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THIS SECTION IS BEING UPDATED.  Note that The New Super Systems have replaced the older Refractor, SCT and Newtonian Power Switch Packages.

Please email us with additional questions not addressed here! We will add them to The FAQ section. This is the only way for us to know what issues are not being addressed here. 


Q: What is meant by "Premium" & "Standard"  Coatings"?
A: This is among the most frequently asked questions that we field. More often, the question is "How can I tell if I have Standard Coatings or Premium Multi-Coatings?" We always make it very clear that there is a difference between our Standard and Premium Coatings and the chart (LINK) detailing the quantitative difference in transmission has been on the Denk website for several years now. We always make certain that our Standard and Denk II Binoviewers have the proper logo cap on them and we never sell logo caps separately. All Standard Denk Binoviewers have single layer magnesium flouride (MgF2) coatings. These coatings have a reflectivity rating of about 1.5% per air to glass surface. Since there are 7 air to glass surfaces in all Denk Binoviewers (an 8th surface is the internal beam splitter wall which has a different and specialized coating), the total reflectivity for a Standard Binoviewer is about 7 X 1.5% = 10.5%. Another way to state this is that the Standard Binoviewer has about 89.5% transmission. The Denk II Binoviewer on the other hand has very specialized Multi-Coatings and 1/8th wave flat prism surfaces. The coatings have an appearance that is different than that of the Standards. See the images below.

This image below on the right image shows The Standard MgF2 coating (left prism) and the Denk II Special Multi-Coating (right prism). It has not been retouched or processed in any way other than resizing for the web. The pale blue coating that is indicative of MgF2 can be seen on the Standard Prism. The Denk II orism on the right has a coating appearance that is deep blue/purple. A very highly anti-reflective multi-coating is always present on the Denk II Prism (in addition to a flatter surface figure of 1/8th wave). Compared to the reflectivity of 1.5% that Mgfl2 produces, the Denk II coating only produces 0.2% reflectivity! The left hand image shows an actual graph that is generated from a witness sample, always present within the Evaporation Chamber as each surface of a Denk II Prism is Coated using our Ion Beam Sputtering Process. Note that our Beam Splitters are made with our own proprietary coating formula! The reading below was from our June 11th, 2008 run and demonstrates the reflectivity across the visible spectrum. The total reflectivity of 7 combined Denk II optical surfaces is typically less than 3% which translates into 97% transmission, an increase in light transmission of 7.5%.

Unfortunately, those consumers who are unfamiliar with coating technology may purchase binoviewers said to have "Premium" coatings, only to later learn from someone more familiar with the issues that the prisms are actually coated with a single layer of
MgF2. Is there anything wrong with a single layer MgF2 Coating? No. We make our Standard Binoviewer with such a coating. However, we also make our Denk II with a highly precise Multi-Layered Dielectric Coating that is substantially more costly to produce, therefore sold at a higher price point. We at Denk are very serious about not misleading our customers and hopefully, the information above will help them become educated consumers. 

Our "Premium" Denk II Beam Splitters Are Coated At The Spectrum Thin Film Facility

Q: What Package should I select for my telescope?
 It's easy! Our Standard and DenkII Super Systems are the very latest Power Switch and Optical Corrector System (OCS) equipped Binoviewer Systems that we make. Russ Lederman designed the Super Systems so that they work on virtually any telescope. The link at the homepage shows how you use either the Standard or DenkII Super System on an SCT, Regractor, or Newtonian Telescope as well as all the sub catagories of these (ex: Classical Cassegrain will work like a refractor would). We have simplified things to take the guesswork out! Also consider the very economical Big Easy. It does not include a Power switch biut will allow various magnification changes depending on telescope being used. This is accomplished by threading nosepieces on and off by hand rather than automatically by way of the Power x Switch.

Q: Power x Switch Diagonal, or Power x Switch Package?
A: If you own a Refractor or SCT, be sure to read more about our new Power x Switch Star Diagonals. These diagonals offer an option where the Power x Switch System is integrated into our diagonals. Newtonians cannot use star diagonals so this is not a Newtonian option. See the Power x Switch Star Diagonals section on our website. The information provided will help you to decide if this is a preferable option. The Guided Shopping System will bring you to this choice when they will operate with your scope.

