symmetal

Thanks Wim. Most interesting. Looks like more non-stellar objects than stars. 🙂

Alan 

Thanks Göran for another unusual image. Though it reminds me more of a pelican with a runny nose. 😊

Alan

24 minutes ago, bosun21 said:

I have just bought a usb 2 way splitter to accommodate my Electronic filter wheel and my Electronic focuser. Thank the stars I don’t need another camera 🙂

I've used those USB 2 splitters and they work fine. In reality it's an unpowered 2 output hub so the USB2 500mA current supply capacity and data bandwidth will be shared between them. The EFW needs around 120mA so won't cause any problems and the bandwidth required is very small. 🙂

As an aside in another topic where you asked if the USB C output could be used to drive the filter wheel the answer is yes. You would need a USB C to USB 3 adapter similar to this and plug your filter wheel cable into it. USB 2 cables work in USB 3 sockets without issue.

Alan

Some coarse focuser knobs have an extension that slides inside the focuser mechanism so the grubscrew shown next to the coarse knob may release it. The grubscrew may be a dummy one and once removed you can access the actual focus knob grubscrew below. There may be two of them 90 degrees apart so rotate the focus knob to check if you find it doesn't come off when you unscrew one of them.

Alan

@George Sinanis Göran is imaging at f2 so 5min at f2 is the same as about 40min at your f6. So you would need around 80 hours total integration time to match it. Hope Göran doesn't mind me butting it but I'm at a bit of a loose end at the moment as my RASA's broken. 😟

Alan

FLO have had a response from Celestron, and Celestron have asked me to send it to Orion Optics for repair and quotes, and Celestron will supply them the parts as necessary. I'll email OO over the weekend with the details and see what they reply.

It looks like major Celestron repairs may need to go back to China, and they've suggested this for a quicker result.

Alan

1 hour ago, gorann said:

Out of curiosity, are there insurances for accidents like this in the UK? I have no idea if I could insure it in Sweden.

Accidental damage is usually included in home insurance policies, unless you specifically opt out, up to around £5000 or so per item I believe. More valuable items would need to be specified individually on the policy. I'll need to check mine fully and report back.

23 minutes ago, Peter Drew said:

I would have thought that a structure that had a platform to place the OTA on vertically but with a hole in it to avoid the camera unit, would be reasonably straightforward to make.

Yes, that's a possibility, with maybe blocks put around the outside to hold the OTA more securely in position. Care would be needed to avoid squashing the cables going over the rim. I have four cables , camera power, camera output, dew heater ring power and dew heater ring temperature sensor. 🙂

Alan

33 minutes ago, Stu said:

I guess the benefit of the vertical technique is that there is plenty of range  for positioning the dovetail into the saddle, whereas horizontally it needs to be a more exact height match.

Is there any way of supporting the scope either side of the camera, or does that still risk knocking it out of alignment? How about supporting from the rear?

My 3D printed dew shield would support the weight of the scope as the rear slots into the dovetail bars but the whole thing would be a bit top heavy. A shorter one just long enough to clear the camera and a bit beefier could be used. 🤔

The rear is a possibility if the support is shaped to avoid (or incorporate) the rear handle, and avoid the autofocus assembly sticking out in place of the focus knob.

Alan

8 hours ago, ollypenrice said:

I like the video method as well but would not want to be removing the camera from the RASA, given how critical its fitment is at F2. You could make a dedicated stand, though, rather like a saw horse but taller. The scope would sit in the vee in the way a log does. You'd want to design it so that it stood on the paving blocks for consistency of height and some range of adjustability would probably be needed to get the dovetail into the saddle plate for the mounting phase. Might it stand on braked wheels for fine manoeuvres?

Indeed, I wonder if we might not have invented a telescope accessory for the industry to produce...

Olly

Yes, the last part of the video where the scope lay on its side on the chair is the better orientation for a RASA to keep the camera attached. Your saw horse arrangement  sounds good. I thought of mounting it on a low level trolley like this

which would be handy for fine manoeuvering, and I have one in the garage. A raised frame could be fitted around the outside at the corners fixed to the bottom if necessary to stop the horse from sliding off and still allow the trolley handle to fold down when not in use. I can always lay another row of paving slabs if it would help. For use with one specific scope and mount, the height can be fixed so a height adjustment mechanism won't be needed.

