wimvb

Well deserved. That's a very nice bubble & cluster.

Haven't read all the posts in this topic, but be carefull when comparing "brightness". This is a term left over from film photography, but can be misleading in digital photography. If you change the f-stop by changing the focal length, you also change the "resolution", as in how much of an extended object is covered by one pixel. A fair comparison of optical systems in digital photography has to take pixel size into account. Or try to normalise to a 1 um sized pixel (as Stan Moore tries to do in "Lessons from the Masters"). (I realise that this is throwing the discussion right into the jaws of the "F-ratio Myth", but I'm not going to discuss that. That poor horse has been beaten to death many times over already.) I'm leaning more to using resolution ("/pixel) multiplied by aperture diameter, as a measure for light gathering power of an imaging system. This may not be entirely correct, but at least it takes into account pixel size. In the discussion of images, here and in other online communities, the f-ratio isn't mentioned often, but aperture and total exposure time are. As you may be aware of, @gorann and I have been processing data from the Liverpool telescope recently. For this telescope (which operates at a slow f/10), total integration time is measured in minutes, rather than hours. But on the other hand the mirror is 2 m in diameter, and the pixel resolution is 0.3 "/pixel (binned) at 15 um pixel size. Apparantly, f-ratio is less important than aperture, and the f/10 system isn't that slow after all. (Just tossing my € 0.02 worth into the discussion)

Ouch! The belt tension may have been set too high. you can check it when you get a new belt. Julian's post is a good start for a replacement if the mount vendor can't help (might get two, just in case). Good luck

In short exposures, read noise will dominate. In long exposures, dark current (& noise) and sky glow/lp + noise will dominate. These two sources for noise behave differently. That's why you generally can't compare many short exposures with few long exposures, even if the total integration time is constant. The transition between read noise limited exposures and sky or dark current limited exposures is unique for each setup and conditions. The only way to find out what works best, is to experiment, like @Art Gecko did. Generally longer exposures are better, as is taking more exposures. But with modern low noise, cooled cmos cameras the balance has shifted to more and shorter exposures. Again: experimentation will give best settings for a rig/conditions combination. In this game, theory is never simple, nor flawless. And you can't take much for granted.

Great result. It certainly has a large dynamic range.

Hope the cake tasted as good as it looked, and that all went well. congratulations to you both.

+1. Excellent result on this group, Mikey.

A. Yes, but you probably only see the effect if the number of subs dropped is about the same as the number kept. Removing two subs out of a stack of 30, hardly makes a difference. But removing those out of a stack of 5 will. B. Yes again, if you dial in the correct kappa value. Adding a bad pixel map in lieu of darks also helps. As will other methods, such as cosmetic correction, which looks at each pixel neighbours in each individual sub, and then replaces it if it deviates more than a certain amount (again in units of standard deviation).

That looks great! Glad you sorted out the problem. With a coma corrector (I use a baader on my 150pds), stars will look much better too. In phd, you can check how often dec was corrected. This will give you an indication about polar alignment accuracy. Cheers,

Frank, have you tried running the PHD guiding assistent (under the Tools menu)? It will report the status of your setup. If there is backlash or the settings are off, the assistent will suggest what to do.

Good luck, hope you get it sorted out.

I know the feeling. Some time ago, I had a similar experience. I couldn't get polar alignment right, no matter what I did. Finally it dawned on my that I was stepping around on the soggy grass after winter, and my telescope actually bounced up and down every time I passed too close to the north leg of the tripod. This despite it being on fence-post-anchors that are driven into the ground. Sometimes it's those small annoying things that ruin a session, untill you figure out what it is. In the end, I gave up on trying to get polar alignment perfect and just went with it. Guiding was good and the images turned out ok anyway. I'm sure that if you come back another night, everything will run smoothly.

@mAnKiNd: Here's a pic with the focus settings of my scope/cc/camera. The line marked K20D is for just the camera. The line below is for camera with Baader CC.

Welcome to sgl. Fyi, I use the baader cc with my 150pds, and it works great. Together with my pentax dslr, I didn't need any spacers. But the pentax has a little more 'back focus' than a canon. I wouldn't worry about guiding issues for any of the CCs, at the native fl of the scope it's quite easy to guide.

Blair MacDonald had an article in the Canadian astronomy society's periodical about this. It's available online, and easier to read.