Many people purchase a used telescope (or clean the cobwebs off the one in the basement) and wonder if new eyepieces will work with it. Or they plan to buy a new telescope but aren’t sure if the eyepieces they already own will be interchangeable with it. Let’s explore the answer to this common question and find out if telescope eyepieces are universal.
Telescope eyepieces are interchangeable as long as they have the same barrel size (the diameter of the eyepiece’s insert tube). The universal standard is 1.25” eyepieces and most modern telescopes accept them; however, even models that accept 2” eyepieces usually come with an adapter to use a 1.25” eyepiece.
That means you absolutely can use your Celestron 1.25” eyepiece with your new Sky-watcher telescope (or any brands for that matter).
But what about the older telescopes that only take 1” eyepieces? And will an eyepiece get the same result when used with a different telescope? Find out this and more as you read on.
Can I use 1.25” eyepieces on my old telescope?
Many older telescopes are designed for 1” eyepieces (.965” to be precise). Newer eyepieces, unfortunately, do not fit in these telescopes. There are, however, adapters that do allow these telescopes to accept a standard 1.25” barrel eyepiece.
But before you buy one, be sure to ask the manufacturer or seller of the adapter if it will work with your telescope, because sometimes your telescope won’t be able to achieve focus with the extra length of the adapter. Also, an adapter may not work with longer focal length eyepieces due to vignetting, where some of the light rays are not able to pass through, resulting in darkness at the edge of the image.
How do I know which eyepiece fits my telescope?
If you’ve purchased a used telescope, you may have no idea what size eyepiece it is compatible with. In this case, you’ll simply need to measure the distance across the opening in the focuser where the eyepiece goes. That measurement is the barrel size of the eyepieces you’ll need.
If it is a two-inch opening, then of course you can use 2” eyepieces. But see if your telescope came with a 1.25” adapter. If you don’t have one, you can probably purchase an inexpensive one. Then you’ll be able to use both size eyepieces.
Eyepieces perform differently when used in different telescopes
As we’ve seen, you can swap eyepieces between modern telescopes usually with no problem. But you’ll need to consider how an eyepiece might give very different results when used in different scopes.
Swapping between telescopes with different focal lengths
First of all, the same eyepiece will produce different magnifications when used in telescopes with different focal lengths. Focal length is the distance the light travels from the front opening of the telescope to the eyepiece. Longer focal lengths give higher magnifications. The formula for magnification is:
Magnification = telescope focal length / eyepiece focal length
So, if you put a 10mm (focal length) eyepiece in your Dobsonian telescope which has a 1000mm focal length, it will give you 100x magnification. Swap that same eyepiece into your 550mm focal length refractor and it drops to only 55x magnification.
Not only that, you will experience different fields of view in these two scenarios. If you stick a particular eyepiece in the telescope with the 1000mm focal length, your field of view will be much narrower than when you swap the same eyepiece into the telescope with the 550mm focal length.
Swapping between telescopes with different focal ratios
The second difference to consider is how an eyepiece performs in telescopes with different f-ratios. An f-ratio indicates the relationship between the telescope’s focal length and its aperture (the diameter of the front opening). The formula is expressed as:
F-ratio = telescope focal length / telescope aperture
The important thing to consider when swapping eyepieces is that telescopes with low f-ratios (about 3-6) usually require higher quality eyepieces. This is partly because of the steep angle at which the light enters the focal plane, which causes problems only solved by eyepieces with better glass and more lenses.
So, while you may enjoy magnificent views with your cheaper eyepiece in your f/15 Maksutov-Cassegrain telescope, you could be quite frustrated when using the same eyepiece with your f/5 Newtonian.
When you need a 2” eyepiece
Dobsonian telescopes often are designed to accept 2-inch eyepieces. The reason for this is that the owners of Dobs are often looking to view deep space objects, which are faint and wide in the sky. Once they get one of these faint fuzzies located in the eyepiece, they don’t want to have to keep readjusting the position of the telescope as the earth spins.
To get this experience - sometimes called the space-walk effect - you need an eyepiece with a long focal length (low magnification) and a wide field of view. The only way to get this combination is with a 2-inch barrel.
Maintaining a crisp image across larger fields of view is a technological feat. In fact, until recent years the technology didn’t exist on the consumer level. Good 2-inch eyepieces can cost several hundred dollars.
So, if you own a Dobsonian telescope and only have 1.25” eyepieces, you’ll be fine. You can still view just about anything you want to see with these smaller barrel eyepieces. But, if you really get the bug and find yourself wanting a more immersive experience, you’ll want to buy a more expensive 2” delight.
In short, yes, telescope eyepieces can be interchanged between different telescopes for the most part. You can use the universal 1.25” eyepiece in pretty much any modern telescope. Things may get trickier if you have a very old scope that needs .965 inch eyepieces, but it is possible to adapt these scopes to use modern eyepieces.
But remember - any particular eyepiece will perform differently when paired with telescopes of different optical designs. You’ll need to consider this when planning to acquire a set of eyepieces that work with your telescope (or telescopes).
Let me know if you think I missed something important. Your comments are certainly welcome.
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I took the attached photo with my phone through the telescope (with the phone included smartphone adapter)
This telescope is awesome. My wife and I are serious beginners and have been loving it. Ryan with telescope space has been nothing but incredible. So very helpful and a pleasure to work with. Thank you guys so much for a fantastic start to this amazing hobby!!!
My first telescope purchase and I hit the jackpot with Telescope Space! While doing my research, I found that pricing at the various online sites was very comparable. I chose Telescope Space for my purchase because of the avaialability of the equipment in which I was intersted. Little did I know that I would receive the absolute best online customer service I have ever experienced. And when I was having a problem with my newly purchased telescope (my problem - not the equipment's) I made a call to Telescope Space and was provided fantastic assistance by the founder of the company.
