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Thread: Galaxy hunting magnifcation question

  1. #1
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    Default Galaxy hunting magnifcation question



    This is aimed mostly at the Dob owners in the room. I have an SCT but will be taking delivery very soon of a focal reducer. The reducer completely changes the dynamics of my magnification profiles.

    Normally I observe at about 80x when hunting for galaxies. Once found I start increasing magnification to try to suck any detail out of them. With the lower focal ratio what is your preferred magnification for hunting.

    Obviously as you decrease the magnification you improve the contrast up to a point. So I just looking for ideas where you find that point to be in your observing
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    Default Re: Galaxy hunting magnifcation question

    84x is typically my hunting power, usually serves as my initial observing power. From there I will employ 109x, 138x, and sometimes I'll push up to 173x. Very rarely I'll even go up to 227x.

    More often than not I'll simply use 84x and 138x. Hunter/killer.

    That's with a f/5 12" dob.
    Bryan

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    Default Re: Galaxy hunting magnifcation question

    Quote Originally Posted by bladekeeper View Post
    84x is typically my hunting power, usually serves as my initial observing power. From there I will employ 109x, 138x, and sometimes I'll push up to 173x. Very rarely I'll even go up to 227x.

    More often than not I'll simply use 84x and 138x. Hunter/killer.

    That's with a f/5 12" dob.
    That's interesting. So the magnification profile stays about the same. Funny I also refer to my 80x eyepiece as the hunter/killer
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    Default Re: Galaxy hunting magnifcation question

    From 45x (Z10) to 135x (Obsession). Actually my favorite magnification is the same as you guys - about 80x. I actually observed all of the Messier galaxies at 45x. The good thing about the ES eyepieces is the large apparent field of view. I find that with 80x the contrast is a bit better than at 45x, so you aren't just magnifying the skyglow.
    Michael
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    Default Re: Galaxy hunting magnifcation question

    I use the same as Bryan (but then, I also have an f/5 12" and the same eyepieces). I always try 84X to find it (hunter) first. But if I can't see anything, I'll put in the 138X (killer). Once I find it, I start getting silly with my eyepieces and barlows and try to see how much I can magnify it before it gets too dim to see well.

    But on the other hand, I've had a lot less success than Bryan with finding galaxies. His slightly better skies give him an edge. And his younger eyes. Yeah, I'm sure that's the reason.
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    Default Re: Galaxy hunting magnifcation question

    Hello MG,

    I prefer to take as a reference for the galaxies hunting the exit pupil of the eyepieces, as primary, and for some difficult objects the magnification as secondary.

    It looks like, that lots of people prefer for the galaxies hunting the range of the exit pupils 3mm up to 3.5mm in an ultrawide field, like 82°.
    Bryan's 84x magnification corresponds on his 12" Dob with the exit pupil of 3.6mm,
    the 47x magnification corresponds on my 6" refractor with the exit pupil of 3.2mm

    When looking for the details in the bright galaxies, I am using the high magnifications range of my scope, 75x - 125x,
    corresponding with the exit pupils in the range 2mm down to 1.2mm

    And as always, different observers will have different preferences.

    Best,

    JG
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    Default Re: Galaxy hunting magnifcation question

    Quote Originally Posted by j.gardavsky View Post
    Hello MG,

    I prefer to take as a reference for the galaxies hunting the exit pupil of the eyepieces, as primary, and for some difficult objects the magnification as secondary.
    I had been thinking about this as well. Fortunately I found a good place on the web to do the recalculations for my eyepieces. I just wasn't sure how well these calculations held up with field experience.
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    Default Re: Galaxy hunting magnifcation question

    I agree with JG about exit pupil being the only valid comparison, not magnification. You cannot compare 80X from an 8" f/10 scope to the 80X from a 12" f/5 system. Totally different beasts. The exit pupil is the only factor that can be compared, and you still have the aperture difference, so even this falls short.

    Don't forget, with the added focal reducer you are adding a whole bunch of glass elements to the optical train, and so reducing the transmission of light. You are much better off using a 2" diagonal and 2" eyepieces. Also, you won't achieve a wider TFOV with a focal reducer than what a 2" eyepiece will give you with an 8" SCT as the limiting factor becomes the bore in the primary mirror - you can't squeeze in more "sky" as the bore and baffle tube won't allow it. Focal reducers for SCT's are really best left for use with photo applications and not visual. Smarter use of eyepieces and making use of the 2" visual back rather than the standard 1.25" visual back will give you be highest amount of light transmission. Focal reducers for visual are not quite the same thing.

    Sorry, but I'm not going to gloss over the shortcomings of a device that is not being used appropriately. I had one of these f/6.3 focal reducers for my C8 - big mistake for visual. Swapped the visual back to accommodate a 2" diagonal and everything changed for the better.

    Alex.

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    Default Re: Galaxy hunting magnifcation question

    Hello all,

    Quote Originally Posted by mental4astro View Post
    ...
    Also, you won't achieve a wider TFOV with a focal reducer than what a 2" eyepiece will give you with an 8" SCT as the limiting factor becomes the bore in the primary mirror - you can't squeeze in more "sky" as the bore and baffle tube won't allow it. Focal reducers for SCT's are really best left for use with photo applications and not visual. Smarter use of eyepieces and making use of the 2" visual back rather than the standard 1.25" visual back will give you be highest amount of light transmission. Focal reducers for visual are not quite the same thing.
    ...
    Alex.
    This is a very important point, and it applies also up to one or another extent to the other mirror telescopes.
    This is the reason, why we take the refractors with the 3" focusers and 2" diagonals for the richiest field observations.

    Best,

    JG
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    Default Re: Galaxy hunting magnifcation question

    I'll use 28x to star hop, then I'll use 53x to see if I can detect it with that power and then finally 100x or 150x, depending on the size and faintness of the object. My final sketches are usually at 100x or 150x, but sometimes I'll stop at 53x if the galaxy is really big.

    And I'm using a 4.5" F/7.9 Newtonian.

 

 

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