The Barlow Lens ?

Discussion of optical systems and their characteristics.
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Frankskywatcher United States of America
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The Barlow Lens ?

#1

Post by Frankskywatcher »


I’m posting this in the hopes of getting some insight about Barlow lenses.

I’m just really curious how often they are used,the results, price ranges etc. etc. etc.
I ask this because I don’t have one.
I don’t really see people talking about them all that much, but I don’t understand much in terms of how they actually work and when they should be used.
I mean, I know they magnify everything 2×3 times but I’m trying to wrap my brain around how they actually work.
In other words if I’m looking at the moon and using a 6MM EP and I put that EP into a barlow isn’t that just overkill, woun’t the image be super distorted, I’m already so low at six MM?
I guess what I’m really saying is I need an education because I have no clue about this topic so please enlighten me and thank you in advance!
Gee if I had known there was so much to see I would have started decades ago ! :Astronomer1:

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Re: The Barlow Lens ?

#2

Post by Bigzmey »


You got it right Frank. 2x balrow will turn 6mm EP into 3mm, 12mm EP into 6mm, etc. This is useful if you don't have 3mm EP, or if you have a lousy 6mm EP and super good 12mm.

If you have a complete set of good EPs to cover all useful powers, you don't really need 2x barlow.

1.25x, 1.5x, 1.8x barlows could be of more use because using them you can cover intermediate FLs you don't have. Let's say you space your EPs at 2x interval, so you have 5mm EP and next is 10mm. Using 1.5x barlow with 10mm gets you 6.7mm FL.
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Re: The Barlow Lens ?

#3

Post by Makuser »


Hi Frank. Barlow lenses work because they have a negative focal length (usually around -44/45 mm). You can buy Barlow lenses from some outlets with ridiculous magnifications up to 4-5X. However, they are pushing the limits and the quality is usually poor. A feature of the Barlow lens is that a good one can increase your magnification while maintaining the eye relief of the eyepiece that it is used with it. My all time favorite is the 2.5X 1.25" Televue PowerMate, which has been my choice ever since I bought it a few years ago. As Andrey mentioned, at 2.5X you won't be duplicating your current eyepiece collection focal lengths. The PowerMate has 2 Barlow elements with also 2 condenser (collimating) elements, which brings the object back to a sharp focal point (like the old photography enlargers and wall projectors). I hope this helps Frank and the best of wishes on your Barlow lens purchase decision.
Marshall
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Re: The Barlow Lens ?

#4

Post by Thefatkitty »


Good advice and info above :D

I have an old (early 80's) Japanese made Vixen 2X 1.25" barlow that is really good quality. However, like Marshall I now have the Powermate 1.25" at 2.5X. Even better quality. Bit of a price difference, but you get what you pay for :D

Just my $0.02 and probably worth a grain of salt :lol:

All the best,
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Too much Towa glass/mirrors.

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Re: The Barlow Lens ?

#5

Post by The Wave Catcher »


I will add one other thing I’ve noticed about Barlow lenses that will have to be verified. I have a problem with eye floaters. When I use high power eyepieces, say 4 mm, my floaters come into focus and compete with the details I’m trying to look at. However, when I use an 8 mm eyepiece and a 2X Barlow, I get the same power but the floaters seem more out of focus. I’ve even used a 12 mm and a 3X Barlow with an even better, apparent reduction in floater competition. I have not studied what’s going on in the optical path when using Barlow lenses to see if this makes any sense. Is it possible that eye floaters only come into focus at short eyepiece focal lengths, regardless of the telescope’s magnification and so anything that allows for longer EP focal lengths (ie., Barlow) will help?

I wonder if anyone else has noticed this, knows about this, or is willing to do some experiments to confirm? The only caveat to an experiment is that you have to also suffer from floaters.
Steve Yates

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Re: The Barlow Lens ?

#6

Post by Don Pensack »


The visibility of floaters in single eye observing is solely related to exit pupil, whether in a separate eyepiece, or a longer focal length barlowed.

Barlows can increase the eye relief of an eyepiece, and, by making light rays more parallel, reduce astigmatism in an eyepiece, but not reduce floaters.

So, I suspect other factors at work:
--dust on the eyepiece lenses
--eyelash oils on the eyepiece lenses
--the movement of the eyepiece+Barlow focal plane away from a lens element with dust on it.

