14 replies to this topic

[wolfli]

I'm trying to binoview the sun through a 1.25" Herschel wedge, so a barlow / GPC in front of the diagonal would not make sense. Also the binotron 27's body thread was a bit larger than the standard 1.25" filter thread. Who knows what exactly the "binotron-27" thread spec is, and Russ would not tell me lol. Most 1.25" eyepiece filters cannot connect because the male thread is just a bit too small. 

 

I tried out one low tech low budget solution:

A barlow with a detachable lens cell:

https://www.amazon.c...d_source=1&th=1

I was also lucky to find an atypical 1.25 filter that will thread into the binoviewer body. It was maybe just slightly larger than standard. But for some reason it cannot go all in. As you can see in the pic there is still a small gap left between the filter and the body. Anyway, I unscrewed the filter glass and use this as an adapter.

 

 

It worked! The sun comes into focus in my refractor and the contrast was so much better than single eye! I can see so much more! But at the same time it was clear that the barlow is operating at a much higher magnification than designed, due to the long light path of the binoviewer.

 

While it's kinda nice, I am still wondering about the proper solution here. I've heard people say that if the barlow is used with a larger spacing than designed the image will degrade. Not sure whether that is true.

 

Also the connection is not very secure between the binoviewer body and the filter housing.

 

Does anyone know a better solution?

Edited by wolfli, 21 June 2024 - 10:26 PM.

[betacygni]

Best solution would probably be to get a thread adapter that goes from the binotron thread to a t2 thread. The t2 thread is pretty common so should be easier to adapt that to your preferred barlow.

This adapter should do the trick: https://rafcamera.co...-to-m29x0-5m-bi

Within reason the extra distance of a barlow being used in a binoviewer shouldn’t effect image quality, but will increase magnification from its advertised amount.

Edited by betacygni, 21 June 2024 - 10:30 PM.

[wolfli]

Best solution would probably be to get a thread adapter that goes from the binotron thread to a t2 thread. The t2 thread is pretty common so should be easier to adapt that to your preferred barlow.

This adapter should do the trick: https://rafcamera.co...-to-m29x0-5m-bi

Thanks! Are we sure that this is the right thread? because it says Denk II not binotron. (They have a binotron version of this but the thread spec is exactly M28.5x0.6 which is the 1.25 filter thread. This gets me very confused.)

[betacygni]

Thanks! Are we sure that this is the right thread? because it says Denk II not binotron. (They have a binotron version of this but the thread spec is exactly M28.5x0.6 which is the 1.25 filter thread. This gets me very confused.)

I purchased from the same company an m29x0.5 female to male t2 adapter, so I could put a generic t2 adapter on my denkmeier collimation device. It fit that, and since the collimation device is designed to thread into the binotrons, I’d think they are the same, unless perhaps denk has different threads on the powerswitch sides, or some other funny business. That’s probably unlikely through.

Edited by betacygni, 21 June 2024 - 10:48 PM.

[wolfli]

Awesome! This is very good to know! 

I don't think Denkmeier makes a OCS that screws on to the body itself, right?

Edited by wolfli, 21 June 2024 - 10:59 PM.

[betacygni]

There is another option too, though more expensive. Denkmeier sells a baader quick changer bayonet, that allows you to attach the binotron to the baader t2 quick changer system. The baader quick changer uses t2 threads you can attach some barlows to (I use the Astro physics BARADV in this fashion).

[betacygni]

Awesome! This is very good to know!

I don't think Denkmeier makes a OCS that screws on to the body itself, right?

They used to, but I don’t believe currently. I’d wager it’s the same thread though. The video of the collimation device shows it threaded directly into the binotron it appears, not the powerswitch.

Edited by betacygni, 21 June 2024 - 11:03 PM.

[wolfli]

Well my herschel wedge is 1.25, so that also constraints the barlow... the Astro physics would not fit

[noisejammer]

I'm trying to binoview the sun through a 1.25" Herschel wedge, so a barlow / GPC in front of the diagonal would not make sense. ...

... Does anyone know a better solution?

I use a Tak 1.6x extender then a 2" wedge ahead of my Mk V binoviewers to observe Sol. The scope's aperture is 150 mm and its focal length is 1100 mm.

 

 

This might sound unwise but I did the calculation years back. If you decide to follow my approach, I advise you to rework the calculation with numbers appropriate to your equipment.

 

Caveats aside, here we go ...

 

It's worth noting that my focal plane is ~220 mm from the entrance pupil of the wedge.

 

Anything ahead of the wedge is exposed to the sun's intensity but because it's a long way out of focus, the actual solar power per square millimetre is only  (1100/220)² = 25x higher than it would be in normal sunlight. This means the energy density at the wedge's entrance pupil is 25 mW / mm².

