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Equipment Discussions >> Binoviewers

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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Eddgie]
      #6144343 - 10/18/13 07:51 AM

Quote:

This is the way the Binotron is going to work. You are going to have to rack all the way in to get the low power arm to focus.

When you go straight though, you are going to have to rack out quite a bit, and when you go high, you have to rack out even more.

The solution is simply. Set up the focuser with the lowest profile you can.

Use a 2.1" focuser tube.




No, the lowest profile I can have is a 1.5" focuser tube. That's what I have now. If I went any longer I'd probably not be able to come to focus with the filter wheels in some of my eyepieces - besides the one eyepiece, my ES 100 20, that won't come to focus now in the wheel.

Quote:

Ignore the fact that in low power, the tube is going to extend into the light path. At low power, it really doesn't do enough damage to the image to make it possible to detect. It simply does not matter.




Racked all the way in, my 1.5" drawtube barely encroaches into the light path, so no worries there, even if it did matter.

Mike


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: TG]
      #6144394 - 10/18/13 08:35 AM

Quote:

Quote:

I am still not settled as to how important coma correction really is to planet/lunar observation.




For planets, coma may not be a factor if you're using a driven scope and can keep the planet centered. For Lunar, I prefer coma correction across the entire field. I don't own a scope with coma but I do have an eyepiece pair which is bad in this department and I can't stand to use them on the moon.

Tanveer.




My 10" Dob is not driven, which is why I have some concern about the effect of coma on planet/lunar images. My intention is to eventually upgrade to about a 14" Dob with tracking, but for now I have to nudge.

Mike


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6144407 - 10/18/13 08:44 AM

One factor that I keep forgetting is that I now have a pair of Baader 8-24mm Zooms for binoviewing. I haven't even first lighted them yet. During dry runs in the house, my 65mm IPD seems adequate for viewing through the Baader Zooms in my Burgess Binoviewer.

With decent Zoom eyepieces in the binoviewer, do I really need a Power Switch? I'll have to compare the image of planets and the Moon through the Baaders with the image through single focal length eyepieces. If the Zooms work out well, they should be reason enough to cull some of my other bino pairs and eliminate the Binotron.

Mike


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Eddgie
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6144447 - 10/18/13 09:02 AM

The only negative of the zooms is the greatly reduced apparent field when zoomed out.

For planetary and general high power, I think a pair of zooms would be fine.

But you will loose a fair amount of true field at the lowest powers.


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Eddgie]
      #6144480 - 10/18/13 09:26 AM

Yes, since I almost always binoview planets and the Moon rather than DSO, the relatively narrow low power would not matter so much to me.

My lowest power, widest AFOV/TFOV bino pair are Meade 5k SWA 24mm's. I deshrouded them for easier binoviewing. With the mandatory 1.9x OCS, they give me a 43 arcmin TFOV at 95x. If I didn't have to use the OCS, they'd yield about 1.4 degrees at 50x.

Mike


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beatlejuice
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6144846 - 10/18/13 12:59 PM

Quote:

No, the lowest profile I can have is a 1.5" focuser tube. That's what I have now. If I went any longer I'd probably not be able to come to focus with the filter wheels in some of my eyepieces




But Mike, the length of the focuser tube doesn't effect the profile it just adds extra length for outfocus. Thats why I got the 2.37".

Eric


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: beatlejuice]
      #6144945 - 10/18/13 01:50 PM

Yes, this is true. Adding or removing spacers from the focuser itself will raise or lower the profile of the focuser. I misunderstood what Eddgie meant by "profile." IIRC my Moonlite has no spacers now.

In any case, when I ordered my Moonlite I wanted to avoid enchroachment of the drawtube into the light path and allow for use of my eyepieces with both my 1.25" and 2" filter wheels. I did not want the drawtube to dip far into the light path. This cannot be a good thing for contrast. Many observers make a big deal about the CO and spider vanes, but seem oblivious to possible degradation of the image from the drawtube.

If I need more out-focus for some eyepieces, I can always add an extension. In fact, I was doing that even before I upgraded to the Moonlite.

Possible future acquisition of a Binotron was not part of the selection process for my Moonlite. At this point I don't plan on returning my Moonlite to install a longer drawtube.

