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Thank you for visiting Siebert Optics!
Serving Large Observatories and the Amateur Astronomy Community alike.

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Clayton, NC 
USA  27520


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Eyepieces .965" / 1.25" / 2.0" / 2.7" / 3.0" / 4.0" / 4.3"


Large and Small Binocular Cleaning and Alignment services $99 Call or Email for details.


BT70 RA88 / Miyauchi / Kowa eyepieces


Binoviewer Alignment and Supercharge Services


(Specialized Binoviewer services you can't get anywhere else)


Advanced Barlow Lenses including: Modular and 4 element Telecentric magnification multipliers


1.25" and 2" Advanced Binoviewers From $649-$1999


 Binoviewer OCA's and Accessories


Adapters - Meade Scopes and ETX


Binoculars - Quality Modified


Large and Small Non Illuminated and Illuminated Cross haired eyepieces.






Camera Focus Adaptors


Camera Adapters - Universal


H-Alpha Focus Accessories



Special binoviewer services and products you cant get anywhere else 

ICP's Image Correction Prisms for Newts




Extension Tubes


Large refractor modular OTA's


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Focal Length Reducers




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Zero Magnification Adapter





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 Binoviewer Correctors & OCA's and FLR's

We are the pioneers of this design.


Always state the Binoviewer that you are going to use with your OCA. Indicating the telescope is important to. I will use this information to optimize the OCA for your system. I can also supply options to avoid any conflicts in equipment usage. The method of connecting your OCA to the bottom of your binoviewer may differ depending on your binoviewer Type. You may have a TV or Baader binoviewer and have a direct OCA to T-2 connection. This opens up the bottom of the binoviewer for greater illumination.

 Do you want to focus your WO/Burgess or Stellarvue binoviewer without an OCA on your Refractor! This includes the WO SD/Astrotech 66mm and Orion 80/100mm ED refractors. See ad #2 for details  Click Here.

What is the difference between an true OCA and a barlow that is typically supplied with these style binoviewers? (click here)

Supercharge your Baader, Burgess, SV, WO or similar binoviewer to work better with your Telescopes and save $$.  See low power, easy focus solutions  below in Ads #1 and #2. 

Ad for all OCA's

 #1a and #1b Performance low cost OCA's For all binos with 22mm or less Prisms.

 #1C You Don't want any extra magnification? If you have a refractor this might be what you need.

 #2 Discontinued.

 #3 High Output Maxlight OCA's for big Prism Binos (24mm+prizms)(including BW-optics)

 #4 Low Profile diagonal friendly OCA's (Very convenient and versatile.)

 #5 SCT Multi Mag adaptors 1.25" and 2" (No focus help but gives extra magnifications to SCT/MCT.)

 #6 Power Mag wheels for Dobs and Refractors (Quick Changing with limited focus swing.)

 #6a  Denk Power Switch Convertion 1.3x - 2.5x - 3.5x or 1x - 2x - 3x

 #7 FLR's for Mak's and SCT's (Focal Length Reducers to reduce magnification.)

 All of these can be found below with more Details.      

Ad #1a     

1.25x  corrector for  Baader, Burgess, WO, Stellarvue, Celestron, Orion,  Moonfish,   BC&F, Binomate and the like.

Please let me know what Binoviewer you are going to use.

 $149 (SBW -1.25x)  This is a simple 1.25x OCA It is a 3 pc unit and is for any telescope Dob or refractor 1.25" Diagonal friendly

Instructions for corrector here

23mm Baader #(Ba23)and standard T2 nose pieces $30






Ad #1b

1.25x Multi Magnification corrector for   Baader, Burgess, WO, Stellarvue, Celestron, Orion,  Moonfish,   BC&F, Binomate and the like.

 Please let me know What Binoviewer you are going to use.

  (SBW-1235)  This is the 4 pc unit and is for any telescope $169 1.25" Diagonal friendly

1.25x, 2.0x, 3.5x

Instructions for this corrector

23mm Baader #(Ba23)and standard T2 nose pieces $30


Please let me know What Binoviewer you are going to use.




