28 replies to this topic

[jmoore]

I've concluded that I will never find a well-priced Speers-Waler 18mm (80*), or 5-8 zoom on Astromart. So, I just bought these from www.heavensandearth.com
Good pricing here...$120 for the 18mm. $230 for the zoom. $5 shipping total.
My first purchases of new equipment in a long time. Can't wait to get them.

FYI, I have the 10mm and 14mm SW (80*), and think these are wonderful pieces, especially for the $$. Possibly the best values on the market. Near-equivalent performance to Naglers (in some ways, they are equivalent or better even...this is based on my experience with 7mm and 9mm t1s, and also based on some other reviews I've read).

[Tom L]

I saw a 70 degree on AM but I'm also interested in the 80's as well. Really looking forward to your assessment of them, Jeff.

[jmoore]

Too bad Jupiter's almost gone. I want to assess the planetary performance of the 5-8 zoom against other 7-8mm EPs I have, but will I get a chance to properly do this before next year's planet season? I sure hope so.

If the 5-8 zoom compares favorably with my 8mm TV plossl, 8mm RKE, 7.5mm Ultrascopic, 7mm ortho, and 7mm Nagler, then I'll stand to get a lot of money back from selling these pieces. Even if I can sell off just a few of these EPs, this will cover the cost of the zoom.

[wagg]

hi, i have the 10 and 14mm's, and am really curious as to the performance of the 18mm. if you really do sell your 7mm ortho or 7.5 let me know!
cheers, wagg

[rboe]

All this talk about Speers-Walers, especially the zoom is going to cost me money. You guys are expensive to listen to.

Jeff; I forgot which scope you are using - could you remind me? I'm interested in how fast it is.

[David Knisely]

Just a reminder: the 5-8mm Speers Waler eyepiece is *not* really a zoom eyepiece, in that you do not maintain focus (or even stay close to focus) when changing its focal length. It would more accurately be described as a "variable focal length eyepiece", as that is what it was designed to do. The review of the eyepiece is at:
http://www.cloudynig...peers-waler.htm
Clear skies to you.

[jmoore]

Wagg...how do you like the 10mm and 14mm? Do you share my enthusiasm for them? And yes, I'm equally eager to see if the 18mm performs as well as they do. As for your request for my 7mm EPs, I've already had too many requests in the form of "let me know when you sell them". So, I'll have to ask you to just watch for them on AM...wouldn't happen for a couple weeks yet. I'll try to keep you in mind, though.

Ron...this seems fair enough...the costing you money part, that is. You've all cost me a fortune, so what goes around, comes around Oh...and my scopes are f5 (8" Newt), f6.2 (80mm refractor), and f12 (5" Mak). The longer SWs won't focus in my refractor (though I hope the 5-8mm zoom will). My main use for most of these is my f5 Newt (DSOs)...and to a lesser extent in the Mak (mainly lunar and some planetary). The 10mm and 14mm are every bit as well corrected (sharp, flat, etc) in my f5 as my t1 Naglers are.

[jmoore]

Just a reminder: the 5-8mm Speers Waler eyepiece is *not* really a zoom eyepiece, in that you do not maintain focus (or even stay close to focus) when changing its focal length. It would more accurately be described as a "variable focal length eyepiece", as that is what it was designed to do. The review of the eyepiece is at:
http://www.cloudynig...peers-waler.htm
Clear skies to you.

Yep...well aware of this, David (though others might not be). I've got no problem with this.

Thanks again, though, and also for your review. It helped me build my enthusiasm for this piece. So I'll blame you if I don't like it
jeff

[rboe]

David; I had read the review and your exchange with Tom T. but that little tidbit had not stuck. Thanks for bringing that up again. As I sit here and think about it that may be a deal killer. Would have to try in person to see if it's livable.

Jeff; Good! a fast newt. I have a very fast newt that will make eye pieces of questionable heritage show their true colours (pun sorta intended). The RKE looks terrible in it. So I await your report on them.

Still waiting....

[Craig L]

David; I had read the review and your exchange with Tom T. but that little tidbit had not stuck. Thanks for bringing that up again. As I sit here and think about it that may be a deal killer. Would have to try in person to see if it's livable.

Oi vey! Ignore the zoom issue. Think of it as a high magnification set of wide-field EP's (How much would that cost?) in one package. Instead of hauling a 4 or 5 EP's out for high-mag work, you take this one out instead. So what if you have to tweak the focus as you change focal lengths? For the cost savings and quality of the optics, this gem is the deal of the decade. I have several Naglers and Pentax's etc, and this one keeps up with them fairly handily. Mine's a keeper until I'm nailed to me perch and pinin' for the fjords.

