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Stellarvue F50 Finder Scope
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America’s “Nano” Refractor
The Stellarvue F50 Finder Scope
(a.k.a. Sparrow Hawk)
By Preston Smith
In 2005, being “small” was good. Apple Computer launched the iPod Nano which was extremely small – and successful. The same year experienced a strong resurgence in refractor sales when Vic Maris from Stellarvue started selling the small F50 (50mm) achromatic refractor. His goal was to create the best finder scope in its class. But I and other owners of this “nano” refractor across America also use it as a guide scope, a stand-alone astronomical refractor on a camera tripod, a terrestrial spotting scope and as a casual travel scope.
When I first noticed this little $99 scope, I wondered if it would be high quality and could a small, 50mm refractor be effective for astronomical observing. I was pleasantly surprised.
PHYSICAL AND TECHNICAL CHARACTERISTICS
Amazingly light at just one pound, the F50 refractor is only 9.5 inches long and can be purchased with a white or black lacquer finish. There are blackened threads inside the fixed dew shield and the interior of the optical tube assembly is also blackened to add anti-reflection properties. The scope’s focal length is 200mm and has a fast F4 focal ratio.
The objective (front lens) consists of two lenses that are precision centered when they are edged and cemented together. They are fully multi-coated. That means both sides of the objective have multiple, very high-end coatings – not just one side. The glass is a high quality BK7/F2 glass and the edges of the lenses are also blackened to further reduce light reflection. The objective is manufactured by Stellarvue in California or at two other contracted locations. Wherever they come from, Stellarvue has a very good reputation for producing high quality objectives.
Inside the proprietary diagonal is a BAK-4, correct image, erecting prism which allows for easy sky and terrestrial orientation (images appear as they are to the naked eye, not upside down or inverted left to right). I noticed that the prism is also coated on both sides with very high-end coatings. The 90 degree diagonal threads into the back plate of scope and does not currently rotate (please read the “future plans” paragraph near the end of this review for upcoming changes). It cannot be replaced with a common 1.25 star diagonal.
The 1.25” helical focuser is one of the key points of this little refractor. It has a comfortable rubber grip and a knurled screw to tightly hold eyepieces. The refractor also comes with a fully coated, 23mm eyepiece that has exceptional eye relief (about 22mm). It has a fine cross-hair reticle that can be focused separately to maximize its visibility and sharpness. Exit pupil measurement is approximately 6.75mm. Stellarvue claims that it has nearly 7 degrees of field. The field stop inside the eyepiece is a very generous 21mm resulting in a calculated “true field of view” of 6.02 degrees. The great news is that most of your favorite 1.25” eyepieces (especially Naglers, Panoptics, Super Plossls, Plossls and Kellners) will fit into the focuser and work with the scope.
I was very impressed to learn that every one of these small refractors is star-tested by Stellarvue before being shipped. If the scope is not in alignment it is rejected and the offending part is discarded. By the way, the Sparrow Hawk comes with a one year warranty.
Several (finder scope) mounting options are available to mount the scope on a larger scope’s mounting rings, imported scope focusers, SCT telescopes and flat surfaces. The finder rings come with both stainless steel and nylon screws if you want to protect the scope’s painted finish. There are no provisions at this time to mount the scope directly to a camera tripod although many use the threaded base of the finder ring mount (see picture) or (as in my case) make their own tripod mount. Hopefully Stellarvue will offer a direct tripod mount in the future.
The first time I saw the F50 for sale on the Stellarvue website, I wanted one. I didn’t have a need for another finder scope but was amazed at the options, small size, low weight and especially the cost. It came with everything: eyepiece, diagonal and focuser! I wondered, “Could this little refractor be used as a miniature travel scope?” In one month I was traveling to Hawaii and planned on spending four nights observing at Mauna Kea with my 80mm scope. I decided that this little scope, nicknamed the “Sparrow Hawk” (by all the F50 owners on the Yahoo Group) had to come along for the trip.
My new black Sparrow Hawk arrived well packed in a cardboard box with firm, white foam protecting the scope. I cut, reshaped and glued the foam to fit into a small carrying case and then made a small mounting ring out of Corian so I could attach the scope directly to a camera tripod.
The following are observations made with the Sparrow Hawk made by myself and other owners of this fine little refractor who were kind enough to send me their information for this review. For my personal observations, I used the following eyepieces (the Stellarvue provided eyepiece is also included in the chart).
