Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Setting up a Dob for Binoviewers

  • Please log in to reply
36 replies to this topic

#1 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 13 December 2019 - 11:04 PM

I'm looking for advice regarding setting up my Dob for binoviewing while anxiously awaiting the arrival of a pair of Denis' fine Leica binoviewers. This will be my first experience using any binoviewer. They will be primarily used for medium to high magnification only as I have binocular telescopes for low to medium power wide field views.

 

The BVs have 23mm clear aperture on all sides. They will be used on a 13.1" (332mm) truss Dob with 1478mm focal length. The diagonal is 80mm. I currently have only about 25mm of backfocus. Denis suggested 170mm for the Leicas. A quick raytrace with the secondary moved down enough to give that amount of backfocus shows the rays just passing by the outside edges of the secondary. This is with the rays coming to a point at the focal plane. Obviously I'll lose a small amount of aperture (they almost touch the secondary) and have no diameter of fully illuminated zone.

 

So the question, is it better to go that far or make new trusses that move the secondary some part of the way down and use a Barlow or GPC? I don't really know exactly what a Barlow does to the light cone so I'll try to do some research on that as well.

 

Also please correct any misunderstanding about what the three devices do to the light cone. The scope has a focal ratio of 4.45. If the BVs have a 23mm clear aperture and 146mm focal length that works out to a focal ratio of 6.34. Do I need to Barlow, GPC or Powermate the 4.44 native focal ratio of the telescope to make them work best? 6.34/4.45 = 1.42. If one of these devices is needed how does that change the amount I need to move the secondary?

 

I'd like to use the BVs without adding more glass but with no experience I don't know if that is the best plan given the restrictions described above.

 

Thanks in advance for any help.

 

Take care,

Brent     

 

   



#2 TOMDEY

TOMDEY

    Voyager 1

  • *****
  • Posts: 10,169
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 14 December 2019 - 01:02 AM

Well... you already did the math there... showing that your viewer and folding flat will vignette badly... unless you use a Barlow. This is true of most all binoviewers. I believe this one here (see picture) >>> may be able to take that fast feed and has the advantage of zero back focus. It's a peculiar invention that geometrically splits the pupil, rather than using a beamsplitter. It further comprises a positive relay group that works the zero BF magic. Might be worth considering. I'm probably going to get one... just to see how it performs on my big and fast Dobsonian (36-inch with a 135-inch focal length = F/3.75 or F/4.31 with the ParCorr 2 in there).  --- with no great expectations... so, either way (success of failure) will be OK with me.    Tom

Attached Thumbnails

  • 86 Orion Linear binoviewer.jpg

  • 25585 likes this

#3 denis0007dl

denis0007dl

    Binoviewers Expert

  • *****
  • Vendors
  • Posts: 2,742
  • Joined: 17 Apr 2012
  • Loc: Umag, Croatia, Europe

Posted 14 December 2019 - 04:56 AM

Harry Siebert making high optical quality 1x OCA, so there is no added magnification, and it compensate whole light path taken from binoviewer
https://www.sieberto...Optics-OCA.html
  • Ohmless and 25585 like this

#4 wcw

wcw

    Mariner 2

  • *****
  • Posts: 200
  • Joined: 14 Jun 2012
  • Loc: Red Hook, NY

Posted 14 December 2019 - 11:12 AM

Harry Siebert making high optical quality 1x OCA, so there is no added magnification, and it compensate whole light path taken from binoviewer
https://www.sieberto...Optics-OCA.html

Actually the 1.0x OCA is for refractors. The 1.3x OCA is for Newts, which I use on my f/4 Dob and I highly recommend it. It comes to focus and the views are amazing, no paracorr required!

 

It is what Harry Siebert calls the B series for fast Newts, in Add#3 on his web page. Look for part number 2OCA13x38:

 

"B1) 1.3x Large 38mm CA OCA for Newts & Refractors,  $349. (2OCA13x38)  For F2.9 scopes on up."


