windjammer

I like the subdued palette and the stars are just right - both of which I can never get right.

I used an old servo and a direct gear coupling - probably not more than 1.25:1 ratio. No problem with getting bored while focussing - even though the servo will only manage a couple of turns per second. Simon

I recommend GraXpert as a vg gradient removal tool - its a free download, runs as a standalone program. Simon

The ccd in the 490 is a sony icx814 - the well depth is 12,500e. So a 16 bit a/d will have 5 counts for every electron collected (65,636/12,500). Put another way, the 16 bit space can count every electron directly with no need for analogue gain or offset. These can be provided in your processing software. Arguably, the camera is oversampled. I have a 460, well depth 18,000 so 4 counts per e. Depending on your view of Nyquist, you need two bits to count each e. Cmos cams have been moving up to 50,000e so a 12 or 14 bit a/d needs gain/offset to move the sampling range to where the data is. And even the 16bit cmos cams still have gain controls. The whole world is waiting to move past 16 bit! You will need darks IMHO, and if my 460 is similar, definitely if you bin beyond 1x1. Simon

Here is a quick process of the Cave Nebula, bicolour HSS from 6 and 7 June and plate solved. Oiii will have to wait until weather improves. Boo. Ha - 16x600s - 2.7 hrs Sii - 22x600s - 3.7 hrs Imaging scope: SW Startravel 150mm F5 Refractor, Atik 460EX mono, Diy GEM Simon HSS: and plate solved:

re rain - I find this rain radar site really useful. You can see it coming in god time ! https://www.meteoradar.co.uk/zoom/0/0/ActueleBuienradar?zoom=7&lat=51.507351&lon=-0.127758&region=London#

A fantastic result- beautiful. Re your tracking accuracy and smoothness issues, I have similar problems with my homemade GEM (gears are not high precision - made out of cordless drill gearboxes), and I live near a busy road and railway line so ground vibrations. I got over the tracking by using PHD and guiding at 10 to 20msecond exposures with 100msec between exposures. This boxes in the mount and drags it back on track before it wanders too far. For the vibration I made a mechanical shutter - a filter wheel that shuttles back and forth between an open hole and a black filter. When the PHD control lines (I use ST4) waggle up and down too much the shutter closes and saves the exposure. Similar approach might work for you ? Simon

That is competitive with Morten! A heroic crop from the full frame! Very interesting pic. If you have PI it would be worth trying the plate solver (scripts->image analysis->image solver) and annotate (scripts->render->annotate image) scripts. The image solved image has data embedded into it that enables 'annotate' to label all the galaxies in the field, draw the RA/Dec grid etc. Side by side with the original pic it can be very interesting. Simon

Hi The Witch, the Broom, and the Witch's Familiar (lobster like creature playing the piano far left of the stick!), NGC 6960 - SHO composite Here is a more carefully processed version of the Witch's Broom from June. Images are the Western Veil supernova remnant: a letter box crop pic, and North and South segments separately. Also, thanks to an internet 'bot, a fully plate solved and annotated version of the first. Details: Veil Nebula, supernova remnant, NGC 6960 Distance: 2,400 lyrs Diameter: 130 lyrs Age: 10,000 - 20,000 yrs Angle subtended: diameter 3 degrees Magnitude: 7 Constellation: Cygnus, The Swan Photograph taken in Astronomik narrowband filters: Ha (656nm), Sii (672nm) and Oiii (501nm). Total exposure time 11.3 hrs. Ha 1x1 bin - 42x 300s = 3.5hrs, 16-17 June, scope West side, prime focus Sii 1x1 bin - 46x 300s = 3.8hrs, 23-24 June, scope West side, prime focus Oiii 1x1 bin - 48x 300s = 4 hrs, 24-25 June, scope West side, prime focus Rig: Imaging scope: SW Startravel 150mm F5 Refractor, Baader Diamond Track, (2.5x Celestron Luminos 2inch imaging barlow), Atik 460EX mono Guide scope: SW Evostar 90mm F10, with guiding XY stage, ZWO 120MM camera Guiding: 2 stage PHD: high frequency guide scope (mount tracking) and low frequency OAG image train guiding (guidescope flex) Mount: Home made German Equatorial pillow block mount, permanently rooftop mounted. Spring loaded DEC axis gearing. Other gadgets: ST4 based anti vibration shutter, ST4 based PEC Processing: PixInsight: Lights, Darks, Flats, Biases, Align Calibration, Linear fit, BXT, Channel Combination, SCNR(G). StarNet2 star removal/star layer GradXpert: Gradient removal Topaz DeNoise AI: Noise removal Affinity Photo: 32 bit image processing (curves, high pass masking, selective colour) Letterbox: North segment: South segment: Plate solved: Simon

