Telescope Basics 5 (of 6): Learn the basics about barlow lenses for telescopes

Hi there, welcome to Part five of the video
series, “Telescope Basics.” My name is David Fuller, host of the “Eyes on the Sky”
weekly stargazing series that can be found on eyes at the sky dot com.
In this video, I will explain what a barlow lens is and how it works – and what the
benefit is to you in owning one. A barlow lens something known as a “telenegative
amplifier.” That’s a fancy way of saying it increases the magnification of your existing
eyepieces, simply by placing the barlow between your telescope’s
objective lens or mirror, and the eyepiece you view through.
So if your 900 millimeter focal length telescope produces 90 times magnification with a 10
millimeter eyepieces, a 2 times barlow can produce 180 times magnification.
Why not just get another, shorter focal length eyepiece? Well, a barlow effectively doubles
your eyepiece collection, for starters. Let’s say you have the
following three eyepieces: 25, 16 and 10. If you were to get the same doubling of magnification,
you would now have to purchase 12, 8 and 5 millimeter eyepieces.
But with ONE barlow lens, you can effectively get that same magnification with the 25, 16
and 10. In other words, it’s a lot less expensive way to increase your
eyepiece collection. There is a caveat here though, that is both
good and bad. Using a barlow increases the eye relief of a given eyepiece. For shorter
focal length eyepieces, like 10, 12, or 16, this can be quite beneficial,
as it is like using a 5, 6 or 8 millimeter eyepiece with greater eye relief. The problem
comes with longer focal length eyepieces; this increase in eyepiece
is even greater with longer focal length eyepieces. Since a 32 millimeter eypiece, for example,
may have an eye relief of 16mm – a normally comfortable
distance – a barlow may now cause it to have 32 millimeters of eye relief. This can
actualy make it difficult to see the entire field of view, because your
eye is so far away from the lens. One thing to remember is that this effect is greater
with shortie barlows than with longer ones. Either way however,
this is a good thing for shorter focal length eyepieces where eye relief tends to be short,
and barlows are typically of best use anyway. So what kind to get? There are short and long
versions, achromatic types, and various factors of magnification, like 1.8, 2 and 3 times,
just to name a few. Partly this will depend on your scope: Short
ones are usually required for reflectors, as they tend to work better in the shorter
focusers. Refractors, on the other hand, are often the best fit for the
longer ones, but this is not a hard and fast rule. And by the way, to get more magnification
place the barlow AHEAD of the star diagonal when using them with
refractors, to get the maximum effect. Whatever you do decide, make sure to choose one that
does not create the same magnifications for eyepieces you already own.
For example, getting a 2 times barlow if you already own 20, 10 and 5 millimeter eyepieces
won’t help you much, as the 20 and 10 eyepieces when used with
a 2 times barlow would be identical to the 10 and 5. In that case, a 3 time barlow might
make more sense. Conversely, you may not need to purchase eyepieces for
magnifications you can achieve with an already purchased barlow, so owning one early can
help with making future eyepiece decisions. So what is most important to look for? I’d
say fully-multi-coated lenses. By adding another set of lenses into the optical system, there
is potential light loss. By using a higher-quality barlow with minimal
reflections, you minimize stray and reflected light, maximize light throughput, and also
-very likely – get a better quality piece of equipment. Eyepieces may
come and go, but many amateur astronomers hold on to quality barlows for a long time.
Well worth it to spend a few extra dollars and get a quality one. So that is a quick look at barlow; in the
sixth and final video in this series, I will cover various finderscope options. And for
planets you may want to use high magnification to see, check out this week’s
“Eyes on the Sky” videos at eyes on the sky dot com. Thanks for watching; keep your
eyes on the sky and your outdoor lights aimed down, so we can all see, what’s

  • A question,
    I have a 70mm celestron travel scope ,and i want to see the saturn and its rings.I have 3xbarlow,20,10,4mm eyepiece and diagonal.I can not even see the saturn properly as it looks blurry.what eyepiece,or barlow would you suggest for me to see saturn clearly,the only object i see is the moon and even for that i can not see the crater so clearly.I do not know what i am doing wrong and can not see it.Please HELP!

