Maxbrights reducing my image quality
Posted 24 June 2013 - 02:20 PM
The first long session with Saturn this year using my Maxbrights with my AP 175 were very satisfying. However the seeing was average at the time. This weekend the seeing was bordering on spectacular where I live and I started out viewing Saturn mono style, then switched over to my Maxbrights for some more observing. When I switched, I immediately noticed that the image was softer than with the single eyepiece. It wasn't subtle at all. I tried different combinations of eyepieces, with and without the Maxbright, with and without 1.25 and 1.5 compensators, and even with a 1.6x Antares barlow.
The result was undeniable, the Maxbrights when put into the image train were degrading the image. When I say degrade, specifically I mean that it softened the image versus the same eyepiece used singly with a AP diagonal.
I am suspecting that with the excellent seeing, the 175EDF was throwing up a near perfect image that a 1/10th wave (or better) unobstructed scope will show and the Maxbrights are not up to the task of relaying that level of image along.
Am I on the right path here or am I missing something? Anyone else experience this?
Posted 24 June 2013 - 02:40 PM
I will give you my opinion though. It is only an opinion based on my own experience.
For planetary observing, I think that the dimming from binoviewers causes the eye to have more trouble with low contrast detail (for a given exit pupil).
I find that when binoviewing, I have to step down a bit in power.
For example, I might use a 13mm Plossl for monoviewing in my C14, but if I try using a pair of 13mm Plossls in the binoviewer, the image seems dim and not quite as sharp to me as if I put in a 15mm pair of plossls.
I find I can see more detail at slightly lower power in the binoviewers than I can at slightly higher power using Monovision.
And I am using a Mark V, so it is not the quality of the binoviewer.
My bet is that because seeing was good, you were using very high powers with their associated very small exit pupils.
As a result, you simply lost to much brightness with the binoviewers for your eye to properly capture the contrast available at the target.
I have tried to make this point on the refractor forum for many years. Your eye likes a bright image. If you make the exit pupil to small, you actually work against your eye's limitations.
Now in your case, you did not make the exit pupil smaller, but you gave each eye only have the signal that it normally gets, and even though summation was taking place, you still don't get as bright an image.
Bottom line? I think you used to much magnification.
Try dropping down to your next lowest magnification pair in the binoviewers next time.
My bet is that you will be able to see all of the detail.
Even for me using a C14, I find that even when seeing is quite good, I get a better view using my 15mm Plossls than using a single 13mm eyepiece. That little bit of magnification loss is more than compensated for by the added brightness and the added resolution that two eyes provide.
Image brightness is important for planetary observing and my personal advice for years is not to over-magnify. And when binoviewing, I find that the image at a .8mm exit pupil is to dim as compared to a 1.2mm exit pupil.
So, just my opinion, but I think you over-magnified with the binoviewers. This is not a quality issue really.. It is an issue of not letting your eyes have sufficient light to process all of the detail being provided.
Try it next time and let us know how this works....
Posted 24 June 2013 - 02:47 PM
With the C11 you probably never encountered this because you were most likely always running at relatively large exit pupils due to seeing.
You simply never really had the opportunity to "over-magnify" for the binoviewers.
So, all lines up with my own theory which I have been putting forward for years now. If you over-magnify, the image dims and you loose contrast. You never encountered it in the C11, but with the much smaller aperture of the refractor, you ran out of gas.
I could not use my own 6" refractor for high power work with the Binoviewers. Over 250x for planets and the view go to grainy for me.
But I could see as much at 250x with the binoviewers in the 6" APO as I could see at 300x with Monovision...
Posted 24 June 2013 - 03:43 PM
P.S. There is a difference in image quality between the MarkV's and the Maxbright binos! ( why else would people pay the $1,000 price difference?)
Posted 24 June 2013 - 03:55 PM
Posted 24 June 2013 - 05:24 PM
Eddgie, you make some good points. You might be onto something but I'm not convinced just yet. I tried a variety of magnifications and no matter what, the results were consistent, even a lower powers around 170x or so. But then again, you might be right.....
On a side note, the 4.5 Delos I was using at one point gave the absolute best view of Saturn I have ever experienced.
Posted 24 June 2013 - 08:00 PM
Considering that even with summation, the binoviewer only gives an image that appears about 70% as bright as monoviewing, so while 170x gave a 1mm exit pupil in monovision, it was like using a .7mm exit pupil when using the binoviewers.
.8mm Is considered by some the optimal size exit pupil (based on brightness) for observing extended objects.
Using the Maxbrights in the C11 at 200x, the exit pupil would be about a 1.4mm exit pupil which at 70% brightness, would be like 1mm exit pupil. Still pretty bright (as bright as the image in the AP 175 at only 170x!
It is just my theory, but I personally noticed that the view dims badly in the 6" APO and as much as I love binoviewers, I did not like using them for planets in the 6" scope. Fantastic in the C14 though.
Again, this is only my theory, but it seems like it matches your experience in that you did not notice this in the C11, but noticed it in the smaller aperture because of the dimmer image.
It could be a quality issue, but my bet is that it is really a brightness issue when using the smaller aperture at (relatively based on exit pupil) higher powers.
