317 replies to this topic

[russell23]

So with this much agreement on observations, can we finally put to rest the idea that EOFB is an illusion or delusion?
 

Mike

 
Two observers agree there are several examples where there is no consensus..
 
Jon

 
That could be due to a number of things I have outlined before: when observing the planets and Moon EOFB is less obvious.  In light polluted or strongly Moonlit skies EOFB is less obvious.  Light pollution that is not shielded from the observer.  Some people may not realize what it is they are looking for -  perhaps thinking "brightening" means more than it is.  The photos Bill attached to the thread now provide a nice visual of pretty much exactly what we are seeing - and they demonstrated that it is real and not just perceptual.
 
Human perception probably plays a role in how easily EOFB is noticed. 
 
Perhaps also now that it is demonstrated that it can be photographed it might be possible to understand what I described before when I noted that if I shine a flashlight looking for a dropped cap and then immediately go back to the eyepiece I might not see the EOFB, but as my pupil expands the EOFB becomes apparent again.   It is a real phenomenon and better dark adaptation makes it easier to see.
 
Dave

 
Dave:
 
Those are possible reasons why one observer sees it and another doesn't. 
 
But it is also possible that one observer is doing something or has something different about their eye such that it is simply just not there to be seen.
 
Jon

One thing I've suspected is a simple lack of dark adaptation.  Observers using tablets, observing in light-polluted skies, or observing Moon and planets just aren't going to see it.
Bill's observation that f/ratio (i.e. exit pupil) changed how it was seen it also illuminating (pun intended).  I didn't notice a dramatic difference between my f/5.4 refractor and f/12.5 Maksutov the way Bill did, but I did look on different nights and under different degrees of light pollution in the skies.
 
One comment for the people who did not see it in Bill's post #269: turn up the brightness on your monitor.  It will pop out.  At well below max on my laptop's screen it's as visible as chalk on a blackboard.

Also go into a dark room. I saw it much better with lights off - kind of like the real thing.

Dave

[russell23]

So with this much agreement on observations, can we finally put to rest the idea that EOFB is an illusion or delusion?
 

Mike

 
Two observers agree there are several examples where there is no consensus..
 
Jon

 
That could be due to a number of things I have outlined before: when observing the planets and Moon EOFB is less obvious.  In light polluted or strongly Moonlit skies EOFB is less obvious.  Light pollution that is not shielded from the observer.  Some people may not realize what it is they are looking for -  perhaps thinking "brightening" means more than it is.  The photos Bill attached to the thread now provide a nice visual of pretty much exactly what we are seeing - and they demonstrated that it is real and not just perceptual.
 
Human perception probably plays a role in how easily EOFB is noticed. 
 
Perhaps also now that it is demonstrated that it can be photographed it might be possible to understand what I described before when I noted that if I shine a flashlight looking for a dropped cap and then immediately go back to the eyepiece I might not see the EOFB, but as my pupil expands the EOFB becomes apparent again.   It is a real phenomenon and better dark adaptation makes it easier to see.
 
Dave

 
Dave:
 
Those are possible reasons why one observer sees it and another doesn't. 
 
But it is also possible that one observer is doing something or has something different about their eye such that it is simply just not there to be seen.
 
Jon

The photographic proof of its existence means that it is there to be seen. If someone does not see it under dark sky conditions then it would be likely that their eyes cannot sense it. As I pointed out before - people may have different sensitivity levels. Some people tried to tell me before there must be something wrong with my eyes. My response was that EOFB is a low light phenomenon and therefore my eyes could just be highly sensitive to detecting fainter light. Now that we have photographic proof we can dispense with the arguments that it is all perceptual and not there to be seen.

