polar drift alignment - puzzled

[Andrew C]

Having received advice from this forum recently about the value of drift alignment for longer videocam exposures (amongst other purposes), I am now practising same. But I am puzzled as to how long one should check for.

Many comment on the web that checking after the (final) drift alignment for no drift over a 5 or 10 minute minute period is sufficient to ensure no drift during a photographic session over 2 or 3 hours. This doesn't compute for me unless people are using some form of guiding in conjunction with the photographic exposure and are assuming but not stating that guiding is always going to be necessary.

For live videocamera viewing, surely I would need to get the drift down near enough to zero for the periods I am typically exposing for, since there is no guiding involved.

Or am I missing something?

[Zuts]

Hi,

I think when they say a number of hours they mean a number of 5 or 10 minute subs say over a two or three hour period.

Also, depending on the mount you may be perfectly polar aligned using drift alignment but PEC will still kill you. For example you would be unlikely to get over 2 minutes unguided on an EQ6 no matter how well you drift aligned. For more expensive mounts with better machined gears and less PE it may be possible to go for 5 minutes unguided.

Cheers
Paul

[Kal (Andrew)]

No drift in a 5-10 minutes is a long wait. I do it until there is no drift (or extremely minor) for a 1-2 minute period. If you are just live videocamera viewing then the drift method will just help you with having to make less corrections to keep the viewed object centred (if any corrections are needed at all). When I use my GEM for visual I just plong it on the ground using a compass and the basic mounts declination setting and don't even worry about the minor drift.

[bmitchell82 (Brendan)]

to help with the speed of set up one of the guys though this forum spent a bit of time to set up jigs and little bits apon the telescope so that he could "roughly" polar align the scope in broad daylight, and as soon as octanis became visable he said that it drops it within a few minutes of the FOV. though he did say that 5-10 minute to watch for drift was a very good idea. And since i havn't had much experience in the race for drift alignment i can only "speculate"

[bojan]

Originally Posted by bmitchell82

to help with the speed of set up one of the guys though this forum spent a bit of time to set up jigs and little bits apon the telescope so that he could "roughly" polar align the scope in broad daylight, and as soon as octanis became visable he said that it drops it within a few minutes of the FOV. though he did say that 5-10 minute to watch for drift was a very good idea. And since i havn't had much experience in the race for drift alignment i can only "speculate"

I think you are quite right here, I do the same.
Compass and bubble level for day time and then octans for fine azimuth when it gets dark. And that is when I go out of town.
In my backyard, I have fixed holes in the ground, so I just plonk the mount in and do not bother, it is usually adequate for up to 1 minute exposure with 1000mm lens/scope.