Alan64

Yours is a 200mm f/5, my own is a 150mm f/5; here's the collimation-cap scene of my own... At f/5, the secondary-mirror is off-set. Note that the lighter circle is not centred within the black circle. That's the off-setting, and it's correct and normal. Here's the cross-hair(sight-tube) scene of my 127mm f3.3 or f/4... Note that the smaller circle is definitely not centred within the larger. Faster, shorter Newtonians have off-set secondary-mirrors, and the off-setting occurs automatically as you collimate, thank goodness. Both of those are well-collimated. Use them as a guide if you wish.

Here, I've bolted the focusser onto the tube... ...but only as a test-fitting. Much improved it is, very little if any teeter-tottering, and over the condition in which it had arrived. I could just leave it at that. The focusser appears true and square, and with very little deformation of its flange. This type of plastic is rather stiff; not flexible at all. It needs a bit of dust-proofing, and some lock-washers. Now, the angle at which I had taken that photo is by no means true and square.

The focusser teeter-tottered side to side, like a see-saw, but no more since I installed those shims. An aerial view, and after they were trimmed... To those I need to add something...cushiony, like craft-foam, felt, or flocking, or all three.

The tube simply has a steeper curve compared to the shallower curve of the focusser's flange. It was not matched well, at all, at the factory overseas. It would better fit a 130mm or even a 150mm tube.

5-minute epoxy was used to attach the shims. The epoxy set up quite fast, and a credit to its type. The surfaces to be joined were scored, but for some reason I didn't sand them beforehand. I don't think they'll pop off however... After a bit, I'll trim them flush. I only wanted to build up the surface, one step at a time. This is just the first layer of material.

I've had these black-plastic sheets for a while. Shims they will serve as, and to compensate for the gaps. I'll be going inward with them almost halfway from the edge, but not quite as the flange is curved.... Any fine-tuning required, and in getting the focusser, the drawtube specifically, true and square to the optical-tube, can be accomplished with other materials that I have at my disposal.

Are you saying that the resolution per eye would receive that of a 4.25"?

Regarding resolution per inch of aperture, would you get that of a 6" for each eye, or that of a 3" still?

The gaps when test-fitting the focusser onto the optical-tube... How would you go about rectifying that? Where there's a will, there's a way.

Those are for making fine side-to-side adjustments when aiming the mount-head, the RA-axis, towards Polaris. You rotate the mount and tripod side to side roughly to line up with Polaris as close as you can with your eyes, then you use those knobs to fine-tune whilst looking through the polar-scope. You may have to slightly loosen the clamp that attaches the mount-head to the tripod for it to work. If so, then once you're aligned you tighten the clamp. Oh, one more thing: with the "Star Discovery", only short timed-exposures are possible with the camera. With an equatorial, and how accurately aligned you are with the NCP via Polaris, you can take much longer exposures, and in gathering that much more light at one time.

You do need to throw the mount-head back a bit until the pointer(outlined in red) points to 53° N... 53° is in between the first and second white indicator-lines after the 50°-mark. Once you set it to your correct latitude, you'll should never have to touch it again; unless you move or travel considerably north or south from where you are now. When setting the latitude, you are pre-aiming it at Polaris, the North Star. Once you take the mount outside, Polaris will be in the northern part of the sky 53° above the horizon; above the tree-line, where the trunks of the trees meet the ground. You must level the mount, with a bubble-level, and easy enough to do, then rotate the mount-head side-to-side, perhaps the tripod as well, until the mount-head's RA-axis points to Polaris.... When imaging, you'll probably need a polar-alignment scope, which screws into the back of the RA-axis... https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-polarscope-for-eq3-2-eq5.html This is what you'll see through the scope... See where "NCP" is, there in the centre of the reticle? That's the North Celestial Pole. Polaris is very near to the NCP, as you can see. The scope is not illuminated however, unfortunately, but I think you can use a small torch to illuminate it. You want to get Polaris, the actual star, within that tiny circle next to the word "Polaris". The polar-scope itself, however, has to be aligned with the RA-axis, and that will be described within the instructions that should come with the scope. Here's the reticle close-up...

