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Bino C6 or not? Bino experts help!

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#1 mike bacanin

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Posted 24 March 2013 - 12:20 PM

I am pondering whether to bino a C6 for lunar/ planetary. The scope has very nice optics. I currently have a Meade 8.8 UWA 4K, and a 7mm Nagler T1,both very nice ep's. To bino i would have to sell them both, and i'm a bit unsure if its a good thing to do. I use a 50mm long sct 2" V/B, and a GSO type 2" dielectric push fit diagonal. I have several issues. I cannot afford a premium bino. It would have to be a WO, BV3 or simil;ar. I also cannot afford a maxbright/T2 Prism combo. My concerns are, for lunar/planetary, will i get better views than these 2 premium eyepieces? will i lose aperture if i use the v/b and existing 2 inch diagonal and binoviewer? can anyone advise the approximste operating fl of the bino setup? i could use the 1.6x nosepiece barlow that comes with most binos of the chinese class. what would that do to the operating focal length?

i am deeply concerned that once i sell these ep's i may be unhappy with the bino results. regrettably i am no longer in the good times when i could afford a premium bino!!

mike

#2 jgraham

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Posted 24 March 2013 - 12:40 PM

'Better' is a personal judgement. However, my binoviewer setup is pretty economical to minimize the cost and weight; Orion binoviewers with Explorer II eyepieces. I use these on a variety of scopes from an ETX-125, 8" SCT, and my Lightbridge 16. Using both eyes more than makes up for any limitations of the eyepieces. I absolutely love these for lunar and planetary viewing.

#3 REC

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Posted 24 March 2013 - 12:53 PM

The WO bino is a lot of fun on the bigger planets and really great on the moon....kind of gives you a 3D effect and seems like you are hovering over it. It is a nice addition to have, but not sure I would sell your EP's to get one? I would keep the 8.8 UWA, but not sure how much time you get to use the 7mm in that scope. Most times I can't use anything lower that a 9-11mm EP in my 8" SCT.

You will loose some light by deviding it in two, but not two bad on something bright. With your back end configuration with 2" you are probably working at f/13 or so and adding another 20% to the focal length and the power.

The 1.6x that comes with it makes the EP something like 12mm. So you would end up with something like 80x with the 20mm and 135x with the BV.

Just another thought, if you try it and don't like it, you could sell it as they move pretty quick. Check out the classifieds on CN. You will get a lot more answers form others who have these, so enjoy!

Bob

#4 mike bacanin

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Posted 24 March 2013 - 12:59 PM

Hi John,

I appreciate your comment regarding "better". I think primarily, my concerns are that the setup without a barlow/ocs, will create too much backfocus as to cause aperture reduction and bring the sct to operate at a unhealthy f-ratio. Also i have some concern about the tail end weight with the bino. i have a C6 with dovetail bar on a CG5 mount.maybe sliding the ota well forward will balance.

mike

#5 mike bacanin

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Posted 24 March 2013 - 01:03 PM

Hi Bob,

i suspect the bino setup could be operating alot more than f13, i need the experts on the optical path!

mike

#6 Eddgie

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Posted 24 March 2013 - 01:10 PM

You know, you are going to get different opinions on the severity of aperture loss, but you are already starting with a scope that has a 35% obstruction, and any loss in aperture will make that obstruction larger.

And I am willing to bet that using a 2" diagonal with a binoviwer is going to cut your aperture pretty severely.

Even in my C5 when using the Maxbright with a T2 prism with a total light path of about 200mm, my aperture is reduced to 123mm. Doesn't sound like much, but again, this is with only 200mm of back focus.

My bet is that a 2" based binoviwer is going to cut your aperture down 3/4ths inch or more.

Not to say that there is no benefit because viewing with two eyes is very comfortable and all that, but now you are using maybe a 5.25" scope with a 39% obstruction.

Not the best planetary scope for sure.

My advice would be to avoid the 2" diagonal and buy a used 1.25" diagonal and dig out your 1.25" visual back.

Keep the back focus as short as you possibly can.