Stars and Deep Space Objects
The first target was Albireo in Cygnus. The Stellarvue eyepiece provides an extremely large field and low power. But it was so low I almost didn’t recognize the gold and blue of the double star as it crossed the field. At 11X, I could just make out the separation of the double. Next came 15X – there was more separation between the double stars but at 30X, there was plenty of separation between the two stars and color was exceptional. The stars looked like two disks – no coma and all lesser stars in the field were completely focused. The quality of the Stellarvue’s objective (double lens) was quite apparent. I then came across C27 (NGC6888) the Crescent Nebula in Cygnus. It came out very clear in the 6.7mm eyepiece. There was more detail than I would have expected – especially since I was not using any filters and live in a heavily light-polluted area (just north of Philadelphia).
Next on the list was Vega at 30X. It was a brilliant, blue-white, spherical disk. I did not notice any chromatic aberration (CA). It’s important to note that sky conditions were above average seeing and average transparency. The atmosphere can have quite an impact on CA. The surrounding field was fairly dark considering the light pollution.
The Pleiades (M45) are always a wonderful object to observe in a wide-view scope. The Sparrow Hawk proved that again. All the stars fit easily into the field of the 6.7mm eyepiece. I could see a significant amount of the smaller stars – despite the light pollution and that I was viewing it low on the horizon.
Onward to M31: the Andromeda Galaxy. I quickly found the galaxy with the stock Stellarvue eyepiece. But it sure looked small! Then I switched to the 6.7mm and was quite surprised at the amount of nebulosity I saw in this light polluted area and even detected some detail (minor shading). No, I didn’t see M32 or M110! ;-}
Here are two photos I took of the Andromeda Galaxy and Orion Nebula using a consumer digital camera through one of my eyepieces and the Sparrow Hawk. (The scope was mounted on my ETX-125).
The stock eyepiece showed respectable detail of the moon but the image was quite small. At 30x, detail was sharp and clear with no perceived problem with CA (even though seeing conditions were not the best). Here are two photos of the moon I took at 30X with a consumer digital camera through the Sparrow Hawk.
David Elossor, from Kernersville, North Carolina uses the Sparrow Hawk has a finder mounted on his Stellarvue SV102ABV scope. He tested the small refractor with a 2.5x Tele Vue Powermate and 9.7mm and 6.4mm Meade 4000 series plossls giving him approximately 51x and 78x. Here’s his excellent assessment of this configuration and lunar observing. “Considering the resolving limitations of a 50mm objective, I was impressed with the amount of detail around Copernicus. The peaks in Copernicus showed up fine, as well as some terracing detail in the interior rim. But Copernicus is about 50 miles wide. I would say that any target smaller than 5 miles wide could not be resolved. But I could easily make out the Alpine Valley in both powers, but it was much harder to see at 78x due to lack of contrast. Ptolemaeus looked good, but I could not make out nearby Muller's ears. Quite a bit of purple fringe, frizzies actually. But the Stellarvue C.A. filter (from last year's batch) removed nearly all of it and improved the contrast. I would say that you could push the scope to 100x, but don't expect the resolving power of a larger telescope.”
Even without the Powermate, he had some impressive results using three regular plossls: “Putting in the 15mm, (craters) Copernicus, Kepler, and Tycho all prominently showed their rays. Contrast is quite good for this scope, but there is a little bit of flaring. Don't know if it is the scope or the eyepieces causing this. Gassendi showed a strange bar-like feature in its interior. The 12.4mm plossl gave me more striking views of the crater rays. The entire moon was still visible in the FOV: still very sharp, [with] just a hint of flaring, but not a distraction. With the 9.7mm, the crater Gassendi now begins to show detail, the "bar" feature gave way to its true nature, three large interior mountain peaks. Using the SV minus-violet filter completely took out the false color and sharpened the image up a bit, features on the lunar limb were quite easily discernable in this power. Interior detail in the larger craters, such as Copernicus and Gassendi, was very good.
Everyone will tell you that very small refractors are not designed for planetary observing (except the moon). And they are right! Why then, does EVERYONE still turn their small scopes toward the planets to “see what they can see?” I don’t know. Maybe it’s a function of the same part of the brain that makes you want to yell out “MOO” every time you drive past cows grazing in a field (a.k.a. Bovmania)! But we do it. So, here’s the obligatory planetary report! When I looked at Mars with the stock eyepiece, it looked like a small, bright, reddish-orange dot. With the 6.7mm, I could clearly see the canals and ice cap – NOT! Truthfully, it was just a slightly larger, small bright reddish-orange dot. Next I tried the Celestron 2.3mm eyepiece. The eyepiece is 5 inches high and looked pretty funny sticking up out of the tiny, not quite ten-inch long scope! I pointed the “supercharged” 87X Sparrow Hawk towards Mars with the expectation that I would have an eyepiece full of CA and a big red smudge. I was pleasantly surprised to find that there was very little CA and it was not bothersome. Mars was a good-sized disk although its edges were not sharp. I could definitely see surface detail on the planet. A filter would have probably enhanced the sharpness and contrast considerably.
