davies07

See my post on the Catseye collimator here If it's of any help, I've also spent hours playing with the Ocal collimator (not on a Newtonian) but with little success. The key difficulty for me was in establishing a reference pointing direction (offset) that gave a collimated telescope. David

I would say that I never got my 10” F/4 Newtonian properly collimated until I bought a Catseye collimator. I bought the two-port auto-collimator and the 2” sight tube with a set of radiation marker centre spots. You would need to replace the centre spot on the primary with a radiation marker, but the effort was well worth it. The advantage of the Autocollimator is that it enables what I would call the ‘roll’ axis, or twist, of the secondary to be set correctly, looking from the focuser. I believe no other system (laser, mirror outline shapes through a camera or sight tube) has the accuracy and sensitivity of the Catseye system. It was expensive, but I recommend it. David

https://www.dropbox.com/s/dbhncjtzfursg6b/Collimating GSO Ritchey with a plastic disc V2.pdf?dl=0 Try this link for the document on collimation. https://www.dropbox.com/s/i68gibodxszoga6/Testing with Ronchi eyepiece.pdf?dl=0 and this one for the document on checking the focal length. I will PM you Es’s details. D

Hi, You are not alone to be struggling with an RC8. There are many threads concerning collimating and adjusting the focal length of these scopes. They can be tricky to get right but produce really nice images when correct. From the information you give I would think the collimation is correct but the mirrors are too close together and the scope is undercorrected (I think that’s the right description). I owned one of these for for five years and it gave excellent service once adjusted. Interestingly, the focal length of mine was 1660mm. At this focal length a Ronchi test showed no spherical aberration and the scope was ‘correct’. So your correct focal length might not be the quoted 1624mm. You’ll need to do a Ronchi test to find the correct mirror spacing. Have a look at posts in this thread https://stargazerslounge.com/messenger/331416/?tab=comments#comment-730724 I’ve posted some links to documents I’ve stored on Dropbox. You should be able to download these and read up on collimation and doing a Ronchi test. Different people have their own favourite approach to doing collimation of these scopes but I think the hole in card technique works. I’ve moved up to a 10” RC but am still using the hole in card method even though the mechanical design of the 10” is better than the 8”. The hole in card method was developed by Es Reid by the way. I’m away from home at present so will not be able to give quick responses to questions until the weekend. Your scope can be checked and corrected. If you don’t think you could do it yourself, you could always send it to Es to check (Cambridge). David

Hi Adam, See my response to this post

Hi, I'm very late to this discussion (as usual), but I thought to add my two cents worth. I've used a Canon 450D DSLR for a couple of years, and it produced some nice pictures but only after a lot of data gathering on an EQ mount. Uncooled DSLRs are noisy and require at least 55mm of back focus. I could not get mine to focus on a standard SW 200P scope (many years ago) and ended up replacing the focuser with a shallower version which enabled me to focus the camera but was horrible to use in other aspects. I would wholeheartedly recommend a modern CMOS camera and a cooled one if you can afford it. The ASI 662 mentioned at the beginning of this thread would be a good choice, I think. The pixel count matches the resolution of modern monitors, making the camera ideal for live viewing (EAA). The only issue is that the pixels are rather small at 2.9um. For deep sky viewing with a scope around 750mm to 1000mm focal length, I would go for a camera with pixels in the 4um - 5um range. The ASI 482, for example, is 1920 x 1080 pixels at 5.8um and would be ideal for deep sky EAA. One of the advantages of a purpose-built astronomy camera is that the sensor is at the front of the device, giving a much shorter back focus requirement. A modern CMOS camera has a variable gain enabling you to turn up the sensitivity to view fainter objects at the expense of saturating the brighter stars, losing their colour. I don't understand the need to go for cameras with large sensors and high pixel counts unless you want to explore wide field-of-view images such as large nebulae. Most images are viewed on monitors, and most cameras will produce images that match their size and are suitable for exploring the vast majority of deep sky objects, which are rather small. The important aspect is getting the right image scale of around one arc sec per pixel, essentially the field of view of a single pixel. I would recommend Sharpcap as your software. It works very well with modern cameras, and its live stacking feature is remarkable. Even on an Alt-Az mount, it is possible to take a sequence of very short exposures and let Sharpcap align and stack them. After a few minutes, the object will magically appear on the screen, with the background noise correspondingly reducing. Good luck. David

