wimvb

Imaging when you don't have proper astro darkness, is like imaging with light pollution. As long as it's moderate, it's possible. The sky brightness will be removed during processing, but you'll be left with the associated noise, and you need a much longer integration time to bring the noise down to acceptable/ordinary levels. Also, the blue channel will be affected most, and usually this is the part of the light spectrum where cameras are least sensitive. In short, double trouble. For me, imaging season has ended already, and I will be cleaning my scope and drooling over suppliers' catalogues until end August.

Quite so. When @gorann and I processed images from the Liverpool telescope, we only needed few subs to get good data. This is due to the combination of a large, albeit slow by amateur standards, mirror (2 m, f/10) with large pixels (15 micrometers, but binned to 30 um). At 20 m focal length, the pixelscale was 0.3"/pixel.

Worked just fine for me: Image Plate Solver script version 5.1 =============================================================================== Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]): +3.47031e-08 +0.000481831 -0.744175 -0.000481457 -1.24887e-08 +1.2026 +0 +0 +1 Projection origin.. [2497.786717 1544.292000]px -> [RA:13 29 40.606 Dec:+47 07 13.24] Resolution ........ 1.734 arcsec/px Rotation .......... -90.024 deg Focal ............. 441.34 mm Pixel size ........ 3.71 um Field of view ..... 2d 24' 20.9" x 1d 29' 16.1" Image center ...... RA: 13 29 40.641 Dec: +47 07 13.74 Image bounds: top-left ....... RA: 13 25 12.098 Dec: +48 19 02.42 top-right ...... RA: 13 25 24.023 Dec: +45 54 47.72 bottom-left .... RA: 13 34 09.123 Dec: +48 19 02.28 bottom-right ... RA: 13 33 57.317 Dec: +45 54 47.57 =============================================================================== Here are my settings:

I don't know about PS, but in Pixinsight you'd use subframe selector to measure and plot star profiles (fwhm and eccentricity) and backgroynd level on a number of subs. Any deteriorating conditions are easily revealed that way. You'd then set approval/rejection conditions and assign weights based on those measurements, which can be used during stacking.

Focus measurements for a reflector are a little trickier than for a refractor. Software can have trouble interpreting the doughnut profile. Ekos, which I use, at times just measures a bright area on the defocused star and returns sub arcsecond fwhm/hfr. Full frame focus measurements are generally more reliable. Such is astro life.

My ASI174MM-COOL has 5.86 um pixels and a small chip (1900 x 1200 pixels). Paired with a moderately sized scope (1000 - 1600 mm), it hits the sweet spot as a galaxy hunter. Nowadays, ZWO concentrate on large(r) sensors. If you don't want the large files asdociated with these, you can set ROI while imaging. This is like cropping, but without the large files raw data. What I don't like about ccd is the long download times when doing alignment or focusing. In all fairness, this wouldn't be an issue during data capture.

The light gathering power of an imaging system is proportional to (p/F)^2, where p is pixelsize, and F is focal ratio, fl/D. Looks promising for F-ratio, right? Not so, because decreasing F (=going faster) by decreasing focal length puts light from a larger patch of the sky/object on each pixel. The same relationship can be rewritten as The light gathering power of an imaging system is proportional to (rD)^2, where r is pixelscale, and D is aperture. This means that at constant pixelscale (level of detail, if you will), aperture rules. This is basically the math behind @ollypenrice's argument.

I use an ASI174 at 1000 mm, which gives a fov of 39 x 25 arcminutes (0.65 x 0.41 degrees), and do polar alignments withou any problems using kstars. Both astrometry and astap work.

Can you post the image here? There can be several causes: Wrong fl or pixel size Too noisy Bloated stars Star trails Etc

The image may be so strongly underexposed, that the background shows discrete levels. You can try dbe with "normalize" checked in the image correction settings. Then stretch gently with midpoint in histogram not too far to the left.

I don't know about dss, but PI looks for stars among fine structure details. This means that if your images are oversampled, you need to "widen your net", and increase the number of layers (level of detail) that is used to detect stars. My guess is that dss has a similar setting under a different name.

I believe you mentioned tube wall thickness before. At f/4 I would probably go for the sturdiest scope. In any case, get it with rings and a Losmandy dovetail bar. With rings means you can add a top bar (vixen style) for extra rigidity and to allow a guide scope or other hardware.

Works for me (AZ-EQ6 with eqdir cable and EQMOD driver). Although I must admit, it hasn't always in the past, for reasons that were beyond me. I do regular updates of my software. Have you tried switching the computers that control the mounts? Ie, computer from mount 1 (not flipping) on mount 2 (flipping) and vice versa? That should tell you if it is the mount (including cable) or the software that is to blame.

I think @Firas is quite happy with his ONTC which is now operational in my observatory, and remotely controlled from his home in Stockholm city. It looks quite impressive on top of an EQ6-R with a Moravian G2 8300 and a Lodestar X2 OAG. Guiding is good and Firas first image can be seen here. https://www.astrobin.com/fcqzl2/?nc=user

I've had similar problems with PCC on occasion and have had to revert to ordinary CC. You could try to use scnr Red at less than 100% with a lightness mask to tame the red. This will leave the other colours in peace. Just an idea.

I agree, great detail and much better colours in the re-edit. How did you colour calibrate?

That's the one I use. It connects to Aladin, which is an online sky chart where you can click on any target and get information from Simbad.

Ok, that makes sense.

Another pastime (maybe as a follow up) is trying to locate impact craters on earth, using Google Earth.

And so does the severe astigmatism. Btw, @Vega, have you had opportunity to test the scope yet. I read a long time ago that the prudent way to fasten the clips is to tighten them only so much that you can just slip a thin sheet of paper between the mirrors and the clips. And as far as water is concerned, this will always leave stains. When I was still active in the semiconductor industry, we used to apply an iso-propanol rinse (from a squeeze bottle) after a deionised water rinse, and dry with filtered compressed air. Anything to avoid water stains.

How did you ever manage that? The mirror is in a baffled, closed tube. I would imagine that taking the cell out would be much easier.

Pixinsight: process - geometry - resample

Simbad found some 3356 entries within your approximate field of view. In all fairness, some of these are stars, some are double entries, but most are galaxies, quasars, etc. Here's what PixInsight's solver came up with Eg, the one called PGC126753 (bottom edge) is some 2.5 Billion light years distant. Nice catch!

You have to create the aggregated preview image AFTER background neutralisation. Also remember that this image CAN'T BE REUSED. This is because it's a new image, and won't get the same treatment as the original. This is not a preview, but an image made from two previews. workflow: create your previews. Let's call background preview "preview 1" M81 preview = "preview 2" M82 preview = "preview 3" Do background neutralisation with preview 1 as reference. Create aggregated image from preview 2 and preview 3 Do colour calibration with preview 1 as background reference, "Aggregated" as white point reference. Original image as target. Uncheck structure detection. Pull the small triangle over to the original image (target), in order to apply the process.

I posted this image on the Swedish astronomy forum, and got a reply from a member there. He searched a few of the very faintest galaxies in my image (on the right hand side, just on the edge) and found a redshift of 0.36. This puts that faint fuzzy at a distance of 4.6 Gly. Imagine, the photons that I captured left that galaxy when the solar system started forming. Mind boggling.