Confusations help X2/3/4/5 barlow, F5/10/15 argggghhh

[12inchDoB]

Hi fellow Stronies,

Im unable to get my head around something..

i have an 11" Reflector F5,

I was viewing objects and obviously noticed the size gain with/and clarity loss.

I "think" i read i cannot (theoretically) go over 300 X Mag which is what the 9mm X2 Barlow would give me (F10)???,

but cani go further? how do i get to view things larger? I know by using barlows, it doubles the distance and basically halves the clarity, but what is the best formula for biggest/best viewing (on a good night) say Planets/Moon...

9mm & barlow X2=4.5mm/X3=3mm/X4=2.25/X5=1.8 barlow?

I currently own

25mm PLossl

6.5mm Plossl

9mm TMB P2

Celestron X2 Barlow

Should i get a X3 or X4 X5 barlow or consider a new 4mm ?

Thanks

Stu

[rowan46]

magnification equals focal length divided by eyepiece focal length

150x is the usual limiting factor for british atmosphere but you can go a little more on the moon and sometimes on very rare still clear nights you can go higher

[Moonshane]

you are quite right on the logic of magnification that generally you get a bigger a slightly less sharp/dimmer image the higher the magnification.

the basic rule I use with magnification is try a mid range magnification (100x maybe) then increase to the point where image degrades and then back a bit.

as mentioned you can readily get 150x - 250x in my experience with 6" f11 and 12" f 5.3 dobs on the moon. on rare nights of good / excellent seeing and when high in the sky I have still had a decent image up to 500x on the moon with the 6" (which I think is supposedly not theoretically possible!) although more usually 200-250x is more reasonable.

on planets etc this is usually much reduced and generally between 120x-220x but again when the seeing is good the images even at these magnifications are stunning.

a lot depends on optical quality (of all aspects of the optical train) too as well as collimation, stability of mount, cool mirrors etc etc.

don't believe people that say larger aperture fast newts are no good on planets. when the seeing is good the images are quite exquisite.

[Ad Astra]

maximum magnification depends greatly upon your air quality when you are observing.

The more still it is (better seeing = less 'twinkling' by the stars), the darker it is, and the lower the humidity/air pollution is - the better you will do.

Altitude is the best way to improve things easily! if you can find a viewing site that is a bit higher up, you get to eliminate a LOT of junk and stabilize your view. A couple hundred feet of elevation can do wonders for you!

Either that, or pack up your scope and mosey out to my place! We'll take off for Joshua Tree Nat'l Park at about 5000 ft elevation, humidity hovering around 0-10%, and the nearest city lights at least 50 miles away. It's wonderful! 350x and more can be yours - (and you can sleep on the couch, Mrs. Astra won't mind! )

Dan

[John]

I'd push things a little further than rowan46 does and say that 200x - 250x is about the max useful magnification on most nights, with more possible on the best of nights and provided that your scope is in good collimation, that is the mirrors are correctly aligned with respect to each other and the eyepiece.

An 11" (280m approx) F/5 scope has a focal length of 1400mm. To find the magnification of a given eyepiece you divide the focal length of the scope by the focal length of the eyepiece, eg: a 10mm eyepiece in your scope gives 140x, a 5mm 280x etc, etc.

So your 6.5mm plossl is giving 215x which is pretty useful. If you want to go a bit higher, and the seeing conditions are good, you could use your 2x barlow with your 9mm TMB eyepiece to give an effective 4.5mm eyepiece and 311x. That would be the most that would be useable on a good night I reckon.

[12inchDoB]

So your 6.5mm plossl is giving 215x which is pretty useful. If you want to go a bit higher, and the seeing conditions are good, you could use your 2x barlow with your 9mm TMB eyepiece to give an effective 4.5mm eyepiece and 311x. That would be the most that would be useable on a good night I reckon.

So far, that has given me the best formula 9mm TMB P2 with 2X Barlow.. I have never seen the gap in Saturns ring until last night with "V poor" viewing, with limited £££ and months before i get my main recoated, i wanted to purchase a new lens to get ready or push things,

Remember, my main 11" mirror was last recoated 1991 !!

@ AD astra, if i ever go USA, Calif is 1st place id visit,!

Thanks

[rowan46]

So far, that has given me the best formula 9mm TMB P2 with 2X Barlow.. I have never seen the gap in Saturns ring until last night with "V poor" viewing, with limited £££ and months before i get my main recoated, i wanted to purchase a new lens to get ready or push things,

Remember, my main 11" mirror was last recoated 1991 !!

@ AD astra, if i ever go USA, Calif is 1st place id visit,!

Thanks

you can join the queue theres a heap of us wanting to get a look through that big refractor of his:D

[Ad Astra]

you can join the queue theres a heap of us wanting to get a look through that big refractor of his:D

Everybody says that, Mate... but nobody seems to buy a plane ticket.

All that Guinness and the big 'frac just for me? That's no fun!

Dan

[Pete Presland]

the only way to be certain what the maximum acceptable magnification is for any given night is to try it as high as your equipment will allow and see what the view is like.it only takes a minute to swap eyepieces.

i have viewed Saturn at over x500 a couple of times and so far its never been very good,but it always worth a try