symmetal

Hi Brendan, Just out of interest I ran an ASI1600 90s dark through Startools and got this After AutoDev. It has only got the noise to work on and so has applied most stretch to the noise and some to the amp-glow. Much as expected. View it full size to see the noise. After Wipe and AutoDev. Wipe on its own gives an almost black image so needs a develop to see the result. I was surprised that it has actually removed the noise. However it has left some odd artifacts like vignetting and slight banding. This is likely to having no noise to apply a strech to, so has applied a full stretch to a few actual ADU variations, to get black to white. I suspect the Wipe module divides the image into varying size blocks to determine the gradient effects and the edges of these blocks are visible as the bands in the image. In a real image most of the stretch would be given to DSOs and stars and little to the actual noise as you use a ROI. I think your wiped darks are showing more of these banding artifacts having divided the image into different sized blocks. It's likely the tiny light leakage you seem to have has given the Wipe something to work on giving more visible banding. I'd ignore these wiped darks as they are totally unrepresentative of real images and so it seems can produce strange results. In real images the Wipe module doesn't remove high frequency noise but it is doing so here on the darks. 🤔 Gradients are really very low frequency changes across the image which is what Wipe is normally looking for. Alan

Ah, right, slotted grub screws rather than allen key types. Someones made a right mess of those. 😠 For anybody who has the right optical bench setup to align the lenses it would be a bargain. Alan

I suspect that the screw material needs to be softer than the glass they're pushing against to avoid getting 'pinched' optics. They are probably made of nylon. It's likely that whoever tried to adjust them used metric allen keys when they are possibly imperial sized grub screws. You can sometimes get away with it with metal grub screws but nylon ones are likely to burr over. Hope you will be happy with whatever new scope you get George. 😊 I bet it's put you off buying second hand in future though. Alan

Your coma stars all go to a sharp point which implies the focus is actually pretty good all over. If one side was out of focus due to tilt, that side would normally show less pronounced coma as well, as the de-focused point is spread out and dimmer. However, even your faint stars in the centre still show significant coma. Even with bad tilt though, one area of the image at least would be in focus with good stars. With yours, none of them are good, so tilt itself is not a significant concern at the moment. I have 2 ZS61s on a dual rig setup on an HEQ5 though I haven't used it for a while and they both give sharp stars over an ASP-C sized sensor. I haven't tried them with a larger sensor. As others have said they work well straight out the box. I don't have a travel scope as such as I'm lucky enough to have dark skies here, though not often clear. 😦 I preferred it to the Redcat as it was easier to adapt for auto-focus, though there are kits available for redcat auto-focus now. The ZS61 has a narrower field of view and is a bit slower though, compared to the Redcat. Alan

Here's a fairly wide view of the Leo II Dwarf Galaxy taken with a FLT98 and ASI6200MM and just over 5 hrs total integration. Stacked in APP and processed in Startools and PS. I wondered what the odd hard-edged shape objects were until ASTAP identified them as asteroid 747 Winchester. I think APP wondered whether to remove them in stacking as they were not present in the same spot over 5 days of subs and ended up giving them an odd shape. I've labelled them on the annotated image in red. 🙂 UGC06253 is the annotated name for the Leo II Dwarf. I was surprised at how many other galaxies are also shown in the image. Could be valid as an entry for the Galaxy Clusters competition. 😊 Alan

Once the noise from the sky background has swamped the camera read noise, making the read noise component insignificant, there is no advantage in having a longer exposure. You just need to take more subs to get the required total integration time. 10 stacked subs of 2 mins will have the same SNR as 4 stacked subs of 5 mins, if the 2 min subs have the read noise effectively swamped. The 5 min subs though will have more blown cores. I generally take 1 min L subs and 3 min subs each of RGB to get similar sky background levels where the sky background noise has swamped the read noise. Total integration time to start with is usually 3 hrs L and 1 hr each of RGB. This usually avoids having to do multiple layering in PS to recover the cores. 🙂 This method is mainly used with CMOS cameras for LRGB as they have lower read noise than CCD. It's true for CCD cameras too but exposures may be too long to be practical for filters other than L. Alan

George, I assume these are from your Redcat. The two images are showing different results, neither of which are particularly good. I've found that CCDI tends to ignore coma if it's small as the star centre itself is still defined enough to get a reasonable FWHM figure. With your coma being so bad, it is affecting the results as your FWHM figures are also large. To be honest I don't think you can get any meaningful results from CCDI until the coma issue is resolved. 😔 Alan

It suggests to me that the dovetail isn't sitting orthogonally to the RA axis in the 'left to right' direction. That is in the home position with the RA axis pointing down, one side of the dovetail is slightly higher than the other so the scope mounting is rotated slightly cw or ccw when standing behind the scope looking North. Cone error usually implies that the orthogonal error is in the front to rear direction, that is the front of the dovetail is sitting 'higher' than the rear of the dovetail or vice versa. The screws at the ends of the dovetail can allow this front to back error to be corrected. Whether Conesharp will show this rotational error I'm not sure. If the dovetail adjustment screws are sitting in the puck you could try adjusting them on just one side to allow the dovetail to be rotated slightly, or it may be easier to put a thin strip of metal under the dovetail down one side to effectively rotate it when it's clamped. A bit of trial and error should show where it's needed. Alan

There's a lengthy discussion here on CN forum about RC51 alignment though it doesn't seem to describe how to make any actual lens adjustments and seems to focus more on the tilt plate. If you unscrew the dew shield you can see the adjustment screws for the front lens pair. It's worth checking that none are loose, along with the screws around the rear pair of lenses. An artificial star is best for making any checks as you can do it indoors at any time if you want to try it yourself. You really couldn't make it much worse than it is at the moment. Have you tried asking FLO as to whether they would be willing to send it to Es Reid for adjustment, if you cover all the costs involved. It would be easier than sending it back to WO. Alan

It's worth asking. I'm assuming it's not that you've bought from RVO second hand, but from someone else who had bought it from RVO. Guarantees are not normally transferable, one of the risks of second hand purchases. I'm hoping it's not that the person you bought it from found out how bad it was, and passed it on without telling you. Normally coma only exists away from the centre optical axis, getting worse the further from the centre, and it also points towards the centre. Yours is all pointing in the same direction just like one of the examples I had initially, so it looks like the correcting lenses at the rear of the scope which are there to correct the coma and field curvature of the front petzval lens pair have shifted quite a lot. I don't know how the lens adjustment screws are kept in place, so bouncing during transport may well cause them to loosen. There were some postings of people who have made their own adjustments to the rear lenses and had some success, but a proper optical alignment rig is needed really. Good luck, Alan

Hi George, Is this a new scope you're trying for the first time? What your seeing is severe coma over the whole image. Early releases of the Redcat were prone to these problems due to the internal lenses not being properly aligned. I bought one of the first releases and had to return it as they had issues like this. The replacement was worse and FLO sent one off to Es Reid to be aligned. The one I kept in the end has slight coma in one corner but was acceptable. The spacing itself isn't critical as it's a Petzval design and the specified spacing merely makes focusing at infinity line up with the infinity mark on the tube. I'm afraid your only recourse is to return it or get its lenses professionally aligned. 🙁 Alan

I found ConeSharp from the author of SharpCap is a fairly easy way to check and adjust for cone error. It's a free download and the link is a third of the way down the page. 🙂 Alan

I agree. I'll wait until there's no moon unless I have no choice. Alan

Yes, I'll give it a try.The weather isn't cooperating too well at the moment though. 😔 Alan

I halved my usual exposure times, just 30s for L and 90s for RG and B to hopefully reduce the effect of Regulus. Whether it actually did I don't know. Alan

There should be an SGL challenge for most unexceptional galaxies. 😁 Alan

Wow, that's really faint for 12 hours of data. You certainly need the annotations to pick the stars out out. Challenge accepted. On the list of things to do. 😊 Just posted my Regulus Dwarf image too. Alan

