Star Eccentricity Help
|
Tony Benjamin <tonybenjamin@...>
It seems most of my subs (1 min - 2 min) have eccentricities between .5 and .6. Now at .6 I'm throwing those subs out as you can see they are not round to the naked eye. I've been forced to keep .55 and below otherwise I'm throwing out over 50% of my subs.
My imaging gear is reasonably good (AP100 GTO AE / FLI ML16200 / C11 Edge with mirror locked down). I've been using PHD2 for guiding and usually the RA/Dec and below .4 arc/sec and often sub .3 arc/sec. The AE's seem to be working just fine as a run in PEMPro shows a flat line. I checked the PA recently - but might not have since putting the C11 on the mount - would that be an area to check to see if it is askew? What should I try and do to improve the eccentricities or is this pretty much the norm for a .44 arc/sec image scale? I haven't redone a mapping model for the C11 yet - would that help at all? |
|
|
|
Hi Tony do you have a representative PHD guidelog you can share? Brian On Sat, Aug 8, 2020 at 9:32 PM Tony Benjamin <tonybenjamin@...> wrote: It seems most of my subs (1 min - 2 min) have eccentricities between .5 and .6. Now at .6 I'm throwing those subs out as you can see they are not round to the naked eye. I've been forced to keep .55 and below otherwise I'm throwing out over 50% of my subs. --
|
|
|
|
Tony Benjamin <tonybenjamin@...>
Sorry, I sent the wrong log earlier. Heres the correct one.
Tony
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Brian Valente
Hi Tony
do you have a representative PHD guidelog you can share?
Brian
On Sat, Aug 8, 2020 at 9:32 PM Tony Benjamin <tonybenjamin@...> wrote:
-- |
|
|
|
Hi Tony are you running a tracking model with this mount? On Sat, Aug 8, 2020 at 11:05 PM Tony Benjamin <tonybenjamin@...> wrote:
--
|
|
|
|
Roland Christen
Are you using a separate guide scope? If so, you will probably not get round stars. Off-axis guider is almost a requirement for SCTs.
Rolando
-----Original Message-----
From: Tony Benjamin <tonybenjamin@...> To: main@ap-gto.groups.io Sent: Sat, Aug 8, 2020 11:32 pm Subject: [ap-gto] Star Eccentricity Help It seems most of my subs (1 min - 2 min) have eccentricities between .5 and .6. Now at .6 I'm throwing those subs out as you can see they are not round to the naked eye. I've been forced to keep .55 and below otherwise I'm throwing out over 50% of my subs.
My imaging gear is reasonably good (AP100 GTO AE / FLI ML16200 / C11 Edge with mirror locked down). I've been using PHD2 for guiding and usually the RA/Dec and below .4 arc/sec and often sub .3 arc/sec. The AE's seem to be working just fine as a run in PEMPro shows a flat line. I checked the PA recently - but might not have since putting the C11 on the mount - would that be an area to check to see if it is askew? What should I try and do to improve the eccentricities or is this pretty much the norm for a .44 arc/sec image scale? I haven't redone a mapping model for the C11 yet - would that help at all? |
|
|
|
Tony Benjamin <tonybenjamin@...>
Hi Brian,
No, not yet. As I mentioned in my OP I haven't made one for the C11 yet...but will be doing so on the next clear night :) |
|
|
|
Tony Benjamin <tonybenjamin@...>
No, no seperate guide scope. I'm using an Ultrastar guide camera on a QHYOAG.
|
|
|
|
Okay thanks I'm poking around in your logs some, and I'm waiting to hear back from someone else I asked a Q about, but I can see your RA corrections are primarily one-sided at higher altitudes (and a corresponding increase in RA and therefore your eccentricity goes up), and as you get lower in the sky, RA corrections become more even on both sides, and your RA RMS and eccentricity both go down My suspicion is mirror flop or something shifting in your equipment On Sun, Aug 9, 2020 at 8:54 AM Tony Benjamin <tonybenjamin@...> wrote: No, no seperate guide scope. I'm using an Ultrastar guide camera on a QHYOAG. --
|
|
|
|
Tony Benjamin <tonybenjamin@...>
Thanks Brian. I’m sure mirror flop is a definite possibility, even with the Edge mirror being “locked down”. Is the solution a Planewave?? J
What should I expect for good eccentricity - .35ish??
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Brian Valente
Okay thanks
I'm poking around in your logs some, and I'm waiting to hear back from someone else I asked a Q about, but I can see your RA corrections are primarily one-sided at higher altitudes (and a corresponding increase in RA and therefore your eccentricity goes up), and as you get lower in the sky, RA corrections become more even on both sides, and your RA RMS and eccentricity both go down
My suspicion is mirror flop or something shifting in your equipment
On Sun, Aug 9, 2020 at 8:54 AM Tony Benjamin <tonybenjamin@...> wrote:
-- |
|
|
|
>>>
Is the solution a Planewave?? J either that, or I hear AP has a 17" reflector they are working on :) >>What should I expect for good eccentricity - .35ish?? generally eccentricity of 0.5 or lower is considered 'perceptibly round' I'm not sure i would 'expect' that, but i would certainly aim for that On Sun, Aug 9, 2020 at 9:10 AM Tony Benjamin <tonybenjamin@...> wrote:
--
|
|
|
|
Mike Shade
The value of .5 is stated as round, I am curious if .05 is what people mean. According the Maxim's help, a value of .1 means that the star is longer in one axis by 10%, so a value of .5 would be 50%. That would be horribly out of round. Want to make sure that I am following. With my system, PW 17/AP1600 (non AE)/STL6303E camera/Optec Gemini rotating focuser/.63" pixel/5' subs I generally get roundness values from .01 to .05, depending on where the system is pointed/seeing.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
From:
main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Brian
Valente
>>> Is the solution a Planewave?? J
either that, or I hear AP has a 17" reflector they are working on :)
>>What should I expect for good eccentricity - .35ish??
generally eccentricity of 0.5 or lower is considered 'perceptibly round'
I'm not sure i would 'expect' that, but i would certainly aim for that
On Sun, Aug 9, 2020 at 9:10 AM Tony Benjamin <tonybenjamin@...> wrote:
-- |
|
|
|
Hi Mike I think you may be thinking of star flatness? i snagged this description out of PI's subframe selector - btw in this doc they spec 0.42 as being perfectly round Eccentricity is a measure of star profile distortion. Given an elliptical star profile with major axis diameter a and minor axis diameter b where a is greater than or equal to b, the star profile eccentricity equals (1 - b2 / a2)0.5, the star profile aspect ratio equals b / a and the star profile flatness equals a / b - 1. For all stars fit in an image, their Eccentricity is weighted by the StarResidual value to minimize the influence of bad fits. A distortion with an eccentricity less than about 0.42 is not perceptible to most people. The table below shows the relationship between these measures.  On Sun, Aug 9, 2020 at 12:54 PM Mike Shade <mshade@q.com> wrote:
--
|
|
|
|
Mike Shade
Ah, OK, not a big user of PI but the chart helps. Thanks...
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
From:
main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Brian
Valente
Hi Mike
I think you may be thinking of star flatness?
i snagged this description out of PI's subframe selector - btw in this doc they spec 0.42 as being perfectly round
Eccentricity is a measure of star profile distortion. Given an elliptical star profile with major axis diameter a and minor axis diameter b where a is greater than or equal to b, the star profile eccentricity equals (1 - b2 / a2)0.5, the star profile aspect ratio equals b / a and the star profile flatness equals a / b - 1. For all stars fit in an image, their Eccentricity is weighted by the StarResidual value to minimize the influence of bad fits. A distortion with an eccentricity less than about 0.42 is not perceptible to most people. The table below shows the relationship between these measures.
On Sun, Aug 9, 2020 at 12:54 PM Mike Shade <mshade@q.com> wrote:
-- |
|
|
