Telescope Basics 2 (of 6): Learn to calculate magnification for a telescope/understand focal ratios

[@matthias4]

This is so gold! I've read about the different ratios but didn't have an actual understanding of the differences until now. Thank you :)

[@chumpymcchump5024]

Once again, David, you have helped dispell the fog in my beginner's brain. Thank you and please keep the great videos coming.

[@ExperimentAtHome]

I have never seen a video with 577 likes and 1 dislike !!! Respect !!!!!

[@thischannel831]

Holy heck, its you!!!

[@Hexxas]

I know thease videos are old , but i find them very helpfull , please do never take thease down :)

[@Eyesonthesky]

Thanks - actually I did a lot of these during a couple weekends and a week I took off from work, which had a lot of cloudy skies. So I got a lot done - I hope they will help a lot of people understand the basics of telescopes.

[@zcommandante]

Имею 77мм * 1734мм фокусное расстояние линзу. Светосила будет слишком плоха или это нормальный вариант?

[@ayyyylmao-rg3ik]

Amazing, and on point explanation, really easy to understand for a beginner like me. Thank you!

[@NatarajanGanesan]

'I want this host fired' - I was on the floor

[@cosmictywlite]

Hi David,Thanks 4 verifying what I asked about Magnification,& mate you`r a good Teacher,easy to listen to but very interesting,much appreciated.

[@patrogers6297]

I have to rush to an appt. Can’t wait to see the other videos. VERY clear explanations. Thank you.

[@1obx]

EOTS.. I needed to find your vidz, they are helping me to understand my new hobby . Thank you for making us all understand a little more.

[@Eyesonthesky]

I can't speak to the Bresser line, as I haven't heard of them. But in general, the quality of the optics of those other three brands will be very similar when comparing comparably priced models. In fact, I think that some Skywatcher and Celestron products are made in the same factory, if I recall correctly.

[@Eyesonthesky]

Hi - yes, that is the general rule of thumb to follow for maximum magnification. On many nights though - no matter what telescope you use - the max magnification may be less than that, 125x or 150x, very often. On the best "steady atmosphere" nights, and when your scope is well cooled and there are no thermal "islands" releasing heat in front of you (like a parking lot or house), then the power can be pushed up to that 50x per inch range. Otherwise it may be best stay under that.

[@Eyesonthesky]

Those are great questions, but they are beyond the scope of what this particular video covers, and I couldn't possibly respond to it in 500 characters or less here. You may wish to check Wikipedia for articles about telescope design or ask in one of the astronomy forums about that question.

[@brianflynn5841]

Good video. I like how you used the same object to demonstrate the effect of different focal ratios.

[@brandonjhowe]

I want this host fired! Hahaha. Awesome vids. Just ordered my first telescope the other day and I can't wait for it to get here.

[@cricketfreakcf3069]

Nice video really, one Quick question I have a RC8 inch telescope no camera as I want to see the objects and not to do astrophotography as of now but will take this later on, I wanted to see galaxies, I have 9mm, 25mm and 40mm and 2x2 Barlow, what more I need to have to a wide field of view to see galaxies Nebula???

[@tucoelbrutto4491]

Thanks so much for your time I these videos..you have helped me so much!!

[@Eyesonthesky]

Ah, I understand. They are all the same, and will work on any of those types of telescopes or diagonals. So all 2" accessories are universal and compatible with each other. Hope that helps!

[@Eyesonthesky]

2" eyepieces generally provide a wider apparent field of view, but that depends on the type of eyepiece. Some 1.25" ones have wider AFOV's, and therefore may show more than simpler 2" eyepiece designs. It's not a question I can easily answer in 500 characters. That said, if you are doing afocal astrophotography (camera held up to the eyepiece), oftentimes using a 2" eyepiece will make this easier to accomplish, but it is harder to get more magnification then. There's lots of tradeoffs.

