Equipment Reviews - Page 1

1) Astro-Physics 130mm f/8.35 refractor

2) Eyepieces for the Planets

3) Star Bound Observing Chair

4) Roll-A-Table

5) Astro-Physics StarBright, Tele-Vue, and Kenneth Novak 2" star diagonals

6) Sirius Optics Planetary Contrast (PC1) Filter

Click here to see page 2 of Equipment Reviews.

1) Astro-Physics 5.1" (130mm) f/8.35 EDT

The Astro-Physics 130mm f/8.35 on its homemade Dobsonian-style mount


For a number of years Astro-Physics (AP) offered a 5.1" f/8 refractor that utilized the EDT glass. With the introduction of shorter focal ratio refractors that used the EDF glass, such as the 5.1" f/6, demand for the longer focal ratio version of the telescope declined. Eventually the 5.1" f/8 was discontinued.

In 1998, due to requests from a number of observers, a longer focal ratio of the 5.1" was offered again. This time it used the same EDF glass as the 5.1" f/6, but is still referred to as an EDT to avoid confusion. The focal ratio is f/8.35. Essentially the 5.1" f/8.35 is a scaled down design version of the 6.1" f/7 EDF. The cost of the 130mm f/6 and f/8.35 version was the same.

At the time I was looking for a portable high-resolution telescope and debated ordering either the f/6 or f/8.35 version. While I was tempted to go with the f/6 version, I don't do much deep-sky astrophotography, and with low power 2" eyepieces I felt I could still get a relatively wide field of view in the f/8.35 version. For example, a Meade 56mm Super Plossl the field of view is over 2-1/2 degrees, while with the 35mm Panoptic it is over 2 degrees.

Plus, the tube assembly is only a little over 10" longer in the f/8.35 version then the f/6 version, and I did not feel this would impact the portability of the telescope for me. Also, a friend of mine who happens to be an optical designer mentioned that he felt that the 5.1" f/8.35 would be the finest apochromatic refractor production model ever produced by AP due to the glass used and the relatively long focal ratio. For all of these reasons I decided to go with the f/8.35 version.


The telescope arrived in a foam-fitted carrying case, which protects the telescope from damage during shipping, as well as when not in use. As I took the optical tube assembly (OTA) out of the carrying case I was impressed by the fine quality of the workmanship. Everything on it has a nice solid feel to it. The OTA comes standard with a 2.7" focuser and includes a 1-1/4" adapter and 2.5" focuser extension for straight-through viewing. The 1-1/4" adapter is threaded for 48mm filters. The focuser comes with pre-drilled hole on the left and right side to mount accessories such as quick release brackets for finder scopes. The mounting rings come pre-drilled as well for mounting cameras, guidescopes, or other accessories.

One of the nice things about the focuser is the recessed brass locking ring for each thumbscrew location. When the thumbscrew is tightened the brass locking ring clamps onto the star diagonal, binocular viewer, or camera adapter that the user inserts, which helps hold them securely in place without scratching their surfaces. Also, there is a thumbscrew on one side of the focuser so that the focus can be locked for long duration astro-imaging. I racked the focuser in and out a few times and its motion was smooth and precise.

At the front of the OTA is the push-pull lens cell. If the optics should get out of alignment they can be re-collimated using the setscrews on the front of the lens cell. AP provides documentation on how to do this, as well as care for the telescope.

The OTA with dew cap weighs 16 lbs. From the front of the lens cell to the end of the focuser the optical tube assembly is 39" long. As with other AP refractors, the dew cap is stored in reversed position, and an aluminum dust cover protects the lens when not in use. Also, the OTA and dew cap has a pebble finish, as do the new tube rings. Back in the mid-1980's AP had offered their scopes with pebble finishes, but since then the tube assemblies have had a smooth finish.

