davies07

Yes, sorry, Steve. Here goes: I think the OP has two problems: his RC6 is out of collimation and there seems to be significant tilt between the pointing of the primary mirror and the optical train. It will not be possible to properly collimate the scope with any device that is inserted into the focuser. Any attempt to correct the tilt due to the misalignment will result in a scope with what I term "squinted collimation": the mirrors will be parallel (at best) but the optical axes of the mirrors will not be aligned. The way to proceed is to remove the optical train completely and collimate the primary and secondary mirrors on their own on the bench as described here: https://www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating GSO Ritchey Chretien with a plastic disc V2.pdf?dl=0 These notes deal with the RC8 but there is an article on the specific collimation of the RC6 in this issue of my club newsletter: https://www.dropbox.com/s/ni0n7yvsfrwis40/September 2020 Newsletter.pdf?dl=0 Once close collimation of the primary and secondary mirrors has been achieved on the bench, it remains to test the scope on a star test to eliminate any residual coma. This should be done on a star in the centre of the field of view. The scope should be just a smidge out of focus 'out' not a huge doughnut. Here is an image from a star test on my RC8. The focuser is around 100 counts (0.25 mm) out of focus out. The blue lines are part of the centre mark on the N.I.N.A. image viewer. Note the central Poison spot. I adjust the primary mirror to get the Poison spot central. The required adjustments to the primary should be very slight indeed. The secondary should not be adjusted at this stage. Check the symmetry of how the stars look in the corners. They should look the same in each corner. The methods I've described are due to Es Reid, by the way. The method I've described is based on the techniques he uses in his commercial work. As to the misalignment of the optical train with the primary mirror: I think this is a common problem with the GSO designed RC6 and RC8. On my RC8, the primary mirror is secured to the primary support structure with a ring clamp and an O-ring between the clamp and the glass. I had a huge misalignment on my RC8 and I found it to be due to a perished O-ring, so I replaced it. To inspect the O-ring does need you to dismantle the primary mirror from its holder but its not a difficult job if done with care. While you have the primary mirror in your hand, you could paint the edge with black acrylic paint (Warhammer Chaos Black worked well) to hide the rough edge of the glass and the marks of the clamp that held the mirror while it was silvered. Doing this will really tidy up the halo around your star images. Do not over-tighten the ring clamp. You'll stress the mirror. Finally, you can use the tilt focuser to remove any remaining tilt between the focuser and the secondary. I do have a bit of residual tilt on my scope but I don't correct for it. My images seem fine without it. By the way, if I put a laser on my scope it says it is out of collimation!! Sorry for my reticence in posting on the open forum, but I've said all this (mostly) before but forums seem to have short memories. The information is here if people would search for it. David

I've sent you a private message with some information that might help.

Yes, as a follow-up to Malc's comments, I would recommend a move to Green Swamp Server (GSS) to run your EQ8-RH. Some of the features of GSS have been specified by the EQ8 community to get the best out of the mount. There are Google groups for the EQ8 and GSS. David

Hi Peter, Sorry for the slow reply. I agree with Nicholas, there is something strange about your Ronchi patterns. I've consulted with Es Reid and he agrees that something is not right. He wonders if air currents might be responsible. To test this wave a piece of card in front of the scope to see if the patterns change. Alternately, Es wonders if the patterns are due to 'zones' in the primary mirror, these could be due to a manufacturing fault or stress. I wonder if the mirror clamp(s) are too tight. My eight-inch scope has the mirror secured with a single screw-in ring. I once had this screwed in rather too tightly and it produced very strange Ronchi patterns. To check this, and if your 10-inch is the same arrangement as my eight-inch, reach into the tube and unscrew the shade tube. Then check the tightness of the central securing ring. You should be able to unscrew it easily with thumb and finger. If it is too tight then unscrew it and let the mirror relax for a while before gently re-screwing it, but not tightly. The first time I unscrewed the centre screw I discovered that the O-ring, that sits between the centre structure and the mirror, was perished and I had to replace it. Good luck, David

That image looks pretty good to me, but I think it is worth checking the collimation when you have the opportunity. PM me if you have any queries. By the way, it was Es who did the first Ronchi test on my scope and although I had spent weeks getting my scope to give me the specified 1624mm focal length, Es declared it 'very overcorrected' with a barrel-shaped Ronchi pattern inside focus and pin-cushion pattern outside focus. The mirrors were too far apart. Bringing the scope to a corrected state required winding the secondary mirror inwards. Once we had correct parallel Ronchi lines - no spherical aberration - the scope had a focal length of 1660mm, somewhat longer than the spec. Such are the variations in the figures of the mirrors, I guess. By the way, if you are interested in doing a Ronchi test, here is a link to my note. https://www.dropbox.com/s/i68gibodxszoga6/Testing with Ronchi eyepiece.pdf?dl=0

Clerkey, I think you are approaching this the right way, getting the two mirrors parallel and with co-linear optical axes is the way to go. I have a tilt adjuster but don't use it. I also have a HG laser a Hotech laser and a Cheshire but don't use those either. So you will be in good company. I once enquired of Teleskop Service how and when I should use their tilt adjuster. They were very clear, you don't use as part of the collimation process but only after you have collimated the primary and secondary mirrors. The adjuster compensates for tilt between the extension tubes (and focuser) and the primary mirror. Also, they said, the tilt adjuster should be mounted immediately behind the primary mirror, as close to the point were the original tilt error occurs. Interestingly, in that position, it blocks access to the primary mirror adjustment screws and so further adjustments of the primary are impossible once it's fitted there. I would assure you that dismantling the telescope should be perfectly Ok if you proceed with care and mark everything with tape or spots of paint before taking them apart. Give yourself plenty of space and light - I use the kitchen worktop which gives me a good flat surface. Photograph everything you do, so that you can refer back. Count the number of turns of the centre screw of the secondary, don't touch the adjustment screws and they will give you a reference depth. By the way, if you think the secondary is the wrong distance from the primary, you can check that too using a Ronchi eyepiece or grating. PM me if you would like a copy of a note I have on how to do that. Properly adjusted, the RC will give you fabulous images. I love mine. With just two mirrors and a weak flattener or reducer, you'll get true colours and excellent image scale with your cameras. It'll be a step up from your 200P and in a more compact package. I would get a dew shield; not so much for dew protection but to prevent stray light getting into the tube. Keep it; master it; enjoy it. David

This link is to a method for collimating an RC developed by Es Reid about four years ago when I was struggling to collimate my RC. https://www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating GSO Ritchey Chretien with a plastic disc V2.pdf?dl=0 I had tried all the methods, including the very expensive Hotech laser collimator for SCTs, which worked well but is not a simple method for occasional use or rechecking. The limitation in its use, I found, is that the accuracy of the method is dependant on the stability of the surface you are working on. It worked well on a granite worktop, for example, but produced variable results on a desktop due to the slight sag in the desk. And it is not cheap. The GSO 8-inch RC is a [removed word] to collimate whatever badge it is wearing, due to its inherent mechanical design. Forget about tilt adjusters and using the focuser, you need to align the primary and secondary mirrors on their own before anything else. By the way the method described in the note is the same as Es uses. It is simple, cheap and it works. David

Hi Wael, I'm not sure what you are doing here. What are you trying to align with the spirit level? Are you adjusting the elevation of the RA axis to your latitude? I can see you have a cover over the polar scope. Have you tried using that to polar-align the mount? It would be an interesting check. You should be able to get an app for your phone that will show you where Polaris should be relative to the polar scope graticule. I thought this screen grab might be of interest: This is a screen grab from my last evening out. I've labelled the controls on the left of the graph. As you can see, you can make the graph look smoother by changing the scales 🙂 The guiding performance figures are the metrics I normally monitor. As you can see here, my RA guiding is suffering because of the arrival of clouds. We get a lot of clouds. In the list of items to be plotted under 'Settings' you will see 'Star mass' and 'Star SNR'. Star SNR (signal to noise ratio) is marked by the white line at the top of my plot and it is a measure of the clarity of the guide star. I find it a useful metric since it will reduce if there are clouds or other obstructions. I take Malc's point about people having successful guiding solutions using your equipment and finder scopes, which also have short focal lengths. Indeed, I used to use a finder scope myself when I started. So, I remain puzzled by the noisy nature of your guiding results. I wonder if you are looking over a landscape that has been heated by the daytime Sun and is producing poor seeing in the night sky by thermals rising off the hot ground. If so, you would see a lot of star 'twinkle' which is an indication of poor 'seeing'. Good luck on your next time out. D

