Weird optics question

[iebirdie]

Hi,
I use spectacles for driving and watching tv (a small but noticeable correction).
When I use a scope or bins (with a bit of dioptre adjustment) I get a clear image over long distances... How can this make sense ? Is there a risk of eye strain in doing this, or should I be using bins/scope with my spectacles on (and LER lenses). I don't feel any strain so presumably I can keep doing what I am doing (using optics without my spectacles on) and there is no risk of decreasing my eyesight. So, what's the big deal about long eye relief and ads which say that Binocular X or Scope eyepiece Y has LER and is designed for spectacles users ??

thanks for info
cheers
Niall

[Michael Frankis]

Hi Niall,

Perfectly OK. By adjusting the focus to what suits you, the lenses in the scope are acting as both specs and magnifier. It just means that if anyone else has a look through your scope, they'll have to change the focus to suit their eye. Also if you take up digiscoping, and use the same focus setting, all your pics will come out blurred.

The only reasons that a lot of people like to keep their specs on while birding, are that (a) their eyesight may be so poor they are unable to see what they're trying to aim their optics at, and (b) taking specs off wastes time and you might miss a bird while putting them away (or get the specs lost or damaged in the haste of putting them away quickly)

Michael

[robinm]

I agree with everything Michael says. As a specs wearer myself I always keep them on and use my bins/scope with them. I am quite short sighted and couldn't comtemplate finding a bird with glasses on and then taking them off to use bins etc.

As far as dioptre goes it depends on the difference between your 2 eyes. If there is little or no difference then you will not need to use it.

[iebirdie]

Thanks for the replies, and for explaining that the optics also work as a spectacles.... seems obvious now !
It is encouraging to know that doing what comes naturally (i.e. viewing w/out specs) is ok and will not cause further eyesight damage over time.
best rgds
Niall

[mcdowella]

Two other reasons
1) You are so short sighted that you can't adjust the binoculars to focus at infinity without glasses.
2) You have astigmatism, in which case your eyes can't focus horizontal and vertical lines at the same time without barrel-shaped corrective lenses.

From memory, I think (1) applies to me (I have to be REALLY careful to always remember where I put my glasses, because there is no way I will find them again by sight). (2) certainly does.
If you get a decent image without eyestrain I wouldn't worry.

[marcus]

Michael and A.G. are 100% correct.

[Dave G]

I'm not so sure Marcus, I can focus ok with bins and scopes but try to read anything after doing this for 30 odd minutes I just can't focus on the text, and can feel the eyes straining. Don't have this problem with glasses on as everything is in focus and you don't make the optics mucky from eyelashes either ;)

[Michael Frankis]

Hi Dave,

That's because you let your eyes relax so much (by letting the optics do the work), that they feel the strain of having to start work again! I'm surprised you find it takes half an hour to re-focus on close-up stuff though.

Michael

[Dave G]

Sorry Michael wrong way around, I meant using scope/bins for 30 mins. The eyes then take 2/3 mins to re-focus but you are straining them to get that close up focus back. I do think you get a bit more magnification out the optics with the glasses on as well.
Hey, I have got to try to convince myself as I have just started wearing them, hit that dreaded 40 something and the eyes have started giving out :( ....along with the knees etc etc etc

[Geraldine]

Hi Dave,
I also find that my eyes take a few minutes to adjust when I look up from the scope, have to be careful not to stand up and walk immediately! I am at the stage where I need bifocal glasses, but am still taking glasses off to read labels in shops, have reading glasses but can manage without them for short spells. Also have a prism to control vertigo. I'll try to get used to keeping my glasses on for the scope, especially as we are saving for a digiscope, and I hadn't worked out the obvious bit about focus.

[Dave G]

Geraldine,
I found when I first used the glasses a couple of months ago, I turned my head and jumped when the walls apeared to leap out at me, well I think it was the glasses.....:hippy:
Just make sure you have a rubber end to the eye piece as it can play hell with polycarb glasses (scratching lenses).

[KCFoggin]

You know, I just had my yearly eye exam and for the 2nd year in a row, my eyes have improved. I can't help but wonder if it is due to focusing them on distant objects so often now when I am out looking for birds. Sort of exercising them?

[lightshedder]

I wear glasses while birding, but it is because I have astigmatism, a flaw which the focus of the optics can not compensate for. I would suspect that is the reason most of us who do leave our glasses on.

[AlanFrench]

I wear glasses while birding, but it is because I have astigmatism, a flaw which the focus of the optics can not compensate for. I would suspect that is the reason most of us who do leave our glasses on.

I also have astigmatism, and always wear my glasses when using binoculars or a low power telescope. I am quite glad the binocular makers are paying more attention to eye relief these days, and it is much easier to get eye glasses friendly bincoulars!

Clear skies, Alan

[Atomic Chicken]

Greetings!

Just one other thought on all this...

If you use glasses when viewing through binoculars, you have 2 extra non-coated glass-air interfaces that the light must pass through. This will cause a noticable decrease in brightness under low-light conditions, and can also contribute to increased chromatic aberrations. If you can adjust your optics and diopter to view comfortably without glasses, assuming you can see what you are pointing the binoculars at beforehand, you will get a better view overall.

Best wishes,
Bawko

[Pileatus]

Greetings!

Just one other thought on all this...

If you use glasses when viewing through binoculars, you have 2 extra non-coated glass-air interfaces that the light must pass through. This will cause a noticable decrease in brightness under low-light conditions, and can also contribute to increased chromatic aberrations. If you can adjust your optics and diopter to view comfortably without glasses, assuming you can see what you are pointing the binoculars at beforehand, you will get a better view overall.

Best wishes,
Bawko

Bawko,

FYI...eyeglasses can be AR coated. The effect of AR coating on a pair of eyeglasses is nothing short of amazing. It reduces the constant need for sunglasses in average daylight, makes driving at night more enjoyable, and results in a sharper, cleaner, higher contrast image. If you bird a lot with eyeglasses, I strongly urge you to get AR coated lenses. There's no heavy debate on the value of AR coatings! They work wonders.

John

[Bill Atwood]

I totally agree with John on AR coating for eyeglasses. Watch out for DEET or other aerosols though.