Posts Made By: Donald Durbin

Hi Joe,

Other than the fact that you can use 2" filters, I do not think there is any advantage to using a 2" diagonal on a binoviewer that has less clear aperture than a 1 1/4" diagonal provides.

Don Durbin

Hi Slava,

For some reason we got three of this message. I have deleted the other two copies.

I think you have the problem backwards in your DOB OCS question. You would need to be able to move the binoviewer in an extra 4-5 inches, not out. Most DOBs do not have that kind of in travel.

I have heard of people shortening their truss tubes. I never recommend this as it also moves the secondary mirror closer to the primary mirror. This can effectively reduce the size of your primary mirror.

The best solution is an OCS or OCA. You can get these down to about 1.25 mag now.

Don Durbin

All of the Binoviewers should work very well with a C11. You will not need an OCA/OCS because of the wide range of focus in an SCT.

Because the C11 is an F10, you should be able to use most EPs without problems.

You should be able to use anything from 24mm to 10mm with your C11.

You may even be able to add a low power focal reducer to increase the field of view.

Don Durbin

I have 18mm Radians and 19mm Panoptics. I prefer the Radians over the Panoptics. I wish they made 24mm Radians.

Don Durbin

Small aperture scopes make great terrestrial viewers. A lot of refractors will focus a binoviewer when the diagonal is removed from the light path. To see if your scope will work in this manner, focus one of the EP's you plan to use without a diagonal and then measure the amount of in-travel you have remaining. You need a little more than 100mm for a Burgess or other Chinese make. (Orion, WO, Stellarvue, etc.) You need a little over 115mm for a Denk (Remember to remove any PowerSwitch.) A Siebert needs 120mm and a Televue needs 130mm. This is assuming you do not have an OCA or OCS. With a corrector you can probably use a diagonal. Consult the binoviewer manufacturer for more details.


Using the scope without a diagonal can be a real pain in the neck if you are viewing the night sky, but it is a natural for terrestrial viewing if you have the scope at eye height.

For Planets and other near Earth objects a small aperture telescope can give pleasing views. This is especially true for bright objects. The small light grasp of the scope coupled with the light loss through the binoviewer can help bring out subtle detail in a bright object. (Venus, Saturn, Jupiter, and Mars on a close approach.) There is also the two eye binoviewer effect that appears to increase the size of the image by about 30%.

Of course this is assuming you have an optical corrector for your binoviewer or your scope can focus the binoviewer without one. Most all SCT's and even some refractors can do this. (My TAK FS-128 can focus all but the Televue.) Also remember that different EP's focus at different points. You want the EP's that focus the furthest out for binoviewing without an optical corrector.

I have also modified both an SN-8 and an SN-10 with a low profile focusers to use with my Burgess binoviewers without an optical corrector.

Don Durbin

Louis,

First try different EPs. The further out an EP focuses in your refractor, the less in focus travel it will need in the binoviewer.

You can probably come to focus using a Barlow, but the magnification may be too high. You can try putting the Barlow directly on the Denk for the least amount of magnification or in front of the diagonal which will result in more magnification.

Does your Denk have a 2" nose or a 1 1/4" nose or do you have both? A 1 1/4" nose can be used with a 1 1/4" diagonal and needs less in-travel. You can buy a 1 1/4" nose for your Denk. They are not expensive.

Denk also makes adapters to focus your binoviewer in about any scope or you can post a want ad for either a 2" or a 1 1/4" Denk OCS designed to work with your particular scope.

Finally you can try building your own OCA.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=313188&poll_id=&news_id=&page=

Good Luck
Don Durbin

If you are using a 2" diagonal, switch to a 1 1/4" diagonal.

Next try putting the corrector in front of the 1 1/4" diagonal.

Don Durbin

Hi Bob,

I have a different solution.

I have some friends with both a 22" and a 25" Obsession. I introduced them to binoviewers. They also have a Canon 20Da DSLR. They could not reach focus in their scopes with the DSLR.

I have a Siebert 2" binoviewer and I bought a Siebert MultiMag OCA to go with it. I have used it in our clubs 25" DOB and I was sure I could focus in the Obsessions with it. I got to thinking about it and I began to wonder if the MultiMag could solve the focus problem for DSLR's.

The Multimag is a little better than a Barlow because it has lower magnification powers.

My friends setup their new 25" Obsession Tuesday night and I brought over my Canon XSi 12 megapixel camera. We took shots with their 20Da and with my Canon XSi. The live view in the XSi was easier to use than the FC mode in the 20Da.

The colmination was not perfect. This is a new scope and they are still working with it. Also the tracking was not perfect and this was not a guided image. The focus might have been off a little too.

The attached is a 20 second exposure of M13 taken at 800 ISO with the XSi.

WE were concerned about any vignetting but I do not see any. This image was taken at full resolution resized to 800 X 533. It is not cropped. I did use picaso to bring up the overall gain a little.

Don Dubrin

Are the Chinese imports now the name brand products? I suspect in a lot of cases that is true.

Don Durbin

Hi Rod,

I have always been of the opinion that once you go bino, you never go back. So it was not a fad for me. For public events, I often go Cyclops, but for my personal viewing its either a bino or a DSLR plugged into the focuser.

I have a set of 40m clear aperture, 2" Siebert Echelons that I have been playing with for a year or so. I recently got a pair of 24mm Baader Hyperion EPs to go with them. I like the 24mm Baader Hyperion EPs because the 1 1/4" adapter screws right off leaving a clean 2" barrel.


Don