Controversy in highest usefull magnification

[paulastro]

14 hours ago, mikeDnight said:

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.

A good thought provoking post Mike. It's interesting to read the responses to it with some people clearly not sharing your views on the use of higher magnification.  I seldom usefully use mags of up to x800, but I have done so, and might again in the future. 

However, unlike some,  I am willing to accept that it's possible that some observers may have a better observing eye than I have, they may be a better observer than I am and even use better optics, and many are even better artists than me 😁.  I have no trouble though in admiting that just because I dont do something - someone else maybe able to do it.

Anyway Mike, you are in good company.  People questioned the great William Herschel when he claimed, correctly, that he had used powers of over x1000 !  

Mike is quite right that we shouldn't be limited by the myths of observing propagated by people being afraid to push the boundaries.

 

 

Edited May 17, 2020 by paulastro

[mikeDnight]

I'm just trying to imagine the expressions on the faces of those happy apo customers, as the vendor takes their money and then informs them "Remember to use only 1X per mm then"! I'm sure they'ed laugh all the way home!   

 

[paulastro]

Blimey, I hope I havent damaged my SW 80ED, l used over x200 on Venus a couple of days ago !?  😫

[Ags]

20 hours ago, Peter Drew said:

no way would I ever be able to use 50 x 30 = 1500x

Have you tried? Don't knock it till you've tried it! 😂

[andrew s]

Does anyone really care? Apart from the odd visual variable star estimate visual observation have long been discredited as too prone to oberver expectations for serious , ,scientific work.

That has freed it to be a pleasurable pursuit,  a do as you want , disregard what you will hobby. I am not being down on visual astronomy as the same applies to most imaging. 

The aim is to have an enjoyable time and a pleasurable outcome. Magnify as little or as much as you will.

Regards Andrew 

[johninderby]

Been interesting reading all the comments pro and con fir high magnification.

Just shows that there are no fixed rules but there are some general things that affect how much magnification can be used. Namely what are you looking at and good is the seeing and what scope / eyepiece are you using etc. It seems no two nights are the same. Sometimes you can crank up the magnification and the next night you can’t use too,high magnification.

What rules. 😁😁😁😁😁

 

Edited May 17, 2020 by johninderby

[DaveS]

I think J B Sidgwick gave a rule of thumb figure of 144 x sqrt D".

[JeremyS]

11 minutes ago, DaveS said:

I think J B Sidgwick gave a rule of thumb figure of 144 x sqrt D".

He might well have done, although it looks over precise for the reasons discussed above. Sidgwick's 2 books were my Bibles when I was young. Until I read this in his bio in the BAA Journal:

Dr WH Steavenson made a pointed comment concerning these two books……they were “remarkable for the fact that they must both have been written largely from an armchair”….it is clear that the amount of telescopic work he did himself could at best have been fairly limited. The fact that he was relatively inexperienced as an observer is occasionally apparent in his writings.

In my book, practical experience is what counts.

[Highburymark]

1 hour ago, mikeDnight said:

I'm just trying to imagine the expressions on the faces of those happy apo customers, as the vendor takes their money and then informs them "Remember to use only 1X per mm then"! I'm sure they'ed laugh all the way home!   

 

Just to prove that not all Takahashis are cut from the same cloth Mike, the highest magnification I tend to use with my Epsilon 130d is a smidgeon under 16x. Panoptic 27mm, at 0.12x per mm. Normally less than that with 32, 40 and 55mm plossls - the latter producing a dizzying 8x.
 

 

[andrew s]

9 minutes ago, Highburymark said:

Just to prove that not all Takahashis are cut from the same cloth Mike, the highest magnification I tend to use with my Epsilon 130d is a smidgeon under 16x. Panoptic 27mm, at 0.12x per mm. Normally less than that with 32, 40 and 55mm plossls - the latter producing a dizzying 8x.
 

 

Do you have to look last the central obstruction?  It's  shadow in the exit pupil will be significant!