Here's an image showing the Leo I Dwarf Spheroidal Galaxy, 12 arcminutes above Regulus, taken with a FLT98 and ASI6200, reduced to 66% size as it was a bit noisy, being just over 2 hours total integration. Leo I is a Local Group member 820,000 light years away and has an apparent magnitude of 11.2. The ASTAP annotated version shows the many small galaxies present too. ASTAP annotation layer is slightly undersized as it gets misregistered the further away from the centre. The Asteroid and Comet database identified two minor planets visible as well, which I've added in red. The LRGB filters brightness used in turn shows in their trails. Hope you like it. 😊 Penelope is a main belt asteroid 88 km in diameter Sapporo is an Euterpe family asteroid 4.8km in diameter Alan

Stars pointing towards the centre does tend to indicate more spacing required. You need to add spacing if there are filters and camera protect glass panels between the field flattener and the sensor, usually 1/3 the total thickness of the glass in the way, around 1.0 to 1.5mm. Your CCDI examples are showing variations with the point of best focus being near the edge in some of them. This will give worse focus results at the opposite edge which may be diagnosed as tilt by CCDI. The 9 sub luminance one looks like it's almost focused equally around the center, just slightly better nearer the top. If you get the FF spacing optimum then the corners should get better anyway. If you're using an autofocuser it's optimum focus position is set by the algorithm used, whether it's biased towards the centre or over the whole frame, and the distribution of suitable stars in the image, which can vary the point chosen. Alan

Oops. The images I saw were likely Hubble ones. The UMa ones are dim versions of the UMi Dwarf.😁 Still, worth a challenge rather than the usual objects. 🙂 Alan

Thanks. 😊 The other ones you mention look to be more visually interesting and have plenty of stars making them more visible and galaxy like, so I'll give them a go. I was surprised how few stars seem to be in the UMi Dwarf along with no central concentration. Maybe there are fainter stars which will need more integration to reveal the typical Dwarf Spheroidal appearance, or there's dust in the way. I've done the Regulus Dwarf which I'll post shortly. 🙂 Alan

It's quite normal for there to be slight differences shown between subs when using CCDI. To get a more representative picture it's better to take 6 or more subs, load them into CCDI, select them all and then do a curvature/3D test which will then show the average results. To check for tilt you should use a wideband filter, preferably L, so you can take short subs of say 15s to minimize other factors affecting the results. As you're using narrowband filters I assume your exposures are many minutes at least. Your varying results are more likely due to periodic error and/or guiding rather than tilt changing between subs. Alan

CCDI Curvature figure is a bit of a mystery to me. The CCDI help just quotes Curvature: percent defocus between lowest and highest defocus points on the map This is rather vague and no simple manipulation of the FWHM figures stated arrives at this percentage figure so I generally ignore it and just look at the FWHM variations across the image. Your 3D image indicates slight tilt, but a change in FWHM from 3.38 to 4.40 is pretty good in my opinion. If you want to correct the tilt make a wooden test jig like these, which are fairly cheap to make and it can be done indoors during the day. That should improve your FWHM variation too. Don't try and adjust tilt on the scope looking at stars. That way madness lies. 🙂 Alan

How good is your polar alignment? If it's too far off your images will exhibit rotation around the guide star. If your guidescope isn't aligned with the main scope, and the guide star isn't in the image all the stars will show elongation in the same direction. Alan

Thanks @Mr Spock, @juno16 and others. On a single sub it's impossible to spot, and after stacking 20 L subs for checking I really had to convince myself that something was actually there. I processed it gently in Startools using 'FilmDev' as there is nothing for 'AutoDev' to work on and AutoDev tends to give distinct halos on bright stars. No 'sharpening' or noise reduction performed, just star highlight control in the 'Color' module to reduce any residual coloured halos. I resampled it to 66% size in photoshop using bilinear interpolation to reduce the background noise and not alter the star overall shapes which bicubic can do. This also reduced the effect of coma, visible on the right hand side. Full size sensors will easily show any defects. 🙂 It's also a png image instead of jpg which helps too. There are quite a few tiny galaxies visible which aren't shown in the PGC annotation. Alan