Hi everyone.
I have a small problem when attempting astrophotos with my CPC1100 and Nikon D300 , I use a skywatcher 80 refractor and orion autoguider on top for the guiding with PHD program.
I am in a permanent observatory with pier and celestron wedge (will get better one when I am more financial as I dont like this wedge very much)
Now I have used the drift method of alignment as described throughout this site and have 98% confidence that polar alignment is not the main issue.
At 1st when I aligned on eastern star about 20 -30 degrees above horizon the star was drifting slowly Westward so I moved my counter balance weight further back on my losmandy plate attached on bottom of scope then realigned star and no further drifting westward it just sat centered. Now I didnt get North or South Drift as I know that is what you adjust for (had previously done alignment for my latitude and longtitude) when doing alignment. Then I went onto Meridian star and again no problem star sat centered for at least 10 minutes that I watched it for.
Now I will attach some photos that I took all are 1 minute photos at iso500 at f6.3
I still have a suspicion weight balance is my issue as If I expose photos longer the stars become longer eggs , which I have read is usually alignment problem , Could it also be weight problem as motors in mount might be having hard time keeping things balanced?
Looking at those shots. If they are all of the same time. The first thing I see is the movement is not constant. I suspect you have more than one problem. Balance could be a problem. Is it exact or have you got a bias to get a positive drive. Vibration appears to be the main trouble. This could be causing flexing as well.
That scope is pretty big to be stable on a simple wedge. When you use the scope visually does touching the OTA move the view. Fork mounted SCT's have an awful lot of overhang on the main base.
Barry
Last edited by Barrykgerdes; 13-11-2009 at 10:56 AM.
I'm having similar issues atm.
The only thing that comes to my mind would be clutch slippage or you're unbalanced.
My guide scope also had a lot of give in the focuser, just a slight breeze would wobble the cables and in turn wiggle the guide cam. Which of course will stuff everything up.
Good luck solving your problem.
How far out of balance is the setup ??? .. Balance issues are relatively easy to correct.
Not sure why you moved a weight to counter star drift in your alignment either. All adjustments in a drift alignment are RA and DEC.
I had very similar pictures to these when I started and it was all due to guiding. I did have a good polar alignment, but the mount (HEQ5PRO) wasnt up to the task. I must have bought a (Friday build).
So make sure
1. Your balanced WITH your camera gear attached.
2. Drift align and adjust your AZ or ELEV to get a good polar alignment.
3. IF 1 and 2 above are satisfied and you cant get a reasonable result it looks like some function of guiding is your problem.
well for a start lonnie, can you explain how your adjusting for your polar alignment, you say that you move a weight back and forward? if so your doing it wrong as the weight only plays a part in balance of the scope, if its balanced then its balanced. Secondly if you have a fork mount on a wedge the drift alignment that you are using doesn't always work the best, utilize this method
Is the guider actually guiding?
Even if the balance isn't great you should be able to guide better than the last images shows.
I don't think that the polar alignment is the problem. To have as much drift as that image from poor alignment you would need to be 10's of degrees off.
What guide software are you using?
Try images with and without the guider and see if there is any difference.
Hi Barry
When I am using the scope visually and I touch the scope it does vibrate for
about 5 to 10 seconds before it settles down steady again.
So what I do when taking photos is get it guiding using PHD (maybe I should try a different guide program) I get everything setup and then step outside my Observatory and trigger the camera via a cordless remote which lifts the mirror up and delays exposure for further 2 seconds to stop any additional vibration this is a function of the Nikon D300.
My balance is bad I know when I have scope horizontal and release clutch it sits still , but If I raise OTA straight up to meridian or really any higher than say 60 degrees its swings over itself. I am not sure if I should be adjusting weight everytime I move to new object I am photographing or just get scope reasonably balanced overall?
Below are some more photos of setup maybe someone has a better idea by seeing it.
Quote:
Originally Posted by Barrykgerdes
Looking at those shots. If they are all of the same time. The first thing I see is the movement is not constant. I suspect you have more than one problem. Balance could be a problem. Is it exact or have you got a bias to get a positive drive. Vibration appears to be the main trouble. This could be causing flexing as well.
