AG Hybrid
18-02-2014, 01:53 AM
:welcome:
This is my report for the first light review of the ES Coma Corrector. I had a good 2 hours with it tonight to test it out in ultra wide field eyepieces. Due to clouds to the west and a rising 95% moon to the east I had to focus mostly towards the top 70 degrees of the night sky. Luckily Orion was right over head and served as a good yard stick. Its bright stars, and bright doubles allowed for easy comparisons. I focused testing on 3 bright binaries in Orion. Rigel, Mintaka A and Mintaka C, and Nair al Saif. I also used the Trapezium. Trapezium stars observed were the A,B,C,D,E and F stars.
Testing was done in my 12" F5 Skywatcher Flex-Tube Dobsonian.
First thing to note. I found in-focus to be a real issue. Probably the biggest foreseeable problem with this corrector. Now, if you have used or own a Skywatcher dobsonian you know that the focuser is not a low profile arrangement it actually sticks out quite far. Thankfully, due to the the ingenious design of the flex tube I could easily just adjust the height of the upper telescope assembly effectively lowering it towards the primary and creating in-focus travel. For the effective setting for 2 of the eyepieces tested I needed to lower my UTA by about 1.5 INCHES to achieve focus. Also to note my primary mirror has upgraded springs and my mirror is pushed forward as well. This is not a problem for Skywatcher users but I would suggest a solid tube dob users take this into consideration.
First eyepiece. The 30MM Explore Scientific 82 degree's.
A fantastic eyepiece for sweeping the Milky Way, large star clusters or taking in the Carina Nebula or the LMC and SMC. It provides a true 1.5 degree field. Enough to take in the entire M42 complex with room to spare. Without a corrector to my relatively young eyes of 28yo I can see coma noticeably developing from about 40 degrees with progressively worst coma to the edge. I was not really sensitive to it but what I found did bother me the "fish bowl" effect while panning. It is a bit nauseating if I am honest. So much so I got the 24mm ES 68 degree eyepiece to escape it.
Inserting this heavy eyepiece into the corrector was easy enough the triple thumb screws and compression ring gripped that big b*****d tight. No chance of it letting go. I used the bright binaries as my testing targets. My theory behind it as since they were bright and well spaced binaries they could be split at a relatively lower power of ~60x. In the inner 20 degree's of eyepiece fields of view is what some call the "sweet spot". Essentially this is the area of the field of view that is diffraction limited. As you extend out of that area the coma effects the sharpness of the field getting worst at a linear rate as you move outwards. People who are not sensitive to coma may not detect it as easily. They may not notice the field deteriorating till 40 degree or more depending on the magnification, focal length, aperture and target object, if they notice it at all. Anyway, my idea is that in this "sweet spot" or diffraction limited area, the binary stars are easily split and as the field deteriorates as the stars drift to the field they become harder and harder to split to the point the distortion of the stars approaching the edge of field make attempting to split doubles impractical. It worked out to be a pretty good technique for me to figure out the best settings. There were no manuals that came with the corrector and since its such a new produce there are no online guides or tutorials. I literally had to eyeball the location of the settings on the corrector and compare the fields of stars and compare the diffraction limited field between the settings. When I say settings its just unscrew the eyepieces adapter. A lot like a twist up eye cup you might find on an eyepiece. On the sides are these little lines to help you measure what setting your at. These little lines seem to be about 1mm apart. Every 5 or so lines there is a larger line. For the ease of explanation I will call these spaces between the larger lines "bars".
So, I started at the lowest position. 1 bar. Immediately I discovered I did not have enough in-focus. Not to worry. Just lower the UTA towards the primary mirror. I started at about half an inch. I was able to reach focus now. But, no real difference. The star drifting indicated the sweet spot was still small. I raised / unscrewed the corrector to 2 bar. Not much of a difference again. Moved to bar 3. Could not achieve focus again. I lowered the UTA by another half inch. Focus achieved. I did notice at this point the sweet spot widening. Things looked promising. This process continued to 5 and 1/2 bars. To achieve focus again I had to lower the UTA by another half inch. I also recollimated to adjust any alignment errors introduced by the adjustments I did to the UTA. At this point the field of view was genuinely amazing. Stars were truly pin point from edge to edge - save for the last couple degrees. The diffraction limited sweet spot was enormous. Upon close inspection it seemed to be at least 70+ degree's across with the rest being very well corrected indeed. I was staggered with how sharp the field was. And further more how flat the field was. The fish bowl effect that annoyed me so much was completely eliminated. Where the stars would normally be a washed out distorted mess, the binary stars could still be split with ease. Stars held their round shape from one side of the field to the other. While the binaries were separated the entire way.
However, I did notice something. In the outer 15% of the field I noticed the sky darkened. Could this be vignetting? Further testing is required.
Now, moving on to the second eyepiece the 14mm ES 100. Probably my favorite eyepiece. But, I was annoyed by the outer field so much that bought a Delos 14mm to escape it. I was willing to accept a smaller field of view if it was better corrected. I have to say that Delos 14 is damn good. It may be the finest mid power eyepiece I have looked through. Not my favorite just maybe the finest. To start testing this eyepiece I reset everything back to its start position. Telescope and corrector, then recollimated just in case. What happened for the next 20 min was the same routine as the 30mm. Eventually I got to about the same position and recollimated again to remove any introduced alignment errors. I focused on the trapezium in Orion. Stars A,B,C,D E and F were easily discernible at about 120x. I moved the trapezium to the far left and watched it drift through to the far side of the field to the right. What I saw was amazing. The diffraction limited field was once again seemed enormous. 80+ degree's were sharp pinpoint stars. The other 20% were still very well corrected. No complaints there. At no point during the drift did the E and F stars of the trapezium were not visible. Even at the extreme edge as they disappeared they were still there. Is this what its like to own a 13mm Ethos? I digress.
The last eyepiece I had to try was the 9MM ES 100. Now once again I reset everything and collimated. In my time testing it for about 40 min. I never really found the right setting. At least not between the 1st bar and the 5th. It was very strange what was happening. Normally without correction you would have a small field of diffraction limited objects. It would progressively get worst with coma. In this case with the corrector, once again the sweet spot was much larger. But, in an area of the field between 50% to 70% from the center the view would slightly defocus. Just slightly. But enough to change the objects in that section to no longer diffraction limited. But, then from 70% outwards. BAM! Sharp pin point stars to the edge. I have no idea why it is doing this. I tried the 9MM without the corrector. Its just a sweet spot in the middle that progressively gets worst with coma. :confused2: This needs more testing and I may add more information to this review when I figure out the best setting.
I bought a 8mm Delos and 10mm XW to make up for the failings of the 9mm ES in its outer fields. Brilliant eyepieces. But, not my favorite. If I can figure out this 9MM. I will probably sell the 8mm and 14mm Delos as well the Pentax XW. Might pick up the ES 5.5mm 100 in their place.
If I can't figure this out I might still sell them with the ES 9mm and pick up an Ethos instead.
Thanks for reading.
This is my report for the first light review of the ES Coma Corrector. I had a good 2 hours with it tonight to test it out in ultra wide field eyepieces. Due to clouds to the west and a rising 95% moon to the east I had to focus mostly towards the top 70 degrees of the night sky. Luckily Orion was right over head and served as a good yard stick. Its bright stars, and bright doubles allowed for easy comparisons. I focused testing on 3 bright binaries in Orion. Rigel, Mintaka A and Mintaka C, and Nair al Saif. I also used the Trapezium. Trapezium stars observed were the A,B,C,D,E and F stars.
Testing was done in my 12" F5 Skywatcher Flex-Tube Dobsonian.
First thing to note. I found in-focus to be a real issue. Probably the biggest foreseeable problem with this corrector. Now, if you have used or own a Skywatcher dobsonian you know that the focuser is not a low profile arrangement it actually sticks out quite far. Thankfully, due to the the ingenious design of the flex tube I could easily just adjust the height of the upper telescope assembly effectively lowering it towards the primary and creating in-focus travel. For the effective setting for 2 of the eyepieces tested I needed to lower my UTA by about 1.5 INCHES to achieve focus. Also to note my primary mirror has upgraded springs and my mirror is pushed forward as well. This is not a problem for Skywatcher users but I would suggest a solid tube dob users take this into consideration.
First eyepiece. The 30MM Explore Scientific 82 degree's.
A fantastic eyepiece for sweeping the Milky Way, large star clusters or taking in the Carina Nebula or the LMC and SMC. It provides a true 1.5 degree field. Enough to take in the entire M42 complex with room to spare. Without a corrector to my relatively young eyes of 28yo I can see coma noticeably developing from about 40 degrees with progressively worst coma to the edge. I was not really sensitive to it but what I found did bother me the "fish bowl" effect while panning. It is a bit nauseating if I am honest. So much so I got the 24mm ES 68 degree eyepiece to escape it.
Inserting this heavy eyepiece into the corrector was easy enough the triple thumb screws and compression ring gripped that big b*****d tight. No chance of it letting go. I used the bright binaries as my testing targets. My theory behind it as since they were bright and well spaced binaries they could be split at a relatively lower power of ~60x. In the inner 20 degree's of eyepiece fields of view is what some call the "sweet spot". Essentially this is the area of the field of view that is diffraction limited. As you extend out of that area the coma effects the sharpness of the field getting worst at a linear rate as you move outwards. People who are not sensitive to coma may not detect it as easily. They may not notice the field deteriorating till 40 degree or more depending on the magnification, focal length, aperture and target object, if they notice it at all. Anyway, my idea is that in this "sweet spot" or diffraction limited area, the binary stars are easily split and as the field deteriorates as the stars drift to the field they become harder and harder to split to the point the distortion of the stars approaching the edge of field make attempting to split doubles impractical. It worked out to be a pretty good technique for me to figure out the best settings. There were no manuals that came with the corrector and since its such a new produce there are no online guides or tutorials. I literally had to eyeball the location of the settings on the corrector and compare the fields of stars and compare the diffraction limited field between the settings. When I say settings its just unscrew the eyepieces adapter. A lot like a twist up eye cup you might find on an eyepiece. On the sides are these little lines to help you measure what setting your at. These little lines seem to be about 1mm apart. Every 5 or so lines there is a larger line. For the ease of explanation I will call these spaces between the larger lines "bars".
So, I started at the lowest position. 1 bar. Immediately I discovered I did not have enough in-focus. Not to worry. Just lower the UTA towards the primary mirror. I started at about half an inch. I was able to reach focus now. But, no real difference. The star drifting indicated the sweet spot was still small. I raised / unscrewed the corrector to 2 bar. Not much of a difference again. Moved to bar 3. Could not achieve focus again. I lowered the UTA by another half inch. Focus achieved. I did notice at this point the sweet spot widening. Things looked promising. This process continued to 5 and 1/2 bars. To achieve focus again I had to lower the UTA by another half inch. I also recollimated to adjust any alignment errors introduced by the adjustments I did to the UTA. At this point the field of view was genuinely amazing. Stars were truly pin point from edge to edge - save for the last couple degrees. The diffraction limited sweet spot was enormous. Upon close inspection it seemed to be at least 70+ degree's across with the rest being very well corrected indeed. I was staggered with how sharp the field was. And further more how flat the field was. The fish bowl effect that annoyed me so much was completely eliminated. Where the stars would normally be a washed out distorted mess, the binary stars could still be split with ease. Stars held their round shape from one side of the field to the other. While the binaries were separated the entire way.
However, I did notice something. In the outer 15% of the field I noticed the sky darkened. Could this be vignetting? Further testing is required.
Now, moving on to the second eyepiece the 14mm ES 100. Probably my favorite eyepiece. But, I was annoyed by the outer field so much that bought a Delos 14mm to escape it. I was willing to accept a smaller field of view if it was better corrected. I have to say that Delos 14 is damn good. It may be the finest mid power eyepiece I have looked through. Not my favorite just maybe the finest. To start testing this eyepiece I reset everything back to its start position. Telescope and corrector, then recollimated just in case. What happened for the next 20 min was the same routine as the 30mm. Eventually I got to about the same position and recollimated again to remove any introduced alignment errors. I focused on the trapezium in Orion. Stars A,B,C,D E and F were easily discernible at about 120x. I moved the trapezium to the far left and watched it drift through to the far side of the field to the right. What I saw was amazing. The diffraction limited field was once again seemed enormous. 80+ degree's were sharp pinpoint stars. The other 20% were still very well corrected. No complaints there. At no point during the drift did the E and F stars of the trapezium were not visible. Even at the extreme edge as they disappeared they were still there. Is this what its like to own a 13mm Ethos? I digress.
The last eyepiece I had to try was the 9MM ES 100. Now once again I reset everything and collimated. In my time testing it for about 40 min. I never really found the right setting. At least not between the 1st bar and the 5th. It was very strange what was happening. Normally without correction you would have a small field of diffraction limited objects. It would progressively get worst with coma. In this case with the corrector, once again the sweet spot was much larger. But, in an area of the field between 50% to 70% from the center the view would slightly defocus. Just slightly. But enough to change the objects in that section to no longer diffraction limited. But, then from 70% outwards. BAM! Sharp pin point stars to the edge. I have no idea why it is doing this. I tried the 9MM without the corrector. Its just a sweet spot in the middle that progressively gets worst with coma. :confused2: This needs more testing and I may add more information to this review when I figure out the best setting.
I bought a 8mm Delos and 10mm XW to make up for the failings of the 9mm ES in its outer fields. Brilliant eyepieces. But, not my favorite. If I can figure out this 9MM. I will probably sell the 8mm and 14mm Delos as well the Pentax XW. Might pick up the ES 5.5mm 100 in their place.
If I can't figure this out I might still sell them with the ES 9mm and pick up an Ethos instead.
Thanks for reading.