symmetal

This was intended to be a two panel mosaic but have only managed to capture the bottom half at the moment. RASA 11 V2, ASI2600MC and EQ8-r, 2.5 hrs of 90 second exposures. Stacked in APP, processed in PI, and finished off in PS. I thought the tight cluster of yellow stars on the right would have a designation, but apparently not, not even in Aladin. Alan

Most impressive with plenty of detail and colour, including the pink tadpoles.😊 Alan

Very good image, well done, though you should be able to tease more colour from the stars and nebula. 🙂 Alan

Excellent, and very impressive considering the altitude. 😊 My only query is the edge of the area of sharpening on the flame nebula looks a little hard. Alan

Hi Jon, The dB (decibel) is pretty much the standard unit for specifying audio and video gain as it's more convenient for expressing large and small gains without getting into large numbers. I worked in BBC Television broadcasting (back when it actually made real programmes 😉) and the dB was the only unit used. Gain in dB = 20 * log( Vout / Vin ) where Vout and Vin are the output and input voltages. This Wiki dynamic range article links dB and stops which should help. Note it refers to 10 * log as it's referring to power ratios and not voltage ratios as you'd measure in an amplifier. Power is related to the square of the voltage. Power in Watts = Volts ^ 2 / Resistance to make it more confusing. 🙂 With regard to exposure and stacking the only difference as far as noise is concerned between 10 x 1 min exposures stacked, and 1 x 10 min exposure is that the first has 10 amounts of read noise added against 1 for the second. If you expose long enough that the noise from your sky background in each sub is significantly greater than the read noise it makes the read noise added insignificant. Once this point is reached there is no reason to continue exposing and it's better to start another exposure. Sharpcap has a useful utility to work out these optimum exposures if you wish to check it out That being said 3 mins should be fine to be getting on with, unless you have bad light pollution where shorter exposures would be better, as the sky background noise is greater and the read noise is swamped earlier. My RedCat is actually a WhiteCat as they had that option at the time and I had to return my RedCat as it had poor star shapes in one corner. The second was worse and the third I ended up with was a white one, which was a lot better but not perfect. I got mine when they first came out and QC was possibly overlooked in the rush. Nowadays they seem to be excellent performers for the price and there are autofocus mods available now for them if you need it. Alan PS. Your hubble palette version looks cleaner than your original version. 🙂

Altair are using a linear scale for the gain, while Zwo are using a logarithmic scale in dB. Their gain scale is actually in 0.1dB steps. dB gain values are a comparison or relative value only and don't specify an absolute value unless reference units and values are given. The response of the ears to sound levels and the eyes to brightness levels are logarithmic in nature so a logarithmic scale is useful to refer to them. APT will just use the gain values given in the camera driver so using the 26C camera APT gain will start at 100 and you will have a separate HCG on/off switch. If you connect a Zwo camera APT will use gain values starting at 0 with no HCG on/off switch as this is switched automatically. Altair use linear gain 100 and HCG off as the minimum value while Zwo treat this as the logarithmic 0dB reference gain value, corresponding to an actual gain of 0.77e/ADU and the Zwo gain always refers to the e/ADU scale. When Zwo turn on HCG mode at their log scale 100, they reduce the actual camera gain to compensate, to prevent a change in the e/ADU camera output when the HCG is turned on. Altair gain values are not tied to the camera e/ADU output but just the amplifier gain values. The HCG mode gain is treated separately and turning it on will increase the camera output by around 3 times giving a corresponding change in the e/ADU output. To get an actual e/ADU out of their camera, corresponding to a specific effective full well or dynamic range, Altair users have to juggle the amplifier gain and LCG/HCG mode at the same time. Yes, I would use gain 100 and HCG mode on. This gives the same camera e/ADU output (brightness) as gain 300 and LCG mode on (which is the same as HGC mode off.) LCG on really just means HCG is turned off. This is equivalent to the Zwo gain setting of 100, though it's a coincidence the gain values happen to have the same number, as explained above they refer to different things. As you say Altair gain 100 and HCG on gives a lower read noise, and also a higher dynamic range, compared to Altair gain 300 and LCG on, (although they give the same brightness or e/ADU output). There are only really only two gain settings really worth using on the Zwo. Zwo gain 0 = Altair gain 100, LCG mode on = 0.77 e/ADU. Gives highest well capacity and dynamic range, but higher read noise. Zwo gain 100 = Altair gain 100, HCG mode on = 0.25 e/ADU. Gives lower well capacity, almost as high a dynamic tange, and much lower read noise. It's all a bit complicated but hope it's a bit clearer for you Jon. 🙂 For information, Zwo gain values are in 0.1dB steps, so Zwo gain 100 is 10dB higher gain than Zwo gain 0. 10dB is equivalent to a linear gain change of 3.16 times which is very close to the linear gain change when HCG mode is enabled. So Zwo likely chose these values on purpose. 😁 Alan

