VintageBigBlue.org

 

Re: Ovision picture uploaded


Jun 11, 2008

 


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

#37848 Jun 11, 2008

I just uploaded (as was announced) the Ovision star trail. My best

guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

seconds--that would be peak to peak--but I'm using the rather crude

technique of estimating the variation as a % of the thickness of the

trail (the old trail, also in the folder, is roughly 300% of the

thickness and that was 14 arc seconds, so....). If you want to be

conservative and call the variation in the Ovision star trail 50% of

thickness we would be at 3 arc seconds peak to peak but that doesn't

look like 50% to me.



Harvey is still crunching the numbers and when I get 'em I'll post 'em.



regards

Greg N



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

#37849 Jun 11, 2008

Where exactly did you upload the pictures too, I can not seem to find

them?

Floyd --- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...> wrote:

>

> I just uploaded (as was announced) the Ovision star trail. My best

> guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

> seconds--that would be peak to peak--but I'm using the rather crude

> technique of estimating the variation as a % of the thickness of the

> trail (the old trail, also in the folder, is roughly 300% of the

> thickness and that was 14 arc seconds, so....). If you want to be

> conservative and call the variation in the Ovision star trail 50% of

> thickness we would be at 3 arc seconds peak to peak but that doesn't

> look like 50% to me.

>

> Harvey is still crunching the numbers and when I get 'em I'll post 'em.

>

> regards

> Greg N

>



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

#37851 Jun 11, 2008

That's just incredible - but I guess it really shouldn't be all that

surprising when you think about how nice and tightly the worm is held

in place, along with it being a "precision" worm.



Hey, I got an old 5 euro bill in the drawer - it's a start, no?



Bill Shaheen

Gold Canyon, AZ

USA



--- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...>

wrote: >

> I just uploaded (as was announced) the Ovision star trail. My best

> guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

> seconds--that would be peak to peak--but I'm using the rather crude

> technique of estimating the variation as a % of the thickness of the

> trail (the old trail, also in the folder, is roughly 300% of the

> thickness and that was 14 arc seconds, so....). If you want to be

> conservative and call the variation in the Ovision star trail 50% of

> thickness we would be at 3 arc seconds peak to peak but that doesn't

> look like 50% to me.

>

> Harvey is still crunching the numbers and when I get 'em I'll

post 'em. >

> regards

> Greg N

>



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

#37853 Jun 11, 2008

Click on FILES

Click on folder LOSMANDY vs. OVISION

And check out the contents.



regards

Greg N



--- In Losmandy_users@yahoogroups.com, "William J. Shaheen"

wjshaheen@...> wrote: >

> That's just incredible - but I guess it really shouldn't be all that

> surprising when you think about how nice and tightly the worm is held

> in place, along with it being a "precision" worm.

>

> Hey, I got an old 5 euro bill in the drawer - it's a start, no?

>

> Bill Shaheen

> Gold Canyon, AZ

> USA

>

> --- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@>

> wrote:

> >

> > I just uploaded (as was announced) the Ovision star trail. My best

> > guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

> > seconds--that would be peak to peak--but I'm using the rather crude

> > technique of estimating the variation as a % of the thickness of the

> > trail (the old trail, also in the folder, is roughly 300% of the

> > thickness and that was 14 arc seconds, so....). If you want to be

> > conservative and call the variation in the Ovision star trail 50% of

> > thickness we would be at 3 arc seconds peak to peak but that doesn't

> > look like 50% to me.

> >

> > Harvey is still crunching the numbers and when I get 'em I'll

> post 'em.

> >

> > regards

> > Greg N

> >

>



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

#37854 Jun 11, 2008

Y'all let me know what you estimate the PE to be after looking at the

pictures. Sooner or later the numbers will be crunched and then we'll

all know.



regards

Greg N

--- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...> wrote:

>

> Click on FILES

> Click on folder LOSMANDY vs. OVISION

> And check out the contents.

>

> regards

> Greg N

>

> --- In Losmandy_users@yahoogroups.com, "William J. Shaheen"

> wjshaheen@> wrote:

> >

> > That's just incredible - but I guess it really shouldn't be all that

> > surprising when you think about how nice and tightly the worm is held

> > in place, along with it being a "precision" worm.

