Fast Newts

[roughy (Mark)]

Hi all
Am investigating fast newtonians as a possibility in the year ahead. Does anyone have experience with the Boren-Simon Powernewt design? They have a four element corrector and come in at prices that are very competitive with other brands with a corrector.
Cheers
Mark

[astroboy]

Hi Mark
My understanding is its just a GSO with a Keller corrector .

Zane

Originally Posted by roughy

Hi all
Am investigating fast newtonians as a possibility in the year ahead. Does anyone have experience with the Boren-Simon Powernewt design? They have a four element corrector and come in at prices that are very competitive with other brands with a corrector.
Cheers
Mark

[clive milne]

I certainly do not think that they are price competitive,
nor do I think that the information posted on their web page accurately reflects the performance you could expect in reality.

ie) specifically the statement made in the Q&A section:

Q: I have a 6" F/5 Newtonian - How faster is the 2.8-8 ED POWERNEWT Astrograph?
A: The calculation is: (F5/F2.8)^2=3.2, meaning that instead of 3.2 hrs of exposure with your F/5 scope, you will now need only 1hr. Furthermore the 8" aperture (in comparison to 6") will give you far better resolution (read: details !!) in any DSO you'll image.

They either don't understand that focal length (and not aperture) defines resolution (in prime focus CCD images)
or they are being dishonest.

[5ash (Philip)]

I thought aperture decided resolution , not focal length. Focal length only decides the size of the image at prime focus. I'm sure they haven't spent all these years developing telescopes with bigger aperture just to get brighter objects without increased resolution??
Philip

[clive milne]

Originally Posted by 5ash

I thought aperture decided resolution , not focal length

Mate,
They are taking the piss,
The resolution of the powernewt (or should that be gso-keller-newt) is not diffraction limited. The airy disk (and first diffraction ring) is simply too small to effect the spatial resolution achievable with any CCD in existence at f2.8. When you include pixel charge diffusion and the Seidel aberrations inherent in the design there is no way on Earth that the PSF is defined by the aperture of any of the instruments they sell.

... period ...

God I miss Bratislav...

[5ash (Philip)]

I stand corrected , thanks for clarifying
Regards philip

[Tandum (Robin)]

Originally Posted by astroboy

Hi Mark
My understanding is its just a GSO with a Keller corrector .

Zane

I don't know of any 10" or 12" CF GSO scopes. If they where around you'd think Astro Tech would be flogging them. However, the fittings on the steel tube scopes look like GSO. They quote a badder 2" focuser for the CF tube scopes so that makes for an ASA 2" .73 reducer/corrector which seems to work out to F2.93 not F2.8 from an F4 scope. If it is a 2" asa corrector, it would be at least US$1K on it's own and no good for big sensored cameras. You got me ?

I just wacked a 3" keller in a 12" gso here and it seems to work ok. A new focuser at the right price would be nice though.

[Tandum (Robin)]

Originally Posted by clive milne

Mate,
They are taking the piss,
The resolution of the powernewt (or should that be gso-keller-newt) is not diffraction limited. The airy disk (and first diffraction ring) is simply too small to effect the spatial resolution achievable with any CCD in existence at f2.8. When you include pixel charge diffusion and the Seidel aberrations inherent in the design there is no way on Earth that the PSF is defined by the aperture of any of the instruments they sell.

... period ...

God I miss Bratislav...

Clive, I didn't understand one bit of this. Ignorance is bliss