  • Spartinix, Ohmless and 25585 like this

#5 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,908
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 16 December 2019 - 02:53 AM

 Brent

I struggled for a long time trying to make my BVer work on my 17.5"F4.5 Dob, with no success.  Including shortening OTA light path as much as possible, stopping short of cutting the tubes. I just did not have enough in-focus to do it. So I gave up on using the BVer on the Dob.

 

A year later I bought a nice 2" ED barlow. After a while it occurred to me to try it in front of the BVer (the BVer has a 2" nosepiece)...Bingo !  Works perfectly.  Images are great, all you'd expect with a setup like that,  DSO are stunning in general, Stuff like the moon, Saturn, M42, Veil neb, etc are incredible.

Gives me the 2-eyed fix I need while I plug away at my binoscope.

IME, a good barlow is an easy fix to your problem.

BTW is was a great deal, Astronomics had it on sale for $49 iirc. One of my favorite accessories. You don't need to drop $349 to fix your problem !

CS

Bob


Edited by Bob4BVM, 16 December 2019 - 02:59 AM.


#6 Miranda2525

Miranda2525

    Gemini

  • *****
  • Posts: 3,275
  • Joined: 12 Jul 2016

Posted 07 January 2020 - 05:12 AM

Well... you already did the math there... showing that your viewer and folding flat will vignette badly... unless you use a Barlow. This is true of most all binoviewers. I believe this one here (see picture) >>> may be able to take that fast feed and has the advantage of zero back focus. It's a peculiar invention that geometrically splits the pupil, rather than using a beamsplitter. It further comprises a positive relay group that works the zero BF magic. Might be worth considering. I'm probably going to get one... just to see how it performs on my big and fast Dobsonian (36-inch with a 135-inch focal length = F/3.75 or F/4.31 with the ParCorr 2 in there).  --- with no great expectations... so, either way (success of failure) will be OK with me.    Tom

This BV'er is no good!  There's quite a few reports about it not working correctly. Don't buy one.



#7 TOMDEY

TOMDEY

    Voyager 1

  • *****
  • Posts: 10,169
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 07 January 2020 - 05:59 AM

This BV'er is no good!  There's quite a few reports about it not working correctly. Don't buy one.

Hi, Miranda! Oh, I'll buy one, just to evaluate it. If it's no good, I'll just throw it out. I buy stuff all the time and keep what's good. The first-hand testing is well worth the price of admission. I even bought over a dozen Star diagonals and then measured the alignments, wavefronts and spectral throughputs on them. Only two were superior in every way (a Lumicon and an Astrophysics).

 

I know the TS BV operates on the principle of disjoint pupil-sharing with a positive relay in there. I expect it will be problematic, but want to enjoy running it thru its paces. My background is government work through B&L, Kodak, ITT, Exelis, L3/Harris, Logistikos, etc. We were always doing destructive testing on commercial hardware and optics... learn a lot that way and need to do that first hand, eliminate anecdotal vicarious reviews, which are interesting, good starting point, but tend to be quite unreliable.

 

I'll test the TS-Optics BV (Orion branded) on the Televue Genesis F/5 APO Refractor. Expect it will suck, but will enjoy finding out. I expect the F/5 feed will severely stress the 1:1 relay group, to the point of abject failure (aka terrible aberrations) and that the disjoint pupil will render bad diffraction effects, and that image merge will be off and not adjustable...  If/when I get around to kicking it around, I'll post back here with my findings.

 

Checking... yep, $450 and in stock, they still offer them! Meh, cheap enough... here goes...    Tom


  • Zwick likes this

#8 DavidViewer

DavidViewer

    Lift Off

  • -----
  • Posts: 6
  • Joined: 14 Jan 2020

Posted 22 January 2020 - 09:32 PM

Hi, Miranda! Oh, I'll buy one, just to evaluate it. If it's no good, I'll just throw it out. I buy stuff all the time and keep what's good. The first-hand testing is well worth the price of admission. I even bought over a dozen Star diagonals and then measured the alignments, wavefronts and spectral throughputs on them. Only two were superior in every way (a Lumicon and an Astrophysics).

