mount setup when auto guiding

[triggertrevor]

Yeah Cheers I've seen those adaptors on modern astronomy.

Cheers kev.

[Nathan_Pembs]

So if the SW 9x50 finder FL is around 200, and my 150P FL is 750....could that explain why I find guiding near impossible with my set up?

I'm curious

[IanL]

So if the SW 9x50 finder FL is around 200, and my 150P FL is 750....could that explain why I find guiding near impossible with my set up?

I'm curious

I doubt it is the problem. The 450D on the 150 would be imaging at a scale of about 1.43 arcseconds per pixel, and the QHY5 on the SW finder would be guiding at about 5.78 arcseconds per pixel. 4 x 1.43 = 5.72 arcseconds per pixel, so you're pretty close to guiding at 4 x the imaging scale.

Guiding at no more than 4 x imaging scale is just a rule of thumb. I n theory PHD guiding can track stars to an accuracy of much more than 1/4 of a pixel. Also you can (and probably should) slightly de-focus the guide scope. This spreads the image over more pixels and helps PHD to find the centroid of the star (but don't de-focus so much that it can't identify the star or to the point where the star is too dim).

What are you setting the camera gain to on the QHY5 when you connect it up? I set mine to 95%, which is way more than the 50% default setting. This makes a huge difference to my guiding as I find PHD struggles to lock on to a star and keep it tracked at 50%, but never has problems at 95%.

To be honest, I think the EQ3 is probably the weak link in the setup. Check your balancing for one thing, i.e. don't have the mount perfectly balanced. If your scope is on the west side of the mount pointing east, move the counterweights down the shaft a bit so that the mount is working to lift them. If the scope is on the east side and pointing west, move the weights up the shaft so that the mount is working to lift the scope. That may help to keep the RA worm gear engaged and give better results.

Also try moving the scope forwards in the rings a bit or backwards in the rings for the same purpose in Dec. You really want to be guiding only in one direction in Dec, and having the mount's polar alignment slightly off so that stars are drifting slowly in Dec will achieve that.

In the end you probably want a bigger mount to get more reliable results (or image at a much shorter focal length or for shorter durations on the EQ3 so guiding becomes less critical), but you should try to improve things as much as you can before spending more cash, since even with a bigger mount like an HEQ5 or NEQ6 you still have to understand and deal with the kinds of issues described above for best results.

[Nathan_Pembs]

Thanks for the reply

To be honest, I've always kept the gain at the default 50% as I've not had any problems in finding guide stars. Unless I've misunderstood the purpose of Gain.

The mount collaberates fine in PHD if PA is good, but then PHD guides ok for 30 seconds then the screen flashes red sayig it's lost the star usually.

In the PHD graphs, it's the Dec line that shoots through the roof. I really would like to sort this guiding lark out, I've wasted so many hours trying to get it to work

without anything to show for it lol

[Jessun]

Also why do i have so much trouble viewing Polaris through the polar scope is it me do i need new specs or.?

Some mounts have you look through a drilled out hole in the actual dec axis when using the polar scope. The axis inside has a hole that has to be lined up by rotating the mount in dec. Have a look during daylight.

Might this be the reason? (Yes I struggled too before I realized!)

/Jesper

[IanL]

The mount collaberates fine in PHD if PA is good, but then PHD guides ok for 30 seconds then the screen flashes red sayig it's lost the star usually.

Yep that is the problem I was having at 50% gain; stars are visible but you lose lock on them regularly. Bear in mind that PHD automatically stretches the image on the screen display (based on the silder next to the buttons), but the slider does not affect the image it uses for guiding. Even if the camera image is dim, you will usually see stars on screen and get a calibration, but seeing, a bit of dew on the guider lens or a bit of high cloud can dim it enough to lose lock. Turn the gain up when you connect (80 - 95% usually works for me) and you should see that problem go away. Also don't forget to use the 'take darks' option in PHD before you start the calibration process, it will make a difference to the quality of the image and avoid bad guiding if a hot pixel is near your guide star.

In the PHD graphs, it's the Dec line that shoots through the roof.

First check that PHD is able to control the mount; use the menu ("Tools" I think) to send guide commands to the mount manually to check they are being acted on. You should be able to hear the motors working as you send commands in Dec and in RA for west (motor should stop for RA east). It might be as simple as that, but since it calibrates I suspect that isn't the problem.

If the mount is shooting off in Dec in one direction, then your Polar Alignment must be way off target, so you'd need to sort that out first.

[RikM]

I think it is much more likely polar alignment that mismatched focal lengths. If your polar alignment is good, you can get away with a bit more than 1:4.

This is a mix of 5 and 10 min subs with a SXV-H9 and 250PX with a QHY5 finder guider. This is very nearly 1:5.

[russellhq]

If the mount is shooting off in Dec in one direction, then your Polar Alignment must be way off target, so you'd need to sort that out first.

You may also have performed a meridian flip and not re-calibrated PHD. I've fallen foul of this before!