Stub Mandrel

That M33 is very nice, but I'd be tempted to reduce red across the board not just shadows as it is has a lot of bright and blue colour in the arms and taht change might make it sparkle even more.

I can just see the nebula on the preview screen (which shows what a jpeg version would look like although I only save RAWs). I'm not holding my breath for dust, but it would be nice to get a trace of some, hoping for 3 hours subs at least.

Right Ken, I'm having a pop at your favourite - NGC1333 - to see what a DSLR can do - wish me luck, although teh results will be in the EQ3 challenge thread, not here (or I would get lynched by Nigel's bloodthirsty Ninja Clangers!)

When I asked advice on LP filters to remove sodium streetlight glow, I was pointed at a filter on eBay for £10. Not as good as the real McCoy but it made a real difference to my pictures.

Charitably, they are more interested in sharpness at the centre of the FOV and good colour balance. Less charitably, having the right bins matters almost as much as your tick-list in some birding circles

You don't worry that you may be overloading the mount?

I think plenty of the images on this thread were taken with Star Adventurer.

Totally unfair, I got cloud at 7:00pm :-( Early next week looking good though...

... and like yesterday it doesn't show on the satellite IR, although met office are forecasting it, just a gap around 8.

BAH cloudless skies most of the day, vega visible when I go to collect daughter from station at 5:00, watching Venus in clear sky at station until 5:25 return via morrisons by 6:10 and solid cloud!

That's a smashing shot, you'll excuse me if I try to replicate it!

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.

"Behind you!"

The photons from a star average out pretty much to a bell curve, bright at the centre and fading down rapidly to a long 'tail'. The longer the exposure the more of the outskirts get visible, especially after stretching. This is also why brighter stars 'look' bigger although in a perfect world they would all be points.

Cooking on gas!

Interesting. Most of the difference would appear to come from the debayering process failing to completely remove the pattern noise of the RGB sensor. Presumably this could be tuned out?

Fair enough, what I illustrate would only create pointing error, but look again at figs 2a to 2c The scope is cantilevered out from the mount (unless it is a fork mount, but it isn't it's a GEQ) so inevitably there well be some flexure. In 2a this will cause the body of the scope to droop on the side away from the mount and the image will rotate anti-clockwise compared to the view through a weightless scope. But in 2c it is now balanced the other way and it will rotate the image slightly in a clockwise direction. This may be a small effect, but acting in concert with any misalignment between RA and DEC (which will cause a vertical error) and DEC and scope alignment (which will cause a horizontal error) we cloud expect the sort of mis-registration see where the main effect is a pointing error, accompanied by a smaller 'twist'. There may be scepticism the scope will twist enough to cause this, but guide scopes are usually much lighter and their weight can be enough to cause image rotation as the scope tracks. These effects could be compounded or partially compensated by twisting of the OTA as the weight of the imaging train shifts from one side to the other. I'm confident the full mass of the setup MUST make a measurable twisting movement when it is turned upside down. This wouldl be a great challenge for someone who has access to FEA software and lots of time!

It's fundamentally because. the scope itself is not just moved a foot or two to one side, it's rotated through 180 degrees.

I fear you all have bit too much confidence in how well you align your scopes. See below, if your scope, in its rings, is perfectly aligned with the dec axis (1a), a rotation (1b) followed by a flip (1c) will leave the scope pointing at the same spot. If it is not fitted exactly parallel to the DEC plane of rotation (2a), the RA rotation (2b) and DEC flip (2c) will leave it pointing at a very different place, at least with my exaggerated five-degree misalignment. Clearly a 1-minut misalignment, too small to see, would give a 2-minute error in pointing, enough to give two mis-aligned images. There is no need to invoke an inaccuracy in the mount itself.

You could find that hot turbulent air destroys your seeing as well... can you cap it off for a few hours?

How much does the scope tube flex between being loaded on one side and then on the other? (I was going to suggest parallax - those stars are closer than you think!)

Good tip I have experimented with stacking DSLR data with two synthetic luminance layers, one from RGB and one from just R.

Do you sharpen first, then denoise or the other way around? I can never decide which works best.

Cripes a-mighty! I doubt that I could stand there with my vertigo, let along observe!

Good work finding that! As you can see for my camera the noise only goes up a small bit from one ISO to the next, but the sensitivity is doubled, so high ISO seems to be good for the 450D. I guess the open circles are where digital amplification is used which is really just stretching the data (which we do anyway so no real gain). The 520 is a bridge camera with no RAW setting not limited for astro although it does excellent moons and can even resolve saturn's rings with the built in lens(that's what got me in to AP properly!)