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The Astroberry RPi ‘image’ has a whole set of open source software integrated into it. Polar Alignment is just one function within the very powerful KStars/Ekos/Indi package, alongside PlateSolving, Guiding using an internal function or with PHD2 running alongside. Since Radek has compiled this Astroberry version 2.0.1, he has set up a ‘repo’ which is like a one stop shop for updating all the software to the latest versions or adding new functions like ASTAP for platesolving. I bought my (first) RPi4 last summer, and used it for mount control and then polar alignment with my DSLR and the main scope. I added a guidescope and ASI120 in December. Polar alignment is a lot faster now (platesolving takes around 5 seconds) and the ability to use platesolving to synchronise mount alignment at any moment is transforming.

As my ‘signature’ shows I’m a convinced Pi user, these days with the very stable Astroberry package of software. I have several Pi4s, and have no problem using my 2GB one for Astroberry. The program uses ‘zram’ which effectively doubles the RAM available, and there is a memory use monitor display which shows that it is usually around 47% filled. I start a session with Polar Alignment using the guidescope/camera, then steer to a bright star, platesolving with the main scope and camera (in my case a DSLR), Bahtinov mask for focusing, then off to the target. Take a look at Radek’s Astroberry videos on YouTube. [However you can’t run SharpCap or NINA on a Pi].

I believe so (the sensor diagonal is around 27mm). Here is a test image of M101 in that configuration stretched in KStars FITS viewer (alongside the DSS image) which shows some stars near edges and corners.

Further practical measurements of a SkyMax 150 Pro focal length. So I removed the add-on Crayford focuser and reverted to the originally supplied 2” visual back. Into this I fitted a 2” to 1.25” adapter and used this with a T2 threaded eyepiece tube to mount two cameras, firstly the ASI120 and secondly the Canon EOS 600D. Based on the specified focal length of 1800mm, the FOV with the ASI120 calculates as 9’ x 6.6’ (‘=arc minutes). I chose M44 as a target hoping that Ekos and the downloaded astrometry.net files would find a match, but without success. Subsequently I swapped the ASI120 with my Canon EOS 600D, which required refocusing by 1 and a quarter clockwise turns of the knob. This time, the theoretical FOV calculation yields 42.6’ x 28.2’, and with platesolving completed, the measured FOV was given as 41.2’ x 27.4’. This suggests that the actual focal length with this primary mirror setting was 1860mm. I attach photos of the scope and camera for this configuration, and also with the ASI120 in position. My guess is that only with the prime focus position of the ASI120, or with an eyepiece placed directly without star diagonal very close to the visual back, would you achieve the 1800mm standard specification focal length for the SkyMax 150 Pro.

For the secondary mirror (and I checked with Steve before doing this) I first used a plastic bag held by an elastic band around the oval edge of the secondary mirror to fully enclose the mounting metalwork, and then did the same full immersion washing as the primary. Similarly, no need for any touching to dry when rinced with distilled water and propped up to drain naturally.

I am a bit confused about what you’re asking! The camera end of the guidescope has a male T2 thread around a 1.25”-fit focus tube. There is no female T2 thread alternative as far as I can see. Hence my ASI120 can be fixed using the T2 screw thread directly, or with the additional eyepiece tube to T2 adapter supplied with the camera.

I recommend the ‘full immersion’ method illustrated by Steve Richards (steppenwolfwest) on YouTube If you prop the mirror on its side when you have carried out the final rinse (real distilled water if you can get it rather than non deionised water) you won’t need to touch it any further as it dries naturally

I had to follow this up with a bit of measuring........and I was surprised to discover that the distance from the rear body of the Mak to the sensor of my Canon DSLR is almost exactly the same as the distance from the same point (where the visual back screws on) via the star diagonal to the field stop of the standard eyepiece normally supplied with the scope by SW (within about 10mm). In other words, there will be very little adjustment of the primary mirror if I were to go from my present imaging arrangement to visual observing with the standard setup. For me this suggests that the focal length of (my) SW SkyMax 150 Pro as supplied for visual observing mode is closer to 2100mm than 1800mm!

