Eyepiece & Diagonal Recommendations

To begin this topic on eyepiece recommendations, Doc G gives an overview of factors that should be considered in selecting eyepieces for any telescope followed by "Using Max Exit Pupil to Determine Lowest Power EP" by Michael Richmann. Also included is Doc G's suggestion for incorporating a corrective lens to eliminate the need for wearing glasses. Diagonal recommendations can be found at the end of this page or by clicking here.

Subject: Overview of factors that should be considered in selecting eyepieces

From: Doc G

I have followed this thread for several days now and seen a lot of lists of very nice eyepieces. Everyone seems to have a "mark" that they favor. I have not seen much discussion of the principles of the optics of the eyepieces. Perhaps these principles are too obvious to be stated again. But, I will venture just a few thoughts about them herewith.

The first property is the field of view, that is, the actual angular amount of sky that can be seen. It is determined by the focal length of the telescope and the diameter of the field stop in the eyepiece alone. For a 2" eyepiece the largest field stop is about 44 mm.

The second factor is the apparent angle of view of the eyepiece. This is a property of the eyepiece alone. It is usually about 52 degrees for a Plossl, 67 degrees for a Super Wide and 84 degrees for an Ultra Wide.

This apparent angular width is the apparent size of the field stop that the eyepiece presents to the eye. You can see this by just holding up the eyepiece. Mounting on a telescope is not necessary. Thus one could have a Plossl that sees just as much sky as an Ultra Wide, but the Plossl would present to the eye a smaller circle of view than the Ultra Wide. There are several factors to consider. One is the optical complexity required in the Super Wide to present the wide apparent field and another is whether or not your eye, or you preference, is to have such a wide apparent field presented.

With the smaller apparent field, all of the actual field is there but it is smaller and can be seen with little movement of the eye. With the larger apparent field, the objects are spread out more but one has to move the eye around to see them. Some persons may like the former and some the latter. In general, if you use eye glasses, the smaller apparent field of view may be more comfortable. There is actually a best magnification for seeing objects. This is discussed on my web site and in a very nice paper by Robert Preston found on Ed Stewart's MAPUG-Astronomy.net site. (www.MAPUG-Astronomy.net)

Personally, I find the apparent field of view of the Super Wide eyepiece comfortable but that of the Ultra Wide not comfortable. What I am trying to say, is that the Ultra Wide is not better in every sense and may not be as good optically because it has a complex optical design and too much glass in it. It will also be expensive. Cost and a fancy name do not make the best eyepiece for every individual.

I am suggesting that personal desire should not be based only on the high cost of an eyepiece, its weight, or its "mark." It should be based on actual performance for the individual.

I have found that I do not particularly like Ultra Wide eyepieces because I wear glasses and thus cannot really see the whole apparent field anyway. I also have felt, when I compared a good Super Wide with a good Ultra Wide, that the Super Wide field had the light energy more concentrated and thus had more contrast than the Ultra Wide. This observation agrees with the theory of seeing dim objects.

There is a phenomenon that I have observed. Advice from the owner of an eyepiece which cost lots of money may be biased. The owner has a hard time saying that the eyepiece is just OK. I have a rather detailed discussion of these factors on my web site under the optical section which some may wish to read.

Subject: Using Max Exit Pupil to Determine Lowest Power EP

From: Michael Richmann

Well, you have to decide what the largest apparent central obstruction you can tolerate is and work back from there. Let's take 2 mm as an example. Assuming your actual secondary obstruction is 3.7" out of a total aperture of 10", it means your total pupil size at the eyepiece needs to be 2*(10/3.7) or 5.405 mm. Since you have an f/6.3 system and the total pupil size is the focal length of the eyepiece divided by the f/value, then this would correspond to an eyepiece focal length of 5.405*6.3 or 34 mm. One more example: my 8" f/10 LX200 and assumed 1.5 mm is the maximum acceptable secondary obstruction size at the eyepiece. Total pupil size is 1.5*(8/3) = 4.00 mm . Focal length of the corresponding eyepiece is 4.00*10 or 40 mm. Substitute whatever maximum central obstruction size in at the top and take it from there.