Some thoughts upon your new acquisition... The EQ-5 is the sweet-spot among equatorial mounts; not too large, not too small, just right. You can attach all sorts and sizes of telescopes, large and small, for most any purpose, and upon just one, single mount; no need for a collection of mounts, save perhaps an alt-azimuth, for that grab-and-go ease when travelling or other. A manual EQ-5 has a distinct advantage over the others. If the computer or motor(s) fail on an HEQ-5 or EQ-6, they would be dead in the water until repaired, and parts for those are costly; a king's ransom even. With the manual EQ-5 fitted with a motor or a go-to system, you'd be able to strip them off, as though they were clothing, and use the telescope manually with the slow-motion controls. Your 150P won't know how to act when mounted; held fast and rigidly, and ready to sail the celestial seas. Know your mount, and once you get to know it well enough, you can think about making it the very best it can be; just a little something to tuck into the back of the mind for the future... https://www.youtube.com/watch?v=8tZ58AVVyuQ&t=1166s That mount is the same as yours, but with the go-to kit fitted. The metal construction of the mount is the same.

This is the only video I could find, for the manual version... https://www.youtube.com/watch?v=0WqsmXpTqYk&t=375s This video may be helpful as well... https://www.youtube.com/watch?v=yHGmzpsChcg&t=525s How to use any equatorial... https://www.youtube.com/watch?v=v5tfQ7v3GL0 There are only two major parts: the tripod, and the mount-head; then all of the other, smaller bits and bobs to complete it.

That's a good question. Not for visual, but I think that imagers prefer both. You will need to research that online.

The drawtube is completed. I elected not to bother with flocking the tip of the rack... In any event, there will no longer be a reflective tip aimed at both mirrors. On the underside of the focusser's housing, round the opening and the edges of the PTFE strips were matte-blackened... The focusser completed... Quite frankly, I don't think that much of what I had painted will jut into the optical-tube during actual use, if any at all... ...but better safe than sorry.

That will be all the equatorial you'll probably ever need... https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-eq5-deluxe.html You can wait and save up for the go-to upgrade kit, or tide yourself over by motorising just the RA-axis... https://www.firstlightoptics.com/sky-watcher-mount-accessories/single-axis-dc-motor-drive-for-eq5.html The extra part there to the left of the motor would allow you to disengage the tracking, and without having to disconnect the motor from the mount. It also comes with a hand-set that's not shown. The eye and brain can deal with shakes and wobbles, but a camera cannot. A camera must be held rigidly, like a rock, during timed-exposures; else, the images will be blurred or soft. That importance cannot be overestimated... You get the picture, pun intended.

That coincides with spec; 3.8 kg for the plastic version. Your Nikon D3500 weighs about a third of a kilogram, if that's the camera you intend to use; not particularly heavy. I've been wanting that same go-to mount, for visual-use; perhaps a web-cam, definitely afocal-shots through an eyepiece. My Orion(Synta)150mm f/5 weighs 4.08 kg, but I would never place it on that type of mount. It's not just the weight, it's the bulk, and perhaps the moment-arm effect. That type of go-to mount contains plastic gears, with plastic teeth. I'd be afraid of breaking or cracking them, and wearing out the motors prematurely. The harder a motor has to work, the more strain it undergoes, thereby shortening its life. Go-to is fine thing to have, mighty fine, therefore I understand how drawn you are thereto. In the end, it's your decision. If you get the manual EQ-5, you can upgrade it with a go-to add-on in future. In the meantime, you can simply motorise the RA-axis to automatically track.

Ah, found it, so it is; my bad.

The 150mm f/8 OTA is the 150PL, the "L" meaning "long", and out of the question of course. However, the 150mm f/5 that was once bundled with the "Star Discovery" had a plastic primary-cell and focusser, so as not to strain and wear out the mount's gears and motors... https://www.youtube.com/watch?v=mhhs65AWdCk Those aspects of a current 150P OTA, and that of the OP, are of metal; considerable extra weight. A 130P, or even a 130P-DS, would mount on the "Star Discovery". Otherwise, with a full-blown 150P, go with an EQ-5; nothing less if astrophotography of any type is to be pursued.

