Guys thanks for all these tips! I'm feeling a lot more confident now about drift alignment
Quote:
Originally Posted by naskies
What type of tripod do you have? Unless it's very high end, you'll probably find that it flexes a bit - which means that your polar alignment will vary based on the orientation of your DSLR. This limits how accurately you can polar align.
If your DSLR has Live View functionality, you can use it to drift align. Start with the mount off, place a tiny piece of tape on the DSLR screen to mark a star, wait for the star to drift a little bit, turn the mount on, use another piece of tape to mark the star again - now you have the RA axis marked out between the two pieces of tape.
Using this approach, I've been been able to successfully drift align an Astrotrac quite accurately (e.g. see these images), but that was using the Astrotrac wedge and pier which doesn't flex (much).
If you have a polar scope, there's a much easier way to polar align:
1. Start with the mount off and "polar aligning" it by adjusting the geared head so that the polar scope so that it's at a bright star, such as Rigil Kent. Your polar alignment will obviously be way off, but don't worry about it for now.
2. By adjusting the ballhead, point your DSLR so that the same star is near the centre of frame.
3. Take a short exposure, and use a small piece of tape to mark the location of the star. (You now know where the polar axis of your mount is in relation to your DSLR camera.)
4. Take a long exposure (e.g. 1-2 mins), and you'll see some star trailing. Based on the curve of the star trails, you'll be able to visually pick out roughly where the south celestial pole is in relation to your DSLR image.
5. Adjust the geared head (i.e. change the polar alignment of the mount) so that the SCP is approximately where your piece of tape is.
6. Repeat steps 4 & 5 (possibly zooming into the picture) until your polar alignment is very close to the SCP.
It's actually a very ingenious way to do polar align... thanks to a post I read once on the Astrotrac Yahoo group |
Hi Dave. Your pictures are amazing and it's the kind of shots I'm looking to do
I LOVE that Polar Scope idea! Definitely going to give that a try first followed by watching the live view mode on my 5D2.
I have a Benro A257 Tripod, Manfrotto 410 geared head and a Manfrotto 488rc2 ball head. I can attach some weight to the tripod to improve stability.