Understanding Eyepieces for Telescopes - Focal Length, Size, AFOV, Eye Relief
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- Опубликовано: 25 июл 2024
- In this video I talk about eyepieces and some of the most important aspects to keep in mind when looking to buy a new one. This video will hopefully help you with your purchase decision.
⬇️ More Information down below ⬇️
Contents of this video:
0:00 - Intro
1:46 - Focal Length
6:47 - Size
7:31 - Apparent Field of View
8:50 - Eye Relief
10:28 - Important Features
12:28 - Outro
Equipment pieces:
Tele Vue DeLite 9mm
Full review: • Why buy this eyepiece?...
www.astroshop.eu/eyepieces/te...
Tele Vue Panoptic 24mm
Full review: • Is it really that good...
www.astroshop.eu/eyepieces/te...
Tele Vue 2x Barlow lens
Buy here (affl): amzn.to/3Q3LnMc
Omegon SWAN 32mm
Full review: • Omegon/Apertura 32mm S...
www.astroshop.eu/eyepieces/om...
TS-Optics UWA 6mm
Full review: • TS-Optics UWA 6mm - Pl...
Buy here (affl): amzn.to/3F4u2MU
Omegon 12” ProDob
Full review: • Is a 12" Dobsonian tel...
www.astroshop.eu/telescopes/o...
Choosing an Eyepiece - Step by Step By Al Nagler, Founder, Tele Vue Optics
www.televue.com/Pdf/Eyepiece_...
Stellarium free download:
stellarium.org/
Thank you for your support! 
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Sir, ultimate is your knowledge on the eyepieces
Thanks for this very informative review on eyepieces. Very helpful.
Outstanding tutorial!
Excellent information on eye pieces,well done!
Very well explained, great video.
Thank you for your detailed explanation !
Very informative. Thank you. How about talking about the advantages and disadvantages of 2" and 1.25" eyepieces.
@robgerst9943 Great idea, thanks! I'm puting it on the list for future videos.
Very useful video, thank you!
Love your videos man.
I’ve just started using my 8 inch Bintel gso dobsonian telescope.
I got the plossel I think they are called. They came with the telescope
30 mm 15 mm and a 9 mm
Your channel has been very helpful. Keep up the awesome work!
Would love to see more on the gso dob telescopes :)
@Anthony rozos Thank you! I'm glad that my videos are helpful to you. I just added GSO telescopes to the list of reviews to come 🙂
There are man different maximum focal lengths for 1.25" eyepieces, depending on the AFOV. The larger the latter, the smaller the maximum focal length. There are also limits for 2" eyepieces, so you can get even larger barrel sizes. The biggest ones currently available have 4.3", made by Siebert Optics.
Talking about Plossls, I read somewhere that the maximum useable focal length is 32mm in 1.25" form factor. If you want to use even lower magnification (higher focal length eyepiece) then you have to use 2" barrel size.
@Irfan Rashid That is true. Because Plössls have a smaller AFOV the lenses can be fitted in a 1.25" form factor event at longer focal lengths. I believe that for Plössels 32mm is the limit here.
You can use longer focal lengths, but they only increase the size of the exit pupil, not the true field of view. Therefore the apparent field of view will decrease with increasing focal length. I own a 40 mm Plössl frlm Celestron, but the AFOV is significantly below the standard 50° common with this design.
I just got my first Apolo Opticon Telescope,70mm diameter with focal lenght 300mm, maximum useful magnification 50x and 2 0.96' H20mm and H6mm eyepieces. I just like to use the H20mm and spot stars when the moon is behind clouds. Nice video btw!
@mortekay8195 Congrats on the new telescope! Clear skies 🙂
@@BogdanDamian Thanks! The same!
If you use a Barlow lens with a high-magnification eyepiece you might easily exceed the maximum magnification of your telescope so that's something to keep in mind.
Just wooooo 😌😌😌😌 😊😊😊😊😊!!!!
I subbed cause you arnt that type that uploads stupid crap as their nwer vids and it's still astronomy AND post 🔔
Thank you, I appreciate it!
@@BogdanDamian sure thing!