Dave

[Achernar]

My story:

 

Obviously I don't have the skills or experience of Don but I am sure that EoFB is real..  8-10 years ago, I never saw mention of the EoFB, never thought about it.   About 7 years ago, an Orion 13mm Stratus showed up in my eyepiece case and it sat right next to a 16 mm Nagler type 2.  Physically, the 13mm Stratus and the 16mm Nagler are very similar in size and weight and both are 1.25 inch/2 inch eyepieces.  It was very easy to pickup the wrong eyepiece and they were close enough in magnification that it was not immediately obvious I had the wrong eyepiece.  

 

So, inadvertently, I conducted a blind test of these two eyepieces.. 

 

The case that was most obvious was when I accidentally grabbed the 16mm Nagler instead of the Stratus.  My reaction was always the same.. My first thought was, "Wow, the 13mm Stratus is a much better eyepieces than I had thought. the field is well corrected to the edge and it is evenly illuminated. Why was I thinking this was flawed?"  It took just about that long and then I would realize.. "Oh yeah, this is the 16 mm Nagler."  That happened many times, the difference was very apparent and the evenly illuminated field of the Nagler made the EoFB of the Stratus more obvious, more apparent.

 

At that point, I began commenting here on Cloudy Nights in threads about the 13mm Stratus about the EoFB, I called it something like the bright edge or a bright edge ring. Previously I had seen no mention of this phenomenon in these eyepieces but once I mentioned it, a few others chimed in that they had seen it too.  I think the awareness of EoFB has increased dramatically since then.  Someone noted that the increase seemed to be correlated with the advent of more affordable SWAs and UWAs coming from China.  They're not the only eyepieces that exhibit EoFB but they may do so more frequently.  

 

I see EoFB in other eyepieces, the 9mm Expanse type eyepieces show a significant amount of EoFB..  I see it in the 20mm ES 100 degree, though more under light polluted skies.. 

 

Jon

I have all of the Stratus eyepieces except for the 17mm, and it's most definitely apparent in some of them. It was actually easier to see at a dark site than a light polluted one for me. Moreover, they definitely have more scatter than the Explore Scientific 82 degree eyepieces I use, enough to hide Sirius B from view while it was visible through the ES eyepieces. They are not bad eyepieces but clearly the ES 82 degrees are better.

 

Taras

Edited by Achernar, 14 May 2015 - 08:32 PM.

[Scanning4Comets]

Pic 1 & 2 enhanced...(if you don't mind Bill.)...

[EuropaWill]

I will try again, but let's all remember...

 

1. I am not skilled in doing this

2. The wall I am pointing at may not be perfectly evenly illuminated to the nth degree you guys are expecting

3. I am using a relatively high end consumer mirrorless camera (Fuji X-E1), but nevertheless it is not a research device so who knows how uniformly the censor captures illumination levels as these very minimal levels.

4. My goal is to simply capture that it indeed exists, so no need to capture it perfectly to do detailed analysis on this particular scope-eyepiece combination.

 

Bill, 

 

Another thing that might be helpful to validate is that in addition to the photographic evidence on the worst offending eyepiece that you have already provided please repeat the same test on an eyepiece that your visual detection says exhibits it mildly, and on yet another eyepiece that you don't perceive it to exist visually.

 

If those additional photographs roughly match what you are seeing through the additional eyepieces then we have a stronger validation that our visual detection is picking up on a real optical characteristic of the eyepiece and not just a brain/perception phenomenon - while simultaneously eliminating the argument that the photographic technique is giving us a false positive. 

[Sarkikos]

One thing I've suspected is a simple lack of dark adaptation.  Observers using tablets, observing in light-polluted skies, or observing Moon and planets just aren't going to see it.

 

Well, some observers using tablets will be sufficiently dark adapted to see EOFB.  I use SkySafari Pro on an Android tablet every time I go to my dark site.  I see the EOFB.  It depends on how well you filter the tablet screen, and set the dimness and other settings on the tablet.  It can be done.

