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I think either will be fine. I think that popularity of Skywatcher is due to it's availability back in the day. In fact - I would go for Bresser over SW if they have the same price. Bresser OTA can be mounted on other mounts more easily than Skywatcher (if you ever for example want to do planetary imaging with 8" F/6 scope and you decide to mount it on your future HEQ5 or better mount ). One thing that I don't like about Bresser telescopes is their finder scopes - they look flimsy and plastic. I ended up replacing finder on my SW dob anyways as RACI / right angle version is so much easier to use. Do budget for additional few eyepieces - Bresser seems to come with only 25mm SPL eyepiece.

I would say - do 20 measurements rather than stack and do one measurement. Result will be the same, but when doing 20 measurements - you can also do standard deviation to see level of error for your average value.

Oh, come on, why no zooms? I don't have favorite zoom - but might one day - and then it will be my favorite eyepiece ES82° 11mm - because it's razor sharp

You don't have to do it right away - you can do short exposures without guiding - if you have shorter focal length telescope. You don't really need to spend much money on guiding system. Your finder scope + cheap web camera that you'll modify and make adapter to guide scope will be good enough guider system to start with. Problem is - if you start having difficulties - you'll often blame poor web camera for poor guiding and you'll end up buying more expensive stuff (although it might not be down to web camera in the first place). Greatest thing that you can do is - understand what you are getting into with astrophotography before you start spending money on equipment. This will make your life much easier.

Here is my experience, as I've been (and to some extent still am) where you are now. It takes about hour or so to set up Heq5 for imaging. It takes 5 minutes to get my 8" dob out and be ready for observing. I keep my gear in my basement and I have back yard. For observing I usually take 3 trips from the basement to the back yard - not much to it really - take out my observing chair and a small table. Take out dob base and finally take out OTA. Leave it there about 20 minutes to half an hour to cool down and I'm ready to go. When I want to do imaging - things get complicated really fast. I need to do at least 10-12 trips to/from basement. - tripod - mount head - counter weights - computer equipment - telescope - camera assembly - power supply - ... Setting up involves: - hooking everything up - polar aligning - placing telescope and all the accessories on the scope - balancing the whole thing - initial alignment / plate solving - guider calibration - ... This is with HEQ5 and 8" scope on it. I have 8" RC - which is much shorter than that newtonian. That is a big scope and I would not recommend that you start with that. Sure, if you are going to use it for both visual and imaging - then yes, that is probably the best choice, although I would urge you to consider 6" PDS instead. 8" will be preferred for visual but 6" will be better for astrophotography - less weight, less focal length. In fact, to be honest - 130PDS will be the best newtonian on Heq5 to get you started - however, it will be visually the least attractive option as it has the least aperture. I don't like Newtonian + EQ mount for visual. You can't use it while seated down and being relaxed - you need to stand. You constantly need to rotate tube as you move the scope around the sky so eyepiece does not get in awkward position. Even if you manage to put eyepiece in the right place - finder usually won't be. Larger the scope - bigger the issue. It will be harder to rotate in rings - it will be bulkier so eyepiece will be harder to reach and finder particularly. My first scope was 130 newtonian on EQ2 mount. That was actually manageable, but again, one needed to stand in order to observe. Just to put things into perspective, 8" scope on Heq5 is this big: and depending on your height, you might even have issues to reach eyepiece in some positions. My only concern is that you are purchasing setup based on idea that you want to do astrophotography - without knowing all that is involved and sacrificing visual observing because of that. Imagine you have to setup your telescope 40 minutes each time with 30+ Kg of equipment to assemble before you even start observing. Very quickly you will be in position that you really don't want to do that and you'd rather watch TV or whatever (just because you don't feel like setting up everything). Astrophotography is expensive. When you purchase mount + telescope - you only really started to get gear for astrophotography. Did you leave some of the budget for coma corrector needed with newtonian type scopes? Did you account for T2 adapter for your DSLR? How about guiding? Do you have a lap top. No you don't have to guide - but at 1000mm you'll be limited to say 20-30s exposures without trailing, maybe even less. Once you start guiding - you'll realize that really 1000mm is long focal length and your mount, although excellent beginner mount is suited for half that focal length out of the box and if you want to go 1000mm - you need to tune it, belt mod it, add different bits to it, ...

Just to be clear, above image is not mine - it was just image that I found in google search and I thought has good color representation of the object. Image is found on abc.net.au domain (Which I believe is ABC network domain in Australia, right?).

