Tony, I will try this as soon as it clears up here..
Mark, could you perhaps share a bit more detail with us on your Bi-Newtonian?
Why F4.5, do you intend to use coma correctors, what size secondaries, what diameter focusers and how are you going to allow for interpupillary adjustment....and what is a "fast cooling conical mirror" ?
Hmmmm
It may be a good time to clearly state what I do not like about the Denk Big Easy:
Lack of grip (ANY grip) on the body makes it easy to drop...
The OCS uses bright retaining rings for the lenses causing reflections especially in the focal reducer.
It claims the highest clear aperture yet vignettes with the Pan 24's
Bright stars or planets cause reflections from my eyes back into the bino and the bino combines the reflections - this may be a common problem with all binoviewers...
Most recently I have discovered that my new Denk is out of collimation without dropping it or even shaking it. It does not hold collimation and I do not know what is worse - not collimated properly from factory or loosing collimation in use. The unit is only few months old.
The eyepiece locking mechanism is crude and flimsy (but it works).
That is all for now...
I use it on 10" SCT with the 1 /1/4" OCS.
Joe
The Big easy performs at it's optimal with Denk eyepieces. I'm not surprised that the Pan 24mm vignet a little. This is not a problem with the binoviewer, in fact if you were to use the pan 24mm in another binoviewer system they would vignet more, For this reason I always recommend Denk 21mm for the Denk binoviewer. The Denk Binoviewers has a larger clear aperture which will give you a lower power and wider angle view then what can be achieved with any other binoviewer with out vigentting, This plus the Big easy package works on just about any telescope and has better multi-coatings providing better contrast is what sets the big easy apart from other binoviewers.
The eyepiece locking mechanism is designed to lock the eyepiece in the centre of the barrel, binoviewers that use set screws on the side push the eyepiece to the side of the barrel, and there for they are not centre, merging would be a lot harder. In my experience I have found them to work better than the other alternatives.
I'll check out the Burgess too, thanks. The Baader is 23mm clear aperture.
If you are serious about visual planetary observing then best to buy a patch for one eye to give more relaxed viewing in a mono scope or use a real binocular.
Binoviewers contain beamsplitting prisms, mirrors and optical windows which all degrade the optical path.T Theres just no way around that.
Regards
Quote:
Originally Posted by Prickly
Hi Mark,
Keen to hear how the Baader Maxbrights go. I also noticed a new burgess optical binoviewer. This one has 24mm diameter barrel to avoid vignetting on 1.25 inch eyepieces 27mm prisms and 3 screws to centre the eyepeices. Also sells for about $300 US. Havent seen any reviews.
Interested to hear if anyone else has been able to use binoviewers sucessfully for detailed planetary viewing and if so what binoviewer / barlow/eyepiece combination.
The idea of planetary viewing with a binoviewer seems very attractive but its hard to see the point forking out the money if they images arent too great. Agree minimising optical surfaces would have to be a key factor. Some ortho eyepieces might go some way to achieving this and use of a high quality barlow?
The Big easy performs at it's optimal with Denk eyepieces. I'm not surprised that the Pan 24mm vignet a little. This is not a problem with the binoviewer, in fact if you were to use the pan 24mm in another binoviewer system they would vignet more, For this reason I always recommend Denk 21mm for the Denk binoviewer.
Frontieroptics:
The Panoptioc 24 gets vignetted because of the insufficient aperture of the binoviewer, and the long light path. No 20mm eyepiece will show vignetting in these units because the field stop is smaller ( Panoptic 19mm is the low power eypiece of choice for Binoviewing ) . Can you point to any special feature of the Denk 21mm that makes them specially suitable ?
Mark, could you perhaps share a bit more detail with us on your Bi-Newtonian?
Why F4.5, do you intend to use coma correctors, what size secondaries, what diameter focusers and how are you going to allow for interpupillary adjustment....and what is a "fast cooling conical mirror" ?
Hi Joe
My 14" will follow on same design as Paul Shopis's 12" but more lightweighted so no surprises accept I'm going for pushbutton electric collimation using dc servo motors and bits and pieces from Jaycar. You'll want to follow Omaroos progress too, he is building a 12" F5.