Ad #1c

You Don't want any extra magnification? If you have a refractor this might be what you need to come to focus with your binoviewer.

Click Here





These low power correctors are guaranteed to focus in any scope both Dobs or Refractors. 

1.25x oca

23mm Baader T2   #(Ba23) Standard T2 nose pieces $30

Total Dob penetration 3 3/4"

Instructions for corrector here




This is a corrector below that  gives 1.25x magnification with any of these short path  binoviewers. See instructions for a bonus magnification.  Right picture is with optional T2 nose.


1.25x Multi oca

23mm Baader T2   #(Ba23) Standard T2 nose pieces $30

Total Dob penetration 3 3/4"

Instructions for this corrector




  Click Here for more info.  

    Universal Binoviewer MAX Light OCA's 

We are the pioneers of this design.

These will focus any Binoviewer in any telescope.


  Ad #3    

2"   1x and 1.3x Multi Magnification High Output OCA's For all Binoviewers

New 38mm CA available. B) SERIES

See 2" filter thread adaptor below for the (B) series OCA.  (A) series OCA already threaded for 1.25" filters

F2.9 Scopes and above.

No back focus needed. These are Adjustable focus full compensations OCA's and x1 means Zero magnification is added to your eyepieces.

Please let me know what Binoviewer you have and The attachment it has at the bottom EX: T-2. Also Click Here.

OCA's with T-2 male thread tops available for Baader and TV Binoviewers upon request.  

Also Multi Mag adaptors below for all Binoviewers. 

Instructions for All OCAs Belows.


Standard A) SERIES Size OCA here (Large below these)

A1)1.3x Two Piece for Newts & Refractors,  $249. (2OCA13) for F5 scopes on up 

A2)1x Two Piece for Refractors, for F5 scopes on up $249. (2OCAx1) Actual mag is 0.93x  

A3)1,3x.MultiMag Two Piece for Newts & Refractors, $349. (2multiOCA13) Mags 1.3x,  2.0x, 2.7x  for F5 scopes on up

.A4)1x MultiMag Two Piece for Newts & Refractors, $349. (2multiOCAx113) Mags-1x, 1.3x for F5 scopes on up


New Large OCA here 38mm CA    (B) SERIES

2" Filter adpator $30

Click here to see the (P)ower (M)ag (W)heel additions of these focus adaptors. See A1 and A2 in Ad #6 Click here

B1) 1.3x Large 38mm CA OCA for Newts & Refractors,  $349. (2OCA13x38)  For F2.9 scopes on up.   

B2)1x Large 38mm CA OCA for All Refractors,  $349(2OCA1x38)  For F2.9 scopes on up.

B3)1.3x /x2 Large 38mm CA OCA for Newts & Refractors,  $549. (2MultiOCAL132x38)  For F2.9 scopes on up. 

B4)1x / 1.3x Multimag Large 38mm CA OCA for Newts & Refractors, $549. (2MultiOCA113x38)  For F2.9 scopes on up.   

B5)1x / 1.5x Large 38mm CA OCA for Newts & Refractors,  $549. (2MultiOCAL1-1.5x38)  For F2.9 scopes on up.  

B6)1x / 1.5x OR 2x Large 38mm CA OCA for Newts & Refractors,  $549. (2MultiOCAL1-2x38)  For F2.9 scopes on up.  


TV and  Baader 28mm nose piece and is $30

2" base for your binoviewer $99


B) SERIES. More pictures below


 No back focus needed.                                                                                                                   No back focus needed.


OCA's Shown above in Newtonian mode.


Baader Left above can use the quick ring to mount the OCA on the bottom of the Baader binoviewer and used in Dob or other telescopes. The Baader MB and TV on the right can have the OCA screw into the bottom with threaded T2 top on the OCA(See picture on the far right. More below.

                     TV and  Baader MB/28mm nose piece and is $30

To use the OCA in refractors, the Diagonal must have an standard 2" eyepiece holder and the nose of the diagonal must have a 2" dia and standard 2" filter threads at the nose to hold a portion of the OCA. Baader Diagonals can be used but only in the configuration  just specified. EX: Televue diagonals are good like the one above left. Baader above center is setup similar.

