ES82* 4.7mm Internal Reflections...

[Stargazer McCabe]

A little while ago I purchased a “previously cherished” ES82* 4.7mm from @Mark at Beaufort. Being Nitrogen purged, it is an earlier variant than all the other 82* eyepieces we have which are Argon purged. It was passed on in excellent condition and has done well on the deep sky and planetary observing done to date.

Recently, I’ve used the eyepiece for the first time on lunar viewing with our Takahashi. It’s actually a nice magnification and FoV with this set up.

However, when switching from the 6.7mm to the 4.7mm (or even our 3-6 Nagler zoom) a reflection has been noticeable on the right hand side of the eyepiece (with the moon placed at the left hand side of the eyepiece).

Given this is the only eyepiece that both my wife and I notice this in, it has provoked a few questions:

1) Is this a trait of this particular eyepiece or might we have an odd one out

2) I know it’s nothing to do with the gas, but did ES improve any internal blackening with the newer variants if this is something common to other 4.7mm Nitrogen variants ? Would a newer 4.7mm show similar ?

3) Is there any blackening or modifications I might be able to make to the eyepiece we have ? If so, might someone more familiar with this direct me towards an idiot’s guide please ?

4) Could it be nothing to do with the eyepiece construction as such, and actually be a factor of exit pupil and reflection from the surface of our eyes ? (If so, out of curiosity, could someone explain why we might see it in the 4.7mm and not in the zoom when set at 5 or 4mm please?)

Thanks in advance 

[Stargazer McCabe]

@Mark at Beaufort Mark I saw you were perusing this earlier this evening. Did you ever encounter anything similar with the eyepiece ?

[Ricochet]

I see something similar with my binoviewers and the highest strength barlow. I think it is something to do with the stronger barlow diverging the light path more and diverting the light at certain angles onto an unblackened part. You could have found something similar with the ES eyepieces where the main lens groups are the same and the only difference is the negative lens section. 

[Stargazer McCabe]

@Ricochet Interesting. Thank you. Have you been able to find a way around your encountering of it that I might adapt ? 

[Mark at Beaufort]

Hello Simon I was trying to remember if I ever encountered any reflections especially when viewing the Moon. I did own the complete set of ES82 EPs but it was only the 4.7mm that was Nitrogen filled all the others were Argon. I sold my collections not because of any disappointment but I wanted to return to 100 degree EPs and Binoviewers for higher magnification.

As far as I can remember the 6.7mm and 4.7mm gave similar performance I don't recall a reflection problem. I am sorry if this is now causing you concern.

[Stargazer McCabe]

Not a problem at all Mark. It’s just an unusual occurrence given i’ve not encountered anything similar with the rest of them. I couldn’t even replicate using the 8.8mm and a 2x Barlow. 

On all other targets it works wonderfully. It’s obviously just the bright and big moon that tests it...

Susie particularly likes the eyepiece in her Takahashi. I’ll think about ordering her a new one to see if the problem occurs in the more modern ones...

[Mark at Beaufort]

Simon thinking back I usually used the 4.7mm on Double Stars with the occasional high mag on the Moon and Planets. Let me know how you get on.

[Stargazer McCabe]

Mark, that’s exactly how we’ve used it in the main thus far... 

I’ll see whether Susie would put up with the 8.8mm and a Barlow. If not, and nobody has a fix, I’ll see if a modern variant does similar. 

I like a puzzle ??

[Ricochet]

31 minutes ago, Stargazer McCabe said:

@Ricochet Interesting. Thank you. Have you been able to find a way around your encountering of it that I might adapt ? 

Unfortunately, not. To do so would require a complete strip down of the BV and I'm not sure that is something I want to undertake. 

Thinking about it I did once have some internal reflection problems with my Meade telextender (i.e. pre-ES variant) and the problem was a shiny internal barrel between the two lens groups. The solution was to flock between the two and now it is excellent. Not so easy a fix with a purged eyepiece that can't simply be opened up and put back together though. 

[Stargazer McCabe]

Once again Steve G at @FLO nails it... I wrote posing the same question to Team Flo this morning and, as per usual, had a helpful and informed response within 30 minutes... 