Longest focal length that can fit in 1.25 inch is 32 and 40mm
What type of OTA is that to the rear left of the gentlemen's shoulder?
so much educational info in one video, thank you so much. I'm about to buy the Apertura AD8 8" dob and it comes with a 2" 30mm super wide view eyepiece and a not-so-great 9mm 5 ER 52° plossl. I wanna buy 2 not so expensive eyepieces, 1 for DSOs and 1 for planetary viewing.
Q1: what's a good compatibility between ER and AFOV for DSOs? I don't wanna buy an eyepiece with wide FOV and a short ER.
Q2: What focal length is the sweet spot for DSOs
Q3: What's the lowest exit pupil i should go for when purchasing a planetary eyepiece? Do you agree with the 0.5mm exit pupil rule?
Thanks..
@maloukey M Thank you! Regarding your first and second question, it depends a bit on your preferences and if you wear glasses. I wear glasses and for me anything below 15mm ER isn't very comfortable. I also don't necessarily like EP with very wide AFOV. That is why my minimum requirements for a DSO eyepiece would be 15mm and 66°-70°. Here the 24mm Panoptic fits right in. The 22mm Nagler with it's 19mm of ER and 82° AFOV would hit the sweet spot for me. A great balance between ER and AFOV would be 17-20mm ER and 68°-72° AFOV.
Regarding the minimum exit pupil for planetary viewing, where the objets are fairly bright I would say that anything below 1mm won't get you any additional details of the target. The object will get bigger, but no new real detail will be perceived by your eye. For fainter objects you could go lower, possibly down to .5mm.
This may of course vary from person to person.
I hope this helps. Clear skies!
@@BogdanDamian thank you for taking the time to answer. Your videos are very informative and well edited and put out. Much love all the way from Saudi Arabia lol
Thank you, Bogdan. I really enjoy your reviews. Two questions, if I may:
1. Can you speak to the pros and cons of using 2" EP as opposed to 1.25"? I have an Apertura AD8 dob (f/5.91) and I want to go with the highest quality EP relative to "useful" AFOV, clarity, and magnification.
2. At what point do diminishing returns for that scope no longer justify the expense of high-end EPs?
@Brian Hart From an optical quality point of view there isn't any difference between 1.25" and 2" eyepieces. Up to a certain AFOV and focal length, the diameter of the light cone coming from the telescope and entering the eyepiece is small enough so that it's not obstructed by the smaller diameter of the eyepiece barrel. From that point upward the light would get obstructed. That's why manufacturers jumped to a larger 2" diameter.
In my opinion the best eyepiece that offers the widest AFOV and longest focal length, but still utilizes a 1.25" format is the 24mm Panoptic from Tele Vue.
I think that diminishing returns start to happen from the 400$ Mark upward. For example the jump from a standard eyepiece to the Tele Vue DeLite is big, but from this eyepiece to a Delos the gain in viewing experience, is much smaller.
@@BogdanDamian Thank you for your detailed response.
@@BogdanDamian Yet another question...What are your thoughts on the 31mm Nagler Type5 in general and compared to 24" or 27" Pan?
@Brian Hart The T5 31mm Nagler is a fantastic end game eyepiece, however it is also very expensive. It's hard to compare it to the Panoptic lineup since it sits in a different category. The Nagler offers very sharp, bright and contrast rich views at an 82° AFOV. So does the Panoptic but only with an 68° AFOV. If you value AFOV more than anything, then the Nagler is worth it. As an eyeglass wearer I struggle taking all 82° AFOV in at once (I can't get close enough to the lens), which is why I much more prefer 60°-70° eyepieces. The 24mm Panoptic is great also because it still comes in a 1.25" format, which ensures compatibility with almost every telescope and accessory piece out there.
Beginner question here about eye relief ...
I plan on getting the Explore Scientific 68° 24mm eyepiece and the TeleVue 2x Barlow.
When used in combination the eyepieces eye relief of 18 mm would be doubled up to 36 mm, if i'm not wrong. Would this already be too much with this particular EP or would it work just fine?
Is there a general threshold for eye relief from which problems start? Or does it depend on the specifications of every eyepiece?
Have watched several of your vids, so far. Very informative, at least for me as a total beginner👍
Subbed ...
