prusling

Hi, I have read a number of articles about appropriate ratios for image scale between guider and imager but I have a potential setup where the ratio will be less than 1:1 and would like to know whether this could cause image problems. If my thinking is right I can see that the guiding could look good but the error would be multiplied at the imager. I'm considering switching from a guidescope to an OAG - the main scope is an 80/480mm f6, the guide camera is a ZWO ASI224MC with 3.75 micron pixels and the imaging camera in question is an Atik 314L+ with 6.45 micron pixels. With all else being equal in this setup the scale ratio is that of the pixel sizes (i.e. 0.58x) whereas general wisdom seems to indicate that less than 4x is OK but nowhere seems to mention how low you can go. More generally is the OAG approach sensible in this setup? I've been using a guidescope but want to free up its space and weight to mount a Raspberry Pi and powerblock on the scope.

The better-calibrated the image (darks, flats, etc) the more you can stretch it to obtain fine detail; my crib sheet for calibration frames is below (any comments very welcome). Darks are pretty well essential with a DSLR, especially at this time of the year; also it is best to turn off LiveView when imaging as that adds to the noise. I also cover the optical viewfinder to avoid stray light entering. I judge the exposure time and ISO according to the darkness of the skies and the camera. I have a Canon 550d (precursor to your 600d) and use 1-minute subs with ISO800 in dark skies and the same exposure with ISO400 in light pollution at home. This means that you can afford to discard poor images and use a sigma clipping algorithm when stacking to eliminate outlier pixels giving a cleaner image. Lights Darks Flats Dark Flats Bias/Offset When Before/after or can use a dark library Ideally every session; can be next day Optional if using Bias Occasional Number The more the better 20+ 25 20+ 50++ (> Darks) Format RAW RAW RAW RAW RAW Optical Setup Capped Exactly the same as lights Capped Capped Temperature As close to lights as poss any As close to flats as poss any ISO 400 (LP) or 800 (dark sky) Same as lights Same as lights Same as lights Same as lights Exposure time Can vary with tracking / guiding, I normally use 1 min when tracking but not guiding Same as lights AV mode until 50-70% histogram then set manually Same as flats Shortest e.g. 1/4000 sec Lens F Stop Widest / 1 click or more back any As used for lights any n/a Lens Focus LiveView x 10 on a bright star / distant target any As used for lights any n/a Stacking algorithm Kappa-Sigma if >15 frames otherwise Average Median Median Median Median

This is the workflow I use for DSLR; for other cameras I adjust the Wipe params (e.g. Aggressiveness 83%, Drop-off Point 50%). I don't think your result is caused by 'Canon banding' but if so, there are ways of fixing this. STARTOOLS EXAMPLE WORKFLOW Command Action Params Notes (for DSLR imaging) Open Open the stacked image from DSS (ideally from fits format) Use left option on opening - DSS actually does some white balancing which can't be disabled Bin Scales down pixels and noise and reduces subsequent processing time 50% (default) 50% converts each 2x2 pixels to 1 pixel AutoDev 'Digitally develops' the image - stretches it to show faint signal and issues to be addressed Drag RoI around target Will probably look horrible but this shows you the worst of the image that the processing will fix Crop Discards unwanted border around target (and stacking artefacts) Drag area to be left Best to eliminate worst of gradients, vignetting, etc around the edges Wipe Removes light pollution, gradients, vignetting and colour casts Drop off point 0% Say Yes to Temporary AutoDev as well and maybe a few pixels of dark anomaly filter Dev 'Digitally develops' the image - stretches and applies curves Re-do global stretch Use "Home in" or manual % to stretch until best compromise achieved (detail vs. noise) (Decon) Compensates for atmospheric distortion (e.g. tightens stars) 2 pixels Optional - set Mask manually first using Clear, Auto, Stars, Do, Shrinkx2, Invert, Keep (Sharp) Sharpens the image using wavelets Optional (Contrast) Increases local contrast Clear mask from Decon beforehand (Mask, Clear, Inverse, Keep) (HDR) Optimises dynamic range - replaces manual curve manipulation Choose algorithm Optional - apply algorithm to suit the target - e.g. Tame, Reveal, Optimize, etc (Life) Brings back life into an image by remodelling uniform light diffraction Moderate Optional - not sure how natural this action is - may border on artistic licence! Colour Adjusts the colours of the image (e.g. compensates for modded DSLR) Fill mask if not already Can adjust to suit - presets for scientifically accurate or artistic (latter can seem more natural!) Filter Modifies features in the image on the basis of their colour e.g. Ha Can boost nebulae Track Switch off tracking in top menu to reduce noise and finish image 10 pixels? Initial example screen makes it look as though everything will end up fuzzy, but it is selective Save Save resulting image to storage Need to put type e.g. TIF Not supported in trial version Key commands are in bold N.B. Can re-do the AutoDev (or manual Digital Dev) any time before tracking is switched off and it reapplies the other changes made

Resurrecting an old thread, I rarely use my Star Discovery but tonight I thought I'd have one more go at dialling out the 'backlash' in Az. I've found the cause and fixed it so I thought I'd pass it on to anyone who may be suffering with this. It's not backlash after all! The Az drive assembly is held in position by two pairs of screws on either side (one pair is shown on the left of Slightly Brown's first photo above) and I noticed that the movement I had was because these were not fully bearing on the assembly and so were allowing it to move a little from side to side. I carefully tightened these down evenly on both sides using a flat head screwdriver and that eliminated the movement completely. I notice that there is a similar setup on the Alt drive assembly but I had no movement there. I've tested this in the house and the motors seem to operate fine. When it's clear I'll test it outside and report any issues. Hopefully this will improve performance significantly - I hope so as these mounts are well engineered and streets ahead of the old Az Goto. They seem to have ended up as an under-utilised stop-gap between that and the Az Gti but with a wifi adaptor they are equally competent.