[@Eyesonthesky]

Thanks Brandon - just trying to keep the videos a little lighthearted and fun. Hope you enjoy your new scope when you get it! Clear and dark skies.

[@animeja]

Very very good Friend! Thank you for this class. Robinson - Brazil - São Paulo

[@gaskitten1]

Thanks for doing these videos. They are great. Keep up the good work!

[@cosmictywlite]

Hi David. Is there much difference between looking through a, 2" diagonal eyepiece & a 1.25" diagonal eyepiece,do you see more with a 2" ,or are they both similar, as I want to try Astrophotography,

[@sraufstok]

Hey thanks for these videos. I am buying a telescope but don't really know what to buy even though I've been watching a lot of videos and reading reviews of various models. Are there big differences in quality between brands such as Meade/Bresser and Celestron or Sky Watcher?

[@cosmictywlite]

hi David I Meant, for differant Telescopes like Refractor`s Reflector`s Maksutov-Cassegrian`s are 2" Diagonal universal or do you need different one for different Telescopes, sorry if I confused you mate,

[@kkbossop7223]

How do you calculate the focal length of the telescope??

[@Eyesonthesky]

Most telescopes list this number either on or near the focuser.

[@kkbossop7223]

Ok, so I am making a telescope by myself for a science project and my eyepiece has a 700mm focal length. What would be an estimate length of the telescope?

[@Eyesonthesky]

Most eyepieces are not longer than a 50mm focal length, and most are 32mm or shorter. 700mm is often a telescope focal length.

[@kkbossop7223]

@@Eyesonthesky ok noted, I’ll use that lens as my objective. So I’m ordering a lens which has a 10mm diameter. Will that be fine for the eyepiece? If yes what should be the size of the telescope tube? Any idea? Also thanks for replying!!

[@Eyesonthesky]

@@kkbossop7223 you have several questions here, a couple of which I am not sure I can answer. A 10mm eyepiece will produce 70x magnification with a 700mm focal length. I don't know the size of your objective lens or, more importantly, the lens cell, so I cannot possibly provide any information about what size tube you may wish to get that will work. The Stellafane website has a lot of good information about building telescopes; you may wish to peruse that for tips. I hope that is helpful.

[@mauriciopeterlevitz8902]

Excelent video buddy. Straight to the point thanks for sharing

[@AjinkyaNaikksp]

Hello David, I was planning to make a telescope at home, but I messed up with focal lengths, I just want to ask you that if I am going to make a 20x telescope then what should be the magnification of eyepiece lens and what should be the magnification of objective lens. It would be great if you answered.

[@christobean1997]

this is good info dave i am going to be doing an space pod cast i wanted to know what telescope i should use thanls

[@ghadaalmahri9418]

which telescope do you suggest to buy ??and where can i find a trusted shop?

[@ryanronczka766]

David, I was wondering how the focul length of the aperture affects magnification. Does a larger lense produce a greater magnification, etc??

[@ryanronczka766]

also does this same principle apply to microscopes too ( in terms of math)? just curius

[@danh1202]

Very good information . Great video Thanks for the easy to understand information

[@WealthHealthPeace]

Excellent videos, you've helped to interest me in telescopes more! :)

[@rich6661]

Hello and thank you for your videos. I recently purchased an older reflector telescope. Its a Simmons FL 900MM D4.5 with no barlow lens but SR 4MM (225x), SR 6MM (150x) and a F 20MM (45x) eye pieces. According to your calculation the F Ratio would be 7.9. I hope my calculations are correct in both magnification and F ratio. Is the telescope decent and should I purchase a shorty Barlow lens or look to buy a new telescope?

[@123callumrox]

this is one of the first videos i have seen with no dislikes. good job. thanks for this very well constructed and informative video.

[@aryanandaleebazim823]

At 5:13, what do you mean by focal ratio getting "FASTER" ?

