How often can you use magnifications of280x and 370x in a 10"scope?

[Astrodob]

I wanted to know this so I'll know what focal length eyepiece I should buy.

Thanx,Astrodob

[NGC 1502]

With my 10" Dob, I very rarely use magnifications that high.   At the moment my most used eyepieces are a 24mm and a 9mm for 50x and 133x.

Sometimes on a good night 150 - 200x is useful for planets, splitting double stars, and small deep sky objects.

Very occasionally 240x and above for splitting very close double stars, and exceptionally steady nights for the planets.

I had a good session last night and just used my 24mm and 9mm eyepieces, one in the focuser the other in my pocket.

Others may have different findings.  My motto for what it's worth - smaller and sharper trumps bigger and fuzzier.

Regards, Ed.

[Moonshane]

It depends on several things:
Target objects
collimation
seeing
patience
experience
Optical quality

E.g I observe double stars and moon and regularly use such magnification
When I observe planets and dsos I rarely do.

It is worth having highest mags for your scope for those occasions when you can use them but a raci finder, red dot finder, star map, observing chair, red torch and more regular quality pieces would come first for me

[ronin]

Probably a fair few but the period you could use 300x and above may be 3:30 in the morning when thermals etc have reduced.

So how many days do you intend to set the alarm for 3:00 then get up set up scope and find out?

That would be a chance to use that magnification, however I suspect 99.99% will never take it, and so you say no chance.

The missing "constraints" on your question are how many times at a convenient 9:00 PM or 10:00 PM can you use that magnification. As the atmosphere may not have stabilised then the number are much reduced.

It is rather like how many nights are clear enough to observe - do you count a 2 hour period from 2:30 to 4:30 AM.

Most will not have made use of it as they have work and are fast asleep, so people say no chance to observe last night, but there was.

If you want to get eyepieces for useful magnifications then stick to 150x and 180x.

I suspect that only for viewing Mars will more then that actually be of any use.

And trying to view Mars leads to dispair and maddness, quite rapidly. :BangHead:

[RikM]

I don't really observe the moon or double stars. I will look at planets if they are about but that is not my main area of interest either. I also have a 10" Dob and very rarely use more than 240x. I have 300x and 342x available but use those powers maybe two or three times per year. My most commonly used high magnifications are 171x and 240x.

[timwetherell]

I use 200 to 300x pretty regularly on planets with my 7" refractor from a suburban site. Though if they're low in the sky or the seeing is bad that would be hopelessly excessive. I find the moon and doubles will sometimes take a little more. personally i like to have enough eyepieces to go too far then come back so I know I'm viewing at the top of what the seeing will allow. 

[Paul73]

Re re 10" Dob element.

150x is about the top of "normal" seeing for me in my 5.5mag UK back garden (unaided visual limit).

Sure you can use more on the moon so worth having something in the box, but if budget is normal, I would invest most heavily in the 8 to 16mm range.

I'm pretty happy with this selection for the 10" 1200mm f4.7 scope:

Vixen SLV 5mm @ x250 (yet to buy)

Vixen SLV 5mm @ x200

TV Delos 8mm @ x150

TV Delos 12mm @ x100

MaxVision 16mm @ x75

MaxVision 20mm @ x60

MaxVision 24mm @ x50

ES 82° 30mm @ x40 (yet to buy)

If you want to spend a bit less. Bin the MV24 & ES and just get the 28mm MV, swap in the BST Starguiders for the Delos offerings at 1/5 of the price and loose the 5mm Vixen.

Hope that this helps.

Paul

[Laurie61]

I tend to find I can use 200-250 x quite often, nights that allow much more then this are few per year. There is another way to look at this which is how much mag do I need to see all detail my scope can produce. This is a function of eye and scope working together, as increasing mag dims the image and reduces contrast too much mag is counter-productive  So ideally we want to reach the magnification level where all resolution is shown and no more.  Below is a graph I found which shows ideal mag for a range of apertures.  As you can see a 10" scopes optimum high mag is around 325 X 

 

[Mr Spock]

For planets I tend to favour x235 in the C9.25. For the moon and doubles I can use x294, x336 and x392 when seeing permits.

[John]

That chart is interesting but seems over optimistic to me given the "real world" situations we observe in, or at least I seem to observe under.

My 12" dob delivers it's best planetary performance at around 250x - 320x rather than the 400x indicated above. I have used 400+ magnification on the Moon and binary stars but on Jupiter, Saturn and Mars I found the former range delivered the optimum sharpness, contrast and detail.

I guess these figures will vary depending on the observers location and conditions, the latter can vary from hour to hour too.

[RikM]

As a chart of maximum magnification I think it is okay. I have used 342x and it has been fine, but only about three times in the past two years. About 1x per mm of aperture seems to be the realistic maximum on an average night based on 4.5 years observing experience with 6 different telescopes.

[Laurie61]

That chart is interesting but seems over optimistic to me given the "real world" situations we observe in, or at least I seem to observe under.

My 12" dob delivers it's best planetary performance at around 250x - 320x rather than the 400x indicated above. I have used 400+ magnification on the Moon and binary stars but on Jupiter, Saturn and Mars I found the former range delivered the optimum sharpness, contrast and detail.

I guess these figures will vary depending on the observers location and conditions, the latter can vary from hour to hour too.

