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

Why does no one sell occulting bars?

This topic has been archived. This means that you cannot reply to this topic.
30 replies to this topic

#1 MikeBOKC

MikeBOKC

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 6282
  • Joined: 10 May 2010

Posted 23 September 2012 - 12:22 AM

One useful tool that seems to be missing from astronomy is an eyepiece occulting bar to allow the observer to occult a bright centered object to allow visualization of associated much dimmer companions -- i.e., Diemos and Phobos around Mars, Sirius B and other hard to split doubles that vary significantly in b rightness and the moons of Uranus and Neptune. It would seem that someone could come up with a simple-to-install narrow rod, perhaps spring loaded on one end, to fit easily inside the bottom of 1.25 and 2 inch eyepieces . . . or a clear screw-on filter with the bar running across the center. Manufacturers? I'd definitely buy one in each size and would not quibble at a $20 price tag for a simple, easy to use and effective gadget that would be a handy addition to any eyepiece kit.

#2 David Knisely

David Knisely

    Hubble

  • *****
  • Posts: 16844
  • Joined: 19 Apr 2004

Posted 23 September 2012 - 12:40 AM

Because it is too easy to make one out of aluminum foil......

#3 Fireball

Fireball

    Viking 1

  • -----
  • Posts: 534
  • Joined: 24 Mar 2006

Posted 23 September 2012 - 02:32 AM

David, tell us how you make such a narrow bar with Al foil?

Tried the moon of Uranus and Neptune last night and thought as well of such a bar ...

#4 Mirzam

Mirzam

    Aurora

  • *****
  • Posts: 4740
  • Joined: 01 Apr 2008

Posted 23 September 2012 - 07:13 AM

You need to use an eyepiece with a field stop that is in front of the optics. Orthos are one eyepiece type that is designed like this. Some Televue designs have a field stop that is internal to the optics and cannot be easily modified.

The field stop should be in sharp focus as you view through the eyepiece. All you need to do then is glue a narrow (1 mm) strip of aluminum foil across the field stop. The foil needs to be in exactly the same plane as the field stop. Tweezers are helpful for making small adjustments.

JimC

#5 Cotts

Cotts

    Just Wondering

  • *****
  • Moderators
  • Posts: 8641
  • Joined: 10 Oct 2005

Posted 23 September 2012 - 07:21 AM

Making a narrow bar from foil is easy.

However other difficulties do mount up.
---Getting the bar exactly at the focal plane of the eyepiece for a sharp cutoff of light?
---Attaching the bar to the eyepiece? You want to fool around with glue near your lenses?
---Easy on-off removal? Easy to switch from eyepiece to eyepiece?

I would salute an entrepreneur who would make a range of eyepieces with occulting bars machined in. Orthoscopics or Plossls would do as we're talking about Hi-magnification here. Say a 6mm and a 12mm (1 1/4") pair. Have a range of widths of occulting bars you could screw in depending on telescope focal length and the angular size of the thing you're trying to block. Or just make the screw-in inserts for 1.25" eyepieces. You could put the bar in the eyepiece focal plane by adjusting how far in you thread it. Use your own eyepieces this way.

Hello machine-shop types! Opportunity knocks....

Dave

#6 helpwanted

helpwanted

    Aurora

  • *****
  • Posts: 4696
  • Joined: 04 Jul 2007

Posted 23 September 2012 - 07:59 AM

Just a thought... The illuminated cross hair eyepieces... Can you unscrew the light part, leaving a hole into the focal plane, where this could work?

#7 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 28140
  • Joined: 18 Dec 2007

Posted 23 September 2012 - 08:18 AM

You could first install the aluminum bar in the interior ring of a filter - after removing the filter - then fit that metal ring inside a larger ring cut out of black foam core. Wedge the whole gizmo up inside the eyepiece barrel to the focal plane of the eyepiece. This would be easier if the lower barrel of the eyepiece can be unscrewed and taken off.

Mike

#8 helpwanted

helpwanted

    Aurora

  • *****
  • Posts: 4696
  • Joined: 04 Jul 2007

Posted 23 September 2012 - 10:20 AM

Wait... Back to my idea of taking apart a crosshairs eyepiece... What if you leave the light off, and just put one of the crosshairs over the star you are trying to occult?

#9 lightfever

lightfever

    Vanguard

  • *****
  • Posts: 2146
  • Joined: 27 Sep 2004

Posted 23 September 2012 - 11:13 AM

I would salute an entrepreneur who would make a range of eyepieces with occulting bars machined in. Orthoscopics or Plossls would do as we're talking about Hi-magnification here. Say a 6mm and a 12mm (1 1/4") pair. Have a range of widths of occulting bars you could screw in depending on telescope focal length and the angular size of the thing you're trying to block. Or just make the screw-in inserts for 1.25" eyepieces. You could put the bar in the eyepiece focal plane by adjusting how far in you thread it. Use your own eyepieces this way.