> >

> > Hey, I got an old 5 euro bill in the drawer - it's a start, no?

> >

> > Bill Shaheen

> > Gold Canyon, AZ

> > USA

> >

> > --- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@>

> > wrote:

> > >

> > > I just uploaded (as was announced) the Ovision star trail. My best

> > > guess is that the periodic error peak-to-peak is roughly 1 to

1.5 arc

> > > seconds--that would be peak to peak--but I'm using the rather crude

> > > technique of estimating the variation as a % of the thickness of the

> > > trail (the old trail, also in the folder, is roughly 300% of the

> > > thickness and that was 14 arc seconds, so....). If you want to be

> > > conservative and call the variation in the Ovision star trail 50% of

> > > thickness we would be at 3 arc seconds peak to peak but that doesn't

> > > look like 50% to me.

> > >

> > > Harvey is still crunching the numbers and when I get 'em I'll

> > post 'em.

> > >

> > > regards

> > > Greg N

> > >

> >

>







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

#37855 Jun 11, 2008

I had no problem finding it from the upload notice. In case anyone

didn't see it, here's the link to the folder -



tech.groups.yahoo.com/group/Losmandy_users/files/%20Losmandy%20vs\

.%20Ovision/

tech.groups.yahoo.com/group/Losmandy_users/files/%20Losmandy%20v\

s.%20Ovision/>



The bottom 2 pics.



By the way, Greg, the version prior to the NS was the NG.



Bill

























--- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...>

wrote: >

> Click on FILES

> Click on folder LOSMANDY vs. OVISION

> And check out the contents.

>

> regards

> Greg N

>

> --- In Losmandy_users@yahoogroups.com, "William J. Shaheen"

> wjshaheen@ wrote:

> >

> > That's just incredible - but I guess it really shouldn't be all that

> > surprising when you think about how nice and tightly the worm is

held > > in place, along with it being a "precision" worm.

> >

> > Hey, I got an old 5 euro bill in the drawer - it's a start, no?

> >

> > Bill Shaheen

> > Gold Canyon, AZ

> > USA

> >

> > --- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@>

> > wrote:

> > >

> > > I just uploaded (as was announced) the Ovision star trail. My best

> > > guess is that the periodic error peak-to-peak is roughly 1 to 1.5

arc > > > seconds--that would be peak to peak--but I'm using the rather

crude > > > technique of estimating the variation as a % of the thickness of

the > > > trail (the old trail, also in the folder, is roughly 300% of the

> > > thickness and that was 14 arc seconds, so....). If you want to be

> > > conservative and call the variation in the Ovision star trail 50%

of > > > thickness we would be at 3 arc seconds peak to peak but that

doesn't > > > look like 50% to me.

> > >

> > > Harvey is still crunching the numbers and when I get 'em I'll

> > post 'em.

> > >

> > > regards

> > > Greg N

> > >

> >

>









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



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

#37859 Jun 12, 2008

Hi Greg,

Congratulations on the fine tracking with the new worm holder, it looks

like it's as good as you can get on a G11. Your posts prompted me to go

digging again on the Ovision website. I found a really telling document

in their tests area:

www.ovision.com/tests/Feedback-client.pdf

It is a graph of before and after the kit upgrade with FFTs and

declination data. The DEC data tracks the seeing that night and gives a

feel for what spikes in RA are seeing and what is not. I might have seen

before but had not paid enough attention to a not very noticeable but

very important feature. The reduction in the main PE components is

evident, just like in your experience however there are a few components

in the 60sec range that should be scrutinized.



As best I can eyeball from the graph: (BTW looking at he graph is far

easier than reading my slapped together ASCII table!)

Component (sec) HPSS worm Ovision NS kit (arc sec)

240 1.6 0.7

120 0.9 0.1

80 0.6 0.2

76 0.2 0.4

58 0 0.2

48 0.2 0.1

40 0 0.2

34 0.4 0.5

25 0.5 0



It is interesting that the very nasty 0.5" component at 25sec has

disappeared, from my experiences this could be random (from one night to

the next some of these fast components change substantially), but if it

is from the better worm holder then fantastic. Repeated tests are the

only way to find out.



