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ED80 v ED100 for AP


RonC
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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


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Guest Kheldar

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 by Kheldar
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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 :P As I was saying, faster is better as a rule of thumb of comparable quality scopes.

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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! :)


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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 :D

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Guest Kheldar

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

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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.

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Guest Kheldar

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 :)

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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

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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 ;)

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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

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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

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