Keep your eyepeices light because the 1.25" visual back will struggle to keep the binoviewer from rotating to one side of the other. It is just hard to get enough torque on the little lock screws on a 1.25" visual back to keep the binoviwer from twisting in the visual back.

But better to fight with that than to accept a big aperture reduction.

Just my opinion of course, but the reason I personally put so much emphasis on back focus is because I have run into several configurations where I could see that the image was being rendered with less brightness and fidelity than I thought appropriate for the aperture being used.

I now question if my first experience with binoviewers many years agon in an SCT was in fact so disappointing becuase the scope was loosing aperture.

When I mentioned on a forum several years ago, everyone said that I must have had a bad binoviewer.

Now though, I realize that my SCT was loosing aperture and that was the real reason. I tried so hard to see the benefit that everyone was talking about, and just was not seeing anything with the binoviewer that I could not see using mono.

And when I tried binoviewing again last year, I hit the same problem using a 2" based system. I just was not getting the performance that everyone was raving about.

When I shortened the light path though, it was a major BANG! Suddenly the Binoviewers were nailing it.
Now, for planets, I can't stand to use mono because the binoviewer is so much better.

But it is better now because I learned about the damage that occurs with aperture loss, and I take great pains to reduce or prevent it.

If you want the best performance possible for a binoviewer in your C6, I would highly recommend you do the same.

Get short. Get as short as you can. A 2" diagonal is not going to get you where you should want to be.

#7 Mark9473

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Posted 24 March 2013 - 01:27 PM

I am willing to bet that using a 2" diagonal with a binoviwer is going to cut your aperture pretty severely.

Even in my C5 when using the Maxbright with a T2 prism with a total light path of about 200mm, my aperture is reduced to 123mm. Doesn't sound like much, but again, this is with only 200mm of back focus.

My bet is that a 2" based binoviwer is going to cut your aperture down 3/4ths inch or more.


Ed, I've had a bit of a discussion with Mike on this in the eyepieces forum where he first posted.
The C6 does not loose aperture up to 200 mm back focus, which the MaxBright can manage when using a 1.25" prism diagonal.

The question that remained, is: will the 1.6x WO nosepiece bring the focus point back by a sufficient distance so that he could use his available 2" mirror diagonal without significant aperture loss.

It all depends on how much the WO 1.6x nosepiece brings the focus point back. Any data on that?

#8 Eddgie

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Posted 24 March 2013 - 02:35 PM

I don't have any data on the 1.6 unit. Sorry.

The only thing I think we can do is attempt to extrapolate from the Baader GPCs. The Baader 1.25x GPC only buys about 17mm of travel.

The Baader 1.7x unit (not an accurate figure I think, but for this purpose the best I can do) will reduce the light path by 32mm.

Now I know we are not talking about the Baader GPCs, but my guess is that the 1.6x barlow is going to be somewhere in between these two, and closer to the 32mm end.

So, lets say that it buys him 30mm (which I think is generous, likely less than this).

This means that if using a 2" diagoanl, that he will still be over 200mm.

The light path of this model binoviewr is not known to me, but my guess is that it is at least 110mm (similar to the Maxbright).

The 2" diagonal will add about 100mm to 110mm from the face of the diagonal to the top of the eyepeice barrel, and then there is an additional 10mm for the 2" to 1.25" adapter, so this is somewhere between 220mm of back focus.

The connection to the SCT is a big variable. Most of the 2" to SCT adapters will add about 40mm to the light path, though the Televue Short SCT adapter is much shorter than this, but it depends on that.

So this could put the OP to about 250mm to 270mm. If he gets 30mm from the barlow, he is now at maybe 220mm to 230mm of back focus.

This would offer a minimal reduction in aperture and only he can decide if it is worth it.

A 1.25" diagonal though, along with a 1.6x barlow would bring him home for sure.

The light path though a 1.25" diagonal is only about 75mm, and when used in a 1.25" visual back, you only add about 10mm to 15mm to that.

So now you go to less than 100mm for the VB and light path, and you get 110mm for the BV, so this is right over 200mm.