As you say an opportunity for someone to make them for sale. 😀

Haven't heard anything back from Celestron via FLO at the moment so it may be the New Year before anything happens in getting it repaired. 😐

Alan

1 hour ago, Stu said:

This always struck me as a potentially useful technique, could it be applied for the RASA in any way?

That's a good video Stu. The second part where he had the scope in the horizontal position on the chair would be more applicable for the RASA to avoid having to remove the camera each time. I just need to find or make a stool of the correct height. Got plenty of time to do that now until I get the scope back. 😉 I was thinking of getting some thick foam mats to put around the base to catch falling scopes but the method in the video is much better.

52 minutes ago, gorann said:

Well, as an alternative to the video above, I made this arrangement in the obsy where I keep my 40kg Meade for safe handling, I am a bit of a coward I know:

Thanks Göran. I was also thinking about how to arrange a pulley system to lift it which would mean having a temporary frame over the pillar which is a lot of hassle but your arrangement made me think I could put a couple of wooden uprights and cross beam in the roll-off plastic shed you can see to the right in the blurry last photo I posted, above where the scope sits when it's in the shed. A channeled cutout in the base ensures the scope always ends up in the same location. Then have a pulley system similar to yours attached to the cross beam. The rope can attach to the handle I fitted to the top dovetail bar.

That's two good methods. The stool system shown in Stu's video is quicker to make so I'll likely try that method first. 😀

@Paul M One of these two methods may be suitable for you too. 🙂

Alan

Thanks @ollypenrice and @JeremyS I was a bit trepidatious when I first received it about lifting it on to the mount as there's only me here, but found a technique that seemed to work OK. The main issue is as you're lifting it from underneath to keep it upright all the time and not to let it tip to one side, as it quickly gets out of control. When the locking bolt seemed to tighten early I should have slackened it off and jiggled the scope around, instead of trying to see what was wrong.

I have fitted a handle to the top dovetail bar which is fine for carrying it around but is too high to use when putting it on the mount. I could try finding a position to place a  mirror so I can see the far dovetail groove while manoeuvering it into position.

Alan

9 hours ago, Stu said:

Oh no, that’s really not good. At least it sounds like it can be repaired which is great, hopefully covered by insurance?

Yes, it should be covered by insurance, whether it comes under items in outbuildings, as it technically wasn't at the time of the accident, or personal items I'll have to check. I'll see what Celestron quote for repair first, as it'll no doubt impact the next premium. 😬

Alan

Thanks everyone for your replies. Much appreciated. 

I've contacted FLO and they are contacting Celestron UK and helping to arrange shipment and repair costs. Waiting for their response. Hopefully they can get and fit a new corrector plate and align it without it needing to be shipped back to China.

I have an ADM losmandy clamp fitted to the lower dovetail bar which hooks over the top of the saddle to help take the weight while getting it into position though it's still back heavy without the dew shield attached so upward force is needed on the rear handle all the time until it's locked in. I think the right side dovetail edge clamped on the edge of the saddle at one point as the locking bolt didn't travel as far as normal. I should have loosened it off and jiggled a bit more but bent down to have a look while still applying upward force on the rear handle. The dovetail right edge likely dropped into the correct position at that point and the rolling motion to the right it created was too much to stop with the one hand on the rear. It continued rolling to the right and I had to let go when it had tolled 90 degrees or I might have broken my wrist.

If I'd kept hold of it it would have likely swung down and landed camera first which would have broken the camera, corrector plate and possibly the front lens assembly.  As it is, the top dovetail bar spread the force of the guide camera hitting the ground and corrector plate end got the most of the shock. I did find some scuff marks on the rear black casting where it rolled on to its side before coming to rest though they don't look too deep so I don't think there is any mirror damage.

I could have left the scope on the mount in the shed all the time which in hindsight would have been better, but with November being very wet I would bring it in if the forecast looked bad for the next few days to save it sitting there in very high humidity all the time. I've lifted it on and off without incident around 20 times already so didn't think this would be any different. 😪

FLO were due to ship my Astronomik fast 6nm NB filters today, and they have kindly quickly added the ADM losmandy/vixen adapter to the shipment so I can at least put the FLT98 on the EQ8 while the RASA is away.

Alan

2 hours ago, gorann said:

While waiting - just do a two panel mosaic!

I'm going to be waiting quite a while now due to my  RASA 11 Disaster 😭

Alan

Took the scope out to put on the EQ8 for two clear nights imaging in a row, first for a long time. Lifted it onto the dovetail, tightened the middle screw until it was tight and while still holding the rear handle, moved around the other side to check it was in the dovetail groove on the other side before doing it up fully. Half way round it slipped and rolled off landing upside down on the concrete before rolling over on the grass. I found you can't hold back 22kg with one hand. 😖 In the freezing temperatures the dovetail bolt may have stuck while doing it up and the other side apparantly wasn't in the groove.

The guide scope took the full impact and the 5mm thick adapter plate fixing it to the top rail bent significantly. The RASA looked OK until I went round the front. 😭

There are no dents or even paint scuff marks on the RASA casing or dovetail rails. The cameras and PC assembly attached to the top of the scope are fine too. It just looks like the corrector plate couldn't take the momentum of the central lens and camera assembly when the guide scope scopped the scope moving forward. The main mirror and central lens assembly look fine too as far as I can tell. The guide scope itself looks good apart from the dented dewshield. Objective looks OK.

I won't be able to try for Göran's Blue Dragon now which was the target for 5 hours of moonless night tomorrow. 😟.

I thought I'd at least put the FLT98 on the EQ8 and get some imaging done but that has a Vixen dovetail while the EQ8 is Losmandy. I've put an order in to FLO for a Vixen/Losmandy adapter plate to use the FLT98 on the EQ8 until the RASA comes back from being fixed by Celestron, but that can't be here until Friday so the two nights are lost. I could put the FLT98 on the AZ-EQ6 on a tripod tomorrow if I get the urge but I'm rather flat at the moment.

Alan

I'll also have to try this with the NBZ and ASI 2600MC and RASA 11. I'm still waiting for my fast NB filters to arrive so I can let the 6200 loose on it. 😀 I've managed to get the flats sorted out now pretty much, with the Aurora panel, ND filters and longish exposures.

Alan

Thanks for posting Wim. Very good for 90 mins. 🙂 Always interesting looking around the less familiar subjects. I wonder if the few smaller and fainter galaxies also visible have designations.🤔

Alan

This map may be useful for those searching for the mainly very faint Local Group dwarf galaxies, like @wimvb 🙂 It shows the positions of those listed in 

The observed properties of dwarf galaxies in and around the Local Group, McConnachie, A.W., 2012, AJ, 144, 4

along with the 2019 update. Small maps are included in the article though I've plotted them on a constellation map obtainable from In-The-Sky.org to make it easier to see where they actually are. Right-click to download it (3250 x 1710 pixels)

The Milky Way generally obscures any lying within its plane which is why none are shown there with a few exceptions like HISZZ 3 which is only visible when imaged in Hα.

Alan

6 hours ago, Stuart1971 said:

The whole idea is not to have any pure black pixels and no pure white pixels, so neither are clipped….

There will almost always be white clipped pixels in astro images due to the stars but they don't cause a problem. Black clipped pixels are an issue only because we apply massive amount of stretching in the dark areas of the image to bring out the details, and black pixels which can't be stretched, then stick out like sore thumbs. 🙂 The white image areas are never stretched, and are often compressed so a clipped white pixel doesn't look bad.

Increasing offset will actually increase the number of white clipped pixels as it shifts the whole histogram uniformly to the right, and it's why it's called brightness in some capture programs.

Alan

I assume this is your ASI2600 and these values are normal. Increasing offset by 1 adds 10 ADU, so your standard offset of 50 adds 500 ADU which may seem high, as your minimum ADU value on your dark is 468. In reality this is not significant as your output dynamic range has dropped from 65536 ADU to 65036 ADU which is a drop of 0.7% which is insignificant.

