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Sweep

45mm Masuyama eyepiece usage

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Hi

I am a beginner and need some useful advice.

Looking at a Masuyama 45mm eyepiece, however with only a resulting 20 x magnification  for my 130mm refractor, I think it would not be used  much at such low magnification (binoculars territory)

Just got an es 30mm 82 degree with a magnification  of 31 degrees which should I think cover my low magnification widefield  needs?

Any seasoned advice would be most helpful thanks.

 

 

 

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If you want good low power / wide field eyepiece, there are couple of things to keep in mind:

- with low magnification, you will get larger exit pupil. Depending on your age, larger exit pupil might be wasted. Young people have pupils that will dilate to 7mm or there about, but with older age that becomes less (6mm, then 5mm, ...). If exit pupil of eyepiece is more than this - light is wasted and you get what is effectively setup with smaller aperture (less light grasp).

Keep exit pupil up to 5mm or so

- sky brightness. Again with small magnification light from sky background is less spread around and sky is brighter (just use any higher power eyepiece and you will see how sky turns black rather quickly compared to medium/low power eyepiece). If you live/observe in areas with light pollution - again higher magnification is preferable.

- with some long focal length eyepieces, eye relief can be too much - this can mean that eye positioning is not easy and can cause blackouts and other artifacts.

- true field of view is limited by barrel diameter. This means that eyepiece with 45mm focal length and one with 30mm focal length can happen to show you same amount of sky if 30mm eyepiece is wide field (wide enough). To establish differences you need to use tools that are available like https://astronomy.tools/calculators/field_of_view/

image.png.9d31d17b13b33c4c67d109e26daab1a8.png

Here is comparison between the two eyepieces in 130mm F/7 scope (I guess you have something similar).

- 30mm ES 82 will have smaller exit pupil at 4.3mm - you are safe with exit pupil size regardless of age, while Masuyama 45mm gives 6.43mm - not as good if you are older

- 30mm ES 82 will give x30 magnification vs x20 of Masuyama 45mm - darker sky background and better contrast

- 30mm ES has 22mm eye relief - and M 45mm has 32mm - I think you are safe with both there (maybe 32mm will be too much for someone).

- 30mm ES 82 will sport a bit wider true field of view - it will show same or even larger extent of sky, so you are no loosing anything there.

Only thing that I personally don't like about 30mm ES82 would be the fact that it weighs at 1Kg - that is just massive EP :D - I'm quite happy with my ES68 28mm for wide field needs.

 

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I think you're right in that the 45mm would be used only on rare occasions. I've found that 40mm and over brightens the sky background reducing contrast, so personally I tend to avoid these focal lengths. Currently my longest focal length eyepiece is a 35mm Pseudo Masuyama in the form of the 35mm Baader Eudiascopic. It's clarity and sharpness is excellent, but it isn't wide field. Having said that, it shows a decent chunk of sky. It's also only 1.25" fit.

59a659c0825e5_2017-08-3007_23_51.jpg.f5ffbc2a04e82f214ba087efdc7dff00.jpg.b5b6a8fb917e3a5754918af61b2ac49a.jpg

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The Masuyama 45mm eyepiece (53º AFoV) will show less sky than the 82º Series ExSc eyepiece as Vlaiv's illustration clearly shows above, therefore I cannot see the point of pursuing it any further, esp. with the exit pupil equation taken into account.   The 30mm ExSc eyepiece is a superb piece of equipment so my advice is to stick with that, you cannot improve on it.

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The only use for the 45mm over the 30mm that I can think of would be in conjunction with a nebula filter.  The lower power and larger exit pupil will lead to a higher surface brightness of the object's nebulosity, but at a smaller image scale.  Without the nebula filter, sky glow would dominate in the 45mm negating any possible advantage.  With the nebula filter in place, much of the sky glow would be eliminated leaving only the brighter nebulosity.

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Hi Louis That is what I had exactly in mind.

I have a 2’ OIII filer which may help with fainter detailing on nebulas which the Masuyama is renowned for!

I know the field of view is not improved upon , but was hoping to find out from more experienced  observers if this option of 21x magnification  with a nebula filter had any advantages on Dso”s that suited this lower magnification with OIII filter

Are there any recommended dso’s targets at 21 x  that experienced observers view quite regularly?

I reside in a rural area bortle 4 sky mag 21.39.

Also hoping the Masuyama  45mm will bring additional contrast on axis to the viewing experience, compared to the es 30mm .

 

 

 

 

 

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5 hours ago, Sweep said:

Are there any recommended dso’s targets at 21 x  that experienced observers view quite regularly?

Perhaps the North American nebula?  You'd need it to be large, otherwise it will be hard to pick out details at such a low magnification.

I just remembered the Veil Nebula for another possible target at low power.  As a whole, it is quite large in angular diameter at about 3 degrees.

Edited by Louis D
Remembered another large nebula
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Hi 

I wanted to try a Masuyama eyepiece and was trying to conclude if the 45mm was a viable option, on reflection it would seem an overkill having purchased an es 30mm 82.

21x mag and slightly smaller FOV just did make sense, although I think a lot of people feel the same when buying eyepieces.

So what did I do??

I went through what I now have a 4mm Wo uwan, 7mm Delite, 12mm es 92 ,17es92, 30mm es 82 and bought the only conceivable size to justifying buying a Masuyama so purchased the 10mm Masuyama.

Just had to, too tempting!!!!

Hope its worth it!!

Its Friday and payday.

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