If you value customer service, I strongly suggest using telescope Space for all your astronomical optical needs - you won't be sorry you did. . .
Astronomer myself, I choiced this telescope for my 5 years old son who wants to explore the Universe.... And I ve been very impressed by the global quality of this product... all the optics are good enough to watch planets and near Messier objects....It s a great deal for all beginner (young and even expert)...
I thought my ED80 Triplet was nice but this ED102 FCD100 is awesome. Delivery and customer service was excellent.
I bought this scope for an industrial client whose needs are industrial, not astronomical, and this Explore Scientific ED127 is intended to be a beam expander in various Interferometric testing setups. For this, optical quality must be high and the carbon fiber tube is a plus for thermal stability. My purchase of the Explore Scientific ED127 F7.5 APO Triplet through Telescope Space was straightforward and pleasant. Ryan made sure everything was smooth.
Upon receipt I tested the scope by looking at a power pole 700 feet away, one that I have used for many such tests. The star test from the insulator glints was good – the focus snap was crisp, the in-focus diffraction blur was round with a faint first ring. I did not look at the through focus balance with a narrow passband filter as it was obvious there was no SA3. Color correction is very good as you would expect with the glasses used. There is no color in focus, and only a hint of subtle color fringing in the just out of focus edges of details. Extended details on the pole were rendered as well as, or better than, with any similar scope I have used on this target – this includes TMB, Astrophysics, and Takahashi scopes.
The build quality of the carbon parts is gorgeous. The metal parts are good quality anodized machined. I would prefer machined tube rings as the cast ones supplied are a little chintzy compared to the rest of the scope. The rack and pinion focuser works well, but the feel is not as good as some stock friction focusers I’ve used. Considering the extra high weight capacity of the focuser the feel may be the price paid. Overall I think the mechanical appearance and function is in line with the price.
I would certainly consider the Explore Scientific ED APO FCD100 triplet scopes for my personal use. My transaction with Telescope Space was great and I will do business with them again.
A great package for the price! The mount is steady! The Optics excel, in that the resolution and contrast are everything to be expected in a quality refractor! H.B. Appleton, Hi.
The staff at Telescope Space were very supportive and helpful as well!
I did considerable shopping around and finally decided to buy my 152 Mak from Telescope Space. Ryan was very helpful with all my questions concerning Explore Scientific and my specific purchase. After a short period using my scope and mount, the mount seemed to have more play than it should have. Ryan had the Explore Scientific owner call me directly, where he immediately offered to exchange my mount. He also had the factory ship out the new mount while I was still using my original unit. Excellent service and sales support from both Ryan at Telescope Space and Explore Scientific. I will buy again from Telescope Space!
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As a higher-level amateur, I was looking for a decent scope & mount that I can modify for my needs. The 130mm Newtonian scope fits my needs quite well. It comes with a 25mm eye piece--which is great. I would consider purchasing other eye pieces at the same time to give you a variety of magnification options. I'd recommend something like a 12mm and 8, or 6mm eye pieces to complement the 25mm. Getting a 2X Barlow will double your eye piece viewing options. The higher number will give you a wider view, smaller number a tighter, more magnified view. In order to just resolve the bands & zones of Jupiter, I need to use an 8mm eyepiece. For exploring Lunar geography, or seeing the Galilean Moons, the 25mm is sufficient. Saturn is just discernable, until you switch-out the eye piece for a 12mm, or smaller. The heavy & stable tripod mount is easy to set up, and the large rotation nobs allow you to smoothly track your subject as the Earth rotates. The Red Dot spotting site is dead-on accurate (once you dial it in). If you want a good, intermediate telescope: one that's neither too cheap, nor one that's too expensive, the 130mm Newtonian should fit your needs quite well. (Image of the Moon has been rotated and adjusted with photo software).
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For an amateur astronomer, this scope fits quite nicely. Everything arrived about 2 days after ordering. Assembly took less than an hour, and that was with a cat continuously attacking plastic wrapped items (cat not included). After assembly, I spent about 30 minutes fund-raising the control placements, mount angles, etc.... It comes with a 25mm eyepiece, which is a decent, general purpose unit. Perfect for observing the geography (selenography?) of the moon. Was also able to observe Jupiter and 4 of its moons. Couldn't resolve the Jovian bands with the 25mm eyepiece, so will purchase other eyepieces for viewing the gas giants. The red dot spotter scope was easy to dial-in for accurate spotting. It came with a battery, so all good. I would recommend this scope for serious amateurs, consider buying other eye pieces at the same time for various magnifications that you might need.
I wanted to take advantage of the recent Explore Scientific sale on their 8” imaging Newtonian Optical Tube Assembly when I came across this new company. The deal included a well discounted OTA, an in-store discount and a choice of accessories for which I wanted a nice bahtinov mask. I decided to call before I order. I received a call back within 15 minutes. All my questions were answered, my concerns about a new company were eased and I placed my order. Shipping literally took one day from the Explore Scientific facility. I’ve received a couple of follow-ups from Ryan from Telescope Space just to see how I liked my new scope! I’m looking forward to my next purchase from them!
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I purchased this telescope at Telescope Space and was very pleased with the process and the follow up support. Ryan made every effort to answer my questions that came up. I know that smaller companies have a tougher time to sell their merchandise compared to the "big" ones, but that does not necessarily mean that they are better. I have a good comparison right now since I purchased some other items from a different vendor and the answers I got from them were by far not as good (and timely!). The telescope itself is a wonderful piece of current technic, I already spent many hour taken some photographs through it (since I was lucky to have several cloudness skies since I purchased the telescope). Attached some examples what is possible with this telescope!
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