Putting in the 1.6x gets him comfortably under 200mm so in this configuration he would have no aperture loss.

EVery millimeter can count when binoviewing a scope with moving mirrors.

A lot depends on the exact light path lenghts and I don't have that for the binoviewer he is considering, or for his diagonal, or his visual back.

Getting there with a 2" diagonal though might be impossible, though he may come close enough to feel good about it.

The 1.25" though would get him there.

#9 Mark9473

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Posted 24 March 2013 - 02:45 PM

I was hoping the WO 1.6x would be in between the Baader 1.7x and the 2.6x as the Baader 1.7x has been measured to be 1.45x in reality.

#10 Eddgie

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Posted 24 March 2013 - 03:53 PM

Yes, I know this, but the problem is that while we know what it has been measured at from a magnificaiton standpoint, we don't know what the acutal back focus reductionus is.

If we take the Baader Maxbright User's manual numbers at face value, then it would imply that if it were at 1.7x, then the light path would be cut 32mm.

But we don't know that for sure.

And that is why I don't know the answer.

I can only say that the best chance of working at full aperture is to be had with a 1.25" diagonal because the numbers add up.

It is very complicated with a moving mirror scope though. The added back focus of a 2" diagonal is already turning the scope into something like f/10.7, ad perhaps becuase the light cone is a bit slower to begin with, the 1.6 will buy more.

But I don't know.

So, the risk is that the OP tries it and it doesn't reach full aperture with a 2" diagonal.


Maybe it will be close enough though. Maybe he will only loose 5mm of apeture? Maybe more, maybe less and maybe it would not be enough for him to be concerned with.

Worse case, he can still add a 1.25" diagoanl to try to recover some or all of the aperture.

I just think that for this limited application, going with a 1.25" diagonal will get him the best chance of working with 100% aperture.

Maybe he can get there with the 2" though. I don't know.

#11 Mark9473

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Posted 24 March 2013 - 04:28 PM

My own measurements on the Baader 1.7x GPC reported here show that it brings the focus out by 28mm when put between the T2 prism and the MaxBright BV (and is then effectively 1.4x), and by 46mm when put in front of the T2 prism (and is then acting as a 1.5x).

I should note that this was with a refractor, so the results would be different in a scope with moving mirror. I haven't gotten around to doing these tests with my Mewlon yet.

All we need is have somebody do the same measurements with the WO 1.6x lens. Actually I'm surprised to have difficulty finding the information on this forum.

#12 Eddgie

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Posted 24 March 2013 - 04:48 PM

Yes, that is why it is hard to know for sure.

The Baader data is bad, and we have no data on the 1.6 unit that comes with the WO.

We can only surmise.

But that is why I suggested that the best path would be to go with a 1.25" based system. That will yield the best possible chance of running the scope at full apeture.

But a couple of tenths of an inch apeture loss will go unnoticed by just about everyone, and perhaps the 1.6x unit with the 2" diagonal will come in under the wire.

#13 johnnyha

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Posted 24 March 2013 - 04:53 PM

Post deleted by johnnyha

#14 mike bacanin

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Posted 24 March 2013 - 06:03 PM

Hi Mark, Edggie,

I still have the original c6 1.25 v/back. I am very uneasy that it will hold the weight of even a typical WO or similar bino well. It is difficult to get at the two locking screws with enough pressure to really get a purchase on the diagonal well. I could certainly obtain something like a WO 1.25 diagonal though.
A much better grip would ben if i used my existing 2" v/back into which i insert a 2 to 1.25" self centring adapter, eg by revelation or orion. this would grip the 1.25" diagonal nosepiece well, but the combined length of the 2" v/b and self centre adapter would be around 60mm.
most WO etc are about 110mm light path. i think this would still bring a total light path over 200mm with a 1.25" diagonal. i am still concerned if i am operating at an undesirable f-ratio using the WO 1.6x. that then brings in issues about eyepieces to use. a friend has a pair of meade 5000 14mm plossls. i used these in the past and they were superb. will they offer a sensible mag in this potential setup? i do not know, as i do not know the operating focal length.

btw, i am actually looking at the original celestron 1.25 v/back, and to me it still looks to be around 50mm long to where a 1.25 diagonal would insert.
so, say 50mm v/b + 75mm for 1.25 diagonal + 110 for bino less 30 for 1.6x = 205mm. am i right? but still do not like the idea of all the weight on 2 little thumbscrews on that v/back!

mike

#15 Eddgie

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Posted 24 March 2013 - 06:17 PM

These binos are fairly light, though I agree with the issue of supporting them.

