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.



Conclusion

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.

She Blinded Me With Science



 Amateur astronomy has long been a pursuit that loves to debate the controversial topics, even from its earliest days.  All those hours spent studying, observing and watching the sky frees the mind enough that it can form hypotheses and compare them with those of nearby observing companions.  The earliest known controversy occurred one night long ago when one observant dinosaur looked to the heavens and said, "Look, a meteor!  I think it's going to hit the ground!"  His observing buddy looked up, pondered the scene for a moment and said, "No it isn't."  History doesn't record for us the rest of that conversation.  Thus was established the scientific method as it's typically practiced in amateur astronomy circles.  These discussions contributed to some of the most fundamental philosophical changes ever conceived in the early 1600's when everyone in the world said "The Earth is the center of the Universe".  To which Galileo simply replied, "No it isn't." 

                A topic that seems to generate slightly less debate amongst modern amateurs is the subject of star party light pollution and there' s no shortage of opinions on the topic.  With the advent of electronic go-to telescopes, CCD Cameras and modern astronomical software the laptop computer has invaded star parties worldwide.  The encroachment of electronics onto the observing field has been one of uneasy tension since the successful release of the Meade LX200 line of go-to telescopes back in 1992.  The noise of the coffee grinder mount slewing across the sky forever changed the landscape of the star party.  In the years since, more and more electronics have come to the observing field.  Among them has been the advent of the laptop computer and a significant amount of controversy. 

                Some observers swear by them and their use in the field.  Some observers insist that they're a nuisance and have a disruptive influence on productive visual observing.  The modern astrophotographer has little choice but to use a laptop computer in the field for CCD imaging.  The problem is that a laptop computer can generate an enormous amount of unwanted light on the observing field if they're not properly shielded.  Some would maintain that it's not possible to properly shield a laptop computer in the field to preserve night vision.  For someone who has a deep love of  hopeless addiction to astrophotography like I do this presents a conundrum.  I also enjoy visual observing and the fellowship of observing with other members of my club.  I was quite cranky when astrophotographers were sequestered to a separate end of the airstrip at this year's Messier Marathon.  "My laptop and the way that it's shielded is less damaging to night vision than many of the red lights that I see on the observing field on any given night!!".  "Why do we have to go to the North end of the observing field?  The visual observers should have to move to the south end if it bothers them so much!!"  My own reactive hyperbole does nothing to further the discussion or find a way for all observers to co-exist peacefully.    So instead of writing my own defensive but highly entertaining rant, I've opted to stage my own informal experiment to compare the effects of various observing field light sources on night adaptation.

 Test Subjects

 My test is designed to measure the amount of light pollution generated by five different test subjects:

·         Laptop Computer - Unshielded:  Anyone not named Ray Charles knows that this will be the most obnoxious test case in the group.  The test will be done using a 16.4" Sony laptop and a SkyTools 3 generated chart of M31 with the laptop screen at full brightness.  No red film or "night vision mode" is employed for this test. 

·         Laptop Computer - Shielded:  Naturally this will be a test of the laptop as I use it in the field.  I have used a laptop for almost 10 years in the field, even for visual observing.  The test will be done using the same laptop and a SkyTools 3 generated chart of M31 with the laptop screen at minimum brightness and covered with a sheet of fitted, dark red acrylic plastic.  In addition, the "night vision" mode implemented by SkyTools 3 will be turned on.

·         Regular Star Chart/Dim Red Light:  A common red LED flashlight (Celestron Item #93588) with the dial set to "minimum" and a chart from Uranometria 2000.0.  The light itself will be suspended over the chart about 8 inches (20cm) away from the paper to approximate a typical observer's use in the field.

·         Regular Star Chart/Medium Red Light:  The same LED flashlight with the dial set to its halfway point and a chart from Uranometria 2000.0.  The purpose of the medium light test is to establish a result for a standard red light that is typical of an average observer's use.

·         Regular Star Chart/Bright Red Light:  The same red LED flashlight and Uranometria chart, this time with the brightness dial set to "maximum".

            Test Conditions

·         The Eye:  To provide an objective means of measuring the results I employed a Canon 60D DSLR camera operating at ISO 800 with an 18mm f/3.5 lens.    This is in an attempt to approximate the optical specifications of the average human eye without a negative impact on the financial specifications of this particular observer's bank account. 

·         The Measurement:  Each test subject will be photographed in a darkened room in aperture priority mode.  By using aperture priority mode, the camera will adjust the length of the exposure based on the amount of light hitting the light meter (center weighted average metering).   A shorter exposure indicates a more destructive light source.  A longer exposure indicates a more night vision friendly light source. 

·          The Observing Conditions:  Measurements will be taken from two distances.  The first will be from 30 inches (76 cm) to approximate the effect of the light source on the observer that might be using it.  The second will be from a distance of 10 feet (3 m) to approximate the effect of the light source on a nearby observer. 

