+RonC Posted January 23, 2014 Share Posted January 23, 2014 Why is the SW ED80 the preferred scope for AP and not the bigger Ed100? I realise the ED100 has a FL of 900mm giving an f9 while the ED80 is only a 600mmFL giving f7.5. Is f9 to slow then? Not sure about the ED100 but there must be a reason the ED80 is so popular apart from the price? Cheers Ron Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 For AP you need speed. Link to comment Share on other sites More sharing options...
Guest Kheldar Posted January 23, 2014 Share Posted January 23, 2014 (edited) Hmm, guess if I'm imaging at f11.5 on Saturday then I'm doing it wrong? The ED80 is the beginner imaging scope of choice for just the same reason as the 200P is the beginner Dob of choice - superb value for money, punches above it's weight and won't break the bank Faster is better for imaging but not a limitation, you could image with the slightly slower ED100 quite happily (as many do!) but if you put it's images against the ED80's images over the same time/exposure - the ED80 will produce the better results Edited January 23, 2014 by Kheldar Link to comment Share on other sites More sharing options...
+Ibbo Posted January 23, 2014 Share Posted January 23, 2014 and the 100 is harder on the mount Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 Hmm, guess if I'm imaging at f11.5 on Saturday then I'm doing it wrong? The ED80 is the beginner imaging scope of choice for just the same reason as the 200P is the beginner Dob of choice - superb value for money, punches above it's weight and won't break the bank Faster is better for imaging but not a limitation, you could image with the slightly slower ED100 quite happily (as many do!) but if you put it's images against the ED80's images over the same time/exposure - the ED80 will produce the better results I like the way you poke fun then prove my answer right later in your own post As I was saying, faster is better as a rule of thumb of comparable quality scopes. Link to comment Share on other sites More sharing options...
+RonC Posted January 23, 2014 Author Share Posted January 23, 2014 Also been reading some of Olly's stuff on SGL and anything slower than f8 is not for DSO's! So I guess the ED80 is the scope to go for, and I only have an EQ5 pro to mount it on anyway! Link to comment Share on other sites More sharing options...
Sheila Posted January 23, 2014 Share Posted January 23, 2014 Also been reading some of Olly's stuff on SGL and anything slower than f8 is not for DSO's! So I guess the ED80 is the scope to go for, and I only have an EQ5 pro to mount it on anyway! well that would make a Tak 130 extended useless for DSO's when i try it i will let you see the results to judge Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 ED120? F/7.5. Any advantage of additional aperture? Or just more weight and a longer tube to battle with. Jd Link to comment Share on other sites More sharing options...
Guest Kheldar Posted January 23, 2014 Share Posted January 23, 2014 ED120? F/7.5. Any advantage of additional aperture? Or just more weight and a longer tube to battle with. Jd Longer focal length, smaller targets Forget aperture, it's the focal length and ratio that matters Link to comment Share on other sites More sharing options...
+RonC Posted January 23, 2014 Author Share Posted January 23, 2014 Never mind Sheila, Make sure Olly see's the results though! Link to comment Share on other sites More sharing options...
Sheila Posted January 23, 2014 Share Posted January 23, 2014 Never mind Sheila, Make sure Olly see's the results though! you can absolutely sure i will but only if its good Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 ED120? F/7.5. Any advantage of additional aperture? Or just more weight and a longer tube to battle with. Jd Narrower FOV for the same chip for a start and something to do with better resolution. More than f8 is not a no no at all for DSO's but I would say it does if you're unguided (with a mount that's built for non millionaires) such as the eq5. It will take longer to get the same lum at higher focal ratios. Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 If the ED80 is f/7.5 as in ron's original post, isn't the fov the same in the ED120 which is also f/7.5? Jd Link to comment Share on other sites More sharing options...
Guest Kheldar Posted January 23, 2014 Share Posted January 23, 2014 If the ED80 is f/7.5 as in ron's original post, isn't the fov the same in the ED120 which is also f/7.5? Jd No, that's just the ratio of focal length to aperture (the speed.) FOV is calculated against sensor size and focal length Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 Well you learn something new every day! I though all scopes with a given F/ number had pretty much the same field of view with a given eye piece! See they didn't teach me that on the "introduction to astronomy" course! Jd Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 Well you learn something new every day! I though all scopes with a given F/ number had pretty much the same field of view with a given eye piece! See they didn't teach me that on the "introduction to astronomy" course! Jd They did if you think about it long enough small angle approximation would tell you that Link to comment Share on other sites More sharing options...
Guest Kheldar Posted January 23, 2014 Share Posted January 23, 2014 They did if you think about it long enough small angle approximation would tell you that :D Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 If you remember I used trig for that question; my mind just does not work the same way as yours. Jd Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 So in two scopes with different focal lengths, but the same focal ratio, if using two eye pieces with the same apparent field of view (say 50 degrees) which resulted in the same magnification in each scope, say 100x mag (2032/100 = 20mm ep in 8 inch; 2800/100 = 28mm ep in the 11 inch), would then the field of view be the same in each? Jd Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 roughly speaking yes, because there is no such thing as magnification as such, that is a common mis conception and even more common bad choice of phrase. Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 Are you talking imaging now, or visual? Jd Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 You were asking about eyepieces, so I assume we are talking visual, the same applies though, it's not magnification it's FOV. Link to comment Share on other sites More sharing options...
Perkil8r Posted January 23, 2014 Share Posted January 23, 2014 f5 or f25, it makes no odds to the FOV, focal length does though. All the focal ratio does is alter the effective brightness of the projected image for a given aperture. Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 But the eye piece magnifies the image it is presented with by the telescope, no? Link to comment Share on other sites More sharing options...
dawson Posted January 23, 2014 Share Posted January 23, 2014 f5 or f25, it makes no odds to the FOV, focal length does though. All the focal ratio does is alter the effective brightness of the projected image for a given aperture. So for two 8 inch scopes, one at f/5 and one at f/10 (tricky i know), and with eye pieces to produce 100x "magnification", the f/5 image would appear much brighter than the f/10 one? Jd Link to comment Share on other sites More sharing options...
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