60 replies to this topic

[TayM57]

I've just re-acquired the 17ES92 and working on re-acquiring the 12ES92. 

 

Since ES has all but abandonded the ES92's, we are left with only two native focal lengths, the 12mm and 17mm. 

 

So I've been thinking about getting screw on barlows that thread onto the bottom of the barrel, where filters go. One option is the Astro Physics BARADV. Does anyone use the BARADV on their ES92's? Does it give 1.6x or 2x? 

 

Another option is Siebert Optics telecentric barlows, but I do not believe those screw onto the barrel like the BARADV can. 

 

My goal is simple: 

 

12mm can be barlowed 6mm

 

17mm can be barlowed to ~8.5mm 

 

 

I'm looking for the most simple solution, that is, a screw on barlow. If it's telecentric, great but I don't think there is a screw on telecentric barlow. 

 

Also, would a screw on barlow have to be threaded to the paracorr 2 if the ES92 is paired with a paracorr 2? or can the barlow be left on the ES92? 

Edited by TayM57, 25 March 2025 - 03:16 PM.

[CrazyPanda]

A non-telecentric barlow (that is, a telenegative) added to the Paracorr will dramatically increase the multiplication factor by the time it gets to the eyepiece.

 

I tested out the 2" EiC thread-on barlow that came with the 17 Nikon NAV-HW by threading it onto the bottom of the Paracorr, and it was a dramatic increase in magnification. This is not surprising since it's a telenegative design.

 

Any thread-on telenegative barlow should be added to the eyepiece, I just don't know what the multiplication factor would actually end up being - most certainly less than the stated multiplication factor when used with the barlow's body.

 

If you were to use a PowerMate, Tele Vue recommends PowerMate -> Paracorr -> Eyepiece. But doing that with an ES92 is going to make your focuser yelp.

[Astro-Master]

I use a shorter 1.5" by 2" extension tube on my Astro Physics BARAVD to make a 1.75x Barlow.  when using with my 17 Ethos it becomes a 9.7mm Ethos.

 

For my 13 Ethos I added a 2" diameter Baader 14mm fine tuning ring as a barrel extender to prevent contact with the barlow lens, this makes a 1.61x Barlow and the 13 Ethos becomes an 8Ethos, and I don't have to switch the barlow lens in the dark.

[areyoukiddingme]

When I have dickered about with the AP barlow, I've found that screwing it to the bottom of eyepieces typically generates a lot of what I assume is astigmatism at the edge.

 

I can try the AP barlow section with the 12mm ES/92. . . and it doesn't fit. So you will need some kind of adapter to make it work at the very least.

[nkoiza]

My experience is identical to Scott's, i.e., screwing the nosepiece of this barlow to the bottom of either of the ES 92 eyepieces generates some noticeable astigmatism, although I own the predecessor to the AP BARADV known as the AP BARCON, which is also an excellent AP barlow.

 

Therefore, I only use the AP BARCON using the standard drawtube, i.e., as supplied. On my set up (16-inch F4.4 dob), this yields an amplification factor of c. 1.5x with the ES 92s (and only about 1.3x when screwing the nosepiece to the bottom of the ES92s which is non optimal as mentioned above). I have drift timed extensively to verify this magnification factor. What I tend to do is maintain a 20mm spacer between the drawtube and nosepiece to yield c. 1.65x. 

 

Although I have no direct experience of the newer AP BARADV version, AstroPhysics have advised that the amplification factor of the BARADV is slightly higher - c. 1.7/1.8x without the use of spacers rings. Therefore, I would imagine that using a 20mm spacer with the BARADV should allow you to achieve your goal of turning the 12mm into a 6mm and 17.5mm into an 8.5mm - there or thereabouts - I'm confident of that.

 

The ES92s work great in the AP barlow, but I also use this barlow with my 16.5mm Pentax XW. I would say the AP BARCON works better with the ES 92s - completely flawless!

 

Hope this helps.

[TayM57]

That is a bummer that the AP Baradv doesn't work as a bottom-only barlow for the ES92 without introducing significant astigmatism, which for me, is a deal breaker.

