Telescopes & magnification

[mik]

Hello,

Convention says that the max magnification for a scope is 50x per inch of aperture under a good sky, what do you think the ideal magnification is for an average UK city observer, I was thinking around 35x per inch or do you think ive gone to low.

Mick.

[MikeP]

Using the 50x rule of thumb, my f/5 12" dob would max out at 600x which I'd get with a 2.5mm eyepiece or equivalent.

I live in a semi-rural area and the light pollution (looking away from Gatwick ) is not too bad but I find a 5mm eyepiece is pushing it most nights ie magnification of 300x or 25x per inch.

Perhaps my theoretical max is 50x per inch but I sincerely doubt it. On that basis, I'd say if your light pollution is bad, 35x per inch is too high not too low.

Just a subjective opinion, no scientific basis whatsoever.

Mike

[jgs001]

I've no clue about what is max or not... theoretical or otherwise... Using my C80ED, I've hit 240x (yes I know... I actually made a mistake and forgot about the longer focal length 600mm compared to my Konus 400mm and used a 5mm with 2x barlow ... ) and I have to say the view of the moon was quite spectacular and didn't disintegrate into mush as I would have expected. That's 80x/inch, I guess I was lucky and it was just a night of superb seeing.

[mik]

Using the 50x rule of thumb, my f/5 12" dob would max out at 600x which I'd get with a 2.5mm eyepiece or equivalent.

I live in a semi-rural area and the light pollution (looking away from Gatwick ) is not too bad but I find a 5mm eyepiece is pushing it most nights ie magnification of 300x or 25x per inch.

Perhaps my theoretical max is 50x per inch but I sincerely doubt it. On that basis, I'd say if your light pollution is bad, 35x per inch is too high not too low.

Just a subjective opinion, no scientific basis whatsoever.

Mike

Hi Mike,

I think your suggested 25x per inch sounds good, ive been playing around with the ZS66 and have found with my 8mm Plossl 50x the veiw is superb, so with 25x mag x 2.6 aperture i am looking at around 65x or 6mm eyepiece.

I feel your opinion stands up well, and also if you look at one of the most popular scopes the 200p you are looking at 200x mag, this seems to be the planetary observers mark.

Regards Mick.

[mik]

I've no clue about what is max or not... theoretical or otherwise... Using my C80ED, I've hit 240x (yes I know... I actually made a mistake and forgot about the longer focal length 600mm compared to my Konus 400mm and used a 5mm with 2x barlow ... ) and I have to say the view of the moon was quite spectacular and didn't disintegrate into mush as I would have expected. That's 80x/inch, I guess I was lucky and it was just a night of superb seeing.

Hi John,

80x per inch , i think with a very bright object like the moon that is full of fine detail yes you can push things a little, ive had the little zs66 upto 150x on the moon the veiw was ok 50/50.

I guess you also get Gatwick to the east, i get it along with Crawley town as i am 4 miles south. my view from E to SW is not to bad.

Regards Mick.

[jgs001]

Mick, Gatwick is to the North... so East and South is pretty good. West is Horsham and a lot of trees... so a combintion of contrast robbing branches and LP.

[mik]

Mick, Gatwick is to the North... so East and South is pretty good. West is Horsham and a lot of trees... so a combintion of contrast robbing branches and LP.

Sounds like you are on my doorstep, i am 5 mins walk from Buchan Park.

Mick.

[jgs001]

Not far off... I'm about 4 miles south of there. Eastern edge of Horsham

[TheThing]

The general concensus of opinion in the past, is that anything over 300x is pretty useless, regardless of scope EP etc, and then only under good seeing and steady skies. There will, of course, always be exceptions to prove the rule....

[DaveS]

From what I remember reading in Amateur Astronomer's Handbook, the usable max (In x per inch) goes down as the aperture increases.

Many years ago I did try x400 with my 8" Newt, but it was pretty horrible, and anything above x200 was dodgy. Mind you there was less roof insulation in those days, so atmospheric boiling could be pretty severe in London.

Dave

[oceanheadted]

I've no clue about what is max or not... theoretical or otherwise... Using my C80ED, I've hit 240x (yes I know... I actually made a mistake and forgot about the longer focal length 600mm compared to my Konus 400mm and used a 5mm with 2x barlow ... ) and I have to say the view of the moon was quite spectacular and didn't disintegrate into mush as I would have expected. That's 80x/inch, I guess I was lucky and it was just a night of superb seeing.

You're doing well at 240x. Most of the time my C80ED works well with my 7.5 mm pentax, but turns to a bit of a mess with my 6mm eyepice Antares eyepiece - you don't seem to see much more for the extra magnification.

[bish]

I find that on an average night I would keep the max to x200-x250. I expect it wouldn't matter how big the scope is if the conditions aren't good. Under the best conditions I can go up to x375 and still get great views. Anything over that and my 6" scope doesn't show any more detail so is a bit pointless.

[mike bacanin]

The biggest single limiting factor is the seeing. The 50x aperture guide is fine, seeing permitting and quality of optics.

other factors such as tube currents and cooldown come into play.

Observing the planets with an excellent C8 or C9.25, i've found in average seeing around x200 to be the limit.

on odd steady nights i've used the C8 at over x300 on saturn.

the Tak 128 apo i have will take higher mags much better and is less affected by the high level turbulence cells.

I recently reluctantly sold my Tak 9 inch sct, a fantastic scope, because it was constantly hampered by the average seeing.

I've used 4 inch refractors at x150 in the past quite regularly for planets and lunar.

Jupiter for example does not take high mags as well as saturn or mars, so the object itself can dictate the max powers used.

sometimes you have to decide if its worth having a scope that can only really perform several nights a year.

of course when that very elusive great night comes along, then magnification may be taken to and maybe beyond the 50x limit.

I have found many times that the lowest power that shows the detail visible is the best, beyond that you simply increase the image scale.

Mike

[mik]

The general concensus of opinion in the past, is that anything over 300x is pretty useless, regardless of scope EP etc, and then only under good seeing and steady skies. There will, of course, always be exceptions to prove the rule....

I have to agree here but ive never got that high.

Mick.

[mik]

The biggest single limiting factor is the seeing. The 50x aperture guide is fine, seeing permitting and quality of optics.

other factors such as tube currents and cooldown come into play.

Observing the planets with an excellent C8 or C9.25, i've found in average seeing around x200 to be the limit.

on odd steady nights i've used the C8 at over x300 on saturn.

the Tak 128 apo i have will take higher mags much better and is less affected by the high level turbulence cells.

I recently reluctantly sold my Tak 9 inch sct, a fantastic scope, because it was constantly hampered by the average seeing.

I've used 4 inch refractors at x150 in the past quite regularly for planets and lunar.

Jupiter for example does not take high mags as well as saturn or mars, so the object itself can dictate the max powers used.

sometimes you have to decide if its worth having a scope that can only really perform several nights a year.

of course when that very elusive great night comes along, then magnification may be taken to and maybe beyond the 50x limit.

I have found many times that the lowest power that shows the detail visible is the best, beyond that you simply increase the image scale.

Mike

Interesting Mike thanks for sharing you experience, ive found with my ZS66 80x to be great but 100x is not that much of an improvement, the apo versions of this scope may give a slightly better image than my older Achro model, also above 100x CA starts to creep in.

I am looking to update next year not to a bigger scope but to a better quality optic looking at the Megrez 72 have to see how next years bonus goes, eyepieces to get first.

Regards Mick.