Minimum Aperture Rule

[sabana]

This is another one of those statements thats a bit baffling to me. Apparently there is a minimum aperture for viewing any object in space. Is this really true? That is you need say a minimum aperture of 8" to view DSO. Or anything else further away. Is this a hard and fasted rule?

The other thing in line of this statement is after reading the introduction to Turn left at Orion (New Spiral bound ed.). It states that

"Galileo...observed and recorded the position of neptune through a 1" aperture telescope and

"Charles Messier who found the hundred deep-sky objects in the catalog that bears his name started out with a 7" reflector with metal mirrors so poor that according to one account it was not much better than a modern 3" telescope.

So drawing on this knowedge, is the minimum aperture rule just a generalization? And is it indeed possible to observe most of what we know with a 3" refractor.

Thanks all:)

[Miktor]

Take into account, that those astronomers back then didn't have to deal with light pollution. Apart from that, I've been wondering myself.

[Scosmico]

There was not light polution!

This is another one of those statements thats a bit baffling to me. Apparently there is a minimum aperture for viewing any object in space. Is this really true? That is you need say a minimum aperture of 8" to view DSO. Or anything else further away. Is this a hard and fasted rule?

The other thing in line of this statement is after reading the introduction to Turn left at Orion (New Spiral bound ed.). It states that

"Galileo...observed and recorded the position of neptune through a 1" aperture telescope and

"Charles Messier who found the hundred deep-sky objects in the catalog that bears his name started out with a 7" reflector with metal mirrors so poor that according to one account it was not much better than a modern 3" telescope.

So drawing on this knowedge, is the minimum aperture rule just a generalization? And is it indeed possible to observe most of what we know with a 3" refractor.

Thanks all:)

[Sparrow]

Generalisation is the word here.

I think the most important factor is viewing conditions. Clarity of the sky/light pollution. I don't do much visual work - mostly do photography, but I know that I've managed to see Andromeda (M31) through my 88mm refractor easily. With some of the fainter DSOs, if they are being washed out by sky glow or light pollution, they are going to be extremely hard to see, whereas on a good dark viewing sight with good clarity, they are going to be much more visible.

There is no doubt that an 8" reflector will help with its extra light gathering abilities, but smaller scopes will still offer views when conditions are right.

Regards

John

[sabana]

So 8" is a just a ball park figure but you may just be as successful with a 3" aperture given the right conditions?

Is the 8" rule/comment aimed at people living in light polluted areas?

[MjrTom]

So 8" is a just a ball park figure but you may just be as successful with a 3" aperture given the right conditions?

OK you wont see it in as much detail as you would in the bigger scope.

For planetary viewing there is merit in the smaller scope in that its looking through less of our turbulent atmosphere giving it a slight advantage.

If conditions are perfect then the bigger scope will always trump the smaller. When condtions are not great or lots of light pollution then its more equal.

[jimmyjamjoejoe]

I can see several DSOs with a cheap pair of binoculars. More aperture will give you brighter images for sure, and REALLY big scopes start to reveal details like dust lanes etc, but only if the seeing allows (which is rarely).

[MjrTom]

Very true

I have seen M13, M31, & M42 through a pair of 8x21 binoculars.

OK not as impressive as with a larger pair or a telescope but you can definitely recognise what they are.

[todd8137]

"Galileo...observed and recorded the position of neptune through a 1" aperture telescope

i find find that real hard to be leave no light pol or not

[RikM]

You can see plenty of things through a 6x30mm finderscope.

I think the intention behind this 'rule' is that at 8" appeture things start to look interesting. Where in a smaller scope you will be able to see an object, but at 8" it will be brighter and you will start to resolve more detail.

[MjrTom]

"Galileo...observed and recorded the position of neptune through a 1" aperture telescope

i find find that real hard to be leave no light pol or not

From the info I found on the net it suggests it was a 2" scope but with poor single lens optics which were very blury.