Pretty much. Once you have cut the new hole, measure the distances from the top edge of the tube to the top of the hole and the bottom of the hole. The average of these two values gives the distance of the centre from the top edge of the tube. Stick some sticky-backed paper around the top edge of the tube. Use a set square to find where the centre line through the hole intercepts the top edge and mark it. Now cut a band of paper with a length equal to the tube's circumference and fold it in half. Mark the half way point. Now lay the band of paper around the top edge of the tube with the join aligned with the centre line of the hole and mark on the sticky-backed paper where the half way mark comes. Stick a piece of card to the inside of the tube opposite the hole. Mark a line parallel to the top of the tube at a distance equal to the distance of the hole centre from the top. Transfer the position of the halfway point to the card and draw a line down the tube using a set square (small carpenter's square). 🙂 P.S I record almost everything I do with photos. They sometimes come in useful for talks.

I had a 200P on an HEQ5, and it worked fine. Later, I did upgrade the HEQ5 to an EQ6, but I wouldn't say it was essential. EQ6 mounts do come up on Astro Buy Sell, so I would have a look there. I would go for a 200PDS if you are contemplating imaging. The 200P is primarily a visual scope, and the focus point is fairly close to the tube, and the secondary mirror is small, which is all that is needed for visual. The close focus point means that a camera, such as a DSLR, with a deep body, might not be able to reach focus. Modern CMOS cameras with the sensor close to the front face of the camera might work on a 200P but the smaller secondary could give significant vignetting. The 200PDS has a focus point further out from the tube giving space to instal a camera plus filters if needed. The larger secondary mirror gives a wider field of view. David

I'm a bit late to this conversation, but I would add a few words of encouragement. I updated a 10-inch OOUK Newtonian several years ago and replaced the focuser and the secondary holder. Changing the focuser required the drilling of a new fitting hole plus screw holes. As you can see in the photo, I used a Dremel drill and cutting wheel to cut the new mounting hole. The ragged pieces of metal were the remains of the previous owner's attempt to cut a hole for a focuser. Note the use of a marked-up card to provide a template. Here is the new focuser in place. It is a Skywatcher focuser which was surplus to requirements. To get good collimation, you should align the new focuser with the tube. I did this by determining the point on the inside of the tube exactly opposite the centre of the new focuser hole. This point was marked on a card fixed to the inside of the tube, enabling the focuser pointing to be adjusted using a laser. I then flocked the tube with Protostar flocking. The original OO secondary holder was a simple device which gave ugly diffraction spikes. I replaced this with a set of curved spider vanes, which resulted in a telescope giving some beautiful visual views. By the way, I would not recommend curved spider vanes if you plan to use the scope for deep sky imaging, but they are great for visual and planetary. David

FLO should be able to supply a bracket. Just drop them an email.

I agree. Newtonians are good value for money per aperture but need a lot of maintenance, and you will be constantly checking collimation. The secondary mirror obstruction diminishes contrast, and I never liked the diffraction spikes - having used a 200P and a 10" Quattro. A good refractor is a lot less trouble, and you can concentrate on enjoying using it rather than fixing it.

If you're thinking of doing astrophotography, the 200P is not the right scope, it should be the 200PDS. I used a 200P for astrophotography on an HEQ5 mount but eventually upgraded the mount to an HEQ6. I couldn't reach focus with a camera until I replaced the stock focuser with a shallow one.

My understanding is that the adjustment of the primary mirror controls the amount of coma in the centre of the field of view - when properly adjusted you should get no coma in the centre. The secondary mirror controls the distribution of the characteristics in the centre across the rest of the field of view. So a correct secondary mirror will produce symmetrical star characteristics into the corners of the field of view. If you see elongated stars in just one corner, for example, it indicates that the secondary needs adjusting to make all of the corners look the same. The primary mirror has a strong effect on the collimation, the secondary mirror less so. So getting the primary correct is pretty crucial. I guess that is why some advise not touching the primary because messing up the primary can do lots of damage to the image. The advantage of the RC is that, when correctly adjusted, it can eliminate the three key optical aberrations: coma, astigmatism and spherical aberration (SA). The RC doesn't have a strong lens so there is no chromatic aberration (a flattener is a weak lens). Spherical aberration is controlled by the distance apart of the mirrors and you would use a Ronchi test to check it. Astigmatism looks like oval shaped stars, either radial or tangential. You might see astigmatism if you go too far off the centre of the field of view where the mirrors can no longer operate correctly. So oval stars at the edge of the field is astigmatism. Using a very large sensor might lead to seeing astigmatism at the edges. Hope this helps.

