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Pier Design was Re: 76-second error , please explain it


Aug 29, 2008

 


----------------------------

#39394 Aug 29, 2008

Hi all,



What is the 76 error problem? Does it mean that after 76 seconds of

exposure you will have a big problem with not round stars in your

picture? I like to know how long exposure you can aim before you will

suffer from this error.



I'll been following the discussion for a while, and I didn't dare to

ask this stupid question.



By the way, if you want to fix a steel pier down in rock solid, to get

the same (better)stability as the standard G11 tripod, what dimensions

shall I use?



Best



Lars



----------------------------

#39395 Aug 29, 2008

Lars,



There are no stupid questions, just stupid people (usually the ones

too proud to ask questions g>). The 76 second error is a tracking

error that may occur every 76 seconds. It is believed to be caused by

misalignment of the bearing blocks. There is an excellent article in

the Files section by astrokattner that does a much better job

explaining it than I can. Look in the folder Stuff we want Scott to

see, or some such name. Whether you will experience this or not

depends on how well your worm bearing blocks are machined/aligned and

on the focal length you are imaging. I have been imaging in the 700mm

and less range and it has not bothered me. I *want* to move to longer

focal lengths and it is now an issue for me. That is why I am

investing in the Ovision worm; smoother machining and a one piece worm

block, so the PE should be lower and no 76 second harmonic! There is

also talk of a Martin worm block which is also a one piece design. It

too should remove the 76 second error, but as far as I know only a

prototype has been tested to date.



Frank

celestialwonders.com

--- In Losmandy_users@yahoogroups.com, "lgw09" lgw@...> wrote:

>

> Hi all,

>

> What is the 76 error problem? Does it mean that after 76 seconds of

> exposure you will have a big problem with not round stars in your

> picture? I like to know how long exposure you can aim before you will

> suffer from this error.

>

> I'll been following the discussion for a while, and I didn't dare to

> ask this stupid question.

>

> By the way, if you want to fix a steel pier down in rock solid, to get

> the same (better)stability as the standard G11 tripod, what dimensions

> shall I use?

>

> Best

>

> Lars

>



----------------------------

#39400 Aug 30, 2008

Just a minor point: there is no way to avoid this 76 (or so) error since it

is, by definition, not synchronous with the approx. 4 minute period of one

turn of the worm. It is 100% certain you will hit it if your exposure is

more than 76 seconds long. For shorter exposures, one may be lucky now and

then an squeeze them between two 76 anomalies. In practice it means that

many images have to be rejected and only a few kept. Obviously, the shorter

the exposure, the less likely it is to hit this anomaly.







After being frustrated almost for 3 years with my RA worm assembly, I

recently swapped for the Dec assembly that minimized this annoying error

that CANNOT be corrected by PEC, with or without PemPro. Pure chance, of

course. The Ovision $500 replacement is most likely a real solution of this

problem although more data are still needed.







Best, LN







-----Original Message-----

From: Losmandy_users@yahoogroups.com [mailto:Losmandy_users@yahoogroups.com]

On Behalf Of Frank Barrett

Sent: Friday, August 29, 2008 1:25 PM

To: Losmandy_users@yahoogroups.com

Subject: [Losmandy_users] Re: 76-second error , please explain it







Lars,



There are no stupid questions, just stupid people (usually the ones

too proud to ask questions g>). The 76 second error is a tracking

error that may occur every 76 seconds. It is believed to be caused by

misalignment of the bearing blocks. There is an excellent article in

the Files section by astrokattner that does a much better job

explaining it than I can. Look in the folder Stuff we want Scott to

see, or some such name. Whether you will experience this or not

depends on how well your worm bearing blocks are machined/aligned and

on the focal length you are imaging. I have been imaging in the 700mm

and less range and it has not bothered me. I *want* to move to longer

focal lengths and it is now an issue for me. That is why I am

investing in the Ovision worm; smoother machining and a one piece worm

block, so the PE should be lower and no 76 second harmonic! There is

also talk of a Martin worm block which is also a one piece design. It

too should remove the 76 second error, but as far as I know only a

prototype has been tested to date.



Frank

celestialwon celestialwonders.com> ders.com



--- In Losmandy_users@ mailto:Losmandy_users%40yahoogroups.com>

yahoogroups.com, "lgw09" lgw@...> wrote: >

> Hi all,

>

> What is the 76 error problem? Does it mean that after 76 seconds of

> exposure you will have a big problem with not round stars in your

> picture? I like to know how long exposure you can aim before you will

> suffer from this error.

>

> I'll been following the discussion for a while, and I didn't dare to

> ask this stupid question.

>

> By the way, if you want to fix a steel pier down in rock solid, to get

> the same (better)stability as the standard G11 tripod, what dimensions

> shall I use?

>

> Best

>

> Lars

>











[Non-text portions of this message have been removed]







----------------------------

#39407 Aug 30, 2008

Hi Lars,



Try the link below on pier design.



Clear skies,



Dennis Persyk

Igloo Observatory Home Page dpersyk.home.att.net

Hampshire, IL

Pier Design home.att.net/~dpersyk/Pier_Design.htm

--- In Losmandy_users@yahoogroups.com, "lgw09" lgw@...> wrote:

>

> Hi all,

>

> >

> By the way, if you want to fix a steel pier down in rock solid, to

get the same (better)stability as the standard G11 tripod, what

dimensions shall I use?

>

> Best

>

> Lars

>



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