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A good binoviewer for a C11 and a dobson ?

Started by laurent, 07/22/2005 11:52PM
Posted 07/22/2005 11:52PM Opening Post
I have a C11 and I would like to buy a binoviewer for it. At more, I would like if it's possible that the binoviewer is compliant with a dobson.

Could you help me ?

Best regards
Posted 07/23/2005 07:50AM | Edited 07/23/2005 07:53AM #1
Hi Jean,

All the binoviewers on the market today will work with your SCT. However your SCT has a 2800mm focal length. So when using lower powers you will experience some vignetting depending on make and model of your binoviewer.

I myself believe that vignetting is way overrated. You place the object in the center of the field and the dark edges of space are a shade darker when vignetted. You could probably make a case for improved contrast out of that. grin Other people seemed to be really bothered by it so I believe it should be a consideration.

The Burgess/Stellarvue/Celestron binoviewer can use 21mm EPs without noticeable vignetting. That still gives you a magnification of 138X. (I added the 100mm length of the binoviewer to your 2800mm focal length and divided by 21mm.) You can attach a Denkmeier 1 1/4" Starsweeper or a Siebert Optics focal reducer to the Burgess/Stellarvue/Celestron binoviewer and reduce the magnification to under 100X. The Burgess optical corrector may or may not allow you to focus in your DOB. An easy way to determine that is to focus with a single eyepiece that you plan on using in the Burgess binoviewer and measure the remaining in-travel available on your DOB. You will need 1.4" or 35mm of in-travel to reach focus with the Burgess/Stellarvue/Celestron binoviewer and the Burgess corrector. The Stellarvue/Sieberts corrector is adjustable and will allow you to reach focus on your DOB but it also costs a bit more than the Burgess corrector. The Burgess/Stellarvue/Celestron binoviewer is also the lightest weight system putting less strain on focuser and making balancing the scope easier. A big knock against this unit is the lack of Self Centering EP holders found in the more expensive models. I have not had any real problem with cocked EPs but other people have reported the problem.

Another package available is the Denkmeier 'Big Easy' package. This may be the best bang for the buck in an 1 1/4" format. I do not have one of these packages and I have not seen any reviews specifically on this package. My understanding is that this is a Denkmeier standard binoviewer with self centering eyepiece holders and a Modular 1 1/4" Optical Corrector system. This unit should focus in a DOB with out any problem. With the modular unit you have the focal reducer element that when used alone in your SCT will give you wide views. Aside from the Self Centering EP holders, this unit also has an advertised 26mm clear aperture. This should allow use of lower powered eyepieces probably in the range of 27mm without noticeable vignetting. Depending on the optics in the Modular 1 1/4" Optical Corrector system there may be a problem with intrusion into the DOB light path as reported by Sky and Tel. Also when the Denkmeier II came out, a lot of people remarked on how much brighter is was over a Denkmeier standard.

There is also the Siebert 22mm BlackNight unit. This unit has a 22mm Clear Aperture in which 24mm EPs can be used without noticeable vignetting. It has Self Centering EP holders. Sieberts makes a wide array of Optical Correctors for Astronomy and often offers a discount on them to BlackNight owners. Again this unit is a 22mm Clear Aperture and will experience vignetting with 27mm EPs.

Another choice would be the Televue binoviewer with 27mm Clear Aperture and a X2 optical corrector. This unit will focus in an Orion XT10 and will work with or without the X2 corrector in your SCT. This unit has Self Centering EP holders.

The ultimate for Deep Space viewing through your C11 would have to be the Siebert 40mm or 45mm Elites. These are true 2" binoviewers that give outstanding wide field views without need of any Optical Corrector when used with an SCT. The Sieberts Multimag OCA will allow you to come to focus with any telescope that has a 2" focuser. The only negatives about these units are the price and the weight. So far I have not had any real problem with the weight, but where balance is critical this could be a problem.

Weight should be a consideration with any binoviewer setup.

Don Durbin
Burgess BV125 Model C
Burgess binoviewer corrector
Original 22mm BlackNights with Diopters and focal reducer
45mm Elite BlackNights with Diopters
Sieberts 1.3X OCA, Sieberts UltraBarlow, Sieberts Multimag OCA.
Denkmeier Premium Dielectric Coated(Semi, almost Denk IIs
Denkmeier 2" SCT Star Diagonal (Modified)
Denkmeier 2" Star Sweeper SE
Denkmeier 1 1/4" Star Sweeper SE
SAC focal reducer
Meade ETX90
Stellarvue 102APO
Orion 100ED
Celestron C9.25
Orion Atlas 8"
50% Orion XT10
Meade 152ED
TAK FS-128
Coronado SM-40/BF10