I think what you've done looks good to me. Your final tests should should be to test for coma on a centrally placed star. Zoom in on a central star at focus and then slightly defocus it moving the focuser out. Turn off any auto-stretching and defocus only enough to reveal a tiny doughnut. Study the distribution of the light around the central hole. It should be symmetrical but poor seeing makes it tricky to assess. If the annulus of light shows a soft edge on one side and hard edge on the opposite side, you have some residual coma. Also, look for the Young Spot (a tiny dot of light) in the centre of the dark area. It should be in the centre. Make any corrections to the primary, only. You could use Metaguide, for example, for checking the collimation on a central star. I've found it found it to work well. Take a test image on a star field and use Pixinsight to measure the FWHM and eccentricity of the stars (script/Image analysis/FWHMeccentricity). Click the support button to see the graphs. They should show the smallest and most circular stars symmetrical about the centre of the field.

Hi, Yes, I would agree. Your scope is out of collimation. The asymmetric halos around the stars are a dead give away. That is coma. Unfortunately, RC scopes need care to collimate well and the RC8 is particularly tricky to collimate because of its mechanical design. In a normal RC scope, eg the RC10 truss, the focuser is bolted to the back plate of the scope and forms a fixed positional reference for collimating the mirrors, but in the RC8 scope the focuser is attached to the back of the primary mirror. When you move the primary mirror you also move the focuser. So normal collimation methods might not work so well. You can end up in an endless loop of adjustments which can be time consuming and very frustrating. Imagine being out under a lovely sky, collimating your scope and anything you do seems to make matters worse. I've got the T-shirt for that one. I got Es Reid's help to sort mine out. What we developed was a method to collimate the scope on the bench during daylight. Then do a final check on the stars. Es's method does not involve using the focuser at all - no lasers, no Cheshire eyepiece. Just a piece of card with a hole in it. This thread: tells the story of how this method unfolded and why. The end result was a successful technique which I've written up here: https://www.dropbox.com/s/avpu2vn6s3ynsz5/Collimating GSO Ritchey Chretien with a plastic disc V2.pdf?dl=0 Alternately, I see that you are a couple of hours away from Cambridge and an option would be to contact Es and take your scope to him for collimation and tuning. This would have the additional benefit of getting Es to do a Ronchi test to check focal length and a knife edge test for the quality of the mirror. Es has recently subjected my new RC10 to such tests. Well worth it. You could PM me to discuss more. David

I put the assembly in the freezer for a few minutes then warm the outermost section in hot water.

That's a very pleasing image. Yes, I would agree, I think the camera upgrade might be a more interesting to start.

Forgive me, but I wouldn't go for a OO UK ODK 12. The optics are nice but the mechanics leave a lot to be desired. A friend of mine has had nothing but pain from one his12"ODK. They are 'collimated' on assembly and should you dismantle the primary mirror assembly - say to clean the mirror - then the chances are that you won't be able to collimate the scope on reassembly. There is no facility to adjust the position of the primary mirror. Moreover, the method of attaching the primary mirror is a quite primitive mechanical arrangement and if you are really unlucky - as was my friend - the primary mirror might shift sideways slightly due to poor machining and fit of the central mirror support in the hole in the mirror. My own recommendation would be one of the newer GSO 10" RCs, such as the FLO's StellalLyra giving a focal length of 2000mm. Anything bigger would be a real handful to manage. Stay away from the older design Mk1 RCs such as the RC8 and older RC10s and 12s; collimation of these is possible but a challenge. For a camera, one of the modern 16-bit CMOS cameras would suit but, as already mentioned, you would need to bin 2 x 2 or 3 x 3, to bring the image scale to around 1 arcsec/px. For that reason I would go for a mono camera which can be binned in hardware. That then leaves the question of filters; you would need to spend some money on these to get filters with good colour cutoffs and good matching of green and blue gains across 500nm, the OIII waveband. David

