ollypenrice

Not necessarily. The better the data, the easier the processing. Let's assume that, in the first example, you have a number of contributions which fully overlap. That's to say a single image, not a mosaic. These should be linear at this stage. These might be RGB, one shot colour (the same thing), luminance, Ha and OIII. Using Registar, you would put them all into one folder with nothing else in it. One of these frames would be your definitive crop, meaning all the others can cover it fully with, probably, a bit to spare. 1 Open just your definitive crop (AKA Reference Image) in Registar. 2 Choose 'multiple source' and click once on 'Register Images.' The software will open all the images and register each one, resizing and re-aligning where necessary, 3 Go to 'Crop and Pad' and click once so that each image will be cropped to be a perfect fit on your reference image. Save these. So... in just two clicks you have a full set of linear images which fit each other perfectly, just as if they all came from the same telescope. Absolutely nothing to it. Next, you'd want to remove gradients on all these images individually. I'd use DBE or ABE in Pixinsight. I'd also run SCNR Green where needed (it usually is) and Blur Xterminator. Any images with the same filter would then need to be blended together. Eg you have three Ha contributions. I think some software will read them and weight them according to S/N ratio but I don't know about that. I'd probably give the three Ha images a basic stretch, stack them as Photoshop Layers and adjust their opacities till I got the cleanest blend and flatten them. Someone will know a more mathematical way of doing that. It wouldn't be the end of the world if you just gave all three to Registar, weighted them equally and settled for that, assuming they were all worth having. Now a multi-source mosaic is always going to be more difficult. They are hard enough when everything comes from the same rig. I think APP is the software of choice for mosaics, at the moment. The first and most vital step would be flattening each panel (ABE or DBE/SCNR Green) before asking the software to make the mosaic. I'd start with a single panel project! If nobody in the group has Registar I'd be happy to do the Register-Crop bit and send them back out. (Possible now we have fibre internet... ) Olly

This has already been done very successfully - more than 13 years ago, no less. https://apod.nasa.gov/apod/ap101005.html In the past it really needed Registar to be workable but, these days, other software can co-register and resize data from different setups. I collaborate with other imagers fairly regularly and also collaborate with myself, in that I use very old data to enhance a new image. The Squid data for this new image are about 10 years old and from a setup I no longer have. Olly

Nice clean image. Olly

This is an unusual target. What you have is as tight as a drum, which is obviously a good thing. I think your stars are small and crisp, given their brightness. Spikes or not spikes is just one of those things. In any event, they are good spikes. There is also nicely structured detail in your nebulosity. For an M45 of this depth, it's very good. More than very good, in fact. The question is, How deep do you want to go? There is an enormous amount of nebulosity not showing at this depth but going after it is not compulsory, it's just an option. All depths are valid, in my view, if the data are properly respected. Olly

Nice to see them isolated in this way. 11 LY long, it seems... Olly

It might very well simply stop working, though. A guest here made a cool box for his DSLR and killed it! I'm pretty sure he would have been nowhere near -20C either. In the last 8 years, very cold nights here have simply stopped happening, as has significant snowfall. We'd routinely see -12C and sometimes -19C. Nowadays -6C counts as cold. Olly

The 'Insulate rather than cool' solution is popular here on the continent but never seems to get much exposure in the UK. Olly

Sorry, I was thinking only of the speed of the system, not its resolution. Flux Per Pixel, maybe? Olly

I'm always wary of WO. Too much 'pretty' and not enough substance for my taste. (I have one and have used many.) Olly Edit: As an example, I wouldn't hit a burglar with a WO scope...

If we really want mental clarity, what matters is aperture per pixel. There is just no standard, commonly used, term for this but I think there should be. I'd love a RASA 11. Our RASA 8 (actually Paul Kummer's RASA 8) has proved to be very stable once set up. The biggest surprise is the way it holds focus so well but another treat is the absolute freedom from dewing caused by the camera heat and fan. Olly

Thuggery!!!! lly

After @gorann spotted that he had the data to combine a Bat image with a Fireworks image, Paul Kummer and I found that we could do likewise with one more filler panel. Here's the result. I also found, at last, my 10 year-old CCD Tak106 OIII linear data for OU4, the Squid. Despite having 24x30 minutes of OIII, the signal was weak but brutal stretching using the X-suite software allowed me to get far more out of it than I did originally. It was added to green and blue in Photoshop using Blend Mode Screen, heavily clipped. (I usually use Blend Mode Lighten.) This is the only narrowband in the image. Paul drove the scope and stacked up the data, I did the post processing and the OIII. The galaxy has also been very gently enhanced using a TEC 140 image. The big version is here. https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-ct23L2q/A Thanks to Goran for the good idea. Olly

