4 hrs trying to align my EQ3-2 !

[stan26]

Last night looked so promising for my first real proper attempt at DSO photography, the plan was to get as much data as I could....

It started with a simple polar alignment using the polar scope. I have had acceptable results with 30sec exposures by just polar aligning like this using my DSLR prime focus on my startravel 102.

As this would be my first proper effort at AP I wanted to make sure the alignment was as accurate as possible, so being that my ST102 OTA/EP's are for low power widefield work they're not really suitable for accurate drift alignment, so I opted for the "slew drift" method using my DSLR. I didn't take me to long to adjust my AZ-ALT bolts to get the stars in south and west to slew in a dead straight line over 1.5 minute slewed exposures.

So a final check over everything, camera set up etc, swung the mount around to orion got the M42 nicely centred, motor on, mirror locked up, shutted pressed off we go!...................

30 sec's later......."click"...realeased shutter, and a nice load of star trailing apears on the preview screen!

do the same again.....same results, and again, and again, and again........

A re check of south/west align, everything seems ok...?

After messing around for a couple of hours I still had no joy, even tried aligning using illuminated crosshair reticule. So I reset all my efforts by doing another simple polar scope alignment. This improved things slightly , but still nowhere near the ratio of good pics as i was getting on my last two outings.

I noticed that in my sequence of images the trailing would go from bad to almost acceptable and then to bad again over a course of a couple of minutes, I guess this is periodic error..?

The trailing is only in RA direction.

Can anyone suggest where I go from here...?

Thanks

Stan.

[stan26]

Also (this could be the source of all problems)

I have noticed that on the brass tube connector between the RA motor and mount there are 2 x threaded holes which I assume 2 x grub screws or simular need to be in there screwed up tight to lock the motor shaft's together...?

There is no screws of any sort in these holes......but the shaft must still turn or else it wouldn't track at all surley....?

[Ant]

Was the mount actually tracking?

Sometimes of the scope is balanced very very well you can forgot to lock the axis which means that the drives won't drive.

The axis lock is not the little thumb screws.

Batteries all ok? What happened if you turned the drives off?

Cheers

Ant

[Ant]

See the attached pictures for what I mean on the axis locks - I've circled them.

Cheers

Ant

[Vega]

Another factor is... if you were imaging in the Northern part of the sky and getting 30 secs... you wont get the same results when imaging something in the Southerly direction. Reason being when your scope is pointed South its pointed much farther from the pole star (ie it has to be much more accurate while tracking as the sky is moving at a faster rate).

The illuminated reticule should give better results with drift polar alignment in theory. My EQ-3 had lots of periodic error too. One way to try and minimise this is keep one side of the mount slightly heavier than the other when balancing in R.A. (the side that is being lifted from East to West as the night progresses). This can be either the weights side or the scope side depending on how its orientated at the time. The theory is that if the motors are continually having to 'work a little' to pull the weight of the mount up, the more smooth the gears will rotate... slightly.

I used to image with the EQ3-2 and it was a testing time trying to get above 60 second exposures with my 1000mm focal length frac. The best I ever got was 90 seconds and that was in the Northerly direction (M81/82 I believe was my target)

Matt

[stan26]

Was the mount actually tracking?

Sometimes of the scope is balanced very very well you can forgot to lock the axis which means that the drives won't drive.

The axis lock is not the little thumb screws.

Batteries all ok? What happened if you turned the drives off?

Cheers

Ant

Hi Ant, thanks for your reply,

Yes the mount was tracking, and the clutches where locked/engaged. Although im very much a newb, I am familiar with all the functions on the EQ mount.

The batteries are new, installed last night!

Thanks

[stan26]

Another factor is... if you were imaging in the Northern part of the sky and getting 30 secs... you wont get the same results when imaging something in the Southerly direction. Reason being when your scope is pointed South its pointed much farther from the pole star (ie it has to be much more accurate while tracking as the sky is moving at a faster rate).

The illuminated reticule should give better results with drift polar alignment in theory. My EQ-3 had lots of periodic error too. One way to try and minimise this is keep one side of the mount slightly heavier than the other when balancing in R.A. (the side that is being lifted from East to West as the night progresses). This can be either the weights side or the scope side depending on how its orientated at the time. The theory is that if the motors are continually having to 'work a little' to pull the weight of the mount up, the more smooth the gears will rotate... slightly.

I used to image with the EQ3-2 and it was a testing time trying to get above 60 second exposures with my 1000mm focal length frac. The best I ever got was 90 seconds and that was in the Northerly direction (M81/82 I believe was my target)

Matt

Thanks matt, il bare this all in mind, very handy to know...

Cheers

Stan

[JKB]

Stan

I have 3/2 also and there should def be 2 grub screws on the connector from RA motor to Slow motion shaft. I only saw 1 on my set up and it didn't work well but on tightening up the other tracking worked a treat.

I was out last night and imaging the Owl Neb with 2min exposures with very small amounts of drift. (although I dont yet have Polarscope which should help)

Also my 'connector' from RA motor to slow mo is a flexible metal job not brass?

HTH

Jamie

[valleyman]

I would think you need to get those grub screws in, you could still get a bit of movement if the shaftis tight onto the motor drive. but not secre enough to give good tracking.

[philj]

I used to manage at least 1 minute subs at F6 focal plane with an ST120 and a canon DSLR for 7 out of the 8 minutes that the worm took to do a complete revolutioon on my old EQ3 when I started imaging. For the last minute out of the 8 the PE would send the image 1st one way then the other resulting in trailing. So what you descibe is not really PE, I should imagine that it may be the screws you talk about being missing.

The coupling between the motor and the RA worm shaft should be tight, if you are missingt a screw then this may be slipping if the scope is out of balance.

Try fitting a screw in there and give it another go

Philj

[stan26]

Guy's, thanks for all your replies I really appreciate your help!

I had another go last night at the M42. I made sure the balance was slightly offset towards the counter weight so the motor was pulling the weight up from the east to west. Hope this was correct. A combination of this and another longer more precise slew drift alignment on the DSLR resulted in "some" good image's.

BUT, out of about 60 images taken only around a 10-15% sucess rate with regards to no oval shaped stars

I have since noticed that there IS infact two grub screws in the drive coupling, however there are a total of 4 threaded holes, 2 on each side of the coupling and two on one side have no screws in. I suspect that this does not matter? but im not sure why they manufactured it with holes on both sides? I removed the hex screw that holds the RA motor to the mount and tried pulling the RA drive shaft out, but it wouldn't budge so I guess its all held in nice and secure.

hmm back to the drawing board.......

any suggestions welcome

Stan