Subject: Eyepiece recommendations for 10" LX200 f/10 -- part 1 of 6

From: Louis Halikman

I have the 10" LX200 f/10, and I have assembled my own "dream team". Each of us, of course, has his or hers own preferences.

First of all, forget the 55mm Plossl and the richfield kit. I had that eyepiece and sold it, as I did not find the small image size and the narrow AFOV (apparent field of view) to be pleasing. It seems to be better suited to the 12", as it needs the longer focal length to improve image size. With a 2" diagonal, the UO (University Optics) 40mm Konig is best for the money. It gives the widest actual field of view possible with this scope with a fair image size. A 35mm Panoptic is the favorite of many others.

Next in my lineup is the 32mm Meade SWA. This relatively inexpensive eyepiece gives an amazingly flat field with good eye relief and no color. It is my most frequently used eyepiece for deep sky work. It is also quite light in weight, making balance less of a problem.

My crown jewel, however, is the 20mm Nagler II. This massive eyepiece is hard to balance, but the wide field is stunning. If I had to keep only one eyepiece, this one is it. No longer manufactured, but readily available on the used market.

I have a Meade 18.5mm SWA left over from a Mak that I owned, but it is no competition for the Nagler except that it is much smaller and lighter in weight.

Finally, for nights of exceptional seeing, a Nagler 12mm II rounds out the field. I use it a lot less than I originally thought that I would. In my suburban Baltimore location, the skies will seldom support this much magnification.

-----------------------------------

Subject: Eyepiece recommendations for 10" LX200 f/10 -- part 2

From: Jack Estes

I have that exact scope. After much experimentation, I believe I have the ideal set of rather high-end eyepieces for my 10" LX200 F/10:

From low power to high power:

40mm Pentax XL SMC
27mm TeleVue Panoptic
22mm TeleVue Panoptic
14mm Pentax XL SMC
10mm Pentax XL SMC
7mm Pentax XL SMC

Note the 40, 27, and 22mm (low power eyepieces) are all 2" barrels. The three higher power Pentax are all 1.25". Finally, none of this matters much if you use a cheap diagonal. After owning the Meade 2" for a couple of years, I bought the premium Televue 2" diagonal with the diaelectric coatings about two months ago. Boy did that ever improve the view through all the oculars! If push comes to shove, spend 75% of your eyepiece dollars on your one or two lowest power eyepieces. That's where you will spend 90% of your visual time.

The Pentax oculars are unsurpassed for high power viewing. It's pretty much a toss up between the 35mm Panoptic and the 40mm Pentax. I chose the 40mm because it is a bit lower power and a bit wider FOV, plus it's considerably lighter in weight.

---------------------------------------------------------

Subject: Eyepiece recommendations for 10" LX200 f/10 -- part 3

From: Chris Vedeler

The 31mm Nagler IS the ultimate eyepiece. I use it 95% of the time when doing visual work with my 10" f/10 LX200. I've never used anything even remotely close to it's equal. It is worth every penny! For the higher power stuff a 17mm Nagler would be nice too (that's on my wish list).

For those extremely rare nights where the seeing is unbelievable, a 9mm Nagler would completes the package.

If you plan on doing any eyepiece projection astrophotography, then a few simple (and much cheaper) eyepieces would work better than the Naglers.

In my experience, it is better to buy a few awesome eyepieces that will get a lot of use, than a whole plethora of eyepieces that will see very little use. Reality being what it is, the low power eyepieces will see a lot more use than the high power eyepieces (on a 2500mm focal length LX200 at least). Instead of buying three or four eyepieces in the 50mm to 20mm range buy a single 31mm Nagler.

-------------------------------------------------------------

Subject: Eyepiece recommendations for 10" LX200 f/10 -- part 4

From: Don Tabbutt

Although I own 6 eyepieces, from 6 to 32 mm, my 13.8 Meade SWA gets used the most. Although I would like to use it more, the 32mm TeleVue Plossl rarely gets used because it requires such a dark site, which I can rarely get to. If there's any extraneous light at all, it's exit pupil is larger than my eye's entrance pupil, rendering it next to useless to me...I just can't get used to that effect.