An SGL member on here may remember a club visit to my place during which, on their first night, she was sent to find me because nobody in her group could find Polaris. She reckoned they'd asked her to do it because she was the only woman in the group. If you're used to a dark sky, and can routinely see Ursa Minor, it is very easy to pick out Polaris but you have to be used to it, as you say. Olly

I'm doubtful about the wonders of computerization. It very easily turns itself from the solution into the problem. Olly

That's very kind of you, Goran, but unfortunately it only extends our Fireworks panel downwards by a small amount. The overlap with ours is considerable though we go over to include the open cluster. I think it will be well worth another panel. Olly

We almost have it, with just one small block missing in the bottom right hand corner. It looks great. Thanks! Olly

Great idea! We probably have most of this FOV as well. Hmmm... Olly

Don't forget that plate solving isn't compulsory. You can derive the RA and Dec co-ordinates of your image centre from a planetarium loaded with your specific field of view and then go to a nearby star, re-centre your mount on that star, then simply drive to the co-ordinates manually. Olly

There's a lot to be said for being undersampled when starting out since the undersampling will absorb errors in tracking and focus. You'll also catch more light per pixel which speeds things up. Up to 50mm or so, you're in very tolerant terrain. Going up to a hundred mm increases most of the difficulties. One of the instruments I use is a 135mm Samyang but it is not an easy setup to use. Quite the opposite. Olly

Regarding focus, the usual advice is to focus on a star located at one of the four points where the one third lines intersect. (These are four imaginary lines, each parallel with one of the edges of the chip and one third of the way over to the opposite edge.) This is supposed to give the best compromise between centre and corners. Olly

Sampling rate is an important consideration in astrophotography. It defines how many arcseconds of sky are projected onto each pixel. While this will affect the resolution of detail in terrestrial photography, it is far more important in AP because stars are very awkward things for lenses to control. All the lenses above will leave you undersampled (pixels too large to separate details which can be separated by the optics) but keeping to the longer end will give a smoother result. That argues in favour of 50mm. Prime lenses have fewer elements than zooms, generally meaning cleaner stellar images. I'd always go for a prime in AP. The Canon Nifty Fifty on your list has form in AP - and very good form. How its Sigma rival compares, I don't know, but the Canon has done good things. While it would be nice to shoot astro shots wide open to get more light in the time, it is usually difficult in reality because stellar distortions creep in. Rather than stopping down with the diaphragm, which will create artifacts around stars, you can consider stopping down with a front aperture mask instead, either cut from card with a compass-cutter or made up using stacked filter rings. Another factor, though, is tracking. Do you intend to use a tracking mount to 'unwind' the rotation of the earth? There are many available, the cheapest option being a home made 'barn door tracker' - it will Google. On a fixed tripod the case for a shorter focal length arises from its ability to expose for longer without trailing. Why is a shallower depth of field easier to focus? I can see that it 'snaps into focus' more readily but, conversely, the focal plane is much shallower and, therefore, more critical. I'd have thought that the two characteristics cancelled each other out, at best, and more probably mean that a deeper focal plane/slower F ratio is easier to focus. Olly

Long subs are strictly for cooled cameras. My standard narrowband sub with that rig was of 30 minutes. Olly

Not the RASA, no. Tak FSQ106 with an Atik 11 meg at 3.5"PP - so a lot of light per pixel but only 50% QE. Olly

For many years I've preferred my own experiments over the widely accepted orthodoxy. The orthodoxy is, let me stress, usually right but there are exceptions. Two examples: 1) in CCD imaging I found that a 30 minute sub did go deeper than 2x15 minute subs. 2) Dither is no big deal with a cooled camera. You don't need to dither if it creates new problems. In post-processing I reject far more of the orthodoxy but that's another story. Olly

It's very good, no question. But it is also, by a mile, the brightest DSO in the sky. When I last imaged M42 I used 11 second subs for this, the Trapezium region, and 15 minute subs for the outer nebulosity. That gives an idea of just how bright the Trapezium is. Olly