Field of View, explained for telescopes (both telescopic and apparent) - Telescope Basics 4 of 6

[@bokkchoi]

Your videos are insanely digestible. They got me into astronomy and I bought an 8" dob a few years back. I moved and didn't use my scope for about 3 years and forgot most of the stuff I needed to know. Found your videos again and it's all coming back to me now. Even thought you don't post too often anymore, I really thank you for making all these videos.

[@atawahinta948]

I wish I had discovered this series a couple of months ago when I began Astronomy as a hobby. This series is absolutely excellent for a beginner.

[@Eyesonthesky]

Thank you so much for saying so! Clear and dark skies.

[@garywayne8567]

Thanks David. Thats pretty cool. This morning I was blown away. At 5:15 am I aimed my scope North West toward the horizon. I saw a star that had Blue, Green, red, white light shooting out of it. It was like watching someone welding. I have only had this thing for a week but I am eat up with mosquito bites from being in the field! I love this scope! Your videos have made it wonderful to pursue. Now if I can just remember to shut off the spotting laser pointer/aimer. Thanks for the info.

[@whydevin5409]

Top 5 tips for improving planetary views with eyes on the sky telescopes are pretty basic to use in my opinion but the solution is safe and reliable

[@RahulPatel-kx7zr]

Agreed my brother in law! Such useful advise you give to this world, may god bless your soul till eternity. Stay safe!

[@chakalonzote]

What a great video, I think it's the first time I actually understand it. I can't way to try my telescope!

[@rodneyjohnson4794]

love this series!

[@GaryMcKinnonUFO]

Thanks again, clear skies in the UK tonight, nice night for Lunar observing :)

[@staindoiram]

Great job In explaining very helpful!!

[@pratt123]

Gary, understand that even though the best views will be in the darkest areas, you can easily get good views even in heavily light-polluted areas. A nice dark corner of your yard with no direct light contact on your eyes or the telescope can reverse much of light's masking effects. You can even put a cheap bedsheet on a wire to create a portable shroud for this. The best telescope is one you use often. Better to use your scope in your yard often instead of getting perfect views rarely.

[@johnhawkes7681]

Superb informational video. So much for stereotyping mentioned in some of the comments.

[@garywayne8567]

David, your very talented at explaining things related to Astronomy. Thanks again for taking the time to do these videos. One question, have you noticed certain areas of the USA that are better for viewing the sky? I am in SW Florida but will be moving to Washington State in a few days and was just curious if their is any difference. I can't wait to carry my scope to the top of Mt Baker or somewhere like that. Very excited.

[@igrieger]

David did a great job back then, as usual! Clear skies!

[@Eyesonthesky]

Thank you! Just trying to provide solid information so people can more easily see things in the night sky.

[@guptaprasoon]

can you please explain how you calculated the diameter for tube you used to show 52 degree view. I need to understand the math behind it, so i can make wire frame circles equal to the TFoV of my eye pieces to use on star map( deep sky hunter) to star hop arond the sky.

[@mustafaeraslan5373]

hi I have a question I have a 70/900mm telescope I see only a part of the star closter . I have a 10mm and a 20mm eyepiece do you recommend larger eyepices like 25mm or more will it be better to see the whole closter

[@JavierRueda]

Hi, +eyesontheskyDOTcom, how is that sometimes it is used 52 AFoV and other times 40 it is used?

[@Eyesonthesky]

I don't know how to tell you to use it, b/c when I search for that I am finding many different EduScience models that are 50mm in size. As for what can be seen with a telescope of that aperture, it doesn't collect a lot of light, so the Moon, planets, and double stars are going to be the best objects for you to view with it. I cover many of these objects in my weekly videos; see some of the past ones a the "Videos" link on my site (look in November 2012 and the Herschel double stars videos).

[@ddcll9538]

Does aperture play any part in the field of view you get? Or does it only depend on the focal length of your scope and eyepiece?

[@Eyesonthesky]

It is aperture *and* focal length (that determines focal ratio) couples with the eyepiece combination.

[@ddcll9538]

@@Eyesonthesky wow thank you so much for replying to me! If a SCT and a refractor have the same focal ratio, but one is 10" and the other is 76mm, would they have the same field of view for a given eyepiece?

[@Eyesonthesky]

@@ddcll9538 it may not be perfectly identical, but very, very close, yes.

[@ddcll9538]

@@Eyesonthesky got it. Thank you sir

[@videoman4424]

Because of a tight budget, I am looking at the Celestron C90 are the C5. after watching this video I will upgrade the eyepieces. I Plan on taking photos with my d7200 do you recommend any adapters to enhance the photos

[@PraveenKumarSuryavanshi]

Following are the AFOV values you have mentioned for various eyepieces of 1.25" barrel diameters on website. My question is that, are all the values for 25mm focal length? Ramsden / Huygens: 35 degrees Orthoscopic: 40 degrees Keller / RKE: 45 degrees Plossl: 52 degrees

[@Eyesonthesky]

Praveen Suryavanshi those generally apply to other 1.25" barrel eyepiece too. 2" barrels would have wider AFOV. 0.965" have narrower ones, in some cases for longer focal lengths.

