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Binotron and SV 102ED refractor

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#1 coconut

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Posted 10 October 2019 - 03:45 AM

Hi all

 

I would like to mate these two with the Baader  system diagonal.With all the Baader parts available whitch part # would achieve this with the best configuation ? Do I need a special dovetail between the diagonal to dock with the Denk,I beleive I do and if so who sells it ?

 

thanks



#2 Eddgie

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Posted 10 October 2019 - 08:14 AM

There are two ways to attach a Denk II to a T2 diagonal.  The first is to have a custom made dovetail that attaches to the Denk, then use the Baader Quick Connector.  I had such a dovetail made for my Binotron.  Denkmeier made it for me but they no longer make this part. You could probably get the dimensions from a Mark V.  That is what I did.

 

The second would be to buy a T2 adapter from RAF Camera. This would screw on to the bottom of the binoviewer and then thread to the top of the T2 diagonal).

 

https://www.rafcamer...-t2-to-denk2-v2

 

Now, here is why I would not recommend it if you have a Denk II with power switch (which you did not say you had, but I am just making sure that I cover your question.

 

First, with the power switch, even with the T2 diagonal, it is doubtful that you will reach focus in straight through mode. The power switch and binoviewer have a light path that is in excess of 140mm and even with the short light path T2 prism, you are talking about 39mm of light path, so by the time you add the adapter, you are over 180mm, and even binoviewer ready refractors will struggle to accommodate that much inward travel.

 

Next, even if you are lucky enough to reach focus in straight through,  you won't have enough travel to reach focus in low power mode.  It is just impossible.  The amount of inward focus travel is extreme.  This means that you would be limited to two powers and again, that assumes you would be able to reach focus in straight through mode.   

 

So, if you are using a power switch you won't reach focus in low power mode, and unless you have a binoviewer ready telescope, you might not reach focus in straight through mode.

 

In these cases, it just seems to me (but maybe not to you) that you would be better off simply using the OCS with a standard 2" diagonal.  Yes, you throw away the ability to work at native focal length, but you gain the ability to have three useful powers.

 

If you are only working with the Denk II and no power switch, measure flange to focal plane distance carefully (distance from the back of the fully racked in focuser to the focal plane).  Again, just putting your BV on a T2 diagonal does not guarantee that you will reach focus.  The light path for the T2 prism is 38mm or 39mm (I forget) and the light path through the Denk II is as I recall, 116mm, but I would measure that too just to be sure, or search the forum for people that have measured it, or ask, but as I recall, it is 116mm.   The light path for the RAF Camera T2 adapter is about 3mm, assuming that it screws all the way in.  

So, the total would be about 158mm.

 

The easy way to estimate the flange to focal plane distance is to put a 2" diagonal into the focuser, and using an eyepiece that has the field stop of the eyepiece near the top of the eyepiece holder (junction of the eyepiece barrel and lens housing) and focus at infinity.   Now, measure the amount of focuser tube that is exposed between the rear of the focuser and the front of the diagonal. Since most 2" diagonals have a light path of around 100mm (you can measure this too to be exact, but I have never seen one shorter than 100mm) you would have need to have 58mm of focuser tube exposed for the Denk II to just reach focus.

 

If my number for the light path of the Denk II is correct though, you now know how to determine if you can reach focus with a T2 diagonal and the RAF Connector, but no power switch.

 

Since I was never able to get the low power arm to work in any refractor configuration without the OCS, I had to make the decision as to whether to work at native focal length and change eyepieces, or to accept the 1.3x low power mode (using the Denk diagonal because standard diagonals only give 1.4x for low power).  I chose to go native focal length (no power switch) an use zooms on smaller scopes that were intended on wide field, and use the OCS on larger scopes that were intended for smaller DSOs (which lets be fair, is mostly what we use larger scopes for) so I would have three useful powers with wide field at each setting.

 

So, I have shared how you can do it, but I have also cautioned you on things that you should consider before spending any money on this, and things you can measure to see what configuration options would be best for you.  Until you know your flange to focal plane distance, you really don't know what options you have.


Edited by Eddgie, 10 October 2019 - 08:29 AM.


#3 coconut

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Posted 10 October 2019 - 09:34 AM

Thanks Edggie

 

This gives me confidence to make sure it will work.I was gonna be using the powerswitch but it seems it will not work but in native.

I have my eye on a SV 110ED  bino friendly so I assume it could work with the powerswitch ?

Also you refer to Denk II but mine is the Binotron are the calculations the same ?

 

your most helpful as usual.



#4 Eddgie

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Posted 10 October 2019 - 01:23 PM

First, for some reason I thought you had the Denk II.   Most people that have the B27 (Binotron) say it specifically.  Anyway, my fault.   The RAF Adatpter above will not work for the Binotron. Now if you are patient, you can ask Rafael at RAF Camera to make you one. Just give him the thread size.  He will charge you the "Prototype" price and this will be probably 50% more than the cost of the Denk adapter, so probably $50, which is far less expensive than you will get it custom made anywhere else.  Rafael has made several things for me over the last few years and his prices are always extremely reasonable.  Just tell him you want the same as the Denk II one but tell him the thread size.

 

I had the SV110, and as I recall, I did get it to work with the Binotron and T2 configuration, but I don't remember if it reached focus in all three modes.  The power switch takes about 2.5" of focuser travel from the lowest to highest mode.

The problem is that if you use the T2 diagonal, you might not have enough inward travel with the low power mode (using a 55mm extension, and if you don't use any extension, I don't think there was enough out travel for high power mode.

 

It was a long time ago.  If I sill had the 110ED and Binotron, I would check it for you.  My advice would be to post on refractor forum for that configuration.  I am truly sorry that I don't remember what was what, but there are so many combinations I tried with this particular scope that they all run together.  In the end, I wound up using it with the Mark V, and that memory alone suggests that If I could have found a configuration that worked with all three powers, I would have used the Binotron.   But again, that was a few years back, and a lot of scopes have come and gone since then.  

 

If you ask on the Refractor forum, you are more likely to get an answer.  This forum does not get nearly the traffic that the Refractor forum gets.



#5 Eddgie

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Posted 10 October 2019 - 01:35 PM

You can reach Rafael though the Contact link at RAF Camera.  He is super nice.  Just tell him what you want.  It might take a couple of days to hear back from him for a price, and then usually 2-3 weeks for manufacture and shipping. 

 

Again, sorry for not remembering the specifics of the SV110ED but I seem to recall going to the Mark V simply because I could not get a non-OCS solution that would reach focus in all three modes because had I been able to do that, I think I would have done it.  But that was several years ago and I just don't remember. 



#6 coconut

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Posted 10 October 2019 - 02:16 PM

All good Eddgie

Thanks for the great info.




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