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Is a scope in focus for everyone, even with glasses?

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#1 deanbrown3d

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Posted 18 March 2019 - 09:26 AM

Is it correct that a telescope is in focus at one 'best' position for all users, and that different users would wear their glasses if necessary, or do people need to focus the scope for their own eyesight? It's just that I went to a star party recently and it looked like the focus was out (for me), but I was not 'allowed' to touch the scope. But the person controlling the scope was convinced it was in focus. (I'm trying to understand star party etiquette if I go to another one!)



#2 RyanSem

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Posted 18 March 2019 - 09:30 AM

I've never heard of another scope owner not letting you adjust the focus. Everyone's eyes are different. When I go to a dark site with some older friends I typically have to roll back the focus just a bit (on one of their scopes I know exactly where his eyesight is in focus vs. mine). Even when I'm viewing with younger individuals they'll have to make the focus fit their own eye. 

 

I'd argue there is definitely not one "best" position for all eyes. Getting a perfect focus requires some serious fine tuning, and what's sharp for one observer might be blurry for another. 


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#3 konrad

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Posted 18 March 2019 - 09:31 AM

Everyone needs a slightly different focus but generally 2 people with perfect vision will not need to refocus


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#4 petert913

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Posted 18 March 2019 - 09:45 AM

The person who owned that scope was not very smart when it comes to how optics work......... 


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#5 deanbrown3d

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Posted 18 March 2019 - 09:46 AM

Ok thank you both! That is extremely useful information for me smile.gif



#6 msl615

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Posted 18 March 2019 - 09:46 AM

 I wear glasses to see all the