TheSkySearchers

Creating a basic set of eyepieces for your new telescope
by Graeme1858

By: Lady Fraktor One of the most asked questions by beginners, What eyepieces should I get? There is always a lot of discussion from people on what eyepieces to get with their new telescopes. Most people seem to want to get the most magnification possible right away, but unfortunately, reality in the...
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Well, I dunno... I read that... For one thing, Lady Fraktor places a lot faith in numbers. To me, as a rationalist and a materialist, when it comes to people, numbers are guides, only. She notes that your dark-adapted pupil diameter changes with age. But there's no chart or formula for that, and even if there were, people are individuals. Even your right eye and left eye will be different.

And if that changes over time, then you will need to be changing your oculars ("eyepieces") over time. What worked when you were 40 or 50 will not work when you are 70.

The last time I got glasses (March of this year), I asked the optometrist (doctor of) to tell me my dark adapted pupil diameter. She said she was never asked that and would not do it as part of a routine exam. So, the first measurement remains unknown. You guess based on experience at night with your telescope and eyepieces.

Perhaps more to the point, my first (adult) telescope was a Celestron EQ-130 for $400 (give or take) back in 2014. I sent back the motor drive (unused) and bought the Celestron Lens and Filter Kit, which then retailed for $159. (It's like $100 more now.) But, I just bought a Nagler 82-degree for $299. (I lucked out. The retailer had one of these Series-1 oldies left unsold from 2014 or something.) Of course, I have a different telescope now. I bought the eyepiece to go with my $1399 AT-115 APO Triplet. My point is that at average prices for better eyepieces (not the Celestron kit), the recommendation for a full set is about $1000 (eight oculars at $129 each.) Of course serious lensing will cost two or three times that. A single TeleView 21mm Ethos will retail at $859. That's three times the cost of my Explore Scientific 102mm Refractor (used and factory reconditioned at 40% off) and twice the price of my Bresser 8-inch Reflector (also used and factory reconditioned).

I understand and appreciate the need for quality instrumentation, but you can't make a silk purse from a sow's ear. The oculars ("eyepieces") must match the optical tube assembly (OTA) for quality and utility. I live in the city. I go out every clear night that I can, even on "school nights" (work), at least for an hour before 2300 and midnight at the latest. I still rely on the Celestron kit. (I added a 25mm and a 40 mm to it.)

I have never been out with either of the better two telescopes. I did buy oculars to go with them, the Nagler 82-degree 7mm and an unsold Meade 82-degree 14mm that showed up in a warehouse. So, I appreciate the general advice to build your instrumentation over time based on the best quality you can afford. Slow and steady wins the race.

For a "new telescope" i.e., a first telescope, if you do not go with a full kit - and the Celestron box is the same as marketed under other labels - then find a smaller kit, also marketed under various brand names. If you want to build the best possible set for your best of all possible worlds telescope, then start with Large-Medium-Small: one 40 to 32mm, one 25 to 20mm, and one 10 to 6 mm; and add a Barlow 2X (maybe 3).

Last night I was out with my 102mm refractor specifically to view Delta Cygni which I "discovered" with a binocular a couple of nights back lying out on the chaise longue. I have an 8mm ocular but the best view came from the mathematically equivalent and very different 40mm with 5X focal extender. And both of those were impluse purchases that I regretted when I first tried to use them and have since over time learned to use to advantage. No one recommends a 5X focal extender. When I mentioned it in a club meeting, there were mild guffaws of disbelief: "What for?" Even the Explore Scientific customer service person tried to talk me out of it: "You're just going to magnify the turbulence and light pollution." And yet... last night... I had a great view of stunning stellar field.

Best Regards,
Mike M.

Exit pupil is not very intuitive concept to grasp. I did not buy it either when I was a beginner. My revelation came later when I have used more than one scope and observed over 200 targets. Comparing my notes I suddenly realize that the best views for many targets were achieved not at the same power, but at the same exit pupil in different scopes. By now I have observed over 2000 DSOs using over dozen different scopes and the exit pupil rule still works.

Since my main targets are galaxies I start building my sets not from 0.5mm but from 2mm (this is where most of the galaxies look the best) and then step down and up by 1.3-1.5x increments. But, similar to Gabby I like to cover 0.5mm to 6mm exit range. As I am aging I may need to step down to 5 or 4mm exit pupil at the lower power, but you don't need to change whole set for that. Besides what give me 6mm exit pupil in one scope gives 3mm exit pupil in another, so most EPs will be still useful.

The thing of it is that technical performance goes pretty much by the numbers. As a trained physicist I can be expected to take that as my credo. Of course the numbers are a guide, but a guide has some built in range in which it is useful. Demanding complete precision is, of course, absurd. For instance my SV ED80A is f7 and I'm not going to sweat over not having an exact 21mm fl eyepiece to cover a 3mmexit pupil! I have it nicely bracketed with the 19mm Panoptic (exit pupil 2.71) and its 24mm cousin (exit pupil 3.43). So within rounding error I've got it covered in Pans. (Though sometimes I fantasize about the 22mm type 4 Nagler, the type 4s are the only Naglers I miss a little. Then I look at the price tag and think of other things to buy and sanity returns).

