wimvb

Vizier & Simbad, so far. I haven't really looked at GAIA yet.

Yes, the 150pds is retired for now.

While waiting for my main target to reach its best position, I decided to test my rig on a faint target. UMa I is a dwarf galaxy of the Milky Way, in the constellation Ursa Major. This galaxy was discovered in 2005 by studying images from the Sloan Deep Sky Survey. It is also supposedly the dimmest dwarf galaxy ever found. UMa I is located approximately 330 000 ly from the sun, and has a radius of 11.3 arcminutes. The galaxy consists of very old stars, red giants mostly, created in the early days of the history of the universe. As most other dwarf galaxies surrounding the Milky Way (some 100+ in total), this galaxy is slowly being ripped apart and absorbed. "This object was detected as an overdensity of red, resolved stars in Sloan Digital Sky Survey data. The color-magnitude diagram ofthe Ursa Major dwarf looks remarkably similar to that of Sextans, the lowest surface brightness Milky Way companion known, but with approximately an order of magnitude fewer stars. Deeper follow-up imaging confirms this object has an old and metal-poor stellar population and is ~ 100 kpc away. We roughly estimate MV = -6.75 and r1/2 = 250 pc for this dwarf. Its luminosity is several times fainter than the faintest known Milky Way dwarf. However, its physical size is typical for dSphs. Even though its absolute magnitude and size are presently quite uncertain, Ursa Major is likely the lowest luminosity and lowest surface brightness galaxy yet known." (From B Willman et al. ApJL, 2005, 626(2) L86 - L 88) I couldn't find any amateur images of this galaxy online, understandably. The data for this image was collected 27 March 2020. Setup details are in my signature. Total integration time was only 1 hour (30 x 120 s exposures) using an L filter, calibrated and stacked and annotated in PixInsight. What is in this image: Most of the stars are Milky Way stars in red colour: very few member stars (very faint red giants) of UMa I (only 50 - 60 are catalogued to date) in yellow colour:marked V1 and V5, two RR-Lyrae variables in UMa I in gold colour: two quasars in pink colour: several PCG galaxies at distances up to 500 Mly in gray colour: a galaxy cluster which I haven't been able to identify yet. Simbad reports a cluster ([SPD2011] 47308) in this area that is 6 600 Mly distant, but I very much doubt that this is it. An inverted image, showing the extent of the dwarf galaxy

My ASI174MM has 5.86 um pixels, and at 1000 mm focal length, my images are still moderately oversampled most of the time. Detail in your images will depend more on sky conditions and tracking (guiding) accuracy, than on pixel size. With smaller pixels, the signal will be smeared out across more pixels. Each pixel collects light from a smaller section of the sky than if you have large pixels. With 1000 mm fl, and even with 650 mm fl, a 3.8 um pixel camera has enough "resolution" for any practical purposes, even for galaxy hunting. As for sensor size, you can always crop empty sky from a galaxy image. Small sensors won't give you larger or higher resolution images than large sensors. But they will give you smaller files to work with. The main reasons I bought an ASI174MM, was that it has large pixels with a high full well capacity, and good pixel scale (arcseconds of sky covered by each pixel) at the focal length I wanted (1200 - 1600 mm at that time). Price was also an important factor. The small sensor meant that files wouldn't be large, and stacking would be faster.

Altair and qhy produce(d) a camera with the same sensor. These may still be available. What's your budget? There are several alternatives available from ZWO, QHY, Altair Astro.

I think that a fast acting 5 A fuse is better. On the camera it says that it needs up to 3A. The fuse is there to protect against power surges and obvious malfunctions, but the camera can handle currents slightly above 3A with no problem. Under normal operation, with the cooler running at full power and usb devices connected, the camera may very well draw more than 3A occasionaly. A 3A fuse will very likely blow before there is any real danger for damage. I would use a 5A fuse.

Ok, you've seen it. Replace it with a 5 A fast version. The 2 A is probably blown.

Some of these adapters have an internal fuse. Have you checked that?

That's right. Because of amp glow, any lights, including flats, need to be dark calibrated with matching darks. Several people have also reported that the read pattern of these cameras can change over time. This makes using bias frames questionable. And since the bias signal is slready present in the darks, there's no need for using them if you don't scale your darks.