I think this looks promising. Polar alignment error is larger than I would hope to see; something less than 1' would be better. I assume that you are using the imaging scope and camera to do the polar alignment. You are getting images and they look good. The one thing that strikes me is the image scale of the guide scope. Your guiding errors are around 3.2" r.m.s. and is filling the chart at 4 arc sec scaling, but 3 arc sec is just half a pixel on your guide camera. I find it difficult to think how guiding accuracy might be improved without increasing the focal length of your guide scope or substituting a guide camera with smaller pixels. If we suppose star images in your skies might be 6 arc sec across, your guide camera has just one pixel filled. I imaging the star images in the guide scope might look like little crosses. Your guide scope is F/4 so it would be reasonable to add a X2 Barlow and double the focal length to 240mm. you would still have good brightness at F/8 and it would half your guiding image scale and guiding errors should also be halved. I'm not very happy with how slowly the RA errors are being pulled in. The guider is sending commands but the mount seems slow to respond and the AGR value seems to have little effect, although at 35 the response is noticeably slower. I wonder how much of the excursions we see on the display are due to noise from PHD calculating the centroid of the star image at the image scale, rather than real tracking errors - all the motion we see on the PHD chart is inside one pixel. I would certainly reduce the update time from 2.5s to something a little quicker - 2, 1.5 or even 1.0s if your sky seeing is reasonably quiet. The risk would be that we would be trying to get the mount responding more rapidly to noise. Here's a thought. Just as an experiment make the imaging scope the guide scope and see what sort of guiding performance you get from it. That would show how a longer focal length guider would perform. David

Hi Wael, I confess, I find it difficult to follow threads such as this when many suggestions and recommendations are being posted, and you might be making changes to your setup along the way. So, I thought I'd just make a summary of what I've seen in the various posts. By the way, I've had a look at your guiding log using the PHD2 Log Viewer utility, which you can download for free. So this is what I've observed in the photos and screen shots and these thoughts might trigger a response from others who are trying to help: You are guiding via EQMOD so are not using an RJ 45 cable between guide camera and mount. That fine. That's the way many of us do it. You Guiding Assistant screen shot shows a polar alignment error of 3317 arc minutes. This seriously wrong, 55 deg! How are you doing the polar alignment? If this is the PA error, then I think it could account for the poor guiding calibration. You are using a telescope with 120mm focal length and a guide camera with 3.7um pixels. This gives an image scale in the guide camera of 6.4 arc sec per pixel. This will make the guide stars look small and blocky. rather than fuzzy discs. I assume the guide scope is properly focussed and you can see stars on the PHD screen. The high frequency star motion in the Guiding Assistant screen is showing really large values of high frequency star motion. I don't understand this. The guiding log confirms your guide telescope focal length of 120mm, pixel scale of 6.45 arc sec per pixel and exposure time of 2.5s Some suggestions: You need to look at the polar alignment. The celestial pole is around 30 deg altitude above your northern horizon. The elevation of your RA axis when parked in the home position, should be the same as your latitude - you should be able to get a utility for your phone to measure this by laying your phone on the mount. You can use Scopefocus to do the polar alignment; it works well. If, however, you can't see Polaris, I suggest you set the elevation of the mount as suggested, and then focus on a bright star to the south and and use drift alignment to set the azimuth of the mount. I think PHD has a utility to do this. I would set the guide camera to be upright in the guide scope when the mount is parked - pointing at Polaris. I think the cable will then hang vertically down. Once set, you should not move the guide telescope or camera relative to the mount. I wouldn't worry about periodic error correction for the moment until you've got basic calibration and guiding working properly. But when you come to it, EQMOD will do it automatically for you. Finally, here is a screen-shot from your guiding log which confirms some of these findings: Interestingly, the guiding is converging after doing a Guiding Assist run., but the comment on polar alignment is key, I think. David