Q: What if I own more than one telescope?
The Super Systems work for all telescopes. If you haev a Newtonian and other telescopes such as a Refractor or SCT, you must get the Super System or Big Easy. If you have only a Refractor or SCT or both, the Super Systems will also work but an alternative is a Power switch Star Diagonal and a Binoviewer Ala Carte.

Q: What are the magnification factors that result from using a particular system?
Please see the manual for a particular system. A Download Manuals link is found on the upper right column of the Homepage or a link to The manual for any product is generally included on that product description and order page.

Q: Should I collimate my SCT with the Binoviewer in place?
A: The collimating of your SCT must be done with the binoviewer in place if the best possible images are to be produced. This is because the primary mirror of your SCT must be moved toward the secondary convex mirror (negative) in order to push the focal out of the exit aperture of the tube assembly in order to reach focus with the binoviewer/eyepieces. This is to be done with the binoviewer in "normal" focus. In other words, the Multiplier and reducer of the Power x Switch should not be introduced into the light path. I have seen a very big difference in the quality of planetary images after fine tuning the collimation of our company's Celestron SCT with a Denk Binoviewer in place. I will outline my procedures below. The reality is that the scope becomes a different instrument when switching from single eyepieces to binoviewer usage. This must not be ignored if you want the best images possible with the binoviewer setup.

You should certainly have collimation instructions/diagrams that came with you telescope and we assume that you have some familiarity with the collimation procedure. After-market collimation devices may or may not work but our outline below is quick and easy and very accurate and requires no lasers, just a bright star high in the night sky. Bob's Knobs are very highly rated by SCTs because they allow the secondary to be tilted without the use of hex tools.

1. Place binoviewer in the scope and focus on a star near zenith. Use a bright star such as Vega, Capella, Acturus, Regulus etc.

2. Center the star in the field of the eyepiece. This is very important. magnification is really not that important and I collimate using our Denk 21s. You simply are looking at the geometry if the defocused stellar image and as long as you can see the outer bright diffraction rings and the central shadow produced by the secondary mirror, you can achieve a very fine level of collimation.

3.Rack the star out of focus so that it is expanded to approximately the size of a pea.

4.Note the secondary shadow (a circle of darkness in the center of the diffraction pattern). The extra-focal star image will look like a doughnut. The bright outer rings will surround a dark "hole" in the central region.

5. Turn the screws on the secondary mirror until the dark hole is exactly in the center of the bright rings of the extra-focal stellar image. This entire star image will shift anytime the secondary screws are turned. You must re-center the star image before you assess whether the shadow is truly in the center of the star image or not. The advantage of using a wide field eyepiece pair is that the star will not exit the field of view and can be re-centered quickly without you having to move the scope around trying to find it again. The only disadvantage is that it can be more difficult for you to estimate the exact center of a large field of view. Adjusting the secondary mirror gradually will help keep the star pattern within the field of view and make things easier.

6.Once the shadow looks exactly in the center of the diffraction pattern of the defocused star, you must now look for the Airy Disc of the star that is located within the dark shadow in the center of the defocused star. It is a tiny spec of light that may be off center at this point. Positioning this spec of light to the exact center of the "hole" in the extra-focal image is extremely important if sharp tight images are to be produced!

7. It may be easier if the defocused star image is focused down a little bit as this tightens the dark hole and the Airy Disc may be easier to see and center. Once the Airy Disc is seen, it should be moved to exact center of the shadow by adjusting the secondary and be aware that this requires very little movement of the secondary! The smallest turn will move this spec of light quite a bit.

8. Once this collimation procedure has been accomplished, your images with the binoviewer will be as good as they can be. While moving to "reduction" and "multiplication" requires movement of the primary mirror once again, the differences are not as great as those needed when going from single eyepiece usage to binoviewer observations. However, an argument can certainly be made for collimating in "reduction" or "Multiplication" modes if one or the other are going to be used extensively and exclusively during a night's observations.


