Different focus points.

[Xilman]

1 minute ago, saac said:

There tends to be a dioptre adjustment for each eye on a bino, this narrows the divergence between the eyes. Remember too that the image is interpreted in the brain and it will accommodate to form a single image. There also is usually a more dominant eye which the brain will preference. 

Jim 

My eyes point in different directions and my spectacles include prisms to bring them into alignment. With binoculars I see two images if both optical paths are clear, so I keep one eyepiece cap in place when using them.  This has the advantage as I can swap eyepieces when one becomes dewed up from proximity to a warm wet eyeball.

[Marvin Jenkins]

2 minutes ago, saac said:

When I wear glasses then my daughter, non spectacle wearer, will not need to refocus or only minimal adjustment. If I remove my glasses and focus to suit my eyesight then on handing over my daughter will need to make a pretty noticeable focus adjustment. This makes sense as the point of glasses, corrective lenses, is in effective to provide the wearer close to 20:20 vision. 

Jim 

Thank you for this but I my confusion is that spectacles in my mind, are for wearing for reading, driving, and even more distant vision correction.

I am still wondering why specs are needed at the EP when the Focuser is doing the work?

Marv

[ollypenrice]

9 minutes ago, Marvin Jenkins said:

Thank you for this but I my confusion is that spectacles in my mind, are for wearing for reading, driving, and even more distant vision correction.

I am still wondering why specs are needed at the EP when the Focuser is doing the work?

Marv

Astigmatism is not corrected by the focuser, so if that's what the specs are for they remain necessary.

Binoviewers and beginner observers?  Nooo!!!  What a nightmare. You have both the distance between the EPs and twice as many elements to adjust, then you have the location of the eyes relative to the oculars to deal with.

Keep it simple.

Olly

Edit: Children in particular, but also some adults, are not sure which eye they are closing. This may seem crazy but the human brain's 'sidedness' leads to many paradoxical complications and I think the best solution is to ask them to cover the unused eye.

Edited June 4 by ollypenrice

[saac]

8 minutes ago, Marvin Jenkins said:

Thank you for this but I my confusion is that spectacles in my mind, are for wearing for reading, driving, and even more distant vision correction.

I am still wondering why specs are needed at the EP when the Focuser is doing the work?

Marv

Spectacles are not just for reading (nearby) and distant correction. They can be if that is the prescription but they can also be for everything in between, it all very much depends on the prescription (corrective requirement).  It is also quite possible that a person with a particular corrective requirement will be unable to focus an image from an eyepiece. 

Remember too that the focuser is not focusing the image on the retina, rather it is presenting a focused image at the eyepiece focal plane. The eye of the observer still has to focus that image on their retina in order for it to be sharp. 

Jim 

 

Edited June 4 by saac

[Marvin Jenkins]

Just now, saac said:

Spectacles are not just for reading (nearby) and distant correction. They can be if that is the prescription but they can also be for everything in between, it all very much depends on the prescription (corrective requirement).  It is also quite possible that a person with a particular corrective requirement will be unable to focus an image from an eyepiece. 

Jim 

Good info. I didn't know that. Thank you. Seems I need to take a course in ... The eyeball. So much I do not know obviously.

[ollypenrice]

15 minutes ago, Xilman said:

My eyes point in different directions and my spectacles include prisms to bring them into alignment. With binoculars I see two images if both optical paths are clear, so I keep one eyepiece cap in place when using them.  This has the advantage as I can swap eyepieces when one becomes dewed up from proximity to a warm wet eyeball.

A friend had this after a fall fractured his cheekbone and, after more than a year of misery, the introduction of prismatic glasses saw him comfortable again.

Olly

[saac]

1 minute ago, Marvin Jenkins said:

Good info. I didn't know that. Thank you. Seems I need to take a course in ... The eyeball. So much I do not know obviously.

I like the idea of a course on the eyeball - sign me up too.  I must admit whenever I go for my annual check up at the optometrist I'm like a kid in a candy store asking questions about all the tests and all the equipment. It really is fascinating, as is anything to do with the human body, a remarkable machine. 

Jim 

[Marvin Jenkins]

Just now, saac said:

I like the idea of a course on the eyeball - sign me up too.  I must admit whenever I go for my annual check up at the optometrist I'm like a kid in a candy store asking questions about all the tests and all the equipment. It really is fascinating, as is anything to do with the human body, a remarkable machine. 

Jim 

Well you know eyeball courses are very informative. I am signing up right now when I see one.

[Marvin Jenkins]

20 minutes ago, Xilman said:

My eyes point in different directions and my spectacles include prisms to bring them into alignment. With binoculars I see two images if both optical paths are clear, so I keep one eyepiece cap in place when using them.  This has the advantage as I can swap eyepieces when one becomes dewed up from proximity to a warm wet eyeball.

That is incredible. Do your glasses look much different to normal spectacles?

[Xilman]

2 minutes ago, Marvin Jenkins said:

That is incredible. Do your glasses look much different to normal spectacles?

Yup.  The outside edge of each lens is markedly thicker than the inside edge.

[Marvin Jenkins]

1 minute ago, Xilman said:

Yup.  The outside edge of each lens is markedly thicker than the inside edge.

So the whole spectacle lense is like a wedge shape? In effect acting like a prism?

[ollypenrice]

13 minutes ago, saac said:

I like the idea of a course on the eyeball - sign me up too.  I must admit whenever I go for my annual check up at the optometrist I'm like a kid in a candy store asking questions about all the tests and all the equipment. It really is fascinating, as is anything to do with the human body, a remarkable machine. 

