjoy, like telescopes, books, etc. He has a family and not a whole lot of money to spend on a scope. So he thought he was getting a steal with that junk store scope until he aimed at Jupiter and saw a white blob with a blue circle around it. He was very disappointed. If he is willing to sell me that junk scope, I'll properly dispose of it. waytogo.gif 

 

~Robin



#31 stargazer32864

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Posted 23 October 2020 - 10:42 PM

A 6 inch f8 Dobsonian is the perfect beginner telescope. Does your nephew drive yet? Going to dark enough viewing sites, he can observe all 110 Messier objects with this scope. A scope this size fits into almost any vehicle. You are a super aunt for thinking if this!❤

Yes, he's married with kids. But no experience in astronomy. I'm going to get me one too. I'll use Betty Lou (my XT10 Plus) on DSO and the XT 6" Plus on the moon and planets. Maybe, much later, get a SCT.

 

~Robin



#32 Bill Weir

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Posted 23 October 2020 - 11:52 PM

I'm a much bigger fan of tension springs than I am of tension clutches.

I also wonder how well a 1.5" secondary would illuminate a 2" eyepiece.

True though about the price and equipment.

Again the false assumption that you can’t use a 2”eyepiece with a F/8 6” dob. I use 2” eyepieces with mine all the time. 2.1°using a 31mm Nagler panning around and for large nebulae and clusters is marvellous.

 

Works well on conjunctions too. Jupiter and Venus July 2015. The FOV with a 100° 20mm ES. Hand held P&S shot.

 

Bill

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#33 aatt

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Posted 24 October 2020 - 12:16 AM

I have used a 6” f/8 for 22 years and it does not disappoint. All the categories of celestial objects can be observed with it. The Mars opposition of 2003 was unforgettable in that scope. Easy to transport, Collimate and cool. Truly versatile and easy scope to use.
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#34 donald41

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Posted 24 October 2020 - 09:44 AM

i have a lot of eye pieces, the orion expanse is my favorite, i have all of them from 6mm-20mm. they are light and a wide fov and most of all, not too expensive.


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#35 donald41

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Posted 24 October 2020 - 10:00 AM

i have orions 10,8 and 6" intelliscopes. i have had also 2 12" scopes. but my favorite is the 6" f/8. there is something about the smallness of the scope is a lot of the draw. and the views are outstanding. just wish these companies would use a lot lighter material to made the dob, this particle board is really heavy. don 


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#36 gwlee

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Posted 24 October 2020 - 11:52 AM

i have orions 10,8 and 6" intelliscopes. i have had also 2 12" scopes. but my favorite is the 6" f/8. there is something about the smallness of the scope is a lot of the draw. and the views are outstanding. just wish these companies would use a lot lighter material to made the dob, this particle board is really heavy. don 

I would also prefer a lighter base that’s less shaky. I had Baltic Birch base built for my XT8 to test the widespread assumption that it would be lighter in weight and less shaky. To limit the variables, it was a line-for-line copy of the factory particle board base, and it was assembled using factory hardware. 

 

The BB base weighed exactly the same, #21. In side-by-side testing, I could detect no difference in shakiness either. I think it looks better than the factory base, and it might resist the elements better though. 
 

The 6”f8 XT6 is also my favorite. It’s focuser needs a substantial upgrade though. 


Edited by gwlee, 24 October 2020 - 12:07 PM.

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#37 gwlee

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Posted 24 October 2020 - 12:13 PM

I would go with a Variable Polarizing Moon Filter instead of a fixed ! With a variable you can have it all, lol !

I tested the Orion 13% filter and the variable filter and found variable filter degraded resolution, so kept the fixed version. 


Edited by gwlee, 24 October 2020 - 12:13 PM.

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#38 stargazer193857

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Posted 24 October 2020 - 12:31 PM

I would also prefer a lighter base that’s less shaky. I had Baltic Birch base built for my XT8 to test the widespread assumption that it would be lighter in weight and less shaky. To limit the variables, it was a line-for-line copy of the factory particle board base, and it was assembled using factory hardware.

