M106 revisit

[Rodd]

4 hours ago, ollypenrice said:

The details will be larger but will they be more - ahem -  detailed?

I think this discussion ends up right next to the one about reducers.  There is theory and then there is actuality.  It certainly seems that a pixel scale of, say .5 arcsec/pix with an 11 inch scope SHOULD provide greater detail than a pixel scale of .5 arcsec/pix with a 5" scope.  If the only thing in the equation that changes is aperture--that has to be the case no?  I suppose it could be that the extra aperture just gets you to point A faster and the detail look the same.  Is that what you are suggesting?

Rodd

[ollypenrice]

8 hours ago, Rodd said:

I think this discussion ends up right next to the one about reducers.  There is theory and then there is actuality.  It certainly seems that a pixel scale of, say .5 arcsec/pix with an 11 inch scope SHOULD provide greater detail than a pixel scale of .5 arcsec/pix with a 5" scope.  If the only thing in the equation that changes is aperture--that has to be the case no?  I suppose it could be that the extra aperture just gets you to point A faster and the detail look the same.  Is that what you are suggesting?

Rodd

Why we must be careful with the numbers:

-The atmosphere may (and often does) impose an upper limit on resolution well below the theoretical capability of the system.

-The guiding may do likewise.

-Within the usual range of amateur apertures the Dawes limit may not be the limiting factor.

-Optical quality is very variable between instruments and produces what seem like anomilies: why do SCTs produce such high levels of resolution on planetary images while producing relatively large stars in long exposure DS applications? (I think they do but I've no idea why.)

-The cameras which actually exist are not equivalent. The large pixel cameras best suited to large aperture/long FL are less sensitive than than their small pixel rivals but they have greater well depth.

-Software sharpening requires strong signal.

As I said earlier, see what you find. It may not be the same as what I found!

Olly

[MartinB]

2 hours ago, ollypenrice said:

The cameras which actually exist are not equivalent. The large pixel cameras best suited to large aperture/long FL are less sensitive than than their small pixel rivals but they have greater well depth.

I'm not sure this is correct Olly.  I thought the indicator of sensitivity was quantum efficiency, how effective a pixel is at converting a given number of photons into signal.  Doesn't full well depth relate to quantisation error and useable dynamic range?  My non antiblooming gate KAF 3200 chipped camera has a max QE of a little over 80% with 6.8 micron pixels.  It is super sensitive but has other issues!

[Rodd]

3 hours ago, ollypenrice said:

As I said earlier, see what you find. It may not be the same as what I found!

I understand.  I think in my case, the atmosphere will be the controlling factor.  If that is true--and what you say is true--I have no chance at finding anything different than you.  But I will postulate that on night of good seeing and transparency 2 scopes side by side, mounted such that guiding is decent for both and focus is good, using the same camera, the 11" scope will reveal more details (including finer resolution of existing details) than a 5" scope-providing the details are there to begin with.  For many nebula, fine details seem to be lacking--or at least there seems to be a limit- until you get really far in on a small area (enter your 24 inch super scope).  One advantage that the 11" scope has is that there is more signal-always.  That certainly is an advantage.  It means there is potential for details that are too faint to be picked up with the smaller instrument to be revealed by the larger one.   Please, let me know if you would bet the other way on this.

Rodd

[ollypenrice]

1 minute ago, Rodd said:

I understand.  I think in my case, the atmosphere will be the controlling factor.  If that is true--and what you say is true--I have no chance at finding anything different than you.  But I will postulate that on night of good seeing and transparency 2 scopes side by side, mounted such that guiding is decent for both and focus is good, using the same camera, the 11" scope will reveal more details (including finer resolution of existing details) than a 5" scope-providing the details are there to begin with.  For many nebula, fine details seem to be lacking--or at least there seems to be a limit- until you get really far in on a small area (enter your 24 inch super scope).  One advantage that the 11" scope has is that there is more signal-always.  That certainly is an advantage.  It means there is potential for details that are too faint to be picked up with the smaller instrument to be revealed by the larger one.   Please, let me know if you would bet the other way on this.

Rodd

I'm not a betting man! I just compared images taken here by two different rigs and was surprized to find no significant difference in real resolution between TEC140 and ODK14 setups. But if you can find more resolution then we'll both be delighted. This isn't a competition, after all.