 

I would really like to avoid using the 2x PM because with the ES92+P2+2x PM, the stack is getting to be a bit tall and heavy, and the moonlite focuser will start losing axial alignment with that big of a stack. Not to mention tube flexure on my solid tube scopes.

Another option is the Siebert 2" 2x telecentric barlow which weighs 8.5oz, compared to the 24oz of the 2x TV PM.

 

There is no information as to the weight of the AP Baradv.

 

Anything I can do to reduce the weight on the focuser when I need to barlow is helpful.

[John Huntley]

I wonder how the Antares 1.6x barlow would work with the ES 92's ?

 

It works very well with Ethos eyepieces, provided that the change in focus position can be accommodated.

[25585]

TV advise putting an eyepiece in a Paracorr2, then putting that assembly in your 2" Powermate. 
 

I have a BARADV which I screw on, with a short extension between the ep and Barlow lens, but have only used it with the 12mm ES92. Not sure what magnification exactly though.

[TayM57]

Another option is the GSO 2x barlow, which has a bottom lens that can be unscrewed and screwed onto an eyepiece for 1.5x.

 

No idea if it will introduce abberations like astig.

[areyoukiddingme]

That one does screw into the bottom of the ES12/92. 

 

A quick gander at some house lights a mile or so away shows a bit of astigmatism. Not as bad I as I thought it would be.

[TayM57]

That one does screw into the bottom of the ES12/92. 

 

A quick gander at some house lights a mile or so away shows a bit of astigmatism. Not as bad I as I thought it would be.

With the GSO 2x?

[areyoukiddingme]

Mine is Zhummel branded, but yes I believe its GSO

[TayM57]

I have no idea if this would work for you but Baader makes a 2.25x barlow that screws onto it's 8-24mm zoom eyepiece. It will work on any 1.25" eyepiece as well. Good luck! 

 

https://agenaastro.c...oom-barlow.html.

Likely not, as it's 1.25" and the ES92's are 2". 

 

Likely I will try two options: 

 

ES92's with GSO 2x barlow screwed on bottom for 1.5x mag effect AND Siebert Optics Ultra Telecentric 2x. 

 

If the optical aberrations are too much for me, I will just use the TV 2x PM and accept that it will be a long stack with the Paracorr 2. 

 

The Siebert Optics Ultra Telecentric is 8oz, compared to the TV 2x PM at 24 oz. So, it's a significant weight difference. 

[nkoiza]

That is a bummer that the AP Baradv doesn't work as a bottom-only barlow for the ES92 without introducing significant astigmatism, which for me, is a deal breaker.

 

I would not say the astigmatism is significant - only a small and not necessarily objectionable amount is visible with the AP BARCON nosepiece screwed on either ES 92.

 

I have also tried screwing the nosepiece of a 2X GSO barlow with my 12 ES 92. From memory, I recall a tiny bit more astigmatism with this barlow. I also measured the amplification factor with the 2X GSO barlow, which is c. 1.5X in your desired barlow nosepiece screw in configuration.

 

I would probably recommend buying the AP BARADV rather than the GSO barlow, mainly because of the AP's other strong features, although the GSO is by no means a poor barlow. When I tried the 2X GSO, I intended to use it with the nosepiece screwed on my 16.5mm Pentax XW. In that configuration, lower off-axis performance was apparent through the 16.5mm XW - the 12 ES 92 worked better and I am certain of that.

Edited by nkoiza, 26 March 2025 - 03:44 PM.

[sevenofnine]

It's not what you're looking for but if you can't find it, consider this. It is a 2x focal extender so it doesn't double the ER which can be a problem. I have the 1.25" version and like it a lot. The views are just as clear and sharp as the eyepiece without it. Good luck! 

 

https://agenaastro.c...w-fe02-020.html.

[TayM57]

Ok, if I wanted to use the AP baradv (what's up with the goofy names?) with the ES92s, it's my understanding that the barlows don't thread into the ES92s. Assuming this is true, what kind of adapter do I need? What is the thread size of the ES92s, and the AP baradv?

