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Maximum useful magnification depends on couple of things: - seeing on particular night - telescope can deliver magnification but it is atmosphere that blurs the detail and there is not much point going with higher mag - your visual acuity - how sharp is your eyesight? Some people have sharper eyesight and can use less magnification to see what is there to be seen, while others need more magnification to comfortably observe (similar to font size on computer screen - some people are fine with small letters while others prefer larger font for easier reading). For 20/20 vision we can say that threshold magnification is about x100 per mm of aperture. Below that - you won't be able to resolve detail that is still there - above that you'll see all there is to be seen and additional magnification will just make it easier to see but also more blurred once you increase magnification too much. If you have different acuity - just multiply x100 with given number. For example - if you have 20/10, or twice as sharp vision as 20/20 - you can use only x50 per mm of aperture to fully resolve image, and if you on the other hand have 20/30 vision - then you need x150 per mm of aperture to fully resolve image. Just two additional notes - above is for perfect telescope and your visual acuity after corrective measures. If you wear eyeglasses - it is your acuity with glasses - not without. - collimation and quality of optical figure of telescope. Collimation is important and optical figure as long as telescope is diffraction limited - has the least impact on usable magnification.

Most people report best experience of M31 with binoculars. I suspect that this is due to exit pupil size. With 750mm F/5 scope - I would try 32mm Plossl or if you have it - 35mm AeroED for widest view. Both will give very large exit pupils so you need to be dark adapted and your pupils dilated to the max. I've managed to see the hint of first dust lane once from my SQM 18.5 back yard with 8" Dob and 32mm Plossl. M31 was very high in the sky - very close to zenith and transparency was exceptional.

Author's website (contains a lot of info and images): https://astroanarchy.blogspot.com/

It's a bit "hidden", but still available: (click on ... icon in top right corner and menu pops up with edit option)

Very sound advice. Sometimes manufacturers even state payload for visual and payload for AP and AP payload is about 60-70% that of visual. For visual, you won't see if mount skips odd step (ones with stepper motors) for example - but you will notice that in AP - as worse guide performance and larger stars / blurrier image. More mass on the mount means more inertia when trying to guide - it can mean more under / over shoot in correction and need for additional corrections. Again - worse looking stars and blurrier image. If mount can carry it - you can image with it, but question is - will you like results. I have put imaging gear on the mount weighing close to its visual payload - and mount indeed tracks - but results were not good. Any breeze would wreak havoc on my guiding and setup would produce decent results only in perfect conditions (scope pointing at high DEC where RA error is smaller so guider does not need to do aggressive work).

Price / performance thing. In order to get large clear aperture - you need to use oversized prism because of the way light bends thru it. I tend not to use amici prisms for astronomy as astronomical quality amici prisms are very expensive. These cheap models are not as good as regular diagonal mirrors. In space there is no really "up/down" - it depends on orientation of observer. Here on earth - we think there is down because of gravity - but different observers looking at the Moon will see it oriented differently depending where they are on Earth's surface. If you are on northern hemisphere and observing the moon and on southern hemisphere observing the moon at the same time - image will be flipped by 180° between the two. I think it is better to get brain accustomed to that sort of thing right from beginning.

What you were seeing was vignetting rather than usual blackouts from eyepieces. If prism is not sufficiently large - it will be stopped down and you can only use it with eyepieces that have field stop of similar diameter. When looking at particular prism / diagonal - it's worth noting what the clear aperture of the item. You want it to be at least 28mm for 1.25" versions

I don't think there is anything in that price range. Why don't you use 130PDS as wide field scope - or wider field scope? All you need to do is learn how to shoot mosaics and bin your data. Want scope that is about 325mm in FL? Shoot 2x2 mosaic - use 1/4 of the time on each panel (that you would otherwise use on whole target with actual 325mm scope) and bin each panel 2x2. That will give you approximately the same result as using 325mm F/5 scope, with difference being in slight overlap between panels that you must make in order to stitch mosaic together and very slightly different SNR - which you can offset by altering your exposures (but you don't have to - it is very small difference indeed - with longer FL scope impact of read noise is just a bit larger than with shorter FL scope - but if you use same rule - that single exposure swamps read noise with either LP noise or thermal noise - you are ok and need not worry about it). Similarly want to shoot at about 217mm - shoot 3x3 mosaic, use 1/9th of time on each panel and bin each panel 3x3 in software while still linear prior to stitching. Only drawback is added difficulty and processing time, although with right software - it can be automated (I think that APP can do automatic stacking and stitching of mosaics, but not sure if it can software bin).

I replaced focuser on mine because stock focuser does not come with threaded connection and I had issues with tilt with all of my accessories. I think that threaded connection is a big plus for imaging rig. I'm not sure where you read that it is primarily lunar scope - that must be CC (Classical Cassegrain) - or this one: https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f12-m-lrs-classical-cassegrain-telescope-ota.html These are different scopes - first one that I linked is F/8 RC type scope. Second one, is F/12 CC type scope. First one is better at DSO astrophotography, while latter is better suited to planetary / lunar imaging although it can work as DSO imaging scope - but with smaller field of view. Do pay attention to exact model as the very much look alike and have the same price. 600D has 4.3µm pixel size and if you get that x0.75 Reducer, or maybe this one: https://www.teleskop-express.de/shop/product_info.php/info/p8932_TS-Optics-Optics-2--CCD-Reducer-0-67x-for-RC---flatfield-telescopes-ab-F-8.html for that one you can use with 61mm distance instead of 85mm to get x0.75 reduction. I don't recommend that you go with x0.67 reduction for APS-C sensor as you'll get strong astigmatism in corners. In either case you'll get 1.45"/px if you use superpixel debayering - which I would recommend. That is very decent all around sampling rate. Close enough for small objects and with enough FOV to capture larger things. Some things may need mosaics. In the end, I need to warn you about collimation of this scope. You mentioned that you don't like collimation - well this one has tricky collimation. I did not find it particularly demanding but people have struggled with it. Some seriously enough that they ended up letting go of the scope. Here is some light read on that subject:

I actually prefer nebulosity in first version. Like that you added RGB color to the stars - that is very nice touch. Not sure what process you followed - but StarNet++ for star removal is good way to do it - make starless version, subtract from original to have stars only version - apply RGB color to that version (to Ha channel - stars tend to be tight in Ha). Combine starless versions into color image and then blend in stars with RGB color. In any case - first rendition of nebulosity has more 3D feel to it - second one came out flat. That can happen if you push data too much. I understand that additional data gives you incentive to push it further - but sometimes it does not work as expected (as we tend to over do it). Here is example of what I'm talking about: vs Although signal in second is stronger - it just looks flat and lacks structure shown in above one. Or perhaps this: vs

8h does not happen in one night - you need multiple nights to get that much data. Yes, I know - that is a problem, but that is a cost of light pollution. If you want to image emission type nebulae like Rosette, Veil or HH - use UHC type filter. It blocks most of the light pollution and passes light from these targets. Problem is that you won't be able to get proper star color with such filter. You can either shoot separate images just for star color and do some gymnastics in PS to blend that in or settle for strange color stars. Do try LP filter - I've used Hutech IPS P2 and it helps quite a bit. With LED lighting - LPS filters are not as efficient. SCT-s are not good imaging scopes, even reduced. Internal focusing is a problem even with focus lock. OAG is solution for that. But you really want EdgeHD instead of regular SCT if you want to do DSO AP. Maybe take a look at this scope: https://www.firstlightoptics.com/stellalyra-telescopes/stellalyra-8-f8-m-lrs-ritchey-chrtien-telescope-ota.html You'll need a focuser upgrade if you are sensitive to focuser quality. I replaced focuser on mine with: https://www.firstlightoptics.com/ts-focusers/ts-25-rack-and-pinion-focuser-m90.html You can use this to reduce scope to F/6: https://www.firstlightoptics.com/reducersflatteners/astro-essentials-075x-reducer-for-stellalyra-gso-ritchey-chretien-ota.html

Ok, that now makes much more sense. Your worst enemy is LP - you live in very high LP area - SQM around 18.5. I know how that feels - as I also live in SQM 18.5 zone. Fact of life is that you'll need a lot of exposure time. I mean a lot. This is two hours with 80mm scope and cooled dedicated astro camera. With additional 1.5h, and some careful processing - I believe you would match or even surpass this result with your setup. In order to get really good image - we would need to image, say 8h, or even more in SQM18.5

Are you sure? First image looks like it might be taken with ED80, but second one looks like it was taken with camera lens, maybe 100mm or so lens?

I'm trying to put my finger on what would be most beneficial to your imaging. I'm still unsure what to recommend to you as I don't fully understand your AP needs. So far I've gathered that you want large aperture scope capable of all sorts of targets. You have considerable budget. I'm inclined to say - go with about 1200mm of FL and use super pixel mode on your camera. That would mean 10" F/5 Newtonian - something like SW 250PDS. However, that is large and heavy scope and long focal length. It is not something that I would recommend unless you have enough experience to handle scope like that for imaging. You've shown image of 30 minutes with ED80 and you mention that you can't get color out of Rosette. I tried to look up where you might be living and only Nissan plant that I've found is one in Sunderland. If you live somewhere south of there - you are still in red zone - that whole area is in pretty heavy LP: Gradient in your M81/82 also suggests presence of LP. What you need is more total exposure - as @The Lazy Astronomer already pointed out. Large scope will certainly help if you can manage it and process data appropriately, but I'm wondering if I'm doing you a disservice by recommending such a large and demanding telescope?

Ok, I can see why you might not get along with C5, but what would be your objection to ED80?

So you have EQ6 and C5. That is what we know so far. What camera are you using? Are you guiding or not and if yes - how? What is your processing workflow and what is typical total exposure time for your images. What is light pollution level at your location (you mentioned garden exclusively)?

Yep, good point, is that USD600 or CAD600?

$600 could be considered as entry to the mid-range. Planetary resolution depends on aperture size. It also depends on what is called atmospheric seeing - how calm or turbulent atmosphere is. This changes considerably based on many factors and can range from poor (very often) to exceptional (maybe few nights a year). This in principle means that you want larger scope but you won't be able to utilize it to full potential all the time. However, on nights where atmosphere is calm enough - you'll appreciate the fact that you've chosen larger scope. Cool down means letting telescope equalize its temperature with temperature of the air. This is very important in climate where conditions are very different than room temperature. For example - in the north where it is often colder outside than indoors - telescope needs to cool down properly once it has been taken out of the storage (even if storage is not heated - it is often a bit warmer than outside air - especially at night). Same holds for hot climate - where telescope needs to warm up if it is kept inside with air conditioning. Any temperature difference will cause optics to stretch as it cools down / warms up and it will cause image quality issues. Air inside telescope will also have convection currents (small scale turbulence like in atmosphere) - that also impacts image quality. Depending on the size of telescope, design and temperature difference - you need between 10-15mins and up to couple of hours from setup time until you can enjoy high power views without thermal issues (few hours is for large telescopes - and sometimes it can be whole night that telescope does not thermally stabilize if it is large enough and temperature changes rapidly). Given your budget, here are some recommendations: 8" F/6 dobsonian. This is really universal instrument that will provide you with excellent planetary views. You'll have enough of a budget to get additional eyepieces and barlow to provide you with high power views. Issue with this option is that it will not track - or rather tracking is manual. Some people don't mind this and some are bothered by this. Fact is - tracked telescope will be more relaxing for observing and will let you concentrate better on object, but it is not necessary for observation. 6" F/8 dobsonian. Same as above with a bit less aperture. There will be enough budget left to maybe find good EQ platform. There will certainly be enough budget for DIY EQ platform. This solves tracking issue With above kind of budget - SCTs are really not an option any more. 5" SCT starts at around $700 - NexStar 5SE for example. 6" version is $800. These are goto telescopes meaning they both find objects for you and track them across the sky. Goto is not really necessary for planets - but it is handy addition. You can find 5" Maksutov telescope on EQ mount in your budget. You'll need to add a tracking motor (still within a budget). Problem at the moment is that most telescopes are out of stock and in limited supply. In fact - I'm looking at the prices now - and it looks like there has been quite a bit increase in prices recently. I'm not sure that you could get 5" Maksutov and EQ mound with motor for $600?

For comfortable viewing - driven mount helps. You don't have to nudge scope all the time. Simple tracking motor on EQ mount will be sufficient. I'd say that 6" is starting to be serious planetary scope. SCT, MCT, Slow newtonian with small secondary obstruction or Classical cassegrain are all very nice options in 6" or above range. If you go with EQ mount - then I'd say - skip newtonian although it is probably best bang for buck scope. It is awkward to use on EQ mount as eyepiece and finder scope get into strange positions when mount tracks - you need to rotate OTA in its rings to get some level of comfort. If newtonian telescope appeals to you - look into EQ platform + dobsonian mounted scope. 6" or 8". Even 10" if you have funds, storage and way to move it around. This is also very good all around performer. SCT and MCT will need more cool down because of more glass and closed tube design. CC is alternative. All of these sit nicely on EQ type mount. SCT will be closest to all around scope but CC and MCT will be very good dedicated planetary telescope. MCT is hard to find in 8" or larger version. You really have a lot of options - which means that you can be very specific with your requirements. Budget, size, portability, etc .... That will help narrow things down.

I guess that means that there were a lot of supernovae going off in that galaxy as heavier elements are only formed in such cataclysmic events?

yep

Yep, very cool!

Does it act like filter or simply changes refractive index when added to certain type of glass?

You are oversampled at 1.38"/px with 60mm scope. You want to be at least twice that sampling rate at about 2.76"/px. Airy disk size in Ha light for 60mm scope is 5.45". Add a bit of seeing and guiding error to that and you end up with star FWHM of almost 4" and in poor seeing even more. You really want to bin your data x2 while still linear before you start processing to gain some SNR as well. That is the fact of life - small scopes simply don't have resolving power of larger scopes and are suited to low resolution wide field work. If you put small pixels on them - you get blurry image when zoomed in.

Good idea would be to cross reference your records with AOD forecast. https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts?facets=undefined&time=2021031000,3,2021031003&projection=classical_europe&layer_name=composition_aod550 Local transparency can be significantly different depending on your observing site. Fog near lakes / rivers and a lot of smog during winter time if people burn fossil fuels for heat can change things considerably. Good intro article on transparency / extinction: https://skyandtelescope.org/astronomy-resources/transparency-and-atmospheric-extinction/