Tracking and alignment

[Bone_Idle]

It's been a while since I posted, I've been using scope and after some initial disappointments, am really enjoying my nights in the garden.

We have a northish facing garden, so Saturn has been off limits up to this month, not it's viewable round the side of the house from around 10:30. I've had chance to use my TMB Planetary 6mm, and it's excellent.

My one question (maybe two), is that the planet seems to zip across the field of view. Probably stays in view for a minute/minute and a half max. Does this seem about right? (EP is 58 degrees, 6mm, 150x mag).

I have a refractor with Star diagonal and the planet starts bottom left and moves up and right.

I polar align by levelling the scope and looking through the hole for the polar scope until I can see Polaris, it's not the most accurate method, but it can't be too far off.

I can keep the objct in the centre if I use just the RA slomo, and I am considering a motor kit to allow me to do some imaging, but I just need to be sure that the speed of objects is right.

Do I need to look at drift alignment, or would a polar scope be a decent aid to better alignment?

Sorry if this post is a bit rambly.

[rowan46]

If you can get drift aligning pat it's much the most accurate way to align your scope. and yes the higher the mag the faster the object zips across your eyepiece

[Bone_Idle]

Thanks, I got a DVD with the scope that explains it, but it seemed a bit of a faff!

Would minute or so in view seem about right for 150x? Or do you think my alignment is bit out?

[Ad Astra]

That does seem about right - depends a bit on your eyepiece.

An older design like a Kellner with a narrower than average field of view (typically 40 deg) would cut that down to about 40 seconds viewing time, while a very wide angle like a Meade SWA or a Teleview (70-80 deg or more!) can increase the time to about 2 minutes.

Dan

[rowan46]

to be frank I couldn't tell you, my scope tracks and its such a long time since I used an eq mount

[Astro Imp]

If you can keep the object in the centre of your FOV by only using the RA slo-mo then your polar alignment must be close.

[Bone_Idle]

Sounds like I'm on the right tract. EP is 58 degrees FOV, so I guess 1.5 mins is about right.

I think I will buy the tracking motors, I can use the slo-mo controls, but as it's quite a long scope it's a bit awkward.

Thanks for your help.

[ollypenrice]

If you're not turning the drives on your RA axis (scope not moving at all) then the time taken for an object to cross the eyepiece is entirely unaffected by polar alignment. It is affacted by the declination of the target and the field of the EP. If you point at Polaris, almost Dec+90, it won't move significantly at all. If you point at a star on the celestial equator (the planets can't stray too far from this) then the object will scuttle past PDQ.

As stated above, if you pick an object close to the celestial equator and simply tracking it in RA keeps it in the EP for a decent length of time (20 minutes?) then your Polar alignment is fine for visual.

However, for long exposures you will need it to be seriously accurate and a properly aligned polar scope is a must.

Olly