Mike


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Mirzam
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6147372 - 10/19/13 08:01 PM

I am using a Binotron with a 10" home-built f/6.5 newt. I asked Russ if a Paracorr would be useable and he said it was not needed--even at shorter f-ratios. I suspect that this may have to do with the OCS. However, the magnification effect of the OCS alone would not affect coma correction as coma scales linearly with magnification.

Other problems that had to be solved were these:

1. The OCS protrudes into the optical path a lot. I moved my mirror an inch forward and used a taller focuser--not a low profile focuser which will only exacerbate the problem.

2. The weight of the binotron requires a very robust focuser. I ended up with a large format Moonlite focuser and this works quite well.

3. The weight of the binotron (which reportedly is not particularly heavy as binoviewers go) nonetheless required a serious effort at counterbalancing. I made a custom 2.5 Lb counterweight opposite the focuser that is easily removed in case I want to use a mono-view eyepiece.

JimC


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beatlejuice
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Mirzam]
      #6147783 - 10/20/13 02:01 AM

I certainly agree with you Jim on 2 & 3. The regular moonlite focuser + the counterweights that I already had solved those issues.

As far as a taller focuser is concerned I am not so sure. Since the binotron reaches focus with the reducer arm in at a certain height above the tube it seems that the taller the focuser is the more you would have to extend the newtonian spacer to still achieve focus at low power thus marginally reducing the FOV the more it is extended.

I have found that the views have not been noticeabley effected by the protusion into the light path in low power and is a non-issue at mid and high power as the low profile focuser is racked out enough to clear the light path in these settings. This without unscrewing the newtonian spacer at all, giving a seemless transition between all 3 powers without any added procedures.

Eric


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Eddgie
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: beatlejuice]
      #6147972 - 10/20/13 08:09 AM

Quote:

the more you would have to extend the newtonian spacer to still achieve focus at low power thus marginally reducing the FOV the more it is extended.





I agree. Kind of.. I did not see the field reduced, but rather the off axis light rays were badly cut of. I would say that at f/4.9 in my scope, having to extend the OCS was causing about 50% light cutoff.

I believe that it is better to use the lowest profile focuser possible that will allow the OCS to be used at the shortest length (OCS screwed all the way in).

In low power mode, it is impossible to see the effects of the additional obstruction into the light path because if it extends into the light path by one inch, it still only take 3% of the light from a 12" scope, and at low power, you can't see the contast loss.

And yes, at medium and high power, when you need it to be out of the way, it is.

I recommend the lowest possible focuser height with a longer tube to allow the OCS to be screwed all the way in, even if it projects into the light path at low power. It simply does not do enough damage at low power to be seen.


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Eddgie]
      #6148086 - 10/20/13 09:42 AM

When monoviewed, won't short focal length eyepieces tend to require the drawtube to be racked farther in? In fact, the only times I've needed an extension on a drawtube is when I'm using a long focal length eyepiece. IIRC, in those cases the drawtube was racked all the way out from the telescope. (It must depend, though, on where the field stop is located in each eyepiece.) Why is the situation seemingly reversed in the Binotron with its Power Switch? Why all this talk about the drawtube intruding into the light path at low power but not at high power?

I don't intend to do all my viewing with a binoviewer, even if I upgrade to a Mark V or Binotron, so I need to live in both the monoview and binoview worlds.

Mike


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Mirzam]
      #6148114 - 10/20/13 10:02 AM

Quote:

I am using a Binotron with a 10" home-built f/6.5 newt. I asked Russ if a Paracorr would be useable and he said it was not needed--even at shorter f-ratios. I suspect that this may have to do with the OCS. However, the magnification effect of the OCS alone would not affect coma correction as coma scales linearly with magnification.




Russ did not answer your question of whether a Paracorr would be useable with the Binotron. I doubt very much if a Paracorr is useable with a Binotron. He said the Paracorr was not needed. Of course, it's not really needed - with your telescope. But that's because your Newt has an f/number of 6.5!

I don't see what the OCS has to do with reducing coma unless is a coma corrector. As you say, coma should not be affected by magnification. I do think, though, that if you magnify to the point where the entire DLF of the primary is contained within the AFOV of the eyepiece, that ought to reduce the perception of coma.

Of course, there would be a greater need for a Paracorr if the f/number is below 5. My 10" Dob is an f/4.8.

