Stacking power mates question

[Ramjo]

Hi all

If you were to stack a 2xtelevue power mate in front of a 4x would your increased magnification be 6x or 8???

[LukeSkywatcher]

This was discussed a while back. I think i am right in saying that the result would be 6x.

[MG1]

Pleas tell me you're not going to but a ethos or other massive EP on the end...that's one heck of a load on a focuser!

[Ramjo]

Pleas tell me you're not going to but a ethos or other massive EP on the end...that's one heck of a load on a focuser!

Next clear night, these things have to be tried, will crown my creation with a 2" 32mm Meade, the 250pds will handle it, so who's in agreement with Luke 6x or 8x...?

[LukeSkywatcher]

This is what WiKi says:

The amount of magnification is one more than the distance between the Barlow lens and the eyepiece lens, when the distance is measured in units of the focal length of the Barlow lens. A standard Barlow lens is housed in a tube that is one Barlow focal-length long, so that a focusing lens inserted into the end of the tube will be separated from the Barlow lens at the other end by one Barlow focal-length, and hence produce a 2x magnification over and above what the eyepiece would have produced alone. If the length of a standard 2x Barlow lens' tube is doubled, the lenses are separated by 2 Barlow focal lengths and it becomes a 3x Barlow, if the tube length is tripled, the lenses are separated by 3 Barlow focal lengths and it becomes a 4x Barlow, and so on.

[Ramjo]

So by that reckoning you would be magnifying an already doubled image by 4x therefore resulting in 8x

[Adrian]

However, Powermates are not barlows - changing the powermate to eyepiece distance has much less/no effect compared to a barlow.

I would still say 8x - the apparent focal length of the scope (F) is multiplied by the powermate, say the 2x to give 2F, this is then multiplied by the 4x to give 8F.

As usual, I await being proved wrong the intuitive answer often is

Ramjo: Do you have a 5.4mm and a 4mm eyepiece to compare directly?

[LukeSkywatcher]

According to this it would give 8x.

http://stargazerslounge.com/discussions-scopes-whole-setups/126879-double-up-barlows.html

Granted powermates are not barlows, but the maths is the same.

[Ramjo]

Well next clear night I'll try, I have a 6.5 so I can do a rough comparison with that and the 2x, will post any conclusive results

[x6gas]

Yes, the magnification will multiply, not add...