I have done exactly what you suggest in order to produce high powers on the Moon before I owned a number of short focal length eyepieces.
For me, in my scopes, and having eyepieces that lack astigmatism, the separate eyepieces yielded better images than the longer eyepieces with Barlow added.
But I saw floaters in both cases--any time the exit pupil drops below about 0.6-0.65mm.
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Re: The Barlow Lens ?

#7

Post by Makuser »


Hi Steve. I too have some floaters in my right (viewing) eye. I am no expert but I notice that they show up more prominently when I look towards a distant bright object with a light background (sky, white or light yellow colors) but they don't seem to be as much annoyance when looking at something close in lower light. Using a Barlow lens in a telescope, your image is darker with the added magnification and you are looking directly into the eyepiece. So what this may be is a combination of brightness, contrast, and focus. Sheri and I have a eye doctor appoint coming up in the next week or so for annual check up and I will ask him why this happens.
And to cover another base on this thread topic, here is something that many folks don't know about using a Barlow lens:
If your telescope uses a diagonal the Barlow lens can be placed before the diagonal giving you an even slightly higher magnification factor. However this configuration requires several inches of outward focuser travel and you may need an extension tube to achieve focus. I have never done this because of the extra time, trouble, expense, and weight. Besides, how much magnification do you need? :icon-smile:
Marshall
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Re: The Barlow Lens ?

#8

Post by SkyHiker »


I will definitely check to see if the floater observation is real but rationally speaking, it can't be.

I find my Barlow convenient because it multiplies the number of available focal lengths, not add one at a time like with individual eyepieces. In fact, my GSO 2" ED Barlow can be used at magnifications of 2x and 1.5x so the multiplication factor is 3 if I want to nitpick. I can use them with both 2" and 1.25" eyepieces so what's not to like. It's not a crummy Barlow and you can buy a few 1.25" eyepieces for its price, but the idea of a quality 2" Barlow appeals to me. For 1.25" eyepieces only, the advantage might be less.
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Re: The Barlow Lens ?

#9

Post by The Wave Catcher »


I’m sure you are all correct, except there is no doubt that it is floaters that I see and they become clearly focused with small focal length eyepieces. However, if seeing floaters is related to lack of eye relief with short focal length eyepieces, and if a Barlow allows one to use a longer focal length eyepiece with more eye relief for a given power, then isn’t it safe to say a Barlow reduces the visibility of floaters for a given power? I know it isn’t the Barlow lens itself reducing the visibility of floaters but by using one, you can use an eyepiece that doesn’t focus your floaters and still view at the same high power.
Steve Yates

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Astro-Tech AT80ED, 80 mm, F/7, ED Achromatic Refractor
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Re: The Barlow Lens ?

#10

Post by Frankskywatcher »


Wow thank you everyone for the input and not just about Barlow’s BUT I also get “floaters” I see them every once in a blue moon not as bad as The Wave Catcher and Makuser so this also interested me.
Gee if I had known there was so much to see I would have started decades ago ! :Astronomer1:

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Re: The Barlow Lens ?

#11

Post by jrkirkham »


I think it is a matter of choice and everyone is different. Some people don't use barlow lenses and others always use them. I have had a number of eye problems. I like the extra eye relief I get by using a barlow with a lower powered eyepiece. I have three barlows: 2X, 2.5X, and 3X. I use them every time I oberve. My favorite is my 2.5X 1.25 Powermate.
Rob
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Re: The Barlow Lens ?

#12

Post by Frankskywatcher »


jrkirkham wrote: Wed Mar 01, 2023 2:55 pm I think it is a matter of choice and everyone is different. Some people don't use barlow lenses and others always use them. I have had a number of eye problems. I like the extra eye relief I get by using a barlow with a lower powered eyepiece. I have three barlows: 2X, 2.5X, and 3X. I use them every time I oberve. My favorite is my 2.5X 1.25 Powermate.
Thank you for your input because what you said about eye relief was what got me thinking about them.
For example trying to look at Venus no matter what EP I use all I see in reality is a bright disk.
When looking at Jupiter or Saturn this past few months I could see the rings on Saturn and the” lines”on Jupiter as well as the moons on both planets.
However looking at both Venus and Mars all I see is a yellow disk and an orange disk and I can’t look at them for long or my eye will tear up,I don’t know if that because of the eye relief of the lower MM EP’s and or would a Barlow help with that ?

