Whirlwind

It is important, but can't just be considered in isolation with considering the optics and camera that is being used and what is being imaged. For narrowband filters OD outside of the wavelength of interest is important (as otherwise you get other wavebands being recorded) but then if your camera is not sensitive in that band and/or the target of interest is bright in the region of interest then the handful of photons from other bands is less of an issue. On the other hand if your target is faint in the band of interest and your camera is more sensitive in other wavelengths compared to that of the targeted band then those 'off band' photons are more likely to have an impact.

The 'right' filters can also be dependent on what you are imaging with. If you have a purely reflective system (RC/CC etc) then you can go with wider pass band filters even if you have a blue sensitive camera. On the other hand if you have not the greatest corrected refractor and a blue sensitive camera then you would want to have a narrower passband set of filters to reduce issues with blue halos etc. The slight differences in pass bands will also effect the colour of any image. I note the comment on Astrodon filters but they specifically designed these so that they were naturally 'white' for G2V for interline / full frame Kodak CCDs. For any other camera images should be calibrated against a G2V to get the right proportions for these same colours. The same goes for Chroma/Baader/Astronomik etc. However out of the box some may be more natural than others with certain cameras. Finally you should take into account how you are intending to guide. If you use varying filter manufacturers with filters of the different thicknesses then you will need to refocus for each filter. If you are using an OAG then this could push the OAG to being out of focus depending on the focal ratio of the telescope (so an F3 system might be way out compared to an F12 etc).

Have you had a look at the Panther TTS160 mount as an alternative, based on your preferences? An alternative would be to see if there are any second hand Mach1GTO. The initial views of the E.fric mount also seem to be favourable. The disadvantage of US mounts is that repairs will generally mean a return which can be daunting given the amount of paperwork needed. Staying within the EU has advantages in that any repair in the internal market should be relatively straightforward.

Strictly speaking you want the telescope to point to the opposite side of the sun at about 30 -40 degrees altitude to minimise the sky gradient. So in the evening you want to point east, and vice versa.

Do not underestimate how much of a 'sail' a large newtonian is. It also requires a very robust mount. It isn't the overall weight that is the problem but the moment arm of the telescope. A 300PDS is an 18kg beast with most of the weight at one end. That puts an awful strain on your mount and is even worse in windy conditions because of how far the non optic end has to extend to balance the mirror. You also have to think about set up time. If you want a longer focal length have you considered a 6" - 8" RC or CC (but similar focal length and still both reflectors per se). They are slower, but as noted above you are limited by seeing most times so you may need to bin images to get the most out of them at these lengths anyway.

Difficulty is the amount of energy required. Phosphine does exist in the atmospheres of both Jupiter and Saturn but they have a lot more energy to play with (in the atmosphere). The bigger problem is we know very little about Venus and its processes. We don't even know whether it is volcanically active today really (there are evidence of volcanoes but unclear whether it is really active). There is also evidence that its surface is relatively young (lack of craters etc) so something has recently resurfaced Venus - I once read that it was postulated that Venus periodically goes through a surface melting process because the rock acts as an insulator and there is no evidence of plate tectonics. As with any such discoveries they can be short lived as other reasons are discovered or researched so I would generally caution that it isn't until absolutely we can prove it is life.

The conditions on Venus are very extreme though so we may be missing chemical pathways at this point. It's fascinating either way because either potentially life exists on Venus (and we've been looking in the wrong place all the time, i.e. Mars) or we have excluded a gas that we could have detected on exoplanets and avoided a bit of a fubar. There's also some other fascinating possibilities if correct in that Venus may have been more habitable in the early solar system and if an impact dispersed life from Venus to Earth then we'd all be Venusians! Nevertheless expect space missions to be proposed in the boat load now to Venus (hopefully we didn't seed the planet with Venera or Pioneer!)

As a wild stab in the dark....It may be that the output from the Canon1100D is being converted to 16 bit on the screen. If that is the case then you will have 2^16 levels (65536) hence 20,000 would be about 30% of saturation. On the other hand the ASI533 is 14 bit naturally so would have 2^14 levels (16384) hence 5000 would be again about 30% of saturation. Maybe check what the maximum level you have in the DSLR vs ASI to confirm this is what is happening.

I think mature would be a better way of describing CCD technology. It still has advantages over CMOS (more stable, for the avoidance of doubt necessarily lower noise) and is still readily used in scientific applications. The real issue for CCDs is that the consumer demand for CCDs is decreasing. Most CMOS have way better download speeds because each pixel downloads individually and the consumer market is moving more towards being able to take high speed videos (webcams/cameras/mobile phones etc) where there is usually sufficient signal that a bit of walking noise is not a huge issue. Hence manufacturers are moving away from CCD except for the specialists (e.g. e2v etc). They are still fine for Astronomy (and still have some advantages for deep sky) but it largely now depends on how long Sony think it will continue to be profitable to keep a CCD line going.

