Explore Scientific 1.25" 2x Focal Extender

[russ.will]

Back in this thread I was looking for a planetary EP, dismissing barlows on the grounds of an unrequired increase in eye relief and the faffing around involved. The forum faithful persuaded me otherwise and the imminent relase of the ES Focal Extenders at a price well below one of their EPs, had me flexing the plastic. The main reason I folded, was because these are not barlows. They are, like the Meade Tele-Extenders with which they share a common heritage, what is often refered to as a Televue Powermate clone. I'm not actually sure that the concept is actually a Televue innovation, but as TV have been selling more of them, for longer than anyone else, lets run with the assumption that it is theirs.

The important bit, is that unlike a barlow, which extends eye relief, a Powermate/Focal Extender doesn't. Instead of there being two (sometimes three) elements in one group that create diverging light rays to achieve their magnification, the focal extender employs a second group of lens elements to turn the magnified diverging rays, back to parallel. This prevents the increase in eye relief.

The disadvantages are three fold. For starters, four elements are never going to be as cheap as two. Focal Extender prices start roughly where mid to higher price barlows leave off.

Second, with a barlow, you can normally unscrew the lens element holder from the barlow body, which is handy. If you screw these elements directly onto the front of the eyepiece, you get a 1.3-1.6x increase in magnification instead. Indeed a less mentioned effect is that if you screw in an extension between the barlow body and the element holder, you can get a greater magnification than the native 2x (or whatever) of the barlow. You can screw it into the nose piece of your camera adaptor to provide a magnification increase for DSLR imaging etc. Barlows are quite versatile. A Focal Extender's magnification is fixed by the relationship between the two lens element groups. Even if they unscrew, the fact that the light rays emerge in parallel (telecentric) from the second group, means that even if they were a foot further away, they would still only provide a 2x magnification.

Finally, a Focal Extender moves the focus point inward by it's own focal length*, which may be an issue for scopes with limited inward focuser travel. This issue, I have only seen mentioned a couple of times, so it presumably a non-issue under most circumstances, as reported by most users. I'd love to add my own experience to the pot, but my ES Focal Extender arrived whilst I stood under crystal clear, Alpine mountain top skies with nought for company but skis, the cloud being anchored at home where the Focal Extender had arrived. T'was always thus.

My point is that Focal Extenders are not necessarily superior to Barlows. If you're into a bit of planetary webcam imaging, or a glasses wearer suffering from tight eye relief EPs, then a barlow may well be a better choice than the addition of a shorter focal length EP. If, like me, you are purely visual and are looking to add some planetary flexibility to some UWA EPs with ample eye relief, then the Focal Extender is a better choice. I see a lot of 'buy 'x', you can't go wrong' type statements, but I personally think there's a bit more latitude in individual requirements, than statements like that allow.

The ES 1.25" 2x Focal Extender cost $79 plus $15 shipping from the USA. Import duty added £31.31, making a grand total of about £87 delivered. I say about, because the vagries of exchange rates, plus Paypal taking it's foreign currency exchange cut fuzzies the total slightly, but it's definitely south of £90. That is about half the price of a 1.25" 2.5x Televue Powermate, but only about a tenner less than a UK sourced TV 1.25" 2x Barlow. The value of this deal is therefore very dependent on your requirements, as mentioned above.

As also mentioned above, I've only been back in the country a couple of cloudy nights, so I'll add my viewing impressions later. In the mean time, here's some piccies coupled with first impressions of the product:

The ES packaging has changed, Whereas the ES 82s arrived in a plain black box with an ample expanded foam, clamshell inner, the Focal Extender has cranked it up a notch. The hefty foam remains, but the box is much thicker card, that by nature of it's wrap around magnetic fixing, is also now a double thickness. Gone is the plain black, all surfaces now resplendent in artwork by Will Tirion, the base of the box carrying a history of his work. A nice touch to add to seriously improved packaging. I would also note that, the box is only a shade smaller than that which carried the hand grenade weight and portions of my ES82 30mm EP which is a LOT bigger. If the Focal Extender arrives damaged, it won't be the fault of the packaging.