Q: What eyepieces should I use with my Denk Binoviewer System?
A: It depends on what telescope and Denk system is being used. We will offer some guidelines that will allow optimal performance to be achieved. We always recommend our own Denk D21 and D14 eyepieces first because we assemble, and test them as matched pairs at our Hauppauge NY Facility. Both focal lengths are optically fantastic (ssee a Cloudy Nights Review) , and were developed with our binoviewer systems in mind. However, those already owning certain single eyepieces of other brands that have been previously purchased may wish to mate them with a second unit as a pair for their new Denkmeier Binoviewer System so we will attempt to offer some basic and general guidelines.

Because both The Standard and DII Super Systems allow for focal reduction, it is important to select the proper eyepiece focal length and design to allow for maximum illumination of the eyepiece field stops. It is also advisable to collimate the SCT Secondary with the binoviewer in place for best correction. In focal reduction mode, wide field eyepieces with apparent fields of 60-82 degrees should not exceed 21mm in focal length (ex: 25mm is too long) if edge darkening is not to occur. Also remember that high power modes are possible with the Super Systems including an optional 3X thread-on cell. Here are some recommended eyepieces for each system: 

Note: Denkmeier D21 wide field eyepieces have been carefully designed to operate in any SCT or Universal Package. The 21s operate as if they were 32mm, 65 degree eyepieces in an F/10 SCT when the SCT Power Switch Package of the Standard Universal Power x Switch Package is used and they behave as if they were 35mm, 65 degree eyepiece when the DII Universal Power x Switch Package is used. They have been created specifcally to fully illuminate to the edge when the focal reduction of the Power x Switch device is implemented.

Note: The very popular 24mm, 68 degree wide fields being used regularly in many brands of binoviewers have a very large field stop as do the 30mm Ultima® 50 degree eyepieces that are also very popular. These eyepieces have 27mm+ field stops. Use of these in the Super Systems will produce some edge darkening when the low power arm of the Power x Switch is implemented. Our Power x Switch Star Diagonals are designed to illuminate these eyepieces in their low power mode during Refractor operation. In SCT Focal Reduction Mode with either our Binoviewer's Super System Power x Switch or Star Diagonal Power x Switch, edge darkening is likely to occur. Our D21s will be optimally illuminated to the edge and were designed specifically to eliminate this noticable edge falloff. If 24 Pans are to be used with a refractor, we do recommend our #R1 Power Switch Star Diagonal and a Denk II Ala Carte Binoviewer rather than a Denk Super System where the Power x Switch is attached to the binoviewer. Illumination will be betterin the Low Power Mode.

Shortened Bino-Friendly Refractors

Use of: Standard and Denk II Super System 2" Low Power OCS Cell (it is included).  Consider adding our D21s and/or D14 eyepieces for a great matched set. We assemble and test them in a Denk Binoviewer right in our Ocean City, Maryland facility.

Why Are Some Refractors Shortened?

A typical Binoviewer can add anywhere from 80mm to 150mm of lightpath to an optical system. The eyepieces are now that much further away from the telescope objective. This means that the focal plane produced by the refractor objective needs to pass through that additional binoviewer lightpath if the eyepieces placed in the binoviewer are to produce a focused image for the observer. Therefore, some refractor manufacturers offer scopes that are "cut-off" so that a binoviewer will focus without the need for using additional optical corrector systems (that do the job of moving focus through the binoviewer). While this allows focus and 1X magnifications to occur, the refractor must have extension tubes added so that single eyepieces (with no binoviewer) can be used as well. If the extension was not installed making the refractor a normal length, a single eyepiece would not reach focus because the refractor could not rack out far enough. Remember that the refractor is shorter than normal by over 100mms.

Denkmeier Optical's Relay Power x Switch System

Denkmeier Optical's patent pending relay system that includes power switching features was made for normal length refractors, not shortened refractors. We solved the problem that the additional lightpath of a binoviewer creates via an optical approach. The great thing is that power switching is a feature of this solution and one pair of eyepieces will work at three magnification modes. However, the shortened refractor must be brought to the original normal length when the Power Switch System is being used because our system was designed for conventional refractors, not special sawed-off refractor tubes. However, these special shortened refractors can be used in several ways that utilize our power switching system.

