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Discovery 17.5 inch dob

Reflector Visual Astrophotography Dob Imaging Mount
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#1 Astronomygeek

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Posted 10 August 2022 - 11:58 AM

Does discovery 17.5 inch dob has 2 inch focuser or 1.25 inch focuser it looks like a 1.25 inch one and is it dual speed focuser is putting it on ap1200 a good idea ???



#2 JoshUrban

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Posted 10 August 2022 - 12:16 PM

In my opinion, no.  Although I don't own one, it seems best mounted as a dob.  Big mirror, simple mount, lots of fun!  (Big block in an old chevy truck - not designed to "handle" like a Porsche, just deliver raw power.)  


Edited by JoshUrban, 10 August 2022 - 12:17 PM.


#3 siriusandthepup

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Posted 10 August 2022 - 12:18 PM

 

putting it on ap1200 a good idea ???

not appropriate. The Dob OTA is not built to be mechanically stable at all geometries on the equatorial mount.

 

If you own an ap1200, I would expect you to know this already. Do you actually have a mount?



#4 Astronomygeek

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Posted 10 August 2022 - 01:00 PM

I'll do eaa and ap with it



#5 RoofMonkey911

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Posted 10 August 2022 - 03:53 PM

It has a 2” Crayford Focuser. All of their scopes do, according to the website.
 

Does discovery 17.5 inch dob has 2 inch focuser or 1.25 inch focuser it looks like a 1.25 inch one….



#6 MellonLake

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Posted 10 August 2022 - 04:11 PM

The problem with Newtonian Tubes on EQ mounts is that the eyepiece is really high and changes position with the movement of the EQ mount.  Depending on where in the sky you are pointing the eyepiece may point down to the ground or up to the sky.  Also, truss tube Dob's are not set up to rotate through different angles, the collimation would be thrown off as you slew through RA or DEC.   

 

If you want to try AP (key word is try) or EAA with a truss tube Dob you would want to use a multi-axis equatorial table mount.    http://www.equatorialplatforms.com/

 

Rob


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#7 CHASLX200

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Posted 10 August 2022 - 06:17 PM

not appropriate. The Dob OTA is not built to be mechanically stable at all geometries on the equatorial mount.

 

If you own an ap1200, I would expect you to know this already. Do you actually have a mount?

The mirror cell was never ment for a EQ mount if it has a sling.


Edited by CHASLX200, 10 August 2022 - 06:18 PM.

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#8 aatt

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Posted 10 August 2022 - 08:02 PM

Mirror cells in Discovery dobs are aluminum and the mirror is glued with blobs of silicon. Focuser is 2” with 1.25” adapter. Event Horizon single speed focuser.

#9 BrentKnight

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Posted 10 August 2022 - 08:52 PM

I'll do eaa and ap with it

Much more suitable telescopes you can get for these activities.  The Discovery is for looking at DSO's with eyepieces.

 

Curious though...why would you consider a scope like this for EAA/AP?



#10 Astronomygeek

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Posted 10 August 2022 - 09:37 PM

It's tube like and good.for.high mag works



#11 Bill Weir

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Posted 11 August 2022 - 03:08 AM

So this is one of the split tube PDHQs? Could work if the mount is strong enough and you get good balance. I’d also think about reinforcing the connection between the two sections. For years I’ve visually observed with and others have imaged with this f/5 25” scope. It is though built as and astrogragh. You would need to move the primary forward for best results. Extension tube is then needed to achieve focus visually. The mount is custom built and tracks well but as you can see, lots of counterweight. What’s the load capability of the AP mount?

 

Bill

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#12 Starman1

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Posted 11 August 2022 - 06:48 PM

AP1200?  65kg (143 lbs).

It might work with a 17.5" in an observatory on a suitable pier.

In the field?  No way.  It would need 3 guys to attach it and even a slight breeze would oscillate the scope.

Short exposure imaging is usable with the dob mounted on an EQ platform, assuming it's heavy duty enough.

Just not a good idea in general.

 

A Serrurier Truss arrangement for a similar-size scope would be many pounds lighter and could be assembled on the mount, a distinct advantage.

And a shorter f/ratio would be better, like f/3.3 or something.

 

But for photography, a 17" CDK or RC is a much better option on the AP1200.


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