The 14.5" Conicals I'm inspired by as Anthony Wesley is getting such good results. My version will use a new rear mirror attache=ment design and there'll be no perforation in the front face. No flotation cell required so another weight saving there
Frontieroptics:
The Panoptioc 24 gets vignetted because of the insufficient aperture of the binoviewer, and the long light path. No 20mm eyepiece will show vignetting in these units because the field stop is smaller ( Panoptic 19mm is the low power eypiece of choice for Binoviewing ) . Can you point to any special feature of the Denk 21mm that makes them specially suitable ?
Regards
Mark
Hi Mark, Thanks for your question.
There are several reasons why the Denkmeier 21mm eyepiece set it the better option for Denkmeier biniviewers.
As you have said, Denkmeier binoviewers have a clear aperture of 26mm, The Denkmeier 21mm eyepieces have a field stop of 24mm. This allows the field to be fully illuminated to the edge without any distortions.
The Denkmeier eyepieces are manufactured with binoviewing in mine. They are shipped as a fully matched pair. The tolerances in the machining of the housings are tight and one or both eyepieces won't be off centre when used in a binoviewer. Eyepieces that are not matched could have slightly different tolerances to each other in their housings. This means the images will not merge correctly and will give the user eyestrain.
The eyepieces are light weight, anyone who uses binoviewer will want to try to keep the weight down at the eyepiece end.
The 21mm eyepieces have a 20mm eye relief allowing the user to comfortably place their eyes over the centre of each eyepiece.
The Denkmeier eyepiece use rotating L-shaped rubber eyecups. This features eliminates stary light entering in through the side of the eyes when viewing.
If you look at the 24mm Panoptic, The housing tappers up to the eyecup. Depending on the user, this feature can make it difficult for them to position their eyes correctly over the centre of the eyepiece. The Denk 21mm eyepiece have a straight housing where this won't be a problem.
Frontier,
I really enjoyed your responses (apart from the fact we are namesakes), you appear to have given your honest opinion, someone was not quite so sure why, politely disagreeing and you have had right of reply - excellent. this is how a forum should be
The Denk 21's sound like they have some good features for binoviewers.
Quote:
Originally Posted by Frontieroptics
As you have said, Denkmeier binoviewers have a clear aperture of 26mm, The Denkmeier 21mm eyepieces have a field stop of 24mm. This allows the field to be fully illuminated to the edge without any distortions.
Binoviewers have a conical light cone through them not a parallel one so there is always significant vignetting from the nosepiece, but if it can be kept at least 70% lighting at the edge of the eyepiece then cosmetically it is acceptable in the sense that the vignetting will not be obvious to the casual observer.
A quick `thumbnail' calculation suggests that putting for example an F10 cone ( either native F10 or an F5 scope with 2X OCS ) througha 26mm aperture binoviewer with a typical path length of 115mm yields a *fully illuminated field of around 15mm diameter* at the focal plane. Clearly the edge illumination must be better than 70% if you are not seeing any vignetting with a 20mm eyepiece.
For those interested in the technicalities of the issue heres a focal plane vignetting plot of an F10 cone through a 26mm aperture ( ie Denkemeir binoviewer ) with a 114 mm pathlength. It shows why a 24mm Panoptics shows vignetting at the edge and not a typical 20mm eyepiece
If you trace the semi-aperture at the fieldstop of Denk 21mm eyepiece ( about 11mm ) the light transmission is about 70% at the edge, which is on the margin of casual detectability for the human eye. A 24mm of 14mm semi-aperture indicates 45 % illumination which will be obviously appear vignetted to the human eye.
There lies the dillema of binoviewers. The long internal pathlength demands a slow F ratio to get acceptaable off axis lighting which means a narrow field of view compared to a true Newtonian binocular. Astronomy like life is full of compromises if you want to take a shortcut .
Thank you Mark and Frontier (Daniel) you both have given us very informed and totally satisfying responses.
Mark
There is substantial light path length in Newtonians as well as there is a need for diagonal and focuser as well as the need to have steeper light cone at F4-F6. In my limited understanding of the optics this would require larger secondary than normal as well as something like 3" aperture focuser...
All this to fully illuminate a 24 Pan with field stop of ~ 27mm...
Hmmmm
To be fair, the Denkmeier Big Easy does give me around 200 -250 mag with improved detail when compared to a single eyepiece. It is less sharp by a small margin compared to monocular viewing but the brain processes two eyes with ease and allows me to spend more time viewing with the bino thus allowing to discern more detail...
