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Do you need a large scope to view nebulae?


Ags
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Nebulae elude me with my mak. At length I've realized that it is because my setup provides a exit pupil of - at best - nearly 2mm.

Given that a small refractor can easily give an exit pupil of 5mm, could such a small scope give good views of the top 20 nebulae? Obviously smaller more distant nebulae would need more magnification than the small frac could give at a reasonable exit pupil.

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To view nebulas, galaxies, open clusters etc you need a wide fov and light gathering power along with low magnification and crystal clear optics. Good ep's are important cos you'll be working at fast focal ratios typically f5 and less.

Maks and Sct's typically have long focal lengths, slow f-ratios, and narrower fov's than newts, which is why some people go for large dobs. Refractors are expensive but a wide field short tube appo can be very good for LE imaging (doublet or triplet), though they do have less light gathering power for observing. Just some things to bear in mind :)

Edited by brantuk
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you may well be right re exit pupil but personally I think aperture is the key with this. I suspect if you had say an f10 12" SCT (if one even exists) then you'd see more than with a small fast refractor. I don't have experience of these scopes but do with a larger faster newt and the messiers are certainly reasonably straight forward even in light pollution.

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I thought the same but the brightness of a nebula is determined only by its intrinsic brightness and the exit pupil. A larger aperture only allows more scale (which admittedly makes the nebulosity easier to see) but cannot give greater brightness.

For stars aperture always increases brightness, but this does not apply to nebulous objects.

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Hi

When you say Nebulae that covers a vast array of objects with different requirements.

Their are huge amounts of Planetary Nebulae that appear stellar unless very high mag indeed is used they also have high surface brightness so large fields and big aperture is not required for them.

At the other end of the scale some Nebula are vast with low surface brightness that can only be seen with rich field telescopes from crystal clear pitch black skies. Big scopes just look straight through em.

So no a Large scope is not always required to view Nebulae. You just have to pick targets that your scope will see best. Try targeting some high surface brightness planetary Nebulae. Your Mak will have more chance of showing them than low surface brightness diffuse Nebula.

The "Webb society deep sky handbook" covering planetary and diffuse Nebulae gives plenty of examples to observe.

Regards Steve

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Aperture is king when it comes to viewing DSO. I don't agree with SCT or Mak being inferior to Newtonian of the same aperture. People choose Newtonian because they are cheaper per cm of aperture than the other designs.

While an SCT may have longer focal length, you can always compensate by choosing a longer focal length eyepiece. At the same magnification, the telescope with the largest aperture will show the brightest image. I saw more nebulae and galaxies through my 6" SCT than my 3" apo. A C8 with a 40mm XW will show a field of 1.5 deg field, which is plenty wide enough for most DSO.

If you aim is DSO, just look for the largest dob you can afford. The have shorter focal length than Cats so you can use shorter (cheaper) eyepiece to reach the same magnification.

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...But aside from the brightest planetaries and the Great Nebula in Orion, I haven't seen any nebulas.

Yes, but have you actually tried?

NGC 2392 the eskimo Nebula should be visible as should NGC 3242 the ghost of Jupiter, NGC 6543 the cats eye, NGC 6210 in Hercules, NGC 7662 the blue snowball, NGC 6826 the blinking Nebula and NGC 7027 To name just a few.

As for diffuse nebulae check out M17 the omega nebula, M8 the lagoon nebula and M20 the triffid nebula.

There are two Nebulae in the Messier catalogue in the seventies M76 the little dumbbell and M78 in Orion both visible in small scopes.

All these objects have high surface brightness and make good targets for smaller aperture scopes.

As I stated in my previous post there are catalogues with many high surface brightness nebula in.

Good hunting and clear skies.

Regards Steve

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What is your background light level like? Diffuse objects like Nebulae are more easily swamped by light pollution.

You could consider focal reducers to improve apparent brightness and narrowband filters to improve contrast.

Regards

Barry

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Nebulae elude me with my mak. At length I've realized that it is because my setup provides a exit pupil of - at best - nearly 2mm.

Given that a small refractor can easily give an exit pupil of 5mm, could such a small scope give good views of the top 20 nebulae? Obviously smaller more distant nebulae would need more magnification than the small frac could give at a reasonable exit pupil.

I wouldn't get too hung up on exit pupil's. I've used exit pupils of 7mm to 0.5mm on dso's. The best exit pupil to use depends on the object in question AND the prevailing sky conditions.

As a rule of thumb using a small scope, for a large percentage of dso's i've found an exit pupil of 2-3mm handy under less than properly dark skies.

Aperture is king when it comes to viewing DSO's

Aperture may indeed be King.... but patience is queen & Dark skies are undoubtedly the ruling emperor.:)

Personally I'd take an 80mm refractor under dark skies than a much larger scope under more typical uk skies anyday.

Don't be put off trying to track down dso's with a small scope.

With even semi dark skies & the patience to wait for particularly transparent skies, quite a lot of objects can be found.

True, with a small scope, little if any detail will be visible on many objects, but there's still a buzz to be had seeing things with your own eyes.

Indeed for some objects, a small scope might even prove to be preferable- how many 12" dob owners have seen the rosette nebula from there backyard i wonder?....

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Good points. My plan is to get a 40mm plossl for maximum brightness and a UHC filter, a narrow one as I have extreme light pollution.

But the 40mm plossl won't show any more sky than your 24mm Hyperion does, the view will be like looking down a drinking straw (comparatviely) and the extra magnification of the Hyperion will darken the background sky and make DSO's easier to see and make a UHC filter more effective. I'd just get the filter if I were you.

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My theory was that the greater surface brightness of the 40mm combined with a filter might reveal a bit more. I know that the 24mm already shows the maximum true field of view for my scope.

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Good points. My plan is to get a 40mm plossl for maximum brightness and a UHC filter, a narrow one as I have extreme light pollution.

Spend the money on getting out to a dark site instead. If you have severe light pollution no amount of equipment is going to enable you to observe large low surface brightness nebulae.

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Spend the money on getting out to a dark site instead. If you have severe light pollution no amount of equipment is going to enable you to observe large low surface brightness nebulae.

This is by far THE most important factor when trying to observe low surface brightness diffuse nebula.

If I did observe from where I live (under the glow of London LP) I would have trouble seeing many diffuse nebula even with my 16" telescope.

Your scope is capable of showing all the objects I listed and many more if you let it stretch it's legs under a dark sky.

I always find it strange that many AA's will spend money on accessories but not spend on getting away from LP.

Regards Steve

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As has been suggested refractors are recommended for some nebula. For example, an excellent five inch refractor will offer the best views of some Nebula, where you want a large field of view and as much light as you can to see some nebula. Other nebulae also require a large field of view. On the other hand, with a larger telescope some nebula are so complex and fascinating that just looking at the parts are interesting enough... Certainly the most cost effective way to get started is with a small reflector (Newtonian) telescope, and it will offer good views of nebulae.

Edited by MissMessier
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The long FL of a big SCT cannot be overcome by any EP, however wide its field.

It can be mitigated but you will still be boxed in. You have to decide what is the smallest field you can tolerate. I find our 10 inch SCT pretty frustrating in terms of FOV, I must say. It is convenient in other ways but has dire tunnel vision. Why have ten inch f10 when you can have 10 inch F6? The gain on the planets is more theroetical than real.

Ollyu

Edited by ollypenrice
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