Adam J

Nice, be sure to post an image for us all to see. I think that you will find the 130pds complementory. Adam

I think that the thing to keep an eye on is that any of these cameras are going to be vastly better than what you are using at the moment so thr 533 will produce good images for you in any case. I would just try it with what you have first, then decide if you want the 130PDS after testing it. The ST80 is massive overkill for guiding a 130PDS. You are better off with a 50-60mm guide scope. Adam

Yes I have an esprit tested by him. Just always wondered what equipment he actually has etc. Out of interest mainly.

I would think that the larger pixels make up for quite a bit of that difference. Dynamic range is good on the 071 / 168c due to 14-bit A/D so you can use it at gain 200 (ASI) and get 2.3e read noise while still having 11 stops. I think that the ASI294 is better on paper lower read noise higher QE but also much higher dark current, I just have an uneasy feeling about some of the things I have read about it. Equally the 533 is a superior sensor, but its so small and oversampled....... Easy to go around and around in circles with these choices. Its great that we have so many choices in the modern camera market though. OP I have said it before but why OSC? I think a ATIK414EX mono (dont touch the OSC) would be a better choice for pure small galaxy imaging on your scope. But the very small sensor means that is all you can do with it. Adam

I think in this modern world we should expect manufacturers for fix (for a fee) scopes that are second hand and out of warrenty. Imagin if you could not get someone to fix your second hand car....all just adds to the throw away society. Adam

oh and should have said, clearly lens cap off.

Does he recentre lens elements, I always wondered if he had an interfermometer or was working off star tests. Adam

If it will not shift after a week or so then remove the lens cell as above and put it into a sealed bag with some dessicant. Until then keep the scope in a well ventilated area out of its box. Dont try and do anything like putting it on a radiator or heating it for an extended period with a hair dryer. Adam

You can if you dont mind the weight.

I dont know but i dont like the look of it mate. I would not normally say this but its may be worth unscrewing the objective with a rubber strap rench on the tube and one on the lens cell (twist anti clockwize). Try using baader cleaning fluid on it with a pure cotton pad, blow dust off first. I would be surprised if its the coating coming off.... It could also be liquid trapped between the two lens elements. Have you cleaned it recently what fluid did you use? Are you 100% sure that it is a new feature? Adam

Capture the largest number of satalite trails in a single sub frame.

Wow, I did not think that the RASA 8 was spec'd to cover an APS-C sensor. To quote celestron: "Unlike the larger RASAs, the 8" model is not suitable for use with DSLR cameras. Instead it has been optimised for use with cameras that have sensors with a diagonal size ~22mm, which gives an image circle of 3.15°. This makes it an excellent choice for use with today's highly popular CMOS deep sky cameras, such as the ASI183 & ASI1600 series from ZWO. Starlight Xpress' compact CCD cameras also work very well. And whilst ~22mm diagonal is optimal the RASA 8 can also be used with larger sensors up to 32mm diagonal, including the APS-C sized sensors used in many mirrorless cameras, though some compromise must be expected at the image periphery. Celestron advise camera bodies should be less than ~100mm / 4" in diameter." Did you have to crop that at all as it does not seem like you have had to make too many compromises with the APS-C sensor. Adam

I have a prototype version and its got an odd arangement on the front I ended up putting a nose extender on it and threading on a 1.25 inch IR filter. Works well. Adam

No but there is a significant thread on the issue on cloudy nights where some experianced imagers tried lots of different things to try and get the background to calibrate properly and failed. https://www.cloudynights.com/topic/596025-zwo-asi294-mc-pro/page-7 I dont think its a problem with clipping to be honest. It only shows when you try and go really deep. So most less experianced imagers will not experiance it. From the lack of star burst amp glow you can see its been calibrated "correctly". If you have a read let me know what you think. Adam

QE is said to be about 50% on the IMX071 and the read noise is almost half that of the 1100D. Add cooling and it would be a very significant upgrade over the 1100D. You dont need the FOV for small galaxies but you may want to image other things from time to time.

Not sure what you mean by configured properly? The issue with that sensor is calibration is very difficult due to ambient temperature changes between dark frames and light frames resulting in small regional variations in chip temperature. Hence it will only calibrate correctly if you are able to take darks at the same ambient temperature as the lights or at least close to the same, despite the regulated cooling. Basically only a small area of the chip is in contact with the cooler due to the pin layout on the rear. You can see it in deep images of galaxies when a large stretch has been applied you get a pattern in the background that is essentially the contract pads between the thermal cooling and the back side of the chip. You never see it in nebula shots as its buried under the signal....but with galaxy imaging it can be quite nasty. Hence I would avoid it and go for either the 533 or the 071. Well actually I would probably go with a ATIK414 mono is this application but thats a different argument all together. Adam

I get the impression there was supposed to be a link in there somewhere?