[@PraveenKumarSuryavanshi]

Thanks for the clarification. So, 1.25" Plossl 9mm & 25mm would have same AFOV of 52 degrees right. With that, I understand that the TFOV changes as 9mm sees only part of light cone coming at the focuser making the object more magnified compared to that of 25mm which sees larger light cone and shows more light with wider FOV. Correct me if I'm assuming incorrectly. Thanks

[@Eyesonthesky]

Praveen Suryavanshi you have that right.

[@wrnchhead76]

Ohhhhhh, now I get it. This channel makes me say that so often

[@jordandrake9822]

Hello, these videos are very helpful and easy to understand, i just had a few questions. Is there an AFOV limit a telescope can handle? For example, one telscope cant deliver veiws past 100 degrees AFOV while another can go beyond that. If this limit is a real thing, what is it that causes it? Is it the telescope cutting off the rest of the image past that degree limit? Is it the eypeice somehow? And lastly let me pose a scenario. Im outside looking at M31 and my eyepeice's magnification is a little to much to see all of the galaxy in my AFOV. As far as image quality goes, is it better to switch to a slightly less powerful eyepiece to see all of it, or should i get the same eyepiece but with a larger AFOV?

[@garywayne8567]

Hey thanks for the tip, Tonight should be beautiful in the NW for viewing. It's suppose to be clear and cold woot woot.

[@cosmictywlite]

Hi David,I was wondering where I find The AFOV is the number on the eyepiece or do I just work it out in my head,,or is this just a stupid question?

[@Eyesonthesky]

Hi there - not a stupid question at all! It's a great one. The AFOV is often not listed on most eyepieces (that are not 'wide field" ones). There are some general guidelines for them though - note these are for most 1.25" eyepieces, and are guidelines, not hard-and-fast AFOV's. 2 element eyepieces like Ramsdens or Huygen's type eyepieces are usually quite narrow - 40 degrees AFOV or so. 3 element ones like Kellners are usually 45 degrees. 4 element Plossls are typically 52 degrees, though a long 40mm Plossl is usually just 40 or 45 degrees, as the barrel of a 1.25" EP is too narrow to have a wider one. Other eyepiece designs that are looking to highlight their wide AFOV will very often list it on the EP itself - this usually applies to designs of 70 to 80 degrees AFOV or more. Hope that helps!

[@bonniemorgan9062]

Cosmictywlite, thank you for asking about this. David, thank you for explaining so well.

[@Eyesonthesky]

Thank you so much Gary. There are areas that are better for observing. Do a search on Google with the following terms: jshine dark sky finder From there you can find all kinds of dark areas - just keep in mind that even green zone areas are pretty darn dark, though obviously blue, grey and black are best. You shouldn't have much trouble finding those in the Pacific NW though!

[@musasda]

what do recommend for a telescope after my celestron 70az?

[@gomcse]

This is amazing work. Subscribed.

[@dawndavies9706]

Thank you for so clearly explaining Apparent and Telescopic fields of view!!!

[@davidfuller8830]

You're welcome. :-)

[@dawndavies9706]

David Fuller Can you tell me more about the AFOV with regards to specific degrees in EPs? For instance, if I've a 24mm 82º EP. What is that 82º of?

[@davidfuller8830]

Dawn Davies That's an 82 degree field that your eye appears to perceive at the eyepiece. But remember what you actually see there is the telescopic field of view; it just LOOKS wider because the AFOV is wider. So the higher the AFOV, the more of a "porthole into space" you're seeing. The lower the AFOV, the more it looks like looking through a straw. Then you calculate the TFOV based on the eyepiece specs and the telescope. Make sense, I hope? I didn't quite understand what you were asking, so with any luck that clarifies it for you.

[@bhu1334]

Using 10x50 binoculars with an eyepiece of 60 degree afov, I should get 6 degree tfov in each eyepiece. So does this combine to give a 12 degree tfov with both eye pieces due to the stereoscopic vision?

[@Eyesonthesky]

No, because it is 6 degrees for each eye, aimed at the same field of view. So it doesnt double the total field of view, it simply doubles how many eyes you have on that same field of view.

[@bhu1334]

@@Eyesonthesky so is there any advantage of using a binoculars over a telescope??? with the same tfov's?

[@Eyesonthesky]

@@bhu1334 binoculars give a much wider field of view than any telescope. So to see something like the Pleiades or the Beehive clusters, binoculars are better to use than a telescope.