Regards Andrew 

[Stu]

15 minutes ago, Highburymark said:

Just to prove that not all Takahashis are cut from the same cloth Mike, the highest magnification I tend to use with my Epsilon 130d is a smidgeon under 16x. Panoptic 27mm, at 0.12x per mm. Normally less than that with 32, 40 and 55mm plossls - the latter producing a dizzying 8x.
 

 

I think we know why though Mark! Black magic at work!! 😉

[Mr Spock]

The best view I had of Saturn (while it was still high in the sky) was with a 140mm Mak at x313 (Meade 6.4mm Plössl). It's a view I'll never forget.

[Highburymark]

21 minutes ago, andrew s said:

Do you have to look last the central obstruction?  It's  shadow in the exit pupil will be significant!

Regards Andrew 

 

18 minutes ago, Stu said:

I think we know why though Mark! Black magic at work!! 😉

Yep - it’s with a night vision monocular as you noted Stu. Also means there is no problem with the central obstruction. But it provides an insight into the opposite end of the astronomy scale - some wonderful large objects up there (as those lucky enough to have dark skies and a pair of binoculars already know!).

[Peter Drew]

Most other things being equal, seeing is the most levelling aspect.  I have a good C8 in Tenerife where the seeing is often excellent.  During the last close opposition of Mars I was able to use 600x with a decent image though 400x was slightly better and enough.  400x on the Moon was routine.  If I brought the C8 back to the UK I bet those magnifications would be halved.         🙂

[paulastro]

45 minutes ago, Peter Drew said:

Most other things being equal, seeing is the most levelling aspect.  I have a good C8 in Tenerife where the seeing is often excellent.  During the last close opposition of Mars I was able to use 600x with a decent image though 400x was slightly better and enough.  400x on the Moon was routine.  If I brought the C8 back to the UK I bet those magnifications would be halved.         🙂

I agree that seeing can be a leveler of course Peter, bit its not the whole story.  At the extremes it is, if the seeing is so bad you cant see any on belts on Jupiter with any scope they will all be useless for planetary on such a night.  But in my view, it's not true to say that 'most other things being equal' applies on nights when seeing is not so extreme.

On less extreme nights other things do come into play.  Things like; the quality of optics, the observers eyesight, the observers experience and many other factors will all have an effect. Even in the best seeing, what mags can be used, and what can be observed by different observers is still affected by the same things - all be it to a lesser degree.

Other than at the extremes of seeing, the observers experience/ability and the quality of optics are the two factors I would say mostly influences  what magnifications can be usefully employed - and of course what can actually be observed.

 

[Peter Drew]

4 minutes ago, paulastro said:

I agree that seeing can be a leveler of course Peter, bit its not the whole story.  At the extremes it is, if the seeing is so bad you cant see any on belts on Jupiter with any scope they will all be useless for planetary on such a night.  But in my view, it's not true to say that 'most other things being equal' applies on nights when seeing is not so extreme.

On less extreme nights other things do come into play.  Things like; the quality of optics, the observers eyesight, the observers experience and many other factors will all have an effect. Even in the best seeing, what mags can be used, and what can be observed by different observers is still affected by the same things - all be it to a lesser degree.

Other than at the extremes of seeing, the observers experience/ability and the quality of optics are the two factors I would say mostly influences  what magnifications can be usefully employed - and of course what can actually be observed.

 

I think that's what I intended to imply Paul, if all else is equal then seeing is the final deciding factor.     🙂

[John]

Smaller aperture, quality optics, seem to be able to do a better job in cutting through the seeing than larger ones.

 

 

[JeremyS]

6 minutes ago, John said:

Smaller aperture, quality optics, seem to be able to do a better job in cutting through the seeing than larger ones.

 

 

That's what I figured, John

🙂

 

[paulastro]

Thanks Peter, I think you are right, I hadn't grasped what you were saying 🙂. I put it down to not being able to come up and see you at TAC for so long 😁.

