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I recently had to move from my residence and amongst the items in my store was the first telescope I had ever used. It as a Celestron FirstScope 114 that is no longer in production, a 4.5 inch f8 classic newtonian. Unlike the current model PowerSeeker 114, it has a EQ2 mount rather than an EQ1, and a red dot finder instead of the unusable 6X30 plastic unit on the PowerSeeker. So after probably a dozen years since last using it I decided it might be interesting to put it through its paces. I fondly recall seeing things like the polar ice cap on Mars at opposition, the GRS spot on Jupiter, the Cassini Division on Saturn and some deep sky objects like M7, the Double Cluster, the M81 M82 pair and a lot of more with this scope. After using a CPC 1100 almost exclusively since, I wanted to confirm to myself that I had really seen those object through the scope.
The carton it was packed in was not completely sealed so it was covered with a great deal of dust. Looking down at the primary I could see some dark smudges - I didn't know if it was dirt or deterioration of the aluminum coating but luckily very little dust. I decided I would try the scope out before attempting to dismantle and do anything with the mirror.
I cleaned it up the best I could and assembled it with more difficulty than I recalled having in the past. I used to keep it fully assembled with the latitude set at 9 degrees, the counterweight midway between two of the tripod legs and set it down with the polar axis roughly pointing North. I found that this way a could track an object with the RA slow motion control with only occasionally having to adjust the Declination. I tried to do the same this time but was constrained by having to set up on a narrow balcony rather than on the open ground.
After having to wait a few day for the unseasonal clouds to clear (It looks like the bad weather issue also applies when you resurrect an old scope?) first target (Drum roll!!!) Albireo which was high up in the eavening sky. I had difficulty finding the target - I guess it was too much to hope that the battery in the red dot finder would still be alive after a dozen years. Using a 20mm eyepiece that came with a Celestron 102SLT I anxiously searched around and after a few minutes located the unmistakable colorful pair. Encouraged I switched to a 9mm eyepiece from the Celestron Eyepiece and Filter kit - and I must say I was pleased. At 100X the image was sharp and somewhat surprisingly, the collimation seemed very decent.
The big difficulty was the stability of the mount. A touch of the slow motion controls would start it shaking, taking maybe 5 to 7 seconds to settle. Focusing was the real challenge. I would make a tiny adjustment to the focus wait for it to settle then try again till I felt I had achieved the best possible.
That was all I had time for the first evening and packed up not too disappointed.
A couple of days later I had the scope out again. I first tried Jupiter low down in the SW. The seeing was bad but I could clearly see the two equatorial bands and three moons. In the past I had used the 4mm eyepiece from the above mentioned kit for a magnification of 225X. There is a 2X barlow in the kit but I had wanted to use the minimum amount of glass possible. This time I used the barlow with the 9mm eyepiece from the same kit for a magnification of 200X but with a more comfortable eyepoint. When the seeing was more steady for brief moments I though I could see some structure in the belts. My next target was Epsilon Lyrae - the double double. After some difficulty finding the pair and battling with the focuser, I had a rewarding view with both pairs clearly separated at 200X - nice airy discs (almost points) with some hints of diffraction rings.
And finally for the pièce de résistance, I turned my scope to Saturn about 50 degrees above the horizon. With the 32mm eyepiece the rings were obvious. I carefully changed to the 9mm barlow assembly and frankly was amazed! The Cassini Division was in your face visible - no challenge at all. I felt the coloring of the bands on the planet was move vivid that through the CPC 1100. I could clearly see the shadow of the planet on the rings. Titan was visible with direct vision. The view was crisp to the extent that I thought it could take more magnification. With the CPC 1100 I once had the magnification up to 400X and though I could see the Enke gap as a darkening in the outer ring - but the FirstScope does not break your budget or your back!
In conclusion I remember reading a review of a 4.5 inch newtonian (I think in was the Orion XT4.5 Dobsonian) and the reviewer mentioning the apo like views given by the diffraction limited spherical f8 primary. Having never had the chance to look through an apo refractor I can't confirm either way but clearly these cheap reflectors are nothing to sneeze at. Were it not for the unsteady mount I would have loved to continue using this scope. I imagine this scope but on a good quality altazimuth mount would make a very good beginner instrument. Hopefully I can pass it on to a youth who is passionate enough about astronomy to tolerate its quirks as I did and put it to good use.
Thanks for reading!
I recently tried imaging M7 with my 6" f/4 Newtonian. I had earlier commimated it with a Cheshire and Howie Glatter and was sure of the collimation. However, when I imaged using my DSLR with the coma corrector installed, I get focused stars off centre and not on the optical axis. Anyone experience anything similar before? What could this be? Tilt in the optical train? The focuser was drawn out only about 5mm to reach focus along with a 50mm extension tube. Any suggestion is welcome.
By Anthony RS
I bought a GSO 2 inch Coma Corrector for my 8inch Newtonian. I'm still having terrible coma on one of the corners which is actually worse than without the coma. The rest of the corners look fine with proper guiding.
Here are some details and what I've done to try and solve the issue:
1- Spacing is 75 mm just as recommended.
2- Used a Cheshire, laser collimator, and a webcam to check collimation.
3- Squared the focuser so that it's orthogonal to the optical axis.
4- Tried another DSLR
Note that once I collimate and double check that I'm collimated with all the tools, I always try to do a star test and collimation appears off (the dark spot isn't in the middle). Last time I tried to collimate the primary using a star but it's really tough to fine tune since due to the focuser's sag, I can't be sure that the star is in the middle of the fov.
My take on the problem is that when I'm using the DSLR with the coma corrector, the weight is moving the focuser away from the center of the optical axis but I'm not sure this if this is the case. I've tried everything and I'm out of ideas.
Below is a test image I took for Lagoon Nebula. Notice the coma on the left top side mostly, while the right side usually appear to have no coma (not the case in the attached image though for some reason, but usually the right side is fine). One more thing I've noticed, the stars on the left corner appear to be out of focus while the rest of the image appears well in focus (used a Bahtinov mask with APT bahitnov focus tool)
There's also another image I took for a distant light to check collimation (since clouds covered the sky as soon as I decided to do a star test). It appears to be fine and I was able to center it better but didn't capture the image.
Please let me know if you have any idea what's causing this. My number one suspect is the focuser's sag preventing me from doing accurate collimation although everything appears to be normal while collimating. I'm giving this another 2 weeks of my time, if it doesn't work I might quit astrophotography till I'm able to afford an APO.
One more thing that needs to be added, when using the GSO CC I had to move the primary mirror up the scope by around 2 cm to be able to achieve focus.
I purchased a GSO 6" f/4 Newtonian "Astrograph" late last year and eventually found that stars on one corner were egg shaped while taking images. I narrowed it down to improper centering of secondary mirror from the factory and resulting tilt.
Long story short, after numerous iterations, I used the Advanced Newtonian collimation technique by Astro Shed guy and ended up with the below pic of the optics. Does it look ok or do I need to do more? I will be checking with a Howie this weekend too.