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Thread: Messier objects vs eyepiece spreadsheet

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    Default Messier objects vs eyepiece spreadsheet



    Hi all,

    After noticing how small some DSOs appear with my dobson + 26mm EP, I've thought that how big objects will look is a nice parameter to select eyepieces (to buy). I've created a spreadsheet that displays this information for Messier objects. You can see it here:

    https://docs.google.com/spreadsheets...it?usp=sharing

    It uses as input the scope focal length, EP AFOV and focal length, and Messier object's max length. The output is the percentage that the object's max length takes in the view with the eyepiece. I populated the table with three EP from Meade, for no other reason that it's the manufacturer of my scope. The spreadsheet is configured for my scope (first column, focal length). The color scheme for the size percentage is:

    - Orange if object takes less than 30% (meaning bad).
    - Blue: 30% - 60% (ok).
    - Green: 60% - 90% (perfect).
    - Red: more than 90% (bad).

    If anyone has comments about how to improve the table (e.g., the color scheme ranges), or on whether the table is useful at all, I'd appreciate them . Also, if anyone is interested I think the table can be copied and modified of course.

    PS: I have a feeling that Pleiades alone justifies a low magnification EP .
    OleCuss, KathyNS, bigjack and 4 others like this.

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    Default Re: Messier objects vs eyepiece spreadsheet

    That is really cool!!! Some serious work and could be seriously helpful as well.

    One of the best things about it is that it shows the interaction between the size of the target, the eyepiece, and the telescope. Very well done!

    I'm thinking it would be cool to generalize this as a spreadsheet used for doing the calculations for any given scope and/or eyepiece. For your purpose what you did was more appropriate, but someone could use this as the basis for doing that.

    Two suggestions:
    1. Take away some of the digits. 128% is plenty close enough, we really don't need 127.93%. That would be true for most all your numbers.
    2. If possible one should use the field stop for calculating the true FOV rather than using the AFOV. Not always possible, however, and for this purpose using AFOV is really plenty good.

    But I'm nitpicking. I really like what you did.

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    Default Re: Messier objects vs eyepiece spreadsheet

    Just as an aside, one thing to consider is that with the extended diffuse objects, most are not to going to see the full extent because of LP or other localized conditions that render the outer, dimmer portions invisible. For many, only the bright core of M31 is visible. Even globular clusters can loose some of the outer halo to such conditions. I guess you would get the stated percentage of what was visible however. Looks like a lot of work and thought was put into it, and I am sure that for some it might prove a useful tool. For me personally, I don't see any value added as I already have my own methods for determining eyepiece/magnification progression. Good luck with it as you refine your calculations.
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    Default Re: Messier objects vs eyepiece spreadsheet

    Thinking more about what you're trying to do, reminded me of a neat tool I hadn't thought of in quite a while. Take a look at the below linked site. I think what you're doing is something along the same lines, as far as how EPs will frame an object within its prescribed TFOV when used in your scope - though this site goes further. It will generate an observation list based on the data you input, with images so you get a visual sense of how the objects are framed in the EP (it chooses between what you input for a low mag, med mag and high mag EP) it deems best for the specific object. Granted the images are not necessarily representative of how bright and detailed the objects will appear to you since they use deep-space imagery, but rather how well they are framed in the FOV. It is interesting to play with, and while I wouldn't use it to choose EPs per se (I already have what I need anyway), it does give one a visual presentation that is fun to play with, and can help someone build an observing list.

    Visual Sky Assist | Find deepsky objects and print the list
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    ---------------------------------------------------------------------------
    Astro Sky 17.5 f/4.5 Dob || Apertura AD12 f/5 Dob || Zhumell Z10 f/4.9 Dob
    ES AR127 f/6.5 and ES ED80 f/6 on Twilight-II Mount
    ES 82° 24mm thru 4.7mm
    ---------------------------------------------------------------------------
    Astronomers: We look into the past to see our future.

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    Default Re: Messier objects vs eyepiece spreadsheet

    Thank you for your suggestions, added some improvements:

    Quote Originally Posted by OleCuss View Post
    I'm thinking it would be cool to generalize this as a spreadsheet used for doing the calculations for any given scope and/or eyepiece. For your purpose what you did was more appropriate, but someone could use this as the basis for doing that.

    Two suggestions:
    1. Take away some of the digits. 128% is plenty close enough, we really don't need 127.93%. That would be true for most all your numbers.
    2. If possible one should use the field stop for calculating the true FOV rather than using the AFOV. Not always possible, however, and for this purpose using AFOV is really plenty good.

    I thought it could be easily turned into a interactive webpage, though not sure it's worth the effort. At the moment, anyone can at least make their own copy of the spreadsheet, change the focal length, and add the EPs they own or are interested in. I added both suggestions. Formatting the numbers make it look much better. I added "field stop" as another input field. The spreadsheet will calculate FOV in both ways, and will use FOV from field stop if available (EP field stop seems more difficult to find than AFOV).