[@Eyesonthesky]

As aperture of telescopes increase, manufacturers tend to make mirrors that have faster focal ratios so that tube lengths do not get too long.

[@aryanandaleebazim823]

@@Eyesonthesky well what does fast mean here?

[@Eyesonthesky]

@@aryanandaleebazim823 shorter focal ratios.

[@book3100]

So at around f8, it's kind of middle of the road.. field of view and magnification. Sweet.

[@cosmictywlite]

Just wondering are all 2" Diagonal Focusing Eyepieces Universal for Telescopes

[@sibirajsenguttuvan5154]

Very informative video, much appreciated!

[@cosmictywlite]

Gday David,I was told the rule to magnification,was 1" x 50 x times per inch,so if you have a 4" Telescope that would =200x magnification, is that rite or not.!

[@redpillscholar560]

I have a beginner NG 114mm EQ telescope. It came with one 26mm eyepiece, one 9.7mm eyepiece. How can i boost magnification???

[@Eyesonthesky]

A Barlow lens: kzbin.info/www/bejne/mqGpYpKHat6Dqc0 Or a shorter focal length eyepiece.

[@redpillscholar560]

Eyes on the Sky Thank you!!

[@Eyesonthesky]

You're welcome - glad to help!

[@HardWithStyle97]

The aperture of my Newtonian is 130mm, so 260x is the maximum magnification before the object gets fuzzy right? if I use a magnification of 216x with a 6mm + 2x barlow, will the object also get noticeably fuzzy? Thanks for letting me know.

[@bluename4]

how is magnification with primefocus using a DSLR instead of an eye piece?

[@chrissame]

I have a question: My telescope is a Newtonian Reflector, It has an aperture of 114mm and a focal length of 900mm. I find that I am not able to use a Barlow with it. I put the 10mm eyepiece and my 2x Barlow, I am not able to get a focused image. I tried with my 6.5mm eyepiece and 2x Barlow and it could not focus, Presumably because the magnification is too high. But why no focus with the 10mm? Is that normal for a telescope of that aperture and focal length?

[@Eyesonthesky]

Through the Telescope! Some Barlow lenses that come with telescopes of that size are of poor quality. It may be that you have one that just isn't very good. I once bought a 80mm refractor from a well known telescope manufacturer, and the Barlow that I received with it wouldn't even work on my large, better telescopes and high quality eyepieces.

[@wayangede2007]

What kind of lense we use in objective and eye piece? concave or convex?

[@Member_zero]

So ... I am interasted in observing night sky and while I know this video is old, I found it very good and informative! I have a question tho - reflector type telescope seems very simple in it's design so what about making one myself? What if I would say ... grab a 2m aluminum (or plastic or cardboard even) sheet and wrapp it in a tube, then put a big plastic concave mirror on one end and small angled mirror inside. Then I would just need to buy eyepiece - like 10mm one and I would in theory have a telescope capable of great magnification for very low budget?

[@Eyesonthesky]

Some people still make their own telescopes, although it is beneficial to make a small one first. www.stellafane.org has lots of information.

[@Member_zero]

@@Eyesonthesky wow thank you for a response! That is realy good website - thank you. Now I can start observing the night sky and satisfy do-it-yourself hobyist in me at the same time. You are awsome.

[@Eyesonthesky]

You're welcome Chris! Thanks for the email with the Moon pictures too.

[@FinnDillow]

Hi David. I really like your videos, and they helped me out a lot. I recently got a telescope and am hoping on viewing some planets and nebulae. What should my focal length and magnification be for viewing planets and nebulae? Thanks a lot.

[@Eyesonthesky]

+Solipsism Incepted For planets, very often you want to use as much as your telescope will handle. A good rule of thumb is to not exceed 40x to 50x per inch of aperture. Sometimes you may need to use less if the atmosphere is unsteady. For nebulae, it depends on the object. Some are large, some are small. This Telescope Basics series discusses how to understand telescopic field of view, so you can have a better idea of what eyepiece to use. In most cases, regardless of object (even planets) you will want to start with the lowest focal length eyepiece (20mm or 25mm), THEN increase magnification. Don't start with high magnification; it can be hard to find objects that way! Hope that helps.

[@FinnDillow]

Eyes on the Sky Thank you!

[@connorgoosen2468]

Made everything simple. Great vid

[@Eyesonthesky]

I'm not sure I understand the question. If you mean, "Are all 2" diagonals and 2" eyepieces universal / compatible with each other" then, yes.

[@richieb74]

I have a Orion spaceprobe 130mm 650mm focal length. I'm having trouble with deep sky objects. Is my telescope powerful enough to see stuff like the ring nebula and andromeda and Hercules star cluster?

[@Eyesonthesky]

richieb74 yes, it is. But you may be having trouble due to light pollution, light trespass, or other reasons. What exactly are you having trouble with? Finding the objects? Seeing them well once found? Something else?

[@richieb74]

Eyes on the Sky I'm pretty sure I'm pointed in the right spot but I am unable to see anything. I can barely see andromedas core and other things I can barley see or not see at all. The only nebula I was able to see well is Orion's nebula

[@Eyesonthesky]

richieb74 keep in mind that objects at your eyepiece will never look as good as photos. Try observing from a darker location, make sure you are dark adapted, and block excess/stray light. observe when the Moon is not up in the sky. Also, be patient. Look at the object longer. Or wait for a more clear/transparent night. All of these things will help you see more.

[@richieb74]

Eyes on the Sky thanks. I do live in a metro area. There could be light pollution. My back yard is pretty dark though. Unfortunately I don't know if any areas that is pitch dark near me. I only ask because I've read in some books that any aperture under 6" isn't good enough for anything besides the moon. Not sure about that.

[@Eyesonthesky]

richieb74 you can see deep sky objects through light pollution, though dark skies and/or more aperture does help. I always try to highlight objects people can still observe with scopes of your aperture. I started with a 50mm refractor myself. Keep at it, squeeze out every photon you can, and you'll be amazed at what you can see the more you look. then upgrade to a larger telescope when you can.

[@wirymarrow8935]

Can a astro master 70az look at planets good because my telescope makes planets just look like little dots

[@wayangede2007]

Hello I am Wayan from Bali,My telescope is celestron 600 mm focal length and i have twoo eye piece 20 mm and 4 mm,Can I add focal length with alloy pipe to make it longer and more power magnification?

[@festafreak]

interesting actually seeing the difference of the pictures! thanks.

[@Yarmox]

What is the biggest telescope called? and the middle sized one?

[@Eyesonthesky]

you're welcome!

[@Rico-Suave_]

Awesome video thanks

[@alphaphotoandvideo]

my small telescope is 70mm, focal length 350mm, manual says "max practical view is 240X" I don't think it is accurate🤔🤔🤔🤔🤔

[@funtimebandits]

Keep up the great videos!

[@AstroCosmos]

But No Role For The Distance In Between?

[@Eyesonthesky]

The distance in between what?

[@AstroCosmos]

@@Eyesonthesky Distance In Between Of The Two Lens (Objective And Eyepiece)

[@Eyesonthesky]

@@AstroCosmos that's the focal length of the objective.

[@AstroCosmos]

@@Eyesonthesky sorry i don't know that

[@Eyesonthesky]

@@AstroCosmos The focal length of the objective is usually provided on the focuser, in millimeters. What telescope do you have?

[@jr3474]

great informative video

[@EchoHawk1862]

So can you change the aperature of a telescope?

[@Eyesonthesky]

In one direction, yes. It is possible to reduce the aperture with an aperture mask. You cant make the aperture larger though.

[@EchoHawk1862]

So reducing the aperature would give me more magnification?

[@EchoHawk1862]

Would that do anything to the picture quality?

