ONIKKINEN

Looks like there might be a clear night in the next few days so i could test the effects of filter and no filter at F4.2 just for curiosity's sake, IF i were able to free the filter from its prison. I have it sitting in one of these: https://www.teleskop-express.de/shop/product_info.php/info/p10857_TS-Optics-M48-Filter-Holder-for-mounted-2--Filters---Length-15-mm.html Dont really know why i got one to be honest, i could have just screwed the filter to the coma corrector to begin with. I thought this looks sturdier than filter drawers so probably better and since i didn't plan on changing it or ever using other filters i didn't think more of it. But now the filter prison works against me pretty bad. There is nothing to grip in the inner holder ring so i really cant come up with a solution to non destructively take it out. Perhaps i could drill 2 holes to the inner ring and fit a tool of some kind in them to get a better grip, but i would risk destroying the filter in the process. Well, ill throw it in the freezer once more. Maybe it changes its mind and wants to unstuck itself.

The 150PDS on an EQ5 PRO would probably do most of the things you want, but be 200 pounds over budget. I dont know what i would choose were i in your shoes, since i understand the appeal of doing a bit of everything. But try not to undermount whatever scope you get, it will be frustrating to use and you might end up hating it. I also would mention what @Cosmic Geoff wrote about the setup time. My 200mm newtonian and full astrophotography setup takes somewhere around 30-60 minutes to setup to a point where imaging starts after placing the tripod on the ground. Could be as long as 2 hours if the scope has to cool down first.

I would build a desktop PC for processing and get a cheap and small scopeside minipc for capture. Chances are the combination would still be better value for money than a laptop. I wouldnt want to use a laptop in the field or for processing, so this is a no brainer for me. If you dont want to tinker with tech and must get a prebuilt, the value gap is probably smaller, but processing will always be better done on a desktop PC due to thermal limitations in even high end laptops throttling power a lot.

Cant help with the switch problems, but thought id say that without regulation of some sort you will probably run into power problems faster than you would imagine. Just an unregulated "dumb" battery might read 12.75V now, but will drop below 12V really quickly once you start to draw power from it. Its entirely possible that your mount starts having problems slewing in under an hour. Especially true if its cold outside, you can get under 12V from a battery that still has most of its charge left and there is really nothing you can do about it other than have some sort of voltage regulation going on.

Every time you do, someone learns valuable info that seems to be difficult to come by. Perhaps there should be a BIN sticky thread somewhere? Pixels get smaller and smaller so binning is just a necessity for most folks. OSC is also alive and well and like you said, not the same as mono.

@vlaiv has tried to explain it to me several times and in various threads, but im not sure i "get it" yet fully. From what i understood on the matter OSC binning is not the same as mono bining and the data has to be treated accordingly. ASTAP has a binning option that can be used after capture and works for my OSC data, but i wont be claiming i understand why. Another option is splitting the calibrated subs to their individual channels instead of debayering with interpolation, which results in 1 R, 2 G and 1 B subs that are in their actual resolution of capture which is pixelsize x2 since only every 4th pixel contributes. Then stack them as mono subs and process accordingly. I tried this as a proof of concept but since i am shooting hundreds of subs per target i am really not (yet) willing to do this. Maybe once i get a new mount and can take longer subs.

@iantaylor2uk I thought pure mirror systems fold light of all wavelengths pretty much the same. Not exactly the same, some reflection graphs i have seen have a drop in ultraviolet and infrared, but that shouldn't effect the focal point. So the chromatic aberration in the other example is from the coma corrector lenses, both from the fast focal ratio lightcone entering at an angle and from the lenses being curved themselves. I cant really shoot without a coma corrector with the F4.5 primary, its just too messy already quite close to the center. But just out of curiosity i might try without the filter to compare results. The Maxfield 0.95x corrector isn't all that picky about the distance it seems, i broke one adapter and had to swap it for a few others i had lying around and i ended up being 1mm short. Couldn't spot the difference, so the filter thickness is probably also not that important to take into account. Also, its difficult to tell how much spacers are needed when the corrector doesn't correct all the way to the edges. Spot sizes in APS-C size fields are noticeably elongated with mine.

You may find that the EQM-35 does not perform all that well, at least probably not completely trouble free. If you plan on shooting unguided with it you should definitely "train" the periodic error correction in the mount. My mount came with a not very helpful PE curve out of the factory that didn't seem to do anything to the periodic error. Training it can improve things quite a lot, and for your 6 arcsec/pixel resolution should work well. Read through the manual, there is a section on the periodic error in there. Basically you should point the mount somewhere south to as close to DEC 0 as possible, but still high in the sky, so depending on your latitude and location might not be all that close to DEC 0. Center on a star bright enough to be visible in live view, zoom in on the star as far as you can and then manually guide the star for about 8 minutes if i remember correctly? The better you do this the better your results will be in the end. If you dont do this, you shouldn't expect exposures longer than a minute to always have round stars as the periodic error can be quite aggressive on the mount. Picture looks pretty good for what it is, an untracked short exposuretime from light pollution 👍. Although your list does not mention flat frames, which would be the most important of the calibration frames so definitely look into that.

This would be the plan, if i can take the filter out of its holder. Thoroughly stuck this one, in the freezer it goes for a heat treatment 👍.

So the filter stays, one way or another. Any opinions on the filter placement then? Does it matter whether its between the coma corrector and camera or before the coma corrector. My corrector has 2 inch filter threads on the bottom where i could also mount the filter to free up some space in the already narrow 55mm backfocus between the corrector and camera. My gut says it doesn't matter, or why would the thread be there in the first place, but i could be wrong.

Yikes, thats a pretty significant change on the redder stars. How fast was the scope in your example, if i remember correctly you had one of the hypernewts/F2.8 or something of the sort? I would imagine the effect is lesser in my F4.2 but perhaps i wont risk it since this is what i feared when getting the filter.

I am thinking of rearranging my imaging train to incorporate a tiltplate to the camera, but to do this i would need to take out my filter holder and with it the UV/IR cut filter in it. I dont have the necessary adapters in hand to somehow be able to use both, but could if i ordered more (rather not). So this made me think, how useful even is the UV/IR cut filter in a newtonian? The only source of star bloat common in refractors with the newtonian would be the lenses in the comacorrector. I bought the filter because i dont want the near infrared seeping into my images, possibly making true colorbalance impossible. But here are some observations on the matter. Below are pictures of the colour curve and mono QE curve of my camera in both the OSC and mono version (i have the OSC). If im judging the OSC curves correctly, it looks like they all merge to form a basically monochromatic signal (with less blue though) towards the near infrared parts. This i assume just means the pixels are a bit brighter but contain no real colour information anymore. The QE at this portion of the spectrum is also quite low and i dont think it would somehow delete colour information from the rest of the spectrum. Oh and by the way, the sensor window in the OSC version is the same as in the mono, just clear glass and quotes transmission all the way to 1050nm. Of course i can just test this, but since clear skies are rare i would rather hear if someone has opinions on the matter before trying this out. Also, i think i can just thread the filter into the comacorrector bottom threads on the telescope side. Would this cause any issues for some reason? The corrector i use is the Maxfield 0.95x so there is a small reducer effect as well.

768 ADUs is small for the camera. Since its a 16 bit camera that is only 1.17% of the total available dynamic range so not even remotely something you could notice even with your very long subs. On the subject of long subs, 3 minutes is a bit on the long side. Nothing wrong with that if the mount plays along nicely but you also have no real benefits from shooting such long exposures with these sensitive cameras, unless you are doing narrowband or are shooting from a very dark location (maybe B5 or better). But actually even then as long as you swamp read noise and sky noise you probably are fine with 60s subs. If you change the camera to the HCG mode (you should) you may notice that 3 minute subs blow out starcores, so a more reasonable 1-2 minutes would probably be appropriate. Older CMOS cameras like the 1600MM with a 12bit ADC are very different. With a 12bit camera you only have 4096 values to work with, so it really is crucial what you set there as there is no room to spare. With a 16bit camera you never have to worry about this, so just set it to the default value and forget about it. Its convenient also because if your drivers or settings reset for whatever reason you will automatically be in the correct offset. Also this could be related to the gradient in your RisingCam stack as the single sub does not have the gradient that the stack has. You probably have non reproducible banding in your darks and bias frames due to the low offset. Offset too low clips blacks as the read noise can result in a value that is less than 0 = which obviously is clipped to 0 and so all information is lost. Read noise is not an added value, but an average deviation from the "right" value. Offset of 10 means that probably somewhere around half of your pixels have lost all useful data with bias and darkframes. Also if you used the LCG mode you had an unnecessarily high read noise to begin with. I found that i could not reliably use my camera below offset 500 because of this. This will probably also make your flats difficult to calibrate since the offset is not stable. I studied this a bit because im very interested in seeing this comparison roll out but found that this will be difficult/impossible to do "evenly". This is because the QHY version has some really strange design decisions that are very different from the ZWO/other brand offerings. It looks like QHY has gone for optimizing full well capacity instead of read noise like the other brands. Nothing wrong with that, it just means that ideally the cameras would be used differently with different exposure times. Take a look at this site (one of the only sensor analysis graphs i found): https://eu.lunaticoastro.com/product/qhy-268-m-c-camera/ Then compare the graphs/measurements to the RisingCam measurements in the aliexpress site: https://www.aliexpress.com/item/4001359313736.html?spm=a2g0o.productlist.0.0.6f047164JGhOx6&algo_pvid=88c7fc7f-59b2-4b58-9bdc-a75b08237944&algo_exp_id=88c7fc7f-59b2-4b58-9bdc-a75b08237944-0 You'll find that at pretty much no point are any of the performances in any of the modes for both cameras "equivalent" to each other. Interestingly the QHY camera has consistently more read noise in all modes to the RC. But my judging of the graphs is that the Rising cam HCG mode at gain 100 and the QHY with the high gain mode at gain 60 are the closest to eachother. The RisingCam in this way has less than 1e of read noise while the QHY will have more than 1.5, but the QHY will have far more fullwell. Fullwell depth is not an issue for most targets (certainly not for M33) and is just dealt with an appropriate exposure time. The other "fair" comparison would be to set the RisingCam to LCG mode gain 100 and the QHY to the stock(?) photographic mode (mode 0 in the graph) to gain 30. This looks like the same thing for both cameras, although the QHY has a bit more read noise it seems. This might be the closest comparison you could make but in my opinion not really the fairest since the HCG mode is vastly superior to the LCG mode in almost all situations. So you would be doing the QHY a favor and the RisingCam a disfavor with this method.

10 offset is way too low for the risingcam, you will have quantization errors with that. The offset should be at least 500 ADUs to counter this. Also, which mode with gain 100? The results are very different with the LCG and HCG mores on the risingcam. There is a 3x increase in read noise with LCG mode.

First with trails With comet and stars (and some PGC fuzzies here and there in the background) And finally the animation from the best subs, about an hour or a bit more i think. CometLeonard720p.mp4 Shot on the 7th of December between 2:46 and 4:14 UTC, except for the animation which i believe is from somewhere around 3:10 to 4:14. Shot with an OOUK VX8, Maxfield 0.95 coma corrector/reducer and the RisingCam IMX571 OSC with 30s exposures. There are some gaps due to lost subs unfortunately, but mostly uninterrupted. Quality of the subs was perhaps the worst i have taken so far due to Leonard being low in the sky and towards magnitude 17.5-ish skies. Also, since everything sits on top of the absolute marvel of modern precision engineering: The Skywatcher EQM35, guiding was and never is great to southern targets like this was. Most subs somewhere around 2 arcsec RMS, some worse than that. The gaps in the sequence are from subs bad enough to have no usable stars for stacking. The trailed version is pretty straightforward, just stack on the comet with average combination in DSS. The second version is far from straightforward as DSS just does not stack the image to comet AND stars, its only one or the other. Trying to stack with comet and stars alignment only works for the green channel for some reason? Red and blue channels are trailed like the image was only stacked on the comet, leading to green uncolorcalibrateable stars. So it is a mixture of a comet stack and a starstack with aggressive kappa-sigma clipping to delete as much of the comet as possible. Then some layer trickery, background copying, starless layer tricks, healing brush etc, all the "bad practices" you can do for astrophotography processing and there it is. Could be better, or worse so i think its acceptable. The animation was also interesting to do as i couldn't figure out an easy way to do this. In the end i ended up taking the calibrated subs from DSS, processing them with a few simple adjustments in SIRIL and saved a PNG of the autostretched preview. Easy and quick to do for the 120 or so subs i chose for this. PNGs put into ASTAP for blinking and alignment, of which i then took a screen recording of . There is probably a tool for this somewhere in the internet but i couldn't easily find one that is not PixInsight. First time processing/shooting a comet so a lot to learn, feel free to comment/critique if you want to.