 

Optical glass absorbs very little light. The quoted figure is 1.6%  per centimetre of thickness. If we assume the extender has about 1 cm of glass*, it will absorb 0.4 mW / mm². This is spread over the four elements, so each element is absorbing something like 0.1 mW / mm².

 

We've assumed the elements are 2.5 mm thick so the energy absorption is about 40 micro-watts per cubic millimetre. The sun's energy is spread evenly through the volume of the glass, so there are no stresses from a thermal gradient. **

 

Does this matter? Compare it with the temperature rise if you leave the extender in the full sun. I estimated this was 4.5 watts and lead to a 15C temperature rise. The extender was quite safe. I honestly doubt that 0.3 watts from sunlight will matter at all.

 

My experience is that inserting a good Extender ahead of my Herschel wedge is absolutely fine. I've been doing it for years.

 

Slightly off topic - the Baader solar continuum filter is superb at showing fine detail on the sun's disc. If you don't have one of these, an O-III filter is nearly as good. In either case, make sure these are inserted after the wedge and its ND filter. This is to prevent focused sunlight setting fire to the inside of your telescope. (I have actually seen this happen.)

 

* It's probably about 8 mm but I'm being conservative.

 

** This is a good approximation because the energy passing through the element is essentially constant.

[wolfli]

this is interesting, I wonder whether heating up the extender before the wedge will create air disturbance inside the tube that affects the seeing. A few degrees will likely not hurt the glass, but hurt the seeing.

Edited by wolfli, 22 June 2024 - 10:04 AM.

[Reflector1234]

Thanks! Are we sure that this is the right thread? because it says Denk II not binotron. (They have a binotron version of this but the thread spec is exactly M28.5x0.6 which is the 1.25 filter thread. This gets me very confused.)

I have that M28.5x0.6 to T-2 dovetail adapter. It does fit the Binotron 27. It's a better fit than a 1.25" filter thread (I tried it with a 1.25" Orion Ultrablock). But it's not as good of a fit compared to Denkmeier adapters. This is true for the Binotron 27 body as well as the Power x Switch.

 

I measured the thread outer diameters. The M28.5x0.6 to T-2 dovetail adapter threads have an outer diameter of 28.35 mm. The threads on the 2" Denkmeier nosepiece are 28.6 mm. The threads on the Denkmeier nosepiece appear to have a pitch that is less than 0.6 mm, but I don't have a thread gauge to know for sure. I divided the threaded length by the number of threads, not the best method.

 

I would guess that the M29x0.5 thread is closer to the Denkmeier spec. 

[wolfli]

Cool the top secret thread is very likely M29x0.5 then 

[noisejammer]

this is interesting, I wonder whether heating up the extender before the wedge will create air disturbance inside the tube that affects the seeing. A few degrees will likely not hurt the glass, but hurt the seeing.

Thank you.

I have no idea whether it hurts the seeing but say you have a 150mm aperture. The scope is collecting ~17.7 watts through the main optics. All of this is dumped into the wedge's heat sink. It barely causes my heatsink to warm up.

 

The 0.3 watts that might be absorbed by the extender represents a 1.7% thermal effect. I doubt you will see that. (I know I can't.)

[Reflector1234]

I have that M28.5x0.6 to T-2 dovetail adapter. It does fit the Binotron 27. It's a better fit than a 1.25" filter thread (I tried it with a 1.25" Orion Ultrablock). But it's not as good of a fit compared to Denkmeier adapters. This is true for the Binotron 27 body as well as the Power x Switch.

 

I measured the thread outer diameters. The M28.5x0.6 to T-2 dovetail adapter threads have an outer diameter of 28.35 mm. The threads on the 2" Denkmeier nosepiece are 28.6 mm. The threads on the Denkmeier nosepiece appear to have a pitch that is less than 0.6 mm, but I don't have a thread gauge to know for sure. I divided the threaded length by the number of threads, not the best method.

 

I would guess that the M29x0.5 thread is closer to the Denkmeier spec. 

UPDATE: I purchased the M29x0.5 to T-2 rotatable adapter from RAFCAMERA and it does NOT fit the Binotron 27. The adapter binds after about 1/3 of a turn when screwing the male M29x0.5 thread into either the Power x Switch or Binotron 27 body. I checked the OD of the M29 threads: it was exactly 29.00 mm. I tried filing down the threads to 28.6 mm for “fun”, that got me up to a 1/2 turn before binding. 
 

It looks like M28.5x0.6 is the best (male) thread match. 

[Reid W]

I recently picked up a Binotron, and have sent a note to Russ about the 1.25" nosepiece.  

Sometimes you need the 1.25" and I would think he has them in stock.

 

 

It's good to see that RAF offers a solution though.