[Reeny]

I have this when using doubled up moon filters, which is most of the time. It appears as a reflection of my eye ball.

Either 2x polarised filters on the moon, or 1x ND and 1x purple tinted moon filter on Jupiter can cause the problem.

It could be a combination of the filters and the eyepiece. I have an 11mm ES 82 degree, but I can't remember which eyepiece causes the problem, or whether it was with, or without the 2x barlow.

The solution was to move my eye position nearer to the eyepiece, mount the second filter further away from the first on the 2"-1.25" adaptor, then simply to try to ignore it. 

Either way, it doesn't bother me any more.

[alan potts]

I'm fairly sure thinking back I use to get this sort of thing with Venus but on the 4.7mm Meade version, don't for one moment feel it has anthing to do with gas. 

Alan

[Stargazer McCabe]

@alan potts I agree that’s why I was looking for alternative reasons or insight as to whether ES changed anything else other than the gas...? 

 

[alan potts]

16 hours ago, Stargazer McCabe said:

@alan potts I agree that’s why I was looking for alternative reasons or insight as to whether ES changed anything else other than the gas...? 

 

It may also be of interest that I later reviewed the ExSc version of the 4.7mm, 2 of them infact and working from memory ( agreed not the best thing to do) I would say that niether of them were as good as the Meade 4.7mm, I don't remember checking them on something like Venus though, may be it was not in the sky. I always include a bright star though, say Vega, and can't recall ghosting. I can't check my notes as it never got written as my son put them in the wood burner.

I did always wonder how Meade marketed this eyepiece at at about 180 pounds where as the ExSc version, some couple of years later was a mear 119E, I will grant you Meade had a tendency to over price but at the time this was close to half price.

Alan

[Stargazer McCabe]

@alan potts From other discussions held, I think I’m forming the conclusion that putting a bright target like the moon at one edge of an eyepiece is one of the sternest tests. And with as wide a view as the 82* and with as many elements in the eyepiece, reflections are almost guaranteed at that magnification...

Apparently, even more expensive 82* eyepieces than the ES would struggle with that test according to those that have used them in similar circumstances... That’s why high power lunar and planetary eyepieces are of completely different construction Alan

[Louis D]

On 19/11/2018 at 13:51, Stargazer McCabe said:

However, when switching from the 6.7mm to the 4.7mm (or even our 3-6 Nagler zoom) a reflection has been noticeable on the right hand side of the eyepiece (with the moon placed at the left hand side of the eyepiece).

I'd like to look for this in my eyepieces for comparison sake; but first, where exactly did you see this reflection and what did it look like?  Was it simply a ghost image on the opposite side, a flaring of unfocused bright light across the opposite side, a specular reflection off of an inner element edge, ring, or spacer visible when you pull your head back and refocus on the eyepiece rather than the image, or was it something else entirely?

[Stargazer McCabe]

@Louis D Let me see if I can describe coherently to be of use. 

Takahashi FC100DF being used with 1.25” Baader T2 Prism. Moon at 88%. On scanning the terminator the bulk of the bright moon was situated on the left of the eyepiece view. On the opposite side was what appeared to be an unfocused, “cloudy” light “patch” along the edge of the eyepiece. It wasn’t a ghost image and it was only visible with the eye to the eyepiece. It could be “avoided” by moving one’s eye placement  But in doing so, one was reducing the observable FoV, to the point a Ortho would have yielded wider !!

This was with the 4.7mm. With the 6.7mm there was no sign whatsoever. 

I’m led to believe the wide FoV of the eyepiece, allied to its numerous elements and a stern test with a bright target on one side of the eyepiece led to the “reflection”. To avoid it, I am reliably told, one should use narrower eyepieces with fewer elements...

I’d be interested to hear what someone with your experience and critical eye can replicate Louis...

[Don Pensack]

Try painting the filter threads with flat black paint.

If that doesn't work, try a rubber washer that just fits in the bottom of the eyepiece but which has a center hole large enough for the lens.

This type of rubber washer is common at plumbing supply places.

Insert the washer to be flat/flush with the bottom of the eyepiece.

That should do it.