Olly

 

[Rodd]

30 minutes ago, ollypenrice said:

This isn't a competition, after all.

I wouldn't be that foolish!?

Rodd

[ollypenrice]

4 hours ago, MartinB said:

I'm not sure this is correct Olly.  I thought the indicator of sensitivity was quantum efficiency, how effective a pixel is at converting a given number of photons into signal.  Doesn't full well depth relate to quantisation error and useable dynamic range?  My non antiblooming gate KAF 3200 chipped camera has a max QE of a little over 80% with 6.8 micron pixels.  It is super sensitive but has other issues!

Yes, that's a camera I'd overlooked since it has high QE and fairly large pixels - which bucks the trend - but doesn't the lack of an ABG restrict its use somewhat? 

Olly

[Rodd]

6 hours ago, ollypenrice said:

I'm not a betting man! I just compared images taken here by two different rigs and was surprized to find no significant difference in real resolution between TEC140 and ODK14 setups. But if you can find more resolution then we'll both be delighted. This isn't a competition, after all.

Olly--may I ask what target it was?  Some targets are light on fine detail--or, rather, would not be prone to looking terribly different at different focal lengths.  Some, however, are teh opposite.

Rodd

[MartinB]

2 hours ago, ollypenrice said:

Yes, that's a camera I'd overlooked since it has high QE and fairly large pixels - which bucks the trend - but doesn't the lack of an ABG restrict its use somewhat? 

Olly

Yes, you wouldn't want to image M45, M42 or the Witch's Broom with it.  Generally though, the odd bloom is very easy to deal with and gives you a nice indication as to when your stars are getting saturated!  The big problem with this chip is microlens artefacts which rear their very ugly head when you are trying to pull out really faint detail

[Rodd]

38 minutes ago, MartinB said:

M45, M42 or the Witch's Broom

Interesting that you put the Witches Broom in the same category as M45 and M42 (bright with a wide dynamic range!).  I know its one of the brightest parts of the veil complex--but did not know it was in the big leagues!

Rodd

[MartinB]

It isn't the nebulosity Rodd, it's the star right in the middle, same problem with the trapezium stars in M42

[gorann]

Not sure if it was completely clarified in this thread but I just read on a CN thread that what affected your bright stars Rodd are micro lens effects from the chip, which is characteristic of the ASI1600. It may also have to do with the lack of AR coating on this chip (in contrast to Sony chips). It is generally only a problem with the brightest of stars, so avoid the Horse head, see:

https://www.cloudynights.com/topic/599475-sony-imx183-mono-test-thread-asi-qhy-etc/page-11

I am right now thinking of buying a mono CMOS from ASI and have real difficulties to decide between the 1600 and 183, but I think (at this moment) that I am leaning towards the 1600 due to its real estate.

[Rodd]

18 minutes ago, gorann said:

Not sure if it was completely clarified in this thread but I just read on a CN thread that what affected your bright stars Rodd are micro lens effects from the chip, which is characteristic of the ASI1600. It may also have to do with the lack of AR coating on this chip (in contrast to Sony chips). It is generally only a problem with the brightest of stars, so avoid the Horse head, see:

https://www.cloudynights.com/topic/599475-sony-imx183-mono-test-thread-asi-qhy-etc/page-11

I am right now thinking of buying a mono CMOS from ASI and have real difficulties to decide between the 1600 and 183, but I think (at this moment) that I am leaning towards the 1600 due to its real estate.

Yes--the size of the chip is great.  It is quite amazing when you realize that you have multiple images in one.  You have a wide FOV image--but due to the small pixels, you have much greater than normal resolution for the FOV.  If your seeing is good (unlike mine most of the time), I think you will be truly amazed at the detail you get from widefield shots.  My HaSHO Heart Nebula accomplished this to some degree--The Elephants trunk as well.  In the ET-there is a very close double star near the end of the trunk that is not commonly separated--the stars usually glob together.  Under normal viewing with the ASI 1600 and a focal length of 310 it looks like a single star--but zoom in and there is as much separation as I got using the TOA 130 at a focal length of 1,000 (with STT-8300).  Have fun!

Rodd