Controversy in highest usefull magnification

[Supernova74]

Hi all hope you are all keeping safe and are well at moment and not killing each other in the lock down.

the topic of choice this evening is lowest and highest use full magnification and obviously this goes down to a number of factors mainly seeing conditions firstly as we all know is king in a good nights observing session and make and break nights on occasion and I’m mainly talking about for visual observing.from personal experience some scopes do seem to handle more powerful magnification then other telescope designs ie a good APO refractor and another good performer is a maksutov cassagrain as offer very high quality optics with nice sharp images and seems more forgiving on higher power per inch of aperture and general rule of thumb is roughly 40-50x per inch of your scope so anything with a lens in theory should perform better anyway wouldn’t it be nice to have an 10-12” APO APM springs to mind yes sell the house a kidney and an arm and a leg.when I initially brought my Meade 12” ACF from a certain well known dealer lol not flo and maybe a few others at that point in time when I decided to purchase and when I was nearer the time in deciding my eyepiece collection which consisted of an ES 40mm 68 degrees,ES 24mm 82degree ES 16mm 68 degree followed by an ES 2” Barlow lens above average eyepieces regarding price and quality!? I was told not over power the scopes usefull power which was in between 200-300x so I was told as the lower focal length eyepiece will hardly be used due to seeing conditions which in most part I do agree with.however in similar terminology it’s kind of having a Ferrari and only able to 60mph in if you got it why not try and use it yes to a certain degree in seeing conditions like I said is key to use the lower focal length eyepieces to there advantage and in some cases in what I’ve been told anyway can be a bit of a myth really as for exsample last year I was viewing Jupiter and Saturn and even low In the meridian at moment decided to put in my diagonal an Televue 10mm Delos with focal length of my scope 3045mm which gave me a shade over 300x so was that the limit I believe not as when a scope is well collomated and high quality eyepieces I could definitely gone further to 400x and still of managed a half decent observable image with out sacrificing light gathering power also then again just recently last month I was observing the moon 🌓 close to full phase and decided to go up a notch or two was a half decent night regarding sky conditions and moon reasonably high very little atmospheric turbulence initially around 70x gradually worked my way up untill I went for it and said to myself not expect to much and then decided to put the 10mm Delos in diagonal and ES 2” Barlow this was at over 600x to my amazement the image was very observable even tho turbulence was evident at this power it was like I could touch that mountain ridges and craters on the moon just shows really what potential of thease scopes can bring and if I never decided to ignore the advice given to me just may not of tried and doubled the viewing experience even tho image quality was,nt tack sharp it was well worth it 

[johninderby]

Worth reading these articles.

https://starizona.com/tutorial/understanding-magnification/

https://starizona.com/tutorial/observing-theory

The moon is a special case as it can be so bright that you can exceed the magnification normaly possible in other observing. As magnification goes up the image darkens so the brightness of what you are observing has a big effect on the maximum magnification. Then of course there is the matter of how good the seeing is. 

 

Edited May 16, 2020 by johninderby

[Peter Drew]

50x per inch of aperture really only works well for small apertures and good quality ones at that.  I have a 30" Dob and no way would I ever be able to use 50 x 30 = 1500x.

Seeing in the UK generally sets an upper limit to about 400x regardless of the telescope type or aperture and then mainly for the Moon, close double stars and perhaps Mars when well placed.    🙂

 

[miguel87]

As above. I think up to about 4 or 6 inches the 50x/inch rule is about right. Above that is more limited by conditions to somewhere between 250x and 350x in my experience.

Sometimes you CAN zoom in more and get an image but it often isnt worth it as no detail is gained and brightness is lost.

My current scope and eyepiece setup tops out at 333x and I never feel the need for more. It is very rare that I end up viewing at 333x for more than a minute or 2.

This mostly relates to my experience with an 8 inch scope.

✌

[dweller25]

I think I read somewhere that the optimum magnification of a telescope is it’s diameter in mm x 1.1, above that no more detail can be seen.

Having said that I have used my 128mm scope at x280 on Mars when it was high 😁

[niallk]

In my 15" f4.5 dob I use 330x often on planets on good nights - this was when they had a bit more altitude 😂  - and when the jetsream plays ball (based in Ireland).  I will always check the jetstream forecast before setting up to  observe.

I've had 560x on Jupiter with the image holding up nicely on an exceptional night, but backing off to 420x was an overall better compromise vs the speed at which the planet traversed the fov (manually tracking).

[mikeDnight]

I think resolution limit and magnification limit can get confused. It may be true that 50X per inch is the resolution limit, but if the object being studied is small, it may require a higher magnification to be able to see it well. Much depends on the stability of the atmosphere, the quality of the optics, the object being studied and the stability of the mount.  Jupiter and Saturn tend to be best observed between 150X and 250X as much beyond this and the intricate detail softens, and so definition suffers. Planet's that display albedo features such as Mercury, Venus and Mars can take significantly higher magnifications, but even then the power used should be tuned to the seeing. The Moon takes magnification well, but although the mountains and craters may look awesome, once the finer features such as rille's lose definition there's little advantage to going higher other than for fun.  Stars are something else, as these can take extreme power. For example, in my 100mm refractor, which has a theoretical maximum power of 200X, I can happily and very effectively exceed that limit.  Observing Izar only a couple of nights ago i was using 500X and the image was perfect.  I regularly observe Venus at 335X and even well beyond this. Just recently I studied the north cusp of Venus at the rediculous power of 800X in my 100mm refractor and other than a little undulation of the atmosphere, the image remained sharp and contrasty.

