vlaiv

I also like the looks of that scope. I haven't used or seen one in person, but I think it is a good scope. Sure, at F/6, being ED doublet - it will have some chromatic aberration, but as far as I can tell - it will be less than say 4" F/10 achromat. That second scope I've used and in fact I own one, and I can say - it is a lovely instrument and amount of CA is far less objectionable than I thought it will be. Since I owned F/5 4" achromat at one point - I do have idea of how bad CA can actually be - and F/10 version really has little. Any ED scope with less CA than that is very capable instrument.

I think we will need more information of what you consider light weight. If I'm considering light weight setup - I'm with Olly - I'd get something in 4" class. Maybe something shorter - like this scope: https://www.firstlightoptics.com/stellamira-telescopes/stellamira-110mm-ed-f6-refractor-telescope.html It will give you some residual chromatic aberration - but it will be good all around scope - showing you low and high magnification views well. Then, I would suggest mounting it on a good mount with slow motion controls - my choice would be this: https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/skywatcher-skytee-2-alt-azimuth-mount.html Together with tripod, this combination weighs total of about 16Kg if I'm not mistaken. You also need about a meter and 20 in length of space to store it in your car. 6" Dob telescope weighs about the same at 16-17Kg, requires about the same length of space being 1200mm of focal length (So tube is approximately that long as well, only difference is that you need some more space for base / rocker box since it is more cumbersome then folded tripod. I've transported my 8" F/6 dob in different size cars without problem, so dob telescopes fit in cars. If you need something lighter weight than above - then you are looking at perhaps 80mm of aperture, but again, you won't save much on weight as mounts tend to be heavy for stability. 80mm F/7 ED doublet has only like 3Kg and mount that can handle it - say this one: https://www.firstlightoptics.com/alt-azimuth-astronomy-mounts/sightron-japan-alt-azimuth-mount.html Has only about 1.5Kg - so that is 4.5 total. Now, depending on the tripod you decide to use - you can either end up with 5Kg steel tripod - which will bring total weight to ~10Kg, or you can perhaps get very good / stable carbon fiber tripod. That option can help save storage / transport room as such tripods tend to collapse to smaller size. For example - this is only 2.5Kg: https://www.firstlightoptics.com/tripods/stellalyra-carbon-fibre-tripod-with-38-thread.html That brings total to 7Kg - ok, now that is really light weight setup.

Depends on the mount and the way you guide. Amount of "preload" or imbalance will depend on how aggressive is your guiding in terms of guide rate. In any case - it should be slight - enough for gravity to keep the gears engaged when changing guide direction. Not needed on mounts with minimal backlash or pure belt reduction system of friction drive or direct drive. All those like as close balance to perfect as possible.

No problem what so ever. I did not really test the clamp, but I did find a slight issue with it - that might or might not be issue in real use. It actually has two "issues" - none of them is real issue until it proves to be issue in use. First is clearance of the clamping side. As designed it sits flush with rest of the clamp, and I'm afraid if I bolt down the thing to a mount - it won't move freely to perform its clamping action. There should really be at least some designed clearance for it to move freely. Second issue is the fact that I used springs around securing nuts instead around linear rods that act as guides: Both springs and nut are right handed and when this is the case - they can sometimes "mesh" (spring gets caught on thread if thread is coarse enough and spring is fine enough). Ideally, you want different handedness of bolt and spring to avoid this or just put spring around smooth part and not threaded one. Other than that, as was pointed out in this thread - this is best printed out of some other material - Namely ABS or ASA. I've since started working with other materials and I'll probably reprint this in ASA at some point. Only drawback that I've found so far with this PLA - is creep. Other than that, it is very mechanically sound and does not deteriorate. There is small amount of creep and I had to re - tighten bolts that hold the thing together after a few months - nothing major, like quarter of the turn - but it shows that creep is there. I would not leave scope for prolonged time sitting on the plate - but during single session - I think it will be just fine. Just take scope of the mount after the session to avoid prolonged loads on such piece. ASA / ABS don't have this issue (nor PC for that matter, but it is much harder to print - maybe only Prusa PC blend could be printed on my machine at the moment). As far as mount goes - I managed to acquire all parts necessary. Bearings, aluminum tubing, large PTFE washers that will be used for friction adjustment, some springs and so on, and I've started design work. Here is where I am at the moment: Horizontal arm of T-mount: Left side is where counterweight rod will screw in (I already designed M6 blind rivet nut place to accept M6 threaded rod) and right side is where clamp will be bolted down: All the bearings are in assembly there and I'm just missing friction clutch part of mechanism there and attachment to vertical piece. Similarly, I did vertical column of T-mount: It again has 3/8 UNC (for photo tripod) blind rivet nut on the bottom side and all the bearings. I just need top piece that will hold horizontal arm (T joint) and friction clamp. Not sure when I'll find time to finish design and start building as I started some work on printer itself. I did Y axis linear rails mod and now want to fit cable drag chains for cable management and waiting some parts from AliExpress to do Core XZ conversion on my Ender3 (fun part is that I'm designing and printing all bits myself :D).

