By: Vlad Fedosov
4” refractors… I just seem to keep on coming back to them over and over. I have had many 4” class refractors over the years including the: Explore Scientific AR102, Celestron GT102, William Optics 102GT, TeleVue NP101, Astro-Tech 102ED(the ones I can remember off the top of my head, there may be more). At the time owning only a 3″ and 5″ APO when a Stellarvue SV4 4″ triplet LOMO “Super APO” popped up for sale locally I was intrigued. I did a lot of research on the scope and found that this is a fairly rare instrument. Word is that there were less than 100 of these produced because Stellarvue had such a hard time getting the LOMO lenses from Russia in any kind of timely manner. Even more interestingly when I was doing research on these LOMO optics the opinions on them ranged from them being just a bit above average to surpassing the likes of Takahashi and even being equals to Astro Physics(Who would dare to say that??? Is this not punishable by death??? LOL). To add to the intrigue, since I’m Russian myself, I really wanted to see what the best that a Russian optics manufacturer has to offer. I took the 2-hour drive to go and see the condition of the scope, and see if I could make a deal. As soon as I saw it in person I knew it had to be mine! It was in almost perfect shape with nice clean optics that had just a bit of dust on them. As they say: and the rest is history. The SV4 was coming home with me! The SV4 uses a triplet lens design utilizing OK-4 glass that operates at f/6.4 / 650mm. The scope is mated with a beautiful 2″ Feather Touch focuser.
Having set up the SV4 I was very impressed with the build quality of the entire package. The scope was heavy feeling for a 4”. The triplet lens is the culprit here as the scope is very nose heavy especially if you are using it with a 1.25” diagonal and eyepieces. To my surprise the first night I brought the scope home the sky was clear enough for me to grab a look at Vega and a few other bright stars to make sure that it was in collimation and do an initial assessment of the color correction. There was good news! The scope was indeed in perfect collimation and I could not see ANY secondary color with the highest power eyepiece combo I had which was a 6mm Ortho with a 2.25x barlow.
A few days later we were blessed with a week of clear weather and I decided that since I was going to enjoy some wonderful time with my new toy I might as well bring some of its frinds out to join the fun! Out came my Meade 127ED and Astro-tech AT80LE refractors. I have never owned a 3”, 4”, and 5” APO’s at the same time so I was really curious to find out how they would stack up! I did this comparison over a few nights during the early fall in my mag 4 backyard with the moon out.
My first order of business was to see how the SV4 does on the planets. Planetary observing is one of the main reasons for me to own such an instrument. It stays setup on a light mount by the back door, and I can carry it out and be observing within minutes. Saturn was positioned well in the early evening so it made an easy first target. The ringed planet was well framed and would take only about 150x of magnification(used Orthos for all comparisons) on the first night of observing. The seeing really quite bad. Comparing all three instruments I was shocked at how close the view of Saturn looked between the three scopes. The biggest thing that I got out of comparing the three scopes the first night out is that the 4” image was noticeably brighter then what the 3” produces. Likewise, the 5” was brighter than the 4”. I played around with the magnifications and concluded that the 3” scope was able to get up to 150x while maintaining an image that was bright enough, with the 4” at 200x, and the 5” at 250x.
The second night of observing a few days later was blessed with much better seeing. In fact, I would rate it as “Good” for the Northwest(I’m sure you guys in Florida and other areas with good seeing would consider it mediocre at best). Starting with comparing the 3” and 4” I was again surprised at how similar the view was at both 150x and 200x on Saturn. The 4” SV4 did produce a brighter image and perhaps did show the Cassini division a bit better but no additional detail where revealed. Moving on to comparing the view of the 4” and 5” I was greeted with a substantially better definition of the Cassini division as well as a better definition in the cloud bands in the 5″. I was actually kind of impressed by how much better these features stood out in the 5”. I will say that the 5″ displayed the same features as noted in the two smaller scopes just with a bit more resolution. No additional details where visible.
Moving on to Mars which was now as high in the sky as it was going to get that evening. I compared the view of all three scopes and to my surprise, the SV4 seemed to dominate here. I was seeing detail in the edge of the albedo features that were just not there in the other two scopes. Mars was still very bright so I did compare the view both with no filters and with a variable neutral density filter trying to match the brightness so that the 4” and 5” views looked the same. I still felt like the SV4 was ahead of the 5” on Mars. The only conclusion that I can come up with is that the contrast must be higher with the SV4 and thus it produced a better overall image of Mars. This is not as important on Saturn as it is a very high contrast object allowing the 127ED to pull ahead there. I will also make a note on how the color correction compares between the 3 scopes. Before doing that I will also note that my eyes are VERY sensitive to blue so I believe I see more secondary color then most people will. The AT80LE(FPL-53 doublet) displays an almost undiscernable mount of color on Saturn and a minimal amount on Mars at 150x. The 127ED(FPL-51 equivalent doublet) displays just a hair of color on Saturn and a noticeable but unobtrusive amount on Mars. The SV4 shows ZERO color on ether planet upto 250x(I don’t have any higher power eyepiece/barlow combo). Very impressive, as this is the first refractor that I have owned that I could not detect any false color with!
Double star performance of all three scopes is excellent. In my neck of the woods, my seeing will rarely let even the 80mm hit its resolution limit so I would be happy to have any of these refractors out for a good night of double star work. I do like the view in the SV4 a hair better at high power compared to the other two scopes(especially the 127ED) as it is secondary color free up to any power that I have thrown at it. The 127ED does show just a hair of color at high power on brighter doubles that is really evident when you are comparing it side by side to the SV4. Before comparing them directly I felt that the 127ED was essentially color free on everything but the brightest stars. It’s not that this hair of secondary color degrades the image in any way, or that it impacts the scopes ability to split the stars, it’s just that the superior color correction of the LOMO lens produces a more pleasing image to the eye.
The difference in deep sky performance is about what you would expect as you go up in aperture. The 4” produces a noticeably brighter image than the 3” and likewise, the 5” outperforms the 4”. Since I was doing this comparison from my light polluted backyard with the moon out it was difficult to judge if the superior triplet in the SV4 produced better contrast on deep sky objects. I suspect that under a dark sky it would. If you are concerned with deep sky performance I will say that an 8” SCT weights about the same as these refractors and is more compact then all of them besides the 80mm. On deep sky observing the 8” SCT blows these scopes out of the water, the image is much brighter and really makes DSO’s start to look interesting. There are a few exceptions to this where a refractor will still be better for deep sky. I feel that a refractor is better for open clusters just because of how beautiful stars are rendered in the scope. They are perfect little orbs, not blobs that an SCT will produce in all but absolutely perfect conditions. The other deep sky object that short focal length refractors reign supreme is in extended objects such as framing the entire Vail nebula, North American nebula, or the Andromeda galaxy. For this, I feel that a 4” refractor with a focal length of less then 700mm is ideal. An 80mm scope is also a very capable tool for this kind of observing and will give you an even wider perspective than the 4”. Do keep in mind that you really need to be under a dark sky to do most of this kind of observing. I do have some of my most memorable nights of observing with a TV-85 that I owned at the time discovering objects such as the North American nebula. The views you get of these large extended objects from a small refractor really rival anything that I have seen even in the largest of dobs!
I thought that I have previously owned true APO refractors. Even though they where excellent scopes in their own right I now know what a true APO really is. The SV4 is a true APO! I have never owned an Astro Physics or TEC APO put its hard to imagine how much better a 4″ refractor can get then the SV4. I truly believe that a premium 4″ APO is about the most versatile telescope that one can own, and if I was forced to pick only one of my telescopes to keep for life the SV4 would likely be it!