 

Mike

[BillP]

 

The photographic proof of its existence means that it is there to be seen. If someone does not see it under dark sky conditions then it would be likely that their eyes cannot sense it. As I pointed out before - people may have different sensitivity levels. Some people tried to tell me before there must be something wrong with my eyes. My response was that EOFB is a low light phenomenon and therefore my eyes could just be highly sensitive to detecting fainter light. Now that we have photographic proof we can dispense with the arguments that it is all perceptual and not there to be seen.

 

 

It certainly is the case that we are all different and our sensitivity levels, especially at night can be way different for a number of reasons.  However, for those that do not see it, can also be as simple as missing the observations.  I can't tell you the number of times folks have said they didn't see the Cassini Division, but then when you explain exactly what it looks like and where and show them, then they eventually "see" it.  So many times things are there and we just don't see them because we are unaware.  Just making the point that when someone says they do not see it, can be lots and lots of reasons why even though it is actually there.

Edited by BillP, 15 May 2015 - 06:02 AM.

[Jon Isaacs]

The photographic proof of its existence means that it is there to be seen. If someone does not see it under dark sky conditions then it would be likely that their eyes cannot sense it. As I pointed out before - people may have different sensitivity levels. Some people tried to tell me before there must be something wrong with my eyes. My response was that EOFB is a low light phenomenon and therefore my eyes could just be highly sensitive to detecting fainter light. Now that we have photographic proof we can dispense with the arguments that it is all perceptual and not there to be seen.

Dave

 

Dave

 

As you might have noticed, I am encouraging Bill to test his photographic system, particularly the camera placement. As my boss likes to say, before performing a test, you must first test the test.  Show the system works and is repeatable, show it is imaging the entire field, afocal imaging is not so easy. Take some flats with no light entering the camera..

 

Consider alternative hypothesis,..If, for example, eye placement or some other individual characteristic plays a role, then that same characteristic or placement issue could also affect the camera's image.

 

As an experimentalist, I am a skeptic by nature..the easy explanation is not always the right explanation. I have to see a lot more data to understand what is going on. 

 

Here is something to consider: Very few telescopes are fully illuminated across a wide field of view, a camera will easily show this but to the observer, even rather large dropoffs are not obvious.  How does this fit with the EoFB and the camera?

 

 The EoFB I see is quite bright. These images have enhanced contrast, is that a realistic thing to do? 

 

Testing the the test..looking at the measurement system and understanding what one is seeing.

 

Jon

 

PS. I see it under light polluted skies.. As Glenn pointed out, it should be linear.. Why is it you don't see it under light polluted skies? 

[russell23]

Jon,

Let's assume that the behavior of the optical system you are using has a linear behavior as the sky brightens. The problem is your pupil will change as the sky brightens. If I am looking at the EOFB under dark sky conditions my pupil is larger. When I observe a washed out moonlit sky my pupil is smaller - just due to the brighter sky background presented at the eyepiece - even if I have a hood. That is a physiological reaction you cannot control. What I see with regard to EOFB - and I reported this not that long ago with the 9mm Expanse - is that near the edges of the field when I was looking at the Moon, the background light was a different shade near the edge - almost white. The EOFB was not being projected against a black sky background so it looked different. It is much more distracting and aesthetically displeasing when skies are black and therefore much more likely to draw a person’s attention.

 

My point then is that people that claim not to see EOFB in certain eyepieces that others do see it in might simply never have noticed it if they are observing under light polluted conditions or really mainly look at the Moon and planets. I can tell you that if my targets were just the Moon and planets I would probably never have given it a thought. And based upon my observations of DSO during near full moon nights I do not think that in heavily light polluted skies EOFB would have drawn my attention either.

 

That is the difference. What happens with eyepieces that show EOFB is that you have a whitish EOFB projected against a bright bluish-gray sky background when the skies have heavy light pollution and/or moonlit. When the sky background at the eyepiece is black the EOFB draws the observers attention - and with the expanded observer pupil the EOFB is even easier to detect as standing out against that background.

