ONIKKINEN

I cant take darks with the camera in the scope with mine. I have to take it out and properly plug the camera to get no extra signal. Also note that some plastic caps are partially transparent in infrared, in which the camera is still quite sensitive so extra signal could find its way through the aperture of the scope.

I'll add my tests to here. They show what i was already expecting just based on looking at the images, but would have appreciated a tool like this when testing in the field. First 3 pictures are with the stock VX8 focuser, the last is with a Baader diamond steeltrack fitted and shows significantly less tilt. Now that i know the mechanical issues are sorted i can start dialing in tilt with a tilter plate. But also, the last sub is of poor quality so it might not make a good test subject so this can change. But the tool works well from what i can tell.

Amazing, and just an hour. What sort of sky quality was this shot from?

If you have Sharpcap pro, you can run a sensor analysis on the camera that will clear out most of the confusion on the different settings. You will get a result like in the attached pic, measured stats on the sensor. If you want to get the data from all the readout modes you need to run the analysis on all the modes separately. Will take a while, so dont run it if you need the camera (or need to do anything else) for a while. My RisingCam IMX571C in high conversion gain mode and low noise on:

Gain is very important, true. RisingCam/Touptek cameras also have 2 readout modes and the gain values are not relatable between these. The ideal gain (IMO) is gain 100 in the HCG mode (high conversion gain or high gain mode, depending on software used to capture). This is the best gain for a low readnoise of 0.86 electrons, while still retaining a fullwell of 16k and a dynamic range of over 14 stops. The lower gain readout mode is realy only useful if you need a fullwell of 51k for some reason, but with it readnoise also triples so the dynamic range remains the same. To further complicate things there is a "low noise" setting for both readout modes that does something. Or does it? I dont know, its just on for me. Havent actually tried measuring sensor stats without it so could be magic and tricks for all i know.

The important part is that 0 pixels have a value of 0 with the shortest exposure time (bias frame, just containing read noise). Increasing the offset high enough to push the lowest pixel values above 0 is the key thing. Whether its a lot more or just a bit more is far less important with such a high fullwell and dynamic range camera. But yes, you lose 268 ADUs of range with 768 compared to 500 offset which i find is not relevant.

How did you capture the data? DSS score can be a bit arbitrary IMO and not a good representation of quality. I had an issue where clouded subs had unusually high scores - probably because DSS thought that was signal. I think the number of stars is more telling of the quality. Often high scores and high number of stars goes hand in hand but not always. Number of stars, guiding RMS error and HFR are what i use to vet my frames. I dont inspect the individual frames at all and just rely on these stats to do the job for me. I use NINA to capture and have set the filename to include the afore mentioned 3 statistics. Very easy and quick to just go through the list of subs at a glance and delete the ones that are not good enough, i go through 500 subs in a few minutes this way. Of course youll have to decide for yourself what is good enough, but i usually try to have my number of stars for all the frames be within 30% of each other. Of course if the conditions are bad i might be more relaxed with the criteria.

It honestly doesnt matter with 65k ADUs to spend. I tested mine and found that 500 (equivalent to offset 50 with ZWO) would also work to bring the noise floor above 0 but just used the stock because its not that relevant.

Resist the urge to get the bigger newtonian for astrophotography. I have an 8 inch newtonian on an EQM-35 (and dont buy the EQM35 for any payload) and it has been nothing but trouble since day 1. While it technically has worked for several projects i would never recommend anyone do the same as its very frustrating. If i had gone for a more reasonable payload like a 130PDS i would actually have more usable exposure even relative to the aperture differences because i would have lost less to the elements. I estimate that only around 20% of my time spent outside with the telescope actually gets put in a stack in the end and that is considering that at one point i decided to only shoot at very high declination targets to make the mount behave better.

As the title says, stacking with the align comet and stars option in DSS leaves red and blue channels almost completely blank, whereas green is present as i would expect it to be. Subs are not missing red or blue component and stacking in other methods (only stars, only comet) results in all 3 channels being there. Any ideas on how to fix this? Shot with the stuff in the signature, most importantly an OSC camera. Red channel Green Blue

I use Siril all the time and didn't know about this, is this a recent addition in 1.0? Looks like it works pretty well on my shots too.

I would suggest your points of 1,3 and 4. Getting a telescope requires a mount and that would be more expensive than anything else you planned for. Starting out with an EQ5 is the cheapest you can make work with many small setups, but ideally an HEQ5 to have some room for growth. Drop the CLS filter as its sort of useless. Go full narrowband with a dual band filter like the optolong L-extreme or no filter at all. A CLS filter or similar will block a lot of light pollution and also with it lots of actual broadband light from the target so they are not suitable for broadband targets (like galaxies, reflection nebulae, dust clouds, star clusters etc). Narrowband filters block basically all light pollution but only let pass light emitted from emission nebulae. Skies are full of emission nebulae so this is the best bet, but note that this is also unsuitable for broadband. For broadband there are no filters for the job that make light pollution disappear without downsides. Darker skies or more total exposure are the only remedies. The 3rd point, guider is very important. Since youre planning on still using very low focal lengths you can get a small guider + guidecam setup working for not that much money if you have a laptop you can use in the field. If not, youll have to get one, or a mini pc setup of some kind. Your 5th point would allow you to do the most, but to be comfortable you would need a mount. Going that route youre looking for a cost of probably at least 2000 euros unless buying used. If you buy a cheap mount youre looking at a price of the cheap mount + the better mount when you get frustrated with it and upgrade and not end up saving money. If you dont want to be comfortable or have room for upgrades, the 61edph will probably run fine on the star adventurer, but personally i wouldnt want to do that as you still just have a manual tracker without Go-to capability.

