Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Variable barlow DIY

accessories DIY
  • Please log in to reply
11 replies to this topic

#1 duri_jk

duri_jk

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 04 Aug 2020

Posted 04 August 2020 - 07:14 PM

I have enough EPs to cover all focal lengths that I need during observation, but after experiencing convenience of Baader Hyperion Zoom, I started to think about zooming with my favorite EPs.

Here is my take on variable barlow.

Idea is that barlow is fixed and I move eyepiece away from barlow to increase magnification or closer to the barlow to decrease magnification. After I move EP I have to refocus, when magnification increases, focuser must move inwards (closer to telescope).
Here is schema:

 

Grey – Eyepiece
Blue – EP holder - 3d printed ring – 1.25’’ inner diameter, 44mm outer diameter, height 20 mm
Brown – metal rods – allows sliding of EP holder from/to barlow element, made of 3 mm welding wire
Black- standard 2''->1,25'' adapter from the telescope
Green – stopper to avoid barlow element falling into the tube
Orange – barlow element – unscrewed optical part of barlow

 

Variable_barlow_v2.0s.png

 

Zoom barlow

variable_barlow_assembled_3.JPG

 

Components (from left: EP, EP holder, barlow stopper, 2->1.25'' adapter, barlow element from TV 2.5x)

variable_barlow_components.JPG

 

Ready for action

variable_barlow_In_focuser_3_plus_sm.jpg

Making of:
EP holder
was printed on 3D printer. You can make it from wood as well. Just drill 1.25'' hole and leave enough material for wall to hold EP fixing screw and metal rods. Alternatively use any 1.25'' EP holder to which you can affix metal rods.
I have made it 20 mm high on purpose, it’s less than length of EP nose. Protruding EP allows me to get closer to Barlow for minimum magnification.

Preparing 2->1.25’’ adapter
Using drill press drill 2 holes into 2->1,25'' adapter. Hole diameter must allow metal rods sliding easily through them, but don’t let it wobble.
I’ve put long barlow into EP holder and protruding part of barlow into 2->1.25 adapter. This way both parts were concentric. Then I used holes in 2->1.25 adapter as guides for drilling holes into EP holder. Drill bit was too short, so I had to finish drilling with drill press after I removed EP holder. I have used 4mm drill bit to drill holes in EP holder – reason for bigger holes is to allow some adjustment during gluing and leave space for glue.

 

Guiding rods
are made of 3 mm steel welding wire, but you can use any strong and straight steel. I had to sand (with sanding paper) it down a bit to allow free sliding in drilled holes. (in fact that wire is 3.15mm in diameter and I drilled with 3.2mm drill bit). Rods are of different lengths - one is 135mm long, another one is 140 mm. When I’m assembling the kit, it’s easier to stick them into holes when you can make it one by one, rather than both at once.

 

Assembly
Put a glue into EP holder holes - I have used Mammut construction glue, but any silicone would be good as well, it does not have to be super strong, there are very low forces on such long contact surface. Put rods into holes. Until they are flush with top of EP holder, remove excess glue. Put rods into holes of 2->1.25 adapter, push them in until EP holder touches 2->1.25 adapter. Put long barlow into EP holder and 2-1.25 adapter to keep them concentric and let the glue set. 

 

Barlow stopper
I have used some spring wire that I can easily put into bottom part of 2->1.25 adapter and simply remove it when I need to use 2’’ filter. Shape is crazy and I did not bend it - it was already shaped that way, so made it simpler for me, I just made those “handles” that stick outside of 2->1.25 adapter. When I push then together, I can remove the spring. I needed something removable as this is my only adapter.

What barlow to use
Short barlow like Baader Q-barlow allows big range of magnifications. Long barlows like TV barlows offers smaller range of magnifications. Look at the chart below. How distance between EP and barlow affects magnification.

 

Notes

  • Friction of rods is sufficient to hold EP in place without creeping towards tube, but is still smooth enough to move it without moving the telescope as well
  • Rods are going deep into focuser – I cannot use 2’’ filters and it would not work with diagonal mirrors – unless you can use extension tube.
  • More you zoom more infocus you need, sometimes lack of infocus is limitation for higher magnification – then use Ep with shorter FL.
  • Be carefull not to pull out rods completely – EP may fall non the ground – you can make stopper at the end of the rod
  • High magnification leads to big eye relief – EP with adjustable eye guard helps to hold proper position of eye.
  • When you are too far from focuser (10 cm), you will start seeing things around the focuser – this is distracting and decreases contrast
  • teleextender / telecentric optics / powermate will not work as it's magnification is independent from distance to the EP