[@Eyesonthesky]

@@EchoHawk1862 it is both reducing resolution and increasing the effective focal ratio. So you would have to take a longer photo to get one that would have lesser quality.

[@Eyesonthesky]

@@EchoHawk1862 reducing the aperture would have no effect on the magnification.

[@choochoochooseyou]

What do you mean by faster?

[@Eyesonthesky]

I'm not sure what context you're asking this in. You mean faster telescopes? Those are ones with shorter focal lengths relative to their aperture.

[@choochoochooseyou]

Yes, that's what I meant to say. Thanks for the reply.

[@Eyesonthesky]

That's great to hear! Thank you so much for sharing that. :-)

[@Midgarov]

How do you that 76 mm is 1200 focal length?

[@Eyesonthesky]

Midgarov 76mm is the diameter of the objective lens. 1200mm is the focal length of that lens for light passing through it.

[@Midgarov]

Eyes on the Sky tnx for the realy fast response!

[@donloughrey1615]

Excellent, thank you.

[@Eyesonthesky]

Hi Wayne - unfortunately, it is not that simple. You would need to change the lens or mirror in your telescope in order for changing the tube to make a difference.

[@cosmictywlite]

Thanks very much David .

[@luzvimindavaldez5369]

Is there an reflector telescope under $100? It will help me if someone answer

[@Eyesonthesky]

I see you found my video about the best telescope under $100.

[@karamus962]

What mm mean for telescopes?

[@Eyesonthesky]

Karam Khamis mm = Millimeters.

[@bratcafe5632]

When using an imaging camera with no eyepiece, how is magnification calculated....? Exampe....My Telescope Focal length: 800mm Aperature: 203mm Camera Imaging chip: 8.4 x 8.4mm Cannot find an answer.

[@Eyesonthesky]

I think it depends on the imaging cameras specifications. Many planetary ones magnify similar to a 5mm eyepiece, but you should probably check the instructions of your camera to determine how it would compare to a visual eyepiece focal length.

[@foerdie]

I always run into your videos XD subscribed

[@WiseOwl_1408]

Thank you

[@petmo78]

This is a very good video, the best video, I know videos! tremendous Believe me!

[@feboogi]

You get a like !!

[@christobean1997]

oh good u did get that was not sure if it got thu as it said it froze when i clicked send

[@soldtobediers]

We see past time in a telescope and present time in a microscope. Hence the apparent enormities of the present. Victor Hugo

[@FollowTheSunDown]

STAY UP BRO, COMBINATION OF JOKES AND LEGIT INFO

[@leighash69]

Hello! My wife got me a F700/76AZ Newtonian Reflector. and that all i know about it! its come with all sorts of eye things lenses finders extensions things blablabla... i thought id get it out the box and it would be ready to look through how Wrong could i be!!! Could some one be so kind to give me some popular forums for noobs:) Thanks in advance GT

[@mrnosy1]

4:26 I think u meant reflector

[@k.h.1587]

H20mm is not an eyepiece, it is a dustcap

[@Mikza90]

Wow you got the president to camio.

[@Eyesonthesky]

4 years before he was elected even. (I made the video in 2012).

[@CyberSamurai4Life]

Lovin the Trump impresh. Spot on now hey?!

[@user-vr2ie5qd2j]

He looks like those movie bullies

[@wwrgodz3724]

is that a Donald trump

[@christobean1997]

Thanks typo

[@aryan5311]

You are funny

[@Eyesonthesky]

I hope I am somewhat funny and mostly informative.

[@aeroblaze0001]

Yea and this mixture is just so pure

[@cosmin12365]

Kids are spending money on forknife nowadays where is this world going to....

[@BeybladeMadne55]

My telescope's max magnification is 70x :)

[@kadoman0]

the Trump joke is even less funny four years later.... because I have a feeling that everyone in America is going to get fired

[@OneWithScience]

0:43 didn't age well.