vlaiv

There is not much theory behind this. You need to make sure two things are satisfied: 1. You get good SNR for your flats 2. Your flats are in linear region of sensor (no saturation / clipping or other non linearity of any kind). If you make your exposure too short and you don't compensate with number of subs you stack for flats - you run a risk of adding too much noise from flats into your images. On the other hand - if you expose for too long - you might over expose your flats. Even when you don't over expose your flats - you can create issues if you hit non linear region of sensor. In general - you don't want to be near max value of what your sensor can record. Histogram peak should stay at 2/3 to 3/4 and not more. This is generally just rule of the thumb. Consider following - you are shooting Ha flats and you have gain pushed very far. Your effective full well capacity is say 1000e (although camera has something like 20K normally - due to high gain you reduced it significantly). At large values, Poisson distribution is very similar to Gaussian one, so we can use that to approximate things. Say we place histogram at 900e (or 90% peak) - then our sigma will be 30e. x3 sigma will be 990e. There is a chance that 0.13% of all pixels in the bright part of the flat - be saturated (or at least over 990e). That might not sound like much, but if you have 3000x2000 - that is 60 million pixels, and let's say that 1/9th is in central bright region - that is still around 9000 pixels per image that are saturated. Each sub will have this and if you stack them - they will "skew" things in final stack as they represent incorrect / clipped values. To minimize that - on higher gain settings (or when shooting with smaller full well capacity in general) - go with 2/3 or even 1/2 of histogram as peak. Use 3/4 rule only when using lower gain setting or larger full well. If you want to test your flats without applying them to actual image - use following thing: - shoot one set of flats with very short exposure - shoot one set of flats with longer exposure - following above rule. Calibrate one with another (including flat darks) and you should get perfectly flat image - uniform gray with noise.

Not significantly. In overlap area there is usually "feathering" like effect - or linear transition between the two panels. Where overlap starts 100% - 0% mix is used than that gradually goes to 50%-50% at the middle and then to 0%-100% on the other side of the joint or transition area. In that 50%-50% - data will be "half as blurred" as in 275% panel, or somewhere in between the two.

If you choose panel shot at 510mm FL as a reference, then you run a risk of part of image being visibly more blurred than the rest of it - 275mm FL panel will not look as nice as others when enlarged to their size. If you choose 275mm FL - then whole image will be "smaller" in size - objects in it will be of a smaller size when viewed at 100% zoom level. It will look the same when you fit it to screen - then either of them will be the size of screen so objects in each image will look the same size (by each image I mean one registered to 510mm FL panel and one registered to 275mm panel). Although I know what I meant, I'm not sure I was particularly understandable, so I'll reiterate in bullet points. Registering to 275mm panel: - smaller total size of image in pixels - smaller objects (compared to other option) when viewed at 100% zoom, but equal size when viewed "fit to screen" - whole image will look equally sharp when viewed at 100% zoom Registering to 510mm FL panel: - larger total size of image in pixels - larger objects at 100% zoom level - risk of part of image looking visibly more blurred then the rest of it (panel that was shot at 275mm will look more blurred then the rest).

It is "twisted" spider support such that on one side (say closer to secondary) presents thin profile to aperture and then it twists towards the tube wall presenting thicker section. Here is simulation: I created one spider support so that it presents "twisted" profile to aperture (like a triangle) - and that spreads associated spike away from the star (horizontal edge creates vertical spike and vice verse).

Interesting read. I do wonder about guide performance. If mount is smooth enough and offers 0.3-0.4 RMS guide performance, then it could be very interesting indeed.

That is 9.525mm x 1.968504" for all those that use imperial and metric rather than metric and imperial This web site lists them https://www.wdscomponents.com/en-gb/adjusting-screw-steel-imperial-unc-wds-605/c-385/p-1595 (you want 3/8 2" long version)

I'm not so sure. There is like order of magnitude in distance between the two versus diameter of each. Milky way has about 110000Ly in diameter and Andromeda has something like 220000Ly in diameter. Distance between the two is 2.5 million Ly. Best "visualization" of the relationship of the two galaxies - and indeed observable universe if you try to "visualize" it - would be as follows: You extend palm of your hand - to be one galaxy and palm of your other hand to be the other galaxy - and then stretch your hands as far as you can. That is approximately the distance between the two at that scale (where M31 is the size of your stretched palm with fingers and Mw is just palm). If we extend that analogy - imagine some place that is about 40Km away from you in that moment - that would be the edge of observable universe. If you are standing on the hill (or mountain) top - you would actually be able to see Milky way and Andromeda and edge of the universe if someone puts their hands like described above for you

