Nov 5, 2012

Test Report: Explore Scientific ED127 Carbon Fiber Apo Refractor

Before we start, let's just get the obvious question out there right now.  You're wondering: "What makes this guy qualified to review any sort of equipment?"  It's a pretty simple answer really.  I have an opinion, a few minutes and a keyboard.  Those are the extent of my qualifications and I possess no other.  If you came here expecting me a dissertation on refractor theory and to debate the finer points of chromatic aberration and glass types at some nauseating level of tedium, you have come to the wrong place and should stop reading now.  I am not that astronomy creature that I refer to as "refractor guy". 

You know him.  He's the one who takes his refractors far too seriously and is ready to escalate any discussion on the topic to a Defcon 5 incident.  Casually drop the phrase "TeleVue scopes are overpriced" and you'll awaken to find that he's kidnapped your dog (dognapped?) until you publish a retraction of such heresy.  If you don't know that guy, you should swing over to the refractor forum on Cloudy Nights.  There's a few of them there.  After you've done that...if you still don't understand what I mean by "refractor guy" - then you're probably "refractor guy".  Please don't think that I'm picking on "refractor guy".  He's not the only eccentric personality in this hobby.  There's also Celestron guy, Zambuto guy, Double Star guy, Binoviewer guy, etc.  It's part of what makes our hobby obsession so great. 

How Did I Get Here?

I reached a point late last year where I was ready to move into some longer focal lengths for deep sky imaging.  I'm also not a fan of diffraction spikes in an image and the wiring hanging down in front of my Hyperstar rig was causing them with no real way to get rid of them.  Finally, with the Hyperstar I did find it difficult to get pinpoint stars all the way across the APS-C sized sensor of my QHY8PRO CCD camera.  One corner or another was always out of focus and it was a constant battle with collimation.  In summary, I'm a huge fan of the Hyperstar system.  There isn't a better way to develop some chops in this thing we call deep sky imaging and it makes it easy for a newcomer to get good images.  However, it was time for me to move on.  Back in December of 2011 I was curious to experiment with a refractor, and I had an 80mm f/7.5 Vixen doublet that wasn't being used right at that moment.  So I put it on the mount and shot a dozen frames of the Double Cluster through it.  I was blown away at the increased color saturation and the pinpoint stars through the refractor.  I knew then that the new imaging scope would be a refractor. 

Double Cluster as shot with an 80mm Vixen refractor.  This shot convinced me to shop for
a refractor as my next imaging telescope.  Just 12 frames x 2 minutes at f/7.5.

I began researching refractors and shopping around in the 900 to 1200mm focal length.  Ultimately, I was hell bent on finding a 12" f/5 color-free triplet that weighed less than 50 pounds and only cost about $2000.  Apparently that telescope doesn't exist.  It makes me wonder what Al and Roland and Yuri have been doing with their free time, but I digress.  Soon I began to assemble some realistic expectations and narrowed the field.  I had the good fortune last summer to meet up with my friends Alan and Jerry where they had setup their respective refractors and I was able to compare them visually side by side on similar objects at similar magnifications.  Alan's TEC 140 is just a gorgeous scope and it renders me as useless as a teenage boy at a lingerie convention every time I see it.  The views through the telescope are just astounding and I've become a better visual observer from using it and letting him teach me how to tease out detail in the objects that are being viewed.  But at nearly $6000 by the time you buy it, ship it and put it on the mount, the TEC 140 is expensive. Nearby, Jerry had setup his brand new Explore Scientific ED127.  With its 5" aperture and carbon fiber tube it was an attractive scope in its own right - especially at its introductory price of $1999. 

After a long night of comparing views and enjoying the company, my friend Chris put it all into perfect perspective.  His review (and I paraphrase):
"The view through a TEC 140 is better, there's no question about it.  But, the only thing wrong with a view through Jerry's ED127 is that it's sitting next to a TEC 140.  And the only thing wrong with the view through Alan's TEC 140 is that I'd be just as happy looking at the same objects through an ED127 with $4000 in my pocket."
Artist's conception
of Refractor Guy
Let's pause for a few seconds while "refractor guy" finishes hyperventilating.  Breathe into a paper bag refractor guy.  Apparently, it helps. I couldn't write a better comparison myself and it's this exact reasoning that led me to choose the Explore Scientific scope as my new imaging platform.  Now before you start penning me that email that says I have no qualifications whatsoever - please remember that I started out this review by admitting that.  Please save your breath telling me that I'm an idiot.  I've been aware of that far longer than you have.  Chastising me in any way for this opinion/decision will introduce no new information to this topic other than to possibly identify you as "irrational refractor guy".  If the budget had allowed for a $6000 refractor at the time I might have made a different decision, but I doubt it.  All better now?  Good. 

