Bins v scope - stupid question alert!

[F1Bird]

Just got a lovely shiny new set of binoculars for my birthday (Olympus 10x50 DPS I) and have been enjoying the view. I also have a Celestron 114 EQ scope and am a little baffled by the difference in view. I am 100% certain that this is a ridiculous question but hey, what the hell! When I look through the bins I can see thousands of stars in the field of view compared to the 10 or 15 I can see with the naked eye - its truly amazing! I understand that the field of view of the bins is larger than that of my scope but what I cant quite get my head around is why, considering the scope is so much more powerful (if that is the right word) than the bins, when I look through the scope 8 times out of 10 there are no stars whatsoever in the field of view?! Surely as the scope is more powerful it will be able to see even more stars than the bins and so surely at least a few should always be in view? And yes, I have taken the cover off the OTA and the eyepiece!

[Pete Presland]

i cant do the maths regarding difference in the size of the field of view they both give, but i do know that the binoculars field with be massive compared to the telescope. look through the scope at the moon and then look through the bino's you will see what i mean. also you will know whether the scope is focussing correctly

[Alien 13]

I always think looking through a telescope is like like peering through a letterbox, binoculars open the  door..

[bingevader]

Or bog roll!

But you're right, it's field of view compared to power/magnification and it's not a stupid question.

An exaggerated comparison would be to imagine looking at a page in a book with your eye or a microscope.

The eye sees hundreds of words and thousands of letters, the microscope lets you see the detail of the individual letters or if you are unlucky, the gaps in between.

Neither is wrong or better.

Maybe a better analogy would be a flower; how beautiful in it's entirety, but how amazing to see detail of individual cells!

Cheers

[frugal]

We have a 114eq as well. The one thing I have found is that the focussing is very twitchy. It seems to go from focused too far to focussed to near in just a slight turn of the focuser. This will also mean that most of the fainter stars will not show up at all unless you have it perfectly focused.

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[ollypenrice]

It's just field of view. The scope will be picking up stars not visible in the bins but it's looking at a fraction of the sky.

Olly

[ronin]

As already pointed out the binoculars have a bigger field of view.

The binoculars have a view of 6.5 degrees, if you put a 10mm in your scope I am guessing that you get something around 0.5 degree. So you have an angular view of 13x more. You will be seeing something like 170x as much sky so can expect that many more stars in view.

Additionally at 10x the stars will be small but brighter, since in all cases small is a point you in effect get a brighter point. In the scope the magnification pushes many of the dimmer stars below the threshold of your eye's to "see" them.

Depending on the set up and performance of the scope some stars may be lost if they are not focussed well.

Binoculars are good for viewing as you have found, however before you go selling the scope Jupiter, Saturn etc will remain small disks, whereas in a scope you see bands and rings.

They complimenmt each other well, but one is not a replacement for the other.

[F1Bird]

Thanks everyone, this makes more sense now! And don't worry Ronin, I have no intention of selling the scope! As you say I had hoped they would complement each other. I wouldn't trade the view of Saturn's rings through it for anything! Except perhaps a bigger scope.....

[Naemeth]

Thanks everyone, this makes more sense now! And don't worry Ronin, I have no intention of selling the scope! As you say I had hoped they would complement each other. I wouldn't trade the view of Saturn's rings through it for anything! Except perhaps a bigger scope.....

Speaking of, perhaps this would be a good upgrade:

http://telescopeoutlet.co.uk/index.php/telescopes/sky-watcher-skyliner-200p-dobsonian-telescope.html

[Sir-Henry]

Boy oh boy. Am I tempted or what? Sadly my 'refinancing' hasn't come through yet and my overdraft is giving off a serious glow that is more orange than merely red! Still, such bargains are like buses ... there'll be another one along in a minute or two

[Mr Q]

  One more point worth noting is the fact that when using bins, we use both eyes and in doing so, the effect is like looking through two binocular sections at the same time - the effect of doubling our eye sensitivity for faint stars compared to just one ocular as when using a scope. A small point but it adds to the effect you notice when comparing bin's views with a scope's view.

[Charic]

+1 Mr Q & ronin........... also, as you increase magnification the image field is reduced compared to the width offered by the binoculars, and when  you double magnification, you lose 4 times the light (Inverse square law) so the image through the telescope, is narrower and darker in comparison. The telescope offers the magnification all be it very tight on target, but the binoculars offer panoramic vista views. So you need both as already stated.  Enjoy!

Wooohooo! I can edit now! 

[Okeydokey]

Congratulations on the editing function Charic!

I had a deep and meaningful discussion with my better half about which she thought was better Bins v Scope.  The answer was elegantly simple, the best scope is the one you use, which in all honesty is in my case categorically the bins.  I pop out whenever there is a break in the clouds, front and back of the house without hesitation, monopod will be my next investment  and I can't see me going beyond the 10x50's for all the reasons stated above. 

I think Maslow understands my point well enough  http://www.simplypsychology.org/maslow.html

[Charic]

............lost me there on that one 

[Alien 13]

I have often wondered with visual observing if there is a sweet spot, imagine you have a perfect dark sky then what you see with your eyes would take some beating add binoculars more light but you loose the full sky a telescope moves you into the detail but is dimmer ( maybe dimmer is the wrong word but i hope you know what i mean) overall. I would personally have the 1st option but would like an eye upgrade to see mag 11 objects.

[michael.h.f.wilkinson]

Magnification does NOT dim stars until you magnify so much the Airy disk is resolved. A point source remains a point source, until you go into silly magnification. If I use my C8 with a Nagler 31T5 at 1.25 deg FOV, that gives me loads of stars in the FOV. Two factors which are important are aperture, true FOV, and the fact that binoculars have twice the amount of light gathering capacity per mm of linear aperture.

The distance from which a star can be seen doubles when you double the aperture of your scope. So assuming a more-or-less uniform random distribution of stars a single 50mm sees half the distance into this field. However, the volume you scan scales with the distance cubed. This implies seeing twice as far means seeing 8x the number of stars. This suggests the scope should win hands down, but it is not the whole story.

Now put the field of view into the equation. Assume both scopes work at the same focal ratio, and use the same eyepiece.  In this case a scope twice the diameter has a 4x smaller true FOV, so sees 4x fewer stars. Combined with the 8x more through distance, it should see twice the number of stars. So what is wrong?

What is wrong is that we do not take into account the differences in focal ratio and EPs. The Newtonian works at roughly F/8.8, not F/4 or F/5 which is usual for binocular. Comparing the 10x50 bins to the 114mm scope at the same exit pupil, we need 22.8x magnification, or a 44mm EP as the 114EQ has 1000mm focal length. The bins have 65 degree apparent FOV, which for a 44mm EP means you must use a 2" barrel. The binoculars get away with a 20mm super-wide angle (assuming F/4 optics or F=200mm). If we use that EP in the Newtonian, the area of sky in the FOV is (200/1000)² or 1/25th of the size, i.e. showing 25x fewer stars. Even when combined with 11.8x larger distance you will see 0.474x the number of stars.

Now add the fact that you usually get Plossls, with only 50 deg apparent FOV, not the SWA 65-70 deg. This further reduces the ratio to 0.28 (or 3.56x more stars in the binoculars). Finally, the bins gather 2x the amount of light for a given aperture, reaching out 1.4x further into space, gathering a 2.83x more stars than a single scope of the same objective diameter. This adds up to 10x more stars in a single FOV.

If you ever get to use a 100mm scope with 2" EPs like my 31T5, you will ba astonished at how many stars are added. In my 80mm with 31T5 at 82 deg apparent FOV and 5.3 deg true FOV, the number of stars is just amazing.