Barlows and did I do the math correctly?

[MarkVIIIMarc]

Having just bought my first scope it might be a bit before I buy another lens but I want to see if I understand correctly.

My scope is a Zhumell Z10 with a listed 1250 mm focal length.

My 9 mm 1.25" eyepiece gives me 1250 / 9 = 138.9 x magnification.

My 30 mm 2" eyepiece works out to 1250 / 30 = 41.7 x magnification.

Remember, I am testing what I have been reading and maybe retaining:

A 10" scope in theory is good for 10 x 50 or so magnification, 500 x.  But in reality if I push 10 x 30 so about 300 x for all but the clearest nights of the year I am wasting my time.  Do I recall reading 200 x magnification is really the max for most of us?  I am in a decently dim spot on the north side of St Louis, Missouri, in the humid central U.S.

So, to make Jupiter bigger in my eyepiece I can use a 2 x Barlow pretty safely bringing my magnification to 277 x?

And assuming I do, the planet will be a bit dimmer and the field of view will be half the size....and time finding my target at least double lol.

Thanks for your time correcting me as necessary!

[rockystar]

all sounds about right to me. Find it first with your 30mm, then make sure your finder is as accurate as possible, it will make it much easier to re-centre it. Then swap in your 9mm, you may find this is a good enough view for Jupiter - I'm currently getting great views with even less magnification (14mm with the same focal length scope). Then try your Barlow. And have fun, welcome to the club

[cloudsweeper]

Depending on conditions, if you push the mag too high, the image will just get fuzzier.  The dimming effect won't be a problem with a bright object like Jupiter.  And it will still be well within the field of vision, although you might have to relocate it with the aid of the finder.

As for theoretical max mag, I suggest just trying it.  My max is meant to be x250, but I've used x300 on the Moon with great success.

But remember with mag that "less is often more" and low mag, sharp views can be more pleasing than high mag ones.

Doug.

[baggywrinkle]

As said above the theoretical max magnification and the actual useable are often two very different things.

If the seeing is poor due to lots of thermals and hazy thin high clouds then pushing the magnification to high results in soft images with poor definition.

For planets the temptation is to push the magnification, do so, but work from low to high and see what the limits are.

For DSO use low mags and get wider fields of view.

[Dave In Vermont]

Your math is good on finding the magnification by dividing the focal-length by the focal-length of the EP (EyePiece). As for the maximum being 200X due to climate - this is true in the UK, aside from some rare and sought after moments. But you are in/near St. Louis? As in Missouri? If so - then no, you can likely push it higher. Your major complaint in the Summer is humidity. So you need to find your maximum for this by trial & error. I know the oppresive weather you have in the Summertime. I used to spend my Summers' in Iowa - just up the Mississippi River from you in Burlington, IA. But never had a scope with me!

Iowa is a Native word that means: A place where you lay down and sleep. And we both know why!

From Burlington to Burlington -

Dave

[brantuk]

The 200x mag average limit is often quoted here in the UK simply cos we get worse weather than the US. Being a more temperate climate all round we tend to have fewer clear nights with good transparency than you guys get across the pond. I don't know what your useful limit is - but I've heard reports of good views using 300x and 400x mag from US folks now and then. 

[John]

Some good replies already here.

It's worth bearing in mind that Jupiter does not respond as well to really high magnifications as targets such as the Moon, Saturn, Mars and binary stars. It's to do with the nature of the features we are trying to oberve on Jupiter I think - while the apparent size of the planet is increased by the additional magnifications, the contrast differences between the various fetures tend to get more washed out and less well defined. It's one of those targets where stepping down the magnification a bit will often bring more rewarding viewing even though the image scale itself is smaller.

 

[MarkVIIIMarc]

14 hours ago, brantuk said:

The 200x mag average limit is often quoted here in the UK simply cos we get worse weather than the US. Being a more temperate climate all round we tend to have fewer clear nights with good transparency than you guys get across the pond. I don't know what your useful limit is - but I've heard reports of good views using 300x and 400x mag from US folks now and then. 

Interesting.  Its a big country over here.  My guess is on the east coast where all the cities are packed together and the atmosphere is moist from the ocean our skies support less magnification than out in the desert southwest. Man, one night driving between Phoenix and Las Vegas the sky was soo dark and clear it was on a scale different than those in farmfields by me.

[brantuk]

Yeah I must admit I was thinking of the deserts with big skies and dry nights. Nearest I ever came to that was the bush in S.Africa - couldn't believe how many stars were visible - from horizon to horizon the sky was jam packed full of shiny twinkly things. We rarely get to push our magnification in the UK much over 200x to 250x.

[Dave In Vermont]

Yes - Jupiter responds differntly than distant objects like stars and clusters and such. I believe the word one could apply to Jupiter is: Amorphous. As in a swirling mass of clouds (gas) with what are essentially an undefined surface area. All of which throws a monkey-wrench into using it for a test for the optics of a telescope. Or for 'seeing' for that matter.

Your mileage will vary,

Dave

 

[Owmuchonomy]

As a demonstration my best views of Jupiter last night were with an ES 14mm 82' eyepiece in my 9.25" SCT 2350mm FL scope. The seeing was good for this area and it was easy to see details such as a split in some of the cloud belts and a salmon pink GRS. Very pleasing.