ASI178MM

[michael.h.f.wilkinson]

Just now, vlaiv said:

x0.63 reducer and bin x2 could still be doable? It would sample at 1.26"/px - and that is still too high in my opinion, but not that far away from 1.5"/px

That should work. The Starizona is better, but this is doable. You could even let everything hang out at and bin in software later if you don't like it

[vlaiv]

1 minute ago, michael.h.f.wilkinson said:

That should work. The Starizona is better, but this is doable. You could even let everything hang out at and bin in software later if you don't like it

I would actually recommend binning in software since there is no difference with CMOS sensor and it gives you more control over the process

[Lucas Barclay]

 

3 minutes ago, vlaiv said:

I would actually recommend binning in software since there is no difference with CMOS sensor and it gives you more control over the process

Ah I see, is there a link you could attach to do with binning? I've definitely come across the terminology before but never tried the process myself.

[michael.h.f.wilkinson]

35 minutes ago, vlaiv said:

Indeed.

Two sample images on TS website show rather nice stars on ASI183 sized sensor.

The M51 must be a crop, given my image of M51 at 762 mm focal length and the same sensor

[vlaiv]

20 minutes ago, michael.h.f.wilkinson said:

The M51 must be a crop, given my image of M51 at 762 mm focal length and the same sensor

Looks like it - but M16 looks like genuine FOV without cropping - at least when compared to Astronomy Tools FOV.

Probably cropped for effect / framing rather than to remove ill shaped stars.

[michael.h.f.wilkinson]

1 minute ago, vlaiv said:

Looks like it - but M16 looks like genuine FOV without cropping - at least when compared to Astronomy Tools FOV.

Probably cropped for effect / framing rather than to remove ill shaped stars.

Really interesting. They don't seem to be in stock in many places

[vlaiv]

33 minutes ago, Lucas Barclay said:

 

Ah I see, is there a link you could attach to do with binning? I've definitely come across the terminology before but never tried the process myself.

Not sure that I can. It is really basic concept.

It is taking group of 2x2, 3x3 or larger of pixels and summing their values. Result is the same as having x2, x3, etc larger pixel size than original.

There is hardware binning - that is inherent in CCD design, and there is software binning. CMOS cameras due to their design are only capable of software binning. Even if you bin at capture time - it is effectively done in firmware of the camera and not in silicon.

Difference between the two approaches is level of read noise. With CCDs and hardware binning, summing is done on electrons them selves - they are "counted" together, before ADC is performed. This results in single "dose" of read noise added to binned result.

With software binning - each pixel gets single "dose" of read noise and total read noise on 2x2, 3x3, etc bin is equal to 2 * read noise, 3 * read noise, etc ...

Binning works very similar to stacking and is equivalent to having larger pixel size in terms of sensitivity (both ways of viewing it yield same SNR improvement - so you can look at it either way).

I prefer to bin my subs in software as that lets me choose bin factor. If I judge that 2x2 bin is enough and I have resolution in the image to match  - I can leave image at x2. Sometimes atmosphere is just too unsteady and I need to bin x3 or even x4. ImageJ has that option - simple command will bin your sub by chosen factor. PixInsight has it also - called integer resample.

[michael.h.f.wilkinson]

On 23/03/2021 at 21:00, vlaiv said:

Looks like it - but M16 looks like genuine FOV without cropping - at least when compared to Astronomy Tools FOV.

Probably cropped for effect / framing rather than to remove ill shaped stars.

Just pulled the trigger on the Starizona Night Owl 0.4x reducer. Couldn't resist (or to quote Oliver Hardy "Now look at what you have made me do!" )

[vlaiv]

3 hours ago, michael.h.f.wilkinson said:

Just pulled the trigger on the Starizona Night Owl 0.4x reducer. Couldn't resist (or to quote Oliver Hardy "Now look at what you have made me do!" )

I'm really looking forward to see what sort of results you get from it with ASI183.

I think that it could really be solution to old problem - "scope that can do it all". I mean 5" or 6" Cat and this reducer. Such scope would be good for visual DSO and planetary as well as imaging DSO and planetary.