            Test Results

                I conducted all of the photography in my state of the art darkened laboratory which also doubles as the storage room for my astronomy and camping gear in its spare time.  I conducted all of the tests as described before learning that there wasn't a memory card in the camera.  I put a memory card in the camera and conducted the tests again.  The table below lists the results of each test scenario.  As would be expected  an unshielded laptop computer will instantly turn you into one of the fabled three blind mice.  The main point of the experiment though was the comparison of a shielded laptop with that of a standard red LED flashlight.  Results show that a properly shielded laptop computer is no more damaging to an observers night vision than the ubiquitous red LED torch that we all use - placing 2nd overall of the five test cases.

                In the table below are the test results listed in order from the dimmest to the brightest.  The 2nd and 3rd columns show the results of the tests from a distance of 30 inches.  My patent pending and proprietary "Fried Retina" Factor measures the additional light output of each additional test when compared to the dim red light test.  For instance, an unshielded laptop is 250 times brighter than a dim red light. The 4th column shows the test results as measured from a distance of 10 feet - designed to measure the effect of the light source on nearby observers.   The magnitude column attempts to express the results in the form of star magnitudes as another basis of comparison.  For instance, if an unshielded laptop is equivalent to Vega (0.0 magnitude), then a dim red light shines with the magnitude of a 6th magnitude star.

Test Case	30 in. Exposure	FR Factor*	Magnitude	10 ft Exposure
Dim Red Light	5 seconds	1	6.0	8 seconds
Shielded Laptop	3.2 seconds	1.56	5.6	6 seconds
Medium Red Light	2 seconds	2.5	5.0	8 seconds
Bright Red Light	1/3 second	15	3.4	4 seconds
Unshielded Laptop	1/50 second	250	0.0	.6 seconds

                                *FR Factor - Fried Retina Factor

                My own subjective thoughts on the experiment:

                Dim Red Light:  The output created by the light source at this setting would have been unusable for me.  Ten years ago I would have been able to use this light with a chart, but there's no way that I could do it now with my aging peepers.  I believe that very few observers would be able to use the light at this dim setting.

                Shielded Laptop:  The laptop with all of the shielding methods in place is a about 1/2 f stop brighter than a dim red light.  This is right in line with a typical observers red flashlight that I typically see on the observing field.  I did find it interesting that at a distance of 10 feet the laptop appears to be marginally brighter than a red light at medium setting.  This is almost certainly due to the fact that it's still a backlit light source. 

                Medium Red Light:  This light setting is a touch brighter than what I see from most observers at a star party and would be too bright for me to use without damaging night vision unnecessarily.  I actually added this test after completing the other four in an effort to provide a fairer comparison of real world conditions.   

                Bright Red Light:  This light was really, really bright.  I can say that I've never seen an observer use a red light to look at a star chart at this setting.  I have used a light at this setting when crossing the observing field to keep an eye out for tripping hazards like dark colored dogs sleeping on the ground or random satellite dishes.  Don't laugh.  I've found myself face first in the ground because of both. 

Figure 1:  Comparison photo showing a 3.2 second exposure of a shielded laptop, and a medium brightness red LED flashlight.

            Conclusion

                In a case of astronomy imitating life, everything old eventually becomes new again.  The laptop computer, go-to hand controller and smartphone are simply new expressions of an old issue:  proper light control.  A properly shielded laptop is no more damaging to night vision than a properly shielded flashlight.  Even with the influx of technological advances to the observing field the age old task of maintaining proper dark adaptation is still the same, just in a different form.    Without question, there are additional precautions necessary with many laptops.  In my case I generally take four steps with my laptop on the observing field to properly shield it for myself and my fellow observers:

1.       Red Fitted Acrylic Cover:  I cover the laptop screen with a dark red fitted cover and tape it down to prevent any unfiltered light from leaking out of the screen.  These can be custom ordered from http://www.tapplastics.com/shop/product.php?pid=519 .  I also cover every indicator light on the laptop with electrical tape. 

2.       Red Light Mode:  Most charting/observing programs have a night mode that will turn everything on the screen to a red light type of color scheme in an effort to help.  I use SkyTools 3.  The red light mode in Sky Tools 3 turns everything on the screen black and all of the relevant text to a deep red.  In conjunction with a red plastic cover, the screen is very readable.

3.       Adjust Screen Brightness:  I adjust the screen brightness to be as dim as possible.  These three steps were taken to create the results in these tests on a 16.4" laptop screen.

4.       Point the screen to the North:  I try to setup so that the laptop screen itself is always pointed to the north on the observing field.  Few observers are ever trying to observe an object that is low in the north, so this setup puts my screen out of the line of fire of almost every observer on the field. 

                I don't expect that this will be the final word on the subject.  Astronomers love a lively debate and this will continue to be debated long into the future.  I simply hope that my admittedly unscientific experiment has added to the discussion in a positive manner.