8 replies to this topic

[ris242]

I'm guessing you could have a powermate before or after a binoviewer.

 

Apart from needing two,  is it better to have powermates after the binoviewer?

I currently have one and testing without and then adding it, the focus only changes about 5mm inward on a MBII

 

 

 

 

 

[EboO]

Hello,

I use it before the bino (for a PM2.5), never tried after.

[balcon3]

The magnification factor will change depending on where you put the Powermate. The stated magnification is for when the Powermate is right in front of the eyepieces. If you put it before the Binoviewer, the path length of the Binoviewer will change the magnification factor. Here is a chart from Televue that shows the effect of distance to the eyepiece on magnification.

 

https://www.televue....?id=53&Tab=_app

 

Note that some Powermates give higher magnification when further away from the eyepieces, some give less, and some stay about the same. For Barlows, as opposed to Powermates, the magnification always goes up.

 

There is no "correct" place to put the Barlow/Powemate, and indeed some observers place it in a particular location in order to get a specific magnification effect.

[Eddgie]

Given the fact that all of your telescopes are refractors, my own advice would be to put the amplification ahead of the binoviewer. This is because it will greatly reduce the amount of spherochromatism you would see when using the binoviewer.

 

A simple test is to use a very bright star on one of your faster refractors, and view Sirius or the limb of the moon with it. If you  put the Powermate after the BV, you will likely see some violet fringing in the field around Sirius or on the limb of the moon.  Assuming that the refractor has a very high level of color correction, with the Amplifier ahead of the BV, this should go away..

 

In slower scopes it probably does not matter, but if you have one already, you can test it in both configurations using the equipment you already have.  At f/7, for low power, I don't use a GPC or amplifier, but for all higher power work (doubles, planets, lunar). I use a GPC and it completely eliminates all color error coming from the prisms in the binoviewer. A 2x Barlow does the same thing. 

Edited by Eddgie, 16 February 2025 - 07:38 AM.

[ris242]

Given the fact that all of your telescopes are refractors, my own advice would be to put the amplification ahead of the binoviewer. This is because it will greatly reduce the amount of spherochromatism you would see when using the binoviewer.

 

If I add the 1.25x GPC before the bino and the powermate after is that better again?

 

 

[the reason I am chasing this idea is I like the eye relief on my 24mm APM's......so thinking using them at a higher mag........and as a whole it gives me more mag options for when the sky behaves with my other eyepieces]

[balcon3]

If I add the 1.25x GPC before the bino and the powermate after is that better again?

 

 

[the reason I am chasing this idea is I like the eye relief on my 24mm APM's......so thinking using them at a higher mag........and as a whole it gives me more mag options for when the sky behaves with my other eyepieces]

Why not just use a 2.6x GPC ( which is actually 2.9x). It’s cheaper and more compact than two 2.5x Piwermates and will have about the same magnification as a 1.25x GPC and two 2.5x Powermates after the binoviewer. You could still use your 24mm APM’s.

[ris242]

Why not just use a 2.6x GPC ( which is actually 2.9x). It’s cheaper and more compact than two 2.5x Piwermates.

Good point...........but I think it may move the focus too far inward on the evostar?

[balcon3]

Good point...........but I think it may move the focus too far inward on the evostar?

You will likely need an extension tube to reach focus, but this is pretty trivial to insert. But you are correct, a Powermate after the binoviewer will change the focal plane location much less.

[Spikey131]

I use the Baader 1.25x and 2.6x GPCs with my refractors.

 

With the Dob, it is the 2x Powermate with a T2 Adapter to reduce the length of the binoviewer train.

 

 

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