  • A Celestron Travel Scope is really a spotting scope intended for terrestrial observing. It will be difficult to get good views for astronomy viewing with it: 1) The focal length is quite short; increases chromatic aberration & hard to get full magnification. CA not as noticeable during day, but very evident at night with stars/Moon 2) The diagonal is a 45 degree style, which orients the image upright; a 90 degree type is better quality for night sky. (Not enough space to diagnose here easily.)

  • Would you suggest for me to change my eyepiece to plossl and diagonal or go for a better telescope??in that case what would be the best option to see the rings of saturn or other planets with detail?i want to also be able to view at least some of the brightest objects in the sky in detail such as arcturus,or vega well as possible galaxies or nebulas.Thank you

  • I would suggest a better telescope. A 114mm f/8 reflector would be a good option to consider; if your budget allows it, a 150mm f/8 or 200 f/6 Dobsonian reflector would be even better.

  • thank you so much :),i will order one of those asap.I have to go out to the park in 3 hours to observe saturn tonight as it is going to be in the opposition.could you please tell me what eyepiece,or eyepiece with 3xbarlow or with diagonal i should use for the best result for me to see saturn?i will be using my celestron 70mm travel scope tonight.

  • Hello, I have a Celestron Astomaster 90 with 20mm and 10mm eyepiece, which Barlow should I get to attain maximum best viewing? Thankyou

  • Because that telescope comes with the 10mm that would effectively be the same as a 20mm with a 2x barlow, and since a 2x barlow put the magnification at 200x, which is really beyond what that scope should do (175 is the practical max), I would suggest a 1.5x or 1.8x barlow.

  • Have you used any of the zoom eyepieces 8-24mm, with any of the barlow lens? some say the zooms are quite as good as dedicate eyepieces. The Astromaster 90, says max magification is 218, but, you mentioned 175 probably being the optimal range, that max range of 218 is based on the perfect set of parameters such as being on an island in the ocean on clear night, more so right?

  • Is there any Exit Pupil Amplification in the Telescope or Binoculars market? Just like Digital camera has lense digital Amplification too.

    Is that u means, Bigger magnification Eyepieces 66deg/40x=1.65deg FOV. Also plus
    your Exit pupil will also drop down from 80mm Lense size/40x = 2mm Exit pupil left.

    Is that correct? 2mm Exit pupil + 1.65deg FOV left? "How to see it in that way?"

  • I have this scope…..used it for a light weight birding scope, but its got awful CA, so i ended up stealing bits off it to use with a better quality scope. also cheap diagonals/erecting prisms can cause problems too…..some of the cheap 45deg ones also introduce image problems.

  • Amigo… Me compre un helios 900×76.tengo lentes de 20mm; 12,5m; 4mm; un erector 1,5X y un barlow 2X….

    y quisiera ver saturo,, tengo la localizacion, pero cuado le apunto se me ve demasiado chico..mucho que no se diferencia…. que lentes podria convinar para verlo con los anillos masomenos ? ..


  • Just realized that I was putting my shorty in the wrong place (that's what she said), I placed in behind instead of before.. thank you EOTS.. Great videos..

  • Hi there, with my telescope (9mm eyepiece) I have never been able to see much more than I could with a pair of binoculars. Being new to stargazing, I have wondered whether there is something simple which I have overlooked. I don't know whether I have been wrong to expect to really see anything with a telescope straight out of the box, or whether all this time I simply needed a barlow extension to see things up close?

  • What is the aperture and focal length of the telescope? Planets will always look very small, even in very large telescopes at high magnification; they won't ever look like the great Hubble, Cassini or even Voyager photos.

  • It is a Celestron Nexstar 130SLT, so the sights I have expected to see are what I have seen from others with the same product. It all but seems that it doesn't have any magnification at all, as if it just simply points in the right direction. I guess it is either the case that there is something that I am not doing right, or the magnification I need lies in additional lenses, or that the telescope is broken!

  • It only has a 650mm focal length, so with a 9mm eyepiece, you're only getting 72x magnification. That's fine for some star clusters and other deep sky objects (even the Moon), but it won't make the planets look large at all. You really need either a 2x or 3x barlow, or some 3mm, 4mm or 5mm eyepieces to get sufficient magnification from that scope. It should give you nice wide field view of larger objects like M39, M45, M42, M31 and the Double Cluster though.