 

In use
When I’m observing in my 10’’ F5 Dobson I use 35mm EP along with RDF to find an object. Then I switch to 21mm Pentax XL. When I want higher magnification a use 21mm EP and zoom:
Install stopper, throw a barlow element into 2->1.25 adapter, put rods with EP holder into holes on 2->1.25 adapter, put 21mm EP into EP holder and I enjoy zooming. I will purchase new 2->1.25 adapter so I can have one standard and one with permanently installed zoom mechanism.
I do not claim that zoomed EP is better than native focal length EP, but this concept is very usable. Last observations of Saturn, Mars and Jupiter were very convenient with this zoom barlow. I have quickly found ideal magnification for current seeing conditions. I tried also to resolve double double in Lyra, or look at M13 - works great!!!
Even if it’s open system, stray light is not affecting contrast unless someone shines light directly on a “zoom barlow”
Considering simplicity of construction, quality of views and convenience of use, I really recommend you to try to build it.
I’m yet to try it with Morpheus 17,5 mm EP. That can be a dream combo.

 

Which barlow to choose?

I don't have answer, it depends what you have or how much zoom range you'd like to achieve. Here are some measurements I did with barlows I have at home.

Res1.png

If you'd like to look at pictures, here they are,

https://www.dropbox....Sfp7aekELa?dl=0

take them with reservation, I took those photos with mobile handheld and it was PITA to position it properly.

 

Juraj


Edited by duri_jk, 04 August 2020 - 07:22 PM.

  • hcf and ButterFly like this

#2 ButterFly

ButterFly

    Apollo

  • *****
  • Posts: 1,286
  • Joined: 07 Sep 2018

Posted 04 August 2020 - 08:35 PM

Very nice.  One isn't constraint to T2 barlows and eyepiece projection adapters this way.

 

Do you use the third post in practice?  I noticed the third drill holes.  Any cantilevering with only two posts?  That third post can also help keep a piece of cloth out of the path to help screen the tube from the field lens of the eyepiece.

 

The rod stoppers are probably a necessary safety feature.  Epoxy blobs on the ends of the rods or the like are probably all you need as a user warning.

 

A compression ring on the eyepiece holder is also a good idea for safety.



#3 duri_jk

duri_jk

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 04 Aug 2020

Posted 05 August 2020 - 02:07 AM

Very nice.  One isn't constraint to T2 barlows and eyepiece projection adapters this way.

 

Do you use the third post in practice?  I noticed the third drill holes.  Any cantilevering with only two posts?  That third post can also help keep a piece of cloth out of the path to help screen the tube from the field lens of the eyepiece.

 

The rod stoppers are probably a necessary safety feature.  Epoxy blobs on the ends of the rods or the like are probably all you need as a user warning.

 

A compression ring on the eyepiece holder is also a good idea for safety.

Thanks.

Third post is from first iteration. It's not necessary. 2 posts are stiff enough and it slides smoother on 2 posts. Cantilevering is minimal and it does not affect viewing - at least I was not able to detect any negative impact on the view. Inserting / removing barlow with 3 posts is more complicated as posts are too close to each other and barlow does not fit in between. So it has to be handled from the bottom of 2->1.25 adapter. With 2 I can insert/remove it from the top.

I was thinking about third post to make it very narrow, not to affect sliding and support the cloth, but then manipulation with barlow will be more complicated. This is limitation to be solved.

I will make a stoppers when I will have additional 2->1.25 adapter. Now I have only one so rods must be completely removable to allow usage of EP without barlow. EP in EP holder without barlow is too far from the focal point of telescope and I cannot reach the focus.

EP holder is tight enough that EP does not fall out, but some EPs did not fit into it. So I have to make it wider and then I will need to add at least retaining screw - it's task for next rainy weekend.

Juraj



#4 PETER DREW

PETER DREW

    Apollo

  • *****
  • Posts: 1,391
  • Joined: 31 May 2017

Posted 05 August 2020 - 03:59 AM

This is the principle that the Speers-WALER zoom eyepiece uses.  Makes a good extended use of your favourite eyepiece.



#5 duri_jk

duri_jk

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 04 Aug 2020

Posted 05 August 2020 - 06:23 PM

This is the principle that the Speers-WALER zoom eyepiece uses.  Makes a good extended use of your favourite eyepiece.

Thanks for info Peter. I was not aware of Spears-WALER zooms. It gives me more confidence in this concept, as one forum (not CN) where I discussed first iteration was rather against this idea. 