David Elosser put his 9mm U.O. Planetary ortho eyepiece into a 2.5x Powermate, placed it inside the scope’s helical focuser and pointed it at Mars. This combination gave him about 55x. At this power, he reported resolving Mars into a tiny, but sharp and distinct disc and observed some dark features on the surface. Looking at Jupiter with just a 9.7mm plossl (no Powermate) he was able to see the giant planet as a clear disc and big enough to make out two large equatorial bands
Jeff Barton was kind enough to take these two shots for this review of Mars and Venus with his Sparrow Hawk using a ToUCam video camera, 2.5X Powermate and a 1.6 Scopetronix Maxpower Barlow (total of 4X magnification) from his driveway in Garland, Texas. The Maxpower Barlow was mounted on his eyepiece which went into the Powermate. Sky conditions were as follows: seeing was a 3 of 5 with a transparency of 8 of 10.
He specifically did not use any kind of filter that would reduce CA because he was interested in seeing how much appeared in the images. The answer was “Not very darned much!” The Mars shot is composed of 600 frames and the Venus shot is 400 frames. Jeff only did very small enhancements – He didn’t even use Photoshop. He stated that this speaks very well for the optical performance of the Sparrow Hawk.
Not too long ago, I had a chance to catch a quick view of Saturn through the Sparrow Hawk at 87X. There was no CA and the planet was an excellent disk and the rings edges were as sharp as razors. Yes, the image was very tiny..... But with averted vision, I was pretty sure I could make out the Cassini division.
Based on my observations it was clear that the little Sparrow Hawk clearly proved its mettle and was ready to go to Hawaii and some of the darkest skies in the world!
Shortly after my arrival on Oahu, I took the Sparrow Hawk up to the 760 foot summit of Diamond Head. It was very easy to carry this compact, low weight scope and a small lightweight tripod up the side of the crater – even though it was a considerable climb. I wanted to test the terrestrial capability of this little gem and this was the place. As they say, a picture is worth a thousand words.
Note the "normal views" on the left of an old ship being towed and a lighthouse with the 30X views through the Sparrow Hawk next to them. These shots were taken with a consumer camera (hand-held) through the Meade UWA 6.7mm eyepiece.
There were a lot of other photos, but these two terrestrial “targets” clearly show why the Sparrow Hawk makes a great little spotting scope.
OBSERVING: MAUNA KEA, HAWAII
The trip to Hawaii gives added credence as to why it’s great to have a small “travel scope” and camera tripod that can be placed in your luggage. Often, our travels take us to geographic locations that have great observing conditions. Yet it’s not always possible or practical to pack a bigger scope and especially a long, heavy tripod on a business trip or family vacation. I have decided to keep my astronomical observations from Mauna Kea separate from the other observations as this demonstrates what the scope’s performance is under “perfect” sky conditions.
The Visitor Center at Mauna Kea is 9,000 feet above sea level on the tallest volcano on the island of Hawaii (the top is 13,000 with observatories). The sky took my breath away. The Milky Way looked like an illuminated, translucent cloud traversing the heavens. Cygnus was backlit by a woven blanket created by thousands of stars. Major constellations jumped out at you. Some smaller constellations were difficult to initially locate due to the vast number of “bright” 3rd and 4th magnitude stars.
My first observations were in Sagittarius:
I was able to get the Eagle Nebula (M16), Omega Nebula (M17) and M18 (open cluster at 8th magnitude) barely into the same field at 30X. Plenty of nebulous clouds were visible on M16 and M17, showing nice clean edges. Hey, with averted vision you could clearly make out the eagle’s talons in M16.... just kidding! The Lagoon Nebula (M8), the Trifid Nebula (M20) and M31 (open cluster) are all within 1.4 degrees of each other and easily fit into the scope’s true field at 30X. I was able to see some resolving and a significant amount of shading and edges in the nebulous clouds, especially on M20. Also shot up to M55, a 7th magnitude globular cluster.
Going right to Scorpius, Ptolemy’s Cluster (M7) also fit easily into the scope’s field. There was a lot of clarity and depth because of the outstanding conditions on Mauna Kea. I also noticed a lot of light coming from the very faint stars within the cluster. The Butterfly Cluster (M6) also showed great depth and nebulosity around its stars. I also bagged C78, NGC6541 in Corona Australis (just below the tail of Scorpius).
