The reasons why guiding is essential for imaging
When you stare at the night sky with the naked eye it appears to be still, however that's not the case. The Earth completes one rotation every 24 hours and the Earth's axis of rotation points roughly at Polaris. So, if you look at the night sky Polaris stays in the same position and all the other stars etc revolve around it. Obviously it's not the night sky that's moving, it just appears to as the Earth rotates. Therefore stars that appear close to Polaris will complete a small circle in 24 hours around Polaris whereas a star towards the horizon will have to make a far larger circle in the same time. So, the further an item appears to be from Polaris the faster it will move across the sky.
If you point a telescope at Polaris it will hardly move and imaging it will be relatively easy. However, if you point a telescope at a star near the horizon you will see it move across the eyepiece. The higher the magnification you use, the faster the star will move across the eyepiece. This is exactly the same when using a camera so if you use an exposure of say one minute you'll see star trails across the image. I'll take an image soon and add it to this page to demonstrate what I mean.
Some telescopes have motors that move the telescope in order to try and counteract the rotation of the Earth. If that scope has an equatorial mount and the mount and scope are polar aligned then you might be able to take short exposure images of a few seconds that might not be too badly affected by star trails.
I use a Meade LX200R which has a motor driven computer controlled mount. I have also mounted the scope on a wedge so that the scope and mount can be polar aligned. I've yet to add a section on polar alignment although I'll try to in the not too distant future. The more expensive the motor driven mount is the better it should track unguided. My LX200R's mount can track ok for fairly short exposures of maybe 10 seconds, but will stand a better chance if using a focal reducer that lowers the magnification.
There are very expensive mounts available such as the Paramount ME (around £10,000 just for the mount) that can track really well without additional guiding equipment. As with most things in life, you get what you pay for.
In my experience the LX200R in addition with the necessary equipment to allow guiding is very accurate. If I image through the LX at f/10 then due to the high magnification I probably won't be able to take images of much over a couple of minutes without getting tracking errors in the image. However, if I image through my ZS66 at f5.9 that is piggybacked on the LX, then as the magnification is much lower I can pretty much take any length of exposure I choose with great accuracy.
If you try taking unguided images and get star trails then reduce the exposure time until the stars appear as they should. However, if you take a series of say 20 images then the image frame is likely to have moved quite a lot between the first and last image. All is not lost here though as there are some very clever software programs out there that will still be able to align and stack your images to make one image.
More to add at a later date...