vlaiv

Significance of that table is such that it needs to be posted at least 3 times per thread discussing CA

Here is another good video - this time high power view of moon thru 120/1000 Note that 102/1000 will have less CA - and how CA on moon shows in crater shadows as slight violet cast instead of deep black

https://www.youtube.com/watch?v=BUtLS-rkLuY https://www.youtube.com/shorts/qIxFAG8ctsM https://www.youtube.com/watch?v=BIRivcUcMxU Do note that the CA is often worse on video recording / image as sensor is more sensitive in short wavelengths then human eye is.

Do keep in mind that 130PDS is also meant for astrophotography - which means it has better focuser and better mirror cell than standard 130 F/5 offerings. Mirror might be of higher quality as well (although I suspect that F/5 parabolic mirrors are all quite good nowadays). It is probably best option for short 5" reflector, but people tend to purchase less expensive scopes as their first scope

Hm, no. While it does use some sort of ED glass - that is still too fast to be well controlled. That scope has about the same level of CA as for example regular 102/600 fast achromat. Check out this report: http://interferometrie.blogspot.com/2017/06/3-short-achromats-bresser-ar102xs.html

In both cases one can make aperture mask to further lessen the impact of CA and filters do help to tame CA further. I would not dismiss long focal length refractor just based on CA alone.

Out of the two, I'd personally choose 102/1000 refractor. This is based on couple of reasons: 1. Ease of use. Reflector on equatorial mount will put eyepiece in different position and will either need tube rotation to get EP in comfortable position or will require some contortion (which is not what you want to do when observing). 2. At F/4.6, figure of of the mirror needs to be really good. Not sure what to expect given the price of the telescope (There are models that are quite good being 130mm F/5) - but overall I think 100mm refractor will win on lunar and planetary. 3. 130mm obstructed aperture with 91% reflectivity mirrors is equivalent to about 115mm refractor, so aperture difference is not that big In both cases - mount will be the weakest link and I agree that a meter long scope is not very stable on such mount.

https://sattvinfo.net/satlist.php?lang=en They are even sorted by position. Depending on FOV - one can capture fair number of them.

If I remember correctly - there are some that are grouped and located in the roughly the same FOV - like 1-2 degrees one from another. I guess search for data can be beneficial prior to actually taking the shot. For example Astra 19.2E now has 4 satellites in that location.

In that case - it might be a better option to try #1. Use your low power eyepiece instead of high power EP - it is probably going to be better corrected.

Oh, right. I thought it was simple 114/500 newtonian.

Something is quite strange with that image. Despite it maybe not being the best scope out there - I'm certain that it can produce better images of the moon. How exactly did you setup your scope and camera to take the image. There are several ways this can be done: 1. Telescope + eyepiece + some sort of adapter to attach the camera + camera with lens 2. Telescope + eyepiece + some sort of adapter + camera without the lens 3. Telescope + barlow lens + camera without the lens (adapter is simple T2 ring in this case) 4. Telescope + camera without any additional optics (again just T2 ring) Fourth way is the best as it places the least additional optics between the telescope and camera - and telescope itself acts as a giant lens for camera. Problem is that with this model - you probably can't reach the focus that way - which is why most people go with option 3. Barlow lens pushes focus point further out - and you can reach the focus that way. Additional benefit is that it makes Lunar image larger. If you can, set it up like that for lunar shots. Then it is down to optimizing your conditions. - Use very short exposure length with higher ISO setting. Ideally - you want exposure to be something like few milliseconds (use manual settings for your camera). - Wait for moon to be high up in the sky. Lower it is - more susceptible it is too seeing disturbances - Wait for scope to properly cool to ambient temperature. - don't aim over larger objects that accumulate heat during the day - like houses or roads or parking lots or even big bodies of water - lakes, ponds, swamps. Ideally, you want to have a field or forest on the ground in direction where you aim your scope. Even if you take all precautions - sometimes atmosphere just want play ball and seeing will be poor. You won't be able to get good image in such conditions. As far as color issues - that is due to some optics element - like eyepiece or camera lens. Not sure what you have been using - that is why I asked about configuration.

Not sure if you can compare images like that. If you for example post DSC_0690 and DSC_0693 and if their background is removed (DC offset subtraction) and we look at them at certain zoom level - one that nicely shows stars - you should be able to see the difference between the two. I'd be happy to perform data reduction for this particular case if you post raw files.

Well, you can - but if you plate solve - you don't need to - computer will figure out where the scope is pointing and point it to the right place automatically. Even if you don't plate solve - use main imaging system to figure out where the scope is aiming - take frame and focus exposure and check out star patterns to orient yourself. Guide scope can be be offset to the main scope - so they don't necessarily point to the same place in the sky (won't affect guiding) - so it is better to use main camera as it will do the imaging after all and where it's pointing is what counts in the end.

That is quite normal since guide sensor is very small. You won't have any problems because of that as sole purpose of guide system is to find and lock onto a star/stars (and there are plenty of stars out there - even on small FOVs). People using OAG (off axis guiders) - always have smaller guide FOV then their imaging FOV as same focal length is used for both and guide sensors are smaller.