When I looked inside the tube I noted there were a number of knife-edge baffles. Instead of the more traditional few baffles in the OTA, wider ones near the front, and narrower ones further back, there are a series of the same sized baffles running the length of the tube. There are a series of 6, followed by one that looks like a small plateau, 7 baffles, another plateau, and another 7 baffles. That makes a total of 22 baffles, and in the focuser I counted another 12 baffles, making a total of 34 baffles (32 if you leave out the two plateau shaped baffles).

Effective baffling is very important as it eliminates stray light as much as possible for maximum contrast at the eyepiece. Roland Christen, who founded AP, has mentioned that this is particularly important when observing deep-sky objects.

Optical Performance

Moon and Planets

First light for the telescope I observed Mars, Venus, and the Moon. Mars, at a diameter of 15.46", showed some interesting detail. Syrtis Major was very prominent, and its northern portion appeared darker then its southern portion. The North Polar Cap was visible, as was Hellas.

Click to see a drawing of Mars June 23rd, 2001 made with the 5.1".

Venus appeared well defined and dusky markings were visible near the terminator.

A thin crescent moon showed good detail in Mare Crisium, including several wrinkle ridges, as well fine detail within nearby craters. The earthlit portion of the moon was visible, including some of the Mare. Light scatter seems well controlled in the telescope as when I have observed the Moon at or near its full phase the sky directly adjacent to the limb appears black.

As Jupiter and Saturn approached opposition I was impressed by the amount of detail visible. Jupiter's moons are all resolved as disks, and it is possible to determine which one is one based on its size and the subtle color differences between them. For example, Io appears white/light yellow/light orange in color, Callisto light gray in color, Europa white, and Ganymede light-medium yellow.

On Jupiter the itself South Polar Region (SPR) appears tan brown in color, has a "cap" to it, and is slightly darker then the rest of the SPR. A dark condensation or spot was noted in South Tropical Zone (STZ), and in South Polar Region. The Great Red Spot (GRS) appears light red or light pink, with the South Equatorial Belt (SEB) following Great Red Spot/Red Spot Hollow (GRS/RSH) gray.

Ovals BE and FA visible south of the GRS/RSH. The Equatorial Zone appears dusky, with the Equatorial Belt visible. The North Equatorial Belt (NEB) appears brown, with dark columns and white plumes visible along NEB south. A rift is visible in NEB center (NEBc). The North Polar Region appears aquamarine in color.

Click to see a drawing of Jupiter made on October 13, 1999 and on January 23rd, 2002 with the 5.1".

On Saturn the South Polar Region appears green gray, and has a light green "cap" to it. The South Equatorial Belt appears light brown, and the Equatorial Zone (EZ) appears light yellow, with the Equatorial Belt (EB) visible within it. The North Polar Region appears gray-brown.

On one night with good seeing I noted shading on the left or preceding ansa of the B-Ring, which extended from near the inner portion of the B-Ring out to almost the Cassini Division, and may have been unresolved patches of spokes. Spokes or shading visible on the following ansa also. The C or Crepe Ring is prominent. Cassini Division was noted all the way around the rings as well as in front of the globe, as was another division further out in the A-Ring which may have been the Encke Minima.

Click to see a drawing of Saturn made with the 5.1" on August 24th, 1999, also on October 5th, 2001, and on January 23rd, 2002.

The telescope takes magnification well. When observing the planets with very good seeing I have used magnifications of over 60x per inch of aperture (308x) and the image is still sharp with high contrast with no image degradation. I have the impression that with excellent seeing conditions I could use higher magnification with no image degradation.


When Comet Ikeya-Zhang graced our skies in 2002 I observed it with the 5.1". With a magnification of 115x, the coma appeared very large and blue-green in color, and surrounded a relatively bright parabolic hood and star-like pseudonucleus. The gas and dust tail were both visible behind the coma, the more prominent gas tail on the left, while the fainter dust tail on the right. The gas tail appeared feathered along its left side, multi-threaded in the middle, and curved on its right side. Tail length was between 2.5 - 3 degrees.

