- Index page with recent astrophotos
- Leeuwenboschfontein weekend starparty 2016 Mar 4-6
- Events observed by me from 2003 latest: Mercury transit 2016 May 9
- Page with sky pictures with the EOS 6
- Lunar and planetary images and phenomenas
- Page with sky pictures with the EOS 40 from Bali jan 2009, feb 2010 and 2012
- Page with sky pictures from La Palma Jan / Feb 2011
- Total lunar eclipse of 2011 Jun 15
- Solar eclipse visible as deep partial in Indonesia on 2009 Jan 26
- Old 1973 Polarex 80mm spotting scope refurbishment.
- > New 2015 Robtics ED110 refractor
- Using a telephoto lens as a small handheld telescope
- Nice sky pictures taken from a plane in full flight
- How to see stars in the daytime ?
- How I learned Astronomy
- Astronomik CLS filter test
- Simple Eclipse calculations
Robtics ED 110mm f/7 telescope
In May 1995 I purchased from Ganymedes a second hand Televue Genesis for € 1350 which was reasonable at that time as a new one costed € 2000. It is the 'original' 102mm f/5 with the 'normal' glass achromat f/10...f/12 objective with two Petzval elements of which one fluorite in the rear to correct the color errors, reduce the focal length and flatten the field.
I had lots of fun with this telescope as it is an excellent visual and photographic performer. Rather compact as its tube weighs only 4kg and tube is 63cm long (excl. diagonal), so can be taken as carry-on luggage on an aircraft. I traveled all over the world with this scope. I mount it on a Vixen Super Polaris mount purchased in 1991 which can be taken in checked luggage. One of the first things was replacing the heavy clamshell by tube rings made from 30x3mm aluminum strips and small blocks of cast aluminum with 1/4"x20 threaded holes in it.
In the latest years however, I noticed that, unlike many other scopes with a simple 2 or 3 element objective lens can be easily disassembled to make the transport length even shorter by removing the objective and / or focuser to fit in the 55x53x25cm carry-on limits observed by most airlines. Due to the Petzval elements this is not possible in scopes like the Genesis (and the successor NP-101). Moreover, many affordable 100mm class ED doublet scopes of around $1000 perform even better in color error correction and have a nice focuser with 1:10 fine tuning and 360° rotation without affecting focus which were not available when the Genesis was new (around 1990). And I really missed this on the Genesis.
An example is the Kson 100mm f/6, which I tested back-to-back with the Genesis. The result was that color correction of the Kson was better but sharpness and contrast are about the same excellent level.
Finally I found a used Robtics ED 110mm f/7 ED in the nice Robtics store in The Hague which is actually the same as the Astro Professional ED 110 f/7 or Teleskop Service ED 100, all from Kunming Optics in China. The price was $700, which is a good price. The scope was in excellent condition, is 64cm long, has very nice CNC machined tube rings and a retractable dew shield. But the two latter parts come at a cost of 1.5kg extra weight. All together the tube weighs 5.7kg but when I replace the tube rings with the same aluminum strip rings as the Genesis, the weight will decrease to 4.5kg. And for travel purposes the heavy dew shield can be replaced by a light plastic one. The only con was that I needed a flattener for photography: a flat field is a strong advantage of the Genesis, but that was $175 not too bad, so I purchased the stuff. For well below $1000 with even 10% extra aperture as a bonus this should be a good deal.
A few weeks earlier (March 2015) an Italian guy (an architect from Civitavecchia near Roma) tested this scope, see here the Google translated report.
At home I stared making new tube rings to get weight loss, the same as for the Genesis, but for a slightly larger tube diameter. I finished this successfully and the scope lost 1kg of weight. Next slimming is the dew shield: it weights 1 kilo. This results in a very bad balancing as the front is very heavy. So I made a new one from a yoga mat of which the latter one is well-insulating as well and weight no more than 0.1kg. The lens cap is made from the bottom of a mayonaise bucket which fits exactly on the objective lens cell. As a result the scope weighs no more than 4kg. The original dew cap and tube rings can be restored very quickly when e.g. the scope is used on a heavier mount such as an EQ-6, as I did not modify anything.
Testing Despite the rainy weather I tested it on the houses 30 meters away. Result: A very crisp and sharp image even with the TMB planetary 3.2mm (240x) and with the Vixen LV6mm it is a high contrast image at 128x. Because of the longer focal length of 770mm the Panoptic 24 field is shrunk to 2 degrees (instead of 3.2 with the Genesis), but very nice and sharp to the edges. When I add the field flattener, the focal length is 570mm which allows larger and flat fields with the long eyepieces.
I ordered Yoga Mat for $10 of 160x60cm meant to be as a mat for yoga and other exercising. It is very lightweight polyethylene foam of 7mm thickness meant to lie on it on a hard floor for exercising. But I cut it to make a dew shield from it. I made the first prototype by replacing the 0.9kg aluminum dewshield by this <0.1kg YogaMat shield. For the lens cap I used a bottom of a mayonaise bucket.... Then I pasted a layer of adhesive white plastic foil over it which is better than spray painting and a laminated all-sky chart over it to decorate the lens cap. I did the same with the plastic lens cap which fits well over the objective cell.