Despite the cloud some great views last evening - a stunning sunset, gas giants and their moons, M57, and a lovely low-down orange crescent moon. A pesky cloud bank did its best to mark the ecliptic which made imaging difficult, but it was worth trying. Not sure what caused the blueness below though... Thanks AdeKing and kev100 for your company. Look forward to the next time.

Hi, I'm keen as well but the forecast for Friday is not great. Fingers crossed it will improve. Cheers, Peter

Amazing skies - went on an excursion called Teide by Night run by local astronomers; even lent us tripods. Highly recommended.

Welcome James There is a Dorset group on SGL and we get together to observe/image from time to time. There are also a couple of local clubs if you are interested in attending. Whereabouts are you based? Clear skies Peter

I suffer from two distinct dark horizontal bands on my Canon and get rid of them after stacking by using the excellent free app Fitswork4 - using the function Processing, Background Flatten, Lines to Equal Values with standard parameters.

A brief update - post-adjustment the tracking is still not great but probably better than before. Gotos are OK and the mount is less prone to accidental manual movements although as noted there is a fair bit of play before real movement. Will persist with it for now, but underwhelmed...

Yes, that is exactly like mine now. I believe there is always backlash in any mount with cogs meshing against each other (belts help) - if not, then there would be other problems. I may be wrong though...! In any event that is not the reason why I needed to adjust mine. If you don't have issues tracking or with too-easy manual movement then I think you have a good one in my experience!

bendiddley: I had two issues - poor tracking and it being too easy to move the mount by hand in Az (freedom find helps but it was a pain to have to reselect the target often). I may have solved both these issues by the adjustments as both Az and Alt drive clutches were slack. I thought you may have been referring to a slight amount of play before real movement occurs in Az which could be backlash - this may be tweakable but I suspect it would require gear adjustment which I'm not happy to do myself. It may well be 'within design specifications' anyway!

Hi bendiddley, yes I too have a small amount of manual play in Az - I expect (or rather hope!) it is normal backlash which would be managed by always finishing with up and right movements. I've not had a chance to check it out in the field yet - maybe Monday evening if the forecast holds here. I've tweaked the Alt as well, now - dead easy! Hope that's not misplaced confidence...! I'd still like to do a more 'scientific' adjustment of the clutches with a spring balance and recommended settings if Slightly Brown was ever able to determine these? Hi happy-kat, I too had a Virtuoso for a while with a 90mm Mak on it and they are excellent mounts. Thanks again, all

A quick update - after the previous post I checked the upper Az clutch and indeed it was not tight enough. After tightening it to a (hopefully) appropriate level, that also had the effect of increasing the resistance to manual movement. Need clear skies to test it out but I'm feeling very hopeful! Many thanks to the OP for posting this thread and to happy-kat for pointing me to other related threads - this has hopefully saved me from having to buy a replacement.

Some progress here - I bought a Bahco 9029T adjustable wrench with thin jaws (not cheap at £21.50 from Amazon prime but I tend to regard tools as investments that I'll probably use for other purposes). It fits the lower spanner flat fine and it seems to fit the upper one too though I haven't adjusted that yet. I had previously managed to tighten the lower clutch as tight as it would go but the mount still seemed to move too easily in azimuth and it would not now slew. I have now backed the lower clutch off and the mount slews fine though it now moves manually even more easily - maybe I just need to be more careful (it's freedom find anyway). My other main issue was that it wasn't tracking well. I now need to see whether the looser lower clutch has removed any stiction to the main drive that could have caused this. I'd very much appreciate hearing other's experiences with these mounts - does yours move manually very easily in azimuth, does it track well, what could I do with the upper clutch to improve things? I was close to ditching it in favour of an Az GTi but it seems to be fundamentally a very-well built mount (much better than the old Az Goto) and is still on sale in conjunction with the wifi adaptor (which I have) for £289 so I feel it's worth persisting with!

Hi, I'm also keen to learn what flat spanner sizes are needed as my closest for the bottom nut (31.5mm - 1.25") is slightly too large - digital calipers show about 29mm? The top nut is harder to get to with the calipers but looks to be about 23mm? Nevertheless I think I managed to get some traction to tighten the bottom nut but the mount seems to manually move as easily as before (far too easily!). Though now the hand control won't move the head at all despite the gears turning. Maybe I adjusted the wrong one...? Thanks for any help.

The version I have (Synscan Pro 1.8.0) has an option in Settings, User Interface called Footer Padding which I set at 100 for my 6+ inch phone screen and works well for me.

Just want to acknowledge great support from SkyWatcher. My one criticism of the Android app was that the slewing keypad was too close to the bottom of the screen and I would often hit the adjacent 'home' button instead of 'down'... I contacted the app developer about this and they've quickly put out an update with adjustable footer padding. Excellent customer service!

Hi Louis, I have an RC6 and found that locking the focuser would tilt it a little. I did get an adjustment ring but that was not ideal. Instead I bought a monorail focuser from TS which have been reduced and seem great value. It's early days yet but they do seem more stable than the stock item and could be a better option than the adjustment ring for not much more cost. Cheers Peter

A truly stunning achievement!