That scope is pretty big to be stable on a simple wedge. When you use the scope visually does touching the OTA move the view. Fork mounted SCT's have an awful lot of overhang on the main base.
You have to go back to basics.! that is start with your polar alignment
Use the guide i sent you to firstly. get your polar alignment so that you can get at least 1-3 min with very minimal if not any drift.!
Just by looking at the angle you have your wedge plate at it looks more like 70 odd degrees correct me if im wrong, but the closer you get to the equator the flatter the wedge should sit. so theres a good start!
Dont worry about taking images as it will only serve to frustrate you!
Hi Brendan
I follow that procedure in the link you attached to do my polar alignment.
I probably should have explained that when I was aligning on eastern star it would only drift west in eyepiece which indicates the mount is driving to fast as I have been told. That is after I have drift aligned properly i.e get no north south drift in eyepiece when on eastern star. Also on meridian star no movement at all stays well centered.
Once I moved the weight a little further back along the OTA it stopped drifting west in eyepiece when aligning on eastern star. Which means I was unbalanced causing mount to run faster than it should , hope this explains it.
Quote:
Originally Posted by bmitchell82
well for a start lonnie, can you explain how your adjusting for your polar alignment, you say that you move a weight back and forward? if so your doing it wrong as the weight only plays a part in balance of the scope, if its balanced then its balanced. Secondly if you have a fork mount on a wedge the drift alignment that you are using doesn't always work the best, utilize this method
Sorry photo was taken at angle as I dont have much room to get whole shot in picture
I live near Bundaberg and I have it set at 24.5 degrees more or less as you cant rely on the sticker that comes with the celestron wedge. Set after I did drift alignment.
I will try more aligning tonight just to triple confirm as you never can be to sure I guess.
Still think my weight (balance) isnt quiet correct.
Quote:
Originally Posted by bmitchell82
something is majorly amiss here cheif.!
You have to go back to basics.! that is start with your polar alignment
Use the guide i sent you to firstly. get your polar alignment so that you can get at least 1-3 min with very minimal if not any drift.!
Just by looking at the angle you have your wedge plate at it looks more like 70 odd degrees correct me if im wrong, but the closer you get to the equator the flatter the wedge should sit. so theres a good start!
Dont worry about taking images as it will only serve to frustrate you!
like i said something is totally amiss, if your getting that much drift in 1 minute your not anywhere close to polar alignment. moving the weights around will not affect if your motors run fast or slow if they do then you either have some massive weight on them or they arn't upto the task of astro photography! it will affect guiding though. but in any case your PHD will be going off its face and donking like a mad man (anybody who has heard the dreded donk will know what im talking about).
What angle is your wedge plate at? it should be at 66 deg.
if your polar alignment is right then your guiding has some problems aka wrong settings. Run a quick test shot without guiding and see if the problem still occurs.
When im guiding with PHD i bias the weight to the side im working with because i am over the recomended weight limit of the eq6 this just helps with a bit of back lash, if i do put the weight to far one way they guiding in Dec stuffs around but easily fixed.
Hi terry I use PHD guiding software that came with the orion autoguider.
I will try unguided photos tonight and then guided and see if there is much of a difference.
One thing I notice is when I go to use the guiding program and I calibrate it for say m42 it finds and holds onto a guide star right in centre of crosshair stays there no problem (i know its a star and not hot pixel ) then if I track over to western side to take photo of m22 or North to take shot of andromeda the stars in guide program move in the screen fairly quickly and its hard to get the guider to hold onto star to guide. Seems to move in the guide square west on computer screen. It does however work after re calibrating by turning the PHD program off and on again.
Any suggestions at a different guide program?
Quote:
Originally Posted by Terry B
Is the guider actually guiding?
Even if the balance isn't great you should be able to guide better than the last images shows.
I don't think that the polar alignment is the problem. To have as much drift as that image from poor alignment you would need to be 10's of degrees off.