I just went and checked how long the imaging session was during the first occurrence and it was over 3 hours of imaging so at least 4 hours of the scope being out of its bag sitting on a mount cooling, so definitely completely ambient by the time i finished shooting. I also checked the first and last subs and both (and all in between) had the extra spike. If memory serves me correct i had the heater in my car on at just barely above 0 while driving to the shooting location because i knew cooling is an issue (it was around -5 outside). On the second case the scope was still cooling down when i started imaging. I actually had to discard about an hour of subs from comet Leonard because i did not have time to cool the scope properly before. I started noticing the extra spike appear only once the tube currents died down and HFR decreased to usable levels. Doesn't mean the extra spike wasn't there when the scope was cooling, but perhaps just that i could not see it because of fat shimmery stars. I will admit i probably couldn't spot astigmatism visually as this is the best scope i have looked through, so how would i know if there are issues? Although people quote astigmatism as a nasty aberration that ruins views, which goes against my experiences of just easily devouring the Moon at no problems whatsoever in clarity at 300x on a decent night. I have glanced at out of focus star shapes but i cant really tell anything from them, and i dont think i have done this at high powers. The coma corrector is possibly part of the issue for all i know so good suggestion. What would this 4 corners kind of test prove or rule out, astigmatism of one or more of the mirrors? Easy to do so ill try to remember to do that next time. I went through the subs where this happened and couldn't come to a conclusion as only very bright stars have this visible well. These bright stars also just have happened to be near the center of the field so hard to tell right now. The Baader focuser is nice and matte black inside, not that it matters much since the comacorrector fills almost all of the drawtube with the way i have it mounted slightly sunk in. Also worth noticing that the effect was present in the old focuser aswell.

Clothes are drying right beside me in my clothes drying room at the moment. Also the same room works as a kitchen, living room, bedroom, telescope showroom, workshop, existential dread and weather based mental anguish room etc (live in a small flat 🤣). None of the images have been taken in a place where power lines or anything of the sort could be above 10 degrees from the horizon towards the targets at the time. I also googled this and came across many such threads over the internet where extra diffraction artifacts have made appearances. But cases like mine where they only happen sometimes are rare it seems.

That's the best thing ive read in a while, thanks for the laughs Tim!

Yes, same offset for everything all the time. Otherwise none of your calibration frames will do what they are supposed to. You can change offset later if you want to for some reason, but then you will need a new set of calibration frames.

And also thought i would mention if the thought crossed your mind: Keep pliers of any kind as far away from the adapter as possible, you WILL destroy it with pliers.

Try a strap wrench, or if you cant find one in a hardware store try an adjustable oil filter wrench (basically a strap wrench). I destroyed 2 small adapter extensions before getting one and now the problem seems to have gone away.

Hopefully this picture shows clearly enough that at the focus position the drawtube does not extend far enough in to cause any obstruction to the primary mirror. Its close, but there is a gap (for parallel lightwaves ofc). I should also note that this still does not explain why it happens sometimes and not other times because the focus position is always the same. Well not always, depending on the temperature there is a few millimeters of thermal expansion on the aluminum tube itself shifting the focus position of the focuser a bit. The temperature range my telescope is used at covers somewhere around +10 for the autumn/spring nights to colder than -20 for winter so the focus position is far from set in stone. In this picture i noticed that just a tiny bit of the secondary mirror peeks from behind the spider, but this is not the case on the opposite side, or on the up-down axis in this orientation. This could be the cause. I also thought that it would be nice to know which axis the extra spike is in, so i will do another test when this happens. Basically just put a piece of cardboard/something in one axis and see if its the same axis as the extra spike. Should narrow down something,. Does it help to narrow it down? That i dont know, but cant hurt. So i will do some arts and crafts and make 3 aperture masks, a primary outer edge obstructing mask, secondary obstruction increasing mask and an artificial extra spider vane to figure out whether its the focuser axis or the one 90 degrees from it. Would be a convenient excuse to upgrade the 63mm secondary to a 70mm one to decrease vignetting for APS-C sensorsize which is quite significant at the edges. Maybe if it bothers me more and more, and if i stop being broke from other astronomy purchases 😂.