The BB base weighed exactly the same, #21. In side-by-side testing, I could detect no difference in shakiness either. I think it looks better than the factory base, and it might resist the elements better though.

The 6”f8 XT6 is also my favorite. It’s focuser needs a substantial upgrade though.


What do you suspect is the source of the shakiness?

#39 gwlee

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Posted 24 October 2020 - 12:37 PM

Again the false assumption that you can’t use a 2”eyepiece with a F/8 6” dob. I use 2” eyepieces with mine all the time. 2.1°using a 31mm Nagler panning around and for large nebulae and clusters is marvellous.

 

Works well on conjunctions too. Jupiter and Venus July 2015. The FOV with a 100° 20mm ES. Hand held P&S shot.

 

Bill

After installing a 2” focuser, and rebalancing the OTA to compensate for  2” focuser and 2” EPs, what does the 6”f8 OTA weigh? 


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#40 gwlee

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Posted 24 October 2020 - 12:44 PM

What do you suspect is the source of the shakiness?

Several years of experimenting leads me to believe the primary source of shakiness in the XT6 and XT8 is the altitude bearing design, not a lack of stiffness in the particle board base as many assume. 


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#41 donald41

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Posted 24 October 2020 - 12:50 PM

my 6" f/8. intelli,

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Edited by donald41, 24 October 2020 - 01:50 PM.

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#42 stargazer193857

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Posted 24 October 2020 - 01:15 PM

Several years of experimenting leads me to believe the primary source of shakiness in the XT6 and XT8 is the altitude bearing design, not a lack of stiffness in the particle board base as many assume.


Please elaborate on the altitude bearing issue. Do the 4 bearing pads fail to contact the same cylinder? Does the OTA tilt up out of the cradle when pushed? Do springs reduce this?

It would be nice to know the exact dynamics so ATMers can avoid doing the same.
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#43 SteveG

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Posted 24 October 2020 - 02:29 PM

After installing a 2” focuser, and rebalancing the OTA to compensate for  2” focuser and 2” EPs, what does the 6”f8 OTA weigh? 

The scope being discussed that comes with a 2" focuser has a 15 lb tube weight. The Orion, that the OP was originally looking at, has a tube weight of 13.5 lb.



#44 LDW47

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Posted 24 October 2020 - 02:35 PM

I tested the Orion 13% filter and the variable filter and found variable filter degraded resolution, so kept the fixed version. 

Everyone has a different finding but ........ ? The poster should get a variable, really !


Edited by LDW47, 24 October 2020 - 02:39 PM.


#45 LDW47

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Posted 24 October 2020 - 02:44 PM

Please elaborate on the altitude bearing issue. Do the 4 bearing pads fail to contact the same cylinder? Does the OTA tilt up out of the cradle when pushed? Do springs reduce this?

It would be nice to know the exact dynamics so ATMers can avoid doing the same.

You will find there is not much shake if at all, its not a big concern, I would call it design play ! They all have movement in their design, if you look at the design, the build how could they not, some look for perfection in every thing, lol ! And I don’t know why but don’t let that bother you in your choice !


Edited by LDW47, 24 October 2020 - 02:45 PM.


#46 gwlee

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Posted 24 October 2020 - 03:12 PM

Please elaborate on the altitude bearing issue. Do the 4 bearing pads fail to contact the same cylinder? Does the OTA tilt up out of the cradle when pushed? Do springs reduce this?

It would be nice to know the exact dynamics so ATMers can avoid doing the same.

The XT8 is OTA  a -48” beam that weighs 20# with much of the weight concentrated in its ends. The OTA is attached to its 21# base at its balance point with two springs that pull it into a pair small diameter altitude bearings. When the OTA is disturbed by touching the focuser for example the image in the EP vibrates (shakes) in proportion to the disturbance.