I'm not sure it can be that simply approximated. It will depend on how shiny / smooth material is and angle of incident light. In computer science / graphics, there are different models for specular highlights. More info can be had here: https://en.wikipedia.org/wiki/Specular_highlight

Issue of color in astrophotography is somewhat controversial. In this particular case - you took raw data from camera and just convert it to image, right? Raw data from camera is not: 1. color balanced 2. color corrected 3. gamma corrected In order to get true color from raw data from DSLR you need to perform above steps. Camera firmware does this for you when you select to shoot image as .jpg instead of raw format. You can also use Canon software to convert raw image to proper color. Colors that you see in images online are not true colors of objects in space. There are several reasons for this: - Most astrophotographers don't understand above color management or don't care about it - Very often astrophotographers use modified cameras and don't adjust for color correction in those - Some of the images are actually narrowband images where false color models are used to emphasize gas distribution rather than produce natural looking color. - People get creative with their astrophotography and do color balance manually for artistic look rather than to produce actual color. In the end - it is actually quite normal for nebula to be greenish in visual appearance if one wants to display true color as would be seen by humans. This is because humans are much more sensitive in green part of the spectrum than in far red. Most emission type nebulae radiate in Ha, OIII and Hb wavelengths. Ha is deep red and we are not as sensitive to it. OIII is mixture of blue and green and Hb is more to blue part of spectrum. Here it is chromaticity diagram: Triangle is sRGB color space (that can be shown on computer images). Outer line is spectral locus - where individual spectral colors lie in this XY diagram. Note that computer screens can't display any pure spectral color. All colors produced by combining sources of particular colors - lie within area made up from these color sources (for that reason all sRGB colors fall within triangle in this image because we use particular red, green and blue colors to synthesize them on screen). I've marked another triangle where all colors that can be made by mixing Ha, OIII and Hb wavelengths lie. You can have any of those colors present in nebula that consists mostly out of Hydrogen and Oxygen gas. If Hydrogen beta is not strong - there won't be much blue in the image. I suspect that this rendition of tarantula is pretty good representation of true color of the object:

What camera is that? Hot pixels stay hot for some period of time - like months. For this reason it is advisable to redo dark library once or twice a year. If you have CMOS camera - what you are seeing might be Telegraph type noise. Mechanism is similar to dark current but reason is different. Electrons build up between pixels due to imperfections in substrate and then leak into pixel making it "hot" (high in value), but this does not happen on every exposure - hence then name Telegraph (think Morse code). Some camera models have these build up zones in between adjacent pixels and pixels "share" accumulation - so sub can have either one pixel turning "hot" - the other one turning "hot", or neither of the two - and this happens at random. If you have this happen on a pixel - you'll get two or three pronged Gaussian distributions of that pixel values in series of your darks.

Problem with ball bearing is that one does not know actual diameter of reflection - which makes it hard to calculate needed distance for resolving and spherical aberration. I thought of DIY-ing it, and in fact it is not hard at all to do it. You need a piece / strand of optical cable (you can even purchase one partially made for data centers), strong LED - small drill - like really small - 1mm or less and some electronics / battery holder to power the LED. Small hole is drilled in acrylic LED housing from the front and you insert clipped strand of optical cable in it and use clear epoxy or superglue to cement it in place. Rest is easy. Once I calculated bill of materials and time spent doing it - price of getting ready made one suddenly did not seem so steep (for someone already having drill and drill bit for modelling and other things like casing and 1/4 thread insert or at least 3D printer to print housing - it would probably be worth DIY-ing it). I ended up getting this one: https://www.teleskop-express.de/shop/product_info.php/info/p10781_TS-Optics-artificial-Star-for-Telescope-Tests-and-Collimation.html

Ok, get it - this was more experiment to that effect rather than optical principles.

This could be the cause of slight movement of dust between lights and flats. Well actually dust stays put but fact that there is some play in connection means whole camera assembly shifted.

Have you tried with Barlow lens? It is also negative lens element and they usually have quite longer FL - like 100mm or so.

Each of those looks like embossed - which means those are dust bunnies but with flats that moved a bit - which is rather strange as you mention no filters at the moment - these usually happen with filter wheel that is not perfectly repositioning itself. Did you by any chance move anything in your optical train between lights and flats. Also, I'm worried about poor flat fielding - there is rather distinct background in this image. How did you calibrate and what is your master flat like?

I would not call that disappointing at all! That looks rather good for 30mm of aperture.

Thank you very much for these recordings. I was interested in general performance of the lens. I'll describe my idea so we can figure out if these lenses will be suitable for it, although I believe it will ultimately come down to testing it in real conditions. Idea is to do EEVA with Mak102. That is of course not the best telescope being F/13 but I wanted to try out this approach that will effectively make it F/4-F/5 telescope. In order to accomplish this, I thought of putting together following setup: Telescope - 32mm Plossl - eyepiece projection adapter - 11-12mm CS lens - ASI178mm camera. Here is rough ray diagram of what I want to achieve: Here is my reasoning for this: - 32mm Plossl has field stop of about 26-27mm and above telescope should illuminate that much field. It will be somewhat vignetted at extreme edges. - Exit pupil of such system is 32 / 13 = ~2.47mm - I use 12mm CS lens. If I'm not mistaken that will give me reduction factor of 32/12 = ~2.667. I will "compress" 27mm illuminated circle into ~10.125mm. ASI178mm has diagonal of 8.93 so it won't capture whole field - but it will be vignetted anyway. - Lens will operate stopped down at about 12mm / 2.47 = F/4.85 - so it should be fairly sharpish at that setting. - Compound system will operate at F/4.875 (13/2.66666) with focal length of about 487.5mm and sampling rate of 2"/px once super pixel debayering is used - rather nice resolution for EEVA. In any case - I just wanted to know if stars will look round or not with such lens. You test suggests that center stars will look nice but corner ones might be distorted quite a bit.