Acquiring The Glass

I pondered and debated the decision over a weekend in early January.  In other words, it took me two days to work up the courage to pry open my wallet and dig out the debit card to place the order.  It's not that I had to await approval from the "CFO" like so many other fellow amateurs have to do.  In fact, I should do a review on my lovely and talented spouse and her suitability as an "astronomy wife" some day;  Best astronomy wife ever - I'll tell you that.  I just agonize and worry and fret the decision to purchase astronomy gear before I buy it.  Once I pull the trigger, I don't worry about it again.  On Sunday morning I pulled the trigger on the refractor.  I got out of bed and placed my order with Oceanside Photo & Telescope with a cup of coffee in one hand and the computer mouse in the other.  Just so I can paint the complete picture, I have to say that I was rocking the most astounding case of bed-head that you've ever seen while I placed this order.  My research had indicated that the large chip of my CCD camera would probably be happy with a field flattener too so I also ordered a Hotech SCA field flattener and a Baader Vari-Lock extension to get the spacing right with my camera.  Both were a wise addition to the purchase.

OPT listed that they had all of the items in stock and that there would be no shipping charges.  As you can see, I started my Sunday off the right way.  By virtue of its stock status I received a tracking number for the shipment the next day indicating that it would be delivered on Wednesday.  Of course, this clearly means that it's imperative that I work from home on Wednesday and that is what I did.  The UPS man delivered the packages very, very late in the day on Wednesday.  This served to reinforce "Mike's Postulate of Astro Equipment Delivery" which states:
If you remain at home awaiting the delivery of exciting new astronomy gear, your package will be the last delivery of the day;  Even if you live across the street from the UPS warehouse and your mom is the driver. Unless you run out for something during the day, then they'll attempt to deliver it while you're gone and you'll end up waiting and being the last delivery of the next day.  This is still true even if you live across the street from the UPS warehouse and your mom is the driver.
The scope is sold with its own case and is packed in that case for shipping.  All the edges of the scope's storage case are lined with heavy foam that helps it fit perfectly into the heavy cardboard shipping box.  I was a little surprised at the weight of the box - heavier than I expected.  I'll spare you every little detail of the shipment.  The box had a couple of dents in it from its transport from China to the US to my house, but the contents on the interior were in perfect condition upon arrival. 

The Case

The case is nice.  It's solid, durable and protects the telescope very well.  It's cut to form fit the OTA as well as the diagonal and finderscope.  There are some additional cutouts to store a couple of eyepieces.  The case is far above and beyond what you would expect in quality for a telescope at this price point.  Problem is, it's almost too good.  The telescope fits so tightly into the case that it has to be put in "just so" in order to fit and have the lid close properly.  With my 2.5" Moonlite focuser attached to the scope it is an extremely tight fit to get the OTA in there.  With the new camera I had to order a focuser extension to get the required out-travel and the scope no longer fits in the case.  Overall though - I'm a fan of the case that came with the scope. 

The Mount

The telescope is light.  In my case it was actually too light by an ounce or two when I first took it out.  Let me explain.  The scope comes with rings and a Vixen style mount that fit nicely into my ADM dual saddle on my previous Celestron CGE mount.  Even with the cameras and finder attached, the telescope was so light that I couldn't completely balance the scope.  I had two of the standard counterweights with the CGE and definitely only needed one.  Even with a single counterweight I had to slide it as far up the shaft as possible.  I slid a piece of cardboard in between the weight and the DEC housing to ensure that they wouldn't hit each other while the telescope slewed.  Still, the telescope was a couple of ounces too light to completely balance.  If I was to keep the mount balanced "east heavy" I had to image only in the eastern sky as the telescope was too light to image in the west and keep the scope "east heavy".  I feel more comfortable with the wider plate and surface area of a Losmandy style dovetail anyway, so I remedied this soon thereafter by mounting the scope with an ADM Universal D plate.  This added enough weight to remedy the weight situation. 

The Focuser

My least favorite thing about the telescope is the focuser that is attached to it.  For visual use, it is probably more than adequate.  I wouldn't know.  I didn't buy the scope to use it visually and I haven't done so.  For very light imaging trains - like a small DSLR it's probably adequate.  I bought the scope with every intention of moving to a heavy duty, computer controlled focuser so it wasn't really an issue to me.  I planned to swap it out all along.  It is a two-speed focuser and reasonably nice all things considered.  There's no way though that it would have been up to the task of supporting the weight of my SBIG ST-8300 and CFW8 filter wheel though and I don't think they're all that heavy in comparison to other imaging setups.   That said, I immediately swapped out the scope for a 2.5" Moonlite focuser with stepper motor control.  It works like a dream.