Your tracking graph looks to me like instability - too much gain for the load. There are short periods where tracking seems to be ok then it takes off, repeatedly making too big a correction and overshooting, then trying to correct that and overshooting in the other direction. My first response would be to turn down the aggression in RA and DEC. Also, make the values of Minmo bigger in both axes, say 0.5 in each axis. This stops the guide software responding to very small errors - currently 0.18, too small. I would try the built-in PHD utility Guide Monitor (from memory) under the Tools menu. This turns off the guiding but PHD watches how the mount tracks the sky and monitors the star movement. This takes several minutes to finish but PHD then gives you a readout of your tracking accuracy, backlash and polar alignment. It also gives you a recommended set of settings and will apply then automatically with one click. I find this works well. I need to close for tonight. Good luck. Let me know how you get on tomorrow. David

Hello, I'm rather late to this topic so forgive me if I ask some dumb questions. Wael, I can see from your EQMOD screen that you are located somewhere in the Middle East (30 deg N, 31 deg E) and your scope is pointed somewhere towards Polaris. 0 deg AZ, 30 deg alt, I hope you are not trying to calibrate your guiding with the scope pointing in that direction. Assuming your scope is polar aligned - Scopefocus has a great utility for polar aligning your mount - you should calibrate your mount with the scope pointing south and upwards towards the celestial equator, Hydra, for example. David

Paul, I think this is a cracking result. I think the readings look good. If anything, there is a slight asymmetry from top left to bottom right which could be corrected with the slightest tweak of the secondary. But it is so close I would hesitate to touch it. There is next to no tilt. The curvature is normal for an RC, I think. Check the star shapes in the corners. They might look slightly soft and oval if you're not using a flattener but should be equally so. If you see more oval star shapes in one corner compared with another then I think that would indicate that the secondary is not quite correct. Central stars should show no coma. I think you should get some good results with this. Your FWHM readings are comparable to mine. Remember that the presence of the secondary obstruction is going to spread the light energy from the Airey disc into the first diffraction ring, so stars will look a bit fatter. On the other hand, it might be that the mirrors are not quite the 'correct' distance apart; a Ronchi test would check that. By the way I found that a headtorch with the lens removed made a reasonably small and bright source to do a Ronchi test from 30m. Good job. David

Hi Paul, Yes, you are right about the RC6. I've collimated one myself and the gaps between the vanes are too small, even for my small hand. I was able to reach in with a couple of fingers and hold the secondary holder sufficiently to unscrew the centre screw, but then discovered that the secondary holder is so large compared with the diameter of the tube that the secondary, resting in the tube, obscured the centre of the primary mirror. So there was nothing for it but to remove the secondary spider support completely by unscrewing the support ring from the tube. This does mean, of course that once the secondary is removed you have to replace the support ring (minus secondary holder) to align the primary mirror. You then have to remove the support ring, once again, to replace the secondary to align it. I think I did find that I could get a light to shine from the front of the tube onto the card in the centre of the primary mirror, without the shade tube casting a shadow onto the card. If this is the case for you, then you do not need to remove the shade tube to adjust the secondary. Hope this helps, David

Hi Rich, I owned a SW 10-inch Quattro and found it a challenge to collimate accurately. I used various lasers and Cheshire sight-tubes but could never get them to quite agree. Eventually, I used a Catseye autocollimator kit and only then did I get good, consistent collimation. Looking at your pictures I find it difficult to work out what is going on. One comment is that in image B, you cannot see uniform reflections of all of the mirror clips or secondary mirror supports in the primary. So something is amiss. I found that I had to start the collimation process by first removing the secondary mirror and collimating the focuser to ensure it was square to the tube. The Quattro focuser has adjustment screws to enable this. To collimate the focuser, you need an accurate laser and then after removing the focuser itself, carefully measure the position of the centre of the focuser cut-out on the tube and calculate where that centre will be projected onto the inside of the tube opposite the focuser. Now mark a spot on the inside of the tube opposite the calculated centre of the focuser; I used a label stuck on the inside of the tube and marked it with a cross using a micrometer. Now reassemble the focuser and use the laser to project a mark on the opposite side of the tube and adjust the focuser to hit the cross. It's very easy to get confused by the view into the focuser with the primary mirror in place. So as a first step, block the tube with some screwed up paper so you can't see the primary. Now put some coloured paper on the inside of the tube opposite the focuser so you can see the ring of coloured paper around the secondary as you adjust it. Getting the secondary centred in the focuser and at exactly 45 deg is the challenge. The Catseye kit includes an adjustable 2" sight tube with an accurate crosswire. It is excellent for getting that rim of coloured paper to show uniformly around the secondary. Now remove the paper to enable you to see the primary mirror and adjust that. In 2017, I rebuilt a 10-inch Newt for a friend and collimated it. that proved an interesting experience and I set out my experiences as a talk. I've put the slides here (lots of photos), so you can have a look: https://www.dropbox.com/s/vsgwk7rvie32vu9/Collimating a Newtonian.pdf?dl=0 Good luck, David

Ah. Dismantling the OTA in the way I showed is not part of the collimation procedure. I was showing what I had discovered when I dismantled my OTA and the sources of the problems I was experiencing in collimating my scope at that time. My description of my collimation procedure begins further down the thread beginning with the photo of the plastic disc. I've realised that this thread has wandered here and there and it is not clear what a newcomer should do. Therefore, I have prepared a write up of the whole process and you can download it from here: https://www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating GSO Ritchey with a plastic disc V2.pdf?dl=0 Let me know if this works for you, or if something needs to be clarified and I'll do my best to update it. That invite applies to all; do have a look. David

Hi Iwannawon, You seem to have achieved an excellent alignment of your focuser with the secondary mirror and these are text book rings. However, I suspect your scope is not collimated. Regarding your query on the appearance of the outer ring, the laser diode in the HG laser is rectangular in shape and produces a ring which varies in thickness around the ring. - narrower in one direction compared with the one at 90 deg - thus the variation in the appearance of the outer ring. You mention that despite this apparent excellent alignment, your stars are still off. This doesn't surprise me as I suspect that although the HG laser rings indicate the scope is collimated, I suspect that it isn't. The key thing is to get both the primary and secondary mirrors parallel and facing each other exactly. Forget about what the focuser is doing because you don't know what angle it is to the primary mirror and I suspect it is not orthogonal. I would urge you to read through the posts on this thread to understand the challenges of collimating this particular design of GSO scope and the methods that can be used to achieve good collimation. If I put the HG laser on my scope, the ring pattern is absolute rubbish. To see it, you would immediately be reaching for your tools to adjust the mirrors. However, the scope is well collimated and as evidence, I 'll share part of a recent image showing what can be achieved with a well collimated RC8. This is the edge of M31, towards the edge of the frame of my latest image of M110. Here is the complete image: And here is the detail: I love this scope. We have round stars no aberrations, nice star colours and lovely detail emerging from the dust lanes and HII regions in M31. This is what you can achieve using the methods described in this thread. Seasons greetings and best wishes, David

Hi John, I agree with Nicolas, using the HG laser is not the way to go to collimate an RC8 due to the mechanical design of the primary mirror support and focuser tube. I would suggest that you read my posts of 22 and 31 March on page 1 of this thread; they explain the fundamental problem and a simple approach to achieve good collimation. Many contributors to this thread have now achieved good collimation their RC8s and RC6s using this method. Nicholas has produced an excellent extension of the method which makes the method more accurate and simpler to do, but it does require the construction of a couple of tools. All you need to undertake the basic method is a piece of good quality card or polystyrene sheet. David