https://github.com/indigo-astronomy/indigo/tree/master/indigo_drivers/agent_alpaca

INDIGO has alpaca agent - which is very handy. You select what device on your setup you want to expose over to ASCOM / alpaca and it exposes it. No need for special driver - indi driver (or rather indigo one) does the job. Alpaca functionality is somewhat limited because of some light mismatch between ASCOM and INDI architectures - but overall it works.

Under linux, there is already free solution available - called USB over IP. I think that there are still no reliable Windows implementation for the other side, but one can use some hacks like running linux + virtual box and windows in virtual machine with usb pass thru and so on. There is this repo as well: https://github.com/cezanne/usbip-win Btw, ASCOM aplaca deals with this nicely without need for USB connection - but suffers from same issues as USBIP would. One really needs fast connection for seamless work. I did some tests yesterday and got very poor throughput on powerline adapters. Although they advertise as 500Mbps, they actually only have 100Mbps ports (not gigabit) so RPI works only in 100Mbps mode. In "lab" conditions, I'm able to get 94Mbps with iperf, but as soon as I include outdoor conditions and 30 meters of extension line and attempt connection over that - it drops to ~35Mbps. That will surely be better and more reliable than Wifi connection, but it is slow. That is about 4 megabytes per second of transfer speed - and I'm using camera that has 3000x2000 - with 16bit - single sub has almost 12MB of data - which means sub download of 3 seconds at best. It was actually more like 5-6 between exposures. Rather slow for someone used to USB3.0 speeds (4.8 Gbps - so even around x5 that of gigabit ethernet). For now, I'll just explore options to see what software works the best and then I'll probably switch to Cat6 cable and direct ethernet connection rather than using powerline adapters. - I might even consider more powerful machine and use network as Remote desktop connection - Explore further INDIGO agents and associated ecosystem of apps. It turns out that agents move some of the processing from client back to server (like exposure control, guiding, plate solving and such) and network is used just for control of agents - so basically UI that connects to agents. I'm not overly confident that it will work without issues, but am willing to give it a go.

I'm trying to avoid having heavy software on the RPI. It will just serve as "interface" to equipment and network and all the apps will be run on my desktop computer. If KStars can run on windows (and it looks like it can) - then it would be alternative. I have RPI running INDI effectively (it is actually INDIGO - different implementation of the same specification with some changes) - so connecting to it with software run on Windows is what I'm after. As far as I can tell - I can use any set of software I'm used on windows if I use ascom alpaca which is "middle man" between ascom and indi and allows for indi devices to be presented to windows software as ascom devices.

It's just implementation of INDI server. Can Nina natively connect to INDI server?

I'll briefly describe my wide field setup and how I envisioned it working. I have AZGti mount converted to EQ mode. ASI178mcc on top of it with Samyang 85mm F/1.4 lens (actually T1.5 version) and 30mm guide scope with ASI185 in side by side arrangement. All of that is connected to RPI4 running INDIGO server. It's connected with power over ethernet adapter to my home wired network and I can access all of that from my work computer. Everything is wired connection for stability (USB/serial adapter for AZGti and powerline ethernet adapter for network). I'm now wondering what to use for imaging stack: - imaging application - guiding application - planetarium / scope pointing app Or rather - I'm wondering if I should go for native INDI connection or Ascom alpaca. I'm inclined to go with: Nina, Phd2 and Stellarium for above, but not sure which is the best way to connect software to indigo server. I've tried ASCOM alpaca connection from SharpCap and it works. I'm getting exposures and can control the camera sufficiently. I can also control all the gear via indigo web control panel if need be. Any suggestions of what I should try first?