[@TheZohan232]

i have a edu sciience 50mm refractor i really need to know how to use it or what i can see with it?? pls pls help

[@JG-bo1pw]

great! helped me with my homework as well!

[@pankajdeshamukh7657]

how can i get to know what is the apparent field of view AFOV,,, so i can calculate FOV for my telescope lencess

[@Eyesonthesky]

+Pankaj Deshamukh For more expensive eyepieces, the manufacturer or retailer will provide that information as a selling point. For less expensive ones, this is often not provided, but in general, Ramsden/Huygen eyepieces are often just 35 degrees or so, Kellners are in the 40-45 degrees range, and Plossls typically around 52 degrees.

[@pankajdeshamukh7657]

Thanks

[@cosmictywlite]

Thanks for that info about ( AFOV) & ( TFOV) much appreciated David

[@blobrana]

Excellent explanation.

[@alphaphotoandvideo]

Finally I got it! Thanks

[@temax]

Thanks for the video! I find it very hard to understand though, since giving numbers and maths is not a good way to explain to newbies. To really understand how it works an eyepiece, there has to be a different way. You start talking about 25 mm eye pieces and degrees, and folks have no idea what does 25 mm mean. You need to go a lot slower in my opinion :) For instance, when you divide numbers, you never say why? Why dividing those numbers give you magnification? The why is the "how it works". Understanding that, rather than memorizing how to divide and get numbers, would make people really get it. Thanks for the video though!

[@gamaltk]

+temax and many terms also, for example, he started talking that a telescope is faster than another without saying what that meant

[@Eyesonthesky]

+Gamal Trinidad Kabil In my second video in this series, Telescopes Basics 2, I do discuss fast and short focal ratio telescopes. Going in order of the series builds the knowledge of the viewer each step of the way. I would suggest starting at Telescopes Basics #1. Thanks.

[@Eyesonthesky]

+temax Most people do know what 25 millimeters is, so I did not want to insult viewers' intelligence by discussing something most people understand from school. Also, I do discuss why to divide the numbers. In Telescopes Basics #2, how to calculate magnification is discussed. Going in order of the series builds the knowledge of the viewer each step of the way. I would suggest starting at Telescopes Basics #1. Thanks.

[@markadams8452]

IMHO His explanation in this video was one of the clearest and easiest to understand of pretty much any video I've seen. If basic grade school math is too much for you to comprehend, perhaps you should take a math refresher or perhaps slow down and watch the video a couple times. I understand math isn't everyone's strong suit(including myself) but the basics are needed if you are seriously considering this as a hobby. Some things can only be dumbed down so much. Good luck in your endeavors! P.s +Eyesonthesky great video bro!

[@hudsonriverlee]

Hey David Fuller hello from David Fuller in Biddeford Maine.

[@bauerconsults2800]

Good insight.

[@bauerconsults2800]

Have a great weekend.

[@gigsandbusking8959]

Brilliant, thanks

[@knowledgeispower5668]

I wish you were my neighbor we bought a telescope 3 months ago we can’t still see anything at night

[@woodfamily5229]

Man, no matter how many times I watch these videos, I am so lost still. I am just going to settle for pointing my telescope up and having a great time seeing things. I know the constellations and everything. That all makes sense. Just the techy part of it.... lost.

[@Eyesonthesky]

Derrick, where do you get lost? Send me an email. I can walk you through the parts where you may be having trouble. Check the "Contact" page (it's under the "Home" tab) on my website.

[@woodfamily5229]

You are wonderful. Thank you. I am brand new to this and I think I was just a bit overwhelmed when I wrote that comment (at 4:30 in the morning which is never a good time to write online!). I feel better about it now. I will be contacting you if needed. Thanks again.

[@Eyesonthesky]

Glad to help!

[@drissdrissso2379]

🖒🖒🖒🤗🤗🤗

[@scottrydings8579]

I have a headache now. I'm going to stick to high powered binoculars !!!

[@Eyesonthesky]

Right? And this doesn't even get into the discussion about exit pupil, which starts to make my eyes bleed. :-)

[@michaelbrissette4487]

It’s insane how people can’t understand the math, you’re literally just dividing twice.

[@sjennings3460]

I guess I should be glad I could find the moon through the finder lense.

[@creepyname]

first again, or my second first

[@k.h.1587]

TFOV stands for true field of view

[@sjennings3460]

i don't understand any of this. I guess I'll just box it up.

[@Eyesonthesky]

+S Jennings What part don't you understand? Maybe I can explain it another way.

[@Agent-vj3ns]

All of his videos REALLY start around 0:40. Fail.

[@manccyclist]

too technical for novices.....

[@LivingLikeMyself]

am i the only one here who just wants to just smoke some weed with this guy