2 inch Barlow to mate with 42mm LVW & 30mm NLVW

[25585]

Mainly for my TV Genesis, I am looking for a 2 inch, 2x Barlow for use with LVW 42mm & NLVW 30mm eyepieces. 

To have good quality 21mm & 15mm equivalent eps with 2 inch fitting. 

Prefer to be able to insert the Barlow fully into my diagonal's ep end. 2x isn't exact magnification, as optical quality is more important. Any increase in eye relief is OK so a TV Powermate's speciality in not increasing the er is not essential. 

I decided to try a decent Barlow with my rich field scope first, to see if I want to really upsize aperture & focal length in a refractor. 

[Merlin66]

I sometimes use my x2 Powermate on the Genesis- placed before the diagonal.

 

[Luna-tic]

I've got a 2" Celestron Luminous 2.5X Barlow that I like a lot. Has a 1.25 adapter with it, and is a 4-element apochromatic lens arrangement. Only $95 USD through Amazon.

[John]

If you want to avoid a Powermate / TeleXtender/ Focal Extender so you get the extension of the eye relief, I reckon the Astro Physics Barcon would deliver the best optical quality in a 2" format barlow.

 

[25585]

16 hours ago, John said:

If you want to avoid a Powermate / TeleXtender/ Focal Extender so you get the extension of the eye relief, I reckon the Astro Physics Barcon would deliver the best optical quality in a 2" format barlow.

 

Hmm. Is it possible to use a Powermate etc as a plain Barlow by unscrewing a lens? Then have both options. 

[Louis D]

4 hours ago, 25585 said:

Hmm. Is it possible to use a Powermate etc as a plain Barlow by unscrewing a lens? Then have both options. 

I don't believe so.  The closest to what you're looking for is a TV Big Barlow plus a TV Panoptic Barlow Interface which essentially mimics a 2" 2x Powermate.  I have a similar setup using a 2" 2x GSO ED barlow in place of the TV BB because they have essentially the same focal length.

I can't get any normal 2" barlow to work well with non-Newtonian designs.  I suppose I could screw the front optical element of the GSO 2" 2x ED barlow onto the front of the diagonal, and it might work, though focus travel might still be a problem.  It would probably still be close to 2x due to similar optical path lengths.

I would never try to use a nontelecentric barlow such as the TV BB or GSO ED with such long and wide eyepieces.  My 40mm Meade 5000 SWA and 30mm ES-82 don't play well with either my GSO ED barlow or my 6" long Japanese made Orion Deluxe 2" 2x barlow.  The natural field stop is truncated and replaced by an artificial field stop introduced by the barlow's diverging rays in both eyepieces.  Eye placement also becomes a bit finicky as well.  However, the GSO ED plus TV PBI yields perfectly magnified views with no artifacts anywhere.  This is only in my Newt.  I can't come to focus in my AT72ED refractor with the combo.  I haven't tried it with my 2" back on my 127mm Mak because I see no point to it.

[25585]

22 minutes ago, Louis D said:

I don't believe so.  The closest to what you're looking for is a TV Big Barlow plus a TV Panoptic Barlow Interface which essentially mimics a 2" 2x Powermate.  I have a similar setup using a 2" 2x GSO ED barlow in place of the TV BB because they have essentially the same focal length.

I can't get any normal 2" barlow to work well with non-Newtonian designs.  I suppose I could screw the front optical element of the GSO 2" 2x ED barlow onto the front of the diagonal, and it might work, though focus travel might still be a problem.  It would probably still be close to 2x due to similar optical path lengths.

I would never try to use a nontelecentric barlow such as the TV BB or GSO ED with such long and wide eyepieces.  My 40mm Meade 5000 SWA and 30mm ES-82 don't play well with either my GSO ED barlow or my 6" long Japanese made Orion Deluxe 2" 2x barlow.  The natural field stop is truncated and replaced by an artificial field stop introduced by the barlow's diverging rays in both eyepieces.  Eye placement also becomes a bit finicky as well.  However, the GSO ED plus TV PBI yields perfectly magnified views with no artifacts anywhere.  This is only in my Newt.  I can't come to focus in my AT72ED refractor with the combo.  I haven't tried it with my 2" back on my 127mm Mak because I see no point to it.

Thank you Louis. I think then I'll stay with a mixture of ep diameter sizes for simplicity.