Is this right of not

[Neil H]

Hi guys I was watching this video and when the guy starts to talk about Barlow  he said it doubles the focal length of the telescope not the eyepiece watch from 3.33 , so what do you think ? Right of not?

 

Edited December 14, 2019 by Neil H

[JamesF]

Well, if you're using one whilst imaging it's not doing anything to the eyepiece.  But it's still doing something.

James

[Neil H]

No just looking through eyepiece , every where I read says the Barlow increases the eyepiece but this video says it increases the focal length of the telescope 

[Cornelius Varley]

The video is correct. The barlow lens acts on the focal length of the telescope not the eyepiece.

[Neil H]

Ok so the maths he shows then is right so I can't go over 224 mag  on my telescope

[John]

What telescope do you have ?

 

[Neil H]

Celestron powerseeker 114 

[John]

The theoretical maxmimum useful magnification would be around 228x with that aperture but very often the planetary views are sharper and more contrasty (which is what we are aiming for) and somewhat lower than the max due to a range of issues not the least of which are the seeing conditions.

 

[Neil H]

Ok what I have done is used the maths to make sure I don't go over 224 when looking at plossl eyepieces and barlows

[John]

Nothing will "break" if you exceed 224x - the image will just loose sharpness and contrast and look fuzzier. Often the best views come at magnifications a lot lower than max. Jupiter, for example, usually looks best with small scopes at 120x - 140x.

 

[dannybgoode]

As per @John’s post the theoretical maximum isn’t always useful. 
 

You’ll often find that you can see more at slightly lower powers as the view is sharper and has more contrast. 
 

Best analogy I can give is when you look at a photo on screen, let’s say of a bird. The bird is a little small but very clear and you can see a lot of detail so you decide to zoom in. 
 

But zooming in makes the bird a bit fuzzy. Sure it’s bigger but the definition is lost as is the detail. 
 

One of the first lessons of astronomy is that often less is more

[Neil H]

Hi guys I worked out I need 8mm 10mm 12mm 20mm plossl eyepieces  2x Barlow and poss a 3x Barlow using the eyepiece with and without the Barlow I won't go near max mag of 228

[Jiggy 67]

I don,t know about the 20mm, don,t forget a 2x Barlow will make that a 10mm which you already have on your list, maybe consider a lower power like a 30mm or similar, though I have no experience with your scope. I wouldn’t bother with the 3x Barlow either, the 2x is sufficient and there’s more useful things to spend your money on at this stage

[joe aguiar]

i norm explain it halves the ep focal length but doubling the focal length is the same thing over all

30mm ep if u divide by 2 (2x barlow) is like a 15mm ep

ok lets say the scope is 1000mm fl then thats 1000/15 =66.66 power

if you mulitpy the fl x2 thats 2000mm fl divide by 30 =66.66 power

so both are the same thing it doubles the focal legth of the scope or double the power of the ep

you choose i norm do the ep way

joejaguar

Edited December 14, 2019 by joe aguiar

[joe aguiar]

2 hours ago, Neil H said:

Hi guys I worked out I need 8mm 10mm 12mm 20mm plossl eyepieces  2x Barlow and poss a 3x Barlow using the eyepiece with and without the Barlow I won't go near max mag of 228

max power is not always needed in fact most times you never go that high as the item becomes fuzzier so you should stay 180x to 200x max

theres only a hand full times that you can go to max or excede it

i just normally go till it get fuzzy then back the power down then you will know for that night conditions

joejaguar

[joe aguiar]

2 hours ago, Neil H said:

Hi guys I worked out I need 8mm 10mm 12mm 20mm plossl eyepieces  2x Barlow and poss a 3x Barlow using the eyepiece with and without the Barlow I won't go near max mag of 228

the problem the 20mm with the barlow is bascailly a 10mm ep so theres no point in doing the same power, thats y i normally use the barlow doubles each ep so you know instead if it doubling the focal length

 

[Neil H]

Hi Joe do me a favor tell me what eyepieces  and Barlow to get please so I don't waste money on things I don't need , forget what I have as they are cheap and came with scope so are not plossl 

[PEMS]

If the scope is 114 I would suggest that you consider magnifications of 80x and 100x, and if you want to try then maybe 120x.

The maximum value given is often based on another consideration that of the exit pupil. Then manufacturers quote a magnification that correlates to that exit pupil. The catch is that it does not mean that the scope is realistically capable of the necessary performance, and usually they are not.

The focal ratio of your scope is 7.89, closest integer is 8 so use that. An 8mm eyepiece will give around 110x, a 10mm 90x, a 12mm will give 75x, a 15mm 60x. For the initial finding a low power eyepiece of 30mm plossl or the 25mm options in the 60 degree line (X-Cle LX, BST Starguiders, Meade HD).

Most viewing will be at the 60x to 80x area, people seem to think that the higher magnifications will dominate, they do not. It is also useful to work out the field of view that an eyepiece will give you. Little use having a 0.5 degree view on a 1 degree object.

Presuming you purchase in steps I suggest a wide 30mm or 25mm, and a 12mm. You can later add a 10mm or 8mm in.

Barlows are a bit odd. They alter the image size, so you have an image as if it were from a telescope of double the focal length. Another aspect is they are not specifically designed for your or any particular scope, and they are made to a cost, so they will often degrade the image you see. Many people do not therefore use a barlow.

[Neil H]

Hi I got this eyepiece as the 4mm was missing this was before I found out I need plossl eyepiece is it any good or shall I replace it 

https://www.amazon.co.uk/gp/product/B0749PC72L/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

[rwilkey]

18 hours ago, Neil H said:

poss a 3x Barlow

Hi Neil, you do not need two Barlows, the 2x one will be the best, but I have found over the years that I use a Barlow less and less, preferring higher mag eyepieces, also less faff.  Good luck with your choices.

[Rob Sellent]

A huge 25 Page look at these eyepieces on Cloudy Nights. General opinion: in slow scopes (+f/8) they perform wonderfully.

[johninderby]

I have pretty well stopped using barlows visually. Prefer a couple of higher powered eyepieces as they are just more convieient.

[vlaiv]

Just as a piece of information on maximum magnification of a telescope - how is it "established" and what it means.

In reality max magnification of telescope as calculated by x2 aperture in millimeters is based on two things - theoretical resolving power of aperture of certain size (airy disk produced) and theoretical resolving power of human eye (20/20 vision).

If you want to see if maximum telescope recommended magnification is just right, not  enough or too much - just do the following - try to see two high contrast features - maybe best case would be two black poles next to each other against blue sky (aerial poles or similar) - such that their angular separation is 1 minute of arc. Another test would be to spot a feature on the Moon that is 1/30th of moon diameter - by naked eye of course. Maybe try to spot a Plato crater for example (as a single dark spot)?

If you can do that - then maximum recommended magnification is just right for you - if not (and odds are that you can't), you will enjoy higher magnification.

Problem with max theoretical magnification for all but smallest telescopes is that it is going to hit atmosphere limit much sooner - around x100 or so in most circumstances, and that would be max for 50mm scope - most of us use larger apertures than that, so we can't reach max magnification of aperture under most circumstances - and that is why going close to max magnification looks blurry - not because it is "real" upper limit of telescope (it is but for a person that has perfect vision).

Edited December 15, 2019 by vlaiv
somehow my sentence ended without much sense - now corrected :D

[andrew s]

3 minutes ago, johninderby said:

I have pretty well stopped using barlows visually. Prefer a couple of higher powered eyepieces as they are just more convieient.

High power eyepieces often have a "Barlow" built in but have the advantage is that they are optimised with the rest of the lenses rather than being generic. 

Regards Andrew