$35 Binoculars Vs. $65 Binoculars

[refractordude]

Why are my Celestron Cometron 7x50 better than my Celestron Skymaster 15x70? I just returned the 3rd pair of Skymasters to Amazon. I give up on Celestron, and just ordered the Oberwerk LW 15x70.

https://www.amazon.com/Celestron-71198-Cometron-Binoculars-Black/dp/B00DV6SI3Q/ref=sr_1_1?ie=UTF8&qid=1534707466&sr=8-1&keywords=cometron+7x50&dpID=31zPva1weyL&preST=_SX300_QL70_&dpSrc=srch

[John]

In what way are your 7x50 Celestrons better than the 15x70's ?

I've had a couple of pairs of the 15x70 Celestrons and they have been pretty good for their price.

The 7x50's will be much easier to hand hold of course.

[Charic]

49 minutes ago, refractordude said:

Why are my Celestron Cometron 7x50 better than my Celestron Skymaster 15x70?

Their lighter, easier to hold, they'll have a wider field of view, the image will be brighter, possibly sharper, unless there's another issue your not content with?

I like the  newer brand you've chosen, I'd like to try their 15x70 Ultras.

My Helios 8x40's feel and appear to better than my 15x70 Revelations for the same reasons I've already quoted, but then some 15x70s are just better, which is why I'd like to try the Ultra.

John has already asked! ........what is it your not liking about the 15x70's and why do you feel the 7x50's are  much better?

[Ruud]

Dude, you now have three pairs of Skymaster returned , a Celestron 20x80 and a Gosky 20x80! (The last two I remember from your post here: https://stargazerslounge.com/topic/318655-do-you-own-these-binoculars/?tab=comments#comment-3485266).

The Oberwerk LW 15x70 is again, at best, only half decent.  

The Oberwerk Ultra is the BA8 clone we mentioned to you in the link above. We know them and find them very good. Mind that they will be less expensive from most other brands that sell BA8 models.

 

 

[DarkTraveller]

I've had a BA8 15x70 for about 7 years now.  Mine are the Garrett branding.  They're very nice instruments and give a great view but they're heavy. Occasionally I'll use them handheld when seated in a reclining camp chair but prefer them on a geared tripod with a fluid head. I use the Farsight mounting system with a red dot finder.

Ted

[LukeSkywatcher]

I have:

20x90, 10x50, 8x30( sunoculars) and 2.1x42 wide field. I love the 2.1 bins. Really wide field and weigh next to nothing. 

[refractordude]

21 hours ago, Ruud said:

Dude, you now have three pairs of Skymaster returned , a Celestron 20x80 and a Gosky 20x80! (The last two I remember from your post here: https://stargazerslounge.com/topic/318655-do-you-own-these-binoculars/?tab=comments#comment-3485266).

The Oberwerk LW 15x70 is again, at best, only half decent.  

The Oberwerk Ultra is the BA8 clone we mentioned to you in the link above. We know them and find them very good. Mind that they will be less expensive from most other brands that sell BA8 models.

 

 

Some people love thier Celestron Skymasters. I have the Celestron 7x50 Cometron binoculars, which are great. If Amazon is going to pay for return shipping, why not try out a few pair. Dude, money does not grow on trees. I don't buy things because other people have them. I buy what I can afford. The Oberwerk 15x70 are highly regarded by a lot of people. Much later in 2019, I will purchase a pair of high end 25x100 binoculars, maybe. However, thanks for your reply and concern.

[John]

1 hour ago, refractordude said:

Some people love thier Celestron Skymasters. I have the Celestron 7x50 Cometron binoculars, which are great. If Amazon is going to pay for return shipping, why not try out a few pair. Dude, money does not grow on trees. I don't buy things because other people have them. I buy what I can afford. The Oberwerk 15x70 are highly regarded by a lot of people. Much later in 2019, I will purchase a pair of high end 25x100 binoculars, maybe. However, thanks for your reply and concern.

Was there anything actually wrong with the 15x70 Celestron Astromasters that you returned or was it that you just preferred the smaller and lighter 7x50 Cometrons ?

I'm asking because you started the thread with a question about why the 7x50's were better so I'm trying to quantify what the differences were

[Charic]

1 hour ago, refractordude said:

The Oberwerk 15x70 are highly regarded by a lot of people

Oberwerk produce  at least two 15x70's, LW & Ultra!

The LW's are very much like the Skymasters, probably having  a  much similar  quality  and feel to the final image , although their supposed to have a tad better coating on their glass.

You'll pay substantially more for the Ultra 15x70 variant, and I think its these that are highly regarded, based on their performance.

[refractordude]

2 hours ago, John said:

Was there anything actually wrong with the 15x70 Celestron Astromasters that you returned or was it that you just preferred the smaller and lighter 7x50 Cometrons ?

I'm asking because you started the thread with a question about why the 7x50's were better so I'm trying to quantify what the differences were

The weight is not an issue. I have them on a very sturdy tripod. Virtually no false color on the moon with the Celestron Cometron 7x50.  The Cometron has a wider fov than the Skymaster 15x70, but far less edge distortion. The clarity with the Cometron is far superior, even more so than my Meade 120mm f/8 achro. The reviews at Amazon USA is 66 percent 5 stars and 19 percent 4 stars. I give them 10 stars for what I have at the price I paid for them.

[Ruud]

The larger the exit pupil, the higher the surface brightness gets.

• The exit pupil of a 7x50 is 7.1 mm,
  that of a 15x70 is 4.7 mm.
• For an f/8 telescope to have an exit pupil as big as 7x50 binoculars,
  the eyepiece needs to be 57.1 mm focal length.
• For an 120 mm aperture to give an exit pupil as big as 7x50 binoculars,
  the magnification must be 16.8 times.

Try it: compare the 7x50 binoculars to your 120mm telescope at 16.8x . They will show equal surfaces equally bright.

Bear in mind: once the exit pupil gets as big  as your own pupil, the image reaches its maximum surface brightness. Bigger exit pupils will not result in brighter surfaces.

Formulas for exit pupil in mm:

(exit pupil in mm) = (aperture in mm) / (magnification)
                             = (eyepiece focal length in mm) / (f-ratio of telescope)

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Larger aperture will show fainter stars.

The magnitude gain of a lens with diameter D1 compared to a lens with diameter D2  is:

    Magnitude gain = 5*log(D1 / D2).

If you compare D1=70 mm with D2=50 mm you get a magnitude gain of 5*log(70/50) = 0.75 magnitudes. A 70 mm lens can show stars that are 0.75 magnitudes fainter than the faintest stars you can see using a 50 mm diameter lens.
A 120 mm lens compared to a 50 mm lens gives a magnitude gain of: 5*log(120/50) = 1.9 magnitudes

A 50 mm lens compared to a 7 mm pupil gives a magnitude gain of 5*log( 50/7) = 4.3 magnitudes
A 120 mm lens compared to a 7 mm pupil gives a magnitude gain of 5*log(120/7) = 6.2 magnitudes

If you can see magnitude 6 stars with the naked eye, 
then through a 120 mm telescope you can see magnitude 6 + 6.2 = magnitude 12.2 stars.

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So, to know what surface brightnesses to expect use the exit pupil,
and to know how which the faintest stars are that you can see use the 5*log(Daperture/Dpupil) relation.

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another point: the price of optics does not scale linearly with the diameter. For instance: the surface of  a lens is proportional  to the square of its diameter, and the volume of objects increases with the cube of the scale. With quality optics, unfortunately, price increases exponentially with the diameter.