4.7mm fl too much??

[-Aldebaran-]

Looking at purchasing a higher power e'p for better detail on planets/moon. Tube focal length is 1200mm and I don't wear glasses,The Ep in question is the ES 82° 4.7mm, my main concern is throwing money away if I can't use it that often due to poor seeing, especially where Big Gassy is concerned! Should I play safe and opt for the 6.7 or even 8.8mm?

[jabeoo1]

I personally find x255 the extreame end of regular seeing conditions here in the UK.   The x200 mark is where most of it happens for me, saying that though last year when Saturn was at its highest placement I squeezed x266 with rewarding results, but i no longer have that 6mm eyepiece and opted one step down to 7.5mm @ x213 and an 8mm giving x200.  The focal length of my scope is 1600mm @ f/6.3.

A used 6mm TV radian would give excellent price/usefulness ratio in your scope, the field of view would give a nice drift to nudge rate to allow good time to concentrate on the view.  It may well end up glued in the focusser like a Tetris cartridge in a Gameboy  

[triton1]

You could try using your Barlow with your 12.4 plossl,might give you some idea

[russ.will]

It should be fine. In an F6 scope, a 6mm EP will give a 1mm exit pupil. Unless you're extraordinarily resistant to floaters, I'd suggest 0.5mm exit pupil an absolute maximum and that would require a 3mm EP. 4.7mm is safe.

Theoretically.

In reality, 4.7mm (255x) is usable on a very well collimated scope, but only on the best - read, most stable nights - which are few and far between. Maybe as little as 2-3 nights a year. As someone who has owned most of the ES82s, plus other Plossls, Orthos, etc - if there is something about the combination of the 12.4mm Super Plossl and the Revelation 2.5x Apo Barlow (which I also own) that doesn't float your boat at an equivalent 5mm EP, then you're not going to get anything significantly different with an ES82 4.7mm.

My personal recommendation would be the 11mm ES82. I know that sounds close to the 14mm, but at these magnifications (85-110x) these are really handy focal lengths for the smaller DSOs. With the Rev Barlow you'll also then have 214x (useful occasionally) and 270x (useful exceptionally) which would better reflect the useful to pounds spent ratio.

I know it's not what you asked, but the 11mm will see far more use across a year and in my book, is a far better place for your funds. The first time you frame M3 in it, you'll see what I mean!

Russell

[-Aldebaran-]

Thanks for the input guys, maybe I will stick and experiment with what I have then for now and use the funds for a Decent UHC filter which I've been wanting for a while.

[Moonshane]

I routinely use 250x with my larger Scopes on double stars and moon, occasionally on planets. That said the level of detail is not greatly enhanced in most cases, although tight doubles split more easily.

I would say that unless you observe doubles the about 200x is plenty to see most things as well as you can. The higher the magnification the longer the wait for fleeting moments of good seeing.

[ollypenrice]

I don't think leeching out the very highest magnification is particularly profitable. As the others have said, having an EP taking you above 200x is a luxury for special occasions which may prove to be few and far between.

Olly

[gbarnett]

+1 for seeing what you like or dislike about your 12.4 EP + 2.5 barlow combo. You could even use your barlow as as a sort of manual zoom to experiment at higher magnifications - loosen the eyepiece in the barlow and pull the eyepiece out of the barlow slowly and refocus say on the moon or Jupiter and see if you like the results. It's a free way of checking if you can squeeze any extra seeing out of your sky - providing you don't drop anything!

The view will be a bit wobbly but I've tried this myself on the moon and Jupiter with my ES 6.7 and 2 x barlow and it works - it's impossible to say what magnification you are using - you can only say if it's a good view or not.

Graham.

[rwilkey]

I think the 8.8mm ES82 is the safe bet at 136x, as Jupiter excels at around 150x, anything above this does not give you any better view.  I use the William Optics SPL 6mm to achieve this ideal magnification, but this would give you 200x, so not the optimum mag for this great gas giant.

[Anderscn]

Hi,

I have a 10" F5 Dobsonian as well as the 4.7mm and 8.8 mm ES82. Yesterday evening the seeing here was pretty good, as I for the first time could benefit from the 4.7mm (266x). On Jupiter I could easily spot the GRS, a moon shadow on the planet surface and tiny swirls along the two main bands. To improve contrast and details, I used a UHC filter in combination with 4.7mm. Then I could even spot the thin whitish rim around the GRS. Amazing, never seen that before with my scope.. 

Yet, despite a "smaller" planet, the 8.8mm (142x) revealed exactly the same, even with still better contrast. Focussing was also a lot easier with the 8.8mm.

So, my conclusion is; the 4.7mm is good with a 1200mm scope on the few occasions with good seeing. The 8.8mm is sharper still.. but I wish I had the 6.7mm!! 

BR

Anders

[-Aldebaran-]

O.k it's going to be a clear night tonight with the moon not rising till early hours of morning. I may miss Jupiter high up in sky but Saturn will be along after and I'll see what results I get using that barlow/Meade combo. I didn't do it before in the past as I was not all that keen on the views I was getting out of the Meade Plössl, I'll give it another chance. Thanks for all the input!!

[faulksy]

if your colimated good 250x should be a walk in the park. try my 5mm pentax if you want

[-Aldebaran-]

Had the scope out last night and come to the conclusion that impatience and collimation are my errors, I'm too damn eager to get viewing that I don't allow enough time for cooling or dark eye adaption, rubbish views throughout, couldn't get a clear Jupiter even down to x86!alot of twinkling stars out so a turbulent atmosphere probably didn't help.

[Moonshane]

Sometimes it is as bad as that all night. Just pick your targets. Although even at 77x last night I had great views of the moon transit and band division.

[-Aldebaran-]

Nice offer mike, it's about time I popped down for a visit, message to arrange a date?

The scope is long overdue a collimation so I'll get that done today.

[SpaceWalker]

Had the scope out last night and come to the conclusion that impatience and collimation are my errors, I'm too damn eager to get viewing that I don't allow enough time for cooling or dark eye adaption, rubbish views throughout, couldn't get a clear Jupiter even down to x86!alot of twinkling stars out so a turbulent atmosphere probably didn't help.

To avoid wasting time when the weather is unstable you can always check the seeing forecast, e.g. on Meteoblue or similar site.

You can also use the Pickering Seeing Scale to estimate the actual seeing. I usually don't do planetary when the seeing is below 6.

[faulksy]

last week the skys were great to look at pointed the scope at jupiter and it was pants, skys were so unsteady but dsos were great. could only manage around 125 x on jupiter anything more and it was like looking through water. i think thats the worst i have ever none. still great to be out though :grin:

[-Aldebaran-]

Thanks to mike for bringing up collimation, as that was the issue for my prior poor seeing, I was able to get some better views of Jupiter afterwards, used the Meade 12.4mm with the 2.5 barlow and got some good results, saw the GRS for the first time.

Birthday coming up and Ive got my eyes on the 6.7mm ES 82°, coupled with grabbing the chance of good seeing and having a properly collimated scope I'm really looking forward to see what I can get.