Yes, wind. The telescope is physically large but not that heavy = sails in wind.

I always find it shocking how much variation people have with the Astromaster 130. Mine was more like an aluminum foil piece stretched on a frisbee instead of a telescope, yours is clearly working much better 👍. Stars look quite round although i would take shorter subs, maybe 60s. Camera is uncooled but has high QE, target is bright and newtonians suffer from sailing issues. 60s subs are still manageable from a processing standpoint but you will get significantly more untrailed subs if its even a bit windy. Or the HEQ-5 just suffers through it, i dont own one so it might be good.

Ran many of my subs from different nights in the same location through ASTAPs SQM measurement tool and got values ranging from SQM 17.7 to the east down to 20.2 to the north on an excellent transparency night. The worst sub i found was mag 16.3 but from another location. Surprising range of values, and especially since the zenith is not the darkest spot. Although that could also be due to rarely imaging towards zenith and so small samplesize of subs and conditions. I would normally never image towards east because of the Helsinki nebula being bright enough to cast shadows to around 50 degrees, but Leonard was there so kind of had to. Wondered for a while how you figured out the location but then realized the FITS header also writes the coordinates reported by NINA to the header.

@han59 Im trying to use the SQM measurement tool in ASTAP but it reports the altitude wrong, any idea whats wrong? The time, latitude and longitude are all correct or at least very close to correct. Edit: Just updated the software and it now reports everything correctly.

Thanks, i was actually already using ASTAP for many other things and didnt know there was this kind of module. Running my subs through it report a wrong altitude though, any idea how to fix that? It says one of my subs is under the horizon and one where it should be higher than 30 degrees at 12.

I have calibration masters as TIF files from DSS and the sub as a FITS file, would this be an issue? Also, i dont have flat darks matching the flats and cannot take them at the moment as the camera cannot reach the temperature needed from ambient (it was -17, camera set to -20). Darks are also for -10 instead of the sub temperature of -20. But i guess better than nothing? Here goes: 2021-12-07_06-13-42_30.00s_0058-1.00-Target-3.17-58.fits MasterOffset_Gain100.tif MasterFlat_Gain100.tif MasterDark_Gain100_30s.tif' For plate solving: 3.75 micron pixels and a focal length of 840. The FITS header has a wrong value in it. The bright star next to the comet is HD 129132.

Looks like we have very different definitions of simple 😅. I know how to do 3-4 and but the others? No clue. Well i mean obviously i can do 1 or 2, but not both? When stacking master calibration frames on a single sub DSS and SIRIL debayers the frame and the split CFA channels option in Siril is no longer usable (since its debayered i think?). But lets try anyway, i have an uncalibrated green sub, but if i just use a part near the middle where flats are not necessary i think its not that important. Dark current is effectively 0 since there is almost no dark current at -20c and offset is 769 ADUs so this is easy to just subtract from the calculations. How do i do 5-6-7 then? Was there something obviously wrong with what i concluded? Lets say im happy with an error margin of a few electrons here and there. The point is just to have some idea better than a wild guess as to what the sky conditions are if i am in a new location or transparency is bad etc.

I came across this tool a while ago: http://tools.sharpcap.co.uk/ This tool was part of the ideal exposure time calculations presented by Dr Robin Glover and with it you can figure out a sky electron rate per given level of light pollution and telescope. It occured to me that i could use it backwards by figuring out how many electrons per second do i get in an image. Last night i was in a "bortle 6" area according to light pollution map and clear outside but the sky is significantly worse than this for many directions. I noticed that i got at worst 1700 ADUs as a median value over offset whereas at best i have gotten down to 150 (measured by NINA). I know the gain i used has a rate of 0.25 electrons per ADU and i know the exposure time which was 30s. So 1700/30 is 56.6 ADUs per second * 0.25 gets me 14,15 electrons per second. What i dont know is my effective QE since i am imaging with a OSC camera. ZWO quotes a peak QE of over 80 for their version of the IMX571 colour camera and i will assume it is around the green spectrum as it is with the mono version. Most of light pollution is also around the green spectrum and a bit towards the red. With this in mind would it be reasonable to assume a QE of around 70% for this specific case? I think its not far off at least. I also dont quite understand how the tool changes when you select mono and OSC. With OSC it seems to cut electron rate to a third. Plotting everything in which in my case is F4.2 and 3.75 micron pixels, 70% QE and a colour camera i get close to 14,15 electrons per second at a staggering Bortle 8.2 or sky brightness of 17.8! Did i get this correct? Someone smarter than me might be able to make more sense of this but i think its at least in the ballpark. Could be useful to gauge conditions at a glance without a sky quality meter.

Clouds cleared out late last night, and while it was still 90%+ humidity, poor seeing and visibility i still went for it and packed all my stuff at 3am and headed to a B6 area. Never getting the chance again (this time im sure). Did manage to see Leonard through the VX8! The sight itself wasn't very spectacular since it was low in the eastern sky, which is by far the worst place anything can be in for the location. Never seen seeing this bad either, Arcturus was like a strobe light with how it shimmers. Still this will probably remain as the best view of comet Leonard i will ever get and while tired i am glad i did it. The comet looked a lot like M31 in terms of fuzziness and brightness, but smaller, more elongated and dimmer. And unlike M31 it was moving, and moving FAST. Shockingly fast in fact, i could see it move in almost real time compared to the nearby star HD 129132 as it overtook it in the view during the 20-30 minutes i spent at the eyepiece. The nucleus was not as bright as the nearby star but this is probably due to the fuzzy nature of the comet. The star is a point source and pierces the light pollution well but the comet loses a lot of contrast against the background. It looked like there was a "veil" of stuff on both sides of the nucleus and a surprisingly long tail in the trailing end. The tail was difficult to see at first but i saw it after a few minutes of observing. It was a really unpleasant humid frosty -17 celsius so i decided to hook up a camera instead and continue in EAA/imaging until dawn. I watched the subs roll in and while the quality was garbage due to the conditions and i don't think there will be a good image in the end i did observe a few things. The comet noticeably moved over a few pixels between every single 30s exposure which means in my resolution that there was probably a movement of somewhere around 2-3 arsceconds per exposure! Really strange to see something so big just fly across the screen like it was nothing. In the images from what i could quickly in-situ process and see i noticed the tail could have been as long as a degree, and unusually green compared to the average object in space which entirely lacks green.

Bummer, since i cant see M31 when its towards east at home with the 7x aculons, background is far too bright. Tonight is one of these maybe clear maybe not nights, perhaps ill try again.

This is what the view from a concenter eyepiece (the one i linked) looks like. I was going to show you my perfect collimation but then realized that it is not in fact perfect 🧐. Well, as an example this is great since its very easy to see where the adjustments are off. You can see that there is just a tiny bit more black background which is the inside of the telescope tube visible between the rings and the bright mirror on the right side. This means i need to push the secondary just a little bit towards the primary mirror. The top part is also perhaps not perfect. To do this you need to block the primary mirror so that you dont get reflections, i do this just by placing a piece of paper between the secondary and primary. Also, bright light makes it easier so there is a powerful LED headlamp in the tube. I have also blackened the non-coated edge of my secondary mirror to further make this easier. I alternate between using this and using a laser to check primary to secondary alignment (paper off for this of course) until its good enough. Honestly i find the whole procedure a bit annoying and i probably wont try to adjust this more, unless stars are truly horrible on one side but i doubt they are for this kind of error.

Took my chances with the weather and drove to a B6 area, some services claim partly cloudy some claim clear skies all night. Well ended up being partly cloudy and i cut my losses early, packed up my gear and headed back home. Wouldn't call it a complete waste though as i did have time to glimpse at a few targets. First light through the newly acquired APM 24mm UFF showed me M81 and M82, Pleiades, open clusters M36-37-38 in Auriga and not much else. I saw no shape in M81 but M82 i did notice as the cigar shape it is named after. These are nicely framed in the same field of view with the 24mm, although this really wasn't a suitable power given the sky conditions. Pleiades was also quite nice with the 24mm UFF, stars were much sharper than what previous eyepieces have shown with the F4.2 newtonian so i was pleased to see that. So in conclusion, eyepiece good 👍 weather bad 👎.

I would say its far more likely that you have tilt between the secondary mirror and comacorrector instead of between the corrector and camera sensor since you're imaging with a newtonian. I recently also thought that i had sensor tilt but the more i looked at it the more i realized that i have no way of knowing for sure whether its actually sensor tilt or not. Therefore its probably a good idea to check secondary mirror collimation first as it will also produce effects that look like tilt. Your focuser could have tilt aswell if its not perfectly in the middle of the tube or if there is focuser slop. Focuser slop is probably not an issue since you have a good focuser. Some focusers have adjustment screws to adjust tilt and with those and secondary mirror adjustments you can be sure to rule optical tilt out. What tool are you using to collimate your secondary mirror to be exactly under the focuser drawtube? Laser collimators or eyeballing will not work for this. You will need some kind of tool that can better show centering of the secondary. This is a cheap and effective tool for the purpose: https://www.teleskop-express.de/shop/product_info.php/info/p5506_TS-Optics-Concenter-2--Collimation-Eyepiece-for-Newtonian-Telescopes.html . There are also the expensive collimation tools like howie glatter lasers but i would try with the cheaper alternatives first.