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Significance of Aperture in Binoculars For Astronomy (8x25 vs 8x42)

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#1 Naraya

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Posted 12 May 2019 - 03:55 AM

Its been a long time since i've been in this here forum (because of 5 months of total clouds), but seasons are changing and lots of new adventures awaits!

 

Now i've been trying to find a new binocular to replace my old ones (soaked-->fungal growth +warranty ended)

and i've narrowed down to these 2 here:

 

Note: I chose roofs because i want these binos to stay with me for a long time ( i really do not wanna repeat my mistakes)

 

Celestron outland X 8x42:

https://www.amazon.c...op?ie=UTF8&th=1

 

 

Nikon Trailblazer 8x25:

https://www.bhphotov..._Binocular.html

 

A lot of you might be asking me why i picked the 8x25s for astronomy. It sounds kinda stupid but i do have a couple of reasons:

 

1) The amount of praise due it's quality:

https://www.outdoorg...blazer-8x25-atb

I've heard the clarity and durability of these binos are unmatched

 

 

2)The difference of limiting magnitude compared to the 8x42s:

From this cloudy nights article (read it, its really interesting), You can calculate the estimated limiting magnitude your binos can bring.

Using this I calculated that the difference of limiting magnitude between the two binoculars is about 0.6

 

TL:DR

I am asking you if that 0.6 limiting magnitude difference is substantial enough for me to pick the Celestron 8x42s over the (presumably) much higher quality of the Trailblazer 8x25s.

 

 

I also do a lot of outdoor exploration, so that might be important to this problem

 

Thanks


Edited by Naraya, 12 May 2019 - 05:31 AM.


#2 MartinPond

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Posted 12 May 2019 - 05:26 AM

There is a definite difference in terms of brightness.

It can be be quite helpful at night, and in the daytime,

it helps you follow critters into shadier places.

(that's birds and other animals, into the woods)

 

 

While higher, I'm not sure the Trailblazers are "much higher quality".

They are both models of pretty low price, and at that price level,

larger dimensions lead to a relatively higher quality image,

due to the same mechanical tolerances applied to a bigger set of parts.

7x50s are a prime example of high 'bang per buck', if you avoid junk

  (but are bulky, of course).

 

I have had several of the Nikon 8x25 ancestors.  They are excellent,

but they do prefer daylight, and aren't quite as pin-**** sharp at night

as an 8x42 or 7x50 of similar price..

(censoring is cute...hehe: p-i-n-p-r-i-c-k)


Edited by MartinPond, 12 May 2019 - 05:27 AM.

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#3 gfamily

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Posted 12 May 2019 - 05:39 AM

0.6 magnitude is quite a difference in  brightness.

 

I'm on a tablet,  so not able to do a thorough  analysis, but if you consider the 50 brightest stars, 46 of them are between 0 and 2.01 mag. 

But only 17 between  0 and 1.4 mag ( i.e. 0.6 mag less )

 

Expect a similar reduction in potential stellar targets at the lower end of the brightness scale, and I'd have thought even more effect on extended objects. 


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#4 TOMDEY

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Posted 12 May 2019 - 06:24 AM

To get the same brightness ratio, just get nice and dark-adapted, pleasant rural Milky Way arching overhead... Admire that, naked eye, and then put on Sun Glasses. And that is about the same as going to the smaller binos...    Tom


Edited by TOMDEY, 12 May 2019 - 06:25 AM.

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#5 ButterFly

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Posted 12 May 2019 - 06:25 AM

The number of stars added in any 0.6 mag range from added aperture depends heavily on your NELM - there are many more stars between 8.6 and 8.0 than there are between 7.6 and 7.0.  It is your skies that will really dictate which is the better option for you.

 

In the 25mm range, I use both Visionking 5x25s and Nikon Monarch 7 10x30s.  The 5x25s are great because of their enormous field of view.  They really prefer a dark site to work well.  High quality - they are not.  The high-quality 10x30s are my carry around pair becuase they are compact and light.  I bring them when I don't have anything in mind.  They work great on buildings and boats in the day, and are much better at fuzzies at night because of the added magnification.  They are not a preferred pair for nighttime observing though.

 

8x42s are the most versatile size.  If you can only get one pair of binos, they should be 8x42 and cost as much as you can afford.  They are my preferred nature size, doing well both inside forest at day and under skies at night.  If the light pollution is severe in your area, maybe 10x42s instead for the smaller exit pupil.

 

Tell us about your sky quality and intended outdoor use for a better opinion.