Cheers,

- Craig

[wilash]

Just a reminder: the 5-8mm Speers Waler eyepiece is *not* really a zoom eyepiece, in that you do not maintain focus (or even stay close to focus) when changing its focal length. It would more accurately be described as a "variable focal length eyepiece", as that is what it was designed to do. The review of the eyepiece is at:
http://www.cloudynig...peers-waler.htm
Clear skies to you.

Zoom = varible focal length. There is no requirement that the focal plane cannot change to be labelled as a zoom. However, refocusing as you "zoom" can be annoying for some.

[rboe]

Craig; you make a compelling argument.

David, I think Wil has a good point - although your original point is still valid but Craig is trying very hard to invalidate it. These discussions always cost me money.

[David Knisely]

Just a reminder: the 5-8mm Speers Waler eyepiece is *not* really a zoom eyepiece, in that you do not maintain focus (or even stay close to focus) when changing its focal length. It would more accurately be described as a "variable focal length eyepiece", as that is what it was designed to do. The review of the eyepiece is at:
http://www.cloudynig...peers-waler.htm
Clear skies to you.

Zoom = varible focal length. There is no requirement that the focal plane cannot change to be labelled as a zoom. However, refocusing as you "zoom" can be annoying for some.

Well, I wouldn't quite agree here. Over the past 30 years or so, the zoom feature in most zoom eyepieces was intended to at least attempt to maintain the focus of the eyepiece as the zoom level was changed. This was achieved with varying degrees of success, but usually what happened was that the focus changed slightly as you changed the zoom level (very few kept it spot-on focused, and in a few really bad ones, the focus changed noticably even with minor changes in zoom level). Optically, the performance of many of the older zooms was less than satisfying, and zoom eyepieces were often frowned upon as a class until probably the mid 1990's. The method for doing the zoom used moving different elements in the system, which often resulted in a variable apparent field of view at times (wide at high zoom and narrower at lower zoom levels). The Speers-Waler acts more like a set of different eyepieces which are not parfocal, as changing from its 5mm to 8mm focal lengths results in an image that is terribly out of focus. The movable Smyth lens basically acts as a variable power Barlow, which is different than the methods used by most traditional true zooms. It maintains its 78.5 degree apparent field of view regardless of the focal length adjustment of the eyepiece, but does not even attempt to maintain the focus. If people are expecting a "parfocal" view at all focal lengths with the 5-8mm Speers Waler, they may be a bit disappointed if they don't know the truth of the matter. The Tele Vue zoom keeps to the original "tradition" of zoom eyepieces by pretty much maintaining focus all the way through. A few of the other zooms I have seen on the market keep things close, but they often don't quite make it. In any case, I like the larger apparent field of view of the Speers a lot more than I would like maintaining focus, so for me, the performance is the overriding issue. Clear skies to you.

[wilash]

Just a reminder: the 5-8mm Speers Waler eyepiece is *not* really a zoom eyepiece, in that you do not maintain focus (or even stay close to focus) when changing its focal length. It would more accurately be described as a "variable focal length eyepiece", as that is what it was designed to do. The review of the eyepiece is at:
http://www.cloudynig...peers-waler.htm
Clear skies to you.

Zoom = varible focal length. There is no requirement that the focal plane cannot change to be labelled as a zoom. However, refocusing as you "zoom" can be annoying for some.

Well, I wouldn't quite agree here. Over the past 30 years or so, the zoom feature in most zoom eyepieces was intended to at least attempt to maintain the focus of the eyepiece as the zoom level was changed. This was achieved with varying degrees of success, but usually what happened was that the focus changed slightly as you changed the zoom level (very few kept it spot-on focused, and in a few really bad ones, the focus changed noticably even with minor changes in zoom level). Optically, the performance of many of the older zooms was less than satisfying, and zoom eyepieces were often frowned upon as a class until probably the mid 1990's. The method for doing the zoom used moving different elements in the system, which often resulted in a variable apparent field of view at times (wide at high zoom and narrower at lower zoom levels). The Speers-Waler acts more like a set of different eyepieces which are not parfocal, as changing from its 5mm to 8mm focal lengths results in an image that is terribly out of focus. The movable Smyth lens basically acts as a variable power Barlow, which is different than the methods used by most traditional true zooms. It maintains its 78.5 degree apparent field of view regardless of the focal length adjustment of the eyepiece, but does not even attempt to maintain the focus. If people are expecting a "parfocal" view at all focal lengths with the 5-8mm Speers Waler, they may be a bit disappointed if they don't know the truth of the matter. The Tele Vue zoom keeps to the original "tradition" of zoom eyepieces by pretty much maintaining focus all the way through. A few of the other zooms I have seen on the market keep things close, but they often don't quite make it. In any case, I like the larger apparent field of view of the Speers a lot more than I would like maintaining focus, so for me, the performance is the overriding issue. Clear skies to you.

We will have to disagree.

The most basic of zoom designs simply moves a negative element in relation to a positive one. The largest problem of this design of course is the shift in the focal plane.

Today, two methods used in zoom design. The first is optical compensation where the elements are moved equal distances. This requires a more complex optical design and therefore more elements. The second type is mechanical compensation which move different elements by different amounts which require a complex mechanical design.

To keep the focal plane from shifting also uses two methods. One is to simply move the lens in relation to the focal plane as it is zoomed. Another uses a positive lens near an afocal componant used to maintain a relative aperture.

The terms "zoom" and "varible focal length" are synonyms. It has nothing to do with a specific construction.

[Mike Hosea]

I know there are people in the amateur astronomy community that believe that to be a "zoom" implies maintaining focus. What I don't know is whether the term "zoom" is really defined in any authoritative sense in the professional optical design literature that implies this or whether it is just one of those opinions that has somehow graduated into putative fact by being repeated often enough.

What we really need to know is that manufacturers do not seem to require this property in order to use the term, and when considering a given "zoom" eyepiece, we might like to know whether it is approximately "parfocal" or not. Setting semantics aside (since I don't have any authoritative sources at my disposal to settle that issue one way or the other), I do think David is quite correct in pointing out that this property of being approximately parfocal is normally attempted by a zoom designer to some significant degree, and so it is definitely noteworthy that the designer of the Speers-WALER "zoom" didn't.

However, I also think that manufacturers do (at least now) use the terms "zoom" and "variable focal length" synonymously, and instead of making a distinction in any other way, we now see "parfocal" used to describe a variable focal length eyepiece that induces very little movement of the focal plane. So we can disagree on how the term ought to be used, but let's at least be clear on how manufacturers are currently using the term when we're shopping.

[wilash]

Make you missed your calling. You should work for the UN.:flower:

However, I also think that manufacturers now use the terms "zoom" and "variable focal length" synonymously

They always have because the terms ARE synonymous.

But don't leave us hanging. What terms are the manufacturers using? Obviously the folks who make the Speers-Waler EP don't believe the focal plane needs to be fixed. I think giving two synonyms different meanings does not add to clarity.

[Mike Hosea]

But don't leave us hanging. What terms are the manufacturers using?

All I know is that generally if you see an eyepiece described as a "zoom" by a manufacturer or vendor, it would be unwise to assume that refocusing is not required when changing the focal length. Whether it is a little or a lot doesn't usually make a lot of difference unless you have a slow helical focuser (but I guess this is debatable--I just don't believe in the utility of small changes in magnification in the first place), and the only ones I've seen that I really could use without refocusing (provided I focused them properly at the shortest focal length) are the 2-4mm and 3-6mm Nagler zooms. Actually, in practice I can rarely use ANY of them without refocusing because the ones that are close to parfocal use a helical adjustment of focal length, and my focusers are helical crayfords. It's not easy to keep the focuser from turning when changing the focal length.

[half meter]

Interesting discussion, but it's a distinction without a difference.

Whether a little or a lot, refocusing seems to be the general case and so the extra word modifier ought to go to the special case, that of parfocal behavior. 'nuf said.

I'm more interested in the performance differences. Is there a reason to avoid parfocal behavior because achieving it causes more complexity, more light-scattering elements, less FOV, or more cost?

Knowing the tradeoffs, I can decide what's important to me. But let's stick to true differences.

I heard this eyepiece isn't good on planets (lack of sharpness?) Is that a tradeoff to achieve more FOV?

[Craig L]

Craig; you make a compelling argument.

David, I think Wil has a good point - although your original point is still valid but Craig is trying very hard to invalidate it. These discussions always cost me money.

Huh? Wha?!? I thought I was agreeing with David! Maybe another cup of tea in me will help the ol' gray matter kick in.

Also, to Mike's point about not seing the utility of small changes in focal length. I agree when it comes to focal lengths over 8mm, but focal length changes below 8mm make a large difference in magnification. My dob has a FL of about 1500mm. A 3mm FL EP gives me a magnification of 500x, while a chage to 3.5mm gives me a magnifaction factor of 428x; 4mm=375x etc. This is why my Nagler Zoom and SW 5-8mm get regular use. I've also found a place for my Televue (Vixen) 8-24mm for Ha solar viewing. Coupled with a 2.5x Powermate, it's a good performer for this kind of observing.

Cheers,

- Craig

[half meter]

Craig, I use that same stack (Televue 8-24mm w/2.5x Powermate) every night I'm observing. I use it to establish maximum seeing.

It yields 270x-800x in my 20" f/5. There comes a point where I can make details larger but not clearer. But it's a lot of glass and a narrow field. So once the range of good seeing is identified, I shift to appropriate fixed eyepieces.

The Speers-Waler 5-8mm by itself would deliver 300x-500x. This is a useful range, plus it has a very wide field. Bringing out planetary detail at over 300x in a 20" is a regular occurrence (large apertures sort of get a pass on the oft quoted rule of thumb about the atmosphere not allowing anything above 300x.)

But if there's a sharpness issue I might as well stick with getting 500x from a 13mm Type 6 Nagler in the 2.5x Powermate. Or getting 400x using a 16mm Konig instead of the Nagler.

Actually, I use the Konig quite often as the ceiling is 400x many nights. The Konig performs well because the 2.5x Powermate actually slows the scope to f/12.5 which is much less demanding of the eyepiece. But its gives a smaller 65 degree FOV compared to the Speers-Waler 82 degrees.

I guess the bottom line is I'm going to have to borrow one and decide for myself.

[Tom L]

Since Jeff just bought one, I think he should send it around to all of us to try!

[Jim Svetlikov]

Jeff

Congratulations!

I hope you're as happy with the SW 'zoom' as I am. Yes. it is too bad about Jupiter because that's where this eyepiece really performed. As well, you'll be able to pop the zoom in while looking at the full moon, and due to the huge field of view, you can get the entire moon in the field at 8mm!

With the TV barlow and the zoom stretched out to 5mm, one can view very good detail of the lunar landscape.

[jmoore]

Since Jeff just bought one, I think he should send it around to all of us to try!

Hmmm....I'll think about that one

Hopefully, I'll get my S-W in a week. And hopefully, I'll good viewing conditions right away (it's been pretty good around here lately).

If I'm lucky in these regards, I'll aggressively make the most of what Jupiter has left to offer (i.e., will try to view in several consecutive evenings, starting before dark...while Jupiter's still *relatively* high in the sky).

I'll compare the SW zoom directly to my 8mm TV Plossl, 8mm RKE, 7.5mm Ultrascopic, 7mm ortho, and 7mm t1 Nagler.

I'll let you all know what I find!

cheers,
jeff

[Mike Hosea]

Also, to Mike's point about not seing the utility of small changes in focal length. I agree when it comes to focal lengths over 8mm, but focal length changes below 8mm make a large difference in magnification.

Notice I didn't say small difference in focal length, rather small difference in magnification. I guess parfocal behavior is helpful when a small difference in focal length results in a big difference in magnification, but what I don't really believe in is that I need to tune the magnification finely enough that I would need continuous control over the focal length rather than, for example, half mm increments. The 2-4mm Nagler Zoom that I use is an extreme case in my 10" f/5, yet I hardly ever use it between the half mm clickstops. Consequently, I don't think I would be much disadvantaged by an eyepiece like the SW 5-8 that requires selecting a focal length and then refocusing.

Which brings me back to the semantic thing just momentarily. As I said, I have nothing that I consider authoritative to go by in a technical sense, but (except in the more recent usage of computer graphics) the term as commonly used implies movement or the simulation of movement (not just the result of movement), and parfocality is needed to simulate movement in our context. For example, people say things like "it was like coming in for a landing" when using one of the Nagler Zooms in lunar observation. They wouldn't say that about the SW 5-8. They might say it about a Vixen 8-24 (perhaps in a Barlow), but I haven't heard it. I suppose the amount of refocusing required by the Vixen, although small, is distracting enough to ruin the simulation of movement for most observers.

[David Knisely]

Interesting discussion, but it's a distinction without a difference.

Whether a little or a lot, refocusing seems to be the general case and so the extra word modifier ought to go to the special case, that of parfocal behavior. 'nuf said.

I'm more interested in the performance differences. Is there a reason to avoid parfocal behavior because achieving it causes more complexity, more light-scattering elements, less FOV, or more cost?

Knowing the tradeoffs, I can decide what's important to me. But let's stick to true differences.

I heard this eyepiece isn't good on planets (lack of sharpness?) Is that a tradeoff to achieve more FOV?

Well, I don't know exactly where you heard this, but the 5-8mm Speers Waler is a good eyepiece for planetary viewing. It is quite sharp and, while it may not be the very best planetary eyepiece, it reveals a lot of detail (as well as allowing you to "tailor" your power to your viewing needs). The wide field is not as wide as some of the Nagler eyepieces, but it wide enough that it is of particular use for moderate and high power in undriven Dobsonians. I used the 5-8mm on Mars last year and was quite satisified with the results, although my favorite use of the eyepiece is for observing globular clusters in my 10 inch (gives me a 178x to 288x power range). I also like it for "pushing the edge" on power in Deep-sky objects by using my 2.5x Powermate with it on small planetary nebulae. As for the reason for the non-parfocal nature, that is for simplicity as well as for better performance. In fact, the manufacturer itself does not call the 5-8 a "zoom" in the literature I got from Sky Instruments, so it is clear that at least somebody there does not think of it as one. Clear skies to you.