-------------------------------------------------------------

Subject: Eyepiece recommendations for 10" LX200 f/10 -- part 5

From: Scott Rosenberg

Here are the specs on the 3 EPs you mention, based on an 8" 2000mm focal length scope. A 10" 2500mm focal length scope will have a different true field of view which is in parenthesis.

55mm Plash (50¬ Apparent Field of View): Field Stop = 46.0

Eye relief = 38mm
Exit Pupil f/10 = 5.5mm
Exit Pupil f/6.3 = 8.7mm
True Field of View = 1.32¬ (1.05¬)

31mm Nagler Type 5 (82¬ Apparent Field of View): Field Stop = 42.0

Eye relief = 19mm
Exit Pupil f/10 = 3.1mm
Exit Pupil f/6.3 = 4.9mm
True Field of View = 1.20¬ (0.96¬)

35mm Panoptic (68¬ Apparent Field of View): Field Stop = 38.7

Eye relief = 24mm
Exit Pupil f/10 = 3.5mm
Exit Pupil f/6.3 = 5.6mm
True Field of View = 1.11¬ (0.89¬)

For my 8" scope, I like the 55mm for the widest field possible as well as the brightest due to the large exit pupil. The images however are pretty small. I like the 31mm Nagler because it ALSO gives me a very wide field of view but increases the magnification of those small images the Plash shows. The 19mm eye relief is still long enough to view with glasses on. As for the 35mm Panoptic, its track record speaks for itself. It has a wonderfully wide field of view (though smaller than the 31mm Nagler) and a nice long eye relief for eyeglass wearers. If I had to choose only one of these though, it'd probably be the Nagler or, if money was tight, the Panoptic. Of course, all three are 2 inch EPs so I'd recommend an excellent mirror diagonal such as the TeleVue Everbright or the Astro-Physics.

----------------------------------

Subject: Eyepiece recommendations for 10" f/10 -- part 6 of 6

From: Danny & Donna <dndcobbbellsouth.net> Date: March, 2000

I have the same scope and have recently upgraded to the following set:

35mm Panoptic
22mm Nagler Type 4
17mm Nagler Type 4
12mm Nagler Type 4
9mm Nagler
7mm Pentax XL
5.2mm Pentax XL
(plus a TV 20mm Plash, Meade 26mm Plash, 6mm Vixen Lanthanum, 5mm Ultrascopic reticle)

I find that a 22mm is my most used f.l. eyepiece for this scope. Very nice for most galaxy and open cluster viewing. I upgraded from a 22 Panoptic to the Nagler. The Nagler has the jumbo FOV, but the Pan is easier to view through and has (IMHO) better edge sharpness. I generally only use the 35 when more FOV is needed for large objects. Others may find the 35 gets the most use, but I generally prefer the maximum practical magnification for the viewing situation. Many (myself included) feel that the 22 Pan is an ideal match for this scope. I've only had the 22 Nagler in the scope once. (Darn weather! Darn schedule!)

I've had the 14mm Pentax too. It works nicely for globulars and planetary nebulas. Now I use the 12 or the 17. For planetary viewing, I can usually use the 9 if the seeing is decent. The 9 sometimes ghosts on the planets, though. When the seeing is good, the 7 is nice (357X, I believe) on the planets. Have only gotten good views with the 6 on rare occasion. Have not used the 5.2 in the LX yet; it was intended for the TV-85. I look forward to the night that it gives good planetary views!

I usually use the Everbrite diagonal that came with my TV-85 on the LX200. I recommend it.

If you want "wide" EPs, I'd consider a mix of Pentax Al's and Panoptics (except for the 55 deg 28mm Pentax.)

If you want "super wide," Naglers are nice (except in the shorter f.l.'s due to the lack of eye relief.)

And from the “Prospective or New Owners” topic

Subject: Wearing Eyeglasses

From: Doc G

Bill Nicoll wrote:

> Several of the contributors to this thread have made reference to wearing
> eyeglasses when looking through their telescope. I wear eyeglasses ( the
> graduated lens kind) but I just assumed that I should remove them while using my
> scope. So far ( I'm fairly new at this) I have only 2 lenses, the 26 mm super
> Plossl that came with the scope and a 22mm Nagler Type 4. I find that I have
> difficulty seeing much wearing my glasses with either lens although the Nagler
> seems to work a little better. Should I expect better seeing with my glasses on,
> or is it best to leave them off and try to correct for my nearsightedness when I
> focus the scope.

