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Eyepieces - The Master Plan

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#1 linux

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Posted 20 January 2013 - 08:15 PM

So I'm a newbie, had the department store refractor when I was 10, now retired and decided to take up this as a hobby. I bought a used Orion XT8 that came with 3 starter eyepieces and after my initial outing I realized I will need to get some quality EP's.

So being an ex-engineer and somewhat anal, I read everything I could on eyepiece optics, and of course I put all the spec's of all the EP's I could find on a spreadsheet, actually a worthwhile exercise I think. The result is a "lot" of variables in terms of focal length, AFOV, eye relief and cost, not to mention the actual quality of the products that can only be appreciated by reading reviews or testing yourself.

The whole thing seems daunting...

I just joined the Augusta Astronomy Club and had a first night looking through some EP's and will do more in a few weeks. I wear glasses so it'd be great if I didn't have to take them off although I guess that's a possibility. Anyway, here's my 1st order criteria:

Eye relief: 20mm. I guess this could drop a little; I'll have to check out some options at the club.

AFOV: ~70 to 80 mm. Here I really have to experience some real EP's at the club, but this seems to be a good cost effective compromise in what I've read. My existing EP's are 6, 6.5 and 16.9. The small one is like looking through a straw, maybe worse.

Cost: I "could" afford the pricey TV eyepieces, but would would not want to if I can get 80% of the quality for half the cost. I do not have problem spending say, $300 for and EP if it will serve me for a long time. I don't want to spend $5000 before I figure it out, but maybe that goes with the territory :)

As far as what I want to view, well, I don't really know. Probably DSO stuff mostly but I'm sure I'll want to spend some time on planets/moon/sun.

Looking at what people choose, I would figure something like; 5, 10, 15, 20, 25, 30, maybe also a 40 for wide screen DSO work.

I can see myself going toward a 12" and 16" dob at some point, maybe more if I love it, so these would have to serve the larger mirrors.

In looking over my spreadsheet and reading some reviews, it seems like the Pentax optics are a good fit. Great quality, but not as pricey as the TV stuff.

Sooooo, I'd like to get some general comments on this "process" and also see what people think about AFOV, eye relief, quality, etc.

PS Being new, I don't know if my spreadsheet would be of use to people. If it would, I'd be happy to post it.

#2 Starman1

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Posted 20 January 2013 - 08:44 PM

Some examples with long eye reliefs:
TeleVue Delos, 72 degrees, focal lengths from 3.5 to 17.3mm
Pentax XW, 70 degrees, focal lengths from 3.5 to 20mm
Baader Hyperion, 68 degrees, focal lengths from 5 to 24mm
Astrotech AF70, 70 degrees, focal lengths from 5 to 22mm
Vixen LVW, 65 degrees, focal lengths from 3.5 to 22mm

Now, there are some longer focal lengths of some eyepieces that have long enough eye relief to be considered long eye relief eyepieces, even though shorter focal lengths in their series wouldn't qualify:
31 and 26mm TeleVue Nagler, 82 degree
41, 35, and 27mm TeleVue Panoptics, 68 degrees
22mm TeleVue Nagler, 82 degrees

Unfortunately, no 100 degree eyepieces would qualify, nor would the vast majority of 82 degree eyepieces.

You might be able to find more longer focal length widefield eyepieces with long enough eye reliefs to qualify on this spreadsheet:
2009 update
It's dated (I'm working on an update) but many of the eyepieces listed (if not most) are still available.

#3 russell23

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Posted 20 January 2013 - 09:02 PM

I'd recommend the 28mm ES68 as your lowest power finder eyepiece for this scope. It would give you 43x and a 1.6 deg TFOV.

I've tried the Vixen LVW's, Pentax XW's, Astrotech AF70's, and TV Delos eyepieces. The Delos and XW's are similar in quality but different in presentation. If it was me, I would get the 12mm, 8mm, and 6mm Delos eyepieces to finish off your set (100x, 150x, 200x).