[michael.h.f.wilkinson]

10 hours ago, vlaiv said:

I'm really looking forward to see what sort of results you get from it with ASI183.

I think that it could really be solution to old problem - "scope that can do it all". I mean 5" or 6" Cat and this reducer. Such scope would be good for visual DSO and planetary as well as imaging DSO and planetary.

Not ideal for wide field, however. I would say the sweet spot is with the C8. It isn't much heavier than the C6, but has the much bigger light grasp. 

[vlaiv]

55 minutes ago, michael.h.f.wilkinson said:

Not ideal for wide field, however. I would say the sweet spot is with the C8. It isn't much heavier than the C6, but has the much bigger light grasp. 

Actually, there is simple way to turn 6" F/4 scope into 2" F/4 "lens" for wide field. In fact any scope can be turned into shorter FL scope of the same speed where shorter focal lengths are "harmonics" of original FL - like 1/2, 1/3, 1/4, etc ... with this trick.

Recipe is as follows:

- take mosaic with number of panels being equal to square root of FL reduction that you want, ie for 1/3 of FL - make 3x3 mosaic

- spend on each panel reciprocal of reduction squared time - or in example case - 1/9th of time on each panel

- bin each panel by reduction factor - in our example 3x3

You will get the same result as if using 1/3 focal length instrument of the same speed.

Here is reasoning: You spend the same amount of time as you would with smaller instrument. You use same camera (same pixel size) so SNR of say F/4 and F/4 is the same.

Each panel will have lower SNR by factor of N because we spent 1/N^2 less time on it, but if we bin NxN - we increase SNR by factor of N - so each resulting panel has exactly the same SNR as other instrument.

We reduced FL by factor of N, but we binned pixels by factor of N - so sampling rate / resolution stays the same as with smaller instrument (we get same number of pixels in final image).

Only difference is being the space lost on overlap.

In another words - with some skill and software support (plate solving, mosaic making, stacking that supports panel stitching) C6 with x0.4 can also do wide field shots.

[michael.h.f.wilkinson]

7 minutes ago, vlaiv said:

Actually, there is simple way to turn 6" F/4 scope into 2" F/4 "lens" for wide field. In fact any scope can be turned into shorter FL scope of the same speed where shorter focal lengths are "harmonics" of original FL - like 1/2, 1/3, 1/4, etc ... with this trick.

Recipe is as follows:

- take mosaic with number of panels being equal to square root of FL reduction that you want, ie for 1/3 of FL - make 3x3 mosaic

- spend on each panel reciprocal of reduction squared time - or in example case - 1/9th of time on each panel

- bin each panel by reduction factor - in our example 3x3

You will get the same result as if using 1/3 focal length instrument of the same speed.

Here is reasoning: You spend the same amount of time as you would with smaller instrument. You use same camera (same pixel size) so SNR of say F/4 and F/4 is the same.

Each panel will have lower SNR by factor of N because we spent 1/N^2 less time on it, but if we bin NxN - we increase SNR by factor of N - so each resulting panel has exactly the same SNR as other instrument.

We reduced FL by factor of N, but we binned pixels by factor of N - so sampling rate / resolution stays the same as with smaller instrument (we get same number of pixels in final image).

Only difference is being the space lost on overlap.

In another words - with some skill and software support (plate solving, mosaic making, stacking that supports panel stitching) C6 with x0.4 can also do wide field shots.

Of course, but a fast APO refractor makes life a lot easier, and for visual there is no substitute for a real wide-field scope. Even if my C8 working at F/4 replaces the 6" F/5 Schmidt-Newton for imaging with the ASI183MM-Pro, the latter scope will still be a great comet sweeper, and allow the use of bigger cameras., capturing more photons in its wider field. 

[vlaiv]

3 minutes ago, michael.h.f.wilkinson said:

Of course, but a fast APO refractor makes life a lot easier, and for visual there is no substitute for a real wide-field scope. Even if my C8 working at F/4 replaces the 6" F/5 Schmidt-Newton for imaging with the ASI183MM-Pro, the latter scope will still be a great comet sweeper, and allow the use of bigger cameras., capturing more photons in its wider field. 

Good point, forgot about visual, yep "do-it-almost-all" scope then