 

I know the TS BV operates on the principle of disjoint pupil-sharing with a positive relay in there. I expect it will be problematic, but want to enjoy running it thru its paces. My background is government work through B&L, Kodak, ITT, Exelis, L3/Harris, Logistikos, etc. We were always doing destructive testing on commercial hardware and optics... learn a lot that way and need to do that first hand, eliminate anecdotal vicarious reviews, which are interesting, good starting point, but tend to be quite unreliable.

 

I'll test the TS-Optics BV (Orion branded) on the Televue Genesis F/5 APO Refractor. Expect it will suck, but will enjoy finding out. I expect the F/5 feed will severely stress the 1:1 relay group, to the point of abject failure (aka terrible aberrations) and that the disjoint pupil will render bad diffraction effects, and that image merge will be off and not adjustable...  If/when I get around to kicking it around, I'll post back here with my findings.

 

Checking... yep, $450 and in stock, they still offer them! Meh, cheap enough... here goes...    Tom

Any update yet? If now what are you thinking on time line?



#9 TOMDEY

TOMDEY

    Voyager 1

  • *****
  • Posts: 10,169
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 22 January 2020 - 11:50 PM

Any update yet? If now what are you thinking on time line?

I've been procrastinating but still curious. The description of the thing in the TS-Optics literature is a cryptic combination of marketing and quasi-tech; rather unusual. I admire the inventor for thinking outside the box and coming up with three pretty creative deviations from the "traditional" binoviewers, which are all mired in the same tried and true old reliable rut. The TS addresses and solves five problems inherent to the old way!

 

1) use of beamsplitting coatings to send half (actually less) of the light to each side.
> Solution: Disjoint pupil-sharing entirely eliminates the BS coating issues: intensity and color balance, polarization, light loss.
2) added optical path requiring huge in-travel or Barlow
> Solution: Positive periscopic relay system/group resulting in net-zero optical path aka no added in-travel, no Barlow
3) Rotating IPD adjustment and all its vagaries and complexities
>Solution: Translating IPD adjustment; no hinge needed
4) long optical path severely restricts both feeding F# and aperture aka vignetting problems
>Solution: Periscopic relay avoids that
5) prisms introduce spherical and chromatic aberrations
>Solution: only mirrors, no aberrations

 

Thing is, that all sounds good, but each solution can manifest problems of its own, especially if executed poorly or cheaply. I would be quite amazed if those three profound deviations from tradition can be / have been successfully addressed, for a mere $450. The Orion Video is good. Only one way to find out!

PS: Here's my sketch of a couple of embodiments of disjoint pupil-sharing. Whether you do it this way or beamsplitting, still obeys Emmy Noether's ~No Free Lunch~ theorem.    Tom

 

Well, I just ordered it. Ironically, the Orion website is a disaster, terribly unfriendly, locked me out of my account and won't even let me order as a guest. What a crummy company --- sliding downhill fast. So, I easily and quickly ordered the exact same thing from amazon, no problem at all... and it will arrive here in one and a half days, free shipping. Orion has morphed into one of those fat/lazy companies... sorta the general trend, used to be somewhat full-service and now seems to just be a drop-ship warehouse.

 

Anyway --- looking forward to getting the gizmo and putting it through its paces! I'll probably report back in a few days!    Tom

Attached Thumbnails

  • 23 pupil-sharing approach.jpg
  • 24 Emmy Noether annotated.jpg

  • Zwick likes this

#10 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 25 January 2020 - 09:03 AM

I want to make a new set of truss tubes for the Dob this weekend. I will provide 170mm of back focus to be able to use Denis Leica binoveiwers without a GPC to see how that works and be able to compare later to using the regular tubes and a 2" 2X Powermate.

