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8 inch Cassegrain VS 6 inch Newtonian

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#1 Christophe1970

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Posted 02 December 2023 - 06:17 AM

Hello,

Need to replace my 10 inch Dob that I sadly departed with due to a  poor back.I ve still got a SW 100ED on a EQ5 that s great for planetary But not so on Deep Sky stuff.

So I ve been looking at a 8" Cassegrain telescopes but they are rather expensive you can buy a New 6 inch F5 Newtonian(the biggest scope I can managed) for far less than a Used 8" Cassegrain.

I was just wondering witch of the two would be best on deep sky? 8 Inch F10 Cass or 6 Inch F5 Newtonian?

Any advices greatly appreciated



#2 CHASLX200

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Posted 02 December 2023 - 06:47 AM

The faster F5 Newt will be better for wide field work.  The cass if sharp much better for planets.



#3 Illinois

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Posted 02 December 2023 - 07:05 AM

Stay with 10 inch for  better deep sky objects and planets than 6 inch f5.   6 inch newt with mount is might be same heavy as 10 inch Dobson.   I add homemade base with ball bearing wheels for easier to move in and out of garage.  8 inch Cass might be good and it’s 2000 mm length is not great for low power but good for planets also longer cool time. It’s up to you and I stay with 10 inch dobsonian with 100 SW. refractor.  


Edited by Illinois, 02 December 2023 - 07:06 AM.


#4 Christophe1970

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Posted 02 December 2023 - 07:51 AM

The faster F5 Newt will be better for wide field work.  The cass if sharp much better for planets.

Thankswaytogo.gif



#5 Christophe1970

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Posted 02 December 2023 - 07:52 AM

Stay with 10 inch for  better deep sky objects and planets than 6 inch f5.   6 inch newt with mount is might be same heavy as 10 inch Dobson.   I add homemade base with ball bearing wheels for easier to move in and out of garage.  8 inch Cass might be good and it’s 2000 mm length is not great for low power but good for planets also longer cool time. It’s up to you and I stay with 10 inch dobsonian with 100 SW. refractor.  

Thanks allready sold the 10" Dob



#6 Notdarkenough

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Posted 02 December 2023 - 08:33 AM

Are you doing visual observations? If so, I would get the SCT every time, because the viewing area is much more comfortable than a newt. Think about the 'window' of space where your ep will be oriented; an SCT is much more comfortable, especially with back problems.


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#7 CHASLX200

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Posted 02 December 2023 - 08:53 AM

A 8" F/5 Newt is also easy to use with a Paracorr.

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#8 Echolight

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Posted 02 December 2023 - 11:23 AM

My C8 is a great fun as a deep sky scope. Easy eyepiece acquisition.

I have it outfitted with a .63 reducer corrector, a lock ring, and internally SCT threaded 2 inch diagonal (to keep near the 105mm spec'd backspace behind the reducer).

It's also terrific on the terminator of the Moon at 400x.

 

(Shown pointing at Sagittarius)

IMG_20230806_225515727~3.jpg

 

It's about 23 years old. And I bought it used for cheap on an original Nexstar mount.

 

The mount to me, didn't seem up to the challenge of holding a C8. So I put it on a manual alt az Unistar. But your eq-5 would also hold it well.


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#9 Tony Flanders

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Posted 02 December 2023 - 03:03 PM

I was just wondering witch of the two would be best on deep sky? 8 Inch F10 Cass or 6 Inch F5 Newtonian?


As far as deep-sky observing is concerned, the three most important attributes of a telescope are aperture, aperture, and aperture. Ignoring any issues of cost or portability, an 8-inch f/10 SCT is far superior to a 6-inch f/5 Newtonian for the great majority of deep-sky observing.

 

There are, of course, always exceptions to that rule. For instance the 6-inch f/5 will do better for viewing very large objects such as the Pleiades, especially if it has a 2-inch focuser. For that matter, there are a number of situations where 10x50 binocular are superior to either of your choices. But any way you slice it, an 8-inch scope gathers 1.78 times as much light as a 6-inch scope.


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#10 Christophe1970

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Posted 02 December 2023 - 05:03 PM

Thanks everyone's

I now  think a SCT is probably the way to go since I do suffer from back problems.



#11 maroubra_boy

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Posted 02 December 2023 - 05:28 PM

I agree with Tony.

There's no licencing requirement that means you cannot view any object that cannot fit inside the FOV of any object.

I have never understood this fixation by some that a long focal length scope is no good for DSO viewing only because of it won't fit "X" size range of objects, even though these very same people will also look at said objects with higher magnification. This logic would also mean that big dobs are rubbish for DSO's too because of their longer focal length. NO ONE limits their viewing of DSO's to only the magnification that fits in their widest TFOV and NO BODY views a large DSO with a static scope so the the object sits only inside that FOV. EVERYBODY moves their scope to view any object, large especially. And buggered if I'm going to limit a sketch I do of say M31 to only what the max TFOV I can get with my 17.5" dob. I'll sketch the whole bloody thing because I can move my scope!

If wide field viewing is a priority of yours, then get a rich field scope.

If rich field isn't a priority, then get the scope design & aperture that is ultimately most practical for you. This can include a more stable collimation situation (SCT & Mak), lighter more manageable OTA (6" Newt), whatever. Nor is it for me to tell you which to get because I am not you and I do not know your physical capabilities nor the situation of backyard & what you need to do to set up a scope & mount. All I can do is bring up certain considerations that need thinking about. The decision is ultimately yours.

Going from a 10" scope down to a 6" is a big cut in aperture. This impacts not just on light gathering but also resolution.

Cost is most certainly a factor. But also the design of closed system scopes, such as SCTs & Maks means the optics stay cleaner for longer. A Cat may cost more, but the is less maintenance with it.

A Newt does allow for more DIY fiddling to help improve the mechanical qualities of the instrument. Focuser, contrast, collimation stability, etc, if DIY is also your thing.

One thing I do consider in my scope purchase deliberations is the "3am factor" - how safe is the largest aperture I can handle at 3am when I need to take it down after a long day. If your scope is fork mounted, you safe aperture size is greatly reduced.

Alex.
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#12 SteveG

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Posted 02 December 2023 - 08:32 PM

Thanks everyone's

I now  think a SCT is probably the way to go since I do suffer from back problems.

Have you picked up and moved a mounted 8” SCT? If the 10” dob is too much, I don’t know that the 8 “ SCT would be much easier. YMMV


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#13 Christophe1970

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Posted 03 December 2023 - 02:35 AM

Thank Voyager1,Good Pointscratchhead2.gif



#14 JohnTMN

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Posted 03 December 2023 - 03:15 AM

Hello,

Need to replace my 10 inch Dob that I sadly departed with due to a  poor back.

Tough question too answer.

If it was the total weight of the 10", then it's simple math, compare the weights of your replacement choices

If it was the handling of the balance during location of the device, the actual coordination of handling,,(?) See where I'm going?

I know of back issues and balance.

I've settled with an 8" DOB, an 8" SCT and a 6" newt/eq,, each have a place. The 8" SCT requires the most strength and coordination of the 3 for set up.

Not hard or overwhelming, but still the toughest.There's a couple of "oof" sounds made hoisting that thing up.

Down-sizing is going to be a tough adjustment for ya, keep reading, keep researching, good luck.