The dust tail appeared as fine streamers behind the coma on the right side. It reminded me of some of the fainter wisp-like streamers I have seen when observing the Orion Nebula. Also, behind the coma and extending over towards the gas tail from approximately the 5:30 to 10:30 positions there appeared to be a faint wedge of lighter material.

Click to see a drawing made of Comet Ikeya-Zhang made on April 11th, 2002, and on April 21st, 2002 made with the 5.1".


Star images appear sharp with high contrast, and snap into focus. At medium magnification Epsilon Lyrae, the Double Double in Lyra, is resolved into its four components. At high magnification bright stars such as Sirius and Vega do not show any false color. I performed a basic star test at 50x per inch of aperture with a green filter and the star images inside and outside of focus appeared to be the same, and no signs of astigmatism were noted.


The telescope performs very well on deep-sky objects. At a star party I was observing with some friends and we were impressed by the level of detail visible. The limiting magnitude that night was approximately 6.0, and no filters were used.

M8, the Lagoon Nebula, showed both the star cluster and nebula very well, in particular the detail opening in the Lagoon which was well resolved and defined.

M17, the Swan or Omega Nebula, showed its characteristic hooked shape, and portions of the nebula appeared mottled. The bottom portion of the nebula appeared serrated.

In M20, the Trifid Nebula, the double central star was prominent, and both portions of the northern and southern nebula were visible, including the rift in the southern portion.

In M31, the Andromeda Galaxy, clearly showed one dust lane, with a second one visible but not as prominent. Also, there was some detail visible around the nucleus of the galaxy, and the center of the galaxy had a star-like appearance to it. NGC 206, a starcloud in one of the arms of M31, was visible as well. Both satellite galaxies, M32, and M110, were visible, with the core of M110 appearing brighter then the outer portions of the galaxy.

I have observed deep-sky objects with the telescope under skies with a limiting magnitude between 5.0 to 5.5, including the North American Nebula, NGC 7000, showed fine detail when using a 56mm Meade Super Plossl, and 35mm and 27mm Panoptics with an O-III filter.

M13, at low power (19x) and without a filter, I could begin to resolve some of the stars. At magnifications between 68x and 121x, more stars were resolved and the central portion of the cluster appeared circular in shape, more dense then the outer portion of the cluster which had a very irregular shape to it. Star chains were noted extending out from the cluster.

M92 appeared noticeably smaller and less dense then M13, but still had a relatively bright core. The cluster had an elongated look to it.

M27, the Dumbbell Nebula, had an hourglass shape to it, with a distinct greenish-bluish color. The "football" extensions on each side were easier to see when using an O-III filter.

M42, the Orion Nebula, without a filter shows a wealth of fine detail, including the cirrus appearance to the nebula, and a bluish-greenish color. With steady seeing conditions six stars are visible in the Trapezium.

M57, the Ring Nebula, was well resolved and the area within the ring appeared lighter then out side of the ring.

M101, at 68x, was relatively bright and showed some variation in tone around its outer edges.

Click to see a drawing made of The Crab Nebula (NGC 1952) and Saturn made in December 2002 made with the 5.1".


The AP 130mm f/8.35 makes a fine portable high-resolution telescope that performs surprisingly well for a telescope of its aperture on the planets, Moon, comets, stars, and deep-sky objects.

This telescope was sold in 2004 and was replaced with a TMB 130mm f/9.25.

2) Review of Eyepieces for the Planets

Zeiss Abbe Orthoscopics, Pentax SMC Orthoscopics, TeleVue Plossls, and University Optics Orthoscopics compared

I first began observing through a telescope back in the early 1970's, and since then have used a variety of eyepeices to see which ones work best for observing the planets. Here is a review of some of the eyepeices I have tried.

One comparison was between the Zeiss Abbe Orthoscopics (1.25"), Pentax SMC Orthoscopics (0.965"), TeleVue (TV) Plossls, and University Optics (UO) Orthoscopics. I did not have duplicate eyepieces of the same focal length, so tried to look for overall general performance characteristics.