@Mabus1288 Hi and thank you for subbing! Using a 2x Barlow lens does increase the eye relief, but it won't double it. The value by which the ER increases depends on the eyepiece and on the telescope.
With the increase of the ER, the exit pupil will increase too and this is what causes problems.
There is however no general threshold for the exit pupil. This is from person to person different and depends on the anatomy of the eye.
Personally I don't like it when the ER gets over 30mm. Combining the 24mm ES with the 2x Barlow from televue won't get you nowhere near that value.
I use my 24mm Panoptic with same Barlow without a problem.
As a beginner I’m still a bit confused and there’s a ton to learn 🧐 I have a Dobsonian Orion XT8 - and I’m still trying to figure it out if the : 3-6 mm Nagler Zoom - from Televue would be a good choice for my Telescope for DSO , nebulas, etc ?!? 🤔🤯
Great video Bogdan! Thanks for your content 👍🏻
@Ionut Iordache It's perfectly ok to be a bit confused when starting out. It will get much better with time. The 3-6mm zoom eyepiece from Tele Vue is way too powerful for observing DSOs. It's only suited for planetary observations. Keep in mind that the higher the magnification the dimmer the objects will appear in your field of view. You want high magnification (>150x) for planetary observations. This is because the planets are very bright compared to DSOs and it isn't bad if you lose brightness by using higher magnifications.
For DSO observations you want to use low magnifications (24mm).
This is because DSOs are much dimmer and (usually)bigger than planets.
Good choices would be the SWAN series (budget), Explore Scientific 82° series (mid tier) or the Panoptic or Nagler lineup from Tele Vue (premium option). Hope this helps.
@@BogdanDamian Thank you Bogdan! So the conclusion is that : if I wish to perform crazy awesome planetary observations ( lets say for example - one of the Jupiter's satellite, Neptune maybe ... ? :)))) - the 3-6 mm Nagler would be perfect for my Dobsonian XT8 ? However, if I wish to have DSO observing sessions - the 32 mm Plossl from Tele Vue ( which I already own and recently got it / but haven't tried it yet ) would be the right eye piece to use ? ( hopefully good enough - I remember got it with a discount ) ... Am I right ? or am I still lost ? Clear skies !
@Ionut Iordache Yes, you are correct. For high magnifications (planetary observations) you need short focal length eyepieces. For DSOs the opposite. You also need to keep im mind that any telescope has a maximum theoretical magnification, which is 2x diameter in mm. So for telescope it would be 400x. So you need to choose your short focal length eyepieces in such a way that you don't go over 400x. The zoom eyepiece from Tele Vue at the lowest setting of 3mm will offer you exactly 400x (FL telescope/ FL eyepiece - > 1200mm / 3mm).
The 32mm plösel is good for DSOs especially now if you are new to astronomy. Further along the way you might want to get something with a wider field of view, something like the Panoptic or Nagler from Tele Vue.
@@BogdanDamian I am very grateful for all the time you took to answer my questions. Also very grateful for all your content, which is truly helping me to learn much faster which is something I need and depend on ( since children are time consuming and the world we’re living in right now… its a TIME BLACK HOLE ! 🤦🏻♂️ )
I pray and hope your channel will continually grow and people will always see the value of your content and dedication. Thank you once again.
Dumnezeu sa te binecuvanteze omule. Multumesc!
I heard somewhere that an eyepiece the same size as the focal ratio gives the sweet spot for magnification. Have I misunderstood, in the case of the telescope I have ordered it is nowhere near its maximum useful magnification. I value your opinion. Thank you.
@aldugas1045 There might be some truth to this theory, but in my experience it seldom proved to be correct. The only aspect regarding this theory worth considering, has to do with the exit pupil (focal length of the eyepiece divided by the effective f-ratio of the scope). An exit pupil above 5mm can be problematic for the human eye. This is when the observer starts to see the image of floaters and blood vessels.
This being said, I don't think that there is a single optimal focal length for the eyepiece for a given telescope. What focal length offers the most details is, in my opinion, always going to be dependent on the seeing conditions and this varies from night to night. Hope this helps.
@@BogdanDamian Thank you.
@@BogdanDamian It's precisely small exit pupil which makes floaters etc issue.