You can focus for your own eyes but the telescope will be out of focus for others. You can do without glasses if you do not have bad astigmatism. If you have bad astigmatism, not wearing your glasses with make fine focus difficult.

A possible solution for you, if you alone view through the eyepiece is to have corrective lenses made for your eyepieces with your prescription built in. Any optical house can do this for you. I took a lens from my glasses and cut a piece out that fit at the top of the eyepiece. Thus I had my prescription right at the exit of the eyepiece. This worked fine, but it would have to be done for each eyepiece.

Subject: Diagonal Recommendations --part 1 of 2

From: John Hilliard <messier27earthlink.net> Date: Jan 2003

----- Original Messages -----
From: Gene Horr <genehorrtexas.net>
> Peter Narkauskas wrote:
> > Excuse my ignorance perhaps, but could you name some quality diagonals.
> > I'm not too up to date with diagonals!
>
> Vernonscope makes the best. 1/20 wave and the mirror squared during
> assembly. But the last I heard there was a waiting list to get them.
>
> Otherwise AP, Takahashi, and Televue all make very good diagonals
> that are in the 1/8 to 1/10 wave range. There are minor differences
> (except for the Tak being adjustable) but the performance is about
> the same. You won't go wrong with any one of these.
----- End of Original Messages -----

Actually there is another diagonal out there that has become very popular on several groups and will not break the bank to get it. The Williams Optics unit from Anacortes, and others, is advertised and marked as 1/10th wave. Very nicely made from an appearance standpoint, and includes the 1.25" adapter. It uses the compression ring to secure the ep's and adapter, and has a safety groove for the visual back set screws to lock into and not slide out if the screws are a bit loose.

I am not deep into the technical aspects of these items, I just know if the views look good to us. It is a marked improvement over the original Meade 2" diagonal, is less reflective inside than our TV Everbright. It was purchased because I did not care to leave use a $300 diagonal in a $300 scope. I have since been swapping it out with the TV in our 12" and do not readily discern any difference.

----------------------------------

Subject: Diagonal Recommendations --part 2 of 2

From: Lawrence Lennox-Beals

Have to second that on the Williams Optic 2" diagonal. I have one and did a swap test back and forth using my 10" LX200GPS with a Televue Everbrite and some Nagler and Meade eyepieces. I couldn't discern any real appreciable difference in the brightness or quality between the two -- neither could the owner of the TeleVue diagonal. Realize that is a subjective (vice quantitative ) opinion since I used no other equipment than my eyeballs. I love having the copper compression rings so you don't leave setscrew marks on your eyepieces. I tend to be fussy about equipment use and misuse, it is a nuclear submarine thing - your life depends on the equipment so you tend to take care of it.

All in all I have been extremely happy with mine. I did upgrade the 1.25" adapter to the TeleVue brass one to make balancing the scope less of a problem when I switch between 1.25" and 2" eyepieces.

EverBrite Diagonal vs. EveryOneElse's? --part 1 of 5

From: Doc G

Bill VanOrden wrote:
> I am not wanting to start a raging argument about
> whether the TV EverBrite diagonal is or isn't the best.
>
> I have heard (read) various arguments from many sources pro and con ranging
> from 2 stops brighter (I doubt it) to absolutely no visible or photographic
> difference what so ever (kinda doubt this one, too).

The reflection coefficient of the ordinary mirrors and the EverBrite is at the most 10%. That is a tiny fraction of a magnitude. I have used all three of the diagonals sequentially on the same scope and same night. The EverBrite is possibly a tiny bit better, but nothing spectacular. It does make a spectacular hole in you wallet.

Pride of ownership is an important factor in your evaluation and enjoyment of the TeleVue EverBrite diagonal. TeleVue equipment is, of course, very finely made.