 

Here is another situation in which you briefly won't see EOFB in an eyepiece that has it: Pick an eyepiece that has EOFB and observe under dark sky conditions to get a sense of its extent. Then turn on a regular flashlight and scan for a few seconds around in your eyepiece box or on the ground.  Do not look directly into the flashlight obviously. I have done this at times when I drop an eye-cap in my backyard. Then turn off the flashlight and go back to the eyepiece immediately. The sky background looks blacker and the EOFB is not seen. But as your pupil expands the EOFB becomes visible again.

 

As I've said before, I've experimented around with eyepieces and various blackening and flocking efforts and equipment change efforts that I've described in other posts over the last couple years.  The conclusion I have come to from all of my experimenting is that EOFB is primarily caused by the eyepiece.  I don’t need Bill’s photograph of EOFB to be convinced it is caused primarily within the eyepiece because there is no other reasonable conclusion to draw from everything I have done to test it and from the many other reports people have made here.  Nobody has yet raised an alternative explanation that is consistent with all of the various efforts I have made.

 

So to me Bill’s picture is very valuable.  How is it he photographed a phenomenon that is perceptual and not real?  

 

And regardless of what doubts any people may have the picture Bill posted does a good job of representing what I see.  So for people that may have wondered now they have a nice visual of the kind of thing to look for. 

 

Be skeptical of the image to as much extent as needed.  I’ve got no problem with that.    But I really don’t think Bill’s purpose was to get involved in a high level laboratory statistical analysis of his image.  His purpose was to demonstrate that EOFB can be imaged and therefore is real.  I think he has done that.   Anybody who has the knowledge and equipment to provide a more rigorous test of the imaging of EOFB is welcome to do so and I would welcome those results.  But I think Bill’s image is a valuable service to the CN community.

 

Dave

Edited by russell23, 15 May 2015 - 09:01 AM.

[Patricko]

Summarizing my experiences:

 

EOFB is influenced by:

 

-Eyepiece design

-Sky background brightness

-Telescope Type

-Observer dark adaptation

-Observer experience and eye sensitivity

-Local light pollution

[BillP]

 

The EoFB I see is quite bright. These images have enhanced contrast, is that a realistic thing to do? 

 

Interesting question.  In some respects I think the answer is very much yes!  Why?  Because the camera sensor does not have near the sensitivity of the human eye (0.1lux), but more importantly it has significantly less dynamic range than the human eye.  This latter is extremely important and why the raw photo needs tweaking if it is to simulate what the eye is perceiving.  While my camera is a new technology and has a rather high dynamic range (12 f-stops), this is only at low ISO settings (which I didn't use).  At the higher ISOs the dynamic range falls to about 8.  The human eye has around 14 f-stop dynamic range.  So in any image taken, we have to always remember that what a sensor "sees" and what a human eye "sees", are too different things.  So we must always take imagery to be something that necessarily needs to be adjusted if it is to represent the human experience of seeing.

Edited by BillP, 15 May 2015 - 03:12 PM.

[Tamiji Homma]

Really amateur technique.  Basically the scope is in the basement pointing at a lightly illuminated wall.  The Olivon 13mm has a wide flat top eyeguard so the camera is actually just sitting on the eye guard.  So it is sitting flush on the top of the eyepiece.  Then I just activate the shutter.  Visually easy to tell that camera lens is centered on the eyeguard as the lens housing just slightly overhangs the eyeguard.  Camera is set to manual focus and set at infinity.  Diaphragm set wide open (f/2).  Scope set at infinity focus (focused on Venus outside with eyepiece then locked focuser position).

 

Attached are two pics (sorry guys but best I can do - I hate astroimaging...even of a white wall  ).

 

Adjusted with contrast boost to reveal what is seen visually (COFD).