My tests were conducted during several observing sessions using my Astro-Physics (AP) 180mm f/9 EDT refractor using a MaxBright diagonal on a variety of objects including the moon, Jupiter and Saturn, double stars, bright stars, and deep-sky objects. The seeing and transparency conditions were about the same during these observing sessions.

The eyepieces I used for this comparison included an 11mm TV (147x), 10mm Zeiss (162x), 9mm UO (180x), 8mm TV (203x), 7mm Pentax (231x), and 6mm Zeiss (270x). Since there was a relatively wide range of magnifications I broke the eyepiece comparisons into six groups with some overlap: the 11mm TV with the 10mm Zeiss; the 10mm Zeiss with the 9mm UO; the 9mm UO with the 8mm TV; 8mm TV and 7mm Pentax; and the 7mm Pentax, and 6mm Zeiss.

I will start with the UO Orthoscopics (Orthos) and TV Plossls first. In general, I found the performance of these eyepieces to be fairly close. The main differences I noted was that the light transmission in the UO Ortho seemed a bit better then in the TV Plossl. For example, I was able to see fainter stars in the Double Cluster in the UO then in the TV. Also, there appeared to be a tad less scattered light around Jupiter in the UO then in the TV. The contrast on the moon appeared to be the same in both eyepieces. Whitish colored areas on Saturn and in its rings appeared a bit more off-white in the TV then in the UO.

When comparing the Zeiss to either the UO or TV, the Zeiss had noticeably better light transmission, contrast, less light scatter around bright objects, and better overall sharpness. The other differences I noted between the Zeiss and Pentax vs. the UO and TV was that the planetary colors seem more accurate. This may be somewhat subjective on my part however.

I felt that the Pentax and Zeiss were very close to each other in overall performance. It is my understanding that the Zeiss eyepieces were designed to work well with their APQ refractors, which are f/8. So if you are using them with a telescope with a focal ratio of f/8 or longer the stars are sharp right to the edge of the field of view.

I feel the UO and TV offer a lot of performance for the money however, so would not hesitate to recommend them.

Clave Plossls compared with TeleVue Plossls, Brandon Orthoscopics, and Aus Jena Orthoscopics

I first began using TV Plossls with my C8 back in the early 1980's after they were introduced and Richard Berry said that they were the sharpest he ever used. They replaced the Meade Research Grade Orthoscopics I had been using for a few years. Prior to this, I had used the Huygenian, Ramsden, Achromatic Ramsden, and Kellner eyepieces that had come with the small achromatic refractors and 4-1/4" and 6" reflectors that I purchased.

Then in the mid-1980's a friend of mine recommended that I try Clave Plossls. When I compared the 17mm TV with the 16mm Clave using a 4" f/6 AP and 6" f/9 AP refractors the Clave seemed to have better sharpness and contrast than the TV, and the TV showed more scattered than the Clave. For example, when observing Sirius the TV showed more scattered light around it, so it made it harder to see fainter nearby stars than in the Clave.

The same was true when observing Mars, where I could see more background stars in the Clave than the TV. Also, the Clave showed higher contrast and sharper details on the moon, planets, stars, and deep-sky objects than the TV. The TV had a slightly wider field of view, reported to be 50 degrees while the Clave were reported to be 48 degrees, and the TV had slightly better edge correction than the Clave.

I did some additional comparisons between an 8mm Clave Plossl and 8mm TV Plossl using the 180mm AP. I noted that the Clave was manufactured back in the 1970's, while the TV was of recent manufacture (late 1990's). I mention this because there is a general impression that the 1-1/4" Clave's manufactured in the 1970's and 1980's were of higher quality then those manufactured after Mr. Clave sold the business in the early 1990's.

The objects I compared the eyepieces on included the moon, Jupiter, and deep-sky objects. Overall, although similar in performance, I would give the edge to the TV, as it had less scatter, darker sky background, higher contrast, and better light transmission then the Clave. Note that this is different than when I compared Clave Plossls manufactured in the 1980s with TV Plossls manufactured in the 1980's.