Using Your Refractor Totally Shortened

Removing the extension(s) included with your shortened refractor should allow your Denkmeier Binoviewer to reach focus when loaded into your 2" star diagonal. Use no extensions when 1X is desired and do not thread the OCS Cell onto the binoviewer nosepiece or the telescope-side tube of the star diagonal (this is explained below). The Power x Switch arms will not be functional. 1X occurs. This means that a single eyepiece normally producing 150X without the binoviewer, will still only produce 150X when the binoviewer is used. This is a method to produce "unit power" which may be desirable, especially when striving to maintain as wide of a field as possible.

Obtaining More Versatility And multiple Magnifications With One Pair Of Eyepieces

Instead of  exclusively using the binoviewer in the refractor while the refractor is shortened via its removable extension tubes so that a 1X situation occurs with a pair of eyepieces, utilizing extensions allows the very convenient Power Switch System to be implemented. So, the refractor becomes very versatile if you are aware of all possibilities. Special shortened refractors that always should include extension tubes allowing the refractor to be restored to normal length for single eyepiece usage include: TMB, Stellarvue,  Takahashi (later models), Tele Vue 102i and Bizzaro, and some William Optics refractors. There may be more refractors being made in this manner. Please check with manufacturers to be sure.

Using The Denk II Power X Switch for 3-way Magnification

 When using a Shortened Refractor with some of the refractor tube extensions installed but not all (if your shortened refractor included more than one extension tube), the OCS Cell can be threaded into Denk Binoviewer 2" nosepiece. Normal Length refractors will not reach focus this way. But your shortened refractor may have various extensions available (ask the scope manufacturer), each being of a different length. By installing the appropriate extension,  the Denk Power x Switch will function at three magnifications with one pair of eyepieces. Many shortened refractors offer extensions of varying lengths so it is not a situation where you can only use or not use one long extension. For example, if there were 2 extension tubes that could be added, only one would be used if the OCS Cell were threaded onto the binoviewer nosepiece. If the full length of extensions were added restoring the refractor to normal length, focus would not occur when the lowest power switch arm was pushed in because in-travel would be inadaquate. If a section were then removed, in-travel would be instantly greater by an amount equal to the removed extension tube and focus at the low power setting of the Power Switch could occur. If your shrotened refractor only includes one extension, the OCS Cell must be used on the telescope-side tube of the star diagonal when the extension is installed or you will have to be creative and find a shorter extension tube for your refractor that is not as long as the "full-length" extension. Again, consult with the manufacturer of the specific refractor. A Denkmeier Extension Tube is soon to be available though 2" extensions are commonly obtainable and inexpensive.

Extension Tubes Totally Removed

Your refractor was shortened to allow binoviewer usage at 1X. This is still possible by removing extensions and keeping Power x Switch Arms in the "OUT" position. No Low Power S Cell is then needed when using your refractor in this manner, nor can it be used! You most likely will not have enough out-travel to reach focus if you try to use the Low Power S and the Power x Switch if there are no extensions installed in the refractor.

For Refractors That Have Included Only One Extension Tube

To utilize binoviewer power switching on a shortened refractor design that included only one full length extension tube, Thread the OCS Cell onto the telescope side of star diagonal. This causes all Power X Switch modes to be higher in power by a small amount than if the Low Power S Cell were threaded to the Binoviewer Nosepiece. For those with two or more extension tubes included with the shortened refractor, installing all extensions will allow this option to also be used. You must test and use the system and decide what configuration you like best.

For Refractors That Have a Sliding Extension System

Some new "bino-friendly" refractors have a sliding tube that allows the bino mode to be implemented by sliding the tube inward until the binoviewer focuses. The nice thing about this is that if the tube is slided outward not all of the way but to a midway point, the OCS Cell can be threaded onto the Denk Binoviewer 2" Nosepiece and the Power x Switch will now be fully functional. Once again, the binoviewer can either be used in 1X mode with no OCS Cell used and Power x Switch arms in "OUT" positions and the sliding tube of the refractor fully retracted, or the Power x Switch will be functional by using the 2" OCS Cell threaded into the Binoviewer nosepiece and the sliding refractor section will be set to a midway point.