    Quote Originally Posted by KT4HX View Post
    Just as an aside, one thing to consider is that with the extended diffuse objects, most are not to going to see the full extent because of LP or other localized conditions that render the outer, dimmer portions invisible. For many, only the bright core of M31 is visible. Even globular clusters can loose some of the outer halo to such conditions. I guess you would get the stated percentage of what was visible however. Looks like a lot of work and thought was put into it, and I am sure that for some it might prove a useful tool. For me personally, I don't see any value added as I already have my own methods for determining eyepiece/magnification progression. Good luck with it as you refine your calculations.
    Added a "% visible" field for each object, the spreadsheet will assume 100% if not indicated. I really have no idea on this! If anyone has some information about visible portion of any object, please let me know and I'll update the spreadsheet.

    Quote Originally Posted by KT4HX View Post
    Thinking more about what you're trying to do, reminded me of a neat tool I hadn't thought of in quite a while. Take a look at the below linked site. I think what you're doing is something along the same lines, as far as how EPs will frame an object within its prescribed TFOV when used in your scope - though this site goes further. It will generate an observation list based on the data you input, with images so you get a visual sense of how the objects are framed in the EP (it chooses between what you input for a low mag, med mag and high mag EP) it deems best for the specific object. Granted the images are not necessarily representative of how bright and detailed the objects will appear to you since they use deep-space imagery, but rather how well they are framed in the FOV. It is interesting to play with, and while I wouldn't use it to choose EPs per se (I already have what I need anyway), it does give one a visual presentation that is fun to play with, and can help someone build an observing list.

    Visual Sky Assist | Find deepsky objects and print the list
    Thank you for this link, the output from that site is really neat. I wanted to make something that gives you a very quick overview of what an EP will achieve given your scope. I wonder whether any of the output of my spreadsheet is realistic at all. Anyway, it's more like a learning tool for me, helps me getting a grasp of all the numbers involved . I think I'll use it with care as a guide when buying a second EP, if only to understand what to expect from the purchase. But before buying anything, I'll run the candidates through the link you posted just to make sure .

    I also added some planets to the spreadsheet for the fun of it, with max size in optimal conditions.

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    Default Re: Messier objects vs eyepiece spreadsheet

    Hi, updated the spreadsheet with a couple more eyepieces. I'm thinking about getting the 8mm Hyperion Baader. Would you say it's a good companion to the 26mm? The others I'm considering are Meade 5000 Series HD-60 12mm, and Meade 5000 Series HD-60 9mm. Any idea on whether these EPs are good for a 10'' f/5 scope?

    Thank you,
    Eloy

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    Default Re: Messier objects vs eyepiece spreadsheet

    Any of the above should do fine in a f/5 scope.

    Mind you that this is getting into "high power" territory, so you'll not be using eyepieces like this for large dim objects, but rather planets, binary stars, and a few brighter DSO's with interesting partial-view features.

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    Default Re: Messier objects vs eyepiece spreadsheet

    Quote Originally Posted by mkettler View Post
    Any of the above should do fine in a f/5 scope.

    Mind you that this is getting into "high power" territory, so you'll not be using eyepieces like this for large dim objects, but rather planets, binary stars, and a few brighter DSO's with interesting partial-view features.
    Thank you for your response. I found a thread in another forum where they didn't talk well about the Hyperium Baader for F/5 :S (Baader Hyperion 13mm with F/5 Dob - Getting Started General Help and Advice - Stargazers Lounge, they mention the 8mm as well), so got a bit disappointed, so I was considering now Explore Scientific maybe, or maybe Meade UWAs. I also saw a £110 2nd hand Radian 10mm, I wonder whether this could be a better option. During my stay in Spain this month (when I have access to the telescope) the Moon will be up there, so it could be a good opportunity to focus on it .

    Another alternative is to just relax and enjoy the 26mm EP, and simply keep learning for a while .

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    Default Re: Messier objects vs eyepiece spreadsheet

    Fair enough, just keep in mind that eyepieces are highly subject to personal preference and opinions of what constitutes unacceptably awful vary quite wildly.

    Opinions of an eyepiece depend on many things, some objective, some experience/skill based, and some entirely subjective.

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    Default Re: Messier objects vs eyepiece spreadsheet

    Hi Eloy. All one can do is try them out. As mkettler said, it is something that is variable person to person and based on personal preference. For example, I used to have Baader Hyperions (21, 13, 8, 5 & zoom), I found them ok at f/5, but not terrific by any means. Whereas, others seem to really like them. They are definitely great performers used in a slower scope (say f/8 or slower), which is more tolerant of EP aberrations. When I tried my first ES 82* EP, that triggered a sell off of the Hyperions and as you can see by my signature, the ES is still what I use today. For my type of observing, and what I want from an EP, they just work better for me personally.

    Quote Originally Posted by evilfer View Post
    Hi, updated the spreadsheet with a couple more eyepieces. I'm thinking about getting the 8mm Hyperion Baader. Would you say it's a good companion to the 26mm? The others I'm considering are Meade 5000 Series HD-60 12mm, and Meade 5000 Series HD-60 9mm. Any idea on whether these EPs are good for a 10'' f/5 scope?

    Thank you,
    Eloy
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    ---------------------------------------------------------------------------
    Astro Sky 17.5 f/4.5 Dob || Apertura AD12 f/5 Dob || Zhumell Z10 f/4.9 Dob
    ES AR127 f/6.5 and ES ED80 f/6 on Twilight-II Mount
    ES 82° 24mm thru 4.7mm
    ---------------------------------------------------------------------------
    Astronomers: We look into the past to see our future.

 

 
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