Help with Long Exposure

09 Sep, 2017 16:38
Hi everybody,

I’m newbie. This is my first shoot of Trifid Nebula (five minutes exposure). I have a Schmidt Cassegrain 8 Advanced VX Equatorial Mount and a DSLR Canon 6D. I tried very hard to Polar Algin, to Calibrate, and everything else that is in the Manual. But, as you can see, the Tracking is not so good because the blur is very easy to see. My question is: do I have to better align my telescope or is it good enough to correct with image processing?

Link to my image:

Thanks a lot!
09 Sep, 2017 18:37

Beck, I had trouble aligning my AVX as well.

1-Do you have a polar scope installed? If so the first thing to do is to align the polar scope with the mount. This is done during the day.

2-Find a steeple of something a mile or two away. Set the steeple in the circle of the polar scope, then spin the mount around the polar axis. If the steeple stays in the circle of the scope great.

3-If not adjust the polar scope with the three allen screws until when you spin the mount, the steeple stays in the polar scope circle. The finer the better.

Once you have this done leave the polar scope in the mount. This will help in the night time alignment. It might be useful to do the 2 star alignment then do extra stars to help improve the mounts performance.

Hope this helps, and good luck.
Edited 09 Sep, 2017 18:37
09 Sep, 2017 19:11
I noticed one other item. Your exposure was 5 min. Without some sort of guide scope 5 min is a little long. When using the 8" at 2000mm, you may want to back the time down to 90 or 120 sec, and do more exposures. 2-3 hour of exposure time is a good time to shoot for. smile
09 Sep, 2017 21:33
Hi Beck,

Why don't you use the polar align function of your mount? It's more accurate than the polar scope but take a longer time before to be ready to shoot.
I'm afraid to say that it's really hard to have a good tracking with such a long focal and a AVX mount. If you don't want to guide your scope, do short exposures (30s - 1min max but you will reject a lot of frames) and increase a bit the ISO settings of your DSLR.

At this focal lenght, guiding is essential. (exept if you have a high-end mount)

Good luck.

11 Sep, 2017 14:28
Hi Beck :-)
First of all, are you sure to be on focus? My impression is that your image is out of focus.
For polar alignment, follow the steps Rusty wrote, be sure that your polarscope is aligned to the mount.
If you can take a polemaster, you can be sure that it works very well (but you need to see Polaris). For me the polar align function of avx is not so accurate for photographic use (well for visual use). Another way to have an accurate polar alignment (good for photographic use) is the drift align with PHD2, but you need a lot of time. You can use also other software, align master or Tpoint of Theskyx (it creates a sky model and, after, make some exposures and it says to you how much is your polar alignment error). On my opinion Polemaster is a good and fast choise (a lot of us bought one in particular for field use), but at my home (where I can't see Polaris) I use drift alignment.
Another thing…think to reduce your C8 to f/6.3.
A friend of mine (Cespe) use a C8 on AVX and his pictures are fine (I have bought a c8 too in this days).
Good luck  smile
11 Sep, 2017 14:30
Sorry Beck…just now I have read you use a focal reducer.
11 Sep, 2017 17:21
Hi guys… thanks a lot for your tips. It helped a lot.

I figured out and took my first DSO Photography:

I appreciate your help  smile
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