PHD2 graph

[sungrazer]

HI All

HOW good is PHD2 - awesome i think. Very happy with it.

I have the attached graph guided - clearly doing well in dec but a little wobbly in RA.

its a dmk21 on a 50 mm orion guide scope attached to an lx200gps 10'

any ideas where i should be looking to correct this as it results in images with slight star trails (and some perfect ones)

thanks in advance
Karen

[cometcatcher]

I'm no expert on PHD guiding but if it's drifting in RA, the scope may need to be a little unbalanced to give the motors a bit of load to stop the scope wobbling back and forth in RA.

[sungrazer]

Hi Kevin

thanks for the reply. a good suggestion - it is perfectly balanced in ra - with lead weights - maybe too perfectly (unlikley)
thanks
Karen

[codemonkey]

Hi Karen,

A graph showing the corrections PHD is sending as well as showing it in arcseconds as opposed to pixels might provide a little more information with which we could better help diagnose your issues.

I can see the RA error is 2.87" which is pretty big, but I can't see what DEC is (even though the graph looks pretty flat, it's in pixels with a 50mm scope so it'll look pretty flat regardless).

Cheers,
Lee

[traveller]

Hi Karen,
I had a similar experience and was told to turn down the RA Hys to 7-8 (you had it on 10).
See this thread http://www.iceinspace.com.au/forum/showthread.php?t=125792
I just downloaded PHD 2 and am learning its drift alignment routine, but looks very straight forward.
Bo

[jsmoraes]

Your graphic is well, and what I saw is some problem in RA. But it seems to be a mechanical problem. There are few information in the graphic to see if it is repetitive.

If it is a mechanical issue, you can not do many things in PHD2. Maybe reduce the mim. motion to 0.05. This will begin the correction of bad area of RA enginge more soon. It can reduce the effect... but only reduce it.

[sungrazer]

HI

thanks for the advice - ill turn it down -
Also the arcseconds graph is quite frightening - which is why i selected pixels. I will have another go tonight (if this wind dies down) with the reduced numbers and upload the arcseconds graph

thanks again to you both
cheers
Karen

[Mosc_007]

When I was having problems with my NEQ6 Pro it was caused by being to well balanced. Causes the Backlash in the gears to wobble.

After I set a slight inbalance it worked fine.


Charles

[sungrazer]

HI all

i aligned using arc seconds and not pixels - its much better. Ive also adjusted the settings as per your advice.

however when guiding and not drifting - this is the graph i get. the first one is western horizon and the second is meridian and equator. Any ideas or is this as good as it gets.

Its taken all night so no photos at this point - the moon is washing out the guidestars a bit too.

cheers
Karen

[sungrazer]

Hi bo
You will find the routine so simple - I'm so impressed -it takes all the guesswork out of it
Now it seems I just have to work out some mechanics
Good luck
Karen

[jsmoraes]

Sory, but I didn't like these new graphics. If RA is more stable, DEC shows error of polar alignment. The values of RA em DEC is dependent from your declaration about your câmera and guiding telescope in PHD2. It seems high: 4 seconds to RA and DEC. Check the value of sensor and focal lenght in the TAB of PHD2.

It seems that there are much noise in the image of guinding star. Try use more strong filter: medium 3 . The noise causes mistakes in movement of guiding star.

Hystersis is something that I didn't undersand very well. But it has something with the mount. As I work with EQMOD plataform and PHD2, I have more control to backslash and speed of movement of correction issues.

[jsmoraes]

Two images of my graphic.
The first: guide system with Tele refractor Vixen 70 mm - camera DSI-1 - PHD V1. Main telescope GSO 305 mm.

The second: guide system with OAG - camera ASI120MC - PHD V2 - GSO 305 mm

note: With both system, Vixen 70 mm and OAG, I reduce the action of PHD in EQMOD plataform. See the graphic of EQMOD with PHD V1. With PHD V2 I reduce only DEC to 15 % of PHD V2 signal of correction.

[Nico13]

Hi guys,
I have found using the target screen in PHD2 is helpful in confirming polar alignment as well.
If you set it to display the last 100 or 200 corrections you can see very clearly if its tending to correct more one way or the other both in RA and Dec.
The picture here shows a pretty even spread of corrections around the target centre but it was a bit windy this night so not a perfect example.
Very happy with PHD2 though.