From the mid-1980's until the mid-1990's the Clave were my standard eyepiece of choice for the planets, moon, and deep-sky objects. I purchased a 6mm, 8mm, 10mm, 12mm, 16mm, and for low power use a 2" 35mm and 2" 40mm. It was during this time that I purchased and tested them with other eyepieces, including Brandon Orthoscopics, Aus Jena Orthoscopics.

I compared a 24mm, 16mm, and 12mm Brandon's with a 25mm, 16mm, and 12mm Clave on the Moon, planets, deep-sky objects and stars using the a 4" f/6 AP and 6" f/9 AP refractors. The Clave had a slightly larger field of view, 48 degrees, than the Brandon's which was 45 degrees. However the Brandon's came standard with eyecups which made it easy to "tuck" my eye into to see the entire field of view. Overall, the Brandon's showed slightly higher contrast than the Clave, while the Clave had slightly higher image brightness.

In 1989 I compared the 16mm, 12mm, and 10mm Clave with the 16mm, 12.5mm, and 10mm Aus Jena Abbe Orthoscopic eyepieces which had 0.965" barrels. Note that the Aus Jena Abbe Orthoscopic 0.965" eyepieces were manufactured in the East Germany (before the Berlin wall came down and East and West Germany were reunited) and were imported into the United States. They are not the same as the Zeiss Abbe Orthoscopic 1-1/4" eyepieces that were imported from Germany in the 1990's into the United States by Astro-Physics.

When observing the Clave and Aus Jena eyepieces on the Saturn, Vega, the moon, and deep-sky objects, they eyepieces were similar in performance. The Clave had slightly better image brightness, while the Aus Jena had slightly less light scatter. The Clave had a larger field of view at 48 degrees, while the Aus Jena had a 42 degree field of view and had better edge correction.

Clave Plossls compared with TeleVue 9mm Nagler

In 1986 I compared the Clave Plossls with a TV Nagler 9mm (the original Nagler 9mm Type 1) using the 4" f/6 AP and 6" f/9 AP refractors. The 9mm Nagler had an impressive 82 degree field of view, and had better edge correction than the Clave Plossls. So it was possible to view the entire disk of the moon, and large portions of deep-sky objects like M42 and M31. However, the Clave had better light transmission and contrast which made it easier to see fine low contrast details on the planets and in deep-sky objects. I have tried some of the newer Naglers, including the 12mm Type 4 and 16mm Type 5, and these show much better light transmission and contrast than the original Naglers, and I often use them when observing and making sketches of deep-sky objects. For the planets I prefer to use Orthoscopic and Plossl eyepieces.

Clave Plossls compared with Zeiss Abbe Orthoscopics and Pentax SMC Orthoscopics

In 1996 a friend of mine recommended that I try Zeiss Abbe Orthoscopics and Pentax SMC Orthoscopics, and so I compared them with my Clave Plossls using the AP 180mm. On the planets, moon, deep-sky objects, and stars, Zeiss Abbe Orthoscopics and Pentax SMC Orthoscopics showed better light transmission, contrast, overall sharpness, less scatter, and better edge correction than the Clave Plossls.

Here is a comparison between the Zeiss Abbe Orthoscopics and Pentax SMC Orthoscopics with the TMB Super Monocentric Eyepieces.

University Optics Orthoscopics compared with TeleVue Radians

I had the opportunity to compare a 12.5mm UO Ortho with a 12mm TV Radian with the AP 180mm. The Radian had a clear advantage in terms of FOV and comfortable (20mm) eye relief. With fewer elements the UO had better light transmission, contrast, and resolved stars better across the core of M13 and showed fainter detail in M57.

TeleVue 20mm Nagler Type 5 compared with TeleVue TV 17.3mm Delos eyepiece

Recently I had the opportunity to try out the new TV 17.3mm Delos eyepiece. I was interested to see how it compared to my Tele Vue 20mm Type 5 Nagler that I have used for a number of years and is one of my favorite all time eyepieces.