Hi Neil, When you say, my results are not necessarily great, but pleasing to you, I detect some dissatisfaction with your current setup but you don't give any details. My own move from an ED scopes (SW Equinox ED80 and Equinox ED120 - yes I had one each) to an APM 107 Apo gave me white stars, where previously I had coloured rings around my star images. Blue rings in the case of the ED80 and red rings (horrible) in the case of the ED120. A second noticeable improvement was the R&P focuser over the Crayfords which tended to slip at high elevations with a heavy camera (really annoying). I suspect that you will also see improvements to the quality of star images. I owned an ED80 Pro scope many years ago but only for a few weeks, before I returned it for the Equinox. I had detected a roughness in the star images from the ED Pro where as they were they were perfectly round and smooth in the Equinox - a feature which was confirmed by testing on an artificial star. The move to the 2600MC camera will be a definite improvement for all sorts of reasons (16 bit vs 14 bit, amp glow etc). I have a 294MC and I'm impressed by its sensitivity, but the major issue for me is the poor (to me) rendering of reds. I believe this is due to the quite high response of the green filter in the Bayer matrix in the region of 600nm to 700nm (red). This high response of green causes reds to be rendered somewhat orange; I believe the response curves of the 2600MC are better at isolating the individual colours. The slightly smaller pixels of the 2600MC will be a better match to your focal length. As you intimate, replacing both scope and camera represents a big outlay. Make sure you won't regret it financially; I don't think you would regret it technically. David

I agree. If you can afford it go with FT.

I think there is an issue as to whether the setting in the options tab references the folder containing ASTAP or the app itself. Here is my setting and I think it's pointing to the app Also, by the way, I have the plate solver exposures set to 10s.

Here is my Sequence setup. I just want to check that you have everything connected to NINA. Forgive me if you have already done this but just checking. You need to connect your mount to NINA. It does this by connecting to EQMOD or GSS, whatever you are using for mount control. So these applications must be running. Once the mount control app is running you connect NINA to it. I use GSS to control my mount and you connect it to NINA with the Equipment/Telescope tab in NINA. The telescope comes up as 'ASCOM GS Telescope' in the drop down. If you are using EQMOD, it comes up as 'EQMOD ASCOM HEQ5/6'. My memory is that I've never got NINA to unpark the mount remotely and I think NINA just stops if the mount is parked. So I always unpark the mount in GSS (or EQMOD). Also, NINA will not start a sequence if you are presently using the camera from the Imaging tab, e.g. taking looped exposures to check focussing etc. You need to stop the imaging exposures before NINA will start a sequence. I suggest setting up a sequence with some short exposures, say 5 sec, as a first test. Here is a bit more information: I use Carte du Ciel as my planetarium software - you could use Stellarium but I find CdC easier to connect and CdC works well with NINA. Start CdC and select 'Telescope/Connect telescope' and CdC will then connect to NINA (and also to GSS or EQMOD). For control of guiding, you need to have PHD2 running and connected to NINA via Equipment/Guider. So my normal workflow is to unpark the mount in GSS (or EQMOD), select the target in CdC and right click and select telescope/slew; (target name). The scope now slews to the target but might not be accurately set. I now know where the target is in the sky and can slew my dome (manual) to have the slot in the right place. You can also slew to the target from the NINA Framing tab by pressing 'Slew and Centre' after having loaded the target to the Framing tab - see below. Note in the sequence definition, above, I have 'Unpark Mount' off. In the target options in the sequencer, I have Slew to target and Centre both on. NINA will slew the mount to point at the RA and Dec coordinates of your target. You can see the coordinates here. There are four ways to set the RA and Dec coordinates. 1. You can simply type the coordinates in on the sequence page. Also, give the target a name. 2. You can search for a target in the Sky Atlas, e.g. galaxy, brighter than 10 mag, in Leo - or just type M65, or whatever. Select a target, check it is correct. Then transfer it to the Framing tab - click on Set for Framing Assistant. In the Framing tab, NINA will load the target image off the internet. It will provide the field of view you have on the target using the telescope focal length and camera details set up in Options/Equipment. You can move the field of view around with your mouse and NINA will recalculate the RA and Dec coordinates as you do. Now click 'Add target to Sequence' and the framing tab will transfer the coordinates of the centre of the field of view to the sequencer and will generate a sequence template for you to fill in. 3. You can transfer the coordinates of the target from your planetarium software (CdC, in my case) by clicking on the button to the right of the Coordinates label in the Framing tab. You can now proceed as in step 2 and transfer the coordinates to the sequencer. 4. You can load an existing image file into the Framing tab to carry on collecting data on an existing target. If your image was saved in FITS format, NINA will have stored the RA and Dec coordinates of the target in the image header. NINA will read this and send those coordinates to the Sequencer. NINA will not only slew to to your target but also centre using a plate solver. which you will need to set up. I use ASTAP which needs to be installed and then NINA points to it under Options/Plate Solver. Plate solving changed my life and give me so much time. You don't have to calibrate the mount against the sky, simply use the plate solver. NINA is a very rich application and will take time to get to know and set up properly. Do read the documentation. I hope this helps and hasn't put you off.