[mithrandir]

Karen, you've got a lot of noise in the image. You might experiment with the gamma setting and a longer exposure. However PHD would be happy with the selected star.

The way the graph is bouncing around I'd say your balance is too good, the mount is not on a stable surface, or there's a lot of wind. You don't say if you are using a wedge, and the way both RA and Dec bounce I'd suspect you aren't. Ensuring the mount is unbalanced slightly will improve things. You need to keep the gears under load at all times.

What would also concern me is the combination of a 50mm guide scope and a LX200. Although PHD does sub-pixel guiding, the ratio of arcsec per pixel (ASP) of the guider and imaging camera can be an issue.

If you mean the "Orion Mini 50mm" with the DMK21 that gives you 7.2 ASP.

You don't say what your imaging camera is or if you are using a focal reducer. Without a focal reducer, if the camera has similar size pixels to the DMK21AS (5.6um) as do most DSLRs it would be getting 0.46 ASP. The ratio of 7.2/0.46=16 is really pushing your luck. You should aim to get it below 10. Even something with a 9um chip like the Kodak 11002 would be getting 0.74 ASP.

You might consider getting a longer focal length guide scope.

[kosh]

Jorge,
Thats a very nice polar alignment you have there! :thumbsup:
Especially the fact that your graph resolution on the y axis is set to +/- 2" and it still looks pretty flat.
I used to think I had a good polar alignment, nice flat PHD graph, but then I changed some settings, and the graph went to y: +/- 4" and I got the shock of my life! I looked much worse than I thought. Looked good when I was default to y: +/- 16" … Sorry for the thread hijack, i'll leave now ;)

[sungrazer]

Hi ANdrew

Thanks for the reply. I am on a meade wedge on a pier in the back yard. no wind when these were taken. Balanc is perfect - ill sort that out tonight - thanks

there is no focal reducer on the DMK. it is straight up on the LX200, mounted separately (on top) .i.e the meade finder visual is there as well next to it.

the imaging camera is a new QSI683. SO i am trying for HA 10 min subs but the stars have a little tail. :-(

I have an ED80- but it is mounted on another set up - plus this is already pretty heavy. I'd be concerned about throwing on more - but happy to give it a go. I usually have a PST on top but i take it off when night imaging, so it may be alright. Ive also just read that the guide scope is good up to 1500focal length - the 10' LX2000 F10 is 2500. Im out by a long way... Damn it

I'll post new images of the PHD2 guide once i change the balance and settings as per your advice

cheers
Karen

[mithrandir]

Hi Karen,

An ED80 would be a bit much. I've got an Orion ST80 guide scope for my 8" SCT or 127ED and that's heavy enough to need careful piggy-back positioning. You could ask someone like Bintel for other suggestions. (An off-axis guider might be somewhere in your future.)

The LX-QSI combo gives 0.44 ASP, so my guess wasn't that far off.

You would probably get away with the min guider if you had a focal reducer on the Meade. A 0.63 reducer would bring the effective focal length down to 1575mm and give you 0.71 ASP for a ratio of about 10.1.

[sungrazer]

HI All

So tonight i am tucked away in my tardis - not much wind but still a little cold. NOt in here though!

Here is the graph - now with the scope with the external weights removed - same everything else as before.

I have it guiding on 47 Tuc so it's close to the pole. All i have done is remove the weights on the left arm of the fork. Giving it something to push against -as per advice :-) - i still have some weights in the battery enclosure - but I am not taking them out tonight) - what a difference it makes having the scope slightly out of balance.

Next stop, the other suggestions.

**I've now added a graph with more information and a longer run. I think the balance is good with it heavier on the motor side so it needs to push. Any suggestions as to why the RA might jump up and down like this - I've tried both high ad low aggressiveness as well. no difference. The RA lock does lock it down but there is still a little jiggle in it - but it was like that out of the box.

ALSO FYI
I have discovered that the CAM dialogue box frequently takes control over the guide camera - and despite me asking for a 2 second image it was giving me 1/254 (something i use with the PST) SO if you loose your guide stars look in the CAm dialogue box for an answer - re -set the settings there and you should be right to go.
thanks
Karen