It would be nice if someone would come along that has actually used that scope for imaging. I've read reports that it is excellent visually, but faster ED doublets don't control color as good when imaging. For example, I was surprised to see level of residual chromatic aberration with 4" F/7 ED doublet with FPL-53 glass. I was expecting something like that from cheaper FPL-51 glass ED doublet but not from FPL-53. Now, granted, this scope is slower at F/7.8 - but it also has larger aperture (significantly so). For comparison - Skywatcher ED100 that is often used for imaging has F/9 and is almost color free. ED80 is not quite there although it is 80mm and F/7.5. And this is 125mm F/7.8. Closest thing to it is SkyWatcher 120mm F/7.5 and I know that some people use it for imaging as well - but I have no idea how well it performs with respect to chromatic aberration. There is a cure for that - in form of L3 Astronomik luminance filter, but I'd rather use sharp triplet than resort to such hacks on doublet (although I would not mind using doublet + filter if similar triplet was unavailable for some reason or too expensive for me).

Well, if you want to get different FOV - just crop 294 instead of spending money on 462 to have to sell it later

How will that help with "more reach" requested (i.e. longer FL and more aperture)?

Here are my thoughts on this - mind you, I don't have first hand experience with said mount and scopes of that class on it. You want a triplet rather than doublet for serious imaging. You want as much aperture you can mount. This really limits you to below 130mm refractors as scopes in that class fast approach over 10Kg in weight. Here are two contenders that I managed to quickly track down: https://www.teleskop-express.de/shop/product_info.php/info/p10181_Explore-Scientific-ED-Apo-127-mm---FCD-100--carbon-tube--Hexafoc.html 127mm triplet with ~7Kg of weight https://www.teleskop-express.de/shop/product_info.php/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-7-Triplet-Apo---2-5--RAP-focuser.html This scope comes under many labels, and I'm sure there is AltairAstro version as well that could be much easier to source locally. 115mm triplet with ~6.5Kg of weight

With guide scope, I'm guessing that it probably is less important than it used to be, but with OAG - it might be different story. Don't know how much guide stars one can pick up with OAG as FOV is much smaller and also, I'm not sure how much seeing is varied across such a small FOV. From planetary imaging and adaptive optics systems - we know that isoplanatic angle is not that large - so seeing disturbance seems to be the same over say 20ish arc seconds if I remember correctly. That is still much smaller than FOV of OAG even at very long focal length with small sensor (say you have ASI120 which has 1280 x 1024 and you use 2 meters of focal length so you end up at 0.4"/px - you still have more than 500 arc seconds across the sensor). However, I have no idea how much tilt component of wavefront error alone changes with angular distance. I'm inclined to think that selection of stars on small FOV such as one gets with OAG won't have enough of diversity in star position to average them out, but I could be wrong. In any case - more exposure, more average star position approaches true star position. There is also "SNR approach" to guiding. I've read once in some document a very sensible argument (and I tent to agree with it) that we could observe guiding in similar way to imaging - by examining signal to noise ratio. In this instance signal is actual mount error and respective correction and noise is well - noise, inaccuracy in both determining star position, but also in issued correction as no mount is perfect and will not respond accurately to guide pulse - there will always be some backlash, some inertia to overcome, some oscillations due to weight on the mount being moved and its inertia and so on ... Conclusion of the paper is that we increase SNR in part by reducing number of corrections issued and that corresponds to long guide cycle. As long as mount does not accumulate significant error in that time (smooth mount) - long guide cycle is better than short because of this, even if we don't chase the seeing.

Don't know where to start with reply Ok, let's address QE question first. Compared to other parameters of sensor - it is really not that important. QE of modern sensors are very close to each other - they differ by 10-20% in peak performance. For example: Simple ASI120mm has QE of 80% ASI178mm has peak QE of 81% - so (81 - 80) / 80 = 1.25% increase ASI290mm has peak QE of 80% - no difference ASI462mm has peak QE of 89% - so (89 - 80) / 80 = 11.25% increase ASI432mm has peak QE of 79% - so less than ASI120 The latest ASI220mm (I did not even know this one existed) - has peak QE of 92% so that is (92-80)/80 = 15% increase So each sensor is within 15% QE of basic ASI120 However, let's compare some other metric - like pixel size since number of photons per exposure depends on both QE, but also on photon gathering surface - which is pixel area. Let's compare ASI120 and say ASI290 with pixel size. One has 3.75um and other has 2.9um. That is 3.75 * 3.75 / 2.9 * 2.9 = x1.67 increase in sensitivity on account of pixel size alone. Much more than any difference in QE that we observed above. When using OAG - you can bin your camera (and you probably should) to increase sensitivity. Sensitivity of guide camera with OAG vs small guide scope will be much much greater if you have reasonable resolution because large aperture creates smaller star image and larger aperture gathers more light - so star image will be much brighter. Now onto very short exposures. That will simply have you chase the seeing. If your mount requires corrections every 250ms - then change the mount. Best mount is the one that is smooth and that has very slow varying error. Best guide exposures are in range of 4 to 8 seconds if your mount can cope with that. If mount needs to be corrected quicker - that just signals serious mechanical issues like mechanism roughness or some sort of very fast period error (I once had ~11s period error on my HEQ5, but that was due to issues with belt / pulley teeth meshing and I had issue on each tooth - which is roughly 11.4 seconds if I remember correctly). Guiding should not attempt to solve mechanical issues - it is there to correct for periodic error (or declination drift due to inaccurate polar alignment). Anyways, if you are guiding with faster guide cycle than a few seconds, in my opinion, you are doing it wrong. To answer your question anyway, I'd say that ASI220 seems to be very good combination of factors for guiding. It has 4um pixel size which is good size for OAG (you might still need to bin if you guide scope with over one meter focal length), it has 91% QE and it has very low read noise of less than 1e (close to 0.6 and best gain setting).

Seeing is expressed in FWHM and guiding in RMS so two are not directly comparable. What you can do is convert seeing FWHM into RMS and then see how much larger it is than guide RMS. For Gaussian distribution, conversion factor is x2.355, so FWHM of a Gaussian curve is x2.355 times larger than RMS or sigma of that curve. 2" / 2.355 = ~0.85 or in another words - having guide RMS of 0.85" in ideal conditions (no atmosphere) will produce same blur as having 2" seeing and absolutely accurate mount that you don't need to guide. I'm always advocating for as low guide RMS as possible - but there is good rule of thumb which says that you need to have it at least half of imaging resolution. This rule of thumb is particularly well suited for 2"/px and 1" RMS case. It's also worth noting that impact is not as large with small scopes as it is with larger apertures. Aperture again acts to blur the image and we can also "convert" it to RMS. 4" of aperture is roughly equal to ~0.95" RMS. When we say that seeing is 2" FWHM - that simply means that with very large telescope (so that aperture does not play a part in star image blur) with perfect mount / or rather in 2 second exposure so that mount issues don't come into equation star image is blurred to the level that it has 2" FWHM in its profile. That has nothing to do with how well we guide. That is average of star images over two second exposure. Some of it is due to star bouncing, but some of it is just because of other types of distortion (star bouncing around is just "first order" wavefront error - or tilt, but star image is distorted by whole wavefront error and that wavefront error changes roughly every 5ms so in two second exposure we have average of about 400 different distorted star images). Guiding RMS simply means average error in mount position compared to true star position. Sure, when there is seeing we have a bit of trouble determining true star position because star jumps around - but: 1. in longer exposure this jumping around tends to average out and star centroid is very close to real star position 2. We can always use longer guide exposure to be more precise about star position (if our mount has smooth enough error) 3. Advances in guiding algorithms now allow to guide on multiple stars - which again adds another layer of "averaging" things out thus getting more accurate star position

Good point. I forgot to say that. My HEQ5 is very far from stock mount. Had it tuned, replaced all bearings for SKF ones, belt modded, changed saddle plate clamp, put it on Berlebach planet tripod

I had my HEQ5 guide as low as 0.36" RMS. Better thing to ask would be - which mounts guide below 0.5" RMS on regular basis. Here are a few that can do it: Mesu 200 E.fric 10Micron mounts Astro-Physics mounts (not sure if all, but I'm certain that some will do that) ASA direct drive mounts