Your HCG on at 26C gain 100 is the same as the Zwo gain 100 setting (which I use), where HCG is automatically turned on, but the gain meanings used in the the camera drivers are totally different, and I've worked out why the dynamic range goes up on the Zwo at gain 100. Using the e/ADU values is the only way to give an absolute gain value. When the HCG is turned on the absolute gain increases by 3.08 times. At the 26C camera minimum gain of 100 this is the difference between 0.77 e/ADU at LCG and 0.25 e/ADU at HCG ( 0.77 / 0.25 = 3.08 ) When the Zwo driver gain setting goes from 0 to 100 it's the same as the 26C camera gain going from 100 to 308 in LCG mode. When the Zwo driver gain reaches 100 ( or 26C gain 308), the internal camera gain setting is reduced by 3.08 times back to the equivalent 26C gain 100 setting so that there is no sudden change in the Zwo camera e/ADU output. This reduction in the internal camera gain in the Zwo, back to its minimum value, increases the effective full well capacity again so the dynamic range increases also. 🙂 The 26C is more versatile but is rather more complicated than the Zwo method. Alan

Hi Jon, Yes, from your graphs, the gain in e/ADU is 0.25 for gain 100 with HCG, and a similar e/ADU for gain 300 with LCG. Note also that in LCG mode there is little real change in read noise with increasing gain. I'm not sure what the dynamic range units are in your graph but they aren't so extreme in reality. The graphs for the ASI2600 show it more realisticly in camera stops. On the Zwo HCG is on at gain 100 and higher and off below gain 100. There is an apparent increase in dynamic range when HCG kicks in (not sure how that actually works) so I wouldn't worry too much about the full well figures. For most images you won't really notice any difference for normal gain ranges, and only at really high gain settings which you'll never use is it an issue. Alan

The HCG mode should normally be used with a lower 'normal' gain setting to get the benefit of lower read noise while preserving dynamic range. This Altair Astro help page should help. It does specifically say that HCG at gain 300 is too high a gain setting, giving more noisy results. This Sharpcap forum page also goes into detail on the 26C and 26M gain settings which should help clarify things. I would assume you can use LCG at gain 300, as unlike Zwo cameras, the HCG on/off is independent from the gain setting. I only have Zwo cameras. Altair Astro also don't seem to publish gain and noise graphs etc. for their cameras by the look of it. With Zwo cameras, with the same sensor, there is not much reduction in read noise with increasing gain, once HCG is enabled, so there is no actual benefit to be had using a higher gain setting with HCG mode. Alan

Have you tried it with focusing runs from other days to compare results. The blue graph not being as high on the right shouldn't be a problem as there are enough points there to work with. If you wish you could increase the number of steps from 9 to 11 to get more points and/or increase the step size a little to give a slightly steeper curve. Alan

I wasn't aware of this tool. It looks very useful. NaN is computer speak fot 'Not a Number' and is generally created when the result of a floating point calculation produces a result which is not a valid floating point number. Your focus data looks reasonable so this is likely a programming error in the application. It's worth contacting the author on the SourceForge support page. Alan

Thanks everyone for your kind replies. 😃 My first attempt many years ago with a smaller sensor and LRGB imaging needed a four panel mosaic and with the more basic processing tools of the time it was impossible to match the panels so I've not tried again until now.🙂 I used to carry the RASA 11 out to the fixed pier in the roll-off shed each time it looked promising, but ended up dropping it one time, so I leave it out pretty much all the time now, until the shed blew down 😬when I had to bring it indoors for a few days. Yes, you're right there. I'd like to see your wider angle view when it's done. I think it stands out more when it's surrounded by a darker background. Using the new GHS (Generalized Hyperbolic Stretch) tool in PI is good for stretching just a narrow range of brightnesses using the Symmetry Point slider, so you can stretch the faint dust without affecting the brighter areas. Just for you Adam, how's this 😊 I think it would need a bigger mosaic to show off the fainter dust better Olly, as Fegato is doing, so I'll have to hope for a longer spell of good weather. 🙂 Alan

