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aperture and fuzzies im more confused than ever

icebergahed

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Moonshane

Moonshane

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aperture also makes the visible extent of objects larger so in fact the objects do appear to be magnified in the eyepiece. I agree that darker skies enhances this in all scopes though.

just look at the visible extent of photons gathered by an imaging rig which is an 'extreme version' of the eye.

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LukeSkywatcher

LukeSkywatcher

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aperture also makes the visible extent of objects larger so in fact the objects do appear to be magnified in the eyepiece

It does, but technically speaking aperture does not physically magnify objects.The brain seems them as magnified..............but the scope has not magnified them. Either way............yes i agree more aperture makes objects appear both bigger and brighter.

Brighter=bigger to the human brain.

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Naemeth

Naemeth

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It does, but technically speaking aperture does not physically magnify objects.The brain seems them as magnified..............but the scope has not magnified them. Either way............yes i agree more aperture makes objects appear both bigger and brighter.

Brighter=bigger to the human brain.

Aperture itself does not magnify objects, it is the increase in focal length that you usually get from an increase in aperture which increases the magnification with any given eyepiece. Unless the focal length is fixed, a larger aperture will always result in a higher magnification with any given eyepiece.

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John

John

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Heres the odd thing. On some deep sky objects, more magnification darkens the background sky and increases the contrast of the object. On other types of object higher magnifications seem to "see right through them" so to speak and lower magnifications produce better results. You almost have to take it object by object with each having their own quirks and responding to little ruses that experienced observers have developed to extract the most from them.

I'm a bit wary of generalised advice as sometimes you can be missing the best an object has to offer on a particular occasion by sticking to perceived wisdom and not trying something a little "wacky" now and then :smiley:

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LukeSkywatcher

LukeSkywatcher

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Heres the odd thing. On some deep sky objects, more magnification darkens the background sky and increases the contrast of the object. On other types of object higher magnifications seem to "see right through them" so to speak and lower magnifications produce better results. You almost have to take it object by object with each having their own quirks and responding to little ruses that experienced observers have developed to extract the most from them.

I'm a bit wary of generalised advice as sometimes you can be missing the best an object has to offer on a particular occasion by sticking to perceived wisdom and not trying something a little "wacky" now and then :smiley:

Ive found that with M42, a lower magnification (say a 25mm EP) is better then an 8-10mm EP. With a hig mag..............i miss it and "see right through it". A lower mag allows me to see and observe it.

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michael.h.f.wilkinson

michael.h.f.wilkinson

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aperture also makes the visible extent of objects larger so in fact the objects do appear to be magnified in the eyepiece

It does, but technically speaking aperture does not physically magnify objects.The brain seems them as magnified..............but the scope has not magnified them. Either way............yes i agree more aperture makes objects appear both bigger and brighter.

Brighter=bigger to the human brain.

Sorry, but that is not right. In fact, quite the reverse is true for fuzzies: a telescope can magnify the object, but it cannot make it look brighter. Put differently, without magnification, aperture is useless.

The telescope as a whole does create a real, measurable angular magnification of the object. To fit the light of a 6" aperture into a human pupil only 6mm across means you have to have an angular magnification of 25.4x or higher (because 1" = 25.4mm, so the scope has a 25.4x larger aperture than the pupil). If you do not provide magnification, no more light enters the eye. If the exit pupil of the scope (aperture divided by magnification) matches the observers pupil exactly, the surface brightness of the object is at most the same as with the unaided eye (which sounds weird, but it is true). The at most stems from the fact that there are losses in the optical pathway. Any lower magnification and the surface brightness does not change, visually, because the scope is now matched to e.g. a 10mm pupil, so most of the light is wasted (in scopes with big central obstruction, you actually get a light loss, and start seeing the secondary shadow).

As magnification is increased, the image becomes dimmer, and larger. Therefore, a scope only makes the image larger, but can only make it dimmer, or at best keep it equally bright, in terms of surface brightness. The ratio between background and object is also constant, so the question is why does increasing magnification help for some objects but not others? I think this lies in the inherent non-linear response of the visual system.

For unresolved objects, the situation is different. Here more aperture focuses more light into an increasingly smaller focal point, and more magnification suppresses the background while keeping the amount of light in the point source constant (until you start seeing the diffraction disk).

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Macavity

Macavity

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Feeling weak at the knees, after all that Dob wrangling? Can't get to a dark site? As ever, you could try Video Astronomy? Not as a replacement, but as an addition. But, looking at sketches of DSOs, I reckon my 8"/F4 Newt goes *some* way towards recreating the *general* visual experience of a 12"... 14"... Scope? On screen, without post processing! BUT an experience otherwise unavailable to me - And an immense... spur to my Astronomy generally. :)

Aside: Last night a sceptical Paxman was discussing the merits SEEING stuff first hand and "videoing" everything on smartphone... with techno-guru Dr Aleks Krotoski. Hmmm... No need to relate what Paxo thought? <G> But at least, unlike current events, you get to try both (more?) methods with the sky? Nothing is lost... as long as the clouds don't roll in meanwhile! :p

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bish

bish

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Feeling weak at the knees, after all that Dob wrangling? Can't get to a dark site? As ever, you could try Video Astronomy? Not as a replacement, but as an addition. But, looking at sketches of DSOs, I reckon my 8"/F4 Newt goes *some* way towards recreating the *general* visual experience of a 12"... 14"... Scope? On screen, without post processing! BUT an experience otherwise unavailable to me - And an immense... spur to my Astronomy generally. :)

Aside: Last night a sceptical Paxman was discussing the merits SEEING stuff first hand and "videoing" everything on smartphone... with techno-guru Dr Aleks Krotoski. Hmmm... No need to relate what Paxo thought? <G> But at least, unlike current events, you get to try both (more?) methods with the sky? Nothing is lost... as long as the clouds don't roll in meanwhile! :p

I've often thought of having a go at video astronomy. Not really investigated too much but guess it will involve some saving up.

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dick_dangerous

dick_dangerous

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Surely what you can see through a telescope is also determined by the state of your eyes - the number and distribution of rods on the retina and the state of your peripheral vision would have a huge effect on what you can detect. In a recent eye-test I astonished the optician with my peripheral vision. While my scope might be small, the light gathering powers of my eyes are really good. It's a shame the focuser is a bit shot...

DD

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