I mainly do imaging, so I don't actually have to be at an eyepiece. Even so 3 or 4 nights on the trot would wipe me out - until recently! My scope rig has now become so reliable that once set up on target and camera running, I can go and kip! The only issues occur coming up to meridian flip or other collision, or PHD guiding losing lock. I set up a remote speaker from PC to bed so that when PHD starts bleeping I get woken up to fix. Other than that an alarm clock to wake every 90 minutes so I can go and check operations - and that is probably overkill. I have only got to this point in the last couple of months, but it has made the hobby a lot more liveable! Simon

How about if you packed out the protruding barrel of the eyepiece with layered tubes of plastic pipe (slit the pipe so it can be compressed or expanded to fit over inner /outer layers) until it fits into a 2 inch eyepiece compression adapter. If the 2" adapter has an M42 or m48 thread at the eyeball end you should be able to finagle your projection hardware onto it. If the eyepiece barrel is long enough you might get a hose clamp around the pipe to eyepiece barrel as well as the 2" adapter for extra grunt. Take your point completely about having a lathe for this hobby! Simon

exposures ?

>> don't have details to hand... could probably dig them out if anyone's interested. Yes - a humungous FoV. What did you do it with?

>>My idea of OK being it was grey, with a slight darker border and with several large dust spots, easily visible. Yep, looks about right

>>that an 11" RASA might be a candidate for the elusive imaging scope all rounder, I think you might be almost there with your 8". I am tempted. V impressive all things considered - an almighty crop! re final, final, on my monitor I think I prefer V-2! Its a little softer and more natural. Simon

Cosmic traffic jam!

Just tried this out - what great fun! Thanks for the info

The LED lights are a menace. Here in London we have had (yet another) Mayor's relighting program. The new luminaires are a step backward - almost no outer lip to suppress side scatter. Light is not in a downward cone but spreads to the horizontal and further upward. The LEDs are very blue, so the light scatters in all directions more than a warmer colour temperature would (think why is the sky blue). London night skies - never great - have become noticeably brighter in just the last couple of years. The LED spectrum has phosphors to generate broad band emission so filtering is very difficult. Narrowband imaging is still viable here, but a sensor histogram shows the light pollution step in only a few hundred seconds over a 1 degree fov. I have had to move down from 600s narrowband exposures to 300s because of this - and this at the zenith. Not enough fuss has been made about this in my view. The night sky is being stolen from all of us, not just astronomers, by laziness, incompetence, carelessness and greed. Don't get me started ! Simon

>> Does that mean every sub would be festooned with dozens of satellite trails? Of course, that's our fate! Pic full of possibilities - are you sure a reprocess aimed at the planetary would not improve it ? Or is it baked in ? Simon

Lovely. Great actually! If I may ask, what did you use to produce the annotated pic ? Very handy. Simon

Hi everyone A quick and dirty process of the Witch's Broom, Western Veil supernova remnant. Close in crop and the whole frame. Ha, 42x 300s from 16-17 June SII, 46x 300s from 23-24 June OIII, 48x 300s from 24-25 June Whole frame: Simon

Yes PHD2, but using ST4 interface through ZWO guide cam, as opposed to ascom or anything like that. PHD2 enbles you to control the interval between guide exposures, go Guide tab ->Advanced Settings -> Camera tab -> Time Lapse box The guide correction is issued as soon as the guide exposure ends. The next guide exposure starts after the time lapse has expired. Simon