On the subject of weight, the Focal Extender, in common with the ES82s, feels pretty dense in the palm. The combined weight of it, plus the 11mm ES82 tips the scales at a not inconsiderable 520g. Half that of the 30mm ES82, but double that of the 11mm alone and so worthy of note to Dob users in particular.

Come to think of it, the weight, combined with the leverage of the complete assembly may challenge lighter EQ mounts. Here's a piccie of the pairing relative to a Skywatcher 20mm Super Plossl, which barely registers on the same scales!

Artificial light and the resulting image tweaking in GIMP, has rendered the sheen of the element coatings invisible. Close inspection through a Canon 50mm f1.8 as magnifier, shows the coatings to be entirely even and resolutely green in hue. If inspection in daylight shows otherwise, I'll add it to my first light report. Likewise, with only LED spots and hammer-head flash, it's hard to show the element groupings, but other details are clear. The lack of blackening to the filter thread is disappointing, in line with all of the ES EPs I have. Liberal application of a black marker will be required to amelioate reflections, although the acid test will be actual use. Hopefully Jupiter will still be around when the cloud clears...

To complete this phase of the review, I see from my original thread that I pre-ordered the Focal Extender on the 21st of December in a pre-Christmas fit of fiscal bravado. It shipped, almost a month to the day, on the 22nd of January. Notification of the 'comandgeddit' from the PO sorting office, was recived on the 4th of February, which is within the 10 working days norm. What I find interesting is that the Focal Extenders finally appeard on the ES website, well after I had ordered mine. The example on their website is number 28. Talk about mine being hot off the press.....

TBC.

Russell

*I stand to be corrected on this one and indeed any other points!

[Damo636]

Great write up Russell, thats a quality looking piece of kit! I look forward to your first light report.

[Bart]

Yes, interesting Russ, as a devoted ES fan, I am keeping an eye on these.

When ordering from the US IN have always been lucky wrt duties/tax

[Dunkster]

Nice one Russell! Look forward to hearing about your first light with it

Btw.. sounds like you got totally stung with duty - sure they got it right? £31 for US$94 doesn't sound right, that's about 50%

[russ.will]

Quite right. I actually got charged £25.42, although that was for VAT and handling only - No import duty which should add another 4%. Odd. Clearly, maths wasn't my strong point last night. But that still seems too much.

Having retrieved the box from the recycling bin, the values shown on the US Customs declaration form are $99 and $39 of postage and 'fees'. If you work out UK VAT and handling on that, it seems about right.

Just to be sure, I checked the Paypal transaction and that was for $97.97. Add £25.24 to that and you end up with £87.28.

At least my £90ish is correct.

Russell

Sent from my iPad using Tapatalk HD using chubby fingers. Sorry.

[Dunkster]

Sorry Russell, didn't mean it to be a maths test just had me doubting my own transatlantic purchasing logic Phew!

The RM 'handling fee' (what else do they do but handle stuff?!?) definitely skews it at this level

[russ.will]

No worries. I knew I was broadly correct, but in the cold light of day, it did look a bit odd.

You're right about the handling fee. I suppose a rough rule of thumb is that if it's £100 or less in this country, then it's not worth importing. I somehow suspect the Focal Extenders won't fall into that category though.

Russell

[russ.will]

Blimey! Look at the date of the original post. It's been three weeks since the ES Focal Extender arrived and I reckon a week longer since the scope was out.

The last few nights have been what passes as clear, around these parts. The level of moisture in the atmosphere was giving decidedly average DSO views, but for that same reason, was giving stable high mag viewing - Bring out the planets. Or should I say planet, because Jupiter is all that is on view. Thus, it was practically the sole subject - Not even the moon, which normally puts a 100 Watt apearance in for me at the first whiff of clear skies.

No matter, because the whole point of buying the Focal Extender was planetary viewing. The Explore Scientific EPs I have, were bought for the range of DSOs that are my main interest, but I'm too mean to consider buying a hat full of EPs just for occasional planets. Actually, I was considering buying cheaper EPs for the planetary purpose but was persuaded, against my will, in the thread linked to at the top, to consider a barlow. I don't like faffing with barlows, but the coincident appearance of the ES Focal Extenders side-stepped a number of the usual barlow issues.

First thing first. Eye relief, which is unaltered from the stock EP, makes for much easier viewing than a barlow. As my ES82s all have an adequate 13-15mm, a barlow pushes this out to 26-30mm, which is too far. I find it hard, over prolonged viewing, to 'hover' that far out from the EP and inevitably find myself drifting in towards kidney beaning and blackouts. Further more, with the excessive ER, you loose the edge of the FOV, which kind of makes a nonsense of having shelled out for UWA EPs in the first place. So, with the Focal Extender in place, actual use is exactly like using a shorter focal length EP. Nice.

But are the views? What do you loose?

I had intended to to compare views between the ES FE and my 2" 2x ED barlow, just to give an indication of how the ES compares to a reasonably decent £60(ish) barlow. The ED barlow just seemed to give a 2x view of whatever EP it was being used with. Before some bright spark points out the obvious, let me qualify that! Yes, I got a double sized view, but I never really experienced more detail, just a larger version of the detail I already had. It was like trying to imagine having a 60" TV, by sitting closer to a 32" TV. Yes the picture was bigger, but it seems grainier and less well defined. Thus, I didn't tend to use it, prefering the smaller, but brighter view of the EP.

I started by comparing the ES82 8.8mm to the 14mm in the FE, to deliver the closest focal length equivalents. Letting Jupiter drift from the centre of the FOV to the edge, brought the same increase in false colour in the last 10-15% of the FOV in both combinations. I came to think that the 14mm+FE was marginally better than the 8.8mm, the FE/14mm bearing up to the last 10%, with the lone EP being closer to 15%, but even on this particulary stable night, moment to moment variations mean that is just an impression.

What I wasn't noticing at any point, was the halo or bloom around the planet that the old ED Barlow produced. Aside from the secondary spider related artifacts, the edge of the great planet were crisp and clear. Further more, I definitely was noticing that the slightly larger image of the 14mm/FE, was delivering more detail without an increase in grain, or a loss of contrast. The cloud bands hadn'tlost any colour, their shape and edges remaing clearly defined and the pale GRS was starting to have more interior detail and delineation from the bands around it. Light transmission and control of light scatter within the Focal Extender is clearly pretty good and as such, I wasn't noticing it's presence in the optical train - It seemed to be delivering the ideal of replicating a shorther focal length EP in terms of image quality and comfort of use.

Buoyed by the planet friendly viewing conditions, I upped the magnification from a perfectly respectable 214x and inserted the ES82 11mm for 272x. I wasn't hoping for much, but what I saw left me slack jawed. Even under such favourable conditions, atmospheric stability was starting to define the limits, but in some surprisingly extended still moments, I could clearly see the peturbations in the two main cloud belts of the gas giant. The vortices formed in the wake of the GRS's progress where there, etched in pale cream against the darker salmon of the darker cloud band above. Other cloud bands presented a greater range of tones than I've seen before, with their variable widths being quite easy to follow. Smaller storms in the tenuous atmosphere were clear as light and dark spots elswehere on the disk, the paths of their progress now obvious. With this level of detail, Jupiter was looking and feeling spherical, rather than a flat disk and indeed, altogether less serene due to all of this now visible activity.

For the record, I did drop the 8.8mm in just in case it was the one night that would support 340x viewing. In brief moments, it did, but they were so brief as to be blink-and-it's-gone moments and again, at this point, I'm not sure I was seeing more, rather than just larger. One day though....

I appreciate that under these conditions, an EP of equivalent focal length would resolve this detail, but the point is that the Focal Extender has delivered two additional focal lengths to my collection, for less than a single eyepiece would have cost. That it has also done this without apparently subtracting anything significant from the view, or the viewing experience, makes it absurdly good value in my book. I can still have my 82deg cake and eat it. I'll let others decide the relationship to Meades past, or value ratio to Televue Powermates present. The point is, at £90 inc duties as a personal import from the USA, it's a very effective addition to your EP case.

I never thought I'd say this, but I'm actually looking forward to the moon coming out...

Russell

[crashtestdummy]

great write up and follow up viewing article Russ and as an explore scientific fan i think i will have to see about investing in one of these when ive stopped hating astronomy due to the clouds and decide i can justify spending more money

[Stargazer_00]

Thanks for this great post Russell. I'm sitting on a fence trying to decide if I want a 2x FE to boost my 6.7 and 4.7

[russ.will]

I can imagine it's tempting, but I bought it to avoid buying the 6.7 or 4.7mm EPs which you already have. In my 1500mm FL scope. They would have been an extravegance, considering the use they could actually get.