I've never been happy with my previous attempts at M45 so thought I'd have a go with the RASA 11 which is a bit overkill for such a bright object but it has revealed some extra dust on the outskirts. RASA 11 v2, ASI2600MC on EQ-8r, 90 mins per panel of 90s exposures. Stacked in APP, processed in PI and finished off in PS. Binned 2x in processing.The PI PhotometricMosaic did a good job in blending the panels too. 🙂 I first processed it without using star removal and tried again using star removal, so see which you prefer. Using star removal Without star removal Alan

Thanks Olly @ollypenrice, On my Horsehead I posted recentlyI did use PS layers to change the hue/brightness of the two small blue flares to match the background which worked very well. Looking at the RASA 11 FOV I'm surprised that the flares weren't a lot worse. I assumed they came from Alnilam, outside the camera FOV but well within the RASA FOV so the effects were minor. It seems Mintaka was just far enough away not to cause the hard edge full width flares, along with the rainbows, as the postings above show. I can use PS layers to reduce the brightness/colour on the triangular flares and 'paint' out the rainbows either with a different image or content aware fill as necessary. My attempt at reducing the aperture from 279mm to 250mm to reduce the flaring only reduced the f-ratio from 2.2 to 2.48 so maybe it wasn't enough to really affect the result. A more restrictive aperture mask, f2.8, f3.3 or f4 even,and subsequent longer exposures may be an easier solution on problem targets if it works. Do you think it's worth a try or is my reasoning wrong? 🙂 The trials and tribulations of fast scopes I suppose. Alan

Over the past good week I've imaged several objects and a couple are spoiled by flares from bright stars around the edge of the RASA 11's FOV circle. I did 3 hours or so on the Leo Triplet to resolve the tidal tail from NGC3628 which it has done but at the cost of a horrible flare from Chertan, a 3.3 mag star near the edge of the RASA 11 FOV. A similar image taken a year ago using the Celestron M48 adapter fares much better in this respect. The M48 adapter is OK with an APS-C sensor but creates massive vignetting on a full frame sensor, which is why I bought the UFC system. Here's a super stretched view of the unprocessed images. The black lines show the hard edges of the flares pointing to the offending star. My 'super black' conical end tube I made, going from the RASA 11 rear lens to the UFC filter adapter cured the multitude of flares from any bright stars nearby which affected almost all images, but it can't fix them at a that problem distance. I did try an aperture mask on the front of the dew shield to reduce the scope aperture from 279mm to 250mm but it had no effect on the flaring at all, which surprised me as I thought that would block light rays from the edges of the mirror and lenses, so would have some benefit at least. I can reduce the diameter of the front opening on my conical tube which may possibly reduce the flaring, but at the expense of increased vignetting, but not enough to be worth doing. I suspect the M48 adapter makes it better as there is virtually no light from the problem distance reaching the sensor due to the almost 100% vignetting at the limit of the RASA 11 FOV. I tried M78 expecting problems from Alnitak so checked it after a few frames, and tried repositioning M78 to the bottom right to move Alnitak further away which helped to some degree but not enough. I now use the above Telrad circles in Stellarium to check any targets before imaging. Bright stars inside the RASA 11 FOV but outside the camera FOV don't really cause an issue. A series of heavily overlapping mosaics should help with most problem targets I suppose. Alan

Ta Daa!! Not much wind today and the sun even appeared, and it's back up in 90 mins. The two roof halves are held together with 6 self tappers but I only recovered one. The ones I have are too narrow so I'll have to order some. So I've put the straps on for the moment as a precaution. The split panel at the back corner should be easy to fix as it's under no stress. The gaffer tape isn't really needed to keep them held together. The 60W tube heater is running inside to dry out any dampness in the mount. The Oculus all-sky camera under the white cover sufferered no ill-effects. Fibre glass resin and cloth has just arrived too. 🙂 Next week is looking promising. Fingers crossed. Haven't seen that much green for months. 😃 Alan

Yours looks very neatly done. 🙂 Mine's a 5' x 4' shed and at the time, (10 years ago) was the only one I could find with full width double doors. As you can see from the pictures the roof locks the sides in place as it's slid in place from the front and back (it's in two halves) along pre-formed grooves. The top door spigot locates in a hole in the roof too. In a very strong wind the front of the roof can lift and the door top spigots jump out and the doors detach. The interior then acts as a sail and the roof side fixings aren't strong enough to hold the sides up and pull out of the side grooves. Putting straps around the whole shed and base front to back when it's windy prevents the roof from lifting and starting the chain of events, which has worked well so far but does rely on accurate wind forecasts, or I leave the straps in place when it's not in use. The shed base is locked to the concrete pillar by utilizing the part of the base that was cut off attached to the wooden board. I could 'glue' the roof to the sides up to where the door spigots are, using fibre glass cloth and resin, (arriving tomorrow to repair the side split) which should prevent the roof lifting too much. Alan