Issue of big exit pupil is possibly not all light fitting inside eye's pupil wasting telescope's light collecting capability.
Hey Damian - do you have any experience with APM eyepieces? I like the idea of supporting a "local" company and the specifications of the eyepieces seem very good for the price?
@ManuelZ Hey, I only had a brief experience with the 12.5mm 84° and I can tell you that they are well built and have a premium feel to them. I really enjoyed the generous eye relief and the large multi coated lenses. They are not quite on par with TeleVue eyepieces in terms of image quality, but they are also much less expensive, which makes them very good value. In my opinion they are however better than Meade, Baader and co. I would put them on the same level as the Explore Scientific eyepieces. Hope this helps.
@@BogdanDamian yes it does! I'll get the 32mm uf 70° I think as overview piece. And maybe the zoom... 😇
Do telescopes all have a standardized image circle? What is it’s size? How much of an optical compromise does such standardization create? Are there times when you need to match the image circle of the eyepiece to the telescope, that is, the optics have been perfectly matched requiring a dedicated integration? Sorry, I don’t know anything about this subject.
@francisfrancis4219 I don't think I understand your question, sorry. Are you referring to the 1.25" and 2" eyepiece size standards?
Is there a difference between using a single eyepiece to get a magnification or using a barlow lens and higher mm eyepiece.
@aldugas1045 In general you want to have as few lenses in an optical system as possible. The more glass the incoming light has to pass through, the more light information will get lost and the quality of the image will get worse. With this being said, if the Barlow is of a good quality (Tele Vue or Explore Scientific) than you most likely won't notice any deterioration in image quality. A Barlow will also increase the eye relief of the eyepiece, which can be beneficial.
@@BogdanDamian Thank you
I have a 10 inch pro dob . I got the 7mm delite, what do you think compared to 9mm ?
@Hugo Phillips Hi! Quality wise both should be identical. In terms of usefulness with regard to your telescope, I would go with the 7mm version. The resulting 178x magnification is good for planetary observations even on nights with below average seeing conditions. If you want more power, you can simply add a 2x barlow and push it to 356x, which is very nice when conditions are ideal.
@@BogdanDamian awesome, glad I picked the right one :) Thanks for all the effort you put into your videos and responses, us subscribers really appreciate it !
Can you use 2’ eyepieces for smaller fl telescopes?
@BigBanannaMan Yes you can, but there is a limit where the eyepieces will start showing optical aberrations. This is is different for every eyepiece, but telescopes faster than f4.5 will start to pose problems eyepieces.
@@BogdanDamian i was thinking to invest in a good set of eyepieces, currently only have a 4’ musk but eventually thinking will end up with a 8 or 9.25’ sct so would it be better to get all 2’ eye pieces now instead of getting them later. Would an 8 sct benefit from 2’ eyepieces even?
@BigBanannaMan Yes, an 8" SCT will definitely work well with 2" eyepieces.
@@AstroBananna If you do general observing including wide showpiece clusters like Pleiades and Praesepe, SCTs aren't good with their limited FOV.
SCTs and all Cassegrains in general are more compact object telescopes.
That's the price of optical/physical design giving short tube compared to long focal length.
F ratio is Focal length/ aperture right? You said it the other way round i think
@Narasimha Kamath You are correct, I said it wrong in the video. The f ratio is focal length dividend by the aperture. Thanks for pointing that out.
Me as a beginner those are a bit pricey. But beautiful.
I understand you. You don't have to get right to TeleVue. Maybe try out some less expensive alternatives like Explore Scientific or Omegon. Those still offer 85% of what the TeleVue do and cost less than half.
Those omegons i was going order but I live in then US and I am a little skeptical on ordering things over seas. Alot can happen the further it has to travel.
If you have access to TS-optics eyepieces, then the planetary HR series for planets and the Expanse series for DSOs are also worth checking out.
I wont bug you anymore. Sry for disturbing you.
kind of lazy to recommend tele-vue gear, of course they are good, they cost a lot more than a lot of peoples telescopes do, just for 1 eyepiece. I know you occasionally do some less crazy expensive gear but your tele-vue being recommended every time is annoying for ppl who could never drop 350euro+ on an eyepiece, regardless of how good it is. Sorry.