I pointed the Sparrow Hawk left to Aquarius and located M2, a 7.5 magnitude globular cluster. Then off to the Andromeda Galaxy (M31). What a difference from seeing it in Philadelphia! I was amazed how much of the nebulous cloud I was able to see with the very dark Mauna Kea sky coupled with this fast (F4) little scope. It filled my entire field. Finally, I pointed the scope down and to the right about 15 degrees to capture the Triangulum Galaxy (M33).
While I was at Mauna Kea, many visitors came over and asked to look through the Sparrow Hawk and my 80mm travel scope. As to be expected, everyone thought the view through my 80mm was superior. That’s a no-brainer. Physics proves that. But everyone was very surprised at what they were seeing through a scope as small as the Sparrow Hawk. I was quite impressed by this little “Nano” Refractor’s performance. Especially after I traveled back down to sea level in Kona, Hawaii and noticed Orion coming up. I grabbed the Sparrow Hawk and headed for the hotel’s parking lot. After enjoying a quick view of M42 and M43, I moved up the left side of the belt to look for M78. I found it! That’s quite an amazing feat considering it’s a diffuse nebula (reflected light) and only 8th magnitude. Now, I have to admit it was a very, faint smudge and nothing more. But it’s another example of how much spontaneous fun this little scope can provide!
The Sparrow Hawk is an outstanding performer, especially at 30X-50X. The user manual states to use wide field, premium eyepieces for the sharpest field possible and that’s good advice. But even inexpensive eyepieces work well with this little scope. David Elosser’s and my tests with the 6.4, 9.7, 12 and 15mm Meade super plossls still had great visual results – albeit with a somewhat smaller field. The Sparrow Hawk works successfully with the 2.5x Powermate and may work with an additional Barlow inside the Powermate. But no one (so far) has had success focusing the scope just using a regular Barlow.
The helical focuser is extremely smooth, has just the right amount of resistance and comes to focus quickly. On cold nights it can get somewhat stiff but still functions well. The correcting prism is great to have. It helps with sky orientation and gives the scope terrestrial capability as well. The focuser holds the eyepiece firmly in place. The stock eyepiece definitely has a wide field and truly great eye-relief. I had no problem using the eyepiece with my glasses on. The cross hairs were always visible in the field, but more difficult to see when observing dark skies. David Elosser graciously alerted all Sparrow Hawk owners from the Stellarvue Yahoo Group to be careful not to touch the exposed crosshairs inside the eyepiece. They are located about 18 millimeters inside the bottom of the eyepiece. Normal handling should not be a problem but, when feeling for the eyepiece in the dark, you should take extra care.
Even though the F50 has a dew shield, it may fog up on a night with high moisture - especially when it is pointed straight up toward the zenith for a long period of time. I would recommend tethering the lens cover to the scope mount and keeping the scope covered when not in use.
This scope is a little light bucket. With a focal ratio of F4, and the optics coatings and anti-reflection properties to maximize transmission of incoming light, it definitely catches a lot of light for a 50mm lens. This makes it a great candidate for a tiny, rich field scope and reduces the time needed for astrophotography. But please note that it can still catch light from any nearby artificial light source, so plan your observing site accordingly.
The Sparrow Hawk was designed to be a finder scope. But since I do not use it in that capacity, I thought it would be wise to get some input from users who do use it in that capacity
David Person has mounted the Sparrow Hawk on his 70mm refractor (please see photo). Here are his comments. ”I observe from suburban Southern California and having this finder has increased my ability to successfully starhop to locate objects (mostly double stars). The correct image view makes it so easy to compare the eyepiece view to the star field in my Sky Atlas 2000. No more mental gymnastics trying to translate the mirror image in my telescope eyepiece to the star map. Some may laugh at a 50mm finder on a 70mm scope, but starhopping with a red dot finder from moderately light polluted skies just doesn't work for me.
Pat Agnew from Fort Myers, Florida also uses the Sparrow Hawk as a finder on his Orion XT10: Here’s his thoughts on the F50: “The eyepiece is probably worth the price of the finder, and has great eye relief. The focuser is smooth, and it comes to focus with a Nagler 13mm T6. One head's up: the outside diameter of the F50 is too large to fit the standard Orion single stalk finder ring, so plan on getting one of the [Stellarvue] ring systems.”
Anything that is “Nano” sized will have limitations. But the Sparrow Hawk’s unique blend of quality and economy offers a lot of possibilities and many users (like myself) use it for different applications
Ken from Florida: “I use it as a spotting scope to look at birds or occasionally as a stand-alone astronomical telescope. I carry it in my truck with a camera tripod (see photo) when I'm on the road…”
If you have children (or grandchildren) then be prepared to share the Sparrow Hawk! Eric, an F50 owner who lives in both Nashua, New Hampshire and Thailand shares this report: “My 2 year old likes to grab [the scope] out of the box and run off to take a peek through it when ever he can. So I set it up on a cheap little tripod so he could act like his daddy and have his own scope.”