The 1.25" nosepiece on the right is for Baader MB and TV with the universal OCA and other OCA I sell like in Ad #4. It has T2 threads at the top and Female 1.25" threads at the bottom. The TV above is using it with the universal OCA.

No back focus needed.

Not enough can be said about the above corrector.  The magnification factor can be as low as .93x and is sharp to the edge of the field of view in a set of my 24mm Ultra Plus's or Panoptic 24mm's.  If you own a refractor and a TV or Denk binoviewer or any other large Prism bino you will be blown away by the bright low magnification images.  It use to be that binoviewing carried a higher magnification price.  Now Siebert Optics has changed all that.  Try this product for 60 days and if you are not completely satisfied return it for a full refund of the purchase price.  This unit has been thoroughly tested in a number of different scopes including specifically TV scopes.  



New Large 38mm CA OCA picture Below





  Ad #4    

Low Profile and 2" Diagonal friendly

Please let me know What Binoviewer you are going to use.

1.25" 1.8x Low Profile Universal OCA for  All Binoviewers including Denk, BW optics, Burgess And  Televue.

Only extends 1.75" below the nose of the binoviewer, similar to the Televue x2 corrector.  


1.25" model, $149 (OCA1#1.8)

Instructions here

TV and  Baader 28mm nose piece and is $30






This corrector has standard filter threads and screws directly into the bottom of your binoviewer's focuser shaft nose.  It is incredibly short and completely parfocal.  Also it is diagonal friendly  like the TV unit.  This means that it does not have to come in 2 pieces, but can be simply be screwed into the nose of your binoviewer and then placed in the diagonal of the scope.  Most 2" diagonals will be deep enough for it to go in completely.  For those that can't a depth adjustment ring  is included which allows you to adjust how deep it goes into your diagonal.   1.25" diagonals usually have their own stop before the mirror or prism.   But this is not all.  


I affectionately term this unit "The Equalizer".  The reason is it takes small format binoviewers and makes them perform like 26mm aperture units in certain key ways.  First it improves light throughput dramatically through the lower 22mm aperture and channels the light to the eyepieces in a very fine beam.  Unlike when using a binoviewer in an SCT where the clear aperture at the bottom of the binoviewer is all important for light throughput, refractors and dobs require an optical path corrector.  So a similar barlow/optical corrector unit must be used anyway.  This is where this unit comes in.  Read the explanation below. 


This little units is going to solve a lot of problems for binoviewer users. There are so many binoviewers out the that have a 22mm clear aperture or less and most people have resolved that there unit will be condemned to being a planetary unit period. But this has now changed. I have heard of people asking about the Televue X2 corrector for their Bino units so they can use lower mag. The TV corrector can give the smaller Binoviewer a great edge in terms of light throughput and wider illuminated fields. But the TV corrector is not threaded for most binos which means that on top of the cost of the corrector you must buy the adapter also for an added expense.  This Siebert 1.8x 1pc OCA can do so much to simplify and enhance small binoviewers.  There are some applications such as in SCT's where a larger aperture makes all the difference in the world.  This is primarily when no corrector is used.  The bottom clear aperture of the binoviewer becomes key to good light throughput.  But in a refractor or dob the playing field can get flat as a pancake, particularly when these correctors are used.  These correctors channel light in a much narrower beam that passes through the smaller aperture binoviewers unrestricted and reach their eyepiece target with almost no light loss except through boundary penetrations.  The end result is unexpectedly bright images.  During tests the Orion was exceptionally bright.  You say, "Well you can expect that".  How about M3?  That globular was fully resolved in my 10" dob, BW optic binoviewer and the 1.8x corrector in place at 140x.   Now keep in mind that my 10" dob is a f/7.2 and is 1850mm in focal length.  But in my scope this was a great magnification for this cluster and averted vision showed a completely resolved cluster.  "Oh, well that is a 6.4 magnitude cluster.  How hard can that be?"  I moved onto the Whirlpool Galaxy which is well over a magnitude 9 and a double smudge was easily viewable in magnitude 5 skies.  In contrast the Whirlpool was not even as easily resolved in my Nexstar 8 with a single eyepiece.     It was easier seen in the 10" dob  with the binoviewer/corrector combo than lower magnification in a single eyepiece on my Nexstar.  For most refractors or dobs the magnification of this corrector provides should  put you in a prime magnification for most deepsky objects.  If you dob has a 1200mm focal length your magnification will be roughly 90x or a 1500mm focal length would be roughly 110x.  This magnification is good for most galaxies and nebulas and, in fact,  you may need quite a bit more on globulars.  One more piece of good news.  Like the Televue x2 corrector it is very short and diagonal friendly so you don't need two separate pieces.  It all fits into your diagonal and has a supplied stop so you can control your depth.  In almost all refractors used it easily came to focus.  In Newtonian's where it can be seated in fully, roughly 2.5", it is completely parfocal with a single eyepiece.  So this optical corrector has it all.  It is short, improves quality of the eyepieces used with it, parfocal and when using a refractor or reflector can illuminate a 65 deg. fov in a 24mm eyepiece as brightly as any large aperture binoviewer can.  This statement is based on comparative tests with larger format binoviewers. 