The Business End

ED127 setup for the May 2012
annular eclipse in southern Utah.
There's a couple of things to talk about on the business end of the telescope - also known as the objective lens.  It has adjustment screws to tweak the collimation, something I haven't found necessary.  The telescope was perfectly collimated when I got it and remains that way despite six months of use hauling it out to the Arizona desert a couple of times a month.  Most telescopes in this size range have a sliding dew shield that retracts for storage and extends to shield the objective lens while in use.  This isn't the case with the ED127.  The dew shield is removable and gets put onto the end of the telescope upside down to achieve the "retracted" position.  To attach the dew shield, simply turn it around and tighten down the two thumb screws to achieve the "extended" position.  This creates one minor annoyance.  In order to put the lens cap back onto the scope, you have to remove the dew shield.  I found my own solution - the LensCoat.  Since I set up typically for a few days at a time, the lens coat fits snugly over the end of the dew shield to keep dust off the objective lens when the telescope is not in use.  Now, about that lens cover.

The lens cap threads directly onto the objective cell at the end of the telescope.  It's a disc of machined aluminum and will protect the lens from all manner of dust and damage - except itself.  Thankfully my friend Jerry warned prior to the new scope's arrival at my house.  There is almost no clearance between the actual glass of the objective and the lens cap itself.  It would be very easy to hit the objective lens with the lens cap itself when unscrewing for a night's observing.  This is the only design flaw in the telescope in my opinion.  I have a pretty simple workaround though.  I mount the telescope and then move the mount so that the object lens is pointed downward toward the ground.  If I should drop the lens cap when unthreading it, this will cause the aluminum cap to fall away from the glass objective instead of toward it. 

The Tube

It's carbon fiber.  It's well finished and it's gorgeous.  The scope is attractive, lightweight and thermally stable as a result.  Some will argue that carbon fiber in a refractor is actually detrimental because it's too thermally stable and will trap a temperature differential within the tube.  I have not found this to be the case though I haven't tried to prove or disprove this information.  I do know that focus is very stable with the scope.  Over the course of an Arizona night the temperature can drop by as much as 50º F (28º C) in the winter.  I refocus the telescope every 2 hours and haven't yet lost a subexposure because of the image being out of focus.  Between the wide critical focus zone of f/7.5 and the thermal stability of the carbon fiber, those frequent stops to refocus the telescope are a thing of my past and I'm glad for it.

Flatness of Field

To satisfy my own curiosity, first light with the scope involved a series of exposures taken with and without the field flattener.  You can see the results below when the camera uses an APS-C sized chip.  To my eye, the field flattener is a required accessory for anyone wanting to use a DSLR or similar sized chip with this telescope. 

I've recently switched from the QHY8PRO to the mono SBIG ST-8300 CCD camera.  Before pulling the trigger on the camera I did some analysis and made the estimation that the flattener wouldn't be necessary with the smaller chip of the SBIG camera.  I judged this by cropping the subs from the test shots taken without a flattener down to the size of the KAF-8300 sensor and to my eye stars look alright.  Actual experience has shown that the flattener is necessary even with this smaller chip.  So if your plan is to use the scope for imaging, plan on a few hundred extra for a field flattener, just as you would with any other refractor.  I've heard rumor of an upcoming release by Explore Scientific of a dedicated field flattener for this scope.  Since I've never actually seen one or even a picture of one, I have this information filed between BigFoot and Unicorns on my list of things that are real.

Color Correction

This is where the refractor discussion gets touchy.  Here's what I know.  The telescope is a triplet which is supposed to provide excellent color correction.  To my eye it does that.  The difference in focus between the blue filter and the red filter in my imaging setup is 57 steps on the focuser - which equates to 234 microns of travel.  Since the critical focus zone of an f/7.5 refractor is something around 170 microns, I'd say that this means that there's a bit of color in the image.  Since I image with a mono camera and focus for each specific filter, this hasn't been an issue for me. 

Abell 85 shot with the ED127CF.  Seems like pretty good color to me.


Overall, I'm very happy with the telescope and will probably be holding onto it for awhile.  I really mean this - but if you've followed this blog for any length of time - you know that I've shown a tendency to mysteriously upgrade equipment just when I say I like it.  With two teenage daughters at home expecting their first car soon, I'd say there are external factors at work that'll keep this scope in my possession.  I understand that Explore Scientific has made some changes in the newer models - a beefier focuser and a sliding dew shield.  Both of those changes make me recommend the scope even more.  It's worth every penny.  It's not my last scope, but that's because my goal is still to get to longer focal lengths for some really deep sky imaging.  I don't think that there's a better refractor out there for $2500.00.