P.S. I forgot to add that this is another reason I’m asking about barlow’s because when they come up for sale on CN they get snapped up !
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Re: The Barlow Lens ?

#13

Post by Makuser »


Hi Frank. Here is a nice deal on the TeleVue 2.5X 1.25" Powermate from a well known popular supplier:
https://www.highpointscientific.com/tel ... e-pmt-2513
I hope this helps Frank and the very best of regards.
Marshall
Sky-Watcher 90mm f/13.8 Maksutov-Cassegrain on motorized Multimount
Orion Astroview 120ST f/5 Refractor on EQ3 mount
Celestron Comet Catcher 140mm f/3.64 Schmidt-Newtonian on alt-az mount
Celestron Omni XLT150R f/5 Refractor on CG4 mount with dual axis drives.
Orion 180mm f/15 Maksutov-Cassegrain on CG5-GT Goto mount.
Orion XT12i 12" f/4.9 Dobsonian Intelliscope.
Kamakura 7x35 Binoculars and Celestron SkyMaster 15x70 Binoculars. ZWO ASI 120MC camera.
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Re: The Barlow Lens ?

#14

Post by Bigzmey »


I don't use barlows often, but when I do I use Baader Q barlow

https://agenaastro.com/baader-q-barlow-bqb-2956185.html

I used to have Televue 2x and 3x barlows, but because of their long factor they were colliding with prisms in my diagonals. Otherwise they are of great quality.
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

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Re: The Barlow Lens ?

#15

Post by Thefatkitty »


Makuser wrote: Wed Mar 01, 2023 6:08 pm Hi Frank. Here is a nice deal on the TeleVue 2.5X 1.25" Powermate from a well known popular supplier:
https://www.highpointscientific.com/tel ... e-pmt-2513
I hope this helps Frank and the very best of regards.
Agreed; and even though I'm in Canada, it was cheaper (even with tax, shipping & duty) to get it from High Point than here in the great white north. I had it in 4 days; meanwhile, no supplier here has stock :lol:

Go for it Frank; you know you wanna!!

All the best,
Mark

"The Hankmeister" Celestron 8SE, orange tube Vixen made C80, CG4 & AZ-EQ5 mounts.
Too much Towa glass/mirrors.

H/A - PST stage 2 mod with a Baader 90mm ERF on a Celestron XLT 102 (thanks Mike!)
Ca-K - W/O 61mm, Antares 1.6 barlow, Baader 3.8 OD and Ca-K filters with a ZWO ASI174mm.
W/L - C80-HD with Baader 5.0 & 3.8 Solar film, Solar Continuum 7.5nm and UV/IR filters with a Canon EOS 550D.

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Re: The Barlow Lens ?

#16

Post by Frankskywatcher »


Thefatkitty wrote: Wed Mar 01, 2023 6:32 pm
Makuser wrote: Wed Mar 01, 2023 6:08 pm Hi Frank. Here is a nice deal on the TeleVue 2.5X 1.25" Powermate from a well known popular supplier:
https://www.highpointscientific.com/tel ... e-pmt-2513
I hope this helps Frank and the very best of regards.
Agreed; and even though I'm in Canada, it was cheaper (even with tax, shipping & duty) to get it from High Point than here in the great white north. I had it in 4 days; meanwhile, no supplier here has stock :lol:

Go for it Frank; you know you wanna!!

All the best,
I can’t stop laughing “ you know you wanna,” ! :lol:
Gee if I had known there was so much to see I would have started decades ago ! :Astronomer1:

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Re: The Barlow Lens ?

#17

Post by Frankskywatcher »


Makuser wrote: Wed Mar 01, 2023 6:08 pm Hi Frank. Here is a nice deal on the TeleVue 2.5X 1.25" Powermate from a well known popular supplier:
https://www.highpointscientific.com/tel ... e-pmt-2513
I hope this helps Frank and the very best of regards.
Thanks for the link I got sticker shock but as they say you get what you pay for !
Gee if I had known there was so much to see I would have started decades ago ! :Astronomer1:

Equipment :
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Polaris 4” Dobsonian

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Re: The Barlow Lens ?