What guide software are you using?
Try images with and without the guider and see if there is any difference.
you do have to re calibrate when you move to different parts of the sky, things change. if you can hold a star in the middle then i don't understand how you have so much movement in your pictures. unless you have massive flexure
brendan I think you are correct its my guiding, I have heard that dreaded donk heaps of times. Although the photos I attached of the stars It didnt donk at all it just kept the star pretty good centre of guide crosshair in PHD.
But they are only 1 minute exposures
I could here the correcting adjustments it was doing to mount. One thing I usually set it for 1 second corrections maybe this is wrong maybe it should be longer?
An other thing I forgot to mention is I always start up PEC playback in celstron hand controller before I start guiding with PHD, maybe this has something to do with it?
Quote:
Originally Posted by bmitchell82
like i said something is totally amiss, if your getting that much drift in 1 minute your not anywhere close to polar alignment. moving the weights around will not affect if your motors run fast or slow if they do then you either have some massive weight on them or they arn't upto the task of astro photography! it will affect guiding though. but in any case your PHD will be going off its face and donking like a mad man (anybody who has heard the dreded donk will know what im talking about).
What angle is your wedge plate at? it should be at 66 deg.
if your polar alignment is right then your guiding has some problems aka wrong settings. Run a quick test shot without guiding and see if the problem still occurs.
When im guiding with PHD i bias the weight to the side im working with because i am over the recomended weight limit of the eq6 this just helps with a bit of back lash, if i do put the weight to far one way they guiding in Dec stuffs around but easily fixed.
i wouldn't run the PEC, it will be battling the guide. 1 second iterations is fine. you have to find what is causing phd to loose your star. have a good read of craig starks user guide for phd (stark labs) that should give you some insight.
Hoping its a clear night tonight and will try all your suggestions.
Make another attempt at drift align
Will balance again to make sure it is ok, I also am running a 5 metre usb extension cable from Orion autoguide camera because the cord isnt quite long enough to get to my laptop perhaps that might be an issue although the guide camera does light up and flash whilst its suppose to be guiding so the cable is probably ok.
Will let you guys know how it went.
Luckily the Observatory director from my local club has offered to come past one night this week and check it out for me.
Quote:
Originally Posted by bmitchell82
i wouldn't run the PEC, it will be battling the guide. 1 second iterations is fine. you have to find what is causing phd to loose your star. have a good read of craig starks user guide for phd (stark labs) that should give you some insight.
It could also be flexure between the guide and main OTAs, or the camera isn't square, or the guidescope isn't square.
My understanding is that you should balance the setup first (with camera attached), in both axis. Then you should do a rough polar align, and then a drift align. You shouldn't need to change the balance for polar alignment, it should be simply adjusting latitude and azimuth (I think that's the right term for what I mean).
I am using an orion xy adjuster for the guide camera which gives play of about 1 inch to find guide star, I know my guidescope isnt square with ota but its not terribly far off. Do you mean as a balance issue for not being square? Its attached ontop of the celestron with a losmandy plate.
Flexure is something I think could also be a problem I am going to try focus with Nikon camera attahced without the focal extender and see if I can focus when it is basically right up against the visual back. Not sure if I can get focus that close but I will give it a try.
Quote:
Originally Posted by dpastern
It could also be flexure between the guide and main OTAs, or the camera isn't square, or the guidescope isn't square.
My understanding is that you should balance the setup first (with camera attached), in both axis. Then you should do a rough polar align, and then a drift align. You shouldn't need to change the balance for polar alignment, it should be simply adjusting latitude and azimuth (I think that's the right term for what I mean).
Well, the first thing I'd say is to remove the guide OTA and guide camera. Just have the main OTA, balanced and drift aligned. Take a few 1 min images and see if there's any star trailing etc. The camera *must* be square to the imaging plane or odd things will happen.
The guide unit needs to be square on as well. That's very important, otherwise mis guiding will occur.
.. hard to tell. Could be anything really. From what you said it might be flexure in the guider or mirror flop? Do you have a picture of your rig?