 

Several years of experimenting leads me to believe that most of the shaking is caused by undamped ringing at the interface of the OTA and the base, which is the altitude bearings. However, I haven’t proved it to my satisfaction. 

Going to a 2-speed focuser reduces the disturbance to the OTA, so reduces the shakes, but adds weight. Astro Goods (https://www.astrogoo.../bearings.shtml) sells a bolt on kit that significantly increases the size of the altitude bearings, but adds weight. When the pandemic ends, I want to take a look at these bearings and perhaps order a set to evaluate. 
 

My original goal was to see if it’s feasible to reduce the weight of the #41 XT8 to 34#, the weight of the XT6, to combine the performance of an 8” scope with portability of a 6” scope, so adding weight is going in the wrong direction. 
 

There’s no doubt that I can reduce the weight of the BB base from 21# to 14# by cutting enough holes in the base, which will definitely reduce the weight of the XT8 to 34#, but the precise effect on the shakes is difficult to predict, and the goal is to reduce the weight without increasing the shakes.

 

It seems possible that some weight can be taken out of the BB base without increasing the shakes if the primary contributors to the shakes are the altitude bearings as I suspect. For the moment, I am using the XT8  with its BB base while I decide the next step. 


Edited by gwlee, 24 October 2020 - 04:52 PM.

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#47 gwlee

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Posted 24 October 2020 - 03:55 PM

You will find there is not much shake if at all, its not a big concern, I would call it design play ! They all have movement in their design, if you look at the design, the build how could they not, some look for perfection in every thing, lol ! And I don’t know why but don’t let that bother you in your choice !

I have owned at least four XT6s and four XT8s over the years. I found that all of them exhibited more shakiness than I want (zero), but I am willing to trade their characteristic shakiness for their generous aperture compared to other designs of equal weight.

 

However, I see no downside to trying to decrease the shakiness of my current XT8 while holding aperture and weight constant; nor is there any downside to decreasing weight while holding shakiness and aperture constant. Succeeding at either will make a good scope better. 


Edited by gwlee, 24 October 2020 - 03:56 PM.

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#48 gwlee

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Posted 24 October 2020 - 05:07 PM

The scope being discussed that comes with a 2" focuser has a 15 lb tube weight. The Orion, that the OP was originally looking at, has a tube weight of 13.5 lb.

Do you know the manufacturer and model of this scope? 
 

I ordered a SkyWatcher 6”f8 a few years ago that came with a 2” focuser, but the actual weight of the complete scope turned out to only 1# less than my 8”f6, so I returned it. 



#49 LDW47

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Posted 24 October 2020 - 08:19 PM

I have owned at least four XT6s and four XT8s over the years. I found that all of them exhibited more shakiness than I want (zero), but I am willing to trade their characteristic shakiness for their generous aperture compared to other designs of equal weight.

 

However, I see no downside to trying to decrease the shakiness of my current XT8 while holding aperture and weight constant; nor is there any downside to decreasing weight while holding shakiness and aperture constant. Succeeding at either will make a good scope better. 

No one is saying anything about a down sided but to be honest I never experienced any great shakiness in my 2 SW 8” and 1 SW 6” dobs ! The only real shakiness was the play that occurs between the upper and lower circular base plates as all there is are 3-4 teflon slide strips and the centre bolt that you can loosen or tighten to get the proper friction / tension in the circular rotating motion of the scope when scanning, when viewing. The way they are designed there has to be minimal movement when adjusted correctly !



#50 LDW47

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Posted 24 October 2020 - 08:21 PM

Do you know the manufacturer and model of this scope? 
 

I ordered a SkyWatcher 6”f8 a few years ago that came with a 2” focuser, but the actual weight of the complete scope turned out to only 1# less than my 8”f6, so I returned it. 

The weight difference when I measured was between 6-8 lbs !




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