Mike


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Mirzam
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6148168 - 10/20/13 10:34 AM

Actually, I have used my binotron (sans Paracorr) with my 20" f/4 Starmaster and did not notice any coma. So something is going on. I'll test it out again because I really was not looking for coma. At f/4 it jumps right out under normal circumstances.

I also have the larger size OCS, which reduces any chance of vignetting.

JimC


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beatlejuice
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6148356 - 10/20/13 12:38 PM

Quote:

Why all this talk about the drawtube intruding into the light path at low power but not at high power?




Mike, when using the binotron's in a newtonian there is a minimum of 4" between the shoulder of the focuser and the OCS. This consists of the regular 2" shaft + a 2" Newtonian spacer which can itself be unscrewed a further 1/2" to help reaching focus in low power if necessary. The newtonian spacer is removed for use in a refractor or SCT thus making the whole system compatible with any type of scope. In my scope (10" f/5) I rack out more than 1.25" for mid power and about 2" for high power.

I should have picked up on this when you talked about using the binoviewer with a filter wheel. Since you already are able to use the filter wheel in mono, when using the binotron you would have to modify the length of your focuser tube or use an extension tube or pull the whole thing out quite a bit when binoviewing with mid or high power. But using the binotron with the filter wheel is of course not possible.

BTW I still don't know how you are able to reach focus with the filter wheel's extra inch of height + the extra 3/8" in height for the 3 thumbscrew compression ring holder. The math just doesn't seem to compute for my eyepieces.

Eric



Edited by beatlejuice (10/20/13 01:41 PM)


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REC
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only [Re: beatlejuice]
      #6148450 - 10/20/13 01:36 PM

I have to screw out the OCS about 3/4 the way out for the low power arm in my 10" Dob. The normal and the barlow arm also will focus ok.

BTW...I had a beautiful view of the Double Star Cluster last week and was able to fit both clusters in the FOV....nice!


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: beatlejuice]
      #6148925 - 10/20/13 07:09 PM

Quote:

Mike, when using the binotron's in a newtonian there is a minimum of 4" between the shoulder of the focuser and the OCS. This consists of the regular 2" shaft + a 2" Newtonian spacer which can itself be unscrewed a further 1/2" to help reaching focus in low power if necessary. The newtonian spacer is removed for use in a refractor or SCT thus making the whole system compatible with any type of scope. In my scope (10" f/5) I rack out more than 1.25" for mid power and about 2" for high power.




Refocusing for the three levels of the Power Switch is not a big deal. In my setup, lower and mid power might not be a problem. But it sounds like I may have to stick in an extension in order to reach high power with the Binotron.

I don't think I'd want to bother with a Power Switch if I'd need to remove the Binotron and stick in an extension every time I wanted to view at high power. Even having to pull the Binotron out an inch or two would be a kludge. These solutions sort of negate the convenience of the Power Switch. If I could insert the extension into the focuser first and then have the Power Switch focus at all three levels, that would be fine.

Quote:

I should have picked up on this when you talked about using the binoviewer with a filter wheel. Since you already are able to use the filter wheel in mono, when using the binotron you would have to modify the length of your focuser tube or use an extension tube or pull the whole thing out quite a bit when binoviewing with mid or high power. But using the binotron with the filter wheel is of course not possible.




The funny thing is, I have no problem using a filter wheel with my old school Burgess Binoviewer in the Moonlite focuser. Of course, I still have to put an OCS on the neck of the binoviewer. But I needed to do that with my old focuser, too.

Quote:

BTW I still don't know how you are able to reach focus with the filter wheel's extra inch of height + the extra 3/8" in height for the 3 thumbscrew compression ring holder. The math just doesn't seem to compute for my eyepieces.




In the 1.5" Moonlite focuser with compression ring - no spacers - I can use either my 1.25" or 2" filter wheel without an OCS and come to focus with all my eyepieces except the ES 100 20mm.

Maybe if I'd gone for a Moonlite without the compression ring the ES 100 20 would have had enough in-focus for the 2" filter wheel? I'm not sure. But I wanted the extra security of the compression ring for filter wheels, binoviewers and heavy 2" eyepieces. I think that's worth not being able to focus for just one solitary eyepiece in the filter wheel.

