Use of Low Magnification in LP Area

[source]

Hey guys

Since I'm new to the hobby I was wondering, is a low mag less than 69x useful in a light polluted area? What is the main purpose of a magnification lower than that? (in deep sky areas or lp areas). Just wanted to get an idea if I need a lower mag than 69x

Thanks

Daniel

[dick_dangerous]

Being able to use low magnification is pretty essential I'd say, when you're trying to find stuff. I live in London and went looking for M81 and M82 in the park. The LP isn't the worst, but it's hardly what you'd call dark skies. At x16 with a 3'' aperture, both galaxies were easy to find, very visible and in the same field of view. I could then up the magnification to find the supernova in M82. Low power for finding stuff, medium to high power for observing it.

DD

[Langy]

I have an entry level scope which came with budget 20mm (x32.5) and 10mm (x65) EP. Now to try and find anythign with the 10mm is a very time consuming job. Even finding something as bright as Jupiter takes a long time and still takes a little while with the 20mm. I know some people use EP with a much wider FOV to 1 degree which this 20mm gives me and I can understand why. If you're looking for a faint object in the sky and need to star hop the wider the view the better. Since bought a 2x Barlows to add to it.

I've also found that often looking at object with the 20mm is far kinder on the eye and often more enjoyable.

There are also other things to consider like atmospheric conditions. I've read posts on here lately where people can't focus or see any detail at high magnification, simply the Jet Stream was over them at the time and had to use a lower powered EP.

The first thing I always have in the scope is the 20mm.

[Stu]

The benefits of low power are really about the field of view it gives you, rather than the magnification as such. I tend to be more interested in magnification at the mid and high power range, and field of view at the low power end.

A wide field of view is very useful for finding things, as has been mentioned. It is also very good for seeing some of the larger objects up there such as the Andromeda Galaxy or Veil Nebula. The problem here though is that you normally need good dark skies to get the best out of these objects, so under light polluted skies low power eyepieces can tend to look washed out.

The exit pupil of the eyepiece in your scope is important to understand. This is the aperture of your scope divided by the magnification. Generally a well dark adapted pupil will be 6 or 7mm at max, so going above this loses light. At these large exit pupils under light polluted skies, the sky background can appear bright which loses contrast. Moving down to the 3 to 5mm range can certainly help under poorer skies as it darkens the sky background and helps objects to stand out more.

Which scope do you have? That would help with making some suggestions

Cheers,

Stu

[michael.h.f.wilkinson]

I use magnifications down to 48.5x in my 8" scope in a suburban surroundings using my LVW 42mm. I prefer the 65.5x of the Nagler 31T5 (a.k.a. Panzerfaust), as the 3.1mm exit pupil gives darker backgrounds. For emission nebulae, I use a UHC or O-III filter which increases contrast a lot. The difference between 69 and 65.5x is minimal. The key feature determining brightness of the sky background in LP is not magnification, but exit pupil. Under dark skies, I love using 5-7mm, but in suburban settings 3-4mm is a bit better. The easiest way to compute exit pupil is to divide the focal length of the EP by the focal ratio of the scope. My 42mm gives a 4.2mm exit pupil in the F/10 SCT and 7mm in the 80mm F/6

[AndyWB]

My most used EP is my 30mm - which gives x21, and a true field of view of over 2.2 degrees in my 'town scope'. It's great for finding things; it's the first in my scope every time.

I'd never really thought about exit pupil, though - fortunately, it appears that I should still be okay with the 30mm in my 250px

[Moonshane]

I agree with the general consensus that exit pupil is more important to consider than magnification. I live in a pretty light polluted area and tend to stick to exit pupils below 6mm and magnifications (partly due to sticking to the preferred exit pupil).

[John]

I take the same line as Shane on this - my max exit pupil is 5.85mm which the Nagler 31 delivers with the 12" F/5.3 dob. I find the 3.96mm exit pupil that the Ethos 21mm produces with this scope creates a darker background sky though, from my moderately light polluted back garden. 

[Stu]

I take the same line as Shane on this - my max exit pupil is 5.85mm which the Nagler 31 delivers with the 12" F/5.3 dob. I find the 3.96mm exit pupil that the Ethos 21mm produces with this scope creates a darker background sky though, from my moderately light polluted back garden.

That's my experience too John, the 21e gives a better result with darker sky background. They said, the extra fov of the 31 is very nice when under dark skies.

In the 12" f6, the 31 will give 5.2mm which should still be very useable.

Stu

[michael.h.f.wilkinson]

Absolutely: I have used the 31T5 in my F/6 80mm without issues. Best from a dark site, but still highly usable from my suburban garden

[swamp thing]

Low power is kinda relative to scope used what's low power in one scope is pretty high in another. As I don't know the size scope you are using its kinda tough to know if 70x is low or high.

[source]

Thanks for all the replies. The exit pupil makes me understand what kind of low power I am looking for. Soz, should have mentioned the scope - which is an Orion xt8i. I plan on getting a 28mm UWAN in the distance future, otherwise plan to get a 17.3mm Delos which should suffice until then. With the intelliscope I at least won't have a problem locating objects while I learn the skies.