Wearing glasses when focusing and viewing

[SkySurfer]

Hi all,

I think this maybe a stupid question but am going to ask anyway

A friend of mine want to buy a telescope, and wears glasses for reading only, not distance, and they asked me whether they would have to wear there glasses when focussing the scope or not, they are concerned that if they focus without, then they will be focusing to there eyes and will be out of focus to others that don't need the glasses,I have never even thought about it before and I could not answer the question as I don't need glasses, so,I thought I would ask here.

I would have thought that because what we look at is so far away and he needs glasses for reading only, that he would not need them, but am really not sure....

I am sorry if it is a stupid question, but too late now

:)

SS

[Stargazer33]

Hi, There are no stupid questions; only stupid answers! If your friend doesn't need glasses for distance vision then focusing without glasses will be the way to go. This doesn't mean that focus will be perfect for everyone else as all our eyes are different, but it should be close.

HTH.

[Feral Rabbit]

I wear varifocals and my personal choice is to remove them for focusing/viewing. I don't think it matters too much either way. I tend to wear glasses lanyard when I'm gazing as I am removing, putting them on all night.

[Ruud]

We tend to focus a telescope with the eye set for minimal accommodation, i.e. with the eye focused for infinity. Your friend can see infinity well without glasses, so he'll focus a telescope more or less the same as would a person who needs no glasses at all.

[daiwelly]

I wear glasses for both reading and distance But I don't wear them when using the telescope

[Charic]

I wear varifocal for driving and fishing. I remove them for astronomy using the telescope or binoculars. The Telrad reticules/ image works better with my glasses on?

You  may ask a question that is actually doing a favour or service to someone else who may be afraid to ask, so no question is too dumb, if you don't know,  just ask.

You'll soon find out if it was a dumb question, but no-one here will pass any insult......

[nightfisher]

I have reading specs, i dont wear them when viewing, but if im doing Luna imaging i wear them for getting focus on the camera

[SkySurfer]

Ok,

Thanks

So,when corpse wing or focusing through the telescope, no glasses, bit when viewing or focusing on a PC screen or live view of a camera, then glasses worn.

Does that sound about right

SS

[acey]

Spectacles correct for two things: focal length and aberration. Short or long sight means the eye's focal point is in front of or behind the retina: spectacles put the focal point on the retina, as would be the case for normal sight. If three people bring a telescope to focus - one short sighted, one long sighted, and one with perfect vision, all without spectacles - then they'll just choose different focuser positions. The adjustment is doing what spectacles do. But specs also correct for astigmatism, and a telescope doesn't, so in that case some aberration may be apparent if the user views without specs. I have astigmatism and I view without specs - the aberration doesn't bother me. I'm a deep-sky observer who mostly uses averted vision and high power - someone with different interests and standards might feel differently (though planetary views also look fine to me). Whatever aberration exists in the eye will mostly be seen at low power. Whether to wear spectacles for viewing is a matter of taste. The finder scope may also need to be focused to match the user's requirement, which is a simple task. In the case of someone who wears reading glasses because of age-related presbyopia, it should be fine to use the telescope without glasses - they'll just need to put them on to read their map.

[SkySurfer]

Ok,

Thanks

So,when corpse wing or focusing through the telescope, no glasses, bit when viewing or focusing on a PC screen or live view of a camera, then glasses worn.

Does that sound about right

SS

Corpse wing......should have said viewing, where does the autocorrect get the words from.....

Sorry for that

SS

[SkySurfer]

Spectacles correct for two things: focal length and aberration. Short or long sight means the eye's focal point is in front of or behind the retina: spectacles put the focal point on the retina, as would be the case for normal sight. If three people bring a telescope to focus - one short sighted, one long sighted, and one with perfect vision, all without spectacles - then they'll just choose different focuser positions. The adjustment is doing what spectacles do. But specs also correct for astigmatism, and a telescope doesn't, so in that case some aberration may be apparent if the user views without specs. I have astigmatism and I view without specs - the aberration doesn't bother me. I'm a deep-sky observer who mostly uses averted vision and high power - someone with different interests and standards might feel differently (though planetary views also look fine to me). Whatever aberration exists in the eye will mostly be seen at low power. Whether to wear spectacles for viewing is a matter of taste. The finder scope may also need to be focused to match the user's requirement, which is a simple task. In the case of someone who wears reading glasses because of age-related presbyopia, it should be fine to use the telescope without glasses - they'll just need to put them on to read their map.

So, if someone who need glasses for reading, focuses a telescope without them, then takes an image through that same focused telescope, will that picture be completely in focus for people who don't need glasses?? Or will it only seem focused for people who have to wear reading glasses? And be slightly out of focus for people with perfect vision...

Sorry for all the questions

SS

[Interested]

As the spectacles correct the vision, if I was taking a photograph then I would wear my glasses to focus. If I am just observing I do not wear glasses, but as others here have said, another observer would need to re-focus to suit their vision. When I am imaging I don't rely on my eyes for focus, I rely on software. I guess you should think of your eyes a part of the optical train. if you need glasses and focus without them, you would likely need to re-focus to take an image as you have changed the optical train.

[Charic]

The picture should look good whoever looks at it, as long as the observer believes it is correctly in focus,  unless the imager has a real bad eyesight problem.  If you can't focus without glasses, then the  final image could  probably be out of focus, for others who view the image. 

Try and get the person behind a telescope and try it for real. The telescope once collimated (optical alignment) and with a suitable eyepiece fitted, should be able to bring the image at the eyepiece into a perfect image. If not, that person will still need further eyesight correction, for their needs. The Camera itself is also fully capable of getting a good focus, but as were talking millions of miles of deep space,  just setting the camera to infinity is usually all that's required for focusing.