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#6 Naraya

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Posted 12 May 2019 - 06:36 AM

The number of stars added in any 0.6 mag range from added aperture depends heavily on your NELM - there are many more stars between 8.6 and 8.0 than there are between 7.6 and 7.0.  It is your skies that will really dictate which is the better option for you.

 

In the 25mm range, I use both Visionking 5x25s and Nikon Monarch 7 10x30s.  The 5x25s are great because of their enormous field of view.  They really prefer a dark site to work well.  High quality - they are not.  The high-quality 10x30s are my carry around pair becuase they are compact and light.  I bring them when I don't have anything in mind.  They work great on buildings and boats in the day, and are much better at fuzzies at night because of the added magnification.  They are not a preferred pair for nighttime observing though.

 

8x42s are the most versatile size.  If you can only get one pair of binos, they should be 8x42 and cost as much as you can afford.  They are my preferred nature size, doing well both inside forest at day and under skies at night.  If the light pollution is severe in your area, maybe 10x42s instead for the smaller exit pupil.

 

Tell us about your sky quality and intended outdoor use for a better opinion.

I live in about the worst place to be (level 7-8), which might be why i am considering high quality 8x25s (to make more use of the day time) 

But your advice is pretty solid, (to get the best 8x42s you can if you are in a tight budget)



#7 Naraya

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Posted 12 May 2019 - 06:40 AM

To get the same brightness ratio, just get nice and dark-adapted, pleasant rural Milky Way arching overhead... Admire that, naked eye, and then put on Sun Glasses. And that is about the same as going to the smaller binos...    Tom

Oof, that does sound... really bad



#8 Tony Flanders

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Posted 12 May 2019 - 06:53 AM

I've used 8x24 binoculars for astronomy a fair amount, because they're so portable. They work OK, but 8x42s are vastly better. The subjective difference is even greater than the numbers suggest. I only use the 8x24s for backpacking, where every ounce and cubic inch counts.

 

The actual difference between them is 1.2 magnitudes, not 0.6 magnitude. If you are comparing diameters, 42/24 = 1.75, which would indeed be 0.6 magnitude. But light-gathering scales as the area, not as the diameter. The ratio of the areas is 1.75 * 1.75 ~= 3.1, which is 1.2 magnitudes. (For those who understand logarithms, a simpler way to derive this is 0.6 * 2 = 1.2).


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#9 dd61999

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Posted 12 May 2019 - 07:17 AM

I carry 7x20 nikons for travel because they are small and compact. The views are also extremely sharp. But the level of detail I get with the 7x35 is higher. Looking at stars, not even a contest!

 

Not only can I see things in shadows a lot better, but overall brightness is brighter, I can see more craters on the moon at night, see more detail on rocks during the day. The only reason I carry the 7x20 is because the binoculars I typically use for astronomy are just to big to carry when I’m on the go. Even 7x35 or 8x32


Edited by dd61999, 12 May 2019 - 07:18 AM.


#10 harbinjer

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Posted 12 May 2019 - 09:40 PM

. The subjective difference is even greater than the numbers suggest.

 

The actual difference between them is 1.2 magnitudes.

Yes, this subjective difference will be much bigger than numbers suggest.  Also, if you can save up for the Nature DX 8x42, that will be a worthwhile improvement over the Outland.



#11 Thphy

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Posted 12 May 2019 - 10:29 PM

I’m posting this because of relevance:

I have a pair of 25x100 Oberwerk binoculars and I recently bought a pair of 20x110 Oberwerk binoculars and before I purchased the 20x110’s I asked Kevin if there was a significant difference in upgrading from the 100’s to 110’s and his answer pushed me to buy. Since the 25x100’s are actually 25x95 because of the prisms, the 110 Ultras use all 110mm and there is a 37% increase in light.

I compared the two this evening on three objects: the Eskimo, M3, and M81/82. Yes the view was 5x more on the 100’s but the view was much darker. All three objects were easily/visually twice as bright in appearance with my 20x110’s and the moon is out...

So to best answer your question, yes more aperture will make the objects brighter. 25mm to 42mm is a big jump. 35% to be exact. Roughly the same as how my binoculars perform. Provided that these binoculars you are asking about are using the full aperture through the prisms inside.

Here is what Kevin said:

The formula is radius squared times pi. So the radius of the 25x100 (operating at 95mm) is 47.5. Squared and times pi, surface area is 7084mm's. The radius of the 20x110 (operating at 110mm) is 55. Squared and times pi, it's 9499mm. That's a 34% increase over 7084mm.

My calculations show a 75% increase instead of 34%. I’m dividing the smaller number into the larger to get the percentage.. is that correct? Been too long since I’ve calculated light grasp percentages.

Todd

Edited by Thphy, 12 May 2019 - 11:15 PM.

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#12 TOMDEY

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Posted 12 May 2019 - 10:39 PM

Well, think of this as the objective lenses and their light gathering areas >>>    Tom

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  • 56 LIGHT GATHERING DIFFERENCE.jpg

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#13 TOMDEY

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Posted 12 May 2019 - 10:56 PM

Full disclosure:

 

I have and use all of these for astronomy: >>>

 

Zeiss   8x20 (carry around is shirt pocket for casual use - always ready)

Zeiss 10x25 (carry around is shirt pocket for casual use - always ready)

Zeiss   7x42 (scanning star fields for more dedicated observing)    Tom

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#14 SECTOR 001

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Posted 12 May 2019 - 11:06 PM

To get the same brightness ratio, just get nice and dark-adapted, pleasant rural Milky Way arching overhead... Admire that, naked eye, and then put on Sun Glasses. And that is about the same as going to the smaller binos...    Tom

 

 

I've used 8x24 binoculars for astronomy a fair amount, because they're so portable. They work OK, but 8x42s are vastly better. The subjective difference is even greater than the numbers suggest. I only use the 8x24s for backpacking, where every ounce and cubic inch counts.

 

The actual difference between them is 1.2 magnitudes, not 0.6 magnitude. If you are comparing diameters, 42/24 = 1.75, which would indeed be 0.6 magnitude. But light-gathering scales as the area, not as the diameter. The ratio of the areas is 1.75 * 1.75 ~= 3.1, which is 1.2 magnitudes. (For those who understand logarithms, a simpler way to derive this is 0.6 * 2 = 1.2).

Better make that welding goggles!!!



#15 Crusty99

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Posted 13 May 2019 - 12:08 AM

7x50s are a prime example of high 'bang per buck'

 

 

I agree. 



#16 Erik Bakker

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Posted 13 May 2019 - 01:45 AM

[....]

 

Note: I chose roofs because i want these binos to stay with me for a long time ( i really do not wanna repeat my mistakes)

 

Celestron outland X 8x42:

https://www.amazon.c...op?ie=UTF8&th=1

 

 

Nikon Trailblazer 8x25:

https://www.bhphotov..._Binocular.html

 

A lot of you might be asking me why i picked the 8x25s for astronomy. It sounds kinda stupid but i do have a couple of reasons:

 

1) The amount of praise due it's quality:

https://www.outdoorg...blazer-8x25-atb

I've heard the clarity and durability of these binos are unmatched

 

 

2)The difference of limiting magnitude compared to the 8x42s:

From this cloudy nights article (read it, its really interesting), You can calculate the estimated limiting magnitude your binos can bring.

Using this I calculated that the difference of limiting magnitude between the two binoculars is about 0.6

 

[....]

 

I am asking you if that 0.6 limiting magnitude difference is substantial enough for me to pick the Celestron 8x42s over the (presumably) much higher quality of the Trailblazer 8x25s.

 

 

I also do a lot of outdoor exploration, so that might be important to this problem

 

Thanks

25 vs 42 mm makes a big difference for astronomical observations,.

 

Quality wise, you may need to spend a bit more money to get something good that will last you a long time. No one can manufacture such an instrument of 42mm new for $60. And even the small 25mm need  more than that to reach a good and consistent quality standard.

 

So you are looking for in instrument that:

 

-stays with you for a long time, even if doing a lot of outdoor exploration (moist, ruggedness?)

-is bright enough for good astronomy use

-is of good quality

 

I am sure there are some good instruments fitting that description available for a reasonable amount of money.

 

Be prepared to go for a nice 42mm that will do all of that. And set your financial limits accordingly. A few hundred dollars should get you an instrument that suits your requirements.


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#17 Jon Isaacs

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Posted 13 May 2019 - 03:55 AM

My calculations show a 75% increase instead of 34%. I’m dividing the smaller number into the larger to get the percentage.. is that correct? Been too long since I’ve calculated light grasp percentages.

 

 

Todd:

 

In terms of light gathering,  one can think in terms of the ratio of the diameters squared,  it's the same as the ratio of areas.  That is 34%.

 

And stars will be 34% brighter.  The brightness of extended objects like nebulae and galaxies depends on the area of the exit pupil.  Less magnification means the object is smaller,  the light is more concentrated,  brighter. 

 

Exit pupil = 95mm/25 = 3.8 mm

 

Exit pupil = 110mm/20 = 5.5mm

 

Brightness ratio = (5.5mm/3.8mm)2 = 2.1 times brighter. 

 

So , galaxies and nebulae are 2.1 times brighter but only 80% the diameter and only cover 64% of the area.  The sky is also 2.1 times brighter so the contrast is unchanged. 

