more image scale?

[northcanadian]

Hi all:

Is it possible to stack a barlow with a powermate or 2 powermates together for more image scale?

Thanks again

Cheers

[umadog]

Possibly. But first you need to ask yourself how much power you can use. It's unusual to stack barlows like that. First you should read a little about power. This is very useful: Useful Magnification Ranges for Visual Observimg - How To

Despite the theoretical power per inch, you are ultimately limited by the atmosphere. There are these recent threads that are relevant to this:

http://stargazerslounge.com/beginners-help-advice/186280-telescope-limits.html

http://stargazerslounge.com/beginners-help-advice/185785-how-much-bigger-would-if.html

[glowjet]

I may be wrong, but I do not think mixing Barlow's with powermates would be such a good idea. the light rays leaving a barlow diverge, whereas with the powermates they are designed to leave parallel, most popular among the imagers where these are stacked to increase the focal length of the scope. For visual use you are, of course, governed by the useful magnification your scope can handle and the limitations of our atmosphere, as already mentioned

[Tribal-Wolf]

I stacked two 2x barlows recently just to see what would happen when imaging mars, all I big blurred Mars that was very hard to track.

[umadog]

Neither diverge and neither produce parallel rays. Both barlows and powermates work by decreasing the steepness of the light cone. Basically, simulating what a longer focal length would do. Here's the ray diagram for a barlow: http://www.cityastronomy.com/barlow-lens.jpg

[jgs001]

I have stacked barlows, and it does work... sort of.. another option is to increase the distance between barlow and ep/camera, this has the effect of increasing the magnification effect. I do not think it's the same with powermates though, I read somewhere, they are designed so that this effect does not happen.

[steelfixer]

It will work but by putting more glass in the image train it will make the image darken.

Best thing I have found is a spacer tube.

Try removing the lens from one of your barlows and just use the tube.

[RikM]

It will work but by putting more glass in the image train it will make the image darken.

Best thing I have found is a spacer tube.

Try removing the lens from one of your barlows and just use the tube.

I have done it this way for imaging as well.

Scope --> barlow --> barlow without lens --> camera.

[JamesF]

Scope --> barlow --> barlow without lens --> camera.

That's my usual approach with the Mak. I stripped the lens out of a kit Skywatcher barlow since it was useless anyhow. The extension sees far more use than it ever did as a barlow.

James

[Merlin66]

Yes,

I've successfully stacked Powermates for solar imaging...no major issues.

I would suggest a x4 Powemate is much easier than a double satcked x2 ;-)

[glowjet]

Neither diverge and neither produce parallel rays. Both barlows and powermates work by decreasing the steepness of the light cone. Basically, simulating what a longer focal length would do. Here's the ray diagram for a barlow: http://www.cityastronomy.com/barlow-lens.jpg

I may have misunderstood what Al Nagler has said about the design of his range of Powermates in relation to the barlow, quote :

(Unique Benefits and Applications for Powermates. Vignetting, edge field aberrations and pupil movement - all introduced when using Barlows with long focal length eyepieces, are minimized. Telecentric operation (field rays leave parallel to optical axis, unlike Barlow lenses which diverge rays). This is ideal for Hydrogen-alpha filter use such as with Daystar models. High performance for image amplification, CCD or film (some of the finest Earth-based planetary imaging is being done with Powermates. Flexible for visual and imaging with all types of telescopes and eyepieces. Essentially Parfocal, and with nearly constant magnification regardless of image distance behind top surface (except 5x model which increases 1x for every 35mm of image distance increase). Higher magnifications are possible with high optical performance compared to "doubling up" Barlows) Some of Al Naglers published explanation of the performance of his range of powermates

[umadog]

Oh I see! We're using different definitions of "diverge". I was thinking that "diverge" literally meant diverging rays (i.e. this: http://www1.curriculum.edu.au/sciencepd/readings/images/read09.gif). Nagler is using it to mean that rays diverge "a bit", so that they converge further from the focal plane than they normally would. The powermate avoids this and the rays converge at the same plane as they would without the powermate.

This nice article shows a regular barlow and the telecentric. http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/BarlowLens.pdf

[glowjet]

Thanks Umadog, as it happens you jogged my memory and I now recall reading that article by Chris Lord quite some time ago, puts everything into perspective. Another very interesting PDF by the same author covered the Bhatinov Mask and how it works, proving that a much more simplified version can work just as well