Was there any advantage to observing Venus at such high power? Not really, but it was fun, and I had to keep checking the eyepiece to make sure I wasn't mistaken, because the image was so good.  The view at 400X showed all the same detail, but even at 400X my scope was well over its theoretical limit.  Planet's do dim but they have plenty of light, so there's little to lose by experimenting. Stars are fantastic and just get better at high power. I think to keep a good scope restrained because of some theoretical limit is a shame. Only by really pushing your scope will you ever come to understand its full potential.

Edited May 16, 2020 by mikeDnight

[andrew s]

If you make the exit pupi too small on a bright object you can see shadows of structures in your eye. This probably what P Lovell did when "seeing" linear features on Mars .

Regards Andrew 

[johninderby]

I have noticed that the more experienced the observer the lower the magnification they seem to use. 🤔

[Mr Spock]

2 minutes ago, johninderby said:

I have noticed that the more experienced the observer the lower the magnification they seem to use.

I'd like to think after 50 years observing I qualify for that!

I have found that the best compromise between detail and contrast comes at x1 per mm. Anything above that is 'empty' magnification, so, larger image but no more detail. So, in my C9.25, x235 is ideal. It also fits in with UK observing conditions which rarely offer seeing good enough for higher powers regardless of scope size. Small and sharp is better than big and blurred 

I do occasionally view the moon at x294, and double stars at x392, but they are exceptions.

[Stu]

20 minutes ago, Mr Spock said:

I'd like to think after 50 years observing I qualify for that!

I have found that the best compromise between detail and contrast comes at x1 per mm. Anything above that is 'empty' magnification, so, larger image but no more detail. So, in my C9.25, x235 is ideal. It also fits in with UK observing conditions which rarely offer seeing good enough for higher powers regardless of scope size. Small and sharp is better than big and blurred 

I do occasionally view the moon at x294, and double stars at x392, but they are exceptions.

I think that works for larger scopes like the C925 Michael, but if you apply that formula to a 100mm apo frac you would only ever use x100 and would miss a huge area of capability of the scope. Whilst I don’t use crazy high powers in my 4” scopes, I do use up to x300 to good effect in the Vixen Fluorite, and even used x280 in the Telementor the other day which was crazy but gave me some very nice splits on doubles. The Moon and doubles can take a lot of power, planets are more fickle as we know, depending on altitude, seeing etc.

Not sure about @johninderbycomment. It’s a case of knowing when to use high mag and when not to depending on the target and conditions. If the conditions are good, and adding power is giving you a view which helps your observing then do it. If the image is breaking down or you lose visibility in low contrast areas, back off the power. That’s where experience comes in I think.

[johninderby]

Optimum magnification is the thing. Not too much and not too little.

[John]

I guess we will have to stop advising newbies that very high magnification is not going to bring any benefits ?

But then again, with entry level scopes and inexperienced eyes, perhaps that is still sound advice ?

 

[miguel87]

23 minutes ago, John said:

I guess we will have to stop advising newbies that very high magnification is not going to bring any benefits ?

But then again, with entry level scopes and inexperienced eyes, perhaps that is still sound advice ?

 

Yeah, I remember with my very first telescope, plastic, terrible 60mm frac. The realisation that stuff doesnt just stay nice and still to be observed!

It wobbles, jumps, moves out of frame, gets knocked out of frame, gets knocked by my eye, won't focus etc etc.

That's why you begin to understand the challenges of high mag. And yes, equipment and experience improve this massively.

I take my hat off to Mike and his 800x mag on Venus. But I think this should be considered the exception and not the rule. I can't imagine how unsteady and blurry that would look on my eq5 mount with modest eyepieces.

I reckon if you averaged everybody's comments we are looking at about 300x maximum useful.

✌

[Supernova74]

Thank you guys mixed opinions I can see from my experience to an certain degree it can be a bit of tricky subject what monkey do what monkey does so to speak without coming across rude of course as that not my intentions here I’m no means an expert in Controversy of the maximum usefull magnification as every one on this topic has a different opinions and yet mainly we all know that good seeing conditions is key here for any scope and is not set rules only guide lines we have learnt from one another I’ve seen some lovely views of Saturn and the moon at 400x no distorted image and still very observable it’s kind of the terminology again for exsample no harm in trying and that Angler will never catch that large carp as he didn’t think outside the box and try a new bait!? Al nagler once said he had the best views of Jupiter once at 400x and was through an 3” Televue and if your observing a planet it’s just a question of waiting for the atmospheric turbulence to die down and think you will be plesently surprised is a waiting game but not impossible 

[Stu]

I think this forum has changed over the years. There used to be a time where anyone suggesting using over x250 was considered as if they didn’t know what they were talking about.