First I compared the Nagler 20mm type 5 with the 17.3mm Delos in the house under a bright light. It appeared that the Delos had darker coatings on the eye lens and field lens than the Nagler. Also the eye lens was noticeably larger in the Delos (35mm or 1.4") than the Nagler. The sliding eye guide is a nice feature in the Delos as well.

The 17.3mm Delos, and indeed the entire Delos eyepiece line, all have an eye relief of 20mm. By comparison the 20mm Nagler Type 5 has an eye relief of 12mm.

I set up my TMB 105mm f/6.2 on its alt-az mount for the comparison. The difference in magnification between the 20mm Nagler (31x) and 17.3mm Delos (36x) is small, only 5x.

First up was the Moon, which was four days from full phase. At first I did not note much of a difference. However after comparing them again I felt that the Delos showed a little more detail.

Next I swung the scope over to the Pleiades Star Cluster, M45. As with the Moon at first I did not note much of a difference. However I later noted that the orange and blue star near the center of the cluster was easier to see in the Delos.

Jupiter was next and I was surprised as I thought that the performance of the two eyepices would be similar as they had been for the Moon and M45. However the Delos seemed to show more detail than the Nagler. For example the contrast seemed to be higher in the Delos so it was easier to see the belts and zones on Jupiter. Jupiter and the Jovian moons were better defined as well.

Looking to the east I saw that Orion was just rising, so I swung the scope over to observe M42. It was still quite low, but the detail was easier to see in the Delos than in the Nagler.

The darker coating on the eye lens and field lens in the Delos may help to explain why more detail was visible in M42 and on Jupiter. This may also be why some observers have suggested that these eyepieces work well for the planets.

The other thing that I noticed was that with the larger eye lens in the Delos you do get the impression of looking out of a window rather that through an eyepiece. It is an interesting observing experience, and not one I have noticed in Naglers, Ethos, or Panoptics.

3) Star Bound Observing Chair

One of the best investments an amateur astronomer can make is a comfortable observing chair. This is because it is easier to relax and focus on seeing detail when one is comfortable. The Star Bound Observing Chair is a very good investment. It comes with a comfortable cushion seat that is 9" wide and 14" across, folds up for easy carrying and transport, and extends from 9" to 36".

You need to be careful when the seat height is low around 9" or less as the chair has a tendency to tip forward. This sometimes happens with my refractors when the tube is pointed at the zenith, but most observers using SCT's or reflectors shouldn't need to set the seat height this low.

Also the sharp edges of the front legs at the bottom can cut through the rubber feet. This is easily fixed by putting a metal washer between the rubber feet and rungs. The chair comes in black or white, which would make it easier to see when you are out observing. Price is around $159. Recommended.

4) Roll-A-Table

Another good investment is a good observing table. This one as the name suggest rolls up into a small compact size since the legs unscrew from the table and fit into the mesh pocket on the left of the photograph above. When it is set up the table stands almost 28" tall and is 32" wide. I find that it supports two heavy eyepiece cases, star charts, sketching materials, and snacks and something to drink during the observing session with ease. Available for around $35. Also recommended.

5) Astro-Physics StarBright, Tele-Vue, and Kenneth Novak 2" star diagonals

The first 2" star diagonal that I ever bought was in 1986 and was made by Kenneth Novak and cost $89.95. Located in Wisconsin, Novak for a number of years manufactured star diagonals, mirror cells, secondary mirror holders, mounting rings, and focusers. He was well known to the amateur telescope makers of the day of producing very good quality products at reasonable prices. The Novak 2" star diagonal was relatively lightweight with aluminum housing and the diagonal was not threaded for filters. Overall the Novak star diagonal offered good performance.