The focal length is 1480mm, the primary is 330mm, the secondary is 76.2mm and will be positioned 1100mm from the primary. This will reduce the usable area of the primary to 320mm. Will the Leicas will be able to handle the F/4.48 native focal ratio? 23mm of clear aperture times 4.48 is 103mm. It seems like the light cone will not reach the focal plane of the eyepieces but I'm not certain yet what the actual distance is between the front aperture and the eyepiece focal plane. The 170mm distance takes into account the hardware on the telescope end of the BV. Once I've brought them to focus I can know for sure. ;-)

 

Thanks for any suggestions.

 

Take care,

Brent



#11 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,528
  • Joined: 01 Feb 2006

Posted 25 January 2020 - 10:14 AM

If you already know that aperture is reduced to 320mm, then we know that the new focal ratio is now f/4.625. 

 

If the light path of the BV is 103mm, and the front aperture is 23mm, then it will pass a 4.48 light cone.

 

So, if the aperture of the scope is now only 320mm, the focal ratio is now f/4.65 and if the binoviewer has a 23mm front opening and a 103mm light path, it will pass the 4.48 light cone with a bit of room to spare, but your fully illuminted field is going to be quite small.   For this, you look at the entering light cone (which we know is f/4.65) and the front aperture (23mm) and for every multiple of the focal ratio that the light travels the 23mm, the circle will be reduced 1mm.  For a 103mm light path that is 22.7mm, so your fully illuminated circle will only be .3mm, but in truth, your fully illuminated circle would only essentially zero becuase in an system with an undersize secondary mirror, only the exact center of the circle receives the full illumination of the 320mm aperture.

 

So, it is going to pass the f/4.625 light cone, but immediately off of the center of the focal plane the aperture is even further reduced and at this speed, the reduction is almost for sure going to show vignetting under brighter skies.  In those conditions, the sky will appear brighter over the central part of the field and will probably fall off enough to make the outer part of the field noticeably darker.  At this focal ratio, edge of field in a 23mm field will likely be reduced to maybe 30% or 40%.  Under darker skies this will be more difficult to see.

 

Remember also that since the secondary size is unchanged, the percentage of obstruction goes up.

 

None of this may matter that much for very small DSOs, but larger subjects like Nebula will suffer considerable illumination falloff. Nebula at the edge of the field will have lost over 50% of its brightness. 

 

Now none of this should stop you from doing it, but when you factor in the 30% brightness loss of the bioviewer and couple that with the reduced aperture over 99.99999999 percent of the field of view, you will of course not be getting the same performance as you would going monoview.  You do get to use both eyes though..  

 

Obviously this would be a horrible setup for planetary use, but for general use, it probably won't matter much to you I suppose, but if 103mm is the light path, then you will work at 320mm of aperture at the exact center of the field, but only at the exact center of the field.   Once the secondary is undersized, only the very very very exact center of the field receives the full brightness of the remaining aperture.  That is nothing to do with the Binoviewer.. That is just what the binoviewer is fed to start with.  The BV only does this once the focal ratio it can pass is reached. Past this, and only the exact center of the field shows the full brightness of the remaining aperture.  In this case though, if you already know the aperture of the scope is reduced, then then the scope is working at f/4.625, and the BV will not further modify this.. 



#12 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 25 January 2020 - 02:21 PM

Eddgie,

 

Thanks for quantifying what I suspected. Likely not worth the work.

 

With a 2" 2X Powermate I can get down to just under 100X. If I want to go lower than that I'll just use one of the binocular telescopes.

 

Denis informed me that F/6.39 is optimal for the Leicas so I'd like at least 1.43X of Barlow/GPC/OCA/Powermate at any rate. I've successfully focused them with the objective from a 3X Trimag unscrewed and attached to the end of the 1.25" adapter. This yielded about 4.2X so my lowest magnification was around 210X, a little optimistic for everyday use from my driveway. The Baader 2.25X Hyperion Zoom also worked and must have yielded a similar magnification factor, I didn't measure it. I just realized I can thread the Baader 2.25X Barlow with its included T2 adapter into the female thread of the dovetail ring (Duh! the 1.25" adapter screw out.). This could shorten up the distance between the Barlow and the focal plane a little and maybe get a slightly lower mag.