#6 MitchAlsup

MitchAlsup

    Aurora

  • -----
  • Posts: 4,610
  • Joined: 31 Aug 2009

Posted 05 August 2020 - 07:20 PM

I am sitting here wondering::

 

Is there some way to connect the Barlow element and the Eyepiece attachment so that one could dial a ring (like on a camera lens) which turns two cams (or one cam with to indexing slots) so the Barlow lens and the EP move such that they stay in focus as the magnification changes.

 

.......



#7 duri_jk

duri_jk

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 04 Aug 2020

Posted 05 August 2020 - 09:40 PM

I am sitting here wondering::

 

Is there some way to connect the Barlow element and the Eyepiece attachment so that one could dial a ring (like on a camera lens) which turns two cams (or one cam with to indexing slots) so the Barlow lens and the EP move such that they stay in focus as the magnification changes.

 

.......

I did it as well. But it led nowhere in my case, so grabbed drill and I'm zooming ... I was thinking about old 35mm zoom lens that extends a lot to serve as EP holder. Or small lens from ultrazoom compact camera to hold barlow and move it into the focuser. Steel rods won. Simple, costs nothing, works great.



#8 kisstek

kisstek

    Viking 1

  • *****
  • Posts: 598
  • Joined: 25 Jul 2018

Posted 05 August 2020 - 10:40 PM

I am sitting here wondering::

 

Is there some way to connect the Barlow element and the Eyepiece attachment so that one could dial a ring (like on a camera lens) which turns two cams (or one cam with to indexing slots) so the Barlow lens and the EP move such that they stay in focus as the magnification changes.

 

.......

Would something like a helical focuser work?



#9 ed_turco

ed_turco

    Mercury-Atlas

  • *****
  • Posts: 2,709
  • Joined: 29 Aug 2009
  • Loc: Lincoln, RI

Posted 06 August 2020 - 10:47 AM

I am quite impressed.



#10 MitchAlsup

MitchAlsup

    Aurora

  • -----
  • Posts: 4,610
  • Joined: 31 Aug 2009

Posted 06 August 2020 - 11:36 AM

Would something like a helical focuser work?

The two lenses (Barlow and Eyepiece) need to move in opposite directions, and one of the cams is nonlinear (?parabolic?) to maintain focus while focusing. The Barlow moves inward while the EP moves outward, 

 

So, no, a helical (all by itself) will not work.

 

The visual question is how does one translate some rotary motion (the ring) into position changes for the two lenses? I see a Cam and 2 barrels, one barrel moving the Barlow, the other moving the EP. Each barrel has 1-2-3 pins and each pin is in a slot of its cam.



#11 PETER DREW

PETER DREW

    Apollo

  • *****
  • Posts: 1,391
  • Joined: 31 May 2017

Posted 06 August 2020 - 05:13 PM

The easiest way to achieve this zoom effect is to have a nice 2" o/d tube and another nice tube that slides inside the 2" one.  A Barlow is fitted to the inner tube.  With the Barlow close to the eyepiece the telescope is focused and the resulting magnification is presented.

Removing the assembly and withdrawing the tube containing the Barlow increases the distance between the Barlow and the eyepiece which increases the magnification, The assembly will need refocussing each time the Barlow separation is altered.  This is of course a bit of a faff to do but you can dial up any magnification and the apparent field of view of the eyepiece you elect to use is maintained and not vignetted as with many commercially made zooms that have a small field at the lower power of their range.



#12 duri_jk

duri_jk

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 04 Aug 2020

Posted 07 August 2020 - 05:53 AM

The easiest way to achieve this zoom effect is to have a nice 2" o/d tube and another nice tube that slides inside the 2" one.  A Barlow is fitted to the inner tube.  With the Barlow close to the eyepiece the telescope is focused and the resulting magnification is presented.

Removing the assembly and withdrawing the tube containing the Barlow increases the distance between the Barlow and the eyepiece which increases the magnification, The assembly will need refocussing each time the Barlow separation is altered.  This is of course a bit of a faff to do but you can dial up any magnification and the apparent field of view of the eyepiece you elect to use is maintained and not vignetted as with many commercially made zooms that have a small field at the lower power of their range.

Hi Peter, 

If I got it right, then it reminds me the first version of my attempt, where posts were affixed to 2->1.25 adapter and Barlow element was sliding on them. I have quickly gave up on this concept, any magnification change required following steps:

  • remove 2->1.25 adapter
  • reposition barlow
  • put back adapter
  • focus

Now its

  • move eyepiece
  • focus

Here is link to pictures of the first version:

https://www.astro-fo...=414829#p414829

 

Juraj




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: accessories, DIY



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics