ollypenrice

It's a mystery to me why this design hasn't been devoloped by others, either from scratch or by using SW optics. Olly

What is unit when 6 is the value? DSLRs benefit from a dither of around 12 pixels to kill colour mottle in the background. (Source Tony Hallas.) The only downside of a large dither is loss of the borders which is unlikely to be a real issue. You can test your dither scale in pixels by aligning one sub onto the other using star alignment. Look at the borders zoomed in to pixel scale. Just count the pixel offset at the borders. Olly

Precisely, and think of the fun you'll have on clear nights negotiating with Bill Gates! Olly

They are pretty common. I have to say that I hardly ever noticed spikes, visually, in all the years that I had a 20 inch F4.1 Newt here. (That had a normal four-vaned spider.) The best Newt through which I ever observed, Ralf Ottow's legendary 12.5 inch watercooled instrument, had a normal spider and was entirely refractor-like. I didn't spend long with it, a couple of hours, but it was exquisite. In imaging it's more of an issue. The obvious solution is to put the camera in the right place! 🤣👹🤣 Strictly joking, Olly

Curved spider vanes are common on Newts, too. Obsession use them as does David Lukehurst. They smear the diffraction artefacts around the 360 degrees so that they become scarcely visible. Another solution for gadget lovers would be a straight cable attached to a ring which rotated slowly during the run! (Or slightly after each sub...) 😁lly

The best way I know involves using Pixinsight's Dynamic Background Extraction but I think other astro-specific programs like APP can also do a good job. If using GIMP (which I don't know but is probably like Photoshop) then you can begin by looking at the histograms of each colour channel. The rule of thumb is to get the top left of the histogram peak aligned in each channel. You can move them by bringing in the black point to move the peak to the left. There is no reasonable way of moving it to the right. Then you can measure the colour balance in the background sky. In Ps you use the colour sampler for this, set to 3x3 pixel average, probably. I'd be surprised if GIMP didn't have an equivalent. I aim for parity in each channel for the background. Some like blue to be higher but I certainly don't. Olly

A very nice result, espeicially under partial moonlight. The weaksest channel in this image is, in my view, the blue. There's a lovely reflection nebula to the right of the Cocoon in your orientation which is just showing, so you might be able to tease a bit more out. It's on the left in mine, below. Some time ago Fabian Neyer did one of his deep Ha background projects on this region. This is my attempt along the same lines: Olly

Refund? Olly

Hi Derek, I'd say that there was evidence, here, for the 'rain' effect to be a stacking artifact. Have you tried an alternative stacking software? AstroArt offer a free trial which won't save but would let you see if it did any better. Olly

I dare say that if you do a basic calibration and then run the guide assistant in PHD2 you'll get a good result. Olly

I would far rather use the Tak focuser than the Moonlite which I think is a poor choice for holding a heavy camera and filterwheel but the FT is superb. Olly

Was it much warmer than on previous imaging nights? The stacking has been done properly because the stars are aligned. Do you see the angled lines on individual subs? Olly

Even that won't get anywhere near covering the Andromeda galaxy at a FL of 720mm. I used the same chip at only 530mm and still needed a 2-panel mosaic. (You link to the supplier 'Robtics.' I'll be happy to receive PMs on that subject and to reply to them.) Fair point. I'm not sure what you feel the F-number has to do with the choice. Uncooled cameras thrive on fast F ratios but with cooled ones you just increase the exposure time. Will you be able to see a difference in fine detail between 1.06"PP and 1.3? You'd need very good, stable seeing and if you don't have it go for the bigger pixels. As far as I can see the field of view is identical in both cameras because the chip size is the same. It would be incredibly helpful if camera manufacturers would stop using the term 'resolution' to say how many pixels per side their camera has. This has precisely nothing to do with resolution which is determined exclusively by pixel size and focal length. GRRRR. What we want to know is chip size in mm per side and pixel size. The rest is 'removed word.' Am I ranting? Oops!! 🤣lly

It's good! Everything in place and ship-shape. Olly

Very true. If your goal is widefield then it makes sense to use the largest chip you can. It may be ironic but I do 20x more mosaics with my widefield rig than with my long FL. Once you go wide you want wider! Olly

Thanks for the link. Dithering isn't provided by the mount but by the guiding software which must, of course, communicate with the mount and the capture software in order to move between captures. I think most modern capture software programs will communicate with PHD and dither. However, not everyone wants to dither: it's a complicated business to dither with a dual rig, for instance, and impossible if using an off axis guider on such a rig. Olly

Let's check a few things. The most important is that you are are using the camera's images of the B-mask diffraction spikes to focus? In other words, you're going straight from the B-mask through the camera to the images through the camera? No eyepieces in the story? Olly

Worth looking into. Do you have a link? Olly

I do quite of a lot of prints for magazine publication and find that a 'print curve' like this is useful since printing tends to darken the faint signal. You don't have to worry about the faint low level noise which it will add when seen on screen at full size. That won't show in print. Olly

That's much better and the processing, I'm sure, could further enhance the result. However, the Veil near full moon with an OSC camera really is a big ask! You can dither manually with considerable advantage. Olly

Many of the best planetary images in the world are taken by SCTs. Collimating them is very simple because they have spherical primary mirrors. Refractors are not widely used for planetary imaging but are excellent for deep sky. The ED120 would need the field flattener but, unlike the majorrity of scopes, it can cover full frame. See the third post down in this thread. The 120 Evostar will not cover full frame and is not in the same class as the Esprit. But, in short, a small format fast frame camera and SCT are the weapons of choice for lunar and planetary imaging. SCTs are very good value second hand because there are so many of them. My 14 inch is at least 16 years old and still perfect. Olly

My head is, frankly, infallible. It's a large, smooth dome which detects droplets from any direction. Sorry Gina, back to business!!! Olly

Your plan to de-star the blue then add it to the image is potentially sound but I'd do it in Photoshop. Also I would only add it to an HaOIIIOIII which had been processed to replicate natural colour in RGB (though there wont be much blue yet.) I don't think there is any sane way to mix false colour and natural blue so I'd start with HOO, as I say. I'd then de-star the blue and stretch it so that the background sky was a point lower than the background in the NB image. That way it won't slew the sky colour. I'd then add it to the blue channel in Blend Mode Lighten. I don't know if it would work but at least it's logical. Olly

This is exactly my personal history! I have no plans to use my 14 inch Meade for imaging since I think I can do better with my TEC140 (a different discussion) but the irony is that I never want to do mosaics with my small field of view/high res rig, only with my widefield. Trust me, I never saw this coming... Let's see if it happens to you, too! 😁lly

You have it all to come, Goran... 😁👹🤣 When you have wide, there is only one way to go and that's wider... Olly