Or go with the 12mm and 8mm Delos and a 2x barlow which would then get you 100x, 150x, 200x, and 300x.

Dave

#4 linux

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Posted 20 January 2013 - 09:15 PM

Russell, yeah, the Delos do come up on my spreadsheet as being similar in AFOV and eye relief and cost not far apart.

Thanks for the input.

#5 Hermie

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Posted 20 January 2013 - 10:57 PM

Linux,

You are on the right track, but there is no need to jump in the deep end! I would recommend to start with a basic set of three or four eyepieces and then build on that. Maybe around 6, 12 and 30mm focal lengths (exit pupil about 1,2,5). Russell's recommendations above are good.

Looking to the future, if you get a larger scope it will have a faster mirror which will be more demanding of your eyepiece. If you do this, I'd recommend getting the better eyepieces now rather than needing to upgrade eyepieces as well.

Hermie

#6 Starman81

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Posted 21 January 2013 - 01:35 AM

I have an 8" dob as my main scope as well and also realized that I needed eyepieces with 20mm of eye relief. I also see myself going to a bigger dob (12" most likely) sooner or later, so it seems like we have a very similar profile. So, hopefully my advice will be useful.

Looks like you've done your homework and you want to buy a lifetime set of eyepieces. One realization that I had is that the differences between some of the options Don Pensack (Starman1) mentioned are often tough to explain in words and quite simply need to be seen by your own eyes. But if you went with the Delos or Pentax XW, you would probably not have to wonder what you're missing if you went with any of the lower priced options since they are the best of the ~70* AFOV eyepieces with 20mm of eye relief. You probably won't need so many different focal lengths and could do with about 4; a low power finder, then a medium, medium-high and high power EP. Lucky for you (and me) there are more options for high eye relief eyepieces at the low-power finder eyepiece end of the spectrum. The ES68 28mm is a fine low power finder as was suggested above. You could flesh out the rest of the lineup with a few Delos (14/10/6) or XW's (20/10/7) and be quite well covered. A decent 2x barlow can could take you the rest of the way or you could add another high power EP.

#7 Jon Isaacs

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Posted 21 January 2013 - 06:37 AM

Sooooo, I'd like to get some general comments on this "process" and also see what people think about AFOV, eye relief, quality, etc.



As Hermie suggested, there is no need to jump into the deep end. There is an incredible amount details to know about eyepieces and as you spend more time observing, you will be come more skilled and more aware not only of the aberrations and features but also of your own preferences.

For example, at this point, 20mm of eye relief may seem necessary but unless you have severe astigmatism and must wear glasses, later on you may find that 12mm is sufficient or even become comfortable with short focal length Plossls and orthos.

As engineers, we know that there is no one perfect eyepiece, everything is a compromise, an optimization based on number of governing factors. Take your time, there is a lot to learn, a lot to see. The eyepiece that seems ideal at this moment maybe disappointing or more likely, just not quite the right one sometime down the road.

In the ideal world, we would all buy our last set of eyepieces the first time around and avoid all the complication of choosing and deciding. But in the real world, the evolution of ones eyepieces is a learning process, as one learns to really see what there is to see looking through the eyepiece, one also learns to see the imperfections and characteristics in particular eyepieces how they affect the observing experience.

Jon

#8 dedo

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Posted 21 January 2013 - 06:37 AM

You should also consider, as an eyeglass wearer like me, that it is very unlikely that you could see the entire FoV in a UWA eyepiece with more than 70° with your glasses on independently from eye relief.

#9 johnnyha

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Posted 21 January 2013 - 09:22 AM

Congrats on your scope, I agree with everything suggested. A really nice planetary/lunar set would be the 10-7-5 Pentax XWs, you can't really go wrong with these and there is a ready market for resale if you don't like them.

#10 Jeff Morgan

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Posted 21 January 2013 - 09:42 AM

So being an ex-engineer and somewhat anal, I read everything I could on eyepiece optics, and of course I put all the spec's of all the EP's I could find on a spreadsheet, actually a worthwhile exercise I think. The result is a "lot" of variables in terms of focal length, AFOV, eye relief and cost, not to mention the actual quality of the products that can only be appreciated by reading reviews or testing yourself.


If you have not already read it, I would highly recommend "Visual Astronomy of the Deep Sky" by Roger Clark (out of print but still available on Amazon). It is the classic in the field and covers the scientific research on human visual response under low light (astronomy) conditions. AFAIK, it is the only science-based approach to choosing your eyepieces. And it will definitely save you a bunch of money on redundant purchases.

#11 mgwhittle

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Posted 21 January 2013 - 11:30 AM

So being an ex-engineer and somewhat anal, I read everything I could on eyepiece optics, and of course I put all the spec's of all the EP's I could find on a spreadsheet, actually a worthwhile exercise I think. The result is a "lot" of variables in terms of focal length, AFOV, eye relief and cost, not to mention the actual quality of the products that can only be appreciated by reading reviews or testing yourself.


If you have not already read it, I would highly recommend "Visual Astronomy of the Deep Sky" by Roger Clark (out of print but still available on Amazon). It is the classic in the field and covers the scientific research on human visual response under low light (astronomy) conditions. AFAIK, it is the only science-based approach to choosing your eyepieces. And it will definitely save you a bunch of money on redundant purchases.


Please correct me if I am wrong, but doesn't Clark's results support the idea of having many eyepieces of focal lengths close together attempting to find the exact magnification that produces the optimum size of the object? It goes against having just three or four eyepieces and encourages eyepiece choices that differ by very small differences in focal lengths meaning an observer would have to have seven or more focal lengths at minimum.

#12 csrlice12

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Posted 21 January 2013 - 12:37 PM

"So I'm a newbie, had the department store refractor when I was 10, now retired and decided to take up this as a hobby."

My God, it's an epidemic.......welcome to the ward.....

#13 Aquarist

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Posted 21 January 2013 - 01:50 PM

By the way Amazon.com has them at a greatly reduced price for new and some used as well. FYI

#14 dan_h

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Posted 21 January 2013 - 01:50 PM

<< Looking at what people choose, I would figure something like; 5, 10, 15, 20, 25, 30, maybe also a 40 for wide screen DSO work.>>

Hi Linux, first, let me say welcome to CN. You have come to the right place to get lots of advice from knowledgeable folks.

When choosing eyepieces you should give a little consideration to the exit pupil. This defines the size of the beam of light that comes from the telescope and enters your eye.

In general, you need a low power eyepiece, 5-7mm exit pupil, something in the mid range, about 2-2.2mm exit pupil and a high power, 1-1.2mm exit pupil. It's a good bet that the bulk of your viewing will will fall into these ranges. Some folks like a very high power about 0.8mm exit pupil but old eyes can have a problem with floaters and stuff when the beam is very small.

Exit pupil is a fuction of magnification, which depends on telescope focal length so an eyepiece that provides 1mm exit pupil with one scope, may provide something completely different with a different scope. You can quickly calculate exit pupil using the formula:
exit pupil = eyepiece focal length/telescope focal ratio.

Using the exit pupil guideline you can see how your focal length selection will fit into the needed range of powers.

Also note that a progression of preferred focal lengths rarely works out to even multiples such as 5, 10, 15, 20....
If you should get a Barlow, you can easily cover the even multiple ranges without having a large number of eyepieces.

A good starter set doesn't need a great many eyepieces. A few well chosen ones will do you better. When you are more experienced, or change scopes, you can add to the stable.

Hope this helps,

dan

#15 BillP

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Posted 21 January 2013 - 02:04 PM

There are a couple of ways to go. Frankly though, being new to it all and if you are not that short on funds, then I think it is a good idea to get a set of EPs to get your feet wet, that later in a few years you will replace once you discover your real likes and dislikes. So without breaking the bank at all, a 5mm, 8mm, and 13mm Hyperions will nicely satisfy the higher magnifications and give you a comfortable 20mm eye relief so you can keep the glasses on. And these three will cost you about $420 total new. So about the cost of a single expensive eyepiece you were figuring. A top line recommendation would be a 5, 7, 10 XW or 6, 8, 12 Delos, but these three new will set you back $840-$1200!! And if it ends up after a year you think you really like 82 degree or 100 degree eyepieces with shorter eye relief then you are not out so much cash.

After the 5mm, 8mm, and 13mm Hyperions, I would go with a Explore Scientific 28mm 68 degree series (21mm eye relief and $150).

These 4 should provide some very satisfying viewing. Only thing missing would be a maximum TFOV eyepiece. The 28mm ES68 will get you about 1.5 degrees TFOV. You could get about 2.2 degrees with a 40mm eyepiece with a 68-70 deg AFOV. So if you wanted to add a 5th max TFOV EP to the stall instead of waiting, then could get a 40mm Titan-II ED for around $160.

So the lesser price but 80-90% of performance of the premiums would be:

5mm, 8mm, 13mm Hyperion ($420)
28mm ES68 ($150)
40mm Titan-II ED ($160) - Optional as you may be able to live without this just fine.

Total Price - $720 (or $560 without the 40mm)

Move this to a premium level and you get something like:

5mm, 7mm, 10mm Pentax XW ($840)
17.3mm Delos ($335)
26mm Nagler T5 ($655 - and gets you "near" max TFOV)

So total for the premium lineup is $1,830.

If it were me, and I was not so strapped that I can afford to experiment, I would go with the lower priced lineup as it is really quite good performers, gets you nice wide fields, and good eye relief. Then after a few years...and possibly a new scope, you will know you likes and dislikes better and move up as needed.

#16 Jim Romanski

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Posted 21 January 2013 - 06:36 PM

The simple answer is to take your time and look through other people's gear and decide what you like. But if you want to jump in then I recommend buying one good eyepiece and seeing how you like it.

The nice thing about Televue eyepieces is that they hold their value if you take care of them. This is especially true if you start off buying them used so perhaps consider that.

If it were my scope and I had a 2" focuser I'd buy a used 22mm Nagler Type 4. You'll get wide vistas with long eyerelief.

#17 russell23

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Posted 21 January 2013 - 07:02 PM

There are a couple of ways to go. Frankly though, being new to it all and if you are not that short on funds, then I think it is a good idea to get a set of EPs to get your feet wet, that later in a few years you will replace once you discover your real likes and dislikes. So without breaking the bank at all, a 5mm, 8mm, and 13mm Hyperions will nicely satisfy the higher magnifications and give you a comfortable 20mm eye relief so you can keep the glasses on. And these three will cost you about $420 total new. So about the cost of a single expensive eyepiece you were figuring. A top line recommendation would be a 5, 7, 10 XW or 6, 8, 12 Delos, but these three new will set you back $840-$1200!! And if it ends up after a year you think you really like 82 degree or 100 degree eyepieces with shorter eye relief then you are not out so much cash.

After the 5mm, 8mm, and 13mm Hyperions, I would go with a Explore Scientific 28mm 68 degree series (21mm eye relief and $150).

These 4 should provide some very satisfying viewing. Only thing missing would be a maximum TFOV eyepiece. The 28mm ES68 will get you about 1.5 degrees TFOV. You could get about 2.2 degrees with a 40mm eyepiece with a 68-70 deg AFOV. So if you wanted to add a 5th max TFOV EP to the stall instead of waiting, then could get a 40mm Titan-II ED for around $160.

So the lesser price but 80-90% of performance of the premiums would be:

5mm, 8mm, 13mm Hyperion ($420)
28mm ES68 ($150)
40mm Titan-II ED ($160) - Optional as you may be able to live without this just fine.

Total Price - $720 (or $560 without the 40mm)

Move this to a premium level and you get something like:

5mm, 7mm, 10mm Pentax XW ($840)
17.3mm Delos ($335)
26mm Nagler T5 ($655 - and gets you "near" max TFOV)

So total for the premium lineup is $1,830.

If it were me, and I was not so strapped that I can afford to experiment, I would go with the lower priced lineup as it is really quite good performers, gets you nice wide fields, and good eye relief. Then after a few years...and possibly a new scope, you will know you likes and dislikes better and move up as needed.


Bill,

He's indicating he is comfortable with $300 an eyepiece so in that case I don't see the point in settling for the Hyperions.

You could go with premium eyepieces and cover the basic magnification needs for a lot less than $1800. For example:

28mm ES68 ($150)
14mm TV Delos ($370)
10mm Pentax XW ($330)
2x ES barlow ($80)

Magnifications: 43x, 86x, 120x, 172x, 240x

Total cost: $930

Average cost per eyepiece $283. With the 2x barlow the average cost per magnification is $186.

Another advantage of this line compared to my earlier suggestion is that it includes both a Delos and an XW so it would be possible to see if there is a preference for one over the other.

Dave

#18 dale67cameron

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Posted 21 January 2013 - 08:30 PM

My favorite eyepiece is the 17mm nagler type 4. It just seems to give wonderful views in any kind of scope. I'm sure the 22mm type 4 would be nice too. I just recently purchased some tmb super planetary II's. i am very impressed with them for a $50 price tag. They are only made in 4-9 mm in 1 mm increments. They are really nice on the planets and moon. Almost as sharp as a 8mm televue plossl, but with a much better eye relief. I bought them from highpoint scientific. The 12 mm nagler type 4 has nice views, but eye placement is bothersome sometimes. Televue plossls are nice in a goto scope with tracking. The narrow field is unhandy in a non tracking scope. I usually end up using a 38mm q70 (which I would replace if I was rich) for finding and my 12mm or my 17mm naglers for viewing dso's. My tmb's are my new planetary goto eyepieces. I hardly use my 9mm nagler anymore.

#19 GeneT

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Posted 21 January 2013 - 11:15 PM

Linux,

You are on the right track, but there is no need to jump in the deep end! I would recommend to start with a basic set of three or four eyepieces and then build on that. Maybe around 6, 12 and 30mm focal lengths (exit pupil about 1,2,5). Russell's recommendations above are good. Looking to the future, if you get a larger scope it will have a faster mirror which will be more demanding of your eyepiece. If you do this, I'd recommend getting the better eyepieces now rather than needing to upgrade eyepieces as well. Hermie


This is good advice. I also recommend that you join your local astronomy club. You could then compare your moderately prices eyepieces with some of more expensive ones. I prefer TeleVue for the most part--Naglers and Delos. However, Explore Scientific also makes some good upper tier eyepieces.

BillP is one of the people I go to for advice. He gave you a pretty detailed list to mull over.

#20 JayinUT

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Posted 22 January 2013 - 01:07 AM

The Pentax XW 5mm, 7mm, 10mm are all $279.99 at Adorama located at this link which is cheaper than anywhere else.

I would recommend the following:

5mm, 7mm, 10mm Pentax XW.
28mm Explore Scientific 68 degree. Try code metpromo at the ES site to get a 10% off. I just tried it and it is still working. That takes the price down from $149.99 to $134.99 which is an outstanding price. Here is a link to the ES site for their 68 degree EP's.

I would then also recommend either the 16mm ES 68 degree (it is available) or the 20mm ES 68 degree eyepiece. I love my 20mm but I don't think it is available. You can use the same code metpromo and get the 16mm ES 68 degree for $89.99. Again, an outstanding deal for a solid eyepiece. If the 20mm can be found I recommend the 20 but you may find you like the 13mm to 16mm range. I use to love that range until several years ago I got the 10mm Pentax XW which is my main eyepiece.

So to summaries, here are my recommendations based on what is available. Remember the Pentax XW are keepers in my opinion. You may change scopes several times if you stick with the hobby. Eyepieces like Pentax or Televue are keepers.

5mm, 7mm, 10mm Pentax XW $280.00 x 3 = $840.00
16mm Explore Scientific 68 degree $89.99
28mm Explore Scientific 68 degree $134.99

I think the OP would be quite happy with that setup in his XT8 or in time, with another scope. Lets not mention ATMing to him or as an engineer he may just build his own dob!

#21 johnnyha

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Posted 22 January 2013 - 04:39 AM

The 16mm ES 68 has extremely tight eye relief however.

I love the 28 ES 68, 10-7-5XW set. Then you got a lifetime setup. Or at least until you start thinking about binoviewing... :grin:

#22 Jeff Morgan

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Posted 22 January 2013 - 05:24 PM

Please correct me if I am wrong, but doesn't Clark's results support the idea of having many eyepieces of focal lengths close together attempting to find the exact magnification that produces the optimum size of the object? It goes against having just three or four eyepieces and encourages eyepiece choices that differ by very small differences in focal lengths meaning an observer would have to have seven or more focal lengths at minimum.


I can see how one might come to that conclusion. Clark's key concepts of the Critical Visual Angle (CVA) and Optimum Magnified Visual Angle (OMVA) are based one two important variables: the apparent angular size of the DSO in question, and sky brightness. Since DSO's come in all sizes, one could say you should have one eyepiece in every focal length. As long as you don't mind schlepping an extra eyepiece case or two (or three) and it puts you in no financial distress, no harm. And the eyepiece manufacturers will love you.

Yet even that would be discrete integer steps, so one may think that the "ideal" solution would be a continuous magnification - a zoom eyepiece. (I knew there was an underlying reason why I can't let go of my Nagler 3-6 Zoom :grin:)

And of course, sky brightness changes the whole thing. Easy to see how one could go kind of crazy here.

But, one must also consider the biological side of the equation - the response of the eye. The key concept for DSO visibility is getting the faint object magnified to a sufficient size (5-10 degrees apparent) to maximize the number of rods and ganglia sensing the object, so the brain will in not dismiss the signal as noise. It would be nice to find the "optimum" size, but that is a moving target. Just get it big and that is close enough for a win.

The key quote is found on page 60:

"The eye's response to light, like the responses of our other senses, is logarithmic. So the sequence of magnifications used should follow a logarithmic trend. For example, you might want a series of eyepieces that each give 1.6 times higher power than the last. If your telescope's minimum useful magnification is 30X, then a reasonable series of magnifications might be 30X, 50X, 75X, 125X, 200X, 315X, 500X, and so on."

#23 johnnyha

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Posted 22 January 2013 - 06:18 PM

1.6X jumps are a good idea for a base kit, but... as a planetary observer in SoCal, this 1.6X formula that jumps from 125X to 200X and then all the way up to 315X doesn't work for me. It just doesn't match my local seeing conditions, 90% of nights I would only be able to use the 125X because the 200X is just a hair too soft. My seeing conditions usually top out before 200X so I would wish to have something around 175X. And most nights 315X is just too much when maybe sometimes 280X would have worked fine. Anyway you get the idea, there are a lot of factors that will determine what the best magnifications are for your own circumstances.

#24 Jeff Morgan

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Posted 22 January 2013 - 07:33 PM

Clark's book is about observing the faint fuzzies.

I would agree planetary is a different game and being able to get up against the limit of seeing on a particular night is valuable. Fortunately for the planetary enthusiast orthos, plossls, and barlows are somewhat inexpensive (compared to the wide fields) so close spacing is not too burdensome for many.






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