3 in 1 1.25" SCT'/MCT Multi-mag  Universal OCA for  All Binoviewers   

Please let me know What Binoviewer you are going to use. Also

Low Profile and 2" Diagonal friendly

This will give you 4 different mags.---0.6x/1.2x/2.0x/3.0x  All with one OCA.

1.25" 4 power model, $149 (OCAmultiSCT4)

2"  4 power model, $249 (OCA2multiSCT4)



3 power SCT OCA shown.

An all inclusive optical corrector has been developed for SCT's. It covers 4 different magnifications as follows: -0.6x; 1.2x 2x and 3.0x. All of these combinations are possible with this simple corrector.  Super lightweight and compact. The corrector takes advantage of the SCT's ability to focus which allow the unit to be super low profile. All aluminum construction. All optics have been ray traced for flawless edge performance. The -0.6 is achieved using the focal reduction cell (#1). 3x is achieved using element #2; then last using #1 first then #2 together with a connecting bridge, you will achieve 2x magnification. 1.2x is the binoviewer with no optics in place.

What does this mean? A tremendous savings in eyepiece pairs. Buy one premium set of eyepieces and every magnification is covered. Even relatively inexpensive eyepieces are augmented with the use of these correctors. . Because these corrector cells are threaded for standard filters the other applications are endless.

Price is


The Power Mag Wheel (PMW) for all binoviewers and telescopes. 

Universal and T2 top for TV and Baader.

This is also compatible with my 25mm Dielectric Binoviewer as well.


A series best for scopes F5 and above

A1)  Power Mag Wheel for Dobs/Refractors  1.3x - 2.6x and three spots for filters with a magnification of 1.3x

  $599 (PMW2REF/DOB5a) 

Total focus swing is 33mm max

A2)  Power Mag Wheel for Dobs/Refractors  1.3x - 2.6x - 3.5x and two spots for filters with a magnification of 1.3x

  $699 (PMW3REF/DOB5a) 

Total focus swing is 33mm max 

Made to work with the Baader and TV binoviewer and any binoviewer with T2 Female threads at the bottom. Great for Dobs too with no changing setup at night.


B series best for scopes below F5

B1)   Power Mag Wheel 38mm CA for Dobs/Refractors  1.3x - 2.6x and Three spots for filters with a magnification of 1.3x

  $699 (PMW2REF/DOB5b) 

Total focus swing is 33mm

B2)   Power Mag Wheel 38mm CA for Dobs/Refractors  1.3x - 2.6x - 3.3x and Two spots for filters with a magnification of 1.3x

  $799 (PMW3REF/DOB5b) 

Total focus swing is 33mm

Made to work with the Baader and TV binoviewer and any binoviewer with T2 Female threads at the bottom. Great for Dobs too with no changing setup at night.