I thought that multi star guiding helped to stop you from "chasing the seeing" as you are averaging the motion of multiple stars, but it cant actually remove the effect of seeing on the image itself. Hence it helps you guide but will not actually improve your FWHM that much. Adam

However, for conventional imaging you are correct there is no cheap CMOS sensor with big pixels. There is the ASI2400MC Pro full frame that was recently announced but its not cheap. Just because you are over sampled does not mean you can’t use a 533 and take a great image with it, its just not optimal, you can resample in software. I think the point most people are making is just don’t expect to achieve 0.7. You are 100% correct about the chip cooling issues on 294 so I would not go that way. Have you thought about a ASI071MC Pro? It will also give you a much nicer FOV at your focal length. Or for that matter the cheaper (and possibly slightly better) QHY168c. QE is lower and read noise higher but the pixel area is almost double so it makes up for that and you end up with a larger FOV. https://www.modernastronomy.com/shop/cameras/cooled-ccd/qhy-cooled-ccd-cameras/qhy168c/ https://www.astrobin.com/full/uy18rl/0/ https://www.astrobin.com/full/nvngqu/0/ https://www.astrobin.com/full/nxqf5h/0/ Your original question was "my question is is it achievable to image at below 1 arc sec or would I be fighting a loosing battle?" I took that to mean guiding and seeing, in which case yes you are probably fighting a losing batter trying to achieve that resolution in the UK. But that’s not to say the 533 will not work at all, it is just not optimal at that focal length with UK seeing. Another option is to ditch the 200mm F5 Newtonian and go with a 130PDS or a 150PDS and the 533. The 130PDS is only £180 new after all you could buy one for the second hand sale of the 1000mm scope you currently have.... thats what I would do. Might be cheaper to do that than go with the larger pixels and sensor and it will be easier to guide also. But totally on the flip side, if its small galaxies you want then maybe you are willing to wait for that one night in ten when you will get the seeing to make the 0.77 scale worth it? Only you know that. Adam

Yes it must change thinking about it in more depth.

Yes it will be extreamly sensitive. Did you know of this issue when you purchased it, assuming its used? Adam

I agree I would think that it would not change the focal length just move the location of focus. Adam

You would perform a star test or if you purchased a scope from someone like FLO in the UK they would do it for you for £75. I would not say its easy to lose colimation on a refractor though, I accidently clipped min with the obsy roof a few months back and its changed its performance a bit. All scopes will leave the factory well colimated and centered usually. They normally even get to the shop well centred and colimated, its the last little bit of the trip with someone like DHL or DPD that is usually the issue as they dont treat it with any respect. I just got this book for my 40th birthday from FLO. https://www.firstlightoptics.com/books/star-testing-astronomical-telescopes-a-manual-for-optical-evaluation-and-adjustment-second-edition-book.html You need a bit of a technical mind for it but its a great read and will teach you to assess your telescope optics. Adam

I did not say that they have to be matched I just said that seeing normally limits resolved detail even at 1.41 for me and hence I doubt there is consistent benefit to deliberately trying to image at 0.7 in the UK. In spain seeing will be much better. And vlaiv just beat me to it as I was typing, if you’re not going to see the benefit of higher resolution then you are going to see a reduction in signal to noise ratio as due to the increased sampling less photons are going to fall on each pixel in a given time. This is why people who jump on the ASI183 with its small pixels as an apparent solution to maintaining sampling in a small aperture refractor never really achieve that in practice as they just end up using more noise reduction negating any potential increase in resolved detail. Adam

How often would you say you achieve that? I image at 1.4 per pixel and I can see the effect on FWHM of my stars changing with seeing from night to night. If I am galaxy imaging I sometimes Chuck out whole nights of images as not good enough due to seeing. I should think that 0.7 is workable but maybe only on 1 in 10 nights and I would not image on that basis. Having said that though it's not a reason not to pair a ASI533 with that scope, mostly because in OSC the matric reduced resolution anyway. I just would not kid myself that I would be resolving detail at 0.7 unless I was doing very short exposures. Other locations around the world then it's different but in the UK....I just don't think it's viable to expect to achieve that resolution the vast majority of the time.