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That 4" F/7 (or higher) doublets are not completely color free. I've seen blue halos around stars in OSC images. Either RGB+ L3 from astronomik or NB imaging with those scopes. OSC is not a good option in my opinion (maybe with L3 again as IR/UV cut) - that will tame some of blue bloat.

Not sure that you'll find suitable scope in your budget. For refractor - I'd look at triplets, and those tend to be expensive. Probably best one would be this one: 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 It is 800mm FL - so you can use standard flattener without reduction, but if you wish - you can use x0.8 FF/FR to get to about 640mm of FL. RC 6" will not take much more than 0.75 reduction. It has smaller corrected field - about APS-C max (28mm) and when you reduce that to x0.75 - you are already at 21mm - that is diagonal of ASI1600. More reduction than that will only work with ASI533 as it is smaller sensor. Look into CCDT67 for that one - it works at x0.67 - but you can push it even higher than that. Maybe this scope would suit you best: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p12005_Explore-Scientific-MN-152-f-4-8-Maksutov-Newtonian-Telescope-with-Field-Correction.html No additional optics needed - it can illuminate larger sensor. Only problem is availability - you'll most likely need to wait few months for it.

Olly, is that a feature of RASA scopes or is it down to processing? I always thought it was down to processing / some sort of star reduction technique, but now I wonder if it is down to scope - as I've ever seen that on RASA images (this is actually second setup that I'm seeing it with). I'm talking about this: Star cores are very tight (much tighter than I would expect stars of that magnitude to be) - but they have halo, rather extensive one, around them.

Yes, excellent point - once you undo it - you can "keep" undoing it (until you unscrew it completely).

Not sure that I follow. If you rotate lever by 90° - it will pointing "up" (in your video) when fully disengaged. How will it then hit plastic box?

Above was taken from a youtube video on eq5 strip down - it is square base, so you can rotate clutch lever by 90° degrees from current position.

I think that you can solve that quite easily. There is a bolt holding clutch in place - if you undo it, you'll be able to pull away plastic leaver lever that you can then put back on at a different angle and fasten bolt again. Look at strip down guide somewhere - it should show clutch leaver lever removal.

I think that OAG will certainly help. It will at least remove one thing from the equation and that is centroid accuracy. It will also help remove any differential flexure if there is potential for any. Do be careful - you'll also need to bin guide camera as well as 2400mm and 2.9µm gives huge over sampling - 0.25"/px. You don't need that much resolution (by again factor of x4 or x5) and that much oversampling will make finding guide stars much harder. I have 8" RC and guide it with ASI185mc and OAG. It has 3.75µm pixel, so my guide scale is 0.48"/px. I bin my guide camera x2 to get to about 1"/px. You can set this in PHD2 - there is option to bin image prior to determining star position Under noise reduction - you can select x2 bin (among other options). If you use ASCOM driver - I think that you can also select x2 bin there as well. This will give you total bin of x4 - which will be ok for OAG. Maybe consider getting a reducer for your scope for DSO imaging. That CC has pretty flat field, right? Maybe CCDT67 would be good combination with it. It would make scope F/8 and that should not be a problem with small sensor like ASI1600 that has ~22mm diagonal. Since CCDT67 has x0.67 reduction, actual imaging circle will be 22mm / 0.67 = 33mm. Scope should still have good correction at that imaging circle size.

You can guide with 120mm FL guide scope. Here are some calculations to help you out figure it if is worth while. Your guide resolution is ~5"/px (120mm FL and 2.9µm pixel size). This guide resolution will provide you with around 0.25" - 0.3" measurement precision, which is in turn good for guiding in 0.75"-0.9" RMS - which is what you'll probably get with AZ_EQ6 GT mount. In good seeing of about 1.5" FWHM with 8" scope and guide RMS of 0.8" you'll be able to achieve ~2.5" FWHM stars which require 1.5"/px sampling rate. With 2436mm of FL and 3.8µm pixel size you will be sampling at 0.32"/px, so you'll need to bin at least x4 if not x5 to get closer to 1.5"/px (x4 will give you 1.29"/px and x5 will give you 1.61"/px - it is more likely that you'll need second one at 1.61"/px). In the end - yes, you can guide with such combination 120mm FL and ASI290 with 2.9µm pixel size, but your scope and camera combination will be waaay over sampled as is and you'll need to bin x5 in software to get decent results at 100% zoom level and optimum SNR. You will also fill up FOV: and I think that a bit larger FOV would suit this target better. I'd personally consider doing 2x2 mosaic on that target with said scope and camera and definitively going for x5 or even x6 bin. With such large bin factor - I'd also go for rather long exposure lengths - like at least 5-6 minutes, due to read noise.

Depend on your mount and your wanted guiding precision. It has nothing to do with scope you put on the mount (except for the weight and moment arm - but again, that is mechanical side of things and has nothing to do with telescope focal length). Focal length of imaging scope is rather irrelevant for this whole process. There seems to be large jump from 135mm to what scope is that again? You say Stellalyra F/12, but which one? In any case, what mount are you using, and what camera will you be imaging with? Even 6" version has focal length of 1800mm. Do you have camera with at least 12µm pixel size, or do you know how to bin your data?

Is that image with autoguiding running? In that case - it is possible to have little lines. OP did not auto guide and barbell shapes were due to PE alone.

Love the sharpness and detail.

Check out this video: and imagine that you don't need to look at the tiny hole with illumination to see marking on the secondary - you can look at computer screen with SharpCap. SharpCap has few reticle types - regular crosshairs or concentric circles that you can turn on. As far as I can see - no need for special software - you just need to center things.

Hi and welcome to SGL I know nothing about binos, so don't take me seriously, but I consider these: https://www.firstlightoptics.com/opticron-binoculars/opticron-oregon-10x50-wa-binocular.html I suspect that they are excellent value for the money to get you stared in astronomy. If you want better binoculars that you'll be using for other things as well - like birding, or nature observation when hiking, ... - then consider more expensive models that are durable, argon filled and so on - but for star gazing, I think above will be more then fine.

Do you have a guide camera? Maybe ASI type with body like this: and wide cs lens like in the picture? Why don't you try inserting that into your focuser with lens attached. Camera has 2" rim that will go nicely into 2" focuser and you'll get very nice centered image of your secondary and primary baffle tube. Maybe you can then perform collimation by looking at the laptop screen?

Yes - there are two types of metric pitches for threads - fine and coarse. M42 is usually refers to M42x1mm - coarse metric thread, while T/T2 refers to M42/0.75mm - fine metric thread. Astronomy equipment uses T2 - or M42x0.75 as standard thread, while old lenses use M42x1mm as their thread - like this one for example:

https://www.teleskop-express.de/shop/product_info.php/info/p7051_TS-Optics-1-25--and-T2-Micro-Helical-Focuser---T2-connection.html + https://www.teleskop-express.de/shop/product_info.php/info/p9107_TS-Optics-T2-Reversion-Adapter-with-full-length-T-thread--female-.html You'll be able to reach focus on Skymax without issues, even with diagonal as scopes with moving mirrors have quite extensive focus range. It will however slightly alter focal length of instrument - as it depends on separation between mirrors, but this effect is very slight ~50mm on 1300mm that you already have, and there will be slight change in spherical aberration - as it also depends on mirrors separation, however this is even smaller change and you will not notice anything (change is probably order of 1/10th of the wave - and it really depends on what is perfect position anyway, so you might even improve spherical correction). With Travelscope 70 - it depends on how much back focus your scope has. Above combination is likely to eat up around 60mm of optical path and if you need to extend current focuser ~60mm or more when viewing with diagonal in place - then it will work. By the way - that helical focuser that I linked can be found on AliExpress for about $25. I haven't checked on Ebay - but it is likely you'll find one there as well for less money - just make sure it is T2 version (there are several different versions with different threads). For example: https://www.aliexpress.com/item/4000922964606.html?spm=a2g0o.search0304.0.0.59342d532mDgqJ&algo_pvid=011411a1-af3e-4bab-b563-a5f45344b2bd&algo_exp_id=011411a1-af3e-4bab-b563-a5f45344b2bd-0

It would only produce uniform line if it was "sawtooth" pattern - constant speed in one direction, then constant speed in other direction. Periodic error is often very non uniform and consists out of few sine waves superimposed. Here is recording of my PE on HEQ5 prior to belt mod: Left to right is due to polar alignment, and obviously up and down is due to PE. Here you can see that stars don't spend equal amount of time along the curve - there are places where star is almost still and other places where it accelerates rapidly. In fact - if you look at some frames - you'll see exact same pattern - two bright spots interconnected with fainter line in between.

Probably because these are most often used for imaging, but addition of M48/2" adapter should be easy thing to do: https://www.teleskop-express.de/shop/product_info.php/info/p4201_TS-Optics-Adapter-from-M48x0-75-to-2--Receptacle.html That is simple compression ring, but if you want something more fancy - Baader does one with twist lock action. https://www.teleskop-express.de/shop/product_info.php/info/p9516_Baader-2--ClickLock-Adapter-Clamp-with-M48-connection-on-telescope-side.html

Here is one - but you'll have to add M48 to 1.25" (or 2") adapter for eyepiece side: https://www.teleskop-express.de/shop/product_info.php/info/p9360_TS-Optics-2--Non-Rotating-Helical-Focuser-with-M48-connection.html It comes with 2" nose piece or M48 on telescope side if your focuser has that thread (that is standard 2" filter thread).

It can be down to SNR and FWHM calculations. I believe that it calculates tilt by simply looking at FWHM of stars (this is why it needs uniform star field so that FWHMs are on average equal) and then finding average in each "corner" (or rather zone of sub). Many faint stars introduce quite a lot of noise in FWHM measurement. Do you have any set of subs where target is not in direction of Milky way? Fewer stars and clean background could help

I think that you need nice uniform star field for that to work properly.

While we are on subject, I'm really interested in these: https://www.teleskop-express.de/shop/product_info.php/info/p1421_TS-Optics-20x80-ED-APO-Binoculars-with-two-Triplet-Objectives-and-Tripod-Adapter.html but not as binoculars I see them as source of two 80mm probably F/5 triplet lens. Who wants to have ST80 with triplet lens and hence much better color correction?

Those have 80mm F/6 lens in them - probably FCD-1 / FPL-51 type. At that aperture and that speed - it's probably still going to have residual CA. Not as much as equivalent achromat - but it won't be color free.

I think there are couple of options available. There is astroberry: https://www.astroberry.io/ then there is IndigoSky (I've started using that one for my remote / backyard wide field setup - rpi4 and controlled from desktop in my study): https://www.indigo-astronomy.org/indigo-sky.html I think that you can also install regular linux distribution onto RPI and use PHD2 guiding software under linux via remote desktop for example. Even if your laptop is old one - it should be ok for basic guiding and imaging tasks. I used laptop with old intel celeron dual core processor and if I remember correctly 4GB of ram when I first started out. It was enough to do both planetary imaging (it had USB 3.0 port) and regular imaging + guiding. Yes you can - there is adapter that will turn 9x50 finder scope into guide scope with camera attachment - like this one: https://www.firstlightoptics.com/finders/astro-essentials-sky-watcher-9x50-finder-to-c-adapter.html Not sure if there is such adapter for 30mm finder - but if you have 3d printer, I'm sure you'll be able to print suitable adapter. You can use dedicated guide camera or even use web cam converted to guide camera role. All you need to do is make nose piece attachment of some sorts and remove lens from web camera. I made one from Logitech c270 camera - which I used for planetary imaging back then. I used 40mm PVC pipe that I sanded down to fit into 1.25" focuser. Alternative is to get dedicated guide camera like this one: https://www.firstlightoptics.com/guide-cameras/zwo-asi-120mm-mini-usb-20-mono-camera.html or if you don't mind ordering from AliExpress, then maybe something like this (much cheaper - but closer to web cam): https://www.aliexpress.com/item/32868532770.html Yes, a lot of 12V 3A adapters (I have 3 of those - one for mount, one for cooled camera, one for flat panel, although I sometimes use one for mount for taking flats after I part my mount and turn it off). Some people prefer batteries, especially if they have mobile setups. You can look into lithium batteries (best are LiPoFe4 type) or lead-acid deep cycle (cheaper and greater capacity but heavier).