Hello machine-shop types! Opportunity knocks....


I may take you up on that, would there be much demand out there?

#10 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 28140
  • Joined: 18 Dec 2007

Posted 23 September 2012 - 11:25 AM

Wait... Back to my idea of taking apart a crosshairs eyepiece... What if you leave the light off, and just put one of the crosshairs over the star you are trying to occult?


I'm not sure about that. IME with crosshair eyepieces, the hair is too thin to fully occult a fairly bright star. There is going to be some light flare around the hair. I think you need something a little thicker to fully occult the star.

Mike

#11 Cotts

Cotts

    Just Wondering

  • *****
  • Moderators
  • Posts: 8641
  • Joined: 10 Oct 2005

Posted 23 September 2012 - 12:26 PM

I,d buy a set if the price was right - say under $100 for a set of three or four of various bar widths. Perhaps there's a way to make interchangeable bars for one housing that threads into the eyepiece.....

The market is limited to people trying to see the moons of Mars, Saturn, Uranus and Neptune and to attempts at seeing Sirius B, Procyon B and other doubles of similar ilk.

Market research is not my forte. I'm more of an ideas guy.... :grin:

Dave

#12 csrlice12

csrlice12

    ISS

  • *****
  • Posts: 21695
  • Joined: 22 May 2012

Posted 23 September 2012 - 01:11 PM

How about a little "toggle switch" that could rotate the bar? If the bar was shaped thin and flat like a Hershey Bar, as you toggled it, it would get thicker/thinner....

#13 kfiscus

kfiscus

    Baltic Birch Dob Bases

  • *****
  • Vendors
  • Posts: 5898
  • Joined: 09 Jul 2012

Posted 23 September 2012 - 01:26 PM

I'd buy one. I can guarantee that someone doing this could eventually sell several hundred, especially when communities like this one began talking the gizmos up. I asked the same question as the OP on a different, much more boring forum (different website) and got similar how-tos that I'm not going to do to my EPs that have green paint. If a cheap add-on could be put on the stock 25 and 10 Plossls that are everywhere, you'd be on to something...
I'd pay $100 for one. Imagine if you just had to send in a check for a $100 and an Orion 25 or 10 EP and they shipped you a modified unit. It could be as simple as making REALLY fat crosshairs or a single hair.

#14 Scott in NC

Scott in NC

    Refractor Fanatic

  • *****
  • Administrators
  • Posts: 29787
  • Joined: 05 Mar 2005

Posted 23 September 2012 - 01:31 PM

The market is limited to people trying to see the moons of Mars, Saturn, Uranus and Neptune and to attempts at seeing Sirius B, Procyon B and other doubles of similar ilk.


You've got a point there, Dave. But then again, how many different objects is a hydrogen beta filter useful for viewing? Not many, but these still seem to sell. I don't see myself trying to fiddle with making an occulting bar, but I'd probably buy one if it were marketed.

#15 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 28140
  • Joined: 18 Dec 2007

Posted 23 September 2012 - 05:42 PM

I think the best solution would be to construct a gizmo that could be inserted into the end of an eyepiece and removed at will, not modify an eyepiece. What would an occulting bar be used for? - to cover up the brighter star of a double in order to see the dimmer star, or to cover up a planet in order to see a close or dim moon. Many observers doing such work would be utilzing Orthoscopics or other eyepieces which have accessible focal planes.

So I don't see that modifying an eyepiece permanently and specifically for an occulting bar would be cost effective or convenient. Personally, I'd rather not send my eyepieces to someone else to modify.

Mike

#16 faackanders2

faackanders2

    Fly Me to the Moon

  • *****
  • Posts: 5353
  • Joined: 28 Mar 2011

Posted 23 September 2012 - 07:04 PM

I used black electrical tape on my cheapest eyepiece.

#17 helpwanted

helpwanted

    Aurora

  • *****
  • Posts: 4696
  • Joined: 04 Jul 2007

Posted 23 September 2012 - 07:04 PM

I'll buy one too!

#18 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 37382
  • Joined: 23 Jun 2003

Posted 23 September 2012 - 07:39 PM

I grew up poor, in the do-it-yourself era.
How to make an occulting bar:
1) Get a simple type of eyepiece in which the focal plane is below the last lens in the eyepiece. Complex designs with the focal plane in between lens groups will not work unless you are willing to take the eyepiece apart (not recommended).
2) Get a wooden matchstick (or its equivalent) and cut the wood with an Exacto knife until it is the same length as the inside diameter of the eyepiece barrel.
3) shove the matchstick up inside the barrel until is is in position on the small baffle or ring that forms the field stop. This guarantees the matchstick is in focus.