Mike


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George9
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6149106 - 10/20/13 09:17 PM

My preferred system for planetary viewing is now my Denk II Supersystem, Denk 21's, the 2" OCS, and an AP Advanced Convertible Barlow on a 18" Zambuto Starmaster with goto. I screw the AP Barlow's optical cell onto the OCS using a Denk-supplied adapter that Russ sent me to accommodate a Lunt blocking filter (the AP cell uses standard 2" filter threads but it requires a spacer between it and the OCS). I could see switching to Denk 14s but I have not bothered yet.

I spent some time playing around with the Paracorr and I forget exactly what configuration finally worked but it didn't add anything so I now skip it. I didn't specifically test for coma, but just got an impression of the view.

This has replaced my monocular planetary viewing, where I used to use a 5.2XL or my orthoscopics plus a Barlow and Paracorr. I only use the Denk on the 18" for planetary and lunar. I go monocular for DSOs.

The biggest advantage of the Denk over the Mark V for me is that I also use it on my solar scopes (Lunt 80, AP130 with wedge, etc.) and I find that the OCS and Powerswitch work very well without major contortions to bring it to focus.

Still, it would be nice to try a Mark V someday.

George


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beatlejuice
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: George9]
      #6149230 - 10/21/13 02:00 AM

Quote:

I could see switching to Denk 14s but I have not bothered yet.




Thats the thing about the power switch, after you get that first pair of eyepieces every other pair will only get you one more magification that is not close to being a duplicate of what the first pair gives you.

Eric


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Sarkikos
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: beatlejuice]
      #6157101 - 10/25/13 09:57 AM

At this point, I think I'll pass on both the Mark V and the Binotron.

The Binotron sounded interesting because of the Power Switch. But in practice it appears too fussy to make work easily for all three settings. Also, the image might not be as sharp through the high setting. That wouldn't work for me, because I only binoview planet/lunar. For deep sky, I always monoview. And the Binotron does not allow for coma correction.

The Mark V, on the other hand, does not have a Power Switch. But it does have optional coma correction. I'd like more information on that feature. Theoretically, binoviewing plus coma correction should be an ideal combination for planet/lunar.

For now, I'll continue to use my humble, old Burgess Binoviewer. It works very well for planet/lunar. But no Power Switch and no coma correction. Nothing is perfect.

Mike


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Eddgie
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Re: Mark V or Binotron for 10" Dob - Planet/Lunar Only new [Re: Sarkikos]
      #6157276 - 10/25/13 11:38 AM

I have to tell you that recently I became aware that the Baader coma corrector might induce some spherical aberration.

I had star tested my new dob when I go it, and SA was actually really nicely corrected. This is not a premium quality mirror, but way better than I had prepared for.

Well, I did not really give it much thougth, but last time I used the scope with the binoviewer, I happened to change from the 35mm Ultmas, which take a lot of in travel, to one of my other pairs that don't take as much in travel.

When I did, for the first time, I noticed when I put in the other eyepices and refocused, the secondary shadow seemed a bit larger than it should have.

I am going to qualify this statement before I even make it. I was not using a 33% obstruction, so the test may not be fully accurate.. Anyway, I decided to rack though focus and to my surprise, the secondary shadow ratio was a lot different on the other side of focus!

This is the classic sign of spherical aberration.

Again, it is important to mention that I did not use a 33% obstruction. The problem is perhaps not really serious and maybe is some higher order spherical aberration (and that is why you use a 33% obstruction rather than the native 23%.. It greatly reduces any influence of HSA).

So, for now, I have to say that I have not had a chance to re-test with the 33% obstruction in place.

I plan on doing this the next time I have the scope out, which hopefully will be Sunday night.

Will try to remember to follow up.

Hoping it is just some HSA that would not be a factor at best focus with the native obstruction. The star test is super sensitive to HSA with small or no obstruction, but you can have a totally meaningless amount of HSA and it can give a bad reading.

Scope seems to perform well on the moon though. I would say at least ad good as my 6" APO and I think perhaps a bit better, but I really haven't done a side by side, so just working from memory of detail around the Triesnecker Rille. I know this area well from the C14 and the 6" APO, and I felt that it was showing detail right between the C14 and the 6" APO.

And that is what makes me think that I am seeing some HSA and not true LSA which I think can be more detrimental.

Still, not conclusive. Will know more when I test with the obstruction.

I love the Mark V and coma corrector though.

But the coma corrector extends into the focuser tube 92mm. This is not much different than the OCS on the Binotron.

So, this may not work for you either..


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