The double diffraction spikes were caused by bent spider veins in the first pic. I installed a new, much sturdier secondary spider and went through the trouble of properly centering that as well as i can to remove said effects. Its much better on the second picture and almost gone in the third one as i am improving it every time i go out and shoot. My collimation routine is quite thorough, i believe. The secondary mirror to focuser centering is done with both the secondary adjustment screws and the focuser adjustment screws built in to the Baader diamond steeltrack, so no need to shim the focuser base. I use a TS concenter to check the secondary centering and a laser to roughly check secondary to primary alignment. Then finally the concenter goes back in to confirm that the cheap laser didn't make things worse. These are also not edge stars, but close-ish to the center of the field where collimation issues (which do still exist as i have a large sensor and a small secondary mirror) are not nearly this apparent. I am hesitant to do this as i believe the mirror and the mirror cell are excellent. I dont get nearly as much mirror clip effects with mine as with mirrors from Skywatcher newtonians tend to. Also, i find it difficult to believe that 3 mirror clips at 120 degrees to each other would produce 2 perfectly symmetrical spikes at 180 degrees, it just doesn't seem right. This thread was a wild ride... Miracle you went trough all that trouble! Sounds like something @malc-c went through, this is the number 1 contender for the issue i think. All of these were shot at wide open spaces to 42-50-30 degrees of elevation where nothing can be in the light path. After reading the linked other thread i thought i would mention a few other things. Since the first picture i have acquired a new camera, a new secondary spider, a new focuser, flocked the tube properly and blackened the secondary mirror edge (only the edge visible from the camera side). And it still happens, but only sometimes. The sometimes part is what confuses me, i have several datasets between these 2 occurrences of the extra spikes where no such spike is present. Im thinking of a test to do when this happens again, and when it does i can notice it immediately in the NINA debayered and autostretched preview as it is quite obvious in bright-ish stars. The test would be to use 2 aperture masks, one to stop down the telescope and cover the primary clips completely and one to increase the central obstruction to a point where none of the secondary can be in the light path and there would only be a round obstruction. Sounds reasonable? Also, ill have a look at my secondary. Although im not quite sure what the flat part thingy refers to.

I have noticed that sometimes i get an extra diffraction spike for no apparent reason with my VX8. It has happened with 2 different focusers and in quite different shooting conditions now so not sure what to think about it. In neither of the cases it has happened has anything obstructed the light path to the primary mirror (like a focuser draw tube). There is nothing inside the tube that could cause an extra diffraction spike. Could it be pinched optics in either the primary/secondary mirror or one or more of the lens elements in the coma corrector? From what i can tell the primary is seated properly in its cell and not tightly held down. I can shim in credit card between the mirror clips and the primary mirror so its not tightly held down. Although i have not done this in very cold weather. But heres the thing, i had the extra spike at -5 last spring but i did not have it at similar temperatures this autumn (the pic with no extra spike). But then again in the most recent shot i had the extra spike again but now at -17. Below are some examples of this. In the picture without the extra spike there are some halo/diffraction artifacts which i think are to be expected from a central obstructed newtonian with possible mirror clip effects in the mix. In the VX8 the focuser is between the secondary spider vanes so it could be from that. But the focuser just does not obstruct the light path so shouldnt, and also the same focuser in similar conditions produced an extra spike once and no spike another time.

Focusers must have a gap between the body and the focuser tube to be able to move and this will let a couple of photons through. Also, the lens cap and mirror cap (newtonian) are really not airtight and could let light trough in some micron gap somewhere. Most of the time i am imaging from Bortle 6 or worse so there is no chance that i am getting decent darks with the camera in the scope. At my gain of 100 in the HCG mode i will get 4 ADUs of signal for every single photon, so just a couple of them on a long exposure and the dark is not a good representation of a pure dark anymore.