  • Are these eyepieces all Plossls? The 8" scope can handle up to 400x magnification on the best nights of steady seeing, though you'll often be limited to 150x or 200x most nights, which the 7.5 should provide (around 160x). Sounds like you might need more eye relief…??? A Zhumell Z-Series, Orion Expanse or Astro-Tech LER series eyepiece might make the observing experience better for you; it's much easier to view through those ones in the shorter focal lengths of 4mm – 8mm.

  • oh thanks for telling me cause i was using my barlow lens opposite of my telescope for 1 month and thats why i was getting blurry image of the moon :DDDD

  • I probably said that before but since I'm watching this video again I'd like to say it one more time: Thank you. 🙂

  • very informative! thanks for the video. i am new to astrophotography and i hope you could answer this, if this kind of setup will work.
    Refractor+barlow+dslr w/adapter. There is no diagonal. Will i be able to achieve focus?

  • I own a Celestron 130 telescope with 10 mm (33 x) and 20 mm (66 x) eye piece. I just wanted to know which barlow lens I should buy, which would improve the magnification without any degrade in picture clarity. Thanks

  • i am new to stargazing so i don't even know how to attach the lenses to the telescope. i have a celestron cpc1100. is there a video out there that explains how to attach the barlow and lenses? thanks for any help, mark

  • I am in plan to buy celestron powerseeker 60 az. But still confused rather ts give me real pleasure to watch the world or not. Is saturn is visible to this telescope? Could i see the asteroid belt or other planets? Please help me

  • hi, great video, i have a problem.
    I have a camera attached to a barlow x2 fitted to my small cassegrain, i have it all fitted into a .965" to 1.25" diagonal. i get a bright spot that fades from the centre like a large hazy star, would this be due to the step up diagonal?

  • Hey there! Im planning to buy a Celestron firstscope 76mm… and its comes with two eyepices 15x and 75x….. Now my question is …. should I get a 2x barlow or a 1.5xto 3x variable barlow? And pls tell me what a variable barlow is along with pros and cons.. Thanks! Hope you see this and reply soon

  • i have a refractor 900 mm telescope i received as a gift over forty years ago. i have not used it much over the last twenty years or so and finally was able too get the lens mixed up while trying too use it again., the barlow lens i thought had lens at each end. i ask not sure about this and need to put the correct lens back on the barrel of it. any help would be welcome..thanks.

  • I have an Orion FunScope which I received as a gift.

    Specs (for those who don't know); A reflector scope. Comes with an
    Optical Diameter 76mm, a Focal Length 300mm; Focal Ratio f/3.9, and
    comes with two 3-element Eye Pieces (20.0mm (15x), 10.0mm (30x)). Its
    highest useful magnification 152x.

    Recommend folks see his video on this scope: "Orion Funscope / Celestron
    Firstscope review/comparison"

    I love it's portability and that sits nicely on my tripod, but like
    everyone here, I would like to improve my experience.

    I'm not a fan of wasting money on poor products, since sooner or later
    it will cost me, but I neither want to spent a ridiculously amount of

    Based on your videos (IMHO they are great introduction to this hobby!!),
    I should consider a shorty Barlow fully multi-coated lens. Based on the
    lenses I have, it should be a 3x or 5x Barlow lens.

    My goals is to be able to see the rings and moons of Saturn. (Just like I
    use to, with an old refractor scope I once had)

    Amazon results gave me few results of brands I'm familiar with:

    Celestron 93428 X-Cel LX 1.25-Inch 3x 3-element apochromatic Barlow
    Lens (~$65)
    Orion 8707 High-Power 1.25-Inch 3x 4-Element Barlow Lens (~$134)
    Orion 8715 High-Power 1.25-Inch 5x 4-Element Barlow Lens (~$175)

    Do you have any advice on these Barlow lenses, or should I consider a
    different vendor/model for my FunScope?

  • I have a 3x Barlow for celestron 60az, the vision is blurred even if I adjust it precisely, it only happens in the Barlow lens, others work fine, is my Barlow lens defective?

  • Hello guys are new to the telescopes, my daughter received a 76 mm Firstscope and I would like to Barlow lens 3x or 5x buy using eye SR4mm and H20mm you think would be most appropriate?