Voila! Cheap. Works. Easy to remove later.

#19 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 28140
  • Joined: 18 Dec 2007

Posted 23 September 2012 - 08:26 PM

:waytogo:

#20 Scott in NC

Scott in NC

    Refractor Fanatic

  • *****
  • Administrators
  • Posts: 29787
  • Joined: 05 Mar 2005

Posted 23 September 2012 - 08:48 PM

Get a simple type of eyepiece in which the focal plane is below the last lens in the eyepiece.


Great advice, Don. Would a Plossl fit in this category?

#21 Cotts

Cotts

    Just Wondering

  • *****
  • Moderators
  • Posts: 8641
  • Joined: 10 Oct 2005

Posted 23 September 2012 - 09:06 PM

I grew up poor, in the do-it-yourself era.
How to make an occulting bar:
1) Get a simple type of eyepiece in which the focal plane is below the last lens in the eyepiece. Complex designs with the focal plane in between lens groups will not work unless you are willing to take the eyepiece apart (not recommended).
2) Get a wooden matchstick (or its equivalent) and cut the wood with an Exacto knife until it is the same length as the inside diameter of the eyepiece barrel.
3) shove the matchstick up inside the barrel until is is in position on the small baffle or ring that forms the field stop. This guarantees the matchstick is in focus.

Voila! Cheap. Works. Easy to remove later.


The above is true, Don, and folks have been doing this sort of DIY for many years. Giventhat most people are using more than one scope and that the typical targets for occulting bar use subtend a variety of angular sizes
a system of interchangeable occulting bars would be interesting and useful. A simple match may be too large or too small for some targets....

Dave

#22 kfiscus

kfiscus

    Baltic Birch Dob Bases

  • *****
  • Vendors
  • Posts: 5898
  • Joined: 09 Jul 2012

Posted 23 September 2012 - 09:59 PM

I like!!!!!

#23 FirstSight

FirstSight

    Duke of Deneb

  • *****
  • Moderators
  • Posts: 13389
  • Joined: 26 Dec 2005

Posted 23 September 2012 - 10:16 PM

Because it is too easy to make one out of aluminum foil......


Or, better still a narrow slit of duck or surgical tape. This also solves the problem of how you're going to mount the thing. What about the risk of the adhesive side inadvertently touching and sticking goo on the bottom lens? Simply make the strip double-sided across most of the barrel aperture width, with adhesive sides facing each other, leave both ends one-sided where you're going to adhere it to the barrel. Or use a similar idea, except use a duct tape strip for one side, aluminum foil strip for the other face to face.

Will it actually work? I saw none other than Sue French use an occulting bar home-constructed this way on the fly at Winter Star Party.

#24 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 37382
  • Joined: 23 Jun 2003

Posted 24 September 2012 - 12:08 AM

I grew up poor, in the do-it-yourself era.
How to make an occulting bar:
1) Get a simple type of eyepiece in which the focal plane is below the last lens in the eyepiece. Complex designs with the focal plane in between lens groups will not work unless you are willing to take the eyepiece apart (not recommended).
2) Get a wooden matchstick (or its equivalent) and cut the wood with an Exacto knife until it is the same length as the inside diameter of the eyepiece barrel.
3) shove the matchstick up inside the barrel until is is in position on the small baffle or ring that forms the field stop. This guarantees the matchstick is in focus.

Voila! Cheap. Works. Easy to remove later.


The above is true, Don, and folks have been doing this sort of DIY for many years. Giventhat most people are using more than one scope and that the typical targets for occulting bar use subtend a variety of angular sizes
a system of interchangeable occulting bars would be interesting and useful. A simple match may be too large or too small for some targets....

Dave

Sure. Now that I think of it, a wooden toothpick is probably going to be easier to find for most people now., and would work equally well and be thinner.
Too thin and it won't be visible against a dark sky, so hair and wire won't work. But a piece of cardboard would work.
I don't really understand the WHY of tape--it would cover most of the field of view. In that case, you might as well use the edge of the field of view.

#25 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 37382
  • Joined: 23 Jun 2003

Posted 24 September 2012 - 12:10 AM


Get a simple type of eyepiece in which the focal plane is below the last lens in the eyepiece.


Great advice, Don. Would a Plossl fit in this category?

Yes,
Kellner, RKE, Plossl, Abbe Orthoscopic, monocentric, etc.


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






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics