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Showing results for tags 'achromat'.
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I'm back from holiday and my 130P-DS imaging scope is being under surgery for a secondary mirror replacement and cutting a bit the focuser. Since last night I had a few hours of clear sky, I put the camera on my SkyWatcher StarTravel 102 achromat. 102/500. It has a focuser upgrade and I used the OVL field flattener that I purchased for using it with my small 72ED. I placed the sensor ~55mm away from the flattener's thread and the image seems pretty flat. I always wondered if this fast achromat could be used for narrowband imaging and I did not find too many examples on this internet. I hope this will help more people trying to find out if it's worthy or not. I let the image speak for itself. 6x60s with the ASI1600 and an Optolong 7nm Ha filter. Clear skies! Alex
Hi, Has anyone noticed any spherical aberration or off axis aberrations (field curvature, astigmatism & coma) in an achromat in h-alpha? Or a better overall image quality in any way (clarity, resolution, sharpness, contrast, brightness etc) using an APO or ED over an achromat? Thanks
Greetings from cloudy and cold NJ! I recently had a lens replaced on a 102mm refractor, 1000mm FL, f/9.8, due to undercorrection of something more than 1/3 λ. The Ronchi lines seen in the double pass autocollimation test with an oil flat were significantly curved. The test is, of course, quite sensitive and allows one to see spherical aberration very easily. The new replacement lens is far better in that respect and a definite improvement over the original. It also shows a measure of undercorrection and I'm wondering if anyone familiar with the test and reading the images would hazard a guess as to the approximate wavefront quality of the lens. Nothing precise, just an estimate would be very much appreciated. Here are the specifics: Lens: 102mm, 1000mm FL, f/9.8 achromat. Ronchi grating: 150 lines per inch or 5.9 lines per mm. Oil flat, Double Pass Autocollimation. The distortions in the shape of the images are due to imprecise alignment and the variations in the line thickness from uneven illumination and slight oil movement. Of course, the 3 image diffraction overlap of the test gives a false impression of the poor edge quality. As I say, anyone who may have a knowledge and experience with the test and an idea as to what these results might translate to would offer an opinion as the the wavefront quality, or a range of same, I would greatly appreciate the information, for nothing else than curiosity about the new lens and a feel for the test. I'm quite happy to have received a much improved lens and I am sure it will be very satisfactory for use. Thanks very, very much! Joe.