Magnification

[MND]

I'm trying to get to grips with magnification for eyepieces.

If I understand correctly the theoretical maximum is Aperture x 50, so my 9.25 would be 460 odd but in reality the maximum usable is only 250x because of seeing conditions, atmosphere etc.

If magnification is Focal length of scope divided by lens focal length, does that then mean then that the highest mag worth using in mine is a 9mm? (2350/9=261)

TIA

[Dreadz]

I've worked under the assumption that theoretical maximum mag is 2 x aperture(mm) so for my 250px (254mm) would be 508x.

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[Bizibilder]

Yes your calculation is correct.  UK skies seldom allow more than 200x - maybe 2-3 night a year, if you are lucky, you could go up to 350x.  Don't forget that for DSO's you can often use very low magnification (around 30x-40x) and the associated wider field of view.

[Mr Spock]

I find most nights with the C9.25 a 10mm eyepiece is the most used.

I do move up to 9mm and 8mm when seeing conditions allow and 6mm when that one steady night comes along.

[rwilkey]

Hi MND, I agree with all of the above, magnification is not everything, at least to me.  I tend to work in the middle ranges, hence my most used ep's are my ES82's 11mm and 14mm.  My planetary is a 6mm William Optics SPL on most occasions giving me 150x on Jupiter.  Saturn can take more mag, up to about 250x.  Anything higher would not get used much in my opinion.

[ronin]

Magnification is an odd thing to define, especially the maximum.

A 100mm apo triplet will give more magnification then a 100mm achro, but both are 100mm.

Not too long ago the maximum I was used to was 1.5x diameter in mm.

Now it seems to be 2x diameter in mm, and I have seen 2.5x, 3x and 4x.

I suspect that the 2x mm diameter is from a reference that said that an exit pupil of less then 0.5mm was unusable as below this factors in the eye become a problem. An exit pupil of 0.5mm is a magnification 2x the diameter in mm.

So I suspect that there is a maximum magnification (minimum exit pupil) that relates to the eye, and "another" that relates to the actual capabilities of the scope itself.

Like most things people will claim, or quote, the one the is the most impressive. Especialliy the Telescope Marketing Departments.

I tend to work on a magnification equal to the objective diameter as a first point, and count anything bigger then this as a bit of a bonus. An eyepiece FL equal to the f number of the scope give this.

[MND]

That pretty much correlates with what I've found. I bought the scope with a set of Celestron plossl's. The 6 and 8mm are not much use viewing Jupiter, makes it blurred compared to 13mm.

I'm thinking of buying 1 really nice eyepiece. Something along the lines of 9mm Nagler or Delos. Would I get full use from these with mag and FOV or would a different size/brand be a better choice for a 9.25?

[rwilkey]

Hi MND, I would have thought a 13mm would hit the sweet spot for you, giving 180x, I would recommend the Vixen 13mm LVW, a cracking ep and one of my favourites.

[LukeSkywatcher]

I tend to work on a magnification equal to the objective diameter as a first point, and count anything bigger then this as a bit of a bonus

I work on the same idea. The packaging and sales pitch will say about 450-500x, but that just doesnt happen here in this part of the world. The "max" i get/use on any given night is 254x.

2032/8=254x 

I'm learning to love planets using say 12-15mm EP. The detail is just so much clearer then with my usual 8mm. 

[proflight2000]

I have to agree, i find if i go in too close it just comes to nothing, 12mm is the highest i ever go and i actually love the wider views especially for galaxies etc as i can see them in the aspect of the space they are in so to speak. Saying that though, id love to try a higher mag eyepiece from the top of the range and see the difference, maybe one day when i am a millionaire.

[Wyvern]

Hi MND,

You've been given all the right info by the people here.

What doesn't help is adverts like the scope below. Celestron ( a "trusted name" in astronomy), advertising a 60mm refractor that can handle x525 .      yeah, when? 

[rwilkey]

I tend to work on a magnification equal to the objective diameter as a first point, and count anything bigger then this as a bit of a bonus

I work on the same idea. The packaging and sales pitch will say about 450-500x, but that just doesnt happen here in this part of the world. The "max" i get/use on any given night is 254x.