#18

Post by Frankskywatcher »


Bigzmey wrote: Wed Mar 01, 2023 6:21 pm I don't use barlows often, but when I do I use Baader Q barlow

https://agenaastro.com/baader-q-barlow-bqb-2956185.html

I used to have Televue 2x and 3x barlows, but because of their long factor they were colliding with prisms in my diagonals. Otherwise they are of great quality.
Thanks for the link this is more in my price range but I still have to make sure I buy something compatible with the EP set that Makuser was so kind to give to me !
Gee if I had known there was so much to see I would have started decades ago ! :Astronomer1:

Equipment :
Apertura AD10” Dobsonian

Polaris 4” Dobsonian

7x50 binoculars
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Re: The Barlow Lens ?

#19

Post by Bigzmey »


Frankskywatcher wrote: Wed Mar 01, 2023 7:02 pm
Bigzmey wrote: Wed Mar 01, 2023 6:21 pm I don't use barlows often, but when I do I use Baader Q barlow

https://agenaastro.com/baader-q-barlow-bqb-2956185.html

I used to have Televue 2x and 3x barlows, but because of their long factor they were colliding with prisms in my diagonals. Otherwise they are of great quality.
Thanks for the link this is more in my price range but I still have to make sure I buy something compatible with the EP set that Makuser was so kind to give to me !
Don't be alarmed by lower price. Baader makes good quality products. In my hands it worked as well as Televue barlows. Otherwise I would not sell those. :)
Scopes: Stellarvue: SV102ED; Celestron: 9.25" EdgeHD, 8" SCT, 150ST, Onyx 80ED; iOptron: Hankmeister 6" Mak; SW: 7" Mak; Meade: 80ST.
Mounts: SW: SkyTee2, AzGTi; iOptron: AZMP; ES: Twilight I; Bresser: EXOS2; UA: MicroStar.
Binos: APM: 100-90 APO; Canon: IS 15x50; Orion: Binoviewer, LG II 15x70, WV 10x50, Nikon: AE 16x50, 10x50, 8x40.
EPs: Pentax: XWs & XFs; TeleVue: Delites, Panoptic & Plossls; ES: 68, 62; Vixen: SLVs; Baader: BCOs, Aspherics, Mark IV.
Diagonals: Baader: BBHS mirror, Zeiss Spec T2 prism, Clicklock dielectric; TeleVue: Evebrite dielectric; AltairAstro: 2" prism.
Filters: Lumicon: DeepSky, UHC, OIII, H-beta; Baader: Moon & SkyGlow, Contrast Booster, UHC-S, 6-color set; Astronomik: UHC.

Observing: DSOs: 3106 (Completed: Messier, Herschel 1, 2, 3. In progress: H2,500: 2180, S110: 77). Doubles: 2382, Comets: 34, Asteroids: 255
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Lady Fraktor Slovakia
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Re: The Barlow Lens ?

#20

Post by Lady Fraktor »


Frankskywatcher wrote: Wed Mar 01, 2023 4:31 pm
Thank you for your input because what you said about eye relief was what got me thinking about them.
For example trying to look at Venus no matter what EP I use all I see in reality is a bright disk.
When looking at Jupiter or Saturn this past few months I could see the rings on Saturn and the” lines”on Jupiter as well as the moons on both planets.
However looking at both Venus and Mars all I see is a yellow disk and an orange disk and I can’t look at them for long or my eye will tear up,I don’t know if that because of the eye relief of the lower MM EP’s and or would a Barlow help with that ?

P.S. I forgot to add that this is another reason I’m asking about barlow’s because when they come up for sale on CN they get snapped up !
When viewing planets with a Newtonian your colimation needs to be exact though Venus can be a tough target so focus must be exact or it will blur a bit.
Features will appear as darker areas so may be hard to spot. Sky conditions will be a major factor in seeing planets clearly.
I cannot think of a cause for your eye tearing up with shorter focal length eyepieces, have you had your eyes checked recently?
Try using your other eye as well as you may get a clearer view.
A barlow will not significantly alter the eye relief of a eyepiece, maybe a mm or so. Powermates preserve the original eye relief and do not extend it, they just change the shape of the lightcone entering the eyepiece.
If you want to try a barlow as a starter I would recommend the GSO 2 or 2.5x as they are good quality and inexpensive. Leave the expensive ones for when you know it will help you.

So collimation, focus and eyes should be checked before spending. ;)
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
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