In 1996 I purchased a used telescope which came with a Tele-Vue (TV) 2" star diagonal. It wasn't clear how old the TV star diagonal was, but may have been manufactured in the early 1990's. It was larger and beefier than the Novak diagonal, and unlike the Novak was threaded for filters. This made it easier when observing deep-sky objects as I could thread the filter onto the front of the diagonal, instead of having to thread it onto the individual 2" eyepieces. Overall the performance of the TV seemed a bit better than the Novak, offering better image brightness, contrast, and slightly sharper image out near the edge of the field of view.

A couple of years later in 1998 I purchased an Astro-Physics (AP) StarBright star diagonal. I cost considerably more ($290) than what I paid for the Novak in 1986 ($89.95), but after a using it on the first night I knew it provided noticeably better performance than either the Novak or the used TV diagonal.

For example, detail in deep-sky objects was noticeably easier to see, and there was much less light scatter around bright stars. Contrast and image brightness was better, and the detail was crisper. I think the reason for this is that the StarBright diagonal comes with dielectric coatings that provide reflectivity above 99% over the entire 4000 to 7000 photo-visual range.

Also the diagonal has a number of baffles, and flat black interior, which allow maximum light transmission as well as reduce scattered light. The diagonal is threaded for filters, and the front element of the AP 2" Convertible Photo-Visual Barlow can be threaded onto the front of the diagonal as well.

Another nice thing about the diagonal is the recessed brass ring is under the thumbscrew location. As the thumbscrew is tightened, the brass locking ring clamps onto the eyepiece or 1-1/4" adapter, and this gives a more secure grip than a single set screw. A nice feature of the brass locking ring is that it does not mar the surface of eyepieces or accessories. The StarBright is extremely well made out of CNC machined parts.

Note that the new TV EverBright star diagonals are suppose to use the high quality mirror as in the AP StarBright, but since I do not have one on hand I do not know how they would compare. However I have been extremely impressed with the AP StarBright, so would not hesitate to highly recommend it. All of my deep-sky sketches and comet sketches made since 1998 were made using the AP StarBright diagonal.

6) Sirius Optics Planetary Contrast (PC1) Filter

I picked up one of these filters recently to see how it would perform for the planets. Al Misiuk of Sirius Optics in Seattle designs this filter. They make other filters as well including the MV1 or minus violet filter for reducing secondary spectrum for achromatic refractors, and the VFS, or Variable Filter System.

The PC1 is an interference filter designed to have three distinct peaks at approximately the red, green, and blue regions of the spectrum. As such it reduces the transition of colors between these peaks, and helps define the detail. It is offered in both 1-1/4" and 2" size.

I ordered a 2" size since I usually observe the planets with a binocular viewer that has a 2" adapter on the end of it. When I took the 2" filter out of its case I noticed that it had a scratch on it, and I wondered how this would impact performance.

I tried the filter first when observing Saturn. The PC1 filter gives objects a mint green color to it. I compared to the unfiltered view it did seem to help bring out detail of Saturn's South Equatorial Belt, and some detail in the B-Ring.

I observed Jupiter as well and once again compared to the unfiltered view it showed increased detail in the belts, in particular the South Equatorial Belt and North Equatorial Belt. The increase in detail was more noticeable for Jovian features than Saturn features.

However for both Saturn and Jupiter the scratch did produce a noticeable and distracting ghost image off to one side. So I decided to return it for a replacement. It took several tries to get a 2" PC1 filter that did not have a scratch on it. It appears that this is not an issue for the 1-1/4" size filters.

Still I have found problems with the 1-1/4" size filters not threading properly onto some 1-1/4" eyepieces. After contacting Sirius Optics about these issue they seemed very interested in taking care of any quality control issues.

Once I got a replacement filter I made a couple of sketches of Jupiter and Mars. The filter did help to bring out detail in Jupiter's South Equatorial Belt. It helped also to bring out the Martian detail during the favorable opposition in July and August of 2003.

While it seemed like this filter could be useful in bringing out finer planety detail in practice the issues of scratches were a concern. If you are looking to buy one I would recommend that you try and test it first.

Articles (c) 2000 - 2017, Eric Jamison, All rights reserved.