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Post by Deleted on Apr 20, 2017 1:50:08 GMT
For some time now my grab&go/winter scope has been a Skywatcher 102/500 on a Star Discovery alt-az mount. It sits on the veranda ready to go and I can control it from inside the house. I’ve been impressed with the performance of both, especially since the total cost was about $700AUD. I now also have the iconic ED80 (80/600) to use as an alternative to the 102/500 – but how much better is it? I didn’t plan this to be comparison so it’s not very scientific - images were captured on different nights, objects were at different altitudes, and the moon was coming up when I was using the 102/500. The following were the same – mount, location, camera (Ex3), software (Toup Sky), technique (get the best detail with a total exposure of about 1 minute and hit the “Snapshot” button). 102/500 had a Baader Fringekiller and exposures were all 10 seconds stacked x4. 80/600 had a UV&IR cut filter and exposures were all 15 seconds stacked x4. Darks at the beginning of the session and tweak gain and histogram as necessary.
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Post by howie1 on Apr 20, 2017 7:48:53 GMT
Go longer on the ED80 Robert. SW 105/500 has focal ratio of 500/102 = f/4.9 and 4.9 x 4.9 = 24.0 ED80 80/600 has focal ratio of 600/80 = f/7.5 and 7.5 x 7.5 = 56.25 so dividing the numbers 56.26 / 24.0 = 2.34 which means to get the same light through / same exp time / same gain you need to go 2 and a bit longer on the ED80. IE try 22 seconds rather than 15 seconds.
Cheers Howie
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Post by Dragon Man on Apr 20, 2017 8:24:36 GMT
Apart from the need for slightly longer exposure in the ED80, the ED80 pics look sharper and tidier which is to be expected up against an Achro. Similar to the results I get when using all my Refractors. Robert, try the method I use here for your 102 Achro to get rid of the blue/violet around your stars: astrovideoforum.proboards.com/thread/1079/using-achromats-video
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Post by Deleted on Apr 20, 2017 10:28:40 GMT
Go longer on the ED80 Robert. SW 105/500 has focal ratio of 500/102 = f/4.9 and 4.9 x 4.9 = 24.0 ED80 80/600 has focal ratio of 600/80 = f/7.5 and 7.5 x 7.5 = 56.25 so dividing the numbers 56.26 / 24.0 = 2.34 which means to get the same light through / same exp time / same gain you need to go 2 and a bit longer on the ED80. IE try 22 seconds rather than 15 seconds. Cheers Howie Yes you're right Howie. I like to keep the exposures a bit shorter with the alt-az mount and tweak the gain up a bit. Having said that there are a couple of shots that are a little under-cooked.
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Post by Deleted on Apr 20, 2017 10:44:21 GMT
Apart from the need for slightly longer exposure in the ED80, the ED80 pics look sharper and tidier which is to be expected up against an Achro. Similar to the results I get when using all my Refractors. Robert, try the method I use here for your 102 Achro to get rid of the blue/violet around your stars: astrovideoforum.proboards.com/thread/1079/using-achromats-video Thanks Ken Yes, Fringe Killer is not the best choice for taking out the false colour at f5. I use it because it has an IR cut at 700nm and is not too harsh on reflection nebulae (cuts off at about 450nm).
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Post by ChrisV on Apr 20, 2017 11:55:35 GMT
Still. If you dont mind a bit of stuff around stars the achro does a nice job of the DSOs Nice "comparison"
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