Hi Kookoo. Your findings have confirmed to me the value of the plastic disc method of collimating an RC scope. All of the methods involving lasers, the Tak scope or a Cheshire, define a reference line in space that you try to align the mirrors to. Such a reference line needs to start at a correct position and point in the correct direction. It is extremely difficult to get both of these aspects correct, with the level of accuracy of design and manufacture of the components we are dealing with. The plastic disc defines only a reference point which is the centre of the primary mirror. You then align this position reference with others, such as the centre of the secondary circle, by eye. I think you are so nearly there with collimating your scope. I think you should make a disc and use it to align the secondary. I bet you a glass of ouzo that you will find that the secondary needs just a tweak in the vertical direction. David

Well, my own focal length turned out to be 1660 mm, not 1624 mm. That is where my Ronchi lines are straight. I guess it is pot luck as to what your optics will give you. I wouldn't try to get back to 1624 mm if the scope is not correct at that setting, you'll get bigger, softer star images. By the way I use a TS flattner https://www.teleskop-express.de/shop/product_info.php/info/p4006_TS-Optics-RC-1-0x-Flattener-Bildfeldkorrektor-fuer-Ritchey-Chretien---2--Anschluss.html But if you already have the 2" refractor flattener then it will do the job equally well. You will need a separation of 109 mm between the back of the flattener and the sensor. David

Hi Nicolàs, Are the ovals in the corners equal? Are you using a flattener or reducer? If the ovals favour one edge of the image, I would suspect the secondary being slightly out as I've suggested to Kookoo. If the ovals look equally distributed and you have no flattener, then I suspect you need one and that the scope is collimated. If you are using a flattener, I would ask if the separation from the flattener rear surface to the sensor is correct. I'm using the TS flattener and this distance is quite long at 109 mm. I also use the CCDT67 reducer (TS also sell this). If it is spaced for x .67 reduction, then in my experience that is pushing the optics somewhat. I've spaced mine for x 0.7 reduction and am seeing some slight oval shapes in the corners but I generally lose these when I crop the image. David

By tweak, I mean just to slightly tighten or relax the tension in the secondary screws, not to turn them. 🙂

Hi Kookoo, I think this looks pretty good. The star field looks very nice with just some oval stars in the bottom right and left corners which are confirmed by the FWHM and eccentricity plots and might be a bit of astigmatism creeping in. The CCD Inspector plot shows a similar result with collimation 8" out in the vertical. The eccentricity and FWHM readings towards the centre are just lovely. So what is amiss? There seems to be some tilt in the vertical axis. I'm suspecting that this might be due to some slight misalignment of the secondary in the vertical axis. since it is the secondary that governs the distribution of the optical quality over the field of view. I'm wondering, if you used the Tak alignment scope in the focuser, is the focuser itself slightly misaligned with respect to the primary mirror? I wouldn't touch the primary at this stage. I would be tempted to tweak the secondary very, very slightly in the vertical and retest. David

Hello Nicolas, I have been away for a few days and have just picked up your post. Thank you very much for the mention and for the information. What you have made is exactly what I imagined was needed but never got around to making. i must have a go myself. David

If you're trying to line up with a previous image, have you tried loading an existing image and then plate solving it in the framing tab. The plate solver - I'm using ASTAP - will then determine the coordinates you need to continue capturing more frames. If you had saved previous frames from NINA in FITS format, the coordinates are written into the FITS file header and no plate solving of the loaded image is needed. As David mentioned above, you can then go to the Image screen and run a plate solve and auto focus before going to the Sequence and starting it with the plate solve and auto-focus options switched off. As you've probably noticed, there is a set of tools available as sub-tabs in the Image screen but you need to load them from the Tools list at top right. One of these sub-tabs is Imaging and I find it handy to check the framing is correct. Once you've loaded the Imaging sub-tab, open it, set the camera control to 'Looping', set the binning to 4 x 4 or whatever your camera will support and click on the start button. Now go the the Image sub-tab to watch the images come in and check the framing. By the way, I'm currently spending time using auto focus with my various filters to work out the offsets of each of my filters from luminance. I am then putting the offset values into the filter options, so I should be able to get away with focusing with only the luminance filter in future. David