The ~34 sec component doesn't go away, and at 0.5" it has the same

effect for an autoguider as a ~3.5" amplitude main PE (= 7" peak to

peak), definitively the limiting factor here.



So if Ovision could cut new transfer gears as well as they can make a

worm, wow, the G11 would really be pushing the APs around.



EB





Appendix: Math sideshow.

Rule of thumb for comparing frequency components with amplitude A and

period T/n (for the G11 T=239sec) is the maximum rate of that component.



RateofChange ("/sec) = A * 6n/T

0.7" * 6 * 1 / 239sec = 0.018 "/sec - the Ovision fundamental

0.5" * 6 * 7 / 239sec=0.09 "/sec - the Ovision worst offender at

34sec

0.5" * 6 * 9.6 / 239sec=0.12 "/sec - the HPSS worst offender at 25sec



The rate of change times the autoguider exposure length gives the

elongation for the main imager. Or put another way the maximum

elongation you can tolerate will put an upper limit on the autoguider

exposure time, hence limiting how faint a guide star one can use.







gnowellsct wrote: > I just uploaded (as was announced) the Ovision star trail. My best

> guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

> seconds--that would be peak to peak--but I'm using the rather crude

> technique of estimating the variation as a % of the thickness of the

> trail (the old trail, also in the folder, is roughly 300% of the

> thickness and that was 14 arc seconds, so....). If you want to be

> conservative and call the variation in the Ovision star trail 50% of

> thickness we would be at 3 arc seconds peak to peak but that doesn't

> look like 50% to me.

>

> Harvey is still crunching the numbers and when I get 'em I'll post 'em.

>

> regards

> Greg N

>

>

>







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

#37860 Jun 12, 2008

I think it is possible that the worm measurement I took is better than

the Ovision specifications that came with it (they ship with their

start test results of the worm--I'll try to put those up later). This

is probably because I burned it in for five days, which Ovision can't

reasonably do due to time constraints.



I do have the Ruland Oldham coupler (acetal) on the mount, it got

swapped at the same time as the worm gear. But I don't know if that

contributes to performance. It makes for a much more solid joining

between the motor and the worm axis, there is no tipping in the

design, only side-to-side movement. I suppose I should upload those

too if I haven't already. The Ruland Oldham (see DATABASE for part

number) is a $15.00 upgrade (if it is in fact an upgrade).



Short of buying my own photography equipment I've done about as much

as I can do (except for delivering the quantitative estimate of PE).

My suspicion is that in most applications this is going to "do it" for

most people. My friend with the AP1200 accumulates 20 hour exposures

in three minute intervals because he has to throw out a lot of

exposures due to satellite and airplane trails. At short to medium

FLs with a DSLR or for that matter a high end CCD, with PE this good I

suspect that a lot of work can be done without autoguiding.



But the proof is in the star trail. Take a look at the 14 arc second

PE shot on the old worm, mentally cut that variance in half. That

would be 7 arc seconds. 7 arc seconds is the basic standard that

Paramount ME and AP use. To get below 7 arc seconds the

AP900s today use electronic correction built in to the paddle. I have

to believe that what we're seeing in that picture is bigtime below 7

arc seconds peak to peak but we'll see when we get the numbers (my

partner in this is in charge of that).



So, perhaps something can be done to further squeeze things down by

making a PE model of an Ovision G11 and feeding that into the tracking

process (no PEC was used in the images we made for this test).