 

Which is more effective depends on the object,  small and bright is probably better seen in the 25x95s. Large and dim , better in the 20x 110s .

 

Jon


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#18 edwincjones

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Posted 13 May 2019 - 04:49 AM

I carry 7x20 nikons for travel because they are small and compact. The views are also extremely sharp. But the level of detail I get with the 7x35 is higher. Looking at stars, not even a contest!

 

Not only can I see things in shadows a lot better, but overall brightness is brighter, I can see more craters on the moon at night, see more detail on rocks during the day. The only reason I carry the 7x20 is because the binoculars I typically use for astronomy are just to big to carry when I’m on the go. Even 7x35 or 8x32

Agree- the purpose of  compact binoculars is to have available when one does not expect to observe,

but not as one's primary pair.

If one is hiking, or working in the garden, the compacts are good to have "just in case",

but if birding, or viewing the night sky, then the larger "see more".

 

My suggestion is to get the one you will use the most first, then the other later if still needed.

 

edj


Edited by edwincjones, 13 May 2019 - 04:50 AM.

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#19 Naraya

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Posted 13 May 2019 - 05:06 AM

So it seems like spending as much money on 8x42s would be the best choice for me huh?

 

 

Yes, this subjective difference will be much bigger than numbers suggest.  Also, if you can save up for the Nature DX 8x42, that will be a worthwhile improvement over the Outland.

 

I did figure out that getting the Nature DXs would be the best choice for me, it is right on the maximum of my budget, and would be a lifetime-binoculars, but when looking at the shipping price to Indonesia it totaled to 37$ bawling.gif  

 

So i'll definitely get the Outland Xs unless some website has better shipping costs, or maybe there are some other binoculars i should look into

 

Thanks, clear skies

 

Naraya


Edited by Naraya, 13 May 2019 - 05:06 AM.


#20 Erik Bakker

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Posted 13 May 2019 - 07:00 AM

For lifetime binoculars to enjoy, it would be hard for the Outland X's to qualify. Consider to spend at least around US $120 on binoculars if you want them to last a bit, though it takes much more money than that to make them qualify for all your needs.



#21 Naraya

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Posted 13 May 2019 - 09:11 AM

GUYS, major game-changer here, it turns out that if I ship the item to Singapore, then have a family member bring it back (it works out dont worry)  the shipping costs will total to 10$!!whee.gif . Now that raises the Budget to 120 USD!!

 

*ahem*

Anyways, i'm now thinking about getting the Celestron nature DXs since they are so widely recommended. Unless perhaps there are any other binoculars that cost 120 USD, i am also still primarily focusing on durability, but most importantly warranty, so that would be nice.

 

I think the contenders would be:

The Nature DXs

https://www.amazon.c...TVYB3SSJSCTE943

 

Nikon Prostaff 3s

https://www.amazon.c...gateway&sr=8-10

 

Meade Rainforest Pro:

https://www.amazon.c...FQ3RJ3FGC5KZ2M2

 

 

Let me know what you guys think!



#22 gfamily

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Posted 13 May 2019 - 09:58 AM

Just be advised that warranties are often specific to countries, so shipping from US to Singapore and then having it privately imported into Indonesia may make resolving warranty issues complicated. 

 

If warranty is the most important focus, then you need to confirm that Celestron have world wide warranty arrangements. 



#23 Erik Bakker

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Posted 13 May 2019 - 10:30 AM

Out of those 3, the Celestron or Nikon. 

 

For me personally, my Nikon's turned out to be better than I expected.

 

If possible, trying them for yourself would be great, since binoculars are a bit like shoes. But either would hopefully show you better images than the instrument they replace.



#24 Jon Isaacs

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Posted 13 May 2019 - 10:30 AM

Just be advised that warranties are often specific to countries, so shipping from US to Singapore and then having it privately imported into Indonesia may make resolving warranty issues complicated. 

 

If warranty is the most important focus, then you need to confirm that Celestron have world wide warranty arrangements. 

 

:waytogo:

In the US, the fine print in the Celestron warranty says that collimation and alignment issues must be reported within 30 days of purchase...  

As far as I'm concerned, that's a deal breaker.

Jon

 


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#25 Naraya

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Posted 14 May 2019 - 04:59 AM

waytogo.gif

In the US, the fine print in the Celestron warranty says that collimation and alignment issues must be reported within 30 days of purchase...  

As far as I'm concerned, that's a deal breaker.

Jon

 

hmm, that might be a problem but then again it'll arrive at my house in max 7 days (if shipping is really that fast)




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