When trying to explain such things to people without necessary background - I find useful to use direct analogy and example. Ask them if they can spot an ant on that tree that is only 50 feed away. Next, ask them if they see that mountain that is 10 miles away. Then ask them, how come that they can see something that is 10 miles away with ease but can't see something that is 50 feet away from them.

Could you do one more internal test? I wonder how sharp are these small CS/C mount lenses. I'm not holding my breath, but I do have a plan of trying one for EEVA myself and wonder what is their resolution. Could you do FWHM measurement on artificial star on those lenses? Does not need to be very long distance - just enough that star is not resolved, I don't care about possible spherical (so 5-10m should be good distance).

One thing is to find a way to fix issues caused by atmosphere (and there is a clear solution for that - get outside of atmosphere), but you can't circumvent laws of physics. Aperture is needed to resolve smaller detail. Either single aperture of aperture synthesis - which can be done for visible light as well as for radio waves, but technical challenges might be too much (you need to bring all the light together with precision of optical surface (fraction of wavelength) from optical systems dozens and hundreds of meters apart - person walking around cases so much vibration that it will interfere with equipment at that level of precision).

I think your AIJ is probably corrupt or something. Try regular ImageJ/Fiji to see if it works and re download AIJ.

As far as I've heard (not tried Faststar myself) - it is sort of a nightmare to operate To begin with - it is not diffraction limited, it is very sensitive to tilt and collimation. Camera goes in front of the scope so you are limited in choice of camera - you want round / slim model in order not to cause diffraction effects. Since you need to route cables (cooling / data cables) - you'll end up with diffraction spikes anyway. Flat fielding is rather difficult to do - you can't use simple flat panel that goes over the aperture of the telescope - you need something much larger. While you can use Faststar / Hyperstar - you really don't want to do that when you can get RASA now which is much better optically.

Maybe this would fit the bill? https://www.teleskop-express.de/shop/product_info.php/info/p4711_TS-Optics-ED-refractor-lens-70-420-mm--w--adjustable-mount.html It is a smaller aperture but focal length is almost exact - not fiddling with tube length change will be required. I think that it is easier to fit smaller lens cell in bigger tube then other way around.

For this sort of analysis you really should include two more pieces of information: - guide log - wind speed measurement and check for any sort of correlation in the data. Sometimes what we interpret as worsening in the seeing - could actually come from rough patch in gearing mechanism or maybe just wind gusts. Alternatively, if you want to do seeing analysis, better approach would be to try very short exposures and part of the sky filled with bright stars - like open cluster. Then you have bunch of stars that have their own random motion but you can still "extract" common motion - which is likely to be just tracking issues (mechanics and wind). If you average short exposures over longer period of time - you should get the same thing as long exposure.

RASA11 cost does not seem justified - since you can purchase two RASA8 scopes for same amount of money, put them in parallel operation and get even faster system After examining both your image and spot diagram that I posted - I've somewhat changed my opinion of RASA systems. I believe them to be very good scopes for their intended use - they are like Samyang 135 F/2 of astronomy world. Indeed, they are not diffraction limited (in sense that you would not expect planetary images with resolution that 8" or 11" is otherwise capable of providing) - but they are sharp enough to produce very good wide field images. In fact, I think I was wrong to say that they would not be sharp at 2.5"/px, as your image above at 2.7"/px clearly shows - that is sharp enough and can certainly compete in sharpness with fast systems otherwise used to image M31 at that resolution (like 80-100mm APO scopes, 130mm hyperbolic newtonians or mosaic with 6" F/4 regular newtonian or similar).

I think it is worth it, provided that one has the mount and money for it and wants to go down that route. Fact that RASA11 has larger corrected and illuminated circle means that it has potential to be faster scope for the same FOV. Faster imaging + added resolution, what is not to like? Thing is - you don't have to pair RASA11 with the same camera you pair RASA8, but you can keep the pixel size the same, or change it to suit your needs. Here is an example of fields of view - red is RASA11 with ASI6200 (as it has 43.3mm imaging circle), yellow is RASA8 with ASI294mm (as it has 22mm imaging circle). RASA8 + ASI294mm = ~2.4"/px RASA11 + ASI6200 / bin2 = ~2.5"/px Second one will obviously be faster due to added aperture. How much will additional resolution show at ~2.5/px - well that depends on spot diagram of the telescope. I managed to find official spot diagram for RASA11: Box size is 9µm and at 620mm FL that equates to 3". Add to that seeing and tracking issues - I don't think that RASA11 can deliver 2.5"/px sharpness, but 3.75"/px certainly (that would be x3 bin of ASI6200 or about 10µm pixel size).