The only addition/modification I'd suggest is that below 2mm exit pupil I like evenly spaced decrements in focal length for finding the highest magnification that the atmosphere allows. Otherwise as a somewhat experienced (67 years at this) observer it's excellent advice. I like using a factor of 1.4 since it halves the area.

Another rational approach is even spacing in exit pupil above 2mm and even spacing in mm below 2mm.

It is unfortunate that in the US the medical profession isn't professional any more. Since optometrists and ophthalmologists ceased being professionals and became worker bees for insurance companies (around ~1990-2000) my experience is that requests to measure pupil dilation are ignored, recently. Hopefully in other parts of the world civilization prevails.

A chart would be nice, if individual differences didn't play such a role. You can expect > 1 mm of variation about the average. There's a chart at this link: https://en.wikipedia.org/wiki/Exit_pupil

But I gotta tell ya I beat this char by loads. It says the best I can expect at my age is ~3.2 mm. Poppycock! I can still manage 5.5-6mm self measured using this technique. https://www.oreilly.com/library/view/as ... 01s08.html

The book https://www.oreilly.com/library/view/as ... 596100604/ is one I highly recommend.

Our Andrey Bigzmey puts two rules, which make sense, and which are supported by a long time observing experience:

1. The same exit pupil (like 2mm) on different aperture telescopes

2. The magnification increments by a factor of 1.3x or 1.4x


Ad2: I am tempted to say, let's take an irrational number for the factor, like the square root of 2. Using the irrational numbers is not irrational.

As my collection of the eyepieces is fairly densely populated across the focus lengths, I can make a choice of the focus lengths close to the prime numbers:
Pentax SMC XW 5mm, Pentax SMC O 7mm, Leica B40x (f=11mm), Zeiss 23x/30x B WW (17mm), Swarovski 20x S W (f=23mm), Leica L Plan 8x/25 (f=31mm)
I sometimes don't mis a 19mm eyepeice, and so there is a dent in the prime numbers sequence.

And back to the topic
I find it often funny, that most people will tell you, buy more eyepieces, but you will hardly find anybody recommending you should get more telescopes.
(I know, I should, as I have only two)

And as a matter of fact,
you don't need many eyepieces, the good ones are enough.

Best,
JG

Agreed, JG, on almost every point. I can't thank or like the post, since the button for that is missing on my screen, so I have to reply to express appreciation.

j.gardavsky wrote: ↑Fri Aug 13, 2021 5:46 pm And back to the topic
I find it often funny, that most people will tell you, buy more eyepieces, but you will hardly find anybody recommending you should get more telescopes.
(I know, I should, as I have only two)

And as a matter of fact,
you don't need many eyepieces, the good ones are enough.

Best,
JG

Excellent point JG! From now on if someone asks for EP advice I would suggest to buy another scope instead.

Isn't the ratio for EPs to telescopes supposed to be 1 to 1 !!!

I'm striving for that (and I'm almost there)!

3:1 is better so you can have variation in the views.

JayTee wrote: ↑Fri Aug 13, 2021 8:40 pm Isn't the ratio for EPs to telescopes supposed to be 1 to 1 !!!

I'm striving for that (and I'm almost there)!

That's how I have started about 60 years ago:
One 80mm aperture repurposed achro doublet plus one cheap repurposed microscope eyepiece.

Today, besides my Leica spotting scope:
One 6" F/5 achro, and instead of having more telescopes, I simply mask down the aperture.
But still don't have as many masks as the eyepieces.

Best,
JG

JayTee wrote: ↑Fri Aug 13, 2021 8:40 pm Isn't the ratio for EPs to telescopes supposed to be 1 to 1 !!!

I'm striving for that (and I'm almost there)!

Thanks for this JayTee. I'm reading your statement as, "Isn't the ratio for EPs to telescopes cumulative f ratios supposed to be 1 to 1 !!!"

So I have two newts at f5.5, & f7, one f9 Cass and & one f12.5 Mak and an f7 and f6.3 refractors.
That means my eyepiece allowance is 47.2?
and I thought I was finished collecting eyepieces.

notFritzArgelander wrote: ↑Wed Aug 11, 2021 10:38 pm The thing of it is that technical performance goes pretty much by the numbers. As a trained physicist I can be expected to take that as my credo. Of course the numbers are a guide, but a guide has some built in range in which it is useful. Demanding complete precision is, of course, absurd. For instance my SV ED80A is f7 and I'm not going to sweat over not having an exact 21mm fl eyepiece to cover a 3mmexit pupil! I have it nicely bracketed with the 19mm Panoptic (exit pupil 2.71) and its 24mm cousin (exit pupil 3.43). So within rounding error I've got it covered in Pans. (Though sometimes I fantasize about the 22mm type 4 Nagler, the type 4s are the only Naglers I miss a little. Then I look at the price tag and think of other things to buy and sanity returns).