2032/8=254x 

I'm learning to love planets using say 12-15mm EP. The detail is just so much clearer then with my usual 8mm. 

Hi Paul, I totally agree with you!

[LukeSkywatcher]

Hi MND,

You've been given all the right info by the people here.

What doesn't help is adverts like the scope below. Celestron ( a "trusted name" in astronomy), advertising a 60mm refractor that can handle x525 .      yeah, when? 

I dont want to "wag the finger" or start a "negative comment campaign" against Celestron, who are the makers of very fine optical equipment, but they do tend to sugar coat and dress up the specs on their products. Those specs may work in America or Australia etc where the climate is generally long hot summers and "seeing" conditions are often near perfect. It simply isnt the case here in North Western Europe. 

60mm giving you 525x magnification?

Maybe in a paralell universe.

[Wyvern]

Hi Paul,

Yep, not trying to start an "anti Celestron" or anti anyone campaign. It just really bugs me that "astronomical names" like Celestron will do this, then "joe public" comes along and buys it as a starter telescope thinking "it's got to be good, just look at the magnification!"

They wack in the barlow and eyepieces combo's, cant see a thing..... or maybe a fuzzy blob of something and chuck the scope and astronomy cause they cant see anything.

It's not magnification that matters but aperture......... oh dear, feel a case of aperture fever coming on again, please pass the tablets Doctor. 

Les

[Owmuchonomy]

As above it's all about conditions on the night and what you are looking at. So for me best is as follows:

2350mm FL SCT; 8mm EP for Moon; 15 mm for Jupiter; 40mmWF for DSO.

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[MND]

Rwilkey, I hadn't considered the Vixen, it is about £70 cheaper than a comparable sized Delos.

Since your post I've read a few reviews of the Vixen's and all seem favourable.

Would the 7° higher FOV on the Delos be worth the price increase I'm now wondering.

[LukeSkywatcher]

No two nights observing in this part of the world are ever the same. What works on a monday may not work on tuesday. As has been said, you can basically take the aperture of your scope as the given magnification................and then some. 

A couple of yrs ago i bought a Celestron Omni 6mm EP. It cost me 60 euros brand new. I have used it twice when conditions were EXCEPTIONAL. I only got to use it on the Moon, but boy oh boy the view was simply STUNNING.

My original plan when i bought it was to use it as a planetary EP. 

That never happened.

[LukeSkywatcher]

Rwilkey, I hadn't considered the Vixen, it is about £70 cheaper than a comparable sized Delos.

Since your post I've read a few reviews of the Vixen's and all seem favourable.

Would the 7° higher FOV on the Delos be worth the price increase I'm now wondering.

Vixen EP's are quality. My preference is the NPL range because they are within my budget and really are very sharp and contrasty. 

I do have a single vixen NLV which i bought 2nd hand @ half price, but i dont like it as much as the cheaper NPL's. The NPL's do not have good eye relief, but i dont notice it..............they work brilliantly for me.

[rwilkey]

Rwilkey, I hadn't considered the Vixen, it is about £70 cheaper than a comparable sized Delos.

Since your post I've read a few reviews of the Vixen's and all seem favourable.

Would the 7° higher FOV on the Delos be worth the price increase I'm now wondering.

Hi MND, from the reviews I have read, the Delos are great ep's but beyond my budget, but in my opinion the 7° higher FOV would make little noticeable difference.  Funnily enough I bought the 13mm LVW as I decided I could not afford the 13mm Ethos in a million years, neither would I consider it morally justified to spend £455 on an eyepiece.  Happily I got the 13mm LVW for £99 new at the SW Astronomy Fair so I was dead pleased with that.

[chiltonstar]

Certainly, with smaller scopes (3", 4", 5" in my case) the 2x aperture in mm rule seems about right. I reckon I can use an 8mm EP in my 5" Mak (x190) about 50% of the time, and a 6mm EP about 10% of the time (x250) when looking at Jupiter, Saturn or Mars. It seems to be accepted that the situation with larger scopes is less favourable.

If you are a double star fan, for example, (I am) then you can go comfortably above these limits on occasions. It's worth looking at a recent article In Astronomy Now on the subject...

Chris