2024-05-28, 04:41 PM
Hello Owen,
It took some digging to figure out what this is about, and you are right, its just a matter of the total amount of light being passed. They should have taken care to say "for a given object" and its not going to be universally true. For example, given an object with mostly OIII emission, the idea is that the OIII will pass only the OIII, whereas the UHC might pass emission from other lines, such as H-Beta, providing a stronger signal from the object. Comparing two views of the same object in these two different filters, the UHC image may have a higher surface brightness. Thus, in the OIII, it is as if its a fainter nebula, and lower magnifications are more appropriate.
That rule of thumb has too many assumptions in it, and does not apply equally to every object. In my experience from imaging, if we can detect OIII visually, then the OIII is likely going to completely dominate the rest of the lines in the majority of cases, rendering this whole idea rather moot. Thankfully, SkyTools can compute the optimum magnification, and once the filters are part of that calculation, these things will naturally be considered.
It does make me think, however.... maybe we need to add a new dimension to the Ideal Eyepiece selection. The mean visual surface brightness of the object is estimated. This value is used to select the eyepiece that will provide the best contrast against the sky background for *visual detection*. So if the object is going to be categorized as difficult or challenging, then this eyepiece gives you the best chance to detect it. But if its so bright as to be easy, the algorithm abandons contrast and attempts to select an eyepiece that provides the most pleasing view, usually based on the size of the object in the eyepiece. What's missing from this idea, is that every nebula has fainter parts to it, and detecting those fainter parts requires the eyepiece that delivers the highest contrast for these fainter parts. Also, what about the contrast between parts of the nebula? The brighter parts and the fainter parts? I presume it is possible to calculate the eyepiece that will allow for the ideal detection of these differences. Right now, it is only looking at the contrast between the mean surface brightness and the sky background.
To be honest, I've always looked at this ideal eyepiece feature as a way to maximize detection for difficult objects. As you may recall, in SkyTools 3 this was not even labeled as the ideal eyepiece, but the eyepiece to maximize visual detection or some such, but people often assumed it was more than that, so I broadened the definition to provide a more complete feature. Maybe I should revisit?
It took some digging to figure out what this is about, and you are right, its just a matter of the total amount of light being passed. They should have taken care to say "for a given object" and its not going to be universally true. For example, given an object with mostly OIII emission, the idea is that the OIII will pass only the OIII, whereas the UHC might pass emission from other lines, such as H-Beta, providing a stronger signal from the object. Comparing two views of the same object in these two different filters, the UHC image may have a higher surface brightness. Thus, in the OIII, it is as if its a fainter nebula, and lower magnifications are more appropriate.
That rule of thumb has too many assumptions in it, and does not apply equally to every object. In my experience from imaging, if we can detect OIII visually, then the OIII is likely going to completely dominate the rest of the lines in the majority of cases, rendering this whole idea rather moot. Thankfully, SkyTools can compute the optimum magnification, and once the filters are part of that calculation, these things will naturally be considered.
It does make me think, however.... maybe we need to add a new dimension to the Ideal Eyepiece selection. The mean visual surface brightness of the object is estimated. This value is used to select the eyepiece that will provide the best contrast against the sky background for *visual detection*. So if the object is going to be categorized as difficult or challenging, then this eyepiece gives you the best chance to detect it. But if its so bright as to be easy, the algorithm abandons contrast and attempts to select an eyepiece that provides the most pleasing view, usually based on the size of the object in the eyepiece. What's missing from this idea, is that every nebula has fainter parts to it, and detecting those fainter parts requires the eyepiece that delivers the highest contrast for these fainter parts. Also, what about the contrast between parts of the nebula? The brighter parts and the fainter parts? I presume it is possible to calculate the eyepiece that will allow for the ideal detection of these differences. Right now, it is only looking at the contrast between the mean surface brightness and the sky background.
To be honest, I've always looked at this ideal eyepiece feature as a way to maximize detection for difficult objects. As you may recall, in SkyTools 3 this was not even labeled as the ideal eyepiece, but the eyepiece to maximize visual detection or some such, but people often assumed it was more than that, so I broadened the definition to provide a more complete feature. Maybe I should revisit?
Clear skies,
Greg
Head Dude at Skyhound
Greg
Head Dude at Skyhound