Stub Mandrel

Just did an experiment comparing two images 224 minutes apart, aligned using my polarscope, the drift over 224 minutes was 102 pixels in one direction, 56 in the other. A bit of Pythagorus shows the drift was ~0.5 pixels per minute or 1 pixel during each exposure.

Obviously this doesn't include any allowance for drift caused by periodic error, the mount sticking or waving in the wind, but it shows the basic tracking is accurate enough for 2 minute subs as long as other issues are minor (which it is). It also suggests that if I want to go beyond 2 minutes I might start thinking of guiding or improving my PA.

I started a thread for people to show what they are doing with EQ3 mounts.

I've just posted an image of M27 using 68 minutes of 120-second subs using the 130P-DS in the thread. Looking at the subs, a few are 'eggy' but not enough to worry about.

I won't jump for one - I may need to get one for work in which case I can justify a bit more RAM and a lot more HDD.

Laptop may be the way to go, but I like the simplicity of not having to use a laptop with my current setup.

Well I've got hold of a huge box made from 1" thick polystyrene and selected a pair of heatsinks/fans that aren't too heavy, but it may be a few weeks before I start as some other projects are crowding in.

Great, spurs me on! I think I will make mine we a removable back so I can see the screen for focusing etc.

How much does it weigh?

I like pragmatic :-)

Live and learn! That's why I'm following this thread.

I was thinking of going completely the other way and making a box out of polystrene.

I shall watch this closely. I have similar bits and may use them for a cool box for my DSLR.

Sound sits transmitted by air molecules moving.

If the air as a mass is moving at a significant speed (say 250 km/s relative to the galactic centre) the propagation of a sound wavefront will be slower in the direction of movement as the energy to accelerate the molecules is constant and therefore can't move them as fast in the direction of movement due to relativistic effects.

Extreme example,  a nuclear explosion of a bomb moving very close to c sends out a wavefront of particles at an equally high velocity in all directions, to a stationary observer the explosion wavefront will barely be progress at all in the direction of travel but will be left stationary in the opposite direction. Siound propagation is not materially different from the propagation of particles by an explosion.

Here's a rather belated update.

I've discovered two issues with my current setup:

• When pointing high I get double and mis-shapen stars. i think this is a combination of backlash in DEC and the fact that the out-of balance I use to combat this becomes negligible. I will try and reduce the backlash and try using a bungee or some other way of 'preloading' the DEC axis.
• My RA stepper had a jerky movement. this has been solved.

As a test of the improved stepping I made a single 2-minute sub after focusing on Arcturus the other evening as an experiment. This was with a relatively light setup, but subs taken later with the 150PL at 60 seconds were clearly much 'tighter'. Obviously this sub was over-exposed and it has only been stretched and colour corrected, but I think it shows that the EQ3-2 can do reasonable sub lengths given my LP-cursed skies.

I find it hard to use an eyepiece for more than about five minutes. Although I can enjoy the views, without imaging it just wasn't be worth me setting up a scope because after 15-20 minutes I felt stiff, uncomfortable and frustrated.

Thanks, I already found the strip down thread. I do plan to do that.

My EQ3 tripod is partly sand filled, braced with bits of studding and one leg aluminium welded solid!

I replaced the top with the top of a Bresser EQ1 type tripod/mount and have a pretty good mount for small scopes.

Yes, I agree, I'm getting 80 second subs from my EQ3 with the new style polarscope, and I reckon I can easily get up to 2 minutes, I just haven't tried yet.

Thanks. I sometimes think people are scared off when they cost up an 'imaging' setup, so I think it's important they realise what can be done with basic gear.