  • Hi, David! Can you tell something about these Eyepieces + Filters + Barlow lenses kits (comes with these fancy aluminium suitcases)? I'm really thinking about buying one ot these – Celeston or Orion – doesn't matter.

  • Hi guys! How important is it to place the barlow in the scope first as opposed to at the end, in the diagonal, and the lens or imager placed directly in the barlow?

  • I started using a 3x Barlow lens with a 20 mm eyepiece and the image is a lot larger but I can't get it to focus as well.

  • Hi David, I am ordering the Orion goscope II 70mm refractor should I get a barlow along with a 25% moon filter? Or will the Barlow create the same magnifications?

  • A couple of questions:

    1.) Does using a barlow impact the Telescopic Field of View ( TFOV)° ? For example my 600mm f-7.5 with a 10mm eyepiece with 82° AFOV gives me 1.36° of TFOV. If I were to add a 2x Barlow does that cut the TFOV in half to 0.68° TFOV?

    2.) Does using a 2x barlow double the eye relief distance of any eyepiece? And does a 4x powermate quadruple the eye relief distance?

    3) Does using a barlow impact the field stop diameter of the eyepiece in use? How is the value impacted?

    Thanks for all your effort. Great videos. I learned a lot. ( a lot more to go)

  • A video about Barlow lenses that doesnt mention the proportional loss of brightness even once (as doesnt the whole series) … big thumbs down.

  • I heard that every telescope has its maximum magnification.
    How do I calculate that?

    my telescope is
    skywatcher pro series(refractor)
    5mm / 20mm lense

  • I might sound dumb but I'm very new to astronomy. Can 2 barlows be stacked say a x2 and an x3 to make x5? I ask because I have a x2 and an x3. Thanks.

  • Hey EOTS, great vid as always. Just wondering, I have a Meade 114eq 1000mm f8.8 bird jones style. So there is already a lens mounted inside the focus tube. Is this effectively a built in Barlow? I read on some forums that I should stick to dedicated eyepieces instead of using barlows due to this added internal lens. Do you have any opinion on this matter? Have you used a bird jones with a barlow? Thanks for any help…

  • Hello David! Irecently bought a Meade LightBridge mini 82mm that came with a H20mm and a H9mm. I'm thinking in buying a Meade PL 4 mm multi-coated. This eyepiece would be good to see planets and nebulas with this scope? also could i use it with a 2x barlow lens? Thanks in advance!

  • Hi David,
    Thanks for the video;
    What is advisable?single or 3 glasses Barlow for better view of planets?
    With double or triple glasses you loose some light,with single you suffer of reflections,so after all,which one would you recommend for a better view and photography for a dark planet like Jupiter?

  • I have a Celestron Firstscope and I'm planning on getting a case with plossl eyepieces. Are they good to use with a the Celestron Firstscope?

  • Hey guys i have a question to everyone here, i see the Jupiter and its 4 moon from northern hemisphere (INDIA). Here is the question,

    If Jupiter and its moon are in the horizontal plane which is same as orbital plane of Jupiter and also same as Earth and its moon plane, then when i see the moons of jupiter should not they be placed in vertical order rather than in horizontal order ? Because if they are placed in horizontal order does it mean they revolve around Jupiter in plane perpendicular to the orbital plane of the Jupiter ?? Can some one please explain these to me…

  • So I have a 8" dobsonian Skywatcher, and I currently own a 2x barlow lens. I want to purchase a x5 barlow lens for better viewing of planets such as Jupiter, Saturn etc. Would you recommend I get one or would that not work very well?

    my 8" is 200mm/1200mm. I have a few eye pieces. The ones I got with my scope are the 25mm and 10mm eyepiece. With the boxset that has the 2x barlow lens I got the 15mm eyepiece and 6mm.

  • Hi David, I wanted to ask you a question on my telescope. So it's a Galileo telescope that has a D:76 and F:700 plus I'm using an eyepiece of 25mm but the problem is that the moon wasn't quite as close as I'd want it to be so I recently got a 3x barlow and it doesn't even show up good!!! Its super blurry no matter how close or far I move the magnification! please help!!!

