help with star trails whileguiding.

[cal1985]

Hi all..

a few months back i bought a HEQ5 synscan mount with a celestrion 80 guide scope and skywatcher synguider.. im having great difficulty using this new setup and all my images are coming out with star trails after around 6-7minutes . should i be expecting subs of longer exposures without trailing or is this setup still not good enough for astrophotography? also do i need the mount autoguide speed set to a certain speed?

i have leveled the mount and use EQalign to polar align the mount. using the drift method there is hardly any drift after around 5mins.

i havent tried backlash or anything to correct the PE

can somebody please help a very frustrated puzzled man?

[ollypenrice]

It should be guidiing properly. No question.

The mount does not have to be levelled to be polar aligned but that won't be relevant here, I don't think.

I suggest a guide speed of 0.5 x siderreal. I have never used PEC while autoguiding.

The trouble with the standalone guiders is that you can't just try a different guide software, you are stuck with what they give you.

Other things to check? Balance. Ideally run just a tad heavy on the east to keep the motors pushing aginst the load. Good ST4 connections. Stable power supply.

Olly

[Catanonia]

pushing it with the guide cam you are using and the mount.

Try reducing the sample rate on the guide star to a lower number, say around 1 - 2 seconds.

[Jessun]

cal1985 do you know what you are guiding on? I mean how does the FOV's compare between that of your imaging scope and that of your guide scope?

I think the guide scope will guide on one star and if your polar alignment is off everything will revolve around the guide star. So if your guide star is way off from what you wish to image, you may see trailing a bit worse than you'd expect. If you guide on a star in the centre of your imaging scope's FOV all will still revolve around this star but it the trailing will be reduced.

Apart from that slightly theoretical problem - are you sure you're actually guiding? Don't know your camera nor software but double check that it works and actually provides signal to the mount.

[cal1985]

hi all thankyou for all your input .. Jessun i think you may have hit the nail on the head with the above comment, i know the guiding is working as i can here the motors adjusting, also the screen on the guider is centred on the star.. i think this maybe a problem with the polar alignment as apose to the equipment.. i use EQalign to polar align the mount by the use of a webcam as directed by the program. i think maybe putting a barlow on the webcam to enchance the offset maybe better as after 10mins without a barlow there does not seem to be much correction needed. if polar alignment is spot on, what kind of exposure times should i be expecting ? or will it be a case of what the camera can handle before introducing sky glow?

[Jessun]

Jessun i think you may have hit the nail on the head with the above comment

Which one?

How do you check that the motors are moving? I use PHD - a universal program that can connect to a range of cameras and it can be forced to send signals to the mount in RA and DEC +/- and you'd listen for the motors moving. Is there a similar routine with the software you use?

I have also never used EQalign so I'm sure others will chip in here with tips.

If you guide on a star within your imaging camera FOV, or at least close to it, I don't see how 30 min plus would pose a real problem.

As to barlow, not sure it would make a positive difference as most guide programs are clever enough to guide sub pixel anyways. (Subpixel on the guide cam that is). With a barlow you'd reduce the light and FOV so not all that desirable.

Good luck finding out what's going on.

[cal1985]

i know the motors are moving as i can hear the ra and dec adjusting accordingly to what is beeing sent via the synguider. the guider is a standalone guider so it does not use any software. the only time i use a laptop is when im polar aligning the mount with the use of EQalign.. i use this programe as it tells you how much you are out by when polar aligning. it watches a certain star in the south by webcam and after a certain amount of time it tells you how much to move the mount by.. does the same for the declination in the east or west as well.... great program. and free which is even better ! this is where i would use the barlow.. as then if there is any error it will so after a smaller period of time and exagerate the error.

i have also unpluged the guider and took an exposure of the same time 10mins. then plug it back in and compared the difference. with it unpluged and not guiding there are huge star trails. once giding there are still trails but not as big.. the trails are no longer than a star width in the image. so i know the guider is working, but something is causeing the drifts... the scope is leveled on flat paving slabs. leveled with a bubble level.. the only other thing i can think of if it isnt the alignment, is that with the synguider you can adjust the agressiveness of the ra and dec signals.. the process is: once found guide star auto calibrate the guider.. which determins the rotation of the guider so the stars move east to west. on the sensor. then it will determin how agressive the signals need to be.. i have been told that u then need to half the agressiveness value. im not sure as to why this would need to be done as the guider has built in software to determin these values.. so i may have a play with this to see what kind of impact this has on the images. main thought though!!! i should have bought a different guider !!!! as for what im guiding on: i try and get the guide star as close to the region of interest as possible, but i find that the guider is not that great on faint stars so cant always have this guiding on the same FOV as the imaging scope. im not far from it maybe a few arc minutes.. will this have quite a big impact on guiding time ? the most i can guide at the moment is 7mins.. i really do think this must have something to do with the polar aligning. it seems the only logical answer..

[cal1985]

ok... very very anoyed with this synguider !! so so frustrating.. i tried again last night, spent hours just on polaralignment, leveling the mount, balanci ng it, everything.... i still cant get any subs above the 5min mark.. i tried on regulas and took a sub for 15mins guided and came out brilliant.. but once i went to a dimmer star and tried guiding no luck what so ever....... it seems great on bright stars and perfect subs are coming out. so i can eliminate the problem lying with alignment.. but the moment i try to guide on anything a little dimmer than about mag 4 my images come out with trails..... please can someone help me. have i wasted my money on this thing or am i really doing something wrong??