I think that has definitely changed now, and people understand that when conditions allow, and on the right target, much higher magnifications can be useful. Even if they don’t add any more detail, if the image quality holds up they allow your eye to perceive the detail more easily.

As I said before, if I had stuck to the advice of 1mm exit pupil, I would have long since given up on apo refractors and would have missed out on a huge amount of enjoyment and observing achievement.

[JeremyS]

9 minutes ago, Stu said:

I think this forum has changed over the years. There used to be a time where anyone suggesting using over x250 was considered as if they didn’t know what they were talking about.

I think that has definitely changed now, and people understand that when conditions allow, and on the right target, much higher magnifications can be useful. Even if they don’t add any more detail, if the image quality holds up they allow your eye to perceive the detail more easily.

As I said before, if I had stuck to the advice of 1mm exit pupil, I would have long since given up on apo refractors and would have missed out on a huge amount of enjoyment and observing achievement.

I think another consideration is the wider availability in recent years of top notch telescope optics AND top notch eyepieces, such as the Vixen HR range, that are comfortable to use, whilst being optically impeccable.

Oh, and the freedom to ignore accepted wisdom about what's possible and what isn't, but simply to give it a try 🙂

A few years ago I wouldn't have considered trying a 2.4 mm eyepiece in a small telescope, let alone a 2.0 mm  or 1.6 mm!!

 

[mikeDnight]

There will always be the doubters who doubt because they haven't experienced high powers successfully as yet. And there will always be the ridiculers, who have minds set in stone, - old fossils who will repeatedly voice outdated and inaccurate views, perpetuating old myths and wanting to stop those moving ahead from advancing any further. The best thing to do with the first group is to offer them encouragement or an opportunity to see for themselves. As for the latter, they are best ignored!   

[Guest]

16 hours ago, miguel87 said:

As above. I think up to about 4 or 6 inches the 50x/inch rule is about right. Above that is more limited by conditions to somewhere between 250x and 350x in my experience.

Sometimes you CAN zoom in more and get an image but it often isnt worth it as no detail is gained and brightness is lost.

My current scope and eyepiece setup tops out at 333x and I never feel the need for more. It is very rare that I end up viewing at 333x for more than a minute or 2.

This mostly relates to my experience with an 8 inch scope.

✌

I'm guessing a 3.6mm EP?

[Guest]

I used to have a 14 inch SW dob and I often used it with their 7mm UWA eyepiece. That would give me a magnification of 235 which I found very comfortable when looking at the moon or Jupiter. I'm 68 and my eyes are not brilliant and I found the high magnification useful.  Sometimes when you watched say Jupiter it would shimmy about with the atmosphere but every now and again there'd be a second or two of brilliant clarity, same with the moon. Just sit there and look.

Cheers

Steve

 

[Guest]

I'm guessing as the quality of the optics has improved, this allows the envelope to be pushed more...

[miguel87]

26 minutes ago, merlin100 said:

I'm guessing a 3.6mm EP?

A barlowed 6mm Vixen SLV gets me 333x in my 200p EQ 👍

[AdeKing]

I regularly use a Televue 3-6mm Zoom in my ED100 and ED120 which gives mags of 150x (6mm), 180x (5mm) 225x (4mm) and 300x (3mm).

When I got this EP, I considered it an itch that I needed to scratch and in all honesty thought that it would see little use, but the opposite is true, it's a permanent fixture in my eyepiece case.

I regularly use the 3mm (300x) setting on the moon and for double stars, but have had success recently using it on Venus early in the evening before it gets dark.

A few years ago, I'd not have gone above 200x with the ED100 but reading posts here on SGL encouraged me to try it on and I'm glad that I did.

[Supernova74]

Thank you guys for some positive feed back from my post.if the god father of Televue al nagler who most probably makes the best eyepieces of this world today who am I to argue in viewing Jupiter like I stated in my last reply viewing Jupiter through an 3” Televue at 400x best views he ever had  I’m an old school visual observer with an modern twist and going by the general rule of roughly 40x,50x per inch is a rough guide only and generally a rule of thumb and lets face it we never know it all that’s the beauty and passion of the hobby and lets face it some folk in this day and age can be stuck in there ways and that’s why thay will not catch the biggest fish!??exsample ronseal  paint products states it does what its suppost to do on the tin however that’s not the complete truth in our Astro gear we use. For instance I’m not comparing a department store telescope as we all most probably purchased at some point when we’re younger and had a fancy picture on the side of box with a lovely blown up pictures of the planets and galaxies,nebula etc and left often feeling very disappointed ☹️ (sorry John mainly tasco) and had ridiculous claims of 500x 600x magnification that was just a fabrication of the truth and let’s face it if the true magnification limit In general terms in the uk was around 200-300x sorry that’s just a myth in my eyes as let’s face it why are we spending ridiculous sums of money and buying the best optics money can buy  if we just heard information ie on the internet or some other source.as for we thought that way mankind would never push the envelope of the true Potential of the quality telescopes of today

[Supernova74]

Lol meant topic