 

This is the front end of the Leica binoviewer. The silver adapter accepts the Baader T2 quick changer dovetail ring which has a female T2 thread. To attach the Powermate I need the PTR-2200 adapter correct?

 

Is this the best option or is there another short and strong way to attach to a GPC/OCA and then into a 2" focuser? I'd like to keep the lever arm as short as possible. In for a penny in for a pound at this point. I might as well go with the best option. Eddgie, you mentioned an RAF adapter to go from the Powermate to the BV front end. Can you link the correct item or is the PTR-2200 the correct solution?

Leica front End

Thanks again for all the help.

 

Take care,

Brent



#13 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,528
  • Joined: 01 Feb 2006

Posted 25 January 2020 - 04:12 PM

I have come to feel that the Televue 2X Binoviewer Amplifier is an excellent option but the Baader 1.7 Newtonian unit is also a very attractive choice, and some people recommend the Seibert OCA which is supposed to give 1.3x or something. 

 

So, lots of options if you want a bit lower power. 

 

But yeah, it is the undersized primary here that would have the big impact but once you get down to the f/4.5 speed, there really is not a 1.25" binoviewer that will allow full aperture performance.  Here though, it would be the undersize primary doing the most harm. Just the geometry of Newtonians.  You can't beat it with bigger apertures really because bigger apertures only work if the prisms are bigger, and the bigger the prism, the longer the light path, which would require even more movement of the secondary to the primary, so that kind of nulls out. You would get a bigger field, but at the cost of more aperture loss. 

 

BV Is very constrained by geometry. 



#14 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 26 January 2020 - 01:58 PM

I thought I might as well maximize the equipment I had while waiting for a 2" 2X Powermate and the requisite adapter.

 

This is the initial configuration using the Baader Hyperion 2.25X Barlow on the end of the 1.25" adapter.

20200126 123424 resized

 

Once I realized the 1.25" adapter could be unscrewed I replaced it with the T2 adapter that comes with the Barlow as shown below. This saved about 13mm between the Barlow and the binoviewer. Even with this The resultant magnification is about 4.5X due the BV light path. That limits me to a low of about 223X with 30mm eyepieces. Also in this image is the 2" PVC adapter I turned to allow my to get away from the 2" to 1.25" adapter that I was using before. It fits over the Barlow and the 1.25" to T2 adapter and slides all the way in to the focuser. 

20200126 123920 resized
 
This is what the stack looked like before...
20200126 123353 resized

 

...and after, freeing up an additional 18mm of additional back focus travel.

20200126 124039 resized
 
The clouds rolled in last night after less than half an hour. I was too busy timing, measuring and calculating to try either the lens cell from the 3X Trimag or the Burgess 1.9X OCA to see if they will come to focus and if so what magnification they provide. Truthfully, I was busy staring at M42 at 223X but... whatever. ;-) 

 

Please read this and correct me if I am in error which is highly likely.

 

If I were going to explain the situation to someone who is sitting where I was a week ago I would say this.

 

If you have enough back focus (read inward travel on your focuser) to bring an eyepiece with a Barlow to focus then that Barlow will also bring your Binoviewer to focus using the same eyepiece. The same is true if you substitute a Powermate for the Barlow in both situations.

 

The difference is the image produced by the Barlow continues to expand as you add distance between the Barlow and the eyepiece, for example by putting a binoviewer in between them. So a 2X Barlow might in fact provide a magnification of 4X or more.  

 

The image produced by the Powermate is magnified by roughly the rating, ie 2X, but then it stays that size so it doesn't matter about the distance between the Powermate and the eyepiece. If you put a binoviewer in between them you will still get about the same magnification, ie 2X. I picture the light cone something like this.

Telescope <======= Eyepiece

 

Thanks for reading.

 

Take care,

Brent


  • denis0007dl likes this

#15 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,528
  • Joined: 01 Feb 2006

Posted 27 January 2020 - 08:58 AM

I thought you already had the Powermate???

 

If not, the consider returning it and getting the Televue Bino Vue Amplifier.

 

https://optcorp.com/...eYaAid2EALw_wcB

 

This will give you 2x, where the powermate would give you a bit more than that (but just a bit, maybe 2.1x)

 

The Powermate though will take about an additional Powermate  will require about 20 mm of inward focuser travel, while the Televue Bino View 2x will be parfocal with a regular eyepiece and will also correct for spherochromatism of the binoviewer prisms.

 

Cost is about $100 less too. 

 

The besides the spherochromatism correction, the nice thing about being parfocal is that you can be assured that it will work in virtually any telescope. 

I am sure the Powermate will be fine too.



#16 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 27 January 2020 - 10:11 AM

Eddgie,

 

I apologize for the confusion. At least no returns will be necessary as I haven't placed any order yet. ;-) Thanks again for all the help you provide on this topic.

 

Two more questions before I order the TV Bino Vue Amplifier.

The Leicas use mirrors not prisms so will the correction provided by the TV Bino Vue Amplifier do any harm to the image?

I have the Baader Quick Connect rings and dovetail. I believe you said the amplifier comes with a T2 thread so I should not need any additional adapters correct?

 

Take care,

Brent 



#17 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,908
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 27 January 2020 - 06:13 PM

Eddgie,

 

I apologize for the confusion. At least no returns will be necessary as I haven't placed any order yet. ;-) Thanks again for all the help you provide on this topic.

 

Two more questions before I order the TV Bino Vue Amplifier.

The Leicas use mirrors not prisms so will the correction provided by the TV Bino Vue Amplifier do any harm to the image?

I have the Baader Quick Connect rings and dovetail. I believe you said the amplifier comes with a T2 thread so I should not need any additional adapters correct?

 

Take care,

Brent 

Brent,

So were you able to reach focus with the barlow ? That's all I use on my f4.5.  I have not noticed the magnification issue with the barlow, it may be there but I have not noticed, maybe because I generally use zoom EP in BVer. BTW the BVers I have are also mirror-based.

CS

Bob



#18 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 27 January 2020 - 06:53 PM

Bob,

 

Yes absolutely. Thank you again for the suggestion. It has allowed me to use the BVs when I could not have otherwise.

 

The reason for going with something telecentric is so I can get down below 200X. The Dob's focal length is 1480mm. The lowest power (so far) I've measured from a Barlow is 4.2X using the objective from a Trimag. That yields an effective magnification of 207X and 0.25 degree FOV with 30mm 52 degree eyepieces. Some nights here just won't support that, other times I'd like to be able to go just a little wider. If I can get down to 2X I could get about 99X and slightly over 0.5 degree FOV. The range would make them much more useful.

 

Since I made the new adapter I may be able to get slightly lower and possibly come to focus using the Burgess 1.9X OCA. I was not able to using the stack I had previously but the additional 18mm of back focus may make the difference. Of course the sky was completely cloudy last night and looks to be the same tonight. ;-)

 

All this makes me want a big binocular telescope even more.

 

Take care,

Brent



#19 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,908
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 27 January 2020 - 10:46 PM

Bob,

 

Yes absolutely. Thank you again for the suggestion. It has allowed me to use the BVs when I could not have otherwise.

 

The reason for going with something telecentric is so I can get down below 200X. The Dob's focal length is 1480mm. The lowest power (so far) I've measured from a Barlow is 4.2X using the objective from a Trimag. That yields an effective magnification of 207X and 0.25 degree FOV with 30mm 52 degree eyepieces. Some nights here just won't support that, other times I'd like to be able to go just a little wider. If I can get down to 2X I could get about 99X and slightly over 0.5 degree FOV. The range would make them much more useful.

 

Since I made the new adapter I may be able to get slightly lower and possibly come to focus using the Burgess 1.9X OCA. I was not able to using the stack I had previously but the additional 18mm of back focus may make the difference. Of course the sky was completely cloudy last night and looks to be the same tonight. ;-)

 

All this makes me want a big binocular telescope even more.