So how do I use it? Mostly as a very small travel scope when I’m on a business trip. I have a great 80mm travel scope but if I want to travel very light, the Sparrow Hawk and a small camera tripod will fit into my carry-on bag along with the rest of my clothes (please note, I said “carry-on” bag). While on the road, I take it outside for an evening observation on the hotel’s property or to a local high school athletic field. My first two scopes were GOTOs so I love using this “Nano” Refractor to learn the exact locations of stars, planets and deep space objects.
I also like to use it periodically for astrophotography as I enjoy the challenge of pushing this 50mm scope for all its worth. For timed exposures, I mount the Sparrow Hawk on my ETX-125 using about $5.00 of hardware and two shaped pieces of wood. It may not be aesthetically pleasing, but works quite well.
My wife Paula really likes the Sparrow Hawk too. It’s small, light, easy to use, and always ready to go out the door. She knows the sky better than I do and is always looking for her favorite stars, deep space objects and the planets.
We also use it as a terrestrial spotting scope. On our way to Hawaii, Paula took some time with the scope to watch the birds and a sailboat glide by at Marina Del Ray near Los Angeles.
OTHER SCOPES ON THE MARKET:
To be fair, there are several other 50mm finder scopes on the market that I have not had the opportunity to test but should mention. Apogee makes an 8X50 erecting finder scope that looks similar to the Stellarvue F50 but does not have the helical focuser (I do not know anything about the quality of the optics or the diagonal). The eyepiece can be focused but you cannot use other eyepieces with the scope. Astro-Physics and William Optics also make fine 50mm erecting finder scopes and have an illuminated reticle. Lumicon is another name to mention. I am sure that the optics from these three manufactures are excellent but again you cannot use other eyepieces with their scopes. The only 50mm scope I have been able to find that mirrors the Sparrow Hawk’s configuration is the Mini Borg 50mm scope. It’s a great scope but to purchase the scope and optional equipment required to match the Sparrow Hawk’s capabilities will cost you about $400!
Stellarvue will be helping the little Sparrow Hawk soar to even higher levels. They will be offering a new version with a rotating back and possibly an illuminated eyepiece very early in 2006. And the little raptor will be getting a bigger brother. Stellarvue will have an 80mm finder scope with even better specifications (such as an air spaced objective) coming out about the same time!
Here’s my evaluation of the Sparrow Hawk’s features and capabilities:
1. Very high-quality achromatic doublet
2. Very high-quality 90 degree correcting prism
3. Smooth, helical focuser
4. Comes with a matched eyepiece that has a focusing reticle
5. The great price – only $99!
6. Many different finder mount combinations are offered - even for SCT and Chinese manufactured scopes
7. Ability to take (most) 1.25 eyepieces and Tele Vue Powermates
1. The scope does not come with a tripod mount that would allow the scope to be directly attached to a camera tripod (nearly every Sparrow Hawk owner I communicated with would like this capability).
2. Modify the eyepiece reticle to be seen more clearly with dark skies (noted by some of the owners). The future illuminated reticle should resolve this issue on 2006 scopes
3. Barlows do not work on the scope (They may work when a Powermate is first inserted into the scope).
4. Most zoom eyepieces do not work with the scope. Some work but not across the entire zoom range.
5. The front cover has a very loose fit and could fall off when being carried or stored (would be wise to tether it to the scope’s mount).
1. Adding baffles inside the OTA might further improve light reduction capabilities.
2. It would be great if Stellarvue would offer a zoom eyepiece that would work in the Sparrow Hawk
This is a fun, high quality little scope worthy of the Stellarvue name. It has outstanding value as a finder scope with plenty of mounting options to complement a larger scope. Yet, this little refractor is so much more than just a finder scope. It is unique: it has a helical focuser, erecting prism and gives you the ability to use your own eyepieces. The sub $100 Sparrow Hawk can be used as a guide scope, a rich field scope, travel scope and terrestrial spotting scope. Most important, it has changed many experienced astronomers’ opinions on what can be achieved with a 50mm “Nano” refractor!
I would like to thank Vic Maris, President of Stellarvue for taking the time to answer all of my technical questions about the Sparrow Hawk. Also Darren Hennig for his tremendous help reviewing my draft (right before Christmas) and the valuable insight he provided. And to all the other Sparrow Hawk owners who are having as much fun as I am with this little refractor and have contributed to this review.
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