If the primary concern is to avoid apetuer loss for planets ( it is much less of an issue for deep sky) then if you are using light weight eyepeices like Plossls, you might not have any problem.

If you go with an SCT to 2" low short coupler (like the Televue) and use a 2" to 1.25" adpater in that, this will keep you pretty short. The Televue is about 22mm I think, but the 2" to 1.25" adpaters are often about 10mm, so you are at 32mm.

So that would be 32mm, maybe 70mm for the diagonal, and maybe 110 for the binoviewr.


That would get you just a bit over 200mm, and this might not be enough loss to be concerned about.

But the .6 unit would almost for sure get you where you back to full apeture.

But again, if you can come in at 210mm or so, you may not need the 1.6 unit, though it might be desirable for high power work anyway.

#16 mike bacanin

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Posted 24 March 2013 - 06:32 PM

Ok, it would be possible to use the self centre adapter in the TV low profile v/back, as it would still only add about 10mm to the TV v/b. that could deal with the issue of supporting the bino and diagonal well enough. But eddgie, do you have any idea what the operating fl would be with a 1.6x ? and you think something like a WO bino would offer a good final image compared to the single ep's i have?
I would love to bino, but it really looks like i cannot go the desired maxbright /T2 diagonal route cost wise. Am i really going to end up feeling let down with a WO or BV3 type bino? btw i really appreciate the feedback from you guys. It is a big step to commit to a bino and sell those 2 fine eyepieces, they took alot of finding!

Mike

#17 mike bacanin

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Posted 24 March 2013 - 07:28 PM

Well, i've spent all night thinking this over. To do it right, and i now understand what is needed, is way more than my budget will take. So, i have decided to forego the bino route. Maybe at some future point, i can try it with the necessary items to achieve the best results. I sincerely thank you for your input. At least i have made a decision now, and i'll stay with that decision.

Mike

#18 Sarkikos

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Posted 25 March 2013 - 02:30 PM

There is another point besides loss of aperture that should be kept in mind when thinking about binoviewing an SCT: induced spherical aberration.

The primary in an SCT has a spherical figure. The corrector plate corrects the image to reduce spherical aberration. But that correction is designed for a focal plane within a finite range. If the focal plane is shifted too far by a long accessory train behind the visual back, then spherical aberration will be induced into the optical system. One of the worst offenders in this regard is a binoviewer. Spherical aberration is not a good thing - especially for viewing planets, which demand a sharply focused image.

Mike

#19 mike bacanin

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Posted 01 April 2013 - 04:01 PM

I just had an interesting conversation with a friend here in the UK. He has suggested using the Baader 60 degree binoviewer with zeiss prisms, high quality. it has a total light path of only 120mm, and obviously needs no separate prism. even with a low profile v/b, the total light path is about 170mm, way under aperture cut off. i reckon it would operate at about f12 max. maybe this could work without all the issues that have been mentioned. Now not sure if i could live with the 60 degree angle. my friend used them and said they were quite comfortable, and were very sharp on lunar/planetary. my calcs reckon a pair of 12.5 ep would give about x148. i never gave this any thought.

mike

#20 Mark9473

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Posted 01 April 2013 - 05:12 PM

On the Baader 60°, there's a review here on CN:

Pluses

Superb contrast and detail on solar system and deep sky.
Superb fit and finish.
Absolutely no color difference between eyes, even in daylight.
Upside down view matches star maps. Not reversed left to right.
Only unit to focus without an aid in a refractor.
Angle was perfect for a piggyback refractor on an SCT.
Least out of field reflection from a nearby bright star.
Razor sharp images.