[todd8137]

am not say in the op was wrong or any one in general just sounds crazy that ya could esp with glass and all the rest back in gals day,modern optics would have gave the great man a heart attack imagine go in back in time and dropping him a 3 meter reflector off in his back garden and some eps and filters

[cantab]

His scopes had ratios something like f/50, which would have kept the CA down somewhat. What I want to know, though, is how (or if) he mounted them.

[AndyH]

I've had great fun tracking down deep space stuff with my 60mm FL1000 refractor.

sure it's brighter n more detailed in my 8" Klev, but half the fun(to me), is the finding and viewing with such a tiny set of glass.

[Stu]

I can see plenty in my 66mm apo, even from my garden. Ring nebula, obviously M42 looks great still, open clusters are good and you.can see globs too. Plenty up there even with a small scope. Of course 8" shows you more, but it has to be with you, and set up to be any good and thats not always possible

Stu

[LukeSkywatcher]

I love the views i get with my scopes and they are all under 6".

[Capricorn]

Well there is a minimum size, in that using a 2mm lens from an eyepiece and building a scope from this and pointing at M31 you wouldn't see anything.

Equally a 70mm scope will show a faint oval blur, a 200mm scope would show more and a 400mm scope even more.

To "just" see something (under the whatever conditions) probably would be OK with a small scope. To see something in detail and with a fair degree of size would take a bigger scope.

It as normal depends on your expectations. I recently viewed Jupiter via a 70mm at 26x. The image was sharp and I could see 2 bands either side of the equator and 4 nice sharp moons. The whole lot was small but sharp.

Last year I looked at Jupiter throught the same scope at 57x, again nice and sharp and bands+moons were visible. The night after that I looked at Jupiter through a 14" scope. Jupiter was worse, yet the conditions were as best I could tell identical.

For DSO's there a lot that are faint and to simply get enough light you need something large. The criteria is what DSO.

Messiers are reasonably easy to "see" with a small scope, say 4"/100mm. The NGC and Cadwell catalogue are a different matter, in many instances.

Maybes we are expecting too much and just seeing is no longer adaquate. All Hubbles fault.

[twotter]

Rules are meant to be broken

[Starlight 1]

I was just playing around on Wednesday with some old camera bit and made one up ,It 300mm long 65mm front lens two 30mm lenses at the back and a 25 ep and it was the best night out all year.

[alowen]

My 4 and a bit " refractor gives great DSO views, however, a 16" dob would be amazing i'm sure.

One day.........one day

Al

[Scosmico]

I don't agree when some people put things as "bigger is better".

I would make an analogy to cars.

If you are going off road, you would get a land rover or a Troller T-4.

But in a motorway, you might find a Ferrari or a fiat punto more suitable.

There are things that I appreciate more with my naked eyes than with any other equipment. Others objects are much nicer through a binoculars etc.

The same principle applies for small x big scopes.

I enjoy doubles, cluster, planets and some DSO with my 4se. But there are many DSO only available to big scopes.

Remember, light polluted areas can limit your observational ambitions.

[FraserClarke]

I have seen M13, M31, & M42 through a pair of 8x21 binoculars.

You can see them through a pair of 1x6 binoculars -- they're naked eye as long as it's reasonably dark (i.e my back garden with two street lights shining into it, in a town of 20,000 people).

Knowing where to look and what you should expect to see plays a large part though.

[Ben Ritchie]

O'Meara uses a 4" TeleVue Genesis refractor, and the sketches in his books show remarkable levels of detail. So it's not just aperture per se, conditions and observational skill are at least as important - O'Meara has superlative skies, but also spends a long time on each object.

We're never going to have his conditions here in the UK, but I do think observing is a skill to be learned, even if most of us will never reach his level of skill.

[RikM]

... I do think observing is a skill to be learned, even if most of us will never reach his level of skill.

This is why I like sketching. It encourages you to spend enough time to fully appreciate the object you are observing. I am sure I can see more now than I use to even with the same kit.

[Beulah]

I can see M1 with my 80mm 'frac...