Russell

[kriss13]

Excellent review. I about to buy couple ES from USA since in EU prices are nuts, 160€ for 4.7mm ~ 200$, means double the price.

Even after vat and taxes they will be less expensive...

Ok, enough with the math.

I am considering the FE to reduce the number of EPs, so 30, 11, and 8.8 are in the cards plus FE resulting in 15, 6.5 and 4.4mm.

How does the 30+FL compared to 14mm EP ?

clear skyes

ps.

I know 14mm is renown for its curvature... so I try to avoid it.

[kriss13]

Oh, just realized you have the 1.25" FE, not the 2".

Well, at least tell me about the 30mm

Will a TV Plossl be better?

I'm concern about the number of lens (more glass) affecting the DSO observing.

ps.

How may I edit my post?

[russ.will]

If it were me doing it all again, I would probably make some different choices, not least because swapping 2" to 1.25" is a real pain once you get a barlow/Focal Extender into the mix. If I were starting with an empty EP box, then I would probably go with some the ES68s for several reasons.

For starters the 16 and 24mm ES68s are all 1.25". The ES68 24mm, 16mm and FE will deliver 24, 16, 12 and 8mm focal lengths. Add in the 11mm ES82 for for a 24, 16, 12, 11, 8 and 5.5mm spread from 3 EPs and the much cheaper 1.25" FE. You could chose the 14mm ES82 instead, but the 11mm is such a good EP it's hard to not own one!

I'll let you do the maths ( ) but the ES68s are a lot cheaper and trade absolutely nothing in sharpness to the more expensive ES82s. In fact, if my experiences with the Maxvison SWAs is anything to go by (same ES68 glass in a Meade body) then they may be a tiny bit sharper. Further more, the biggest advantage of the 82deg FOV is pushing the field stop out of sight - You don't really gain any easily accessible viewing area, without either moving your head, or swiveling your eyeball to uncomfortable angles. By the time you're doing that, you're viewing through the ocular lens at non-optimal angles and all sorts of other optical aberrations make the views at those angles a bit colourful!

The 30mm ES82 is a fantastic EP and owing to the sheer size of the glass involved, involves less eyeball gymnastics. It's 82deg FOV is more useable and it's massive star-scape makes it desirable in it's own right. But you don't use it for the same reasons as the rest of the EP case, so I find I spend time with it for it's own qualities and the subjects it suits and the rest of the EP case for different subjects. Once used, it gets put away and you don't swap back and forth between it and the shorter FL EPs. Therefore, I can't see any real reason to want to FE/Barlow it.

There is another reason not to though. Weight. Mine pretty much lives in an GSO Coma Corrector (which is certainly no heavier than a 2" FE or Barlow) and that is a monster combination. Every time I use the 30mm it requires rebalancing both my refractor and my 12" GOTO Dob, which won't even lift it below about 25deg of elevation. That's before adding the CC! If you're looking to cut down on EP numbers through Barlow/FE use, then weight is a very good reason to stay 1.25". Just to give you an idea, here's the 30mm plus CC 'Stick Grenade' on the scales:

Eek! That's 1.4kg (3lb) assuming the CC is the same weight as a 2" FE. Given that my 1.25" FE is a fair bit heavier than my GSO 1.25" 2.5X Barlow, I see no reason why a 2" ES FE with double the number of optical elements of the CC won't weigh even more. Take your chances on that one.....

Russell

[Adrian]

That's still 25g lighter than the 31mm Axiom on its own

[russ.will]

As the 31mm Axiom doesn't have the advantage of a coma corrector, we must assume that it is punching below it's weight, if not it's price.

[Adrian]

But that neutronium jacket will stop anything....

Who knew that a twist up eyecup would weigh the same as a coma corrector?

[kriss13]

Thank you Russel... your insight and comparisons are of real use for me and clarifies some aspects about using EPs.

I hope I will bump into more reviews from you... a pleasure to read

[kriss13]

Oh, Optcorp has ES 68 and 82 at the same price (some).