I don't think that you should apply "common knowledge" from photography to astronomy as it can be very misleading. F/ratio does not tell the whole story even for astrophotography, let alone something like photometry. Stellar photometry is rather interesting in this regard. Here we have two very different phenomena that compete in SNR race. Stars provide the signal, while noise mostly comes from light pollution. Former is point source while later is extended / surface source. These two behave differently with respect to "magnification" - up to a point. Take for example 4" F/5 scope vs 4" F/10 scope and case where we are under sampling. This means that in both F/5 scope and in F/10 scope - stellar disk is not resolved (seeing disk rather than airy disk) - and both take up roughly the same number of pixels. Aperture does not change - so amount of photons don't change and those photons from the same star lend on roughly the same number of pixels - signal per pixel stays the same. On the other hand - sky is extended source and changing focal length will change sampling rate or how much sky is covered by any one pixel. Using longer focal length will reduce amount of background signal in this case. F/10 scope will have only 1/4 of background sky level for same conditions and same exposure length. Interestingly enough, in this particular case F/10 scope is x4 faster than F/5 scope - although common daytime photography knowledge would suggest it was the other way around. For best photometric performance - one wants for stars to be as tight as possible (occupy as few pixels as possible) - while sky background to be stretched as much possible - or occupy as much pixels per arc second squared as possible. This happens when the seeing is good and optics is sharp. It is usually achieved with larger apertures rather than smaller as aperture also plays a part in how larger stellar profile will be.

There is a bit more "pop" to the nebula as well. Central part is just a tad brighter. I like that.

It will certainly increase level of light pollution recorded - more aperture gathers more light from both the source and from the sky. What more aperture and longer integration times bring is higher SNR. Sky background signal is nothing more than DC offset. It gets removed in aperture photometry when surrounding annulus value is subtracted from the star. What is problematic is shot noise associated with LP/Sky background signal. Shot noise grows as square root of sky background level - so it grows slower than signal itself. If you increase aperture by x2 (by diameter) or integration time by x4 - you will increase signal by factor of x4 (either like time or like surface of aperture), but associated noise will grow by square root of that - or only by factor of x2. Overall SNR improves by factor of x4 / x2 = x2. Once you have good SNR - you can distinguish faint stars from the noise of the background and they become detectable. Just using longer exposure with your current setup does the same - and in principle - you could just use longer single exposure - if there was not for the issue of limited full well capacity. Pixels can only hold so much signal - and if you saturate them - you loose information about the value they were holding. This is where increase in aperture and stacking come in handy - they allow you to gather more signal without pixels being saturated. I understand how you feel about image processing, and yes, that is something that you should not waste your time with - for this purpose. However, there is data preprocessing step - that is always performed in scientific work - like calibration and data deduction steps. These are well defined and not subject to ones opinions or preferences (like image processing is). They can be automated really well. With suitable software and definition of a few macros - whole process can be reduced to just pointing to a single folder containing data to process (ie - here is a bunch of recordings - please produce final calibrated and stacked data image that is equivalent to single very long exposure without fear of pixel saturation).

I like the second one just a bit more.

What about stacking? With stacking you can go as deep as you want - but not sure if that qualifies as "processing". Personally, I don't see any reason why not to stack the data - if one take scare of how it's done. The least intrusive method for stacking would be good old "shift and add". That is literally equivalent of taking longer exposure. no interpolation is done and only difference is level of read noise that is present in such "exposure". Drawback is that you'll get lower resolution data - but given that you are using small lens, and that you are measuring brightness - you don't really care about resolution. Alternative is to increase aperture (while keeping sampling rate the same). Again some "processing" will be required here - like binning the data, but again, I don't see that being disruptive for photometric work in any way.

I think it is snake oil. Plenty of light at 670nm around us each day and I don't see skin nor eyesight getting better ...

Here is a handy website that calculates astronomical darkness: https://www.timeanddate.com/sun/uk/liverpool (I selected Liverpool as example - but you can easily choose different location). You can switch the view to Day/Night length and you'll get handy graph showing you period without true darkness: you can also check the exact times on any given date. This helps you to plan your sessions as you can easily check if there will be enough true darkness for complete session on a given date. (by the way - that website has a bunch of useful calculators for astronomy, it's worth checking out other features as well).

Unless you have very sophisticated algorithms to deal with that - mixing of different SNR subs can be rather damaging. You can end up with worse result compared to not using those subs in the first place. It behaves pretty much as light pollution, and if possible - minimize it. Most people image only during full night and avoid any sort of twilight. I know it is impossible to do so in summer time in northern latitudes (no true night, only twilight), and for that reason some imagers skip summer months all together - or use them for practice and trying out things - without having high expectations of good results.

Not sure how F/3 is relevant for speed. It is after all 11" vs 4" of aperture - if you match the pixel scale between the two then only aperture dictates the speed. In any case - you can always outperform 4" with 11" for given pixel scale if the whole target can fit in the FOV. Btw, feature is more interesting then I first thought. Here is image of it that I found online: On your image I suspected it was splitting in several "streams" - but could not be sure due to calibration artifacts on the edge of the image. Here we can see that it is indeed several "branches".

Not sure how much more exposure would be enough. Here is a little experiment. I further binned x3 (thus making it equivalent to x9 more exposure length) lum: Feature is there as a string of stars in very faint arm - but it seems to be very very faint (no wonder it is missed on 99% images out there).