Jim 

A local Brit, also called Jim, is a retired eye surgeon (and pilot, and aeroplane builder, and motorcyclist, and model engineer...) but talking to him can leave you exhausted in less than five minutes!  Great guy, though.

Olly

[Marvin Jenkins]

3 minutes ago, ollypenrice said:

A local Brit, also called Jim, is a retired eye surgeon (and pilot, and aeroplane builder, and motorcyclist, and model engineer...) but talking to him can leave you exhausted in less than five minutes!  Great guy, though.

Olly

I guess it's all in the perspective?

[Marvin Jenkins]

34 minutes ago, saac said:

Spectacles are not just for reading (nearby) and distant correction. They can be if that is the prescription but they can also be for everything in between, it all very much depends on the prescription (corrective requirement).  It is also quite possible that a person with a particular corrective requirement will be unable to focus an image from an eyepiece. 

Remember too that the focuser is not focusing the image on the retina, rather it is presenting a focused image at the eyepiece focal plane. The eye of the observer still has to focus that image on their retina in order for it to be sharp. 

Jim 

 

That second paragraph seems to answer my initial question perfectly.

In effect the EP and Focuser gets the image sharp, the second optical path 'eyeball' does its bit.

However most EBs are flawed through short or long sight. Other stuff I don't understand including stronger eye, mis aligned eyes.

So to boil it down. I need to put up with my non existent outreach guests, not messing with  my focal position?

Marv

[saac]

3 minutes ago, Marvin Jenkins said:

That second paragraph seems to answer my initial question perfectly.

In effect the EP and Focuser gets the image sharp, the second optical path 'eyeball' does its bit.

However most EBs are flawed through short or long sight. Other stuff I don't understand including stronger eye, mis aligned eyes.

So to boil it down. I need to put up with my non existent outreach guests, not messing with  my focal position?

Marv

Hang a tag from your focuser with the message "virtual outreach guests please refrain from adjusting my focus".

Of  course you could overcome all of this by putting a camera on the scope and displaying the image to guests on either a laptop or phone screen.  Not the same experience I know but no need to adjust for multiple non existent outreach guests' focus requirements .  

Jim 

[Marvin Jenkins]

Just now, saac said:

Hang a tag from your focuser with the message "virtual outreach guests please refrain from adjusting my focus".

Of  course you could overcome all of this by putting a camera on the scope and displaying the image to guests on either a laptop or phone screen.  Not the same experience I know but no need to adjust for multiple non existent outreach guests' focus requirements .  

Jim 

A statement of utter genius. I have no way of thanking you.

[Marvin Jenkins]

2 minutes ago, Marvin Jenkins said:

A statement of utter genius. I have no way of thanking you.

MNOEG is now my non existant friend.

Marv

[Gfamily]

I may have mentioned at one point that our opticians were doing their "two for one" deal, so - as well as the everyday varifocal pair, I got a single vision pair for astronomical use, and they live with the scope box. 

Used them occasionally, but the next year, after something of a 9 month gap (and after a revision of my prescription) I tried them again.  No problems with them at the eyepiece, but when I then looked at theit was a different matter                       

[Marvin Jenkins]

1 minute ago, Gfamily said:

I may have mentioned at one point that our opticians were doing their "two for one" deal, so - as well as the everyday varifocal pair, I got a single vision pair for astronomical use, and they live with the scope box. 

Used them occasionally, but the next year, after something of a 9 month gap (and after a revision of my prescription) I tried them again.  No problems with them at the eyepiece, but when I then looked at theit was a different matter                       

Twofers always seem great at the time.

[Marvin Jenkins]

2 minutes ago, Marvin Jenkins said:

Twofers always seem great at the time.

How is your outreach doing? I remember you were doing more than most to promote our shared interest?

[DaveS]

1 hour ago, Xilman said:

Yup.  The outside edge of each lens is markedly thicker than the inside edge.

I too have considerable muscular imbalance needing quite strong prism. In fact my latest set of lenses could only be provided using the top end high index Zeiss lenses, RI 1.74. They would have cost me £860 if I hadn't already paid for new lenses at £715, the opticians admitted that it was their error which is why I got them "cheap".

[Gfamily]

37 minutes ago, Marvin Jenkins said:

How is your outreach doing? I remember you were doing more than most to promote our shared interest?

Who is this for? If me, read on... 

We had a good couple of school visits back in January, both very fortunate to have mostly clear skies for wow-ing the pupils and their parents. 

An interesting one coming up - a local crystals/reiki/woo and 'healing' shop is running a 'forest solstice retreat' and got in touch via our Club website to ask if someone could "come along with some telescopes for star-watching under the sky". 

I said we'd be happy to come along, but with it being the solstice weekend it wouldn't get dark at all - and with it being full moon weekend, it would be even less dark, but I would be happy to give a talk to the group. 
Back in January I had given a talk to our Astro Soc on the Solstice, the Lunar Standstill* and some neolithic sites that relate to them, so I'll give them a somewhat simplified version of that talk. 

It'll be fun at least. 

* I'd not heard of the Lunar Standstill until last September, when I heard a podcast on the neolithic alignments at Callanish on the Isle of Lewis, and how it seems to be aligned to the Major Lunar Standstill - the next one being next year. Ultimately it means that despite it being Full Moon when we're giving the talk, it'll be slo low that it won't clear the low hill to the south of the site we're giving the talk. 

Also likely to be doing some outreach when we're out staying near Astrofarm France in August or September. 

 

Edited June 4 by Gfamily