Bottom line is that I think for most people's imaging requirements a

G11 at this performance level will, in fact, be pushing an AP around,

in the sense that the Mach 1 would now be wayyy overpriced in

comparison to what it delivers for $8k (with necessary add ons) to

$3800 k for the Losmandy. But my views are very naive so let me know

if I'm wrong. Sounds to me like you're thinking about the nuances of

performance at f/15 over three hours in seeing conditions of one arc

second or better?



regards

Greg N



--- In Losmandy_users@yahoogroups.com, Eric Benson ebenson@...> wrote:

>

> Hi Greg,

> Congratulations on the fine tracking with the new worm holder, it looks

> like it's as good as you can get on a G11. Your posts prompted me to go

> digging again on the Ovision website. I found a really telling document

> in their tests area:

> www.ovision.com/tests/Feedback-client.pdf

> It is a graph of before and after the kit upgrade with FFTs and

> declination data. The DEC data tracks the seeing that night and gives a

> feel for what spikes in RA are seeing and what is not. I might have

seen

> before but had not paid enough attention to a not very noticeable but

> very important feature. The reduction in the main PE components is

> evident, just like in your experience however there are a few

components

> in the 60sec range that should be scrutinized.

>

> As best I can eyeball from the graph: (BTW looking at he graph is far

> easier than reading my slapped together ASCII table!)

> Component (sec) HPSS worm Ovision NS kit (arc sec)

> 240 1.6 0.7

> 120 0.9 0.1

> 80 0.6 0.2

> 76 0.2 0.4

> 58 0 0.2

> 48 0.2 0.1

> 40 0 0.2

> 34 0.4 0.5

> 25 0.5 0

>

> It is interesting that the very nasty 0.5" component at 25sec has

> disappeared, from my experiences this could be random (from one

night to

> the next some of these fast components change substantially), but if it

> is from the better worm holder then fantastic. Repeated tests are the

> only way to find out.

>

> The ~34 sec component doesn't go away, and at 0.5" it has the same

> effect for an autoguider as a ~3.5" amplitude main PE (= 7" peak to

> peak), definitively the limiting factor here.

>

> So if Ovision could cut new transfer gears as well as they can make a

> worm, wow, the G11 would really be pushing the APs around.

>

> EB

>

>

> Appendix: Math sideshow.

> Rule of thumb for comparing frequency components with amplitude A and

> period T/n (for the G11 T=239sec) is the maximum rate of that component.

>

> RateofChange ("/sec) = A * 6n/T

> 0.7" * 6 * 1 / 239sec = 0.018 "/sec - the Ovision fundamental

> 0.5" * 6 * 7 / 239sec=0.09 "/sec - the Ovision worst offender at

> 34sec

> 0.5" * 6 * 9.6 / 239sec=0.12 "/sec - the HPSS worst offender at

25sec

>

> The rate of change times the autoguider exposure length gives the

> elongation for the main imager. Or put another way the maximum

> elongation you can tolerate will put an upper limit on the autoguider

> exposure time, hence limiting how faint a guide star one can use.

>

>

>

> gnowellsct wrote:

> > I just uploaded (as was announced) the Ovision star trail. My best

> > guess is that the periodic error peak-to-peak is roughly 1 to 1.5 arc

> > seconds--that would be peak to peak--but I'm using the rather crude

> > technique of estimating the variation as a % of the thickness of the

> > trail (the old trail, also in the folder, is roughly 300% of the

> > thickness and that was 14 arc seconds, so....). If you want to be

> > conservative and call the variation in the Ovision star trail 50% of

> > thickness we would be at 3 arc seconds peak to peak but that doesn't

> > look like 50% to me.

> >

> > Harvey is still crunching the numbers and when I get 'em I'll post

'em.

> >

> > regards

> > Greg N

> >

> >

> >

>







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

#37882 Jun 12, 2008

"This is probably because I burned it in for five days, which Ovision

can't reasonably do due to time constraints."







Greg



Can you elaborate on precisely what you did to "burn in" the new

worm, ie)speed, equipement, loading, etc.



Thanks

John























--- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@...>

wrote: >

> I think it is possible that the worm measurement I took is better

than > the Ovision specifications that came with it (they ship with their

> start test results of the worm--I'll try to put those up later).

This > is probably because I burned it in for five days, which Ovision

can't > reasonably do due to time constraints.

>

> I do have the Ruland Oldham coupler (acetal) on the mount, it got

> swapped at the same time as the worm gear. But I don't know if that

> contributes to performance. It makes for a much more solid joining

> between the motor and the worm axis, there is no tipping in the

> design, only side-to-side movement. I suppose I should upload those

> too if I haven't already. The Ruland Oldham (see DATABASE for part

> number) is a $15.00 upgrade (if it is in fact an upgrade).