I did a test on the waxing gibbous Moon but virtually no nociceable color errors were visible, even at 240x. It showed a contrasty image but sharpness was good only when the seeing was good: the seeing was not the best.
I tested both telescopes (Genesis and ED-110 side-by-side. I used a TMB Planetary 3.2mm in the Genesis (156x) and a Nagler 13T6+Powermate 2.5x in the ED110 (148x) and watched contrasty stripes in the ISO 12233 test sheet. I did the same with LV6 + Powermate in the Genesis and TMB PLanetary 3.2 in the ED110 to rule out contrast differences in both eyepieces. It turned out that both telescopes showed slight blue fringing but not at all times, so color correction is about the same. Watching the small bars in the center of the USAF 1951 diagram revealed slightly less blue with the ED110. But color fringing is very dependant on correct focus, even the slightest defocus increases color errors considerably. I also swapped eyepieces. I have to note that the TMB Planetary has less contrast then the Nagler and the LV, regardless in which scope it is.
Sky testingMoonSeeing was good and the Moon was a waxing gibbous of 66% (2015 Mar 30). Crisp image even at 148x (Nagler 13T6 + Powermate 2.5), craters and shadows in these showed no noticeable color errors. Only the edge of the Moon showed a very slight blue false color. VenusThe also gibbous evening planet showed a nice phase (good seeing) at 128x (Vixen LV6) but with a noticeable blue false color due to its intense brightness. I also viewed Venus during full daylight and the phase was nice withouit noticeable color error. JupiterExcellent seeing in more nights in beginning of April 2015. Really stunning views. The beginning of a transit of Europe was visible until Europe's ball was completely 'immersed' in front of Jupiter. Then, when Europe is in front of Jupiter the albedos of both are equal and it became invisible, even my 40cm Dobson did not reveal Europe in front of the nice image of Jupiter. And the Great Red Spot was very good visible almost as good in the 40cm. Another night I saw two shadow dots on Jupiter, really very crisp. And the GRS was well visible and the orangish color of the GRS was well noticeable. Even the bulge of the South Equatorial Belt around the GRS was easily visible. I used the LV6 (128x). The two belts were visible with some fainter belts and festoons. Stars in daylightI tested the ability to look up stars in daylight and the Panoptic 24 (32x, slightly more than the Genesis) showed stars like Aldebaran or Betelgeuse easily in full daylight (Sun >20° high). The Nagler 13T6 (59x) showed them even brighter with a still ample FOV of 1.3° Double star CastorDuring another daylight session on a late April afternoon, I looked up Castor ans it showed both components clearly at 60x. Zooming in to 128x (LV6) two bright stars were shown with the diffraction rings against the blue sky. I did not test Castor during night, but then it will be much brighter. Photo test I took a few single frame shots of an area in Auriga, with amd without flattener, it appeared that using the flattener the FOV increased by 25-30%. The vignetting was in both cases the same as with the Televue Genesis. I played with the extension rings to set the proper distance to the camera sensor and about 70mm (got with 1x15mm extension ring) showed the best result: sharp to the edges. I took a shot with flattener of the Pleiades, but due to low position above the horizon, I had not the time to make more flames to stack. For that reason, the single image below (postprocessed with Photoshop) shows a lot of vignetting and poor star images, which is usual in single frame images. Note, the larger bluish spots near some bright stars are no optical errors, but real nebulas around the stars.
Later, a stacked image (using a reducer / flattener) of the Leo Triplet showed a sharp image until the edges. Deep skyOn a late April night, while using the Nagler 13T6, I looked up M51 and it showed some detail in it. The same with M106, also close to the Big Dipper. The Sombrero Galaxy showed its nearly edge-on shape and the Leo Triplet showed two of the three galaxies: the needle one was too faint to get it in the light polluted part of the sky. The Owl Nebula was even visible without filter, but much clearer with OIII filter. Finally, I tried M3 which stars to resolve at 59x but using the LV6 (128x) is was resolving clearly. Not an Omega Centauri or M13, but even resolving not the brightest globulars with an 11cm is rather good.
I did some vignetting tests with a piece of cardboard with a 24x36mm frame drawn on it and held it in the focal plane of the scope with the camera adapter in it with long tube first, short tube and then the flattener in it. I projected tree branches on the cardboard and it appeared that there is a vignetting which can be corrected with flats. I made these flats as well with and without flattener but they did not differ much from the similar flats (no flattener needed) in the Genesis.
ConclusionA really nice scope for an affordable price (new between $1000-$1300) with only minimal color errors which is usual for an ED doublet. Priced for only the half of a triplet APO or fluorite of similar aperture, but very sharp and crisp images up till 240x and high contrast till 150x. Perfomance is way better than a 110mm f/7 Fraunhofer achromat. So a good allrounder for both planets and deep sky. With a 1.25" eyepiece a FOV of 2 degrees can be reached and with a 0.8x reducer 2.5 degrees. And very good for photographic use but a flattener is required.
When you are handy, you can slim the weight by replacing the heavy tube rings and dew shield lowering the weight to 4kg, which makes it a nice travel scope.
Pictures of the making of the new lightweight tube rings