[mikeDnight]

So because of UK seeing being rarely anything special, the true power of the smaller aperture really comes into play.  Larger apertures are affected to a much greater degree by atmospheric turbulence than smaller apertures, so a small scope can show apparently perfect seeing while the larger aperture alongside it on the same night displays an image that is pure vomit. Couple that with the superb optics of many apo refractors (not just Tak!), and you have a formidable instrument that will often leave larger scopes standing when it comes to sharp high power views. If a scope can't form a sharp stable image because of the seeing conditions, there's little point in amplifying that already poor image. If on the otherhand the image is sharp at 200X,  there is no reason why that image cannot be magnified still further, and the better the optics, the greater the potential power range.

As for visual observations having "long been discredited as being too prone to observer expectations and therefore of no scientific value",  well that comes from the micro minds both in our hobby and in science. Of course over-cooking the reality in the the endless barrage of taxidermied images we're relentlessly subjected to, is very scientific and totally trustworthy!  Personally I'd rather trust the observational sketches of an experienced visual observer as giving a truthful representation of what can be seen through an eyepiece, than any image I've ever seen. After all, if you want to really observe something well, you really need to pick up a pencil!

[paulastro]

30 minutes ago, John said:

Smaller aperture, quality optics, seem to be able to do a better job in cutting through the seeing than larger ones.

 

 

Of course you are right John.  Where I live, it wouldn't be much use having any scope bigger than 6 inches for planetary most of the time.  I sometimes use my 80mm when even the 120 is too much for the seeing. Of course this could explain why Mike does so well, only using a 3.9 inch 🤣

Edited May 17, 2020 by paulastro

[Supernova74]

Come on guys keep it clean now or shall I post a topic who,s got the bigger scope it’s what you do with it that counts!?😉

[Paz]

With regard to scope size and magnification about 1x-1.5x aperture or thereabouts is as high as I usually go with smaller scopes up to 127mm and usually 0.75x-1x aperture for my VX14. Thats not to say those are maximums, just that they are as high as I usually go in practice. I will go higher when conditions are very good and I have properly cooled my scope but that isn't so often.

[andrew s]

13 hours ago, JeremyS said:

That's what I figured, John

🙂

 

Which way round do you use it?

Regards Andrew 

[Rusted]

For nearly two decades I was limited to an average of 120x on my 150/8 Celestron refractor.
I couldn't ever see any detail in Jupiter's belts though Saturn was much better and Mars less so.
The scope lived in an unheated shed so cooling wasn't a factor.

Saturn was "orbiting spaceship" razor sharp, when high on one particular, cold night with an inversion layer and snow on the ground.
Though Jupiter remained frustratingly fuzzy and "boring" on the same night. Which of them proved the telescope could be razor sharp?

Swapping to a 180/12 iStar and putting it in a second floor wooden observatory literally doubled my average viewing power overnight.

Telescope or seeing? I think I just lifted myself off the ground where the awful seeing was concentrated around my pier.
Even when  I kept moving it to different bits of the garden to see between the trees and high hedges.

Those who suffer consistently from awful seeing might do worse than building a simple, raised wooden platform or raised ROR.
Domes have their own problems depending on materials and colour.

My supposedly poor 150/8 performed very well on the sun in H-alpha at high magnifications. 
Yet I was never very aware of its f/8 chromatic handicap.  The Fringe Killer was always optional.

The iStar 6" f/10 H-a which finally replaced it can capture Plato craterlets and did very well on a crescent Venus at first try.

My 10" f/8 premium mirror [even badly collimated] Newt trashed them all. Even down on the ground.

I read somewhere, probably 50 years ago, that the average UK seeing is in 10" deep layers.
Which is why it affects larger apertures because the seeing varies across the aperture.
So the optical precision of the larger optic is lowered in comparison with a smaller one.

There are no fixed rules. Only local conditions, instruments and observers.
Being rural detached and surrounded in fields is no guarantee of good seeing. 
Ask me how I know?