The new Optolong filter arrived at my place, I managed to take some pictures with it during the holidays. I was interested to see what this model would look like under the sky. I was not asked to write an article on the subject, but I had the time and the inclination at the end of the year. I also took two pictures, have deliberately chosen different ways of processing the pictures so that everyone can find something to their liking. You will also find a comparison of the whole product family at the end of the article (L-Para, L-eNhanche, L-eXtreme, L-Ultimate filters).
The magnificent Rosette Nebula is a massive emission object in the constellation Monoceros. It surrounds the Rosette Cluster, also known as NGC 2244, a group of hot young stars. The brighter parts of the nebula are given a separate numbering in the well-known NGC catalogue. The cluster itself was first observed by John Flamsteed in 1960 and later discovered by William Herschel. Although he did not record the nebula itself, his sons later identified its various parts.
- NGC 2237: this is usually taken to mean the whole area. It is described in the catalogue as having extremely bright, massive, diffuse features.
- NGC 2238: part of the nebula, identified by Mark and Swift. The catalogue describes it as a small, faint nebula around a star.
- NGC 2239: part of the nebula, discovered by William Herschel. Large, rare and bright cluster.
- NGC 2244: the known cluster of arrows in the centre of the nebula. Identified by John Flamsteed in 1690.
- NGC 2246: part of the nebula, discovered by Swift. A faint, large irregular circular shape, extremely difficult to detect.
The entire object is a huge cloud of dust and gas: it extends more than 1 degree, covering roughly five times the size of the full moon in the sky. With a total magnitude of 4.8, it is the best known cluster of intermediate-gap stars, and can be detected with binoculars. The total nebulosity is estimated at 10 000 solar masses. Rosette is located about 6200 light-years from our Sun, close to the vast Monoceros molecular cloud. It has a diameter of approximately 130 light years and a central area of 30 light years. The ultraviolet radiation from its O-type star NGC 2244 interacts with the nebula, which is responsible for its brightness. The stars heat the surrounding haze to temperatures of about 6 million K, producing a strong X-ray emission. The strong activity has resulted in interstellar winds “blowing” from the cluster to form the central cavity of the formation, putting pressure on the interstellar dust clouds, compressing them.
A prominent dust cloud passing through this part of the object provides an easy opportunity for image spiking. The details suggest animal shapes, hence the title of the image. Thus we can find a cheetah leaping gracefully (1), a donkey (2), a hungarian vizsla dog (3), a magnificent stallion (4), llamas – some of which didn’t even fit in the picture (5), a duckling (6) and a koi fish (7). If anyone finds anything else, let me know! 🙂
The Rosette Nebula is a resident of the constellation Monoceros, although it may be easier to find if you start from the more spectacular Orion Nebula. Look for it at the head of the unicorn, near the binary star ε Monocerotis.
The photo (or rather photos, because the description below is also true for the next picture) was taken in the last days of 2024. The sky cleared on Christmas Eve, but strong winds were blowing around Lake Balaton (the strongest winds in the country at that time). I tried to take pictures, but the quality of the images was not up to par. Therefore, I was able to get good exposure later, from 26th to 29th, when the atmosphere was calmer.
The reason for this picture is the new Optolong model mentioned in the introduction. The L-Para is a brand new dual narrowband 10 nm light filter. To be precise, we are talking about a duo filter, i.e. 10 nm for OIII (500.7 nm) and H-Alpha (656.3 nm).
It is advertised as a light pollution filter because it effectively filters out mercury lamps, sodium lamps and LED light pollution lines. However, it is much more than that: it is a true narrow-band model with a wider transmission. According to the website, it has excellent contrast and anti-halo properties (important given the shortcomings of the previous model) so that detailed and vivid photos can be taken. The manufacturer says the L-Para is suitable for both standard optical systems and fast optical systems such as RASA and Hyperstar. Even when the light falls at an oblique angle, it can maintain high transmission speeds to deliver a clear and accurate photographic experience. I have not been able to test this, as my system is f/4.5. But I can interpret the point of view and show the corresponding figures:
I have chosen a nebulosity as the second object in my description of the filter. There was also a practical reason: from my observatory, the Rosette Nebula can be conveniently detected relatively late, because the light over Lake Balaton in the east can still interfere. Therefore, I had to choose an object for each night after sunset, when it was already past the zenith. As I had not yet photographed the Wizard, I decided to choose it as the second.
NGC 7380 is a bright, irregular, small, concentrated cluster of 45 faint stars, centred around a prominent “V” shaped cluster formed by members of the group with magnitude 8.5-9. This cluster is embedded in a wizard-shaped nebula about 110 light-years across. The stars of NGC 7380 from this star-forming region have formed in the last 5 million years or so, making it a relatively young cluster. The brightest star is located at the southwestern edge of V, and the binary OStruve 480 (8.0,9.0; 30.9″; 117°) is located at the western edge. The cluster is surrounded by the Milky Way, rich in bright stars. Very faint nebulae are embedded in the cluster, the most obvious being east of V.
The Wizard Nebula is an object in the constellation Cepheus. It is located in the vicinity of δ Cephei (the best known variable star of the Cepheid type).
I share the 1-1 frames of the two photos to download and examine.
Light_rosette_600.0s_Bin1_20241229-190604.fit, no dark, no flat, 600 sec, -20°C, gain 101, offset 50
Light_wizard_600.0s_Bin1_20241229-011025.fit, no dark, no flat, 600 sec, -20°C, gain 101, offset 50
The three pictures below show the colour balance of the filter. In the first picture you can see the untreated state of the summed raw. A slightly enhanced version of this without the star field can be seen in the second photo, followed by the false colour highlighting in the third photo. For all three images you can see the typical proportions and the colour characteristics of the product.
The following comparison was made in Balatonalmádi, with the following equipment: the photons were collected by a self-built 400/1820 Newtonian telescope through a Paracorr Type-2 coma corrector into the sensor of the ASI 2600MC Pro camera. The telescope was mounted on the excellent Fornax 150.
In this segment I will share raw images for those interested in how the new L-Para filter compares to the rest of the L family. The images were taken under the same conditions, although in slightly windy weather, so the details are a bit wavy from frame to frame.
In the animation below you can see how much more detail is revealed by the L-Para filter in the Veil Nebula compared to a normal UV/IR filtered image when exposed for 5-5 minutes at the same time.
The pictures of all the family members are 300 seconds each. Click on the small images below to download the FIT files.
Camera UV/IR
Optolong L-Para
Optolong L-eNhance
Optolong L-eXtreme
Optolong L-Ultimate
In the following, it is worth looking specifically at the issue of the halo effect. On the left is a picture of the L-Para and on the right the predecessor L-eNhance. The new filter is indeed an improvement over the previous one. Even if it doesn’t seem huge at first, the fact that the sharp halo line has disappeared is a significant improvement when processing nebulae embedded in stars (where a stronger processing can result in a very badly haloed image). Compared to the other filters, you don’t see such a big difference (L-Ultimate is just as good, for example), but the L-Para matches the L-eNhance model in the whole family anyway.
The above images were taken on 03.01.2025, i.e. the Moon was present as a negligible 11% tidal crescent in the sky at an altitude of only 20°. However, I wanted the filters not to get a very light situation, so I wanted to get my Bortle 4 conditions available from Balatonalmadi, so I lowered the side screens of the observatory.