The only addition/modification I'd suggest is that below 2mm exit pupil I like evenly spaced decrements in focal length for finding the highest magnification that the atmosphere allows. Otherwise as a somewhat experienced (67 years at this) observer it's excellent advice. I like using a factor of 1.4 since it halves the area.

Another rational approach is even spacing in exit pupil above 2mm and even spacing in mm below 2mm.

It is unfortunate that in the US the medical profession isn't professional any more. Since optometrists and ophthalmologists ceased being professionals and became worker bees for insurance companies (around ~1990-2000) my experience is that requests to measure pupil dilation are ignored, recently. Hopefully in other parts of the world civilization prevails.

A chart would be nice, if individual differences didn't play such a role. You can expect > 1 mm of variation about the average. There's a chart at this link: https://en.wikipedia.org/wiki/Exit_pupil

But I gotta tell ya I beat this char by loads. It says the best I can expect at my age is ~3.2 mm. Poppycock! I can still manage 5.5-6mm self measured using this technique. https://www.oreilly.com/library/view/as ... 01s08.html

The book https://www.oreilly.com/library/view/as ... 596100604/ is one I highly recommend.

BTW I happened to have an ophthalmologist appointment today. I timidly ask them to measure my pupil dilation expecting the refusal I got from my Dr back in VA. I was told :"Sure thing!". It's 5mm today and when you were in 2 years ago it was 6mm." If you get them when they are doing the exam apparently it's easy.

Although the loss of 1mm is unfortunate I still beat the chart by 1.8 mm.

Man, I was there (at the opthamologist) just last week and didn't know to ask that question, shoot.

JayTee wrote: ↑Wed Aug 18, 2021 6:09 am Man, I was there (at the opthamologist) just last week and didn't know to ask that question, shoot.

If they record the diameter, there's still a chance.

I measured my pupil dilation last night.

I used drills not hex keys. Hex keys have varying diameters depending upon how you hold them. The shank of a drill is ground to the drill diameter. I could see split stars at 5mm not at 6mm so it was somewhere in between and well above my age predicted 4mm. That broadly agrees with my DSO impression that my 31mm Nagler 5.5mm exit pupil gives me the brightest views of DSO's.

I didn't worry about letting my eyes dark adapt. I just used a bright planet - Jupiter. The dilation of the pupils is near instantaneous, the photochemical adaptation takes time.

Using the age table referenced in an earlier I've created this table but if my eyes and those of other posters are any guide you really need to measure, not use the age table.

Its great that there are so many people that understand exit pupil, but to be honest, for beginners it just flies over our heads and we tend to ignore it. When i got my 10 inch dob i knew it was coming with two eyepieces that were going to be marginal at best. So i asked the sales person for a suggestion for one high power and one low power eyepiece. 2 years later i have 6 or 7 1.25 inch eyepieces and 5 2 inch eyepieces and there isnt a looser in the bunch.

Maybe instead of getting all technical with information that is going in one ear and out the other, we present practical information based on our experience with a certain type of scope and the eyepieces we have used successfully with it.

this thread is very informative. thx to all .

Mike Q wrote: ↑Thu Jul 13, 2023 12:50 am Its great that there are so many people that understand exit pupil, but to be honest, for beginners it just flies over our heads and we tend to ignore it. When i got my 10 inch dob i knew it was coming with two eyepieces that were going to be marginal at best. So i asked the sales person for a suggestion for one high power and one low power eyepiece. 2 years later i have 6 or 7 1.25 inch eyepieces and 5 2 inch eyepieces and there isnt a looser in the bunch.

Maybe instead of getting all technical with information that is going in one ear and out the other, we present practical information based on our experience with a certain type of scope and the eyepieces we have used successfully with it.

The problem is that there are so many variations even of the same type of scope. For example 100mm refractor could have focal ratio from 4 to 12 and the set of EPs which works in F4 will not cover the range for F10. Yes, it takes some effort to understand the exit pupil, but once you there you can select EPs for any scope model using the same set of rules.

Or when someone asks about a 100mm F7 just relate the eyepieces you know that work. It is just simpler for newbies. When asked what eyepieces for a F5 10 inch i relate to them the eyepieces i have used and they seem very happy with a simple answer

Mike Q wrote: ↑Thu Jul 13, 2023 1:23 am Or when someone asks about a 100mm F7 just relate the eyepieces you know that work. It is just simpler for newbies. When asked what eyepieces for a F5 10 inch i relate to them the eyepieces i have used and they seem very happy with a simple answer

No worries there. None of beginner questions left unanswered here on TSS. Jut ask what EP I need for that scope and see what happens.