michael8554

I couldn't find redetails of a Skywatcher 0.9 Reducer, I could find a Skywatcher 0.9 Coma Corrector. To my eyes the bottom-half of the image isn't too bad, the top-half has noticeable Coma. Suggesting tilt - either through the connections to the focuser, or the sensor after the Mod. I believe that a Nikon with a T2-Adapter, and a Canon with a T2-Adapter, are both 55mm spacing from the T2 thread. So if the coma is fine with the Nikon, and if you are using the same connections, sounds like sensor tilt. But try with the CC unscrewed slightly, to give you a mm or so extra spacing. Michael

Post a jpg of a problem sub. Specify which OTA and CC. Michael

My take on the message was that this behaviour was while Tracking? Which makes Guiding difficult. Could be wrong...... Michael

The latest image that actually shows the elongation: Depending on which corner it's from, the camera could be too close, or too far away, from the FF. Or it could be guide errors if the whole frame is the same. Who knows. Michael

Found this on the PHD2 Help Forum. Although it relates to a CEM40EC, the problem is probably the same for the 60EC: "I struggled to guide a CEM40EC for quite a while before learning that iOptron EC mounts suffer from "sub-divisional error" on the encoders. In my CEM40EC, this resulted in the mount oscillating in RA with a 6-second period and a peak-to-peak amplitude of 0.6 arc seconds. There was no way to guide this out. The best I could do was use a long interval (3 or 6s) to try to average out the wobble so it didn't inject noise into the guiding. Eventually, I bought a CEM60 (no EC) and sold the CEM40EC to someone who was imaging at a larger scale." Michael

The image scale is 6.55"/pixel To dither the 100D by the commonly used 12 pixels, the mount needs to move 12 x 6.55 = 78.6 arcsecs. So does a pulse of 0.5ms, or 10, achieve that ? Michael

The info in your screen grab is limited. Despite a 3 second exposure, Signal to Noise SNR is only 4.0, the yellow figure in the toolbar indicates it's of concern to PHD2. If you move the blue slider to the left the display would show the stars better. And if you displayed the Star Profile (Tools - Star Profile) we could maybe tell if that's a hot pixel or not. (Though you are using the PHD2 Darks) "Cal" on the toolbar is red, indicating either that the Calibration failed, or maybe you haven't tried yet - you did press the green button to make PHD2 Cal, and then guide ? Post your PHD2 GuideLog, such as it is, so we can check your settings. Michael

Newer versions of the 4400 have a 1.25" focuser. Maybe the 0.965" part of your focuser unscrews, to reveal a 1.25" fitting ? An image would help. Michael

Which of those two images was that from, I still don't see it in the originals ? Square, but not elongated. Michael

PHD2 / Tools / Enable Server Michael

Yes, the RA and Dec lines should be at right angles, and the circles evenly spaced. The circles indicate the distance between PHD2 Calibration Steps. If the pixel size and focal length have been correctly entered, there should be about 12 circles. PHD2 will then know how far an X ms pulse moves your mount. The bunched-up red dots at the origin shows there is Dec Backlash, which you should manually clear before Calibration. There is a wealth of Help And How To guides available via the PHD2 Help menu, start with this: https://openphdguiding.org/phd2-best-practices/ Michael

The corner stars in the images you posted look fine to me Michael

The 1600MM sensor is over twice as large as the 178MM, so it's edges are much closer to the vignetted regions of the ED102. Michael

Hi Steve There are other examples of the RA problem. Here's part of your Calibration: Note how the RA steps (blue) are bunched together in pairs, instead of being evenly spaced like Dec. So there might be slight stiction that is taking two pulses to overcome. From other posts I've read it's likely your 120 sec problem is something in the belt drive. Try shifting the belt a couple of teeth on the cogs. Try swapping RA and Dec belts if they're the same. Look for signs of trying to jump while slowly slewing. Michael

My comments are based on my PHD2 experience, I'm assuming a good Cal with your software should look like this, with RA and Dec at 90 degrees: And the Dec Backlash causes the southward return from the northmost end of the Dec line to wander off like your S1 to S7, instead of retracing the green line to the origin. But again, your software may Calibrate differently. Michael

From what I've read, keeping the ISS in FOV is challenging, so the much larger FOV of the DSLR will help. Not sure you'll capture more than a dot the with the FL of the ED80, could be wrong. Michael

Try this OAG Calculator to match camera size to prism size: https://www.smallstarspot.com/oagcalc.html Michael

Hi Shimonu Here's from YOUR GuideLog: You never got a decent Calibration, so guiding was bound to be poor: Calibration guide speeds: RA = 1.6 a-s/s, Dec = 1.7 a-s/s Guide speeds need to be at least 7.5 a-s/s. So RA completed in 4 steps W1 to W4. PHD2 aims for 12 steps, your Guide software may be different. North took 3 steps N1 to N3, but the Return South path S1 to S7 should have ended back at the intersection of the axis at W1, and ideally taken 3 steps, not 7. This is an indication of rather large Dec Backlash,. So I'd concentrate on that rather than RA ! I'm afraid the Logs generated by your Guide Software are sparse on detail compared to PHD2. But it showed that you Calibrated at Dec = 40, it's best to Calibrate at Dec = 0. So concentrate on Dec Backlash and larger Guide Rates. Maybe get some good guiding by tweaking in PHD2, then reverse engineer it to work with your guide software 😆 ?? Michael

Apologies Shimonu, That was someone else's Guidelog I selected in Log Viewer. Michael

Have you had any Windows updates on the Tower PC ? Check all the USB power settings in Device Manager. Run the guidecam on its own with PHD2. If it runs okay add other equipment until it fails. Michael

The 120MM-mini sensor is 4.8mm x 3.6mm. The 290MM-mini sensor is 5.6mm x 3.2mm. So the 290 sensor is slightly wider, less high, so not significantly bigger. Michael

Redacted

A little more info would help. What exposure ? Which is RA, which is Dec ? I think from the Dither figures that RA is Blue ? There are excursions of up to 7.5arcsecs that are taking about 5 exposures to correct. Causing RA to fly over the other side of the axis up to 7.5arcsecs, and about 5 more exposures pass before RA is corrected. So I'd say RA is loose and has Stiction. If you have any sort of GuideLog it would be far more instructive than screenshots. Michael

The Focal length is 660mm. Measure 660mm from the front element, that's roughly where the DSLR sensor needs to be. Measure back from that point to the focuser, in the middle of its travel. Subtract 55mm for the DSLR + T-Ring, that's the length of extension tube you need. Get the closest available and fine-tune with the focuser. Michael

After further thought, I think that ASIAir is reporting Dec movement of the guide star. Since you have Dec guiding off, that movement in Dec is due to sudden Dec movement of the mount, maybe a cable snagging, tripod leg sinking, Alt adjustment loose etc etc. Michael