Thanks for the new comments and suggestions. 🙂 I found the roof. It was about 150yds away due East in the scrubland. I had to fight my way through 10 yds of waist high brambles to reach it. It looks undamaged, just muddy, so I have all the parts. I thought of using a fibre glass repair kit to repair the split. It's a resin shed rather than pvc or similar and the panels are quite rigid so it should take ok. It doesn't have to be neat. 🙂 Just need the wind to die down and the rain to stay away for a while now so I can try and put it back together. Alan

Thanks everyone for the kind replies. 🙂 It's been forecast around 50mph winds many days here since before Christmas and as others have said the actual wind speed has been significantly lower. Same here, so I ignored another 50mpgh forecast today. I thought of getting another shed of the same model and using the existing base to save cutting out the slot for the concrete pillar, but it's listed as out of stock on the shed websites that list it, and isn't in the manufacturers catalogue any more so I think it's been discontinued. If I can't find the roof, or it's too damaged, I'll have to start again with another model. 😔 Alan

Went to look for the missing roof but nowhere to be seen in torchlight. There's some overgrown scrub land to the East which is the direction it likely would have blown to, so I'll resume the search when it's light. Alan

My roll-off shed for the RASA 11 is fine up to 50mph winds but if it's forecast higher than that I run straps over the roof and under the base as a precaution. The winds this morning from 10 to 11am were much higher than the forecast 50mph and here's the result. 😭 Luckily there was no rain with the wind, so everything is still dry and the scope looks fine. I've brought the scope indoors and coverered the mount with a taped down bin bag for the moment. The mains power was still working so the 60W tube heater was happily heating up the surroundings. 🙂 Unfortunately one of the shed panels has split down one edge where it bends to form a corner so it's not a simple case of putting it back together again. The large coarse thread hollow plastic screws used to hold the panels together usually work well in that under severe stress they just pop out and don't actually break anything. I may be able to 3D print some brackets to hold the corner together where it's split. While writing this I just realised the shed roof wasn't among the debris so I'll have to go and look for that when it's stopped raining. This coming Sunday is the first forecast 'green' night for well over a month so I'll see if I can get it rebuilt in time. The other plastic shed in the picture housing the 10" LX2000 and the weather satellite receiving gear is fine, as well as the satellite dish, though I've had to kill the mains power to it as it branched off the power to the flattened shed. Alan

I did a test with a Coma Cluster image and indeed SXT does remove galaxies below a certain size even though they are still elliptical shaped. Top is original, bottom left is SXT background and bottom right in binned 2x2 SXT background. The smaller core must look more star like and the elliptical overall shape is assumed to be a distorted star. This explains why the annotated image may indicate small PGC galaxies which aren't visible on the image. Alan

I'll try content aware fill and see how it compares. For filling in narrow areas it sounds a good method. I haven't had the grid artifacts from SXT. It's always behaved itself until now, when it's moved the galaxies too. I have a similar shape cable router though clipped to the scope front edge. I carefully designed it so that the area in front of the corrector was exactly 180 degrees. The RASA 11 has a larger central obstruction so there's room to run the cables down the side of the camera. That's impressive, and indicates what the AI was 'thinking about' at the time. Maybe when it was being trained with analysing thousands of star images a rogue image got inserted for fun. 🙂 Alan

A useful article which put things into perspective: Is it true that bananas are radioactive 🙂 Alan

In my PI SXT processing of the above image it removed the stars but left the extended diffraction effects from Alnitak etc. on the background layer as I expected and so had to carefully remove them in PS. The little galaxies as seen on the annotate image above were left on the background layer, again as I expected. I thought I'd reprocess and bin the data by 2 straight away in PI rather than downsample the final result by 2 in PS as my above image is. This should give better S/N in the image. However when I ran SXT this time it removed all the diffraction effects too and put them on the star layer along with the surrounding blue flaring leaving a really clean background layer with no residual star bits. This should make removing the diffraction effects much easier. However BXT also put all the little galaxies on the star layer too which is not so good, as it'll make the galaxies too dim when I add the stars back in at a lesser stretch. This means I'll have to manually move the little galaxies back to the background layer before stretching. Here's a PI screenshot showing the layers. This is the first time this has happened in my SXT processing. Has anyone one else had anything similar. I've always binned the 6200 mono data by 2 in PI and it's always behaved as I expected, leaving diffraction effects and galaxies on the background layer. Alan