It is more popular (and originates from) France I believe (www.prism-astro.com) so might be worth having a look there

I think Prismv11 is expected to be released around Christmas so I would assume active development and incorporation of new cameras may have ceased with v10 (at a guess). I see you have posted a query on the hyperion forum so you will probably get the best response there.

I would assume that what has happened here is that this has been taken out of the case and looked at / displayed etc. That the stock supply of the telescope is in short supply would suggest this is the last of a stock that hasn't been sent out because of the slight defect. To an extent by 'jumping the queue' there is some sacrifice on quality compared to waiting but getting a 'perfect' clone. To some extent this applies to all things, sometimes getting something 'now' requires some 'sacrifice' which in this case is a dusty lens. You are of course entitled to a full refund if you don't want the telescope (and to some extent even more so if you bought online). Nevertheless the dust is unlikely to impact the view but if it affects your enjoyment of the item then you may as well return it, but ultimately have to decide whether you want the telescope today and live with the dust or happy to wait for new batches to arrive with better QC (or haven't been previously handled).

That's the wrong way round. 1/3 of the filter thickness adds to the telescope's optical backfocus or subtracts from the camera's optical distance of the camera setup. So in your example your camera's optical backfocus would be 19.5 + 6.5 - (1/3)*2 = 25.33mm. You might want to check that the adapters are well seated and not protruding by a mm or so

As noted above you really need to go through a focus routine with each filter to see whether they are each at best focus rather than just flit between the three and assume they are at focus. Also as highlighted stars are different brightness at different colours so more flux will arise in the brighter band. Although it is noted you could observe a G2V star you don't need to use this type of star to see the effect (G2V just represents a solar type star so generally you balance to white using this spectral class as it makes colours look 'natural' to our eyes). Most refractors (even the high end ones) become less corrected towards the near-UV and near-IR anyway. If you want optics that are perfectly colour corrected you need a mirror only system.

The difference in cost likely comes from the more relaxed tolerances. The Antlia filters are 'only' OD3 offband (i.e. they allow up to 0.1% transmission outside of the the targeted filter range). In addition their transmission is >88%. In comparison the Chroma and Astrodons are OD4 (0.01% transmission max outside of the targeted filter range) and have about a 98% transmission level. For most targets this probably doesn't make much difference but around very bright stars it may be a bit more noticeable (especially in refracting systems where the correction will be worse compared to a reflector). The image might also be a bit fainter / need longer exposures to compensate for the slightly reduced signal but would probably only be noticeable in the longest exposures etc.

Pro CCD is still viable. They have well known characteristics. Even at professional level there a pros and cons to each and generally the choice is made on what is best for the task at hand. CCDs can still be custom made to meet specific needs (noise characteristics etc) but they do cost 10's -100's thousands. As for amateur it is unlikely CCD will continue simply as there is not enough interest in a stable technology that has limitations when considering the wider consumer market.

I'm not sure whether it is saturated makes a difference to create such an effect. It's difficult to know the exact scale given it is a crop but would suggest this is a microlens artefact because of the very bright nature of the star. Such effects are commonly seen on ASI1600 style cameras because of less than ideal coatings for astronomy work, but see it less on Sony ones (but assume the bright nature is a culprit here).

Also make sure you take into account any filter you might attach to the DSLR (e.g. light pollution filter/multipass narrowband filter) as the thickness of the filter will alter back focus slightly.

I always find late August to late September as the best time of year. There is a good amount of darkness but can still be pleasantly warm. We can have decent spells of weather at this time of the year and there's generally a good variety of targets to observe.

In PI when there is an option in ImageIntegration for Pixel Rejection (2). In here there is a sigma low and sigma high value. These settings help you tailor how many outlier pixels are discarded. There is a balance (too much and real data gets discarded) but have found it useful to get rid of the remaining hot/warm pixels if used carefully.

