Maximum Magnification

[CSM]

60 x the aperture in ins is normally reckoned to be the maximum magnification for any scope. But is this a purely visual limitation? Does this also apply to imaging? I'm thinking planetary.

[lensman57]

60 x the aperture in ins is normally reckoned to be the maximum magnification for any scope. But is this a purely visual limitation? Does this also apply to imaging? I'm thinking planetary.

That is a theoretical limit in visual observation, nothing to do with reality, magnification does not make sense for imaging. Seeing conditions, the type of telescope, the glass used for the objective and the size of the obstruction in NEWT type scopes all have a say in it. The accepted norm for UK skies under good seeing conditions is about 30~40X per inch of aperture at max for a well corrected scope. I myself prefer a smaller high contrast view of an object with good detail than a larger fuzzy one . IF you have a top of the range TAK or TEC Apo telescope and a decent eyepiece, dark skies and steady seeing then you can push your luck and go for 50~60X per inch and I know that some folks have pushed even harder with good results but don't count that as normal practice. If you need high Mag visual then you have to go for large aperture, 10~12", so a 12" could cope with 300~360 Max.

Regards,

A.G

[ollypenrice]

There is no such thing as magnification in imaging. How big's your print? Your screen? Etc. The same image can be printed or viewed large or small.

We talk about image scale and this comes from focal length. The best thing is to look at the focal lengths used by the planetary imagers. Some of them are remarkably long thanks to the use of Barlows and Powermates!

Olly

[astrosathya]

Its typical 50x per inch Theoritical from Bortle 1 skies. From cities, the max magnification depends on

1) Type of Telescope optical design. From least to highest Achromats < Reflectors < Doublet or Triplet APO

2) Local Weather like Clouds, Seeing, Transparency, Suspended particulate matter.

3) Eyepieces also make a difference.

From a city, with normal scopes its 30x to 40x per inch. Sometimes, Triplet APO's depending on the conditions are known to go upto 80x per inch, but the optical quality, that is Strehl ration has to be really high.

[AlexB67]

Imaging aside, but for visual that rule about 20 - 30 power per inch and 50 or even 60 max needs to be taken with a little caution. I recall reading this article, it sumps it up quite well and stuck with me.

http://www.astronomy...es/magnify.html

I would also add that a useful PPI figure may differ depending on the target, for a DSO or large targets such as a cluster perhaps 10 - 15 would be. A small scope of aperture 4 or 5 inch say 40 - 60 PPI may be useful on occasion to view a planet or may be more for the moon, a high contrast object since a small scope will not be affected by the atmosphere a much as a large aperture scope. Different courses for different horses is my understanding.

[Superdavo]

It's purely a visual limit, though it has been broken. Photography has revealed detail down to 0.25 or even 0.1 arcseconds. Interestingly, if something is longer but thinner than the limit, and has good contrast, it can still be seen. The cassini division is an example.

[CSM]

Thanks for comments guys. Visually I tend to be more in the 75x range with my scope! I was thinking specifically of planetary imaging. I've used a 2x Barlow very successfully and I reckon this gives something in the range of 380x magnification, which comes out at around the so-called 60x 'limit'. Pushing that up with the addition of a 1.6x Barlow merely gave a larger, fuzzy image, but I was wondering if a single good 2.5x or 3x Barlow would be worth it. Obviously seeing conditions have to be good.