Hi - interesting note on your guiding frequency. I guide at 10-20ms exposures and 100ms interval and get sub arcsec rms (normally!). If the mount is unruly, then hanging around for a multi sec exposure won't work. The earlier and smaller you catch a drift and correct the better. I don't totally buy into the 'chase the seeing' thing. What I have seen is resonance between exposures and the mount having time to move to its new position. So important to have an interval between guide exposure - correction issued - next guide exposure. No point in guide exposures while mount is moving to correct. Good thinking for playing with the guide parameters! Oh yeah - great pic IMHO! Good detail (almost) right to the centre. Simon

Hi Here is NGC 6820 and open cluster NGC6823 in Vulpecula. Pic is an SHO composite (SII, Ha, OIII mapped R, G, B). For once the colours came out about right without a huge amount of furious knob turning. PixInsight says: Image Plate Solver script version 5.6.6 =============================================================================== Focal distance ........... 750.73 mm Pixel size ............... 4.54 um Resolution ............... 1.247 arcsec/px Field of view ............ 57' 9.0" x 45' 43.0" Image center ............. RA: 19 43 11.446 Dec: +23 17 50.98 Image bounds: top-left .............. RA: 19 41 15.903 Dec: +23 43 05.63 top-right ............. RA: 19 45 24.530 Dec: +23 38 02.30 bottom-left ........... RA: 19 40 59.036 Dec: +22 57 32.68 bottom-right .......... RA: 19 45 06.259 Dec: +22 52 31.07 Sh2-86 subtends 25'x12'. The open cluster is 50 lyrs across and 6,000 lyrs distant and is ionizing the nebula, and presumably blowing the gas apart. Bok Globules are floating around hiding nascent solar systems. New stars are peeking out at the ends of the gas pillars as per the Eagle Nebula. Some of the twisting gas trails look like they might be Herbig-Haro objects. An interesting region of the Milky Way. Details: Photograph taken in Ha, SII and OIII astronomik filters. Total exposure time 7.8 hrs. Ha 1x1 bin - 14x300s = 1.2hrs, 08-09 June 2023, scope West side, prime focus SII 1x1 bin - 42x300s = 3.4hrs, 13-14 June 2023, scope East side, prime focus OIII 1x1 bin - 38x300s = 3.2 hrs, 14-15 June 2023, scope West side, prime focus Rig: Imaging scope: SW Startravel 150mm F5 Refractor, Baader Diamond Track, (2.5x Celestron Luminos 2inch imaging barlow), Atik 460EX mono Guide scope: SW Evostar 90mm F10, with guiding XY stage, ZWO 120MM camera Guiding: 2 stage PHD: high frequency guide scope (mount tracking) and low frequency OAG image train guiding (guidescope flex) Mount: Home made German Equatorial pillow block mount, permanently rooftop mounted. Spring loaded DEC axis gearing. Other gadgets: ST4 based anti vibration shutter, ST4 based PEC Processing: PixInsight: Biases, Darks, Flats, Lights, CosCor, Align Calibration, BXT, Crop, Linear fit, Channel Combination, SCNR(G), GradXpert, StarNet2 star removal/star layer GradXpert: Gradient removal Topaz DeNoise AI: Noise removal Affinity Photo: 32 bit image processing (curves, tone map, Topaz, high pass masking, selective colour) Simon

OK - here is log and frequency analysis at 19:51 log - looks OK'ish: Here is frequency analysis at 19:51 Here is log at 20:40 - note dither commands Here is frequency analysis at 20:40 I agree you have a period at ca 200 seconds, but worse when you dither! You have guide exposures of 2 seconds and no time delay between guide exposures. It would be interesting to see guide exposures shorter (0.5 or 0.1 sec) and guide interval 0.5s (mount completes move before you re-measure). With a higher time resolution perhaps the excursions would not be so spikey - and thus more controllable. Simon