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Thread: Is there a big difference between 225x and 250x?

  1. #1
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    Default Is there a big difference between 225x and 250x?



    Hi,

    Do you think there is a big difference between 225x and 250x when using a barlow? Especially to see planetary nebulae.

    Regards.

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    Default Re: Is there a big difference between 225x and 250x?

    It would depend on the size of the scope you are using and the atmospheric conditions at the time.
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    Default Re: Is there a big difference between 225x and 250x?

    Quote Originally Posted by caballerodiez91 View Post
    Hi,

    Do you think there is a big difference between 225x and 250x when using a barlow? Especially to see planetary nebulae.

    Regards.
    Hello Caballero Dietz,

    regarding the planetary nebulae, the difference won't be enough to decide to use a Barlow, or to switch between the EPs.

    The small bright planetary nebulae allow for extremely high magnifications in steps of 1.4x
    The visible details inside, if any, are often larger than the seeing blur and than the diffraction limits, and herewith opening the "door" towards the extremely high magnifications.

    A classic reference regarding the use of the extremely high magnifications is the sketch of the NGC 6572 planetary nebula in Ophiucus, made by Ronald Stoyan with a 120mm refractor at the incredibly high magnifications of 340x and 500x , see p. 253 - 354 in Ronald Stoyan: Deep Sky Reiseführer, Oculum Publishing 2000.
    These extremely high magnifications have allowed to see (and to sketch) the oval ring around the center star, and the outer glow in this 0.1arcmin small planetary nebula.
    So, the magnification requirements for the planetary nebulae are totally different from those for the planets.

    Best,

    JG
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    Default Re: Is there a big difference between 225x and 250x?

    Like JG I like to adhere to the 1.4x rule as meaningful steps in magnification. Since I don't observe planets much and stick to DSOs, that rule has served me well over the years as anything less really hasn't had a visual impact.
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    Default Re: Is there a big difference between 225x and 250x?

    Quote Originally Posted by caballerodiez91 View Post
    Hi,

    Do you think there is a big difference between 225x and 250x when using a barlow? Especially to see planetary nebulae.

    Regards.
    The difference between 225x and 250x is only ~10%, by eye the two would look about the same. I played quite a bit with EPs of similar focal length and I can definitely detect difference of ~20% in magnification. But to get visual impact you want 30%-50% depending on seeing conditions.

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    Default Re: Is there a big difference between 225x and 250x?

    No, I like having 40x to 50x steps as I move up to find highest power for the object viewed.
    Newtman but some refractors allowed.

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    Default Re: Is there a big difference between 225x and 250x?

    Quote Originally Posted by KT4HX View Post
    Like JG I like to adhere to the 1.4x rule as meaningful steps in magnification. Since I don't observe planets much and stick to DSOs, that rule has served me well over the years as anything less really hasn't had a visual impact.
    Alan, I might be a little slow today. It's been a long day of crunching numbers so simple stuff befuddles me. If I understand the 1.4x rule correctly, I would increase magnification by a factor of 1.4 to possibly see noticeable detail differences? Say 89x to 125x to 175x and so on?

    With my EP series a one step up in EPs yields about 1.3x and double step up yields 1.6x. I've been stepping using 1.6x.
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    Default Re: Is there a big difference between 225x and 250x?

    Quote Originally Posted by rickg18704 View Post
    Alan, I might be a little slow today. It's been a long day of crunching numbers so simple stuff befuddles me. If I understand the 1.4x rule correctly, I would increase magnification by a factor of 1.4 to possibly see noticeable detail differences? Say 89x to 125x to 175x and so on?

    With my EP series a one step up in EPs yields about 1.3x and double step up yields 1.6x. I've been stepping using 1.6x.
    You got it! Almost . Double step for 1.3x is 1.7x (1.3x1.3). 1.4x is a good rule of thumb, but I like to have more options, since sometimes 1.4x is not good enough but 1.96x (1.4x1.4) is too much. For that I try to populate my EP sets in 1.2x -1.3x steps, in particular in 1-3mm exit pupil range.

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    Default Re: Is there a big difference between 225x and 250x?

    Magnification steps: to each its own

    Well,
    there are differences if you are watching a planet, or if you go for the details in a nebula or galaxy.

    The details on the planets may require fine tuning of the magnification to get the best view, given the seeing conditions, the resolution of the optics, and the comfort zone of viewing - which differs from one observer to another.
    Here I take the Tele Vue Nagler 3mm - 6mm zoom, and make it fine.
    Of course, we can see a difference in magnification like 10% or 20% on the planets, otherwise we would need another hobby.

    The visibility of the details in the nebulae and in the galaxies requires the Minimum Detection Magnification (MDM), which is in simple words about to stretch the detail into an angular spread like 0.5° up to 1°, given the surface brightness and contrast of the detail to be viewed.
    As soon as the MDM on some detail to be viewed is achieved, more magnification does not help more, and when magnifying much more, the detail finally fades away, as the visibility/magnification ratio is slowly decreasing.
    So, the long read short end: here the 1.4x steps in magnifications are by far enough.
    That's also the reason, why the series of some fine EPs scale with the factor close to 1.4x, like the Pentax XW.

    Even if repeated, I hope this helps,

    JG
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    Default Re: Is there a big difference between 225x and 250x?

    Thank you for your answers!
    Regards.

 

 

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