so I would like to add an ideal filter (as in the filter I want to observe with...like O-III or UHC, etc) to my observing list.
I started to go through the Messier List and added it to the Brief...but the Brief note didn't copy to my other lists?
would love for it to show up next to the ideal eyepiece on the list
any way to put it in there so it's permanent and comes up on every list? or what would be the best way to do this so it's right up there and not buried in a note?
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I had Attachments set to AI Northern 100...when I flipped to "My Attachments" in both lists, it transferred everything.
Interestingly a long time ago there were discussions with Greg about using his spectral data to choose an ideal filter for an object. Maybe this will be something for 4.1 in between all the EAA features. In the simplest form this would be if the spectrum was strongest in the OIII lines then a UHC or OIII filter would be best. If it was strongest in the H-Alpha lines then an H-Beta filter would be best. One could of course massively complicate things but this would be quite easy I would think.
I'm super beginner with filters so I am going off of this resource as my starting point. Basically someone with a ton of experience went through and gave ratings to different filters for 100 objects.
As I understand it, having different aperture and seeing conditions could change this...so yeah I would love that feature if that was something simple.
He also found on a bunch of objects that one was better but not by much. that would be awesome if the program could just tell you slightly favor OIII but give UHC a shot, etc..
https://www.prairieastronomyclub.org/fil...n-nebulae/
Hello,
Yes, that was Dave Knisely who did all that work, and its a great resource. I agree this would be useful for SkyTools and it is on my list. But I need to finish the data collection and reduction for HII nebulae first, so it won't be this summer. Because of that, this will likely be a version 4.2 feature.
Unfortunately the issue is also complicated by the exit pupil of the eyepiece you are using so the larger the exit pupil the narrower band filter one should use. So for for low power an OIII filter maybe that of choice. For medium power a UHC type filter and for high power no filter as the magnification will have the same effect as a filter.
Hi Owen,
I'm trying to wrap my head around why there would be a relationship between the size of the exit pupil and the bandwidth. How that work?
I have no experience but read this on Lumicon's site:
"As filter bandpass decreases, optimum exit pupil size tends to increase. To determine the best eyepiece focal length to use with a given filter, simply multiply the Exit Pupil value shown above by your telescope's focal ratio. For example, if you are using the Lumicon H-Beta filter at a dark site and your telescope has an f/6 focal ratio, the best range of eyepiece focal lengths to use with this filter is [(4 to 7) x 6] = 24 mm to 42 mm."
chart in the middle of this page
https://www.lumiconinc.com/uses
I guess this would come into play with people with smaller telescopes trying to push high magnification with an H-Beta filter or something like that. they are recommending it's not optimal...maybe it gets too dim?
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?
That sounds reasonable. I was trying to locate my original source for the statements I made. I was perhaps hasty in linking exit pupil to magnification but of course there is a link between the two. You are right however that personal taste also comes in and some people find a UHC type filter better on an OIII filter on the same object and vice versa so it may not be possible to recommend a filter that suits everybody but just a generic recommendation. As you say as well for seeing the fainter parts may require a different filter. A classic example here would be M42 where an OIII filter shows only the central core, the UHC shows more of the wings and then an H-Beta filter shows the outer tendrils well.
With regards to the comment on the H-beta filter made before it really doesn't work that well on small telescopes because they do not push enough light through except in the brightest cases, like NGC 1499 for instance.