With the Power x Switch System being used rather than the Shortened 1X-only extension configuration (extension removed mode), your single pair of eyepieces operate as three! Two pairs as six!  Since the 1X mode is still available as well, that adds another variation and the attainment of the widest possible field of view in your Denk Binoviewer.

Remember that all refractors can vary and machining can vary as well, so you must experiment a bit. Example: If you place a mid-range extension in the refractor and have the OCS Cell in the nosepiece of  the binoviewer, and when you push in the high power arm of the power switch you find that out-travel falls terminates before allowing focus to occur, just pull the diagonal out a bit from the scope. Or, maybe try a different extension tube or even purchase a small 2" extension tube to accomodate the small amount of additional out-travel required. You might have to make such minor adjustments to have the scope work perfectly, but understanding the information outlined here will allow you to obtain the maximum amount of variability possible with your shortened refractor and our patent pending Power x Switch System.

Power Switch Star Diagonal R1 and Ala Carte Binoviewer with Shortened Refractor

Shortened Refractors can also utilize the #R1 Power Switch Star Diagonal and Denk II Ala Carte Binoviewer rather than the Denk II refractor Power x Switch Package. With the refractor's extension removed from your scope in (Bino-Friendly Mode), the R1 can be used without the Low Power S Cell in the telescope-side of the diagonal. The Power Switch Arms must be kept in "OUT" position. The Binoviewer will focus at 1X. If in-travel has been implemeted and the binoviewer does not reach focus, then utilizing the R1 Dovetail Connector is like created two additional inches of in-travel and focus can then be acheived. Using the R1 as a Power Switch Diagonal requires the re-introduction of the refractor's extension tube. In this case, the extension is added and the refractor is no longer Bino-Friendly. The Low Power S Cell is threaded into the telescope-side of the R1 Diagonal and now, Power Switching is possible. See the Manual for the Power Switch Star Diaognals and see R1 operation. Charts are supplied with magnification factors.

Newtonian Telescopes

Filter Switch FAQs  Detailed operating instructions with illustrations can be found in The Filter Switch Manual in PDF Format here. This section may help answer some basic questions.

Q: I have an existing Power Switch Star Diagonal. Do I have to send it to Denkmeier Optical for retro-fitting of the Filter switch?
A: Yes. We must remove the Power Switch from the diagonal and install the Filter Switch in it's place. Then we install the Power Switch so that it is situated between the Binoviewer and the Filter Switch unit
. We have the proper tools for undertaking this procedure and we want to make sure that all connections are done properly and securely.

Send to: Filter Switch Retro
             Denkmeier Optical
            135 Marcus Blvd 
                   Hauppauge, NY 11788

Include a check for $189 + $15 Fedex Return Shipping or enclose credit card information. You may call in credit card information as well using the toll-free number. 866-340-4578

I have a Power x Switch on my Denk Binoviewer. Can I install the Filter Switch myself?
A: Yes. This is a very different procedure and no tools are involved. The Binoviewer nosepiece is removed from the binoviewer Power x Switch, The Dovetail Adapter is then threaded into the Power x Switch, and then the Filter Switch is Docked to the Dovetail Connector using two thumbscrews. The Filter Switch includes a new special 2" nosepiece that threads to the telescope-side of the Filter Switch. The same installation procedure will apply to all Denk Binoviewers without Power x Switches. The Filter Switch will dock to the Dovetail Connector and can be oriented at any angle and locked into place.

Q: Will additional in-travel be required with my Newtonian when adding a Filter Switch to my current Power x Switch System?
A: No. In fact, 1/8" less in-travel will be required. Example: You currently have .25" of remaining in-travel of your focuser tube when using the Denk II Binoviewer with the Low-Power Arm of the binoviewer 's Power Switch being used. After adding the new Filter Switch with the supplied new replacement Spacer Tubes, there will be .5" remaining in-travel. That's a gain of 1/4" back focus. Magnification will not change.

Q: I have 1.25" and 2" Filters. Can I use them all with the Filter switch?
A: Yes. You must order 1.25" optional step-down adapters at $8 each.