With the Moon and Venus as targets I have been experimenting with imaging with my SW SkyMax 150 Pro. I swapped out my usual 80ED refractor and tried using a Canon DSLR at prime focus on the back of the Mak which is fitted with a Crayford focuser. I calculated the FOV assuming that the focal length was 1800mm as stated in the SW specifications. But there was an obvious and non-trivial discrepancy with the actual FOV. After platesolving with Astronomy.net in Ekos, the FOV measured for the Canon EOS 600D was 36.1’ x 24.1’. A quick calculation makes the actual focal length to be 2122mm, i.e. 18% longer than expected. I appreciate that in its normal visual observation mode my Mak would have a slightly longer optical path to an eyepiece through a star diagonal, and the adjustment to the primary mirror to reach this new focus point would change the focal length, but surely not by so much? And in the case where the diagonal was attached directly to the visual back and not through a Crayford focuser add-on, surely the focal length would be rather similar to the case with the DSLR at prime focus. Any thoughts?

Just out of curiosity, did you buy your Mak new or used? I bought my SkyMax 150 second hand, and wasn’t attentive enough in the buying visit to notice until I arrived home after a few hours of car journey that one of the collimation screws was loose. I presumed that it had shaken loose in the vibrations in the car, but now I’m not so sure. I also noticed (in comparing with a friend’s brand new 150) that there is a short baffle tube fixed to the secondary mirror which in my case seems to have been glued (perhaps clear superglue?) with a little excess adhesive visible, whereas there is no such glue visible in the new Mak. I assume that the previous owner dismantled my scope to clean the correction plate and possibly disturbed the baffle tube and had to reglue it. I researched long and hard before attempting to recollimate my scope, but finally I am reasonably happy with the result, again when I compare with my friend’s new one. However I would caution against touching the screws if you are not confident with the star test approach taken by Captain Magenta, and assume that your disappointment with the scope is influenced by lack of thermal equilibrium, before any comparison with your Dob. Even then bear in mind that comparison between two styles and sizes of scope is always fraught with subjectivity!

I'm not using the ST4 connection. My guide camera is connected via a USB 3.0 powered hub into a USB 3.0 port on the Raspberry Pi 4 but I'm sure it would run fine on USB 2.0. You mention that your camera is not compatible with USB 3.0 connections, but I'm pretty sure that I read on one of the relevant forums (maybe SGL, CN or perhaps Indilib) that the earlier version of the ASI120MC is not entirely compatible with the specification even of USB 2.0. I have an astro friend who lent me a mono ASI120MM of the older type, before I received my ASI120MC-S but I couldnt get it to work with my RPi4 system.

I personally am having success with the SW 50mm Evoguide and the ASI120MC-S (i.e. USB3.0 version of your camera). However if I understand it correctly, the USB2.0 interface of the earlier model is slightly out of specification and so doesn’t always work with software drivers (like Indi). In my case when guiding an ED80 primary scope, I set the guide camera binning to 2x2 which I think averages out the Bayer filter pattern of this colour camera, although it does work on 1x1 binning as well.

There seems to be some confusion about the Raspberry Pi 4 needing ‘a minimum of 3A’. Actually its standard power supply delivers up to 3A which is the maximum limit of the USB-C socket connector. In practice, its power requirement is dependent on what it is required to deliver to accessories through the USB sockets. I run my RPi4 without any issues from a 2.1A ‘charging’ socket on a 7 port USB hub which is itself powered from 12V. My USB devices are DSLR, Guidecamera, Pegasus Pocket Powerbox, EQDirect mount and GPS dongle, hence too many to feed directly from the RPi4 and soon to be added to by a motorised focuser module.

I would mount a SW 50 Guidescope like I have on a piece of square aluminium tube suitably cut and shaped. The mounting knurled bolts are interesting - the are used in the music industry to convert from 3/8" to 1/4" UNC/Whitworth threads for microphone stands and fittings, and they do a great job locking the guidescope to the main scope mounting rings. In my case I found the finderscope base which was supplied with the Guidescope was much less solid, and placed the whole guidescope/camera too far back. The new arrangement is much better for balancing.

Read the advert carefully - you need a strong back to handle such a scope!

If as I understand it, you are concentrating on imaging as such, then a guidescope and camera will be a must have. They will first help you to polar align and then serve in their other role. The ‘polemaster’ does one thing only (although does it well I believe). To answer your specific point, the polar alignment using the guidescope will be the same as using the prime telescope and imaging camera. Any slight offset between the pointing angles of the two scopes is irrelevant. However when you frame your target especially using plate solving then use the main scope, so guidescope alignment offset won’t matter.

Radek has put together a very attractive software package which is quick to download and install in your Raspberry Pi 4. He has also set up an 'Astroberry software repository' which should make future updating simple and streamlined. Until recently I was running the KStars/Ekos/indi software using an iPad as the controlling terminal, but since buying a new (i5) laptop which offers 10 hours of battery life, I am finding that this new combination is ideal. I start off with Polar Alignment using the guidescope and guide camera, then select and track a target star for focusing manually with a Bahtinov mask, Capture and Solve (platesolve) with the main scope and camera then Slew to target to put the star centre of the image, carry out focussing using the image preview facility. At this point I can take the laptop indoors. Then I select my wanted target object, slew the mount, Capture and Solve and leave the software to slew again as needed to line up the object. Next start guiding, and then leave the RPi to perform the required image capture. My latest learning discovery is that the captured images can be easily transfered, by the same VNC Viewer/Server combination which allows me to operate the RPi4 remotely, to a folder on the laptop. The contents of the folder can then be used by SharpCap Pro (running under Windows on the laptop) to carry out some live stacking for EAA, all this while the RPi is doing its work on the mount. On the hardware side I have bundled together the RPi4 (in a metal heatsink 'flirc' case) with its plastic bottom surface outermost for best WiFi Hotspot coverage, a 7 port USB 3.0 hub which is powered by 12V but has three charging ports, one of which powers the RPi4, and a Pegasus Pocket Powerbox (PPB) which provides distribution of 12V to the mount and the USB hub and a dew heater supply for two dew straps which is controlled automatically by a dew point savvy temperature/humidity sensor. The bundle of three similar sized small boxes is held together using a velcro strap, and only a single 12V power cable is led from this group and away from the mount to a battery or mains PSU power source. In principle the RPi4 could also control the PPB via a USB cable (there is an Indi driver for it), but you'd have to pay attention and not switch off the 12V distribution outlets, which would instantly and possibly brutally power down the RPi4.

Marmo, my experiences with a Raspberry Pi 4 running KStars/Ekos/Indi have been very good. Some kind, brainy people have put in a lot of detailed work to come up with simple solutions. After some months using an AstroPi3 package prepared by Rob Lancaster, I am testing an Astroberry Server image prepared by Radek Kaczorek. Each of these packages bundle lots of useful software (free) for astronomy and astrophotography. The Raspberry Pi 4 hardware costs about £75 - 4GB RAM version, mains PSU, plastic case, microSD card and microHDMI to HDMI cable - needed until you run it remotely ‘headless’ and link in from your Tablet or PC. I do my polar alignment with the guidescope which platesolves in 5seconds, and image with a DSLR where platesolving (to check framing and GoTo alignment) takes around 15-20 seconds. Take a look at Radek’s Youtube video -

So would you recommend 2x2 binning in this case? I’m pretty sure I’ve read somewhere that 2x2 binning even for the monochrome 120MM is a good idea when using the Evoguide scope which is 242mm focal length.

I also have the 120MC-S also and use it successfully with the SW 50mm Evoguide scope. I have used it binned 2x2 which I presume means that the software is effectively summing a cell of RGGB pixels, and also 1x1 both quite effectively (as far as I can tell). So far I've used the Indi internal guider but this thread is encouraging me to try PHD2.

I happen to have access to unmodified EOS 450D and EOS 600D cameras plus a recently modified EOS 550D so I’m very interested in all evidence about these models. And of course I’d love to save unnecessary time if shooting lots of darks at various ambient temperatures isn’t really helpful.

A new YouTube video from Peter Zelinka, who seems to make sense in his typical videos, appears to be saying that with DSLRs, Dark frames can't correct the inherent streaks and colour casts of the Lights. I'm sure his heart is in the right place (avoiding unnecessary time wasting) but is his head making the wrong conclusions?

Just to mention that Astroberry 2.0 uses Raspbian (Buster) rather than Ubuntu, and that an alternative installation method uses the AstroPi3 script. I use this with ZWO camera and Canon DSLRs. If Altair Astro camera drivers are available they should get installed when this script is run.

Nice mono image! Which software are you running on the RPi4 that is not compatible?

Great news!