[chiltonstar]

I wear glasses for reading and for extended night driving (distance viewing). I've tried focussing with and without glasses on close double stars, and it really doesn't make any difference - the focus knob position is slightly different, but the view is much the same (slightly different scale perhaps - things seem slightly bigger).

IMO, if there is astigmatism, probably (but not necessarily) better with glasses on. A point to bear in mind is ease of using certain EPs. Some of mine require the eyeball to be practically cemented to the front element of the lens - not possible with glasses, so choose carefully and "try before you buy" (FLO).

Chris

[Dave In Vermont]

I have reading-glasses here. I take a 2.5X diopter pair. No need for them while at the scope. The focuser takes care of my needs just fine.

Clear & Focused Skies,

Dave

[Paul73]

I have to use glasses for finding the less bright constalations and for using the finder scope. However, at the eyepiece, I can focus to correct for my aging eyes. The constant putting on / removing of glasses is a real pain. The best solution is to have an observing pair which have the right arm removed.

My then 2 year old son came up with this marvellous design........ Clouds and silver linings etc.

Paul

[SkySurfer]

Hi,

Thanks for all the reply

I understand about viewing, my real issue is when focusing to take an image with a camera, if my friend focuses his scope by looking throught the back viewfinder on his DSLR camera at a bright star without his glasses, then takes a picture of that star, will that picture be slightly out of focus when viewed by someone who,has perfect vision, because the scope was focused to suit someone with bad near eyesight.

Does that make sense....it does to me, but I wrote it...lol

SS

[Ruud]

The camera viewfinder has dioptre adjustment. If it is set right (for me that would be at zero), one could try using it for manual focus, irrespective of the lens.

But finding the focus on a manual lens is better done with the camera's live view screen - at its highest magnification.

[Astro Imp]

A very interesting thread, thanks for asking the question.

I wear varifocals and messed about for ages until I found a routine that works for me.

Using the Telrad I find I need to remove my glasses otherwise I see a double star image when viewing at steep angles. BTW it took me ages to work this out, as I was trying with my glasses on and had many nights of frustration.

When using the RACI I wear my glasses as I need to look at the chart and then back to the finder.

At the EP I prefer not to wear glasses although I do not use EPs with short eye relief. Most of my viewing is done with Celestron X-CEL LX EPs and I find it more comfortable with the eye guards raised and no glasses.

I shall be following the remainder of this thread with interest.

[vlebo]

When viewing wearing varifocals should you not be using the lower part of your spec lenses as that part is for near distance. Surely the object you are looking at is actually only as far away from your eye as the secondary is from the eyepiece in a newt ( I am probably wrong ! ).

[RichM63]

Hi,

Thanks for all the reply

I understand about viewing, my real issue is when focusing to take an image with a camera, if my friend focuses his scope by looking throught the back viewfinder on his DSLR camera at a bright star without his glasses, then takes a picture of that star, will that picture be slightly out of focus when viewed by someone who,has perfect vision, because the scope was focused to suit someone with bad near eyesight.

Does that make sense....it does to me, but I wrote it...lol

SS

No, a focused image is a focused image, glasses or contacts have allowed the person to correct their vision malfunction in order to acheive a focused image.

Think about the family all sitting around the TV, everyone can watch the program irrespective of eye defects, providing that they all have the appropriate vision correction eye wear.

You can't adjust focusing on a TV Set. Thus individual eye correction makes it possible for everyone to view essentially the same  focused image.

[101nut]

I seem to be the odd one out here in that I've adapted to generally viewing with my verifocals on. I hate the on-off-on-off thing and if they aren't kept warm they instantly fog up on me ... I'd prefer not to use them but it's the lesser of the evils in my opinion. I can see a lovely image through the eyepiece but can't read the star map, see the sky, use the finder or basically see anything that isn't in the eyepiece! I have to say that you need to match eyepieces and specs though - my specs fit very close to my eyebrows which minimises the extra eye relief required and maximises the visible field.

AndyG

[Scooot]

No, a focused image is a focused image, glasses or contacts have allowed the person to correct their vision malfunction in order to acheive a focused image.

Think about the family all sitting around the TV, everyone can watch the program irrespective of eye defects, providing that they all have the appropriate vision correction eye wear.

You can't adjust focusing on a TV Set. Thus individual eye correction makes it possible for everyone to view essentially the same  focused image.

I think you might have misread his question there. He asked if someone focused without their glasses.

If I focused my scope without my glasses it wouldn't be in focus for anyone else.

[Astro Imp]

When viewing wearing varifocals should you not be using the lower part of your spec lenses as that part is for near distance. Surely the object you are looking at is actually only as far away from your eye as the secondary is from the eyepiece in a newt ( I am probably wrong ! ).

I would suggest that you have never used varifocals, as your eye moves around the eyepiece you don't only look through the lower part of the lens. I guess to a large extent we all end up doing that which we find best.

[Scooot]

So, if someone who need glasses for reading, focuses a telescope without them, then takes an image through that same focused telescope, will that picture be completely in focus for people who don't need glasses?? Or will it only seem focused for people who have to wear reading glasses? And be slightly out of focus for people with perfect vision...

Sorry for all the questions

SS

If you attach a DSLR to a scope to take an image you remove the lens so you don't use the auto focus of the camera. You use the focuser knob of the scope. So if I focused the scope without my glasses the focuser and therefore the camera would be further in or out than it would be for someone who focused it with perfect vision. My image would therefore be out of focus when processed. If I wore my glasses to focus it would be in focus once processed.