Max mag for moon in ED80

[yagon]

I've just been enjoying some great views of the moon.

I've been using my 9mm GSO plossl with 3x barlow in my ED80 for 200x magnification. At that mag, the image shimmers a bit, but it feels like I could push it further and still see more detail.

What is a typical upper limit of magnification for use on the moon for an ED80 scope?

[AstroJunk (Jonathan)]

The textbok reply is 50x per inch, so in your case 150x

So why do you think you can go further? Well, probably because you can. With an nice refractor and steady conditions you may well push it to 100x per inch or 300x for you. But beware, whilst the image is larger, you may not actually be getting any more detail out of the view, so only push it when the conditions are really good.

[acropolite (Phil)]

I have read of users pushing the mag on ED80's to around 280x and still getting good results, so anything is worth a try.

[Kyecat (Graeme)]

I have used a 2x barlow with a vixen 5mm ep for 240 times magnification. This works on nights with good seeing - other times you could surf the waves rolling across the surface of the moon. 120-160 times works nearly all the time so the answer is it depends on the seeing.

cheers Kyecat

[janoskiss (Steve H)]

The lowest magnification at which you can easily make out the Airy disk image of a star on a night of better-than-average seeing is the highest magnification that might will reveal new detail on any object. For the ED80 that is around 130-160x. But it is a fantastic little scope and I have taken it to 240x without any problems. At 240x I got a bigger (and dimmer) image but no more detail than at 150x.

[[1ponders] (Paul)]

You can push any telescope as far as you want. Have a look at the boxes some of the hobby scopes come in. You can push them to 500X plus. WOW


yeah right The limiting factor is your scopes ability to *resolve* detail, and as suggested the standard normally stated is between 50 and 70 times per inch. To resolve detail is to be able to clearly distinquish between objects. This is affected by quite a number of factors including atmospheric conditions and the "contrastiness" of the object and your eyes ability to distinguish contrasts. (Determining your eyes limiting factor on resolution takes practice, often on a number of different scopes). This is part of the reason we can use rediculously high magnifications when imaging planets with webcams. It is much easier for the computer to distinguish constrastiness than our eye can. Plus we can muck around with settings to improve this identification.

Anyway back to the issue at hand.

At the magnificatons stated on the side of the hobby scope at 500X for a 60mm scope (2.5" = 125X mag approx). At 500X resolution = zip, none, nada, jupiter is a big fuzzy blob of yellow. 250X still a yellow fuzzy ball, but smaller and maybe you will start to see a bit of coloured banding and maybe a more defined outline (depends on the quality of the lens/mirror of course. Poor quality optics and you won't get to 50X / inch). Now as you drop down from 250X and get closer to the theoretical maximum you will find more and more detail starting to appear, but it is as 125X that you will get the maximum amount of magnifications with the upper limit of resolvability for that size objctive. Remember we are talking 60mm hobby scope here with the associated optics. Oh and I haven't said anything about the quality of the eyepieces affecting image resolution

Now lets look at your ED80. Well for a start you'd hope that you had better optics. Np there I don't think. (And better eyepieces) And your lens is well collimated. I have heard of a couple of people having probs but they are few and far between. Your telescope and lens are at ambient so there are minimal tube currents. Your seeing is good, 7.5-9/10 and you are looking close to the zenith to minimize atmospheric extinction and other atmospheric effect. You should expect to exceed the 50X limit. Let's say 65X. So your theoretical magnification maximum and retain maximum resolution is 192X (say 200X). Anything over this or as you look lower towards the horizon or the atmospheric conditions deteriorate will reduce your *effective* resolution. Your scope resolution stays the same but is limited by other factors.

Ok you look at Jupiter at that magnification (Saturns cassini division would be a better test as it has good contrast for the eye). Assuming that the other factors above have been taken care of then you should be able to a nice crisp image with good resolution. Now you start upping the magnification. Still looks good but you may be starting to notice that the view looks a bit "softer" And the higher your magnification goes the "softer" the view looks. You are exceeding the resolving ability of your scope.

In the long run its a matter of preferences. Do you want to keep to the resolving power of your scope and get sharp crisp but smaller images, or are you prepared to sacrific some resolution for increased image size.

[[1ponders] (Paul)]

Btw I've rarely found resolution with my ED80 to be sustainable over around 55X (175 X mag)

[janoskiss (Steve H)]

That is just cos light, as much as she's particles, she is waves too, and when you squeeze waves through an opening they spread out, interfere, "smear" each other if you like. That is what scope manufacturers mean (or at least supposed to mean) by the phrase "diffraction limited". This implies that the aperture of the scope rather than the quality of the optics optics is the factor that determines the limits of its capabilities. The ED80 certainly lives up to the textbook expectations of the diffraction limit, unlike many other scopes that are promoted to do so. The fact that people have been able to push the magnification on this little scope to 150x and beyond with good results is the only proof I need (but only because I have done it and seen it for myself).