I like the idea and have contemplated that on several occasions. One issue that you might have is with any idea of motor focuser. In fact - you might want to look at this for focusing: https://www.teleskop-express.de/shop/product_info.php/info/p9360_TS-Optics-2--Non-Rotating-Helical-Focuser-with-M48-connection.html Alternative is to use primary mirror focusing - but designing good mechanism would probably be nightmare-ish to say the least. Maybe synced lead screws (much like some CoreXY printers have) to move primary up and down the tube?

These achromatic pairs are seriously cheap on AliExpress - check it out: https://www.aliexpress.com/item/1005001460681644.html?spm=a2g0o.store_pc_groupList.8148356.17.43db7e76OOAAuK&pdp_npi=2%40dis!EUR!€ 26%2C95!€ 24%2C26!!!!!%402100bdcf16720872632597890ec378!12000016213390335!sh All I need to do is get some aluminum tubing (80x2 mm costs something like 10 euro per meter) and to do some 3d printing - for lens cell and focuser (ok, some bits as well like linear rods and bushings). Here is what I've designed for that 70mm version: It is 1.5" non rotating helical focuser with T2 thread at the eyepiece end and M72x1 at telescope side. It has 40mm of focuser travel and 8mm/turn precision Material for focuser is probably around 20 euro total

I later took this one as well, just few weeks later- same gear, same method, but instead of doing 3x3 mosaic, I dedicated more time per panel and did 2x2 mosaic - this one goes deeper, and I might have even recorded the flats (not sure would need to check data from 2016)

Just artifact of using mosaic to compose image. This is 3x3 mosaic. Each panel has slight light drop off at the edge (correctable with flats) - and dust shadows are in same position - so they repeat.

While we are on the topic of budget scopes, I'm building two very budget scopes at the moment. In fact - I'm building one as the lens for it is in the mail, I haven't ordered lens for the other yet but focuser for it is in 3d printer as we "speak". 80mm F/7.5 and 70mm F/6.9 achromats. Both will cost less than £100 (in fact, 70mm might end up costing less than £50) and I will try imaging with those - just for fun. With a bit of trickery, achromats can be made into color free scopes for imaging. Especially smaller and slower lenses.

You are probably right. Using DSLR body on such scope is probably not recommended - but why not use mirrorless camera? In fact - we might be expecting too much of a beginner. Perfect flats for mosaic? Yep, that is no flats mosaic on ST102 (notice lack of chromatic aberration, who said fast achromats can't be used for OSC imaging?) taken from Bortle 7-8 skies with ASI185 - uncooled. I think that while image is not perfect, many beginners would be satisfied with such result?.

Bin data x3 and you are effectively working with 100mm / 433.33mm scope. Yes, three things will be drawback to using it: 1. read noise. it will take quite a bit of exposure to swamp read noise, but it might be viable option in LP conditions where one does not need to expose for long to swamp read noise with LP 2. FOV - of course, FOV will be much smaller, but not that small: quite usable on some of larger galaxies and nebulae. Old favorite - M42 would need a mosaic: but that is also true for someone purchasing dedicated camera like ASI585 and using it with 130PDS: 3. Moving mirror - which probably means using OAG to guide rather than guide scope, but OAGs can actually be cheaper than some guide scopes, so they should be considered a budget option

https://www.firstlightoptics.com/maksutov/skywatcher-skymax-102-ota.html

Ok, I'm going to put a spin on this. How about 4" scope that does not need a corrector, works with up to APS-C size sensor, weighs less than 2Kg, costs £205 and no one "in their right mind" would recommend as an imaging scope? (need I mention that I'm quite happy not to be in my right mind and say that this will actually work if one treats it in particular way).

It might as well be blue hot pixel. Do you have raw data or did you just record jpeg image with your camera? It is better to record raw data and then do a bit of processing on it as things as hot pixels are quite obvious then. Jpeg compression will mess things up a bit and it will be harder to tell.

You can already do some basic calculations based on where you are located. https://www.pvfitcalculator.energysavingtrust.org.uk/ This is for full scale solar array - it it will give you idea of what you can expect (you could scale things by 100 so instead of using 50W - put in 5KW array and see what sort of energy you'll get on average during December/January). Another way of doing it is by simple spreadsheet. Nominal output of panel (say 50W) - is possible if incident light is at 90 degrees to panel surface and sun is at zenith on a clear day. You can calculate the loss due to air mass in the same way we do it for stars - in magnitude change and from magnitude change you can get power factor. Further - you need to account for angle (use cosine of incident angle). Make calculations for each hour on average depending on your install angle. Resulting number will be available power on a sunny day, but you need to account for number of sunny hours during the month. Here is breakdown of production from 10.6KW array in December here (not yet over, so it show only up until today): So it ranges between 15KWh at peak down to below 3KWh of daily production - with average being less than 10KWh. This is for unoptimized angle (or rather suited for whole year round). You should get better performance if you optimize your angle for winter production, but it won't wary by much. 50W panel should therefore produce ~45Wh of power on average daily. Sorry I made mistake in above calculation - it won't take 24 days to fully charge 10Ah / 12V battery - but rather 10 times less - but still over two and a half days (120Wh / 45wh per day = 2.666... days).

If we really want to go budget friendly on newtonian - we should be looking for 1.25" sized coma corrector. There are few very affordable scopes that are 4-5" class. I don't mind 130PDS - I just wonder once you add 2" CC is it still a budget option?

I think it is more down to people entering data on their website than anything else. There is really only one model of that scope and it has been around for quite some time: https://www.skyatnightmagazine.com/reviews/telescopes/orion-starblast-62mm-compact-travel-refractor/ (review from 2015)

I think that 5.5Kg is whole package, including all accessories and case. TS has exactly the same scope, minus some accessories in its lineup at considerably higher price (makes perfect sense - amici prism, T2 extension and two eyepieces cost about -70euro, right? ) https://www.teleskop-express.de/shop/product_info.php/info/p14747_TS-Optics-62-mm-f-8-4-4-Element-Flatfield-Refractor-for-Observation-and-Photography.html there in stats it says that telescope itself is about 1Kg

Probably not. PI4 alone on idle draws about 2.8W of power according to this: https://linuxhint.com/power-consumption-raspberry-pi/ With camera and dew heater - you can easily hit 10W of power consumption total (not sure what is the wattage on that dew heater), and 10Ah battery will provide you with ~120Wh (in reality less than that as you don't want to run your battery flat), so you have something like 12h of operation on a single charge. That will do for the night, but larger issue is recharging that battery during the day. I'm running full scale solar array on my house and in December, stats are as follows: - less than x1 installed power rating in Wh on average. I have 10.6KW array and on a sunny day it manages to produce 12-14KWh, but on cloudy day - it produces only 2-3KWh - and I'm at 45 degrees latitude. This means that on average, 50W panel will produce less than 5Wh of power - so it will take something like 24 days to fully recharge that battery. As a contrast, on a sunny summer day, when you point the array at the sun directly, it will take something like 3-4h to charge that battery fully. If you want to run trouble free - I'd increase size of battery to say 50Ah (this will give you 5 nights autonomy) and to be able to charge that you'll need at least one full sized panel of ~700W if not two.

What sort of budget are we talking about? How about this little fella? https://www.teleskop-express.de/shop/product_info.php/info/p14791_Tecnosky-AC-62-520-refractor---optical-tube.html No need for flatteners / correctors and I think that it has CA well controlled (I used to get virtually CA free images from similar setup - 66 mm aperture 500mm FL with the use of Wratten #8 filter - and that is plain doublet not a Petzval).

That can be easily faked as well as long as one has set of data to base it on (we can take genuine darks and bias subs and apply them to "lights" that we calculate from interpolated data and add appropriate noise levels - shot noise with Poisson distribution), but like you say - it is indeed irrelevant. Not sure who actually awarded record for such a thing - but it is not something I'd consider worthy of record holding. In any case - you have very nice image of M31 there. Maybe overly saturated for my taste and too heavily processed, but nice nonetheless.

Well, that is interesting. If I submit image that is 100,000 x 60,000 pixels that I captured, will I then be contender for the record? It is fairly easy to produce such data, especially if over sampling is allowed.