Adam J

Looks great, never heard of an ASI246 before? Adam

Nothing wrong with it for a good used price. But buying one new would be a little crazy.

yeah but how old are those reports, the camera is over a good decade old.

I used a 130PDS with a ASI1600mm pro and only a 50mm finder guider. Took this with it. Guiding was no problem, the pixel size is the same as the 533. 2x2 panels. Adam

very nice, surprised to hear that any of London is less than Brotle 9 to be honest.

I would have thought that an NEQ6 would easily manage a 130PDS and get sub arcsecond guiding? If not then maybe some turning of balance or a belt drive upgrade? I used to get 0.7 RMS total with my 130PDS on a HEQ5pro. Are you actually thinking of a new QHY8L? I really do think that would be a very poor choice in 2022. In terms of what makes them better, they are just lots more sensitive (higher QE and lower read noise) and suited to shorter exposures, so that might even help with poor guiding? If you pay a little more there is the QHY168c that still has reasonably small pixels and all the advantages of CMOS. But looking through astrobin the ASI294mc pro is just taking better images on average than the QHY8L Adam

But to bring it back onto topic I would say that the conclusion for me is get the IMX533, because: 1) Its back illuminated and the 269 is not, 2) You really dont need to go to 3.3um pixels as per the above discussion, 3) Although the 294 is perhaps the best match to a longer focal length refractor 700mm or so, I dont like the way many have issues with calibration when using duel narrow band filters. 4) The OP says he wants to image smaller targets, so the size difference between the two sensors is probably not a factor. Actually ill amend that and say get the 533 mono when it comes out lol. That way you can get a smaller scope for the same sampling, but OP may not like the idea of mono....,

Actually looking at my original I would say neither image fully matches it. Is something else going on when you put the side by side in your software? My point of comparison for blinking is the small satalite galaxy to the lower left of NGC4565. Wondering if somehow this has undergone a double hit of JPG compression? It is worth noting that the TIF of this looks better.

Probably need to sharpen the original to compare then.

The resized one is on the left, its subtle but I can see a loss in detail / slight increase in softness. I probably resized it to 2 arcseconds myself, it was a while back.

Not sure about FWHM but my Esprit 100 generally produces a HFR of 1.7-1.8 in good conditions according to NINA with a ASI1600mm pro and at 1.4 arc-seconds per pixel. Dont have access to the data as that is archived on a removable HDD. Might have time to dig it out if you really want me to. Best ever HFR = 1.5-1.6 If i am converting correctly i could still be over sampled by as much as 1/3rd. Adam

Yes so I see, well for what its worth having reviewed many images of NGC4565, I have seen very few (taken from UK close to sea level) that have much more resolved detail than what I managed at 1.4acrseconds per pixel at 550mm focal length. With the GT81 and a 533mc it comes out at around 1.65 the 269 would be close to the Daws limit of ~1.4, you might be able to go lower than 1.4 but to be honest I think you would have to start being very selective about what subs you accept into the stack or be very lucky with seeing. So for a larger scope to image smaller targets I would, go no further than say a 533 and a scope with around 700mm focal length but for me in the UK that is unlikely to get you much further than I did below so i see no real harm in going to the larger pixels of the 294. All in all though i think its best to go mono for high resolution imaging as you get more detail at a given focal length and pixel size without the colour matrix. Adam

We know its a GT81 from OP, going to assume he can get an RMS of around 1 arcsecond unless he is under-mounted. As above and more so with OSC than Mono i think that even if you can get better theoretical "working resolution" by choosing a smaller pixel camera then you still need sufficient SNR to take advantage of that available resolution. In the majority of cases it has been my experience that resolved detail is limited by SNR and not pixel scale. I have seen renditions of the vail SNR taken with large aperture long focal length scopes at 1.5arcseconds per pixel that have less resolved detail than my ASKAR FMA180 at 4.5arcseconds per pixel, just because my image has better SNR and I hence have applied greatly less or no noise reduction. Its an extreme but true example. Adam

One thing to think about is if the lower QE 269 may be 2x2 binned and get better SNR than a unbinned 294 with higher QE / lower read noise. Suspect it would be close but am at work so dont have time to run any numbers. Adam

The 269 is not larger then the 294.

Its a smaller sensor so that is why its cheaper, but probably a higher quality sensor. So depends on what you want to take a picture of, if your targets fit on the 533 then its likely the best bet. If you want a wider view then I would say the 294mc pro as its got a higher QE, but calibration while possible is not so reliable. I don't think that under-sampling is going to be an issue for you. Most of the time you will not resolve detail to the pixel level in any case, especially if you dont have good SNR and you have to apply noise reduction. Better to start out with higher SNR from a larger pixel higher QE sensor. Adam

ASI533mc pro is the answer in my opinion. After that the ASI294mc Pro but its a little trickier to calibrate, there are a few long threads on SGL covering this topic. I don't like what i see from the 269 as there seems to be allot of walking noise in most of the images i see. Guiding and dithering would be essential in my opinion. Adam

Depends on your budget. But the ASI294mc pro or the ASI533mc pro spring to mind. Although they will both sell fast when they come up used. Adam

I think there are quite a few options that will give better value for money even used. Unless someone is really giving one away, I. Which case why not.

It's actually really easy to mod a 600D there are detailed instructions on YouTube. Why not have a go yourself?

You don't need 31mm filters and the way astronomik mount them there is nearly no difference to 1.25 inch in terms of clear aperture, 1.25 inch will be easier to handle and mount and will work just as well as 31 on a sensor the size of a 533.

In essence yes your collimation is slightly off if the vignetting is not centred in on the sensor. However, it could also caused by a filter not being correctly centred in a wheel. Although is this is an OCS that is not likely the explanation? Adam

I see your point but consider this. Deep technical discussion is relevant here as we are also to establish what the correct methodology required to improve the implementation of such a tool. While the above may well be too complicated for the majority it is essential that those with the required understanding derive a better / correct methodology in order to provide the majority with a tool that a "numpty" can use and understand without needing to see or understand the nessasary underlying complexities which are being discussed here. It is possible that one answer is to have an advanced user mode for the tool the uncovers additional options also. I suspect that when the tool was produced the market was dominated by CCDs with pixels much larger than the CMOS chips now avaliable and that as such the model did not need to be additionally bounded to prevent extream combinations of imaging scope and pixel size from being incorrectly validated. For me those would include instances when the combination falls in the heart of the green zone but the aperture of the scope simply cant support the resolution being suggested. In this instance the tool is recommending a smaller pixel camera but should not be doing so as the only thing a small pixel camera will result in is lower Signal to Noise with no advantage to resolvable detail. Beyond this adding features such as a tickbox for OSC vs Mono should not over stretch the user. Adam

I have an FMA 180 and it's a good choice in combination with a dedicated astronomy camera, but can't help but think that if you are wanting to use it purely with a DSLR the. The speed of a Samyang 135 would be the best way to go. The difference in focal length between 135 and 180 is more significant than you may imaging in terms of detail gathered though and the ASKAR is much sharper unless you throttle the Samyang right back. Adam

I have heard of a great many people getting them fitted with sheilds to prevent light incursion into their property, however, I have never heard of anyone who got them to dim them. Adam