  C) All Binos  Power Mag Wheel for MCT's and SCT's  0.7x - 1.2x - 1.7x - 2.3x - 3.0x

  $699 (PMWSCT5) 

The above Power Wheels are for Binoviewers,  Some single eyepiece applications and Photography as well.


  The  Multi magnification Low profile Power Mag Wheel OCA  is Here!

 Switch from between 3 to 5 Mags instantly. . 

Simple put it will be endlessly versatile, expandable and configurable. 


Denkmeier PowerSwitch/Diagonal Easy Convertion Mod 


This Mod will -Let you couple my OCA focus adapter with your Power Switch or Denk PS diagonal and switch from between 3 mags without having to modify your telescope or make other adjustment except turning your focus knob to adjust focus after the power change.

This mod is designed to fix the focus issues inherent to the Denk PS and many telescopes limited ability to focus.

These are priced for the Denk Dual arm versions of both the Denk Power Swiches and Diagonals

For  Dobs Refractors and even SCT/MCT. This makes these good for a much broader range of telescopes. Single arm switches could be $70 cheaper depending on the model you have. Other Denk Switches Fall under custom conversions. See below.

Focus swing specs below are mainly for the Basic 2 arm Denk PS but the Denk Diagoanls will be very close to the same as well.

For General questions and Custom Applications Please Call or email for more details. 


A1)   Power Switch/Diag mod Dobs/Refractors  1.3x - 2.5x - 3.5x

  $349 (DPSREF/DOB3a1) 

Total focus swing is less then 33mm - F4.5 and above


A2)   Power Switch/Diag mod for Refractors  1.0x - 2.0x - 3.0x

  $349 (DPSREF3a2) 

Total focus swing is less then 60mm - F4.5 and above.


Large models below. 38mm CA

B1)   Power Switch/diag mod Dobs/Refractors  1.3x - 2.5x - 3.5x

  $449 (DPSREF/DOB3b1) 

Total focus swing is less then 33mm - F2.9 and above


B2)   Power Switch/diag mod for Refractors  1.0x - 2.0x - 3.0x

  $449 (DPSREF/DOB3b2) 

Total focus swing is less then 60mm - F2.9 and above.





 Switch from between 3 Mags instantly. . Top Pictured, A) model - Good down to F4.5


Switch from between 3 Mags instantly. .Bottom Pictured, B) model - Good down to F2.9












































1.25" or 2" 0.6x FOCAL LENGTH REDUCER FOR ALL Binoviewers.


(Illustrations to right)

 1.25" Barlow type  for all binos $129 (looks similar to shorty type barlow. (FLR125Bar)

 1.25" Filter cell  type  for All binos $99 (Works similar to a filter cell.) (FLR125cel)

2" models below

2" Cell type with 40mm optics $179  (Works similar to a filter cell.)(FLR2cel)

  2" 1.25" Holder type with 40mm optics $179  (Works similar to a tall 1.25" to 2" stepdown) See last picture  (FLR2holder)

  2" Holder type with 40mm optics $199  (Works similar to a 2" barlow.)(FLR2barlow)






Have a wider True field with the same eyepieces.

How it works. 

This a focal length reducer for your SCT and binoviewers.  People need to be warned about these.  They can work very well if you don't overdo the focal length reduction.  That is why this unit is limited to a 40% reduction which means that if your scope is operating at between  f/10 and f/12 you will get a roughly 40% reduction to between f/6-F/7.  This may vary slightly depending on your binoviewer.   This is about the maximum that can reasonably be done for two important reasons.  1.  Focusing.  This unit will focus in virtually any SCT 8" and up with some focusing to spare,  2.  By driving down your focal length below f/6 you may introduce so very serious optical irregularities.  Call for more information about this. Do not expect an f/10 system to be reduced to f/5 or under f/5 and perform halfway decent.  These focal length reducers will maintain excellent image quality and color correction while reducing your scopes magnification.  You can use a set of 24mm SWA without apparent vignetting unlike other models which limit you to more powerful types of eyepieces.  


















 Design benefits of the Siebert Optics  OCA's:

This is the way the design has changed and why.  As long as this unit is kept at 3.5" or shorter the entire cone of light easily makes it through the lower optic with a diameter of 25mm-26mm.   Even the Televue x2 Corrector is roughly 3" from the bottom of the binoviewer and only has a clear aperture of 17mm's.  But because of the length of the unit the entire cone of light makes it through that aperture and the unit remains parfocal.  My personal opinion is there are  no present x2 correctors that has better light throughput or superior image quality to the Televue x2.  But anyone looking at the unit will notice that the upper element is substantially larger than the lower one and not the other way around.  The reason for this is as the light passes through the lower negative element a diverging lighjt cone is created which spreads out , but because of its relatively close proximity to the upper element and the fact that the upper element is larger, very little if any light is lost. The result is a fantastic transmission up to the eyepiece.  If anyone needs proof that a lower negative element deverges light, simply plug a barlow into your scope from f/4-f/10 and you will notice the inside of the barlow  tube is illuminated from just above the element all the way up.  Here is a visual illustration to show what this looks like.


      Convergent beam +150mm                                   divergent beam -150mm

This was the same case in an optical system from f/4 to f/8.  On the left a hollow reflective tube was used the same as on the right.   The whole basis of the Televue powermate series is that the upper positive element is a pupil correcting element that reconverges the beam and eliminates the negative aspects of the negative elements used in standard barlows.  So the problems caused by standard barlows are caused by a diverging element (ie. higher eye relief, vignetting and some light loss)  this is corrected in the powermate.

Some of the larger 2" x2 barlows have a very huge baffle about 1/2 way up to the eyepiece and restricts the aperture roughly down to 30mm's.  These barlows have a negative element of almost 40mm's in diameter.  What this tells you is that even though the lower element is 40mm's the manufacturer knows you are not getting the full benefit of the lower diameter element.  So what needs to be done is similar to what the clever engineers down at Televue have done and that is fine tune the optical system using a large enough lower element to make sure the entire light cone makes it through.  The key is to enlarge the upper element so that as much of the diverging light as possible is retransmitted back into a convergent beam towards the eyepieces.  Look at the pictures below.


(click on pictures below to enlarge)

Comparison between 25mm & 30mm optics    


 25mm vs. 30mm comparison showing optics

  The illustrations above shows the light throughput differences between a 30mm positive element and a 25mm positive element.  Theoretically on paper this represents a 44% increase in light.  What does your eyes tell you?  The left side is substantially brighter given they have the same illumination source.  This is not a new concept.  Objective lenses are made larger for increased brightness.  Because the negative element creates a divergent beam the larger 30mm upper element is imperative to good light throughput.  In my tests comparing the 25mm and 30mm elements the 30mm element reduced vignetting tremendously and gave much better illumination.   If a 25mm element was sufficient for transmitting the necessary light doubtful that the vignetting would have been so drastically reduced by the 30mm element.    Also a 30mm element is the max size necessary for most binoviewers on the market today since none have a larger prism clear aperture of more than 30mm's.   So 25mm's is not enough and 31mm is too much.  This is the principal that our new OCA designs are based on.  Instead of having an extremely large lower element 35mm's or bigger, which in reality is only a psychological advantage.  Any benefits of a larger lower element are quickly wasted due to the distance to the second element and the relatively small size of that second element.  In this case the whole unit is shortened so that the optics are spaced much closer.  The lower element has a clear aperture of roughly 25mm's.  which is at least 2-3 mm's larger than the cone of light at f/4.5.  The whole unit is parfocal so that any advantages of the short unit are not wasted by having to rack your focuser all the way in.  The upper element receives and transmits 44% more of the light reaching it over a 25mm element.  The result is a superbly balanced optimal system that works every bit as good in the 1.25" size as in a 2" size.  Hence why in the units below the 2" is designed exactly the same way as the 1.25' units only in larger diameters.  

Understandably other companies will have their own take and opinions on their own optical designs.  

1.8x OCA


See New video instructions below.




1.8x OCA instruction Video (Click here to watch.)








Older instructions below



All listed products come with a 30-day money-back guarantee* unless otherwise stated.

Specialty order items are not refundable (items made specifically for you).

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