I would doubt if a photograph would show any difference because the photographic process whether film or CCD is rather course compared to the optical differences of two flat mirror surfaces. Of course, a diagonal would not normally be used for imaging in any case.

------------------------------------

Subject: EverBrite Diagonal vs. EveryOneElse's? --part 2

From: Gene Horr <genehorrtexas.net>

<awallacejrcharter.net> wrote:
> Just to complicate things, a lot of folks swear by the Astro-Physics 2"
> diagonal and claim they can see a difference between it and others.

Well, to complicate things further, if high power/planetary viewing is in your plans then reflectivity is not the most important factor. Surface error is by far the dominant issue. To avoid noticeably degrading the wavefront error the diagonal needs to be at least 1/20 wave surface error. This diagonal will only add ~1/7 wave to the wavefront error.

Even Takahashi and TeleVue, while being very good, do not quite meet this criteria (I don't know about AP). The only diagonal that I have used that meets this need is Vernonscope. While they aren't cheap, they are in the price range of AP, Tak & TV.

------------------------------------

Subject: EverBrite Diagonal vs. EveryOneElse's? --part 3

From: Shawn Kelly <kelly_shawnsolarturbines.com>

The TV EverBrite and the AP Maxbright are identical in rated optical performance and while it is true their dielectric coatings have higher reflectivity than ***quality*** aluminum coated mirrors, you'd probably never notice the difference except maybe on Jupiter and Saturn and only because they are so bright and aluminum scatters more. The difference between these two and all other diagonals is primarily the durability of the reflective coating. This coating is far more durable than any of the aluminum coatings. Suffice it to say that these two are arguably the top of the lines and I'll forget about others for the rest of this. The difference between the TV and AP is more mechanical than anything else and there are a couple important differences.

One difference is the undercut shoulder on the TV's 2" barrel. (the safety feature that some love and some hate) When the TV is used in conjunction with the JMI NGF focuser the focuser's screws just happen to land right on the edge of that shoulder, no problem with the AP. Rotten luck but easily avoided with the use of a 0.1" spacer (kind of like a really thin parfocalizing ring) or having that shoulder moved by someone who can machine it a little. This is really more of a problem with the focuser than the diagonal though. The VSE monster focuser avoids this, has more features and more travel than the JMI anyway. (Sorry Jim, I just call 'em like I see 'em.) Essentially though If you're not using or going to use the JMI this difference doesn't matter.

The other significant difference is that the TeleVue has a fixed-position mirror, pressed, like most other diagonals against a precision machined surface on the body of the diagonal. The AP has its mirror mounted on a 3 point mount. While the 3-point mount might sound attractive, that feature must be held up to the possible problem that it may be more fragile and may or may not actually improve performance. This could be a biggie if an AP ever has any "rough handling."

OK, so what?...

Now I have been fortunate and only dropped a couple expensive items and so far not damaged any but I worry that an AP 3-point mount may not survive even a single drop. I have never been able to find a single report of a drop test or even any anecdotal references to survivability, good or bad. Anybody ever drop a Maxbright? what happened? mirror fall out? need to collimate it? anything? Nothing ever seems to happen to conventional designed diagonals when dropped, just clean them up and all is well. Despite the reality that the 3-point mount is certainly an optically superior way to mount the mirror, there is no information on weather or not there *really* is any performance superiority of the AP's 3-point mount over the way practically every other diagonal mirror in the entire industry is mounted. All of the manufacturers test their mirrors outside the assembly so the wave specs given are useless here. The conventional mount has the potential to distort the surface of the mirror all the way around the perimeter of the mirror since it is an optical surface pressed up against a non-optically-smooth one... but is that really a problem. I'd like to see the tests. I cannot see a difference when I look through each of them. Even if AP is better, is it enough better to sacrifice durability? and for that matter is there even a durability issue? We don't really know that either. That's the frustrating part.