  • Hi guys, I have to ask because I didn't understand your math equations at all in the video. I just bought the Meade Lightbridge 12. It came with a 26mm eye piece and a 35mm extender (Barlow I think). When I use the two together It's very blurry – what am I doing wrong? Are these two not to be used together? I hope to hear from you soon. Thank you.

  • i have a 5x barlow lense and i cant focus in it has the black dot with the light around it, what will i need?? 114mm mirror

  • @eyesinthesky I have a celestron astromaster 114eq telescope and was thinking of buying a barlow lens for it. the specs of my scope says the highest useful magnification is 269x. My question is, if the barlow lens exceeds that magnification with a particular eyepiece, will it make my views impossible to focus? Will it just make a bunch of blurry planets etc?

  • Hi I'm looking into buying a telescope that's got IR and I can switch out colors but I want to be able to stay planets and star clusters plus the moon but I need to stay under 1000$ I'm a part time student /teachinges kids what I learn! Can you be of any help ? I can send you my e-mail if you want or get yours !! Please lol

  • hey you probably won't get this, but maybe someone else can answer me if the know. whenever i go to focus my telescope, it shakes it up a ton and i can't really see what I'm doing very well. this isn't a very big problem with lower magnifications, or looking at things like the moon, but looking at plants or high magnification it's a really big issue. i was wondering if in most telescopes there happens to be some kind of crank i can pull on the mount or some way to keep it steady. for specifics, i have a celestron power seeker 70eq. I'm a very new astronomer so yeah

  • I had the barlow between star diagnol and eyepiece, couldnt focus on the planet i was after. put it where suggested in this video (although i did it before seeing the video) and got the focus! but the barlow is cheap, need a better one.
    This is a nice series of videos!

  • Hello I'm new to stargazing. I have a Galileo 800mm x 95 mm with a 3x Barlow and a 6 mm and 20mm eyepices I would like to view the planets , how can I do so , what do I need?

  • I've got a noobie question I hope some of you guys could answer. I agree buying a barlow that gives the same magnification as an eyepiece you already own, is a waste of money. However, it does make sense if that eyepiece has a wider field of view (and/or better quality lens). Since, though you dont gain magnification, you gain wider field of view. Is my guess entirely true? Is there something Im missing?

  • A barlow doesn't effect the eyepiece it only doubles the focal length . If you have a 900 fl telescope and use a 2x barlow your focal length will become 1800 fl . If your telescope is 400 Focal length and use a 5x barlow it will become 2000 focal length . If you have a 1500 FL telescope and use a 2x barlow it will become a 3000 FL . Basic maths

  • how to see through a jason 400x telescope model 306s explorer? I have one for my Autistic son and I can't figure out how to place the lens for the death of me. Please help.

  • Hello! I have a 10mm and a 20mm eyepiece and I'm looking to increase my magnification. Should I buy a 4/5mm eyepiece or a barlow?

  • Hi David, nice informational video. I'm planning to buy exploreone 50mm kids telescope for my six year old daughter at 35$. Will this work fine and still have decent view of the planets let me know. I'm on a shoe string budget

  • Hi David, just bought a used Meade ETX 70AT missing the barlow however I do have the eyepieces…can I use the telescope without it until I can purchase one?

  • I will be using the Celestron C5 with a D7200 Nikon camera. The C5 has a threaded t-mount built in. So all I will need is a t-ring for the camera. Is there a way to control the zoom are is it whatever I see through the scope?

  • hi love your videos and was looking for some help just started looking at stars and moon with a bresser NT 114 telescope it has a super plossl 26 mm lens and focal lenght of 500mm i would like to increase my magnification but not to sure what barlow lens would be good for my set up as im very new to this hobby and dont want to buy the wrong magnifier and end up with fuzzy image quality i belive my max magnification can go to 228

  • Your videos are best but I want to know how to set coordinates on ra and Dec circles on the eq telescopes

  • thanks for the information..I'm the new user of telescope and find difficulties in set up my telescope and don't know the differences of each eyepieces, erecting eyepieces and barlow lens

  • I own a Meade 102mm refractor,tried that trick of putting barlow before diagonal,it did not work at all.
    Could not get the thing to focus,think it may be a Meade thing from what i read on other comment boards.

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