If you increase the camera gain then your minimum ADU value will drop as the noise is amplified as well as the signal. The default setting is there to cope with all usual gain values. If you're never going to go higher than your current gain then you could likely use an offset of say 20 and get away with it. When the ASI1600 first came out it was normal to change the offset along with the gain to maximize dynamic range but it was soon realised what a pain this was as you needed separate bias possibly darks for each offset change, and it was changed to a fixed higher offset for all gain settings.

43 minutes ago, StuartT said:

I'm still not really getting what is so bad about a 0 pixel though. If there is no signal, isn't it ok for it to be 0? And if there is a tiny bit of signal then it won't be zero anyway (because the signal will give it a value). 

A zero pixel value can't be stretched in processing and will always be zero giving black dots in your image. If there is a tiny bit of signal it can actually end up below 0 due to the negative values of noise added. These negative values will just be clipped to 0 giving more black dots.

Here's a master bias frame from an ASI224 as an example. The histogram peak is at 314 ADU, set by the offset, but note the bias image data goes from 223 to 602 ADU due to the noise distribution. With no offset used, all the noise values below the histogram peak will be set to ADU 0 and no amount of image stacking will reduce the noise present in the image at those pixels with ADU 0. They will remain as annoying black areas in your image.

This is at gain 134, offset 20 as indicated in the filename. Being a 12 bit camera all ADU values are multiplied by 16 so offset 20 becomes 20 * 16 = 320 ADU. Note the peak is lower at 314 so the actual pixel zero signal output is slightly below the minimum value the ADU can accept. Another reason for adding an offset. The gaps in the histogram are due to presenting 12 bit data on a 16 bit graph.

Alan

3 hours ago, StuartT said:

err...

thanks 😬

You can see if your camera offset is sufficient by looking at a the image statistics of a bias frame. Every image will include the camera bias signal added to it and during calibration this bias component is subtracted. If this bias frame contains zero value pixels calibration won't work correctly.

Noise will also be superimposed on the bias frame so while adding say 50 offset should add 50 ADU to each pixel, if you examine individual pixels, while most will be a value near 50, some will be higher and others lower, due to noise. Noise can add as well as subtract from the ideal pixel value and a few pixels may be ADU 20 or so.

Looking at the bias image statistics this will give the average ADU value as well as the minimum and maximum ADU value. Offset is added until this minimum ADU value is always above zero, with a bit more added on for safety.

So the offset ensures that the camera analogue output with positive and negative noise values added will always be higher than the minimum analogue voltage the ADU will accept to do a successful conversion.

Image calibration will subtract this offset and any other fixed signal values added or subtracted during the read process, but the noise will remain. Stacking many images reduces this noise component.

The number of actual ADU added by increasing the camera offset by 1 depends on the camera design and the camera bit depth, but I assumed it's 1 here to make it a bit simpler.

Hope that helps more and isn't more confusing. 😊

Alan

Great image Göran. The 'dragon's eye' star is very conveniently placed. Planetary NGC40 also looks pretty insignificant in comparison. 🙂

Alan

It's to ensure that the analogue signal from the camera lies within the input range of the ADC (analogue to digital converter). The analogue amplifiers processing the signal before presenting it to the ADC, and the ADC itself need to work on a signal significantly away from the power rails of the amplifiers to ensure they can give a linear response. The camera offset effectively adds an analogue voltage to the camera output to ensure it's within the acceptable input range of the ADC and avoids black clipping or zero ADC output values.

Alan

I've made a couple of dew shields for RASA scopes using similar material and used 3M Super 77 spray contact adhesive to stick the ends together with a 5cm overlap. Works very well with no sign of it coming apart despite several very dewey nights. To keep the circular shape I 3D printed a band to slip over the front of the shield which works well. 🙂

Alan

1 hour ago, skybadger said:

Really, I've always treated the black cable as ground and the striped cable as positive. 

Oops, you seem to be right @skybadger. A solid white stripe seems to be positive while the darker broken stripe is negative.  Sorry, @MG01, but your cable was identified correctly. 😊

Alan