DSCF6372 Contrast Boosted.jpg

 

Unadjusted (other than downsized to meet upload size restriction)

DSCF6372 Orig.jpg

 

Hi Bill,

 

I don't know you took the photo in raw mode and disabled lens profile corrections when you

developed the photo.

 

I think if you take photo in jpeg, Fuji camera applies onboard lens profile corrections to image, such as geometric distortion, chromatic aberration, vignetting, etc...  It may result in different image you are looking to find.  

 

New camera system becomes too smart.

 

I haven't researched how much difference lens profile corrections make in final image, I mean how different corrected image is different from real image.

 

What is real?, Morpheus may ask

 

Just a thought.

 

Tammy

[GlennLeDrew]

That's something I hadn't thought of at all; this business of a camera applying corrections for field illumination variations induced by the geometry of the lens attached. If this is the case, a lens set wide open, which suffers the worst vignetting, will have the largest correction applied by increasing the outer field brightness the most.

[GlennLeDrew]

I neglected to point out that in these images Bill has presented here, any camera-induced field brightness correction cannot replicate the ever more sharply increasing brightness which is then pretty suddenly truncated to darkness. There must be a real such gradient present, by whatever cause, extrinsic to any processing.

The contribution by the camera lens, and the interfacing of the exit pupil with the possibly not-ideally-located lens iris (modal point) is open to question.

But that the images show what was seen visually is pretty supportive of the reality of EFOB, at least for this eyepiece.

[YKSE]

Is there anyone feel like to explain "Stiles–Crawford effect" in layman language and comments on its possible contribution to EOFB?

[GlennLeDrew]

The Stiles-Crawford effect will contribute little if at all here when considering EoFB at night sky brightness levels; the S-C effect appears to be in effect for only the color-responsive cone cells.

[Ruud_]

The only photo I can find of EOFB is Bill’s.

 

In his setup, I understand the telescope’s focuser is set to infinity, the wall is not at infinity and the wall reflects light. The method used to record the image is afocal photography. (The field stop is not in focus, but I don’t think that matters much. Bill’s experiment shows brightening toward the edge of the field. That is clear.)

There is a problem though. Individual spots on the wall are each a light source. The individual light cones coming from these spots after passing the objective are so badly out of focus when they reach the eyepiece, that there is no way of telling without a ray trace analysis how the field would end up illuminated. The eyepiece is subjected to a circumstance widely outside its design parameters.

Bill may have photographed an unintended effect.

 

In real life, EOFB reports describe situations where target and focus both at infinity: a circumstance the eyepiece was designed for. If Bill’s experiment is repeated against the night sky, does the effect still show?

 

Another thing to try might be to take an image by means of eyepiece projection. Does a brighter field edge show up in such an image?
Although the outcome would be interesting, eyepiece projection would introduce a problem of itself. The eyepiece is again asked to do something it was not designed for: produce beams of converging rays, rather than the usual beams of parallel rays. (Normally, parallel rays entering the objective are again parallel when leaving the eyepiece. The ‘final focusing’ is done by the eye.)

 

We have many reports of EOFB and many of the absence of it. We need better. Evidence is not the plural of anecdotes. EOFB needs to be demonstrated in a repeatable experiment under realistic conditions.

 

Once it has been established as real it needs to be explained. If it turns out to be caused by different causes in different eyepieces should we continue to call it EOFB?
If it is for instance caused by scatter from lens edges or the eyepiece barrel, would it then not be better to speak of scatter?

[Starman1]

Ruud,

The eyepiece Bill photographed exhibits EOFB in the field quite well.

A number of observers at my dark site, and in different scopes, all saw the same thing.

It exists and there is no doubt.  Arguing it doesn't exist is fairly pointless by now.

 

But, that certainly doesn't pinpoint the cause or causes.

I've made several posts bringing up at least 6 possible causes.

Instead of posting in this zombie thread, however, you should follow the threads currently running:

https://www.cloudyni...-for-neurotics/

https://www.cloudyni...ible-eofb-clue/

 

Don