I had gotten a laser-collimator a while back, and touted as having a triplet-lens for a tighter spot; "next generation" it was purported to be. It was purchased off of eBay for less than US$30. It arrived mis-collimated, of course. I made a jig for it... The unit touches no wood, only PTFE(Teflon); a strange thing I had crafted. I replaced the set-screws with "thumb-screws", and only then managed to get it collimated... Afterwards, I used it to check a diagonal, and to align an achromat's focusser; that's all. Many years before, I had gotten this passive set of tools, from left to right: a Cheshire(without cross-hairs), a sight-tube(with cross-hairs), and an auto-collimator... Modern Cheshires with cross-hairs are actually combination-tools, which is fine. I want one, but I'm in no hurry. I use the sight-tube when collimating, and a collimation-cap to tweak... At 50x per inch of aperture, I see glory, limited only by the atmosphere; with a 127mm f/3.3 to f/4 spherical-primary and a 4mm symmetrical-Ramsden to boot. With larger, longer Newtonians and Newtonian-Dobsons, I suppose that there's merit in using a laser, in that our arms and hands and fingers will reach back only so far. But then, how in the name of Newton was this collimated, and way back when... You get the picture, pun intended.

In that case, all the better. I prefer rack-and-pinion myself. I do have a Crayford, just one...

The drawtube was carefully masked off, and the bare area satin-blackened... Only one moderate coat was applied, as you don't want it too thick. Once the paint cures, in about a day, the sides and the stop-block of the rack, and the rim of the tube's opening, will be matte-blackened. The tip of the stop-block will be flocked however.

The procedure works particularly well with metal focussers... ...but that is a rack-and-pinion, and as the plastic unit that I'm working on currently. The adjustable bearing, there at the top within the image at far left, allowed for precise centring, with a tolerance of +/- 0.5mm all round. However, I believe that your focusser is a Crayford-type, and has set-screws to adjust its alignment. Although, there just might be a way to improve it nonetheless via this method. This is a distributor of PTFE sheet there in the UK... https://www.directplastics.co.uk/ptfe-sheet The 0.25mm, the thinnest they carry, is nigh the equivalent of a sheet of .010" that I have, and at 0.00985". I've used that slightly thicker within these projects; 0.015" and 0.020". These are the materials I use when working with the PTFE... The roll of clear tape is double-sided. The aluminum-foil tape is that used for HVAC systems, air-conditioning and heating. You may not need the aluminum however. It is only to build up the substrate of the focusser's housing. It all depends upon the spacing round the drawtube when inserted. The aluminum tape does allow for fine adjustments, as it's even thinner than my thinnest sheet of PTFE(0.005"), and at 0.0035" to 0.004". If the spacing is rather tight, then all you'd need is a single layer of double-sided clear-tape applied to the housing's surface, and then the appropriate thickness of PTFE. In addition, all bare surfaces to be joined must be wiped down with either 91% rubbing-alcohol or !00% acetone, and for proper adhesion. If you apply a second layer of aluminum on top of the first, then the first will need to be wiped, and so and so on; also, the surface of the PTFE before pressing it onto the double-sided tape. The PTFE will lift straight up from the double-sided tape easily enough, perpendicularly, but when pulling the PTFE parallel to the tape, it will not budge in the slightest; good thing that the drawtube slides in and out, bearing against and parallel to the PTFE.

I neglected to mention, within my last post, that at f/4 the condition of the focusser is most critical; more so than an f/5, f/6, f/8, et al. It is of particular importance when collimating, and of course, whilst observing. The drawtube was prepped, first by racking the tube all the way inward, then taking a hobby-knife and describing a line all round the tube where it meets the underside of the housing. That lowermost portion of the tube is then sanded, and with 220-grit in this instance... ...including the sides and tip of the rack. Then, the interior of the tube was sanded, and the tube washed, dried, and masked off... The interior of the tube was then matte-blackened... Isn't that lovely?

This is one of the worst plastic focussers, and with which I've ever had to tussle... Hours I spent today, installing the drawtube's bearing materials, ripping them out, then re-installing them. I had to use several layers of aluminum-foil tape, to build up the substrate. However, I had to step the layers, a partial length here and a full-length there... ...trial-and-error, over and over. Now, the drawtube racks in and out along its entire, albeit short, length straight and true, smooth as butter, and with no slop or binding whatsoever. I had almost given up hope, but now, I don't how to act. Now to re-blacken the interior of the drawtube, and satin-blacken that part of the drawtube which descends into the light-path.