Posted 25 June 2013 - 04:27 PM
Mark, i've consistently seen this same effect myself- and i'm using a Denk II BVer in my 15" Dob. The magnification factor doesn't seem to make a lot of difference; even at 200x (~1.9mm ExP, 1.33mm brightness equivalence at 70%) or 250x (~1.5mm ExP, 1.07mm brightness equivalence at 70%) i'll see a slightly more sharply defined planetary image, as well as pointier stars, in "mono" than in "bino"... assuming at least "decent" seeing. If the seeing is excellent, it's more obvious... if merely decent, then it's more subtle.
I tried a variety of magnifications and no matter what, the results were consistent, even a lower powers around 170x or so.
Yet some aspect(s) of what Eddgie is suggesting i suspect are true... others here on CN have suggested something similar- i think i've heard it termed 'empty exit pupil'? But for me it has meant keeping my BVer magnification range generally below 300x, while my mono range frequently runs well beyond that- this no doubt *does* have to do with image brightness!
Still, i don't think this takes away from what you & i are seeing- for all the talk of EPs having "less glass" being sharper for image, which often ranges beyond just EPs to include entire 'scope optical systems (ie. an unobstructed 'fractor versus an SCT with a large CO plus multiple surfaces)... why would a BVer with all its glass & surfaces be exempt from the phenomenon?
If a scope's optical system is sharp enough on its own, plus used under good-to-excellent seeing conditions, a difference should be detectable... independent of the glass-stack's configuration... be it a BVer or a multi-element EP... or heaven help us, BOTH together!
Posted 25 June 2013 - 04:48 PM
Is there sample variation between Maxbrights? Possibly.
Posted 25 June 2013 - 05:30 PM
... or our human eyeballs? Quite probably! Getting BVer samples in use side-by-side, whether same brand, cross-brand, and/or cross-quality (ie. Denk "std." & Denk II) would certainly be fascinating...
Is there sample variation between Maxbrights? Possibly.
Bottom line is to find what works (or, as in this case, *doesn't*), and to adjust one's equipment use accordingly. A large part of that is becoming "convinced", which includes getting past all the hype, and the newness-factor that BVing tends to bring. I know i nearly chucked all my "mono" EPs when i first got into BVing- just out of sheer enthusiasm for two-eyed viewing! But now i'm being a lot more critical of what i'm actually seeing.
It's a process... as is everything in this hobby.
Posted 25 June 2013 - 09:28 PM
I can often see more with the bino at 70% of the magnification than I can with a single eyepiece at 100%.
I am inclined to agree with this. In the last 18 months, I think I have done my best planetary obervations ever, and often I am using lower powers than I did when monoviewing.
Again, like the OP, I find that with the larger SCT, at equal exit pupils, I always see more with the binoviewers, but when using the binoviewers in the 6" refractor, I run out of light before I run out of magnification.
But each of us draws our own conclusion on what works best for ourselves.
So, we can't actually answer the question if something is wrong with his binoviewer or if he is running out of light.
What we know though is that he feels that he is getting more detail using monovision in his small scope, so if that works best for him and he knows that, this is all that matters.
Posted 26 June 2013 - 02:21 AM
Two things are coming into play here:
1. Under the finest conditions, all disturbances in the optical path between the objective and retina make themselves painfully visible. By putting all the extra glass and glass-air surfaces of the bino into the light path, the image can do nothing but degrade. The next step can be taken on the same path by taking out the diagonal in mono-mode. Just repeat the same experiment with and without star diagonal under the same superb seeing conditions and you will be in for another improvement in the image quality. But the results are generally offset by a little pain in the neck.
2. It is likely that your Maxbrights are not of the highest quality. Some samples of these are quite excellent, others are not. With all the money invested in a great scope, you owe it to yourself not to take a chance to degrade the images just before they reach your retinae. I have no personal experience with Denks, but both the Mark V and BinoVue are generally superb. Hand-pick a unit if at all possible. Nothing like QC by an experienced end-user. And yes, the brain will work wonders if fed by 2 images.
A good compromise between all these conflicting factors in showing planetary detail is using the bino straight through when ergonomics allow. In that way you can get the best of both worlds. When observing the sun in the morning or evening, nothing beats seated straight-through bino-observing!
Just look at the attached picture of a newbie taking in his first views of the sun through my FS 102 NSV with BinoVue straight through. It took a lot of persuasion on my side to get him away from the eyepieces
Posted 26 June 2013 - 05:53 AM
This test is sensitive because you're examining a magnified image produced *after* the optic being tested. For one thing, the full aperture of the full train of elements is contributing to image formation, unlike the tapering light cone forming image points in normal use.
I discovered this principle when testing a bino prism assembly taken from an 8X40. In normal use, the image was not great, but not horrible. Removing the 22mm aperture prism assembly and placing it ahead of an 8X20 monocular, it did *ghastly* harm to the image! Indeed, it appeared that the 8X monocular made the aberrations something like 8X more prominent--at least it *seemed* that way.
If the BV under this test does not notably impair the view when held before a 5X+ telescope, it must in normal use perform well.