Yes, the chart ignores seeing and other variables like cool down and collimation so it's really giving a figure you can work up to, with bigger scopes, on those few very good nights.  

[timwetherell]

That chart is interesting but seems over optimistic to me given the "real world" situations we observe in, or at least I seem to observe under.

My 12" dob delivers it's best planetary performance at around 250x - 320x rather than the 400x indicated above. I have used 400+ magnification on the Moon and binary stars but on Jupiter, Saturn and Mars I found the former range delivered the optimum sharpness, contrast and detail.

I guess these figures will vary depending on the observers location and conditions, the latter can vary from hour to hour too.

I guess that's what the horizontal seeing lines are supposed to represent and with a big scope like yours, you'd need sub arc second seeing to really open the throttle to its full potential. It must to some extent depend on one's eyes too. Personally I like a slightly larger image scale so would exceed that chart by 20 or 30%

[John]

I guess that's what the horizontal seeing lines are supposed to represent and with a big scope like yours, you'd need sub arc second seeing to really open the throttle to its full potential. It must to some extent depend on one's eyes too. Personally I like a slightly larger image scale so would exceed that chart by 20 or 30%

I like a large image scale but I also like sharpness and contrast. I tend to add power until I start to loose the latter then ease off a bit

I've had a few nights when everything came right conditions-wise and I could just keep stacking up the power. I seem to recall even 600x being sharp on the lunar landscape on one such night with tiny craters in Plato popping out all over it's floor 

[Astrodob]

So should i go with an eyepiece of a focal length of 6.7 or 11mm (there are under 6.7,but that is a bit too small for me to look through).I have to choose.Do I buy a ES 82 degree 6.7mm or 11mm. So 230x with a 2x barlow and with a 1,5x barlow and get a magnification of 170xusing a 11mm and 115x without or i go for the 6.7 and get a magnification of 180x and 280x with a 1,5x barlow and 370x with a 2x barlow. (these are quick calculations in my mind so there not so precise the focal length of my scope is 1270).

[acey]

With a 10" dob you will probably get the best "general purpose" views at a magnification of about 85, i.e. an exit pupil of 3mm. Since your scope is f5 then this would be a 15mm eyepiece. Go for a good quality one of those (e.g. TeleVue plossl). Or else do what everyone does - get a ridiculously high-power eyepiece and find you never use it.

In general, don't think magnification, think exit pupil. Decide what exit pupil you want, multiply that by the f-number of your scope (in your case 5), and this tells you what focal-length eyepiece you need. Bigger exit pupils will offer low-power wide-field views, but you don't want it to be any larger than your actual pupil, otherwise the light won't all be able to get into your eye. Small exit pupil means high-power viewing, but anything less than 1mm is on the small side, and 0.5mm is traditionally thought to be the limit of "highest useable magnification" (equivalent to  2 times aperture in mm, or about 50 times aperture in inches). In your case that would be a 2.5mm eyepiece. But with a very small exit pupil you may be troubled by floaters, or general bluriness. Look through a pinhole half a millimetre across in daylight and you'll see what I mean. And that's before we consider the effect of the atmosphere or imperfect scope optics at high power.

A fully dilated adult pupil can be anywhere from 5 to 8mm (it gets smaller as we age). So you're generally looking at exit pupils in the range of about 1 to 6 mm, and for an f5 scope that means eyepieces in the range of about 5-30mm, bigger or smaller if your eye can handle it (and everyone's eye is different). My scope (a 12") is f4.9 and the exit pupil range of my eyepieces is 0.8 to 6.5mm, though the vast majority of my viewing is in the exit pupil range 1.6 to 4.9mm (provided by a Baader Hyperion 8-24mm zoom). If you used that zoom in your scope you would get approximately the same exit pupil range (because 4.9 is very close to 5) and feel much the same "viewing comfort" (if your eyes are anything like mine), but you'd be seeing everything at lower magnification, because your 10" has a shorter focal length than my 12". My top magnification is x375 and I do use that on DSOs (tiny faint galaxies at a very dark site) that I wouldn't be able to see otherwise. But for you to reach that magnification on your 10" would require a 3.4mm eyepiece giving exit pupil 0.68mm, which you may find too small to be useable.

It has been shown that visual acuity at low light levels is greatest for a pupil size of about 3mm. So if you're only going to get one eyepiece, get one that's 3 times your f-number, i.e. 15mm, and develop your eyepiece collection gradually from there.

Or get a quality zoom.

Or do what everyone else does.....

[Astrodob]

I have a 16mm Maxvision...

Meade series 4000 26 mm eyepiece i need a high power eyepiece so i think i should go for the ES82 11mm and barlow it or a 6,7mm and i won't barlow it the exit pupil will be ok i think ill go for the without barlow choice getting me a power of 180x which is ok,but a bit pathetic for a 10"scope,but I can use it ofthen,unlike the barlowed 11mm where I get a magnification of 230x which is not usable all the time therefore I think going for the 6,7mm won't be a mistake.

[RikM]

I can happily second that. My 'most used' eyepiece is a 14mm 70deg aFOV that gives me 86x magnification and a 3mm exit pupil.

[Astrodob]

1,36mm exit pupil is that bad?

[RikM]

1.36mm exit pupil should be fine.

[Astrodob]

Thanx RikM I'll still think about it,but I think I'll go for the 6,7mm