You should find several tabs under the Imaging section - leftmost bubble labelled 'Imaging'. One tab, labelled Image, shows the latest Image from the camera but there should be a tab labelled 'Imaging'. You should find your camera controls here. You can set up the camera to perform looped images of some short exposure then inspect these images as they arrive on the Image tab. NINA will offer what ever camera facilities it can governed by the camera driver. So, for example, your camera has a shutter. When you come to shoot darks or bias frames, NINA will keep the shutter closed when shooting the dark frames. NINA will still issue a warning to cover the telescope but you can just click ok on this and NINA will then shoot the darks. If you are connecting via ASCOM, it is worth checking the ASCOM settings on the camera driver before connecting it. To do this, go to Equipment/Camera, select the camera from the dropdown and then click on settings (gear wheels icon). The ASCOM equipment finder then searches for the camera, and once it has found it will bring up the camera parameters. You might be able to edit these. Now click OK on the ASCOM settings, then click on connect in NINA to attach the camera. Note that the Imaging section also has a 'Telescope' tab. Once you have your mount tracking a target using a sequence of exposures, the telescope tab shows where the mount is pointing and how far the mount is from a meridian flip - very handy.

I believe that the StellaLyra 10" RC that you mention is a fine telescope. It has the focuser and image train attached to the backplate of the scope as it should be. This contrasts with the 8", which has the image train hanging off the back of the primary mirror mechanism. The 8" can be a challenge to collimate and is best avoided, in my view. I think that a full-frame camera on the RC would challenge the quality of the optics out to the edges of the frame.; you might see some astigmatism creeping in. I would have thought that you would need a flattener. Your ZWO 2600MC should work fine but the pixels are a bit on the small side (giving bloated star images) for the focal length so I would be inclined to install a X0.7 reducer. The 071MC with its bigger pixels could be a better choice. As mentioned, you might also want to upgrade the focuser and you will need off-axis guiding. I suspect that you would be seeing limited at the focal length of the RC10 and would gain little in terms of resolvable detail over a, say a large refractor, which would be less hassle but cost more. David

Hello Luca, That's an interesting setup you are proposing. Here are a few thoughts. To be honest, I wouldn't go with the Quattro. I owned a 10" with a carbon tube and as Tomato said, they are a difficult scope to collimate well. I could collimate mine properly only after purchasing a Catseye kit and learning how to use it properly. A simple Cheshire sight tube and laser was not accurate enough. Moreover, I suspect the steel tube will move with temperature and will need frequent checking, as will focus. And yes, I checked the collimation every time I used it. My second concern with a Quattro is that it is a very big, bulky tube. Adding a dew shield makes it longer and it will move in a breeze. I could not use my 10" in the open in the UK, the slightest breeze would move it. I had to build a dome observatory to use it. You've got an expensive mount and an expensive camera, the Quattro feels like the wrong scope in terms of balance of costs to me. To be sure it will be very fast at F4 but you could compensate for a slower scope with more exposure time. The large aperture will promise high resolution but you will be seeing limited in practical terms. On the other hand, if a big Newtonian is the way you'd like to go then I would also look at the Teleskop Express OTAs. What's wrong with your friend's F 7 130 refractor? That might make a good start. Or go for a 150mm Esprit. it will be less trouble, I'm sure. Believe me, living with a reflector telescope takes lots of maintenance time. I would look at the ZWO ASI 2400 camera. With 5.8um pixels and 100K well depth, I think it would be a better match to the 1200mm focal length and without sacrificing image size with binning. The 3.8um pixel size on the 6200 has half the well depth and would be better on a shorter focal length scope. On your proposed setup 2x2 binning would work; 3x3 sounds too much to me. I would hope that you get better seeing than I do in the UK. Better seeing favours a longer focal length scope. You'll need off-axis guiding. a separate guide scope will flex with respect to the main tube - the guide scope and main tube will move with respect to each other under gravity as they track. This was another problem I had with my Quattro; my maximum exposure time was 5 minutes due to oval stars caused by flexing. An older EQ8 should be fine. I have an old one and get sub 0.3" rms tracking error using PHD2 carrying an 8" RC and a 107mm refractor; I use GSS to drive it. The primary risk would be getting an old one that has been compromised by the fiddling of a previous owner - as I did. it was fixable but cost and took time. I hope these thoughts help your decision making. Good luck. David