It looks like you are using Pixinsight. It is worth playing with the Pixel Rejection options as this can be quite effective at removing these sort of pixels - but this is a bit OT. This shouldn't be a surprise because of how errors propagate So for example on a single pixel you take 5 30s darks. The values you get are:- 300; 301; 310; 281; 295; So you average value is 297.4 and the standard deviation is 10.644; hence commonly referenced as 297.4 +/- 10.644. This means there is a 67% chance that the 'true' result is between 286.756 to 308.044; there's a 95.4% chance that the result lies between 276.112 and 318.688; and a 99.7% chance that the true value lies between 265.468 and 329.332. This commonly referenced as the 3 sigma value and is usually the minimum that would be considered a 'result' (which is also why figures splashed on news/papers/adverts are all generally nonsense because they don't provide the error but that's another topic). However your camera noise is 297.4, your random noise is 10.644. Back on topic. Lets suppose you now have your uncalibrated image and the same pixel on that has values of 781 +/- 15.344 (i.e. 765.656 to 769.344) Now a dark is subtracted so would be the uncalibrated image minus the master dark So how is this undertaken with the errors. For simple subtraction you have to find the two largest extremes So hence subtract the most extreme values giving the following result 457.612 to 509.588. The average value being 483.6 (also being 781-297.4) so hence the error value is 483.6 - 457.612 = 25.988. Your new calibrated result is 483.6 +/- 25.988. Notice the error is also (10.644 + 15.344). As such although you've subtracted the dark you've added and compounded the errors. Therefore from a simple error calculation it should not be a surprise to see your error increase (now you have to add in your flat which is a divide and that makes the errors compound in different ways - see here for example:- https://thefactfactor.com/facts/pure_science/physics/propagation-of-errors/9502/

You've still got at least some hot pixels in the image so it can't be fully calibrated? These pixels will skew your standard deviation as they don't represent random (gaussian) noise. It's unclear whether you've used the same size box either so they might not be directly comparable (especially if you are picking up more hot pixels)? You may also be picking up actual data whereas before it was more dominated by noise (so you might be sampling signal not noise, but it is difficult to know because the image is too small) - was this just a bias or dark frame?

There are other options that you can consider as well that fall within this type of budget range. You could include the StellaMira 85mm or William Optics GT81 both with an associated flattener/reducer. The benefit from the triplet is colour correction (which would be helpful with a DSLR to avoid some bloat). My concern with a TS telescope is that I'd expect returns to become more difficult as pass the end of the year so may be worth factoring in (returning things to the US is truly a work of the devil with all the paperwork you need) and would expect this to be the same to the EU when the transition period ends (both ways). It can be quite difficult to compare two setups identically. It's rare that people have duplicate scopes just to check certain combinations and even astrobin might have some examples the images will be dependent on seeing, image processing skills etc. None are likely to be bad (though Melon'y Lemons do occasionally get through) so those that provide pre-checks can be a benefit. You will probably see the biggest change when you move to CCD/CMOS with guiding because of the reduction in noise compared to a DSLR.

Sky flats should be fine for the telescope. Gradients only tend to become an issue on widefield setups, but I'm guessing the focal length we are looking at here is 1600mm+ and hence the field of view is small. Just make sure you point the telescope in the right direction (i.e. about 180 degrees from the sun, i.e. west at dawn, east at dusk and about 45-60 degrees altitude). The real trick is that exposure times need to be constantly adjusted. If you have fast downloads then you may be able to run a sequence of 10 or so and then change exposure. Some programs will do this automatically. You want to aim for the exposure of about half the full depth (so a count of about 25000-35000 for 16 bit cameras, adjust accordingly for 12/14 bit CMOS etc). It doesn't matter that you are altering exposure length as long as the counts stay around these figures (though very short exposures and long exposures raise the risk of shutter effects or stars becoming visible so should be avoided). There is also the risk of point source (stars) and there are two ways to avoid this (noting though you should always avoid bright stars). Firstly you can turn off tracking, stars will then trail and hence the area of the sky being observed changes. Hence when you combine multiple flats these blurred areas are averaged away. The alternative is to take a sequence of say 10 images, then slew the telescope slightly and then another sequence (easier with faster downloads). Because conditions change quickly it can take time to build up an appropriate sequence of flats especially when you factor in multiple filters as well. A lot of professional observatories cycle their flats i.e. every day they will take dawn and dusk flats for their filters and then for images use those generated x weeks before. This way they have a continually relevant master flat. They have the same issue in that you can't have a white panel once you get above a certain size. Finally don't use flats when there are any clouds. This will really mess up the flats as you no longer have consistent even illumination.

Dawes limit only really applies to point sources (so star clusters, doublets etc). It means less when you consider extended objects (planets, nebulae, galaxies etc). Some planetary imagers (e.g. Damian Peach) image way past the Dawes limit of their telescopes. Dawes limit applies in specific circumstances. However, it is generally correct though that the finer the image scale you are getting less signal for the same noise per pixel and can have diminishing returns. As for the original post I would suggest an ASI183 for sub-1000 as well - this has the benefit that you can use a wide field telescope and still get decent resolution. For 1k - 2k probably something like the Atik383L - long in the tooth but a good all rounder camera.