[25585]

They are not names but abbreviations or acronyms. BARCON (Barlow Convertible) & BARADV (Barlow Advanced Convertible). 

[TayM57]

They are not names but abbreviations or acronyms. BARCON (Barlow Convertible) & BARADV (Barlow Advanced Convertible). 

Ah, gotcha. Thanks Richard.

[25585]

BARCON  https://astro-physic.../barcon-mkv.pdf

 

BARADV  https://astro-physic..._acc/visual_acc

[nkoiza]

Ok, if I wanted to use the AP baradv (what's up with the goofy names?) with the ES92s, it's my understanding that the barlows don't thread into the ES92s. Assuming this is true, what kind of adapter do I need? What is the thread size of the ES92s, and the AP baradv?

It's good that you mentioned this key point.

 

I can only speak for the AP BARCON, which has M42 threads that protrude above the M48 threads. When I evaluated your proposed configuration with the ES 92s, I screwed in a 10mm M48 spacer in order to raise the M48 threads up for easy attachment to all eyepieces, including those with a field lens at the bottom of the barrel. I will see if I can forward you a photo as this is not too easy to visualise.

[TayM57]

It's good that you mentioned this key point.

 

I can only speak for the AP BARCON, which has M42 threads that protrude above the M48 threads. When I evaluated your proposed configuration with the ES 92s, I screwed in a 10mm M48 spacer in order to raise the M48 threads up for easy attachment to all eyepieces, including those with a field lens at the bottom of the barrel. I will see if I can forward you a photo as this is not too easy to visualise.

Thanks- would appreciate that either via PM or email.

 

Reading Richard's links, it appears the baradv does have 48mm threads. It should be able to thread onto the ES92s. Really the only question is, if I want a 2x mag factor, I probably need a spacer for that. I think it's the older barcon that doesn't have the right threads.

Edited by TayM57, 26 March 2025 - 08:28 PM.

[nkoiza]

Just sent you a PM.

 

Regarding the BARADV - which I have no experience of - you can try contacting AstroPhysics to understand whether 2x magnification factor can be achieved in this configuration, although I suspect they may not recommend anything other than just using their standard drawtube. I am not certain how practical a spacer would be either, as I think you may need a very long spacer for your desired configuration. However, I think this could help to improve off-axis performance. Without spacer, I suspect you would only be hitting c. 1.5x with the BARADV.

 

The best thing to do in my experience (with the BARCON) is to simply screw in a 20mm M48 spacer between the BARADV drawtube and lens cell. I think you would then achieve c. 2x amplification factor. That's how I am currently using my AP BARCON.

Edited by nkoiza, 26 March 2025 - 08:58 PM.

[TayM57]

I've posted to the Astro-Physics io group, since they have no contact email listed (I don't do phone calls since I'm Deaf and use ASL).

 

If stig is in the last 10% of the field when using the baradv, OK, maybe I can accept that since I won't be looking at the edge with foveal vision.

Edited by TayM57, 26 March 2025 - 09:07 PM.

[davidgmd]

It's not what you're looking for but if you can't find it, consider this. It is a 2x focal extender so it doesn't double the ER which can be a problem. I have the 1.25" version and like it a lot. The views are just as clear and sharp as the eyepiece without it. Good luck! 

 

https://agenaastro.c...w-fe02-020.html.

  
Bit of thread drift but I don’t think I’ve ever seen an answer to this:

  

Is there a direct or a consistent mathematical relationship between the power of a (non-telecentric) Barlow and eye relief? Can impact on eye relief be predicted based on the Barlow’s magnification factor alone? Are there other contributing factors?

[areyoukiddingme]

Thanks- would appreciate that either via PM or email.

 

Reading Richard's links, it appears the baradv does have 48mm threads. It should be able to thread onto the ES92s. Really the only question is, if I want a 2x mag factor, I probably need a spacer for that. I think it's the older barcon that doesn't have the right threads.

 

See post #4