For galaxies, the fact that a camera is modded or not, doesn't make much of a difference, unless the galaxy contains many Ha areas. Not necessarily so. This has more to do with sky quality and perseverance. This image, with 11.5 hrs of integration time, contains a galaxy cluster at a distance of some 5.4 billion light years. Not exactly half the universe's age, but close. And that's with a £1000 scope and £900 camera https://www.astrobin.com/jd2hjn/C/?nc=user https://vizier.u-strasbg.fr/viz-bin/VizieR-6?-out.form=%2bH%2bm&-source=J/MNRAS/392/1509&-corr=FK=Cluster&-out.max=9999&Cluster===ZwCl 0848.5%2b3341

Ekos does the same. Alignment to within 10 arcseconds is possible, if your mount allows it. Besides more data, guiding should be on your short list.

Use pixinsight dbe or abe for that.

Nice! More data. People use all kinds of gear, but what will improve your image most is to increase the amount of data.

Göran, @gorann, has a Mesu + oag, which works ok for him. His carries a dual rig Esprit 100 & Esprit 150.

I guide with an oag also. My rms values are atm also around or above 1", but that seems mainly due to issues with my mount, in particular stiction in dec. Last year I tested guiding with my st80, a finder guider, and oag, and I couldn't see much difference in the rms values I got. With the oag I can always find a star to guide on, but sometimes only at the edge, or only weak ones.

1 m, but in combination with a small sensor.

Arp 18, or ngc 4088, is one member of a pair of galaxies. The other member is ngc 4085, here the smaller galaxy near the bottom. Ngc 4088 is situated in Ursa Major, at a distance of some 35 - 40 Mly. Other galaxies in this image are at distances ranging from 270 - 970 Mly. Acquisition details: Telescope: SkyWatcher MN190 on a AZ-EQ6 mount Camera: ASI174MM-Cool with ZWO lrgb filters Exposures: L 106 x 2 min, RGB 50 x 4 min. Total integration time 13.5 hrs Processed in PixInsight.

That turned out very well, with the faint stuff just where it should be: visible but not "in your face".

I recognised ngc 3718 and 3729 immediately, having just spent a few nights with those. Very nice widefield.

My motivation is much simpler than Vlaiv's. I don't want to overexpose the stars, and at the same time I want to get good signal. I tested several exposure times, and settled for 120 s Lum. This also works well with guiding results, and keeps the number of satellites/sub down. At the same time, rgb filters have only 100 nm passband, as Vlaiv noted, vs 300 nm for L. My camera is most sensitive for green, so doubling the rgb exposure time makes most sense to me. It also seems to me that if you use the same exposure time for all four filters, either your L subs are over exposed, or your RGB subs are under exposed.

A mask? Sometimes masks don't work with scripts. In that case you can do the process on a clone and afterwards combine with the original with the help of a mask.

Coma correctors are inserted into the focus tube, so they don't add to the focus distance. Only a mm or 2 protrude. Glass also has an optical thickness, which is different from its mechanical/physical thickness. But that should be irrelevant here. My guess is that a coma corrector such as the Baader or Skywatcher, will work ok. But to be on the safe side, ask the supplier before you order.

CMOS cameras thrive on large number of subs, and most have sensors that have their peak sensitivity in the green part of the spectrum. If you find that the red and blue subs are a bit "thin", you are probably better off shooting more of these to bring the noise down. During post processing, the R and B channels can withstand the increased stretching that is needed to achieve good colours. Again, with the dedicated ZWO filters, this is probably not necessary. The median ADU values that you posted were already close enough. The sky is seldom neutral; natural and man made light pollution will give a varying median level to your subs. Yesterday night at 1 am, the sky looked definitely blue to me, despite the moon not being around. Aurora, even if not visible, will affect your green subs. Man made light sources will affect all channels, depending on the type of light source.

The corrector adds only one or two mm to the mechanical distance between the focuser and the T2 adapter, and doesn't influence the back focus of the corrector. But I can't tell you if it will change the focus position. This may depend on the brand of cc. Better check that with the supplier, or ask if you can buy a corrector under the provision that it will work, and if not, that you can return it for a refund.

3 arcsecs is as good as it gets, and then some. You shouldn't see any drift in dec during 60 s exposures with such a good polar alignment.