Q: Should extra 2" Carriers and extra 1.25" step-down filter adapters be ordered for all of my filters that I use?
A: The purpose of the Filter Switch is to make using all of your filters easy, convenient, and fun to use while offering protection as well. It is a good idea to load all of your 1.25" and 2" Filters into the carriers so that they may be loaded into the Filter Switch quickly and easily rather than removing filters from the same Carrier and replacing them with other filters. Someone who owns two 1.25" Filters and two 2" filters would ideally order two 1.25" Step-Down Carriers and two additional 2" Carriers to hold the 1.25" Dtep-Down Carriers. Two 2" carriers are always included with the Filter Switch. In this way, the 1.25" Filters would be kept in the plastic cases included with the two optional 2" Carriers and those 2" optiona
l Carriers would already be loaded with the 1.25" Step-Down Carriers that contain the user's 1.25" Filters.  The exchanging of Carriers into and out of the Filter Switch Housing only takes seconds. With the proper Carriers ordered, only the removal and introduction of the 2" Carriers into and out of the Filter Switch would be required.

Q: Will I need additional in-travel if I am using a refractor and add a Filter Switch Star Diagonal or have my William Optics 2" Star Diagonal converted? And If I use an SCT, will the Filter Switch add enough profile to cause  base clearance problems or focus problems?
A: There is additional in-travel that is required when using refractors. Your eyepieces should reach focus with a typical 2" star diagonal and have .75" remaining in-travel or focus might not be achievable when adding a Filter Switch Diagonal or having your William Optics Diagonal retro-fitted with a Filter Switch. It is advisable to check this situation before making a decision because if there is less than .5" in-travel remaining with certain eyepieces, those same eyepieces will likely not reach focus after a Filter Switch is added. SCTs will not be effected by base clearance issues when adding a Filter Switch Diagonal because the filter Switch is installed on the eyepiece-side of the Star Diagonal. In SCTs, focus issues are not significantly effected by the additional thickness of the Filter Switch unless there is no additional counter-clockwise motion of the SCT focuser knob remaining. This is not a bad thing to check and be sure of, especially for those using a Denkmeier Power x Switch Star Diagonal in "reduction-mode". In such a situation where there is very little or no additional counter-clockwise turns of the telescope's focuser knob available when using a Denk Binoviewer and the Focal Reduction Arm of the Binoviewer Power x Switch or the "A" reducer arm of the Power Switch Star Diaognal, the Filter Switch might make "reduction-Mode" no longer possible. Call techincal assistance if unsure of how to determine this. 866-340-4578. 

Denkmeier Eyepieces

As previously mentioned, our D21 Eyepieces have been carefully designed to operate with all of our systems. Our new D14s are ready and shipping. Please see Denkmeier Eyepieces for additional information.

Q: Power x Switch Diagonal, or Power x Switch Package?
A: If you own a Refractor or SCT, be sure to read more about our Power x Switch Star Diagonals. These diagonals offer an option where the Power x Switch System is integrated into our diagonals. Newtonians cannot use star diagonals so this is not a Newtonian option. See the Power x Switch Star Diagonals section on our website. The information provided will help you to decide if this is a preferable option. The Guided Shopping System will bring you to this choice when they will operate with your scope.

Q: What if I own more than one telescope?
If any of these telescopes are a Newtonian, The Super System does it all!

Q: What if I own a Newtonian as well as an SCT or Refractor?
If you own a Newtonian and Refractor or Newtonian and SCT, then the Universal Power x Switch Package (System) is a great choice. This will allow a Newtonian to operate at low and higher powers and will allow a Refractor or SCT to be used as well. It will alleviate the need for the purchase of additional specialized parts from Denkmeier. There are differences between the performance in an SCT and Refractor with the Universal Power x Switch Package as compared to the specialized packages for those scopes. We will outline these differences in this FAQ list. It should be noted that selection of the appropriate eyepieces could allow top performance in SCTs and Refractors when using the Universal Packages. We will address this in the FAQs as well.

Q: What are the magnification factors that result from using a particular Denkmeier system?
 Please consult the Big Easy, Super System, and Power Switch Star Diagonal manuals. All have complete information regarding magnification factors.

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