From my point of view I want the dielectric coating for its proven durability and if I want durability of the coating then I also want durability of the whole assembly. I don't want to ever have to collimate one and it's possible that no one would ever need to but without breaking a few APs to see just how durably the mirror is mounted I worry that it could be dislodged by a drop, a heavy bump, vibration, a long adapter or EP etc. I don't see where the unproven durability of the 3-point mount and unproven optical problems with the conventional mount outweigh the proven effectiveness and durability of the conventional design. I bought the TeleVue EverBrite and recommend it to everyone but at the same time I do not recommend against the Maxbright it is excellent too maybe just not as durable. (I don't dislike the JMI NGF either, I have a DX-1 on my Dob and love it; the monster will be better for my LX200 but is overkill and too heavy on my Dob.) You have to weigh the features, problems and benefits yourself.

(...And yes the stock Meade 2" diagonal sucks, having only random acts of quality spread among the quantity.)

------------------------------------

Subject: EverBrite Diagonal vs EveryOneElse's? --part 4

From: Doc G

I understand your concern about getting a bit more for a lot more money. This seems to be very generally true of a variety of products.

We have seen some excellent analysis, data on various diagonals and really useful information in recent posts on this topic. Mapuggers are a great bunch and always come through with good advice. I have learned a few things that I did not know about the very high end diagonals. I am quite satisfied with the TeleVue EverBrite. I felt the difference between the Meade and TeleVue diagonals was, for me, enough to justify the cost. Others may not feel that way.

I believe that when you are talking about the differences between 1/4 and 1/10 wavelength flatness you need to have optical methods to evaluate these factors definitively. That is, that simple techniques like viewing and film will not tell the story accurately.

But, in the long run, if you can see a difference that is the final arbiter or what you need. Enough people report that they can see a difference that I am very happy to give them my trust and am happy that they have pride of ownership of the best. Whatever your choice, you need to feel comfortable that you are working with the best equipment that you can afford and that does the job for you.

------------------------------------

Subject: EverBrite Diagonal vs EveryOneElse's? --part 5

From: Gene Horr <genehorrtexas.net>

"Doc G" wrote:
> I believe that when you are talking about the differences between 1/4
> and 1/10 wavelength flatness you need to have optical methods to
> evaluate these factors definitively. That is, that simple techniques
> like viewing and film will not tell the story accurately.

Well, somewhat true, but that difference should be obvious. A 1/4 wave surface error diagonal will add almost an additional 3/4 wave error to the wavefront! Assuming "diffraction limited" optics (generally defined as 1/4 wave surface error at the film plane) you are bringing the total error down almost to a full wavelength.

A 1/10 surface diagonal (which all high end diagonals appear to be at or better than) will add "only" slightly under 1/4 wave error to the wavefront, bringing the total system to just under 1/2 wave.

From my experience there is a noticeable difference between 1.0 wavefront error systems and 1/2 wavefront error systems. This is why there is so many anecdotal reports of dramatic improvements between mass market diagonals and high end products such as AP, Tak & TeleVue. That improvement _should_ be noticeable.

Now, when you jump up to 1/20 wave surface error diagonals the wavefront degradation becomes only ~1/7 wave. Taking the same 1/4 wavefront optics mentioned above the difference between straight through versus a diagonal would be harder to detect, but is there. The jump down to 1/2 wave is slightly larger. The difference between 1/20 wave diagonals and 1/10 wave is admittedly far smaller and harder to detect than the jump from 1/4 to 1/10. But from my experience even that is still detectable when pushing high power planetary viewing to the system limits.

As an aside - this is a subject which seems slow to sink in with the ATM ranks. Everyone seems to harp on the quality of the Newtonian primaries but try to buy the cheapest secondary they can find, but the secondary is actually more important to the final image quality.

PS - for those of you trying to actually use real numbers - To figure wavefront degradation for a diagonal you take the surface error x 2 x SQRT(2). There was a bit of a squabble a couple of years ago about whether the COSIN(mirror angle) is a factor. The end result is that it is. Wavefront errors add (well, typically. There are exceptions but they generally don't apply in this discussion....)

> Can you elaborate? I always thought the surface error doubled the wavefront error(?)

It doubles it then multiplies that by 1/cosine of the incident angle. For most focusing optics the incident angle is so small that 0 can be used, making the modifier 1X. But for a 45 degree angle the modifier becomes ~1.42X (= SQRT(2) = 1/(COS(45 deg.))) So the wave front degrades at ~2.84X the surface error.