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#15 Dave Mitsky

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Posted 03 December 2023 - 03:27 AM

I have never understood this fixation by some that a long focal length scope is no good for DSO viewing only because of it won't fit "X" size range of objects, even though these very same people will also look at said objects with higher magnification. This logic would also mean that big dobs are rubbish for DSO's too because of their longer focal length. NO ONE limits their viewing of DSO's to only the magnification that fits in their widest TFOV and NO BODY views a large DSO with a static scope so the the object sits only inside that FOV. EVERYBODY moves their scope to view any object, large especially.
One of the telescopes that I use most often is a 17" f/15 classical Cassegrain with a focal length of 6477mm.  Its maximum true field of view is ~26 arc minutes.  I've observed hundreds of DSOs with this telescope.
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#16 izar187

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Posted 03 December 2023 - 07:04 AM

Hello,

Need to replace my 10 inch Dob that I sadly departed with due to a  poor back.I ve still got a SW 100ED on a EQ5 that s great for planetary But not so on Deep Sky stuff.

So I ve been looking at a 8" Cassegrain telescopes but they are rather expensive you can buy a New 6 inch F5 Newtonian(the biggest scope I can managed) for far less than a Used 8" Cassegrain.

I was just wondering witch of the two would be best on deep sky? 8 Inch F10 Cass or 6 Inch F5 Newtonian?

Any advices greatly appreciated

6" f5 weigh around 12 pounds.

More resolution than a 4" on dso's , and planets.

But, as mentioned, very noticeable step down from 10".

If you can wrangle an 8 SCT onto your eq, then optically that could be a way to go.

I'm presuming then the SW 100ED for low power wide field.

An 8" alt-az mounted might be an option too.

Including possibly a newt on a dob mount that you roll out to use...  no dead lifting it.

Perhaps on something like:

https://www.harborfr...ruck-58298.html


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#17 vtornado

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Posted 03 December 2023 - 02:39 PM

Why not an 8 inch SCT vs 8 inch cassegrain?

 

Cheaper, wider, lighter.



#18 JohnTMN

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Posted 04 December 2023 - 12:11 AM

Why not an 8 inch SCT vs 8 inch cassegrain?

Uhm, (?), undecided.gif



#19 vtornado

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Posted 04 December 2023 - 12:33 AM

Uhm, (?), undecided.gif

Ooops (I'll play the senior card on this one)   I got into my reptilian brain the OP was asking about a classical cassegraian.  Maybe not.

 

https://www.telescop...pe/p/131540.uts


Edited by vtornado, 04 December 2023 - 12:36 AM.

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#20 seasparky89

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Posted 04 December 2023 - 11:18 AM

I am fortunate to have several scopes (spread between two houses), and over a given year, I use them all.  IMHO, my 8” SCTs are my “do everything” scopes, both for visual, EAA, and imaging.  I find their size/weight and mounting requirements are close to ideal for my needs.  There is a big difference in portability compared to my 9.25 SCT, and not that much difference compared to my 6” SCT.  



#21 Dave Mitsky

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Posted 04 December 2023 - 02:47 PM

One of the telescopes that I use most often is a 17" f/15 classical Cassegrain with a focal length of 6477mm.  Its maximum true field of view is ~26 arc minutes.  I've observed hundreds of DSOs with this telescope.

Here's a recent iPhone shot of the Naylor Observatory's 17" classical Cassegrain.

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  • 17-inch & the Moon 11-30-23 iPhone IMG_2846.jpg


#22 maniack

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Posted 04 December 2023 - 04:25 PM

6" f5 weigh around 12 pounds.

More resolution than a 4" on dso's , and planets.

But, as mentioned, very noticeable step down from 10".

If you can wrangle an 8 SCT onto your eq, then optically that could be a way to go.

I'm presuming then the SW 100ED for low power wide field.

An 8" alt-az mounted might be an option too.

Including possibly a newt on a dob mount that you roll out to use...  no dead lifting it.

Perhaps on something like:

https://www.harborfr...ruck-58298.html

The 8" SCT would be about the same weight as that 6" f5 you mentioned, 12lbs for the Celestron C8 (or 8SE/Evolution8 OTA).

 

In fact the entire Celestron 8SE system with GoTo mount head and tripod is about 32lbs - that's about the same weight as an Apertura 10" dobsonian base, and lighter than its OTA.


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