Minuses

17mm clear aperture results in vignetting of eyepieces over about 22mm. Better suited for solar system and double star observations in an SCT.
Eyepiece holders use setscrews. Results in less success for people to get the views merged.
Sliding style requires re-focus any time inter-pupillary adjustment is altered.
Upside down view takes some adjustment for many viewers.
Angle frequently not comfortable on SCTs, and probably not usable on reflectors.


Thinking about how often I rotate my binoviewers, that last point alone would almost be a deal braker. But still on the Moon and planets it's better than not binoviewing at all.

#21 mike bacanin

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Posted 01 April 2013 - 05:22 PM

Yes, the angle of viewing is the big concern. Actually i'm kidding myself. I have neck spondolysis, this would be very uncomfortable for me. Pity, as its an affordable route compared to others.

Also Baader IV binos with zeiss prism have come up for sale over here. At about 145mm light path, this is another solution, but way too far off budget. How frustrating!
Mike



#22 RodgerHouTex

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Posted 02 April 2013 - 11:06 AM

I'm coming in a little late on this but I have the Baader Maxbright binoviewer with the 1.7 Glass Path Corrector and I use it on my C6 pretty often. It's killer on the moon and planets. Very well made. Gives up a little light loss but I really love it. Alpine astro sells them for $389 with one Glass Path Corrector. You might want to consider one of them.

#23 mike bacanin

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Posted 02 April 2013 - 01:06 PM

Hi Rodger,

what is the diagonal and visual back you use with the maxbright on the C6?

Mike

#24 RodgerHouTex

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Posted 02 April 2013 - 01:43 PM

I use a Televue SCT Adapter short with a Televue 2 in. to 1 1/4 in. adapter and a standard Televue 1 1/4 in. Everbrite diagonal.

#25 aa6ww

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Posted 06 April 2013 - 05:30 AM

Hi Mike,

I used my Denkmeiers on a C6 sometimes and it seems to enhance whatever your looking at, compared to a single eyepiece.
The C6's have excellent optics. I was using my Binoviewer with a 1.25" Everbrite and using 3 different sets of Orion HighLight Plossl 1.25" Telescope Eyepieces, the 40mm, 32mm and 25mm.
Planetary observing with binoviewers is a real bonus because the extra contras you get with both eyes is really going to improve your views compared to any single eyepiece, regardless of the eyepiece quality.
Whatever you get is going to work fine. The william optics, is a fine binoviewer and any slight vignetting isn't going to mater with the planets or the moon because on planets, your going to keep the planet centered anyways, and the moon is so bright you still could need some type of neutral density filter to tone down the light.
Also, dont be too concerned about not having "premium" eyepieces. Everything coming out of china is pretty good these days, and people are more price savy now than ever, and optical quality has really taken a step upwards. Look at your scope, its Chinese made and is excellent optically.
I also have some 32 TV plossls and 24 panoptics Ive used with my binoviewer and these low cost Orion highlighters are every bit as good as my TV Plossls and the 24 Pans offer more field of view, but the optical quality isn't any better than my Panoptics.
Don't get too hung up on the technical issues of eye relief, field stop, and vignetting with your C6 and the gear you cant afford. Just go for the William Optics and enjoy the views.
Too many out here spend too much time nit picking the smallest details, and that can spoil an otherwise fine time your going to have with your gear. Don't let it happen.
The only issue Ive had with binoviewing my C6, is the binoviewer puts added weight on the back of the scope, so I found myself purchasing a longer dovetail so i can mount my scope further back on the longer dovetail so it will balance properly.
Spend more time learning the sky and less time worrying about your fine gear, and what you cant afford. There's allot more to observe than just the moon and a few planets with your excellent C6.
Get out of these equipment forums and spend more time in the observing forums, then you'll really start to appreciate what you can see with your scope, not what you cant do with your scope and gear.

...Ralph






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