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Maxbright Internal Reflections

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#1 chrisg

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Posted 03 April 2013 - 06:33 PM

My last post somehow didn't show, apologies if this turns into a repeat!
I've been loving my Baader Maxbrights, and all the advantages of using two eyes. However, I've noticed that on some bright objects, as I move the telescope, I see angled reflections on both sides of the view. I've checked to see where these reflections are coming from and they're simply direct reflections coming from the prisms just adjacent to the opening on the telescope side. Is this normal? I can't imagine that this is due to miscollimation - to correct for this, the prisms would have to more fairly far. Perhaps I need to use eyepieces that have rear lenses located far down enough in their housing to avoid these reflections? Is this normal? Does anyone here have experience with this?? :confused: :confused:

#2 daniel_h

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Posted 03 April 2013 - 07:23 PM

i saw it in my pair of WO binos, machining really good prisms would be expensive -on god binoculars i see they make an etch in the prism to prevent the reflections

#3 BBryce

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Posted 04 April 2013 - 01:09 AM

I heard that some maxbright owners have the same problem, but I have never seen any such internal reflections inside mine...I maybe lucky or it doensn't bother me !

Anyway I just purchased a Siebert Black Night BN25 binoviewers so I will be able to compare...

It seems to be a well-known issue with these entry-level chinese binoviewers.

#4 chrisg

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Posted 04 April 2013 - 02:35 PM

Here are the reflections I'm referring to. Don't all binoviewers have these here? Anyone else experiencing problems?
Posted Image
The rear lens of every eyepiece is different, and I think catch these reflections differently.
Posted Image
Could anyone here suggest a bino pair that doesn't have this issue? :question:

#5 GlennLeDrew

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Posted 04 April 2013 - 04:22 PM

In a Porro prism bino you get four such reflections, all of differing intensity, arranged in a 'cross' around the aperture. Here you have just two. In all cases, these reflections result from light entering from an angle off axis, and from one direction only (even for the four of the Porro, which I illustrate and somewhat explain in an image in my Gallery--link below.)

I should expect these reflections to be a bit more clipped on long focal length scopes, due to the angularly smaller objective (as 'seen'' from the BV) effectively narrowing the light source. Compare the BV-alone aspect with that on a fast scope and then a slow scope, then report back.

What you see here you see in miniature as the exit pupil, flanked by the same pair of scaled down reflections. If your eye's iris is large enough (and with BVs it usually is), it will take in the whole lot, leading to the perception of ghost images from bright objects outside the FOV crossing the view as you pan about. If the exit pupil is about equal to or larger than your iris, you only experience the ghost images if you iris is offset so as to take in the flanking 'fingernail' of what are in essence highly clipped, off-axis ghost exit pupils.

#6 chrisg

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Posted 04 April 2013 - 05:24 PM

Thanks Glenn! In most of the eyepieces that this is showing up, it's just an edge abberation. However, with my Zeiss spotting scope eyepiece, which uses an adapter that brings the lens farther than normal away from the binos, the reflection is dead across the middle and is unacceptable. I guess - do all binoviewers have this problem to varying degrees? Aside from using a longer scope (I only have a f7.5 EON120) is there any way I can avoid this? Haven't been able to figure out what kind of eyepieces in particular interacts with the binoviewer in this way. My guess is - the bigger the rear lens and the farther the eyepiece is away from the binoviewer, the greater chance of catching these side reflections?

#7 GlennLeDrew

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Posted 04 April 2013 - 08:51 PM

I couldn't at all reliably say exactly what configurations will lessen the effect. For one thing, the presence of a Smyth lens ahead if the field stop may have a significant impact. And as you surmise, for more 'ordinary' eyepueces, the location of the field stop *and* the location of the field lens behind the stop, likely have some impact.

I don't have a binoviewer, and so you're in a much better position to explore the envelope.

#8 chrisg

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Posted 05 April 2013 - 06:30 AM

Thanks Glenn - your explanation of the phenomenon precisely describes what I'm experiencing. Some searching on these thread have revealed that it may be possible for me to reduce these effects by adjusting the eyepiece alignment, will report results, hopefully successful!!

#9 mark8888

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Posted 05 April 2013 - 10:04 AM

The 10mm Delos has a much-maligned plastic piece over the rear lens. I believe its purpose is to act as a baffle to catch a reflection from the barrel. It's discussed here, among other places:
http://www.cloudynig...5464976/page...

I wonder if it might also block some of the reflections from the prisms you're seeing? And I wonder if adding a disk like that is a modification that one could make on certain lenses to minimize or eliminate such reflections? I don't know, though, what the effect of adding such a disk has on blocking the light cone and then possibly lowering light transmission as a result. That's something else which is discussed in that thread.

#10 chrisg

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Posted 05 April 2013 - 11:11 AM

mark8888 - Just looking through the binoviewers, I can see that something like the baffle you mention would work, as long as I don't go too far and diminish any useful light. Really good idea! I'm mostly getting ghosting from my micro eyepiece set which I've already modified. I'm going to experiment here first but any ATMs know where I can purchase a set of eyepiece baffles?
Awesome! :cool::bow: :cool:

#11 SPO

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Posted 06 April 2013 - 06:26 PM

I see this in my Orion binos. I've been talking to Harry Siebert about his super charging service and he mentioned he notches the prisms so they are properly baffled.

i saw it in my pair of WO binos, machining really good prisms would be expensive -on god binoculars i see they make an etch in the prism to prevent the reflections



#12 chrisg

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Posted 06 April 2013 - 08:30 PM

Thanks everyone -
So I've been able to adjust the eyepiece holders so the image circles align better but I've found that baffling the for eyepieces isn't as easy as I first thought, without reducing the fov. Curious about notching the prisms - will see what Harry thinks, curious if this is cost effective...






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