>

> Short of buying my own photography equipment I've done about as much

> as I can do (except for delivering the quantitative estimate of

PE). > My suspicion is that in most applications this is going to "do it"

for > most people. My friend with the AP1200 accumulates 20 hour

exposures > in three minute intervals because he has to throw out a lot of

> exposures due to satellite and airplane trails. At short to medium

> FLs with a DSLR or for that matter a high end CCD, with PE this

good I > suspect that a lot of work can be done without autoguiding.

>

> But the proof is in the star trail. Take a look at the 14 arc

second > PE shot on the old worm, mentally cut that variance in half. That

> would be 7 arc seconds. 7 arc seconds is the basic standard

that > Paramount ME and AP use. To get below 7 arc seconds

the > AP900s today use electronic correction built in to the paddle. I

have > to believe that what we're seeing in that picture is bigtime below 7

> arc seconds peak to peak but we'll see when we get the numbers (my

> partner in this is in charge of that).

>

> So, perhaps something can be done to further squeeze things down by

> making a PE model of an Ovision G11 and feeding that into the

tracking > process (no PEC was used in the images we made for this test).

>

> Bottom line is that I think for most people's imaging requirements a

> G11 at this performance level will, in fact, be pushing an AP

around, > in the sense that the Mach 1 would now be wayyy overpriced in

> comparison to what it delivers for $8k (with necessary add ons) to

> $3800 k for the Losmandy. But my views are very naive so let me

know > if I'm wrong. Sounds to me like you're thinking about the nuances

of > performance at f/15 over three hours in seeing conditions of one

arc > second or better?

>

> regards

> Greg N

>

>

> --- In Losmandy_users@yahoogroups.com, Eric Benson ebenson@> wrote:

> >

> > Hi Greg,

> > Congratulations on the fine tracking with the new worm holder, it

looks > > like it's as good as you can get on a G11. Your posts prompted me

to go > > digging again on the Ovision website. I found a really telling

document > > in their tests area:

> > www.ovision.com/tests/Feedback-client.pdf

> > It is a graph of before and after the kit upgrade with FFTs and

> > declination data. The DEC data tracks the seeing that night and

gives a > > feel for what spikes in RA are seeing and what is not. I might

have > seen

> > before but had not paid enough attention to a not very noticeable

but > > very important feature. The reduction in the main PE components

is > > evident, just like in your experience however there are a few

> components

> > in the 60sec range that should be scrutinized.

> >

> > As best I can eyeball from the graph: (BTW looking at he graph is

far > > easier than reading my slapped together ASCII table!)

> > Component (sec) HPSS worm Ovision NS kit (arc sec)

> > 240 1.6 0.7

> > 120 0.9 0.1

> > 80 0.6 0.2

> > 76 0.2 0.4

> > 58 0 0.2

> > 48 0.2 0.1

> > 40 0 0.2

> > 34 0.4 0.5

> > 25 0.5 0

> >

> > It is interesting that the very nasty 0.5" component at 25sec has

> > disappeared, from my experiences this could be random (from one

> night to

> > the next some of these fast components change substantially), but

if it > > is from the better worm holder then fantastic. Repeated tests are

the > > only way to find out.

> >

> > The ~34 sec component doesn't go away, and at 0.5" it has the

same > > effect for an autoguider as a ~3.5" amplitude main PE (= 7" peak

to > > peak), definitively the limiting factor here.

> >

> > So if Ovision could cut new transfer gears as well as they can

make a > > worm, wow, the G11 would really be pushing the APs around.

> >

> > EB

> >

> >

> > Appendix: Math sideshow.

> > Rule of thumb for comparing frequency components with amplitude A

and > > period T/n (for the G11 T=239sec) is the maximum rate of that

component. > >

> > RateofChange ("/sec) = A * 6n/T

> > 0.7" * 6 * 1 / 239sec = 0.018 "/sec - the Ovision fundamental

> > 0.5" * 6 * 7 / 239sec=0.09 "/sec - the Ovision worst

offender at > > 34sec

> > 0.5" * 6 * 9.6 / 239sec=0.12 "/sec - the HPSS worst offender

at > 25sec

> >

> > The rate of change times the autoguider exposure length gives the

> > elongation for the main imager. Or put another way the maximum

> > elongation you can tolerate will put an upper limit on the

autoguider > > exposure time, hence limiting how faint a guide star one can use.