Joe
Joe, thanks for your thoughts about this very intriging question of planetary peformance. I'm looking for a better understanding of what is going on and what can be expected. Sounds to me like your Denks perform better than my WO, but I still do enjoy using the WO and the comfort of binoviewing. Just wish it was better!
Nick, have you tried the WO unit without the screw-in barlow using instead a high quality barlow / powermate with your tak eyepieces. Be interested to hear what the outcome was if you have.
Pity to have to jump up to the higher price bracket viewers but perhaps this is not possible with the lower priced bino viewers.
David,
I don't have a powermate and the best barlow I have is a Celestron 2X Ultima (1.25"). At one stage I almost upgraded to something better (unfortunately used a Zeiss Abbe barlow to compare), but decided the best barlow was no barlow! Nevertheless, the Celestron is a reasonably good barlow, and I did try it early on when I couldn't get much use from the WO 1.6X OCA ( I don't own an SCT). I managed to get the barlow to work, but the magnification was very high and I estimate it gave me around 4.5X !!! Makes me think to try it again though, but it will have to be with the original WO 20mm eyepiece pairs, otherwise the magnification will be way too high with my other eyepiece pairs.
I purchased the Seibert Multimag, which gives 1.25X, 2X and 3.5X. At the time I thought this was a much better solution, not only because it works in all my telescopes, and has great flexibility, but optically was superior to a barlow in this application, being a true OCS (see Seiberts website for more info). But I will try it again and report back, just to be sure.
And it is a great pity to have to be considering stepping up to something more expensive. I'm starting to think along the lines of Marks comments though, that there are no free lunches, and the extra glass, prisms, beam splitters, get in the way. What I'm unsure of though is to what degree can a really premium BV'er satisfy my needs. Either will have to eventually look through one at a star party or spend the money to answer this question.
On the other astro site that's cloudy, I have continually read how these affordable chinese binoviewers do almost everything, including change your diaper, when you lose control of bodily functions because the views are so marvellous. Somehow, I don't think so!
For me, the BV'er experience is tantalising, but also frustrating! With time, this may change (I hope).
Mark
There is substantial light path length in Newtonians as well as there is a need for diagonal and focuser as well as the need to have steeper light cone at F4-F6. In my limited understanding of the optics this would require larger secondary than normal as well as something like 3" aperture focuser...
All this to fully illuminate a 24 Pan with field stop of ~ 27mm...
RGDS Joe
Hi Joe
The point with focal plane illumination is that you don't need 100% lighting to the edge, 70% is fine with low power. Also faster mirrors have much more gradual drop of than slow systems ( such as F10 SCT ). The typical figure for 100% illumination area used on large modern truss Dobsonians is around 6mm to 12mm diameter at the field center . At a figure of 70% illumination, light loss is not really noticeable but stellar magnitude loss is about 0.5 magnitude.
My 14" design uses 3.1" diagonals ( 22% obstruction) and 2" low profile focusers ( GSO ) and with a 6mm fully illuminated field I can acheive lighting to 70% at the edge of a Panoptic 24mm. I may well grind the mirrors to F4.75 to get better off-axis performance, although I don't find F4.5 really too objectionable coma wise . At F4.5 I would be able to keep my feet on the ground 95% of the time which is quite important. For a larger instrument I would employ F4 mirrors and Baader coma correctors.
I believe central obstruction is one of the more overated issues in telescope construction( compared to other issues of figure quality ) . As long as you keep it under 25% there will be little penalty ( most SCT's are about 38% measured at the secondary baffle).
Theres a great Java program By Eric Rohr called Binewt designer which allows you to play with all the design parameters and come up with the best solutions for adequate lighting and minimum central obstruction.
Joe (and everyone),
on the subject of collimation, I pointed a laser collimator through my Denk II's, projecting the beam out through the eyepiece holders onto a wall 6.3 metres away. I didn't have a very accurate measuring system set up, but the two red dots were within a few millimetres of where they should be vertically and horizontally, which I guess is a reasonable result over a 6.3m distance. It occurred to me that you might be able to use such a setup to collimate the bino's at home, though I'm not familiar with the adjusting mechanism of the prisms.
