michael8554

Well done.! Before trying tonight on a star, try focusing on a slightly nearer distant object. Then reset on your furthest object. Now you will know which way to turn the focuser to focus on even more distant objects, such as stars. Michael

In theory, no. With modern mono guidecam you should always be able to find guidestars when pointed at the target, so it helps to have the guidescope centralised to the imaging field of view. For instance, upping the exposure to 5 secs or so should show your target galaxy. As almcl says try during the day, with PHD2 or with Sharp Cap in video mode. Which camera driver are you using in PHD2? Did you ever try burning paper with the Sun and magnifying glass as a youngster? Try it with the guidecam (no camera attached ! ). Where it focuses the sun is where the sensor should be, will give you a starting position. Michael

Which camera driver are you using with PHD2 ? Drivers & AltairCapture software download (Windows only): www.altaircameras.com (opens new window). Michael

This image might be a good starting point for the relative distance of the camera from the scope, yours look too far away compared to this. Michael

I wasn't precise enough in my scenario. I'm case 2, front of scope heavy pushing south, PA slightly off (5 arcmins) heading south, guiding north. Thanks Michael

Hi Tom Hmm, I'm beginning to understand what you're saying. Talk me through what happens when you're balanced for guiding, say, north only, and a dither takes the graph the other side of the axis? Michael

Thanks Freddie I have still much to learn about PHD2. Michael

You may be right Freddie, but I thought the Cal step employed was calculated by the number of steps selected, and the focal length of the guidescope. Michael

The ZWO and the Reducer both have T2 threads I believe, the spacers fit the ZWO so should fit the Reducer. Unless those spacers are M42x1.0mm thread for Pentax/ Praktika lenses, not M42x0.75mm T2 thread. Often they are poorly made so will sort of fit on one piece of T2 kit but not another. The SCT mirror focus usually accommodates a very wide length range of kit on the back, but try with the closest to correct length you can get to if you're worried, but otherwise I don't see any point trying wrong length spacers because you'll get Coma on your images. T2 spacers are readily available on all Astro Equipment websites. Michael

You couldn't be more wrong. Those results were the result of deep dives into the graphs and guidelogs. I predicted that despite not entering the focal length, PHD2 did a good Cal with some sort of preset, and I suggested you could continue with that Cal if you wished, of course the graphs would be meaningless. Entering the focal length resulted in the same Cal but with meaningful graph and guidelog results. Michael

Let's say that in the test the mount is balanced so that the worm is already preloaded, is engaged on one face. At the end of the North moves the motor reverses. The motor now pushes on the other face of the worm to move south. Unless the worm is perfect, the move from pushing on one face of the worm to the other face of the gear involves overcoming backlash. And the balance still wants to engage on the other face, but the motor has overridden that load. In the Guide Assistant RA drive is turned off, so you're seeing the RA Periodic Error that most mounts have. It's about 20arcsecs peak to peak which isn't too bad. Use the PHD2 Permanent PEC Algorithm, or investigate recording PEC in your mount. Michael

Yes that's the correct attachment order. But if you read my post you'll see you need 98.5 mm of spacers. 16.5 + 21 + 10 doesn't come to that, if my mental arithmetic is correct.......? Michael

The PHD2 test moves the mount in Dec a goodly number of steps. If it was balanced to have the backlash taken up, then when it reverses and starts to move back it will encounter Backlash, and will measure how long it takes to start moving back to the start. If balanced the other way, it will encounter Backlash at the start of the test. Michael

If you've bought the correct focuser it should screw directly onto the back of the OTA. The focuser must always be before the Reducer, otherwise the crucial Reducer spacing will change as you alter the focus. The spacing for a Celestron 0.63 Reducer is 105mm. Ideally screw it onto the focuser instead of using a nosepiece, for rigidity. The sensor is 6.5 mm inside the camera body, so between the Reducer and the camera you will need 105 - 6.5 = 98.5mm of spacers. Michael

Calibrate at zero Dec but run Guide Assistant ON YOUR TARGET. Now that you've finished testing, don't forget to set the Graph Y Axis to arcsecs instead of pixels. RA 0.69arcsecs and Dec 0.59arcsecs look good and are similar, so should yield round stars. Michael

Which one .....? Michael

We started out discussing Crop Factor, which turned out to involve Field of View. You've now introduced another factor called Resolution, which only involves the size of each pixel. Take a Full Frame camera with 4x4 um pixels, and a APS-C with 4x4 um pixels. Crop the Full Frame to APS-C dimension, each image has the same Field of View, and the same number of pixels. Now this time the APS-C has 2x2 um pixels. Crop the Full Frame to APS-C dimensions, now each image has the same Field of View, but the APS-C image has four times the number of pixels. So yes, the APS-C image has higher Resolution, but the area of sky in the cropped Full Frame image is still the same as the APS-C image. You say this makes the APS-C "better". Better resolution - yes, but you could be Oversampling. And each smaller pixel receives less light than the bigger pixel, so is less sensitive, and to capture dim DSOs, sensitivity isn't something you reduce by this other myth, "more pixels is better". Michael

The PHD2 guys say to disable any backlash comp in the mount or any other software, because it confuses the backlash comp in PHD2. Michael

Here's the RA for your last guiding session: Earlier in the evening the Minimum Move setting was a reasonable 0.28. But on the later runs it was 0.010 !! That's the dotted line indicated by the red arrow, and is the threshold where guiding is applied. So having it set so very very low meant the guiding was continuously being corrected when it didn't need to be. Giving the very choppy result. Calibrate at Dec zero, then run the PHD2 Guide Assistant when you have moved to your target, which will recommend guidecam exposure, and Min Move settings. Looking at the Calibrations there has to have been a lot of adjustments in GS Server that these logs don't mention. For instance why is the mount Calibrating East and North along the same axis, the red and blue circles, instead of at 90 degrees? Below is your last Cal which is at 90 degrees at last - what changed, can't help if you don't say what you've changed in GS Server? Cal has taken 34 steps instead of a more normal 12 or so. RA and Dec Guide Rates reported from the mount are a reasonable 7.5 arcsecs/sec, but the real Guide Rates must be a fraction of this - is there a setting in GS Server that is overiding ? I think your guiding could be very reasonable judging by your last session, if you could just let PHD2 choose the settings , and also get mystery GS Server settings right ! Michael

Ha, didn't spot the "last year" comment ! Michael

Lyrid Meteor Shower April 16th to 25th ? Michael

Nope, you're having a giraffe haha, that runs 23:00:33 to 23:08. Look at the filename : 2020-04-14_230033 Does that give you any clues...... ? Michael

If you run the Guide Assistant in PHD2 it will advise the exposure and Minimum Move settings for the quality of "Seeing" at your location. "Seeing" is a measure of how turbulent the atmosphere is (that's what makes stars twinkle). When Seeing is poor the guidestar image will be bouncing around. Setting a fast exposure like 1 second would have the mount "Chasing the Seeing", so a slower exposure like 2 or 3 seconds will give smoother guiding. If Seeing is good then a faster exposure might be advised, it can help the guiding of a budget mount. Michael

Nearly there, that's the Debug Log, not the Guide Log. Michael

Your log file is incomplete, the Cal was at 22.47, your post only goes up to 21.20. Please don't cut and paste from the file, post the whole file as an attachment. Michael