> >

> >

> >

> > gnowellsct wrote:

> > > I just uploaded (as was announced) the Ovision star trail. My

best > > > guess is that the periodic error peak-to-peak is roughly 1 to

1.5 arc > > > seconds--that would be peak to peak--but I'm using the rather

crude > > > technique of estimating the variation as a % of the thickness

of the > > > trail (the old trail, also in the folder, is roughly 300% of the

> > > thickness and that was 14 arc seconds, so....). If you want to

be > > > conservative and call the variation in the Ovision star trail

50% of > > > thickness we would be at 3 arc seconds peak to peak but that

doesn't > > > look like 50% to me.

> > >

> > > Harvey is still crunching the numbers and when I get 'em I'll

post > 'em.

> > >

> > > regards

> > > Greg N

> > >

> > >

> > >

> >

>







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

#37883 Jun 12, 2008

tech.groups.yahoo.com/group/Losmandy_users/message/37846>



See message #37846.



Greg N



--- In Losmandy_users@yahoogroups.com, "John Wall" jfw@...> wrote:

>

> "This is probably because I burned it in for five days, which Ovision

> can't reasonably do due to time constraints."

>

>

>

> Greg

>

> Can you elaborate on precisely what you did to "burn in" the new

> worm, ie)speed, equipement, loading, etc.

>

> Thanks

> John

>

>

>

>

>

>

>

>

>

>

>

> --- In Losmandy_users@yahoogroups.com, "gnowellsct" tim71pos@>

> wrote:

> >

> > I think it is possible that the worm measurement I took is better

> than

> > the Ovision specifications that came with it (they ship with their

> > start test results of the worm--I'll try to put those up later).

> This

> > is probably because I burned it in for five days, which Ovision

> can't

> > reasonably do due to time constraints.

> >

> > I do have the Ruland Oldham coupler (acetal) on the mount, it got

> > swapped at the same time as the worm gear. But I don't know if that

> > contributes to performance. It makes for a much more solid joining

> > between the motor and the worm axis, there is no tipping in the

> > design, only side-to-side movement. I suppose I should upload those

> > too if I haven't already. The Ruland Oldham (see DATABASE for part

> > number) is a $15.00 upgrade (if it is in fact an upgrade).

> >

> > Short of buying my own photography equipment I've done about as much

> > as I can do (except for delivering the quantitative estimate of

> PE).

> > My suspicion is that in most applications this is going to "do it"

> for

> > most people. My friend with the AP1200 accumulates 20 hour

> exposures

> > in three minute intervals because he has to throw out a lot of

> > exposures due to satellite and airplane trails. At short to medium

> > FLs with a DSLR or for that matter a high end CCD, with PE this

> good I

> > suspect that a lot of work can be done without autoguiding.

> >

> > But the proof is in the star trail. Take a look at the 14 arc

> second

> > PE shot on the old worm, mentally cut that variance in half. That

> > would be 7 arc seconds. 7 arc seconds is the basic standard

> that

> > Paramount ME and AP use. To get below 7 arc seconds

> the

> > AP900s today use electronic correction built in to the paddle. I

> have

> > to believe that what we're seeing in that picture is bigtime below 7

> > arc seconds peak to peak but we'll see when we get the numbers (my

> > partner in this is in charge of that).

> >

> > So, perhaps something can be done to further squeeze things down by

> > making a PE model of an Ovision G11 and feeding that into the

> tracking

> > process (no PEC was used in the images we made for this test).

> >

> > Bottom line is that I think for most people's imaging requirements a

> > G11 at this performance level will, in fact, be pushing an AP

> around,

> > in the sense that the Mach 1 would now be wayyy overpriced in

> > comparison to what it delivers for $8k (with necessary add ons) to

> > $3800 k for the Losmandy. But my views are very naive so let me

> know

> > if I'm wrong. Sounds to me like you're thinking about the nuances

> of

> > performance at f/15 over three hours in seeing conditions of one

> arc

> > second or better?