With regard to merging calendar images through the bino (calendar about 6 feet away) with no eyepieces, my Denks will merge the image whereas my previous Stellarvues would not, even though they performed just fine in the scope at around 100x. I imagine this means the collimation is tighter on the Denks and they could be taken to higher power without running into merging difficulties.
Like you it is tricky reconciling the glowing reports of the binoviewers elsewhere with the possible reality that they dont cut it in practice. I accept that there are likely to be problems with light scatter etc, but I can see that monocular viewing also presents limitations. Another thing is that the Chinese gear is improving all the time. In fact I wonder how much Japanese gear originates in Taiwan / China. Im careful therefore to not discount Chinese gear without looking into it. Also mindful of the earlier post questioning whether it would be been better to go with a budget binoviewer rather than the Denkmeier.
The Burgess 24 looks interesting - it has self-centring eyepiece holders and might be more suitable for deep sky with 24mm clear aperture. A little more expensive at $300 US. Spec wise while not perhaps quite up there with the most expensive models practically it might give them a good run perhaps. Interestingly however for planets it seems that even 18 to 20mm would be ok. The silvered prism coated prism might also make a difference of course (mind you the images get fused in the end - hopefully). I still wonder whether a cheaper budget variety would be that different for planets. Hence the call for further feedback from anyone satisfied with viewing even around 200-250x or so.
Interested that you get a good barlow effect with such a low barlow. Most people already own a 2x barlow (I have a very nice 1.8x televue barlow hence the interest). With a 2x barlow and my setup that would be a fairly acceptable 180x for planets. Thanks also for the reference to the optics of the OCS - worth a read.
Thanks also to Dan from Frontier too for the feedback on the Denkmeier eyepieces. I guess it is great if you can take pot luck in getting similar focal ratios out of the equation.
the 1.8X Televue is indeed a nice barlow. I haven't had much of a chance to try my barlow again, as the skies have been very hazy lately, due to bushfires on Kangaroo Island, unfortunately for the people, animals, and plantlife that live there too.
If I was to revisit the "which BV'er to buy?" question, and didn't want to spend heaps, I'd get the Burgess 24, without a doubt. Probably the best bang for the buck.
By the way, when I said I was frustrated, things need to be taken in context. It's still lot's of fun, so I don't want to put you off trying it. The great thing about our wonderful hobby is how much you learn along the way and make progress,
Just to add something to this thread. I have used both the 14mm and 21mm Denkmeier eyepieces in both cyclops mode and in denk binoviewers. They are an outstanding eyepiece in every respect and consistent with the quality of Televue or Pentax eyepieces and so they should be at the price. Notwithstanding the vignetting issues between the 21mm Denk and the 24mm Panoptic, be rest assured that both the 14mm and 21mm Denks are excellent choices for both binoviewer work and in cyclops mode.
Hope the fires settle down soon (for everyone!). Hang in there with the experimentation - the WO unit was awarded best binoviewer in a test by sky at night so they must be pretty good. Interested to hear how you get on.
From the feedback so far it seems that the detail is no better through a binoviewer than in "cyclops" mode (certainly not by a drastic margin). Maybe more relaxing though with binoviewers with good units.
I think perhaps burgess 24 is a good option. Another slightly cheaper option might be the stellarvue BV3 which has self-centring collets with helical diopter focusing and apparently comes with pretty good 23mm eyepiecese - clear aperture is less though. You could almost buy yourself a new scope for the price of the televues / Denkmeiers but they are no doubt a bit better I guess (as is usually the way).
Hi
Received some notes from Daniel (Frontier Optics) how to check calibration of a the Denk Binoviewer.
All checks passed with flying colours, so I must have been in a really bad shape if I could not merge images the other night.
As for real life observing...in a word perfect, I could not fail the Denk. I do not think I've ever seen the M42 trap and its 6 stars with such clarity and separation. This is at ~250 magnification.
I would say my complaining about the unit being out of collimation was full of s..t.
Hi
Received some notes from Daniel (Frontier Optics) how to check calibration of a the Denk Binoviewer.
All checks passed with flying colours, so I must have been in a really bad shape if I could not merge images the other night.
Joe
Could you post how to do the calibration checks here? My methods are only what I've dreamed up myself.
.
Somehow, I don't think so! 
