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Answer is no. Actually - answer is no, unless there is associated nebulosity and nebulosity is Ha in nature - like stellar nursery type of object - large Ha cloud with hot young stars - but then it would only improve SNR on nebulosity and not stars. Both stars and moonlight are broad band targets - which is sort of intuitive if you think about it - moonlight is actually sunlight reflected of a moon - which in turn is starlight as sun is a star. By using NB filter you will both cut down moonlight but also starlight coming from stars - effect will be same as using ND filter or aperture mask - reduction of received light. Only effect - worse SNR. NB filters work not because they block moon light - but because they block the moon light and pass target wavelength largely unaffected (second part being very important). If second part is missing - well then it ain't gonna work

That will affect image more than defocus in blue and red. We are most sensitive in brightness and green part of spectrum carries the most of brightness information. You can do small experiment. Take any image, separate in R, G and B channels - then blur each channel and recombine image. Create one image with blurred red, one with blurred green and one with blurred blue channel and see which one looks the sharpest.

This is true only for ZWO camera with that sensor. Other vendors can and will use different gain to e/ADU mapping. Try looking up their respective documentation to see what actual gain value is. Altair for example has this table on their website (its only an image so a bit hard to read): I'm not sure what Gain vs Relative Gain vs Rel Gain (db) is. Maybe there is relationship between ZWO version which uses 0.1db units so 117 is 11.7db, and in above table we see that it does correspond to Relative gain of 3.96 / Gain of 400 and e/ADU of 0.98 (11.96db that is). Not sure which value is entered in ASCOM driver - probably Rel Gain in db units so 11.7 would be unity - if you can enter decimal values.

https://www.martinrowan.co.uk/2019/08/wifi-signal-strength-with-raspberry-pi-4-cases/

how about this one: https://thepihut.com/collections/raspberry-pi-cooling/products/xl-raspberry-pi-4-heatsink

I have similar thing to what @Knighty2112 suggested above - whole case aluminum heat sink - and it is causing a bit of a problem for Wifi connection - although it has some plastic in the area where antenna is - precisely because of that. If you plan on using wifi - then I'd say - don't go with very large heat sinks that might interfere with wifi performance.

I would add one - at least passive one. I don't think you need active cooling as night time tends to be cold enough, but small passive heat sink will help move heat away from the chip more rapidly (and prevent any throttling in performance due to thermal issues).

Even if there is - you'll be hard pressed to see it in long exposure photography (where seeing dominates). Regardless of the provenance of that scope - it is fast ED doublet (at F/6) - and it will show some residual CA, especially if you use OSC camera with it. If you can live with that - then it is fine. If not - look into getting 80mm f/6 triplet scope.

R&P are still better option for motor focusers. This is because motor focuser will hold the load on focuser with its own holding torque. With crayford style focuser, there is point where slippage can happen even if holding torque of motor focuser is not exceeded. With R&P - it is effectively a geared connection between motor focuser and focus position and you really need to move motor shaft in order to change focus (and vice verse). For that reason - motor focusers work better with R&P focuser - but that does not mean that there aren't better crayfords out there than some R&P.

I had that focuser on my RC - and my solution was to replace it and get R&P one. I think that R&P are better option to work with motor/auto focusers. I'm surprised to hear that newtonian model of this focuser has plastic bits. Mine is all metal (M90 model).

To be honest - quite a bit. Both wife and I agreed that we wanted slower pace of life and nature as priorities. Our decision was also based on climate change prospects in following decades (moving to higher ground because of increased temperatures and better potential for off grid if need be). In the end - dark sky was put forward as sort of requirement on my part and was accepted. We first looked to buy a house, but after seeing what was on offer - we ended up buying land (I instantly knew when I saw horizon on that location ) and building our new house.

Thank you. I'm still fairly close to Novi Sad - at 25Km distance - that is practically a suburb. Luckily, there is "tall" mountain (to be honest - barely a mountain with 537m above sea floor ) - but I guess high enough to shield me from the most of LP coming from that direction.

Prism diagonals can achieve much greater light throughput. In order to get in high 90s (like 97-99%), mirrors need dielectric coatings - and many layers. These impact surface quality as there is limit to how precise thickness of layer can be. Prisms can easily get 99% or higher (depending on glass clarity and applied coatings on air glass surfaces - two of them). If you want to know more about how each performs - read this excellent article: https://www.cloudynights.com/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

Thank you! Not entirely sure. As far as I recall it - local transparency was excellent. Not many sources of pollution around here (like highways or power plants / people burning wood for heat) and its often windy lately. That, plus higher elevation means that local transparency was excellent (compared to what I'm used to back in town - with all the pollution and large river near by - which often leads to misty / hazy conditions). As far as high altitude transparency is concerned - I remember checking out AOD on Copernicus and I remember that forecast for area on given night was between 0.1 and 0.16 mark (so second best out of values reported by this service, first being <0.1). It's unlikely that I'll give up AP, as I enjoy doing both. Ideal situation would be - finished obsy with imaging gear ticking away while I observe from a lawn next to it

Have you checked? Maybe we should not look - maybe we are in fact there?