> >

> > regards

> > Greg N

> >

> >

> > --- In Losmandy_users@yahoogroups.com, Eric Benson ebenson@> wrote:

> > >

> > > Hi Greg,

> > > Congratulations on the fine tracking with the new worm holder, it

> looks

> > > like it's as good as you can get on a G11. Your posts prompted me

> to go

> > > digging again on the Ovision website. I found a really telling

> document

> > > in their tests area:

> > > www.ovision.com/tests/Feedback-client.pdf

> > > It is a graph of before and after the kit upgrade with FFTs and

> > > declination data. The DEC data tracks the seeing that night and

> gives a

> > > feel for what spikes in RA are seeing and what is not. I might

> have

> > seen

> > > before but had not paid enough attention to a not very noticeable

> but

> > > very important feature. The reduction in the main PE components

> is

> > > evident, just like in your experience however there are a few

> > components

> > > in the 60sec range that should be scrutinized.

> > >

> > > As best I can eyeball from the graph: (BTW looking at he graph is

> far

> > > easier than reading my slapped together ASCII table!)

> > > Component (sec) HPSS worm Ovision NS kit (arc sec)

> > > 240 1.6 0.7

> > > 120 0.9 0.1

> > > 80 0.6 0.2

> > > 76 0.2 0.4

> > > 58 0 0.2

> > > 48 0.2 0.1

> > > 40 0 0.2

> > > 34 0.4 0.5

> > > 25 0.5 0

> > >

> > > It is interesting that the very nasty 0.5" component at 25sec has

> > > disappeared, from my experiences this could be random (from one

> > night to

> > > the next some of these fast components change substantially), but

> if it

> > > is from the better worm holder then fantastic. Repeated tests are

> the

> > > only way to find out.

> > >

> > > The ~34 sec component doesn't go away, and at 0.5" it has the

> same

> > > effect for an autoguider as a ~3.5" amplitude main PE (= 7" peak

> to

> > > peak), definitively the limiting factor here.

> > >

> > > So if Ovision could cut new transfer gears as well as they can

> make a

> > > worm, wow, the G11 would really be pushing the APs around.

> > >

> > > EB

> > >

> > >

> > > Appendix: Math sideshow.

> > > Rule of thumb for comparing frequency components with amplitude A

> and

> > > period T/n (for the G11 T=239sec) is the maximum rate of that

> component.

> > >

> > > RateofChange ("/sec) = A * 6n/T

> > > 0.7" * 6 * 1 / 239sec = 0.018 "/sec - the Ovision fundamental

> > > 0.5" * 6 * 7 / 239sec=0.09 "/sec - the Ovision worst

> offender at

> > > 34sec

> > > 0.5" * 6 * 9.6 / 239sec=0.12 "/sec - the HPSS worst offender

> at

> > 25sec

> > >

> > > The rate of change times the autoguider exposure length gives the

> > > elongation for the main imager. Or put another way the maximum

> > > elongation you can tolerate will put an upper limit on the

> autoguider

> > > exposure time, hence limiting how faint a guide star one can use.

> > >

> > >

> > >

> > > gnowellsct wrote:

> > > > I just uploaded (as was announced) the Ovision star trail. My

> best

> > > > guess is that the periodic error peak-to-peak is roughly 1 to

> 1.5 arc

> > > > seconds--that would be peak to peak--but I'm using the rather

> crude

> > > > technique of estimating the variation as a % of the thickness

> of the

> > > > trail (the old trail, also in the folder, is roughly 300% of the

> > > > thickness and that was 14 arc seconds, so....). If you want to

> be

> > > > conservative and call the variation in the Ovision star trail

> 50% of

> > > > thickness we would be at 3 arc seconds peak to peak but that

> doesn't

> > > > look like 50% to me.

> > > >

> > > > Harvey is still crunching the numbers and when I get 'em I'll

> post

> > 'em.

> > > >

> > > > regards

> > > > Greg N

> > > >

> > > >

> > > >

> > >

> >

>







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