Back spacing is just like you understood it - you need to either increase or decrease distance from sensor to FF/FR. Increasing is easy - you add some thin spacers. Decreasing distance is a bit more involved - you need to add shorter extension and again add some spacers. Alternative is to get variable length extension that you can tweak / adjust. Tilt on the other hand is much worse thing to deal with. It really means that something is not perpendicular to optical axis. It can be sensor or field flattener / focal reducer itself. Often, cause of tilt is in the way everything is connected together. For imaging best type of connection is threaded connection. Clamping mechanisms are not very good (like when you insert eyepiece into receptacle and clamp it down with thumbscrew and possibly compression ring). I think that Baader click lock is exception as it centers the accessory. As far as tilt is concerned - I'd first look into how things are connected. Next thing to check is if camera already has tilt mechanism. Some newer models already have tilt plate in front that you can adjust. If not - there is tilt mechanism that you can add to your optical train - but you must check to see if it's sensor, field flattener or perhaps even focuser that is not squared with the rest.

I'd say that there is some slight tilt and in general - you need to fiddle with spacing of field flattener to get the best result. It is certainly not guiding - that impact whole field in the same way - so you would see same distortion in all stars in the field. In the end, you might need to accept slightly astigmatic stars in the corners - as some field flatteners / focal reducers produce such results. It is more obvious in good seeing when stars are tight and sharp.

@PeterC65 Are you using UV/IR cut filter with that sensor? Most of these astronomy OSC cameras come with just AR (Anti-reflex) coatings so they need additional filtration in UV and IR especially if one is using refractive optics with them. What you are seeing in images might be poor correction in UV/IR part of spectrum.

I think that x0.6 reducer might be a bit too much for this optics. Resulting F/ratio is F/3.6 - and that is tall order. I do know that other FF/FRs do work well with short F/6 optics. For example, I used TSRED279 - which is 2" version of x0.79 reducer by TS on my 80mm F/6 triplet. It works fairly well. Makes stars a bit astigmatic in the corners of 4/3 sensor - but that shows only if seeing is very good. I'm sure that x1.0 Field flattener will work well - as long as flattener itself is good optically. I've heard that TSFLAT2 works very good - people tend to use it for visual as well with small scopes as it has plenty of working distance (needed for 2" diagonal and accessories). I just saw this as well: https://www.teleskop-express.de/shop/product_info.php/info/p10127_TS-Optics-1-0x-Refractor-Flattener-for-APO---ED-with-70-72-mm-aperture.html Maybe that would be best option as it is designed for ED/APO scopes of 72mm aperture? Then there is this as well: https://www.teleskop-express.de/shop/product_info.php/info/p12208_TS-Optics-REFRACTOR-0-8x-Corrector-for-ED---Apo-with-70-72-mm-Aperture.html That is FF/FR with x0.8 reduction - maybe worth a try?

That is not saying very much. It can be refractor, reflector, SCT or even MCT with those specs (although I've only seen F/10 Maksutov in form of photo lens). Main negative aspect can be that you don't get what you are hoping to get with focal reduction, but that really depends on what scope you have, what focal reducer and what you intend to do with it. For example - I've mentioned that I have x0.67 focal reducer. I've primarily intended that for imaging use. There are some people that find this focal reducer not usable for that exact use case (same scope, same focal reducer) - because they want to use it with too large sensor. Scope simply does not provide corrected field large enough to cover large sensor after "squeezing" of the field. On the other hand - I'm using that reducer happily on refractor telescope for visual with particular eyepiece. It might not work as good with different eyepiece though. I even used said focal reducer on my 4" Maksutov - because I tried with very small sensor that I knew won't vignette although back port on 4" Mak is very small. Besides these issues - focal reducer can amplify optical problems if is not suitable for particular telescope design or is used on very fast optics. For example - I tried very strong x0.5 focal reducer for EEA with F/5 fast achromat. Results were horrible - stars were distorted and I was even not able to bring them to focus properly. On the other hand, same focal reducer worked very very well in EEA role with F/6 newtonian with very small sensor.

Btw what scope is this and what focal reducer are you considering using?