newbie question

[Sir Norton 2]

This may be a dumb question but can you stack barlows together? like a x3 under a x2 or the other way, would it be x5 or x6??

I was thinking of getting a x3 barlow for higher magifacation .

 

[CypherK]

I doubt it, due to the way the lenses have been constructed all you'll end up with is a blurred mess.

[John]

You can actually stack barlows I think. The resulting image quality can take a hit depending on the quality of the barlows but it can be done. I believe that you multiply the barlow factors to get the new one, eg: 3x and 2x = 6x. Imagers do use this technique from time to time. It is a compromise compared to having a single barlow with the amplification you are seeking though.

The limits of the scope and seeing conditions will still apply so a 6x barlow might not be much use, at least visually !

 

 

[Sunshine]

I think that would be about as handy as stacking binoculars for a closer peek.

[John]

A better way to increase the amplification that a barlow gives is to increase the distance between the barlow lens element and the eyepiece field lens. This is the principle used in zoom eyepieces and also the Baader Fine Tuning rings when used with the Hyperion eyepieces.

Note: When you change the barlow - field lens spacing or stack barlows the focus point of the eyepiece will change (as it does when a barlow is used singly) and it may well be difficult to reach focus with resulting combination unless your focuser has lots of travel available. This issue is not the case when the Baader Fine Tuning rings are used as far as I know though.

[Stu]

I have never quite got to the bottom of what the result is of stacking Barlows. I don't think it is as simple as multiplying the factors because you are increasing the distance between focal plane and the first Barlow in the stack (ie furthest from eyepiece) so the multiplying factor will increase I think?

The technique John mentions of increasing the distance between the Barlow and eyepiece is one I use frequently with my binoviewers. Rather than changing eyepieces, I use extension tubes to allow me to vary the magnification for high power solar, planetary and lunar observing, it works well.