Then it would appear that @Adam J was right to imply that it is effect of central obstruction - it is modulation that shows as pattern here since individual rings are blurred by seeing?

https://www.firstlightoptics.com/evostar/sky-watcher-evostar-90-660-az-pronto.html

You might be right on that one - but that is under assumption that there is no atmospheric blurring. Look at thickness of diffraction spike. It is at least 6px across. That is consistent with say 3" FWHM or a bit more. This same blur affects fringes and they will be smoothed out. Btw, we should be seeing same concentric rings in diffraction spikes as two "mix" like this: To my eye - they look superimposed rather than "mixed" in above image. I think that simplest cause of action is to alter slightly CC to sensor distance - maybe just shim it with less than 1mm shim. Any change in distance will alter optical path and interference pattern will change if it is due to reflection from CC (which is likely cause in this case).

Obstructed aperture does create different distribution of energy in circles - but minima remains where it is - distance between fringes and their size remains the same. As you can see from graphs above - minima and maxima are roughly aligned, but it is peak intensity that shifts from central disk to fringes. This is causing contrast loss in obstructed aperture.

I'm not sure that it works like that. We see airy disk of aperture because we are "magnifying" image after it has hit the aperture. So 130mm of aperture will cause diffraction with 2.47" airy disk diameter - if we don't have mirror or lens after to magnify that - no way we are ever going to see it. You need extremely small apertures to be able to see diffraction effects without "magnification" of telescope. If you want to see airy pattern in lab - you need pinhole, laser and screen that is far enough so that pattern will be amplified enough (light is disturbed by small angle and you need enough distance for small angle to project into reasonable size image). After light beam has passed primary mirror / lens - hitting secondary (that is flat) or filter aperture - is not going to produce anything. Any diffraction will be tiny as we don't have another "magnifying" element after it.

Yes, some of it is down to strength of Ha in source, and some of it is down to camera sensitivity in Ha, but you can always compensate with exposure length. Double the exposure length - double the signal. NB flats often need much longer exposures than broad band filters - since NB filters only pass about 1/15 - 1/30 of light compared to broad band filters (for example red passes all between about 600 and 700nm - so 100nm range, while Ha passes maybe 3.5nm to 7nm depending on make/model).

I'm not sure this is the case. You are referring to Airy pattern, and yes, every scope will under ideal conditions produce Airy pattern - which is most visible in narrow band images as pattern itself depends on wavelength. Here is pattern produced by laser in lab: (see https://en.wikipedia.org/wiki/Airy_disk) Problem is that Airy pattern is much smaller than represented in your image above. 130PDS has Airy disk diameter of 2.54", which means that distance between fringes is half that or 1.27". Further, this scope has FL of 650mm and ASI1600 has pixel size of 3.8µm which together gives sampling rate of 1.21". This means that single fringe (bright and dark part) is about as large as single pixel. Fringes in your image cover about 4px: I don't think this is Airy pattern we are seeing here, and I think that some other sort of diffraction is happening.

Of course. I've seen people reuse flats from different filters and I simply can't understand that. Not only do filter can and have different distribution of dust particles on them - pixels can have different relative sensitivity in different parts of spectrum. We assume that pixels have same QE curve - but it could be different, and sometimes is - due to manufacturing defects or just nature of material used (and angle of light hitting them). Look at this: Three different histograms for three different filters. Or visually: Yes, dust particles are of different color and that is fine because they are in one filter and not others, but why is background with gradient? How come that pixels on the left part of the image have stronger red response than pixel on the right part of the image, while blue/green response is opposite?

I'm sure that many people already saw this table, but its worth reiterating: I currently have SkyWatcher 102mm f/10 achromat that replaced ST102 that I used to own. SW 102 F/10 is rather good planetary instrument. Yes it shows chromatic aberration, but it shows good detail on planets. According to above table - it has ratio of 2.54. Making aperture mask of 65mm will give you Chromatic index of 3 - as 65mm is 2.56" and F/ratio will be ~7.7. Those two divided give CA index of 3 - which means Minimal or no CA. 65mm will be able to provide one with x100 - x130 views without much of a problem, that means use of 4-5mm Eyepiece. It won't be killer planetary scope - but will shot some detail and image will be nice.

32mm Plossl is probably best "beginner" wide field eyepiece. I highly recommend it to everyone as cheap and good EP for low power views.