 

Take care,

Brent

I see. Yeah i'd want a lower mag myself. Just never payed enough attention to exactly what i'm actually getting, I tend to just enjoy the bi-views... immensely !     That is what keeps me plugging forward, albeit slowly, on my b-scope project !

 

You think you have a cloud problem ?

I had cataract surgery 4 weeks ago and my vision is brighter and clearer than it's been in years, like new eyes ,,,

Now, how many clear nights have I had since then ? You guessed it, ZERO !

This must qualify for the most extreme case of "new equipment = clouds curse"

 

:)

Bob


  • Starry Messenger likes this

#20 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 28 January 2020 - 09:26 AM

Bob,

 

I'm very sorry to hear it. In Central Florida I'm whining if we get three cloudy nights in a row. I'm at two now but the forecast for tonight is no clouds so I hope to test the other two Barlow elements. I also have the Arcturus 1.85X Barlow but the threads don't fit any adapter I own. I hope it clears for you soon.

 

I didn't hear anything to the contrary so I'm going to order the TV Bino Vue Amplifier. I hope to get a lot of use out of these at least until I build a bigger binocular telescope. Leaning toward 12.5" with 3.1" secondaries for that. I need to do a ray trace. I'm hoping I can handle F/5 flat footed at zenith.

 

Take care,

Brent



#21 Mattimac

Mattimac

    Vostok 1

  • -----
  • Posts: 150
  • Joined: 22 Apr 2016
  • Loc: The Stars at Night - are Big and Bright - Deep in the Heart of Texas

Posted 28 January 2020 - 09:32 AM

Eddgie,

 

I apologize for the confusion. At least no returns will be necessary as I haven't placed any order yet. ;-) Thanks again for all the help you provide on this topic.

 

Two more questions before I order the TV Bino Vue Amplifier.

The Leicas use mirrors not prisms so will the correction provided by the TV Bino Vue Amplifier do any harm to the image?

I have the Baader Quick Connect rings and dovetail. I believe you said the amplifier comes with a T2 thread so I should not need any additional adapters correct?

 

Take care,

Brent 

Brent -- This is a question I have wondered about for some time; thanks for asking.  For example, is the TV Binovue with its 2x amplifier really designed for optimal performance only in faster scopes?  Likewise, are the Baader GPC's optimal only with the Maxbrights or Mark V?  Since the Leica and Zeiss "sharpest" binoviewers have prisms only in the beamsplitter, are they somehow "overcorrected" for spherochromaticism if one uses a Baader GPC or a TV 2x amplifier?  Are they "undercorrected" with a TV 2x powermate?



#22 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,528
  • Joined: 01 Feb 2006

Posted 28 January 2020 - 09:48 AM

Eddgie,

 

I apologize for the confusion. At least no returns will be necessary as I haven't placed any order yet. ;-) Thanks again for all the help you provide on this topic.

 

Two more questions before I order the TV Bino Vue Amplifier.

The Leicas use mirrors not prisms so will the correction provided by the TV Bino Vue Amplifier do any harm to the image?

I have the Baader Quick Connect rings and dovetail. I believe you said the amplifier comes with a T2 thread so I should not need any additional adapters correct?

 

Take care,

Brent 

Yes, if it is mirrors, the TV would not be the right thing.  Sorry, I did not know that it was a mirror unit. The Powermate is probably the right thing.

 

You can also use the 2.5x Powermate.  This can be converted to T2 with an adapter sold by Televue.

 

post-14923-0-98834400-1565904779_thumb.jpg

 

With the BV, the 2.5x acually gives very close to 2x and will take only a few millimeters of in travel, so if your focuser travel range is very tight, this might be a better option. I used a 2.5x as a test in a Solar telescope and it took less than 10mm of focuser travel. Televue says the 2x requires about 20mm and most reflectors have this much so you would probably be safe with the 2x, but if not, the 2.5x would almost for sure work and only give about 2.1x.

 

And I do apologize.. I did not know the unit did not have prisms. I know that there are some mirror units out there but most of them are the 45 degree ones.  

 

 

 

My bad.  So sorry for that mistake on my part.


Edited by Eddgie, 28 January 2020 - 09:57 AM.


#23 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 28 January 2020 - 10:43 PM

Eddgie,

 

You certainly don't owe me an apology, you've already saved me from spending a fair amount of money in the wrong direction. ;-)

 

Work has a way of getting in the way of my hobbies so no orders placed even yet anyway. I like the idea of the 1.25" 2.5X. For starters It should be a good deal lighter than the 2" 2X. I'll go that route and use a T2 adapter.

 

I see what you are saying, the magnification chart on the TV website shows thee 2.5X and 2X almost identical for the focus position from Top Surface distances a BV will impose. I would never have noticed that on my own.

 

Take care,

Brent



#24 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 27,528
  • Joined: 01 Feb 2006

Posted 28 January 2020 - 10:52 PM

Eddgie,

 

You certainly don't owe me an apology, you've already saved me from spending a fair amount of money in the wrong direction. ;-)

 

Work has a way of getting in the way of my hobbies so no orders placed even yet anyway. I like the idea of the 1.25" 2.5X. For starters It should be a good deal lighter than the 2" 2X. I'll go that route and use a T2 adapter.

 

I see what you are saying, the magnification chart on the TV website shows thee 2.5X and 2X almost identical for the focus position from Top Surface distances a BV will impose. I would never have noticed that on my own.

 

Take care,

Brent

Thanks for the pass on the error.

 

And yeah, I pay attention to stuff like that.  

 

Hope it works out great!



#25 bcarter1234

bcarter1234

    Messenger

  • *****
  • topic starter
  • Posts: 496
  • Joined: 26 Dec 2018

Posted 30 January 2020 - 06:58 PM

I got a chance to go out Tuesday night and play with some other options that I already had on hand.

1) GSO 2.5X Apo Barlow, most claim 2.2X. It yielded 4.4X when the BV was inserted into it. I only had about 3mm in back focus left of the new found 18mm provided by the no profile PVC adapter.

2) Burgess 1.9X OCA element screwed to the end of the Baader 1.25" / Quick change nose piece. To get to focus I had to stack two filters between the OCA and the 1.25" nose piece but I did have about 5mm of back focus left. The magnification worked out to 2.79X. With the 30mm Parks eyepieces this came out to 145X. I don't think I could have reached focus with just one filter but I will try next time.

 

I think I'll try to make a low profile focuser or holder to see if I could get this to focus without the two stacked filters. I'm curious how low of a magnification this element can provide. Once I get there I'll need to do a ray trace to see if the aperture of the OCA is large enough to take in the light cone at that point.

 

The 1.25" 2.5X PowerMate and T2 adapter are ordered. Thanks again Eddgie.

 

Here is my method for calculating the magnification factor provided by the Barlow/OCA/PowerMate. I only need relative numbers but I might as well learn to do this right so correct away.

Time a star's transit from field stop to field stop. The Parks GS-5 30mm claims a 52 degree field of view. A star transits one degree every four minutes.

A star that crosses the field of view in the eyepiece in one minute has gone 0.25 degree, arrived at by dividing the number of seconds it took to cross the field, 60, by the number of seconds in four minutes, 240.

I now divide the field of view of the eyepiece, 52 degrees, by the result, the apparent field of view, 0.25. to get the total magnification of 208X. 

The 30mm eyepiece would normally provide 1480/30 = 49.33X.

Divide the actual magnification by the native magnification. 208/49.33 = 4.21X This is the magnification factor provided by the Barlow.

 

My shortest transit so far is 56 seconds using the Baader Hyperion 2.25X with T2 adapter. The longest was the Burgess 1.9X and filter stack at 86 seconds. The Trimag objective  and T2 adapter run about 63 seconds. I'm hoping the 2.5X PowerMate will come in around the 120 second mark.

 

Thanks for reading.

 

Take care,

Brent

 

Take care,

Brent




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics