vlaiv

When doing star detection - don't use median filter - and raise threshold. How many stars are detected in test run?

I think that not being dark adapted is the key more than telescope size - or rather having balance - not being dark adapted so that night vision fully kicks in and being enough dark adapted to see the object. I think I saw color in M57 with 5" telescope - but it was more "am I really seeing color or just remembering how it is supposed to look like?"

Turn off all "advanced" options - like hot pixel detection and removal.

Usually PE is far from sinusoid. If it were sine form - it would be easy to fix. To understand how dumbbell shape forms - take a look at second part of this video - try to concentrate only on horizontal motion and "integrate" it in long exposure: https://www.youtube.com/watch?v=S8EWKm2FwBo In any case - I still maintain that it is PE - but happy to be proven otherwise.

Other way around - 5 motor turns for one worm turn http://eq-mod.sourceforge.net/prerequisites.html Eq5 has total ratio of 704:1 and 144:1 is worm ratio

Periodic error is produced by mechanics of the mount rather than motor. If motor is driving unevenly - that will show in similar fashion - but it will be much quicker. This is because motor makes one revolution every 2 minutes - there is 5:1 reduction between motor and worm. Each sub would be then effected by whole motor periodic error - provided that error is of mechanical nature - then it would be tied to motor rotation period. If it was electronic in nature - then motor would simply rotate either slower or faster than sidereal - that would show as constant trailing / leading, or it would be random if it was electronic noise - and not periodic. I'm not against changing the drive train - it will be needed for guiding. I just don't think it will help with mechanical periodic error.

Yes, please try east heavy - just to be sure, but there is another thing to check when periodic error is examined. What was your sub duration? Period of EQ5 mount is 10 minutes - see if pattern repeats every 10 / sub duration frames. If you shot 2 minute subs then pattern repeats every 5 subs.

This is perfect example of two most common causes of star elongation - periodic error - polar alignment error Wobbling up and down is periodic error, it repeats every few minutes - mount trails a bit then it leads a bit and back again ... Motion from left to right is in DEC direction and that is due to polar alignment error. Most people blame elongated stars on polar alignment error - but it is usually much smaller in magnitude than periodic error - you can see that in your animation - drift to the right is fairly slow compared to constant up and down of stars.

That has something to do with cosmetic correction / hot pixel removal or similar Try just regular average stack without fancy options - stars should look fine in that.

Yes, very nice comparison - important thing to note is that this was done with KAF8300 - which is 22mm diagonal sensor and some CCs have ~30% vignetting in the corners of 22mm sensor. This is 10" version of scope - so larger secondary. Larger sensors are probably going to have more issues with correction and certainly more vignetting. Just something to keep in mind to avoid surprises. That would be my pick too - apparently it is tolerant to some tilt - that can't be a bad thing

Due to elongation and other things mentioned in post - it seemed that PE is likely candidate. There was no wind, and if backlash was issue - such perfect symmetry requires perfect balance and very uniform random swaying back and forth. Why only some subs and not all if there is such symmetry? On the other hand - symmetry can easily happen with PE without any special requirements - shape of gear is enough to cause it - just think egg - it will create such symmetric shape - most of the circumference - radius is the same and stars are point like - when approaching hump - radius is increasing and mount is trailing - at hump itself almost no time is spent and then mount starts to catch up again - thus you have symmetry in resulting star shape. Also - do we know many of SkyWatcher mounts that don't have very distinct PE? I don't think I've heard someone bragging not to loose a single sub without guiding - that just does not happen with these mounts. In any case - backlash is easy to sort out by making scope east heavy. @jm_rim You know what you can do to see if it is indeed periodic error - take the subs you shot - in the order of time they were shot and do a crop on them - just a few stars - like in first post - but do that with each sub. Make animated gif out of it. If you get something like this: (up down motion is due to periodic error and left to right is due to polar alignment error - notice that some frames have elongated / split stars) then it is periodic error. If you get random jumps between round and elongated stars that does not follow nice path - it is most likely backlash - but I seriously doubt that.

What did you get? 8" or 10" version?

I was thinking of getting 6" F/4 TS version at some point to serve as wide field instrument. Not sure if I would go larger than that. Also note that these smaller newtonians are really suitable for smaller sensors. I don't think one can get very good correction for APS-C or larger sensors at that speed - even with excellent coma corrector. Larger the sensor - more sensitive it is to tilt and at F/4 - collimation and tilt will be challenging.

I don't think there is any public info on that sensor as it is proprietary Canon made sensor for exclusive use in their DSLR cameras. You can't purchase that sensor separately to use in your own product (Canon does have some industrial sensors but I don't think any of those are used in their cameras). You won't be able to find schematics for it online - only way to figure out how it operates - is to reverse engineer it. Someone with electronics knowledge and skills could open up 450D and see electronic leads and then figure out what pins on sensors do... Maybe look if you can find any info on DIGIC III processor - as it is used to read data from sensor itself.

I think that it depends on cosine of dec. If you think about it - at NCP you are not actually tracking the star you are just rotating the field of view and it stays pretty much in place. At Dec 30°, rate is about x0.86 that at equator, while at Dec 60° it is x0.5 and so on (cosine function - at 90° it is equal to 0). This is "star motion" on sensor - not RA axis - it always rotates at the same rate - sidereal. Of course - guiding is the best way to deal with this - it is exactly why guiding was designed for - to compensate for any tracking errors (both PA errors and periodic errors). If you can - you should start to guide - that will make your stars round in all subs.

That is periodic error. To be 100% sure - see if it is aligned with RA axis - if it is, then it is periodic error. To minimize it - shoot objects closer to NCP/Polaris. PE is the worst around equator (at DEC close to 0). Since you are using single RA motor - you don't have this option, but there is this thing called periodic error correction. It is designed to lessen effects of periodic error. It is available in some mount models, or via EQMod / computer Shorten your exposure length. PE is usually the worst in some parts of worm revolution - if you shorten exposure, you'll throw away less subs. Of course - discard the worst subs. In the end - it might help to "tune" your mount - which is basically term for stripping it down, cleaning, applying suitable grease, possibly changing bearings for quality ones and then reassembling everything carefully so that everything fits tight but does not bind.

Check this website: https://www.photonstophotos.net/Charts/Sensor_Characteristics.htm

Oh, it can make quite a bit of difference on faint objects. It can make half a mag difference in brightness or even more. It can reduce signal to 63% of the other one. Do a light saber check? Do you have torch with you? Shine it up in the sky to see if you get "lightsaber" effect. This will show you if there is local fog. I checked Copernicus - most of UK has excellent transparency at the moment.

Different transparency?

almost there after some fiddling with color channel mixer and saturation in Gimp - but that gradient is a killer ...

You can fiddle around with your version a bit, but it is hard to produce image looking like this other you posted for several reasons (filter use is one). Here is what a quick reprocess gives: I guess that is more to your liking than original image? I just used Gimp to bring background to same level thus removing slight blue cast on background sky and then used Nik collection color effects - remove color cast, to remove reddish cast on the image. Better way to do it would be to remove background while image is still in linear stage and then see about color cast ...

Or go with this one and have best of both worlds https://www.teleskop-express.de/shop/product_info.php/info/p3881_TS-Optics-PHOTOLINE-80mm-f-6-FPL53-Triplet-APO---2-5--RAP-Focuser.html

In my view - you should not be put in a position to pay any shipment fees here - as this is neither your fault nor failure of item while it was in use and still in warranty. It is their fault that they send you used item marketed as new in the first place. Strictly speaking that is illegal - there are consumer protection laws - you can't lie to customers and sell them used goods as new.

You could show these images to icstars staff in an e-mail, ask that they send you replacement item and arrange this one to be picked up by courier at no charge to yourself?

Was there a discount of some sorts when you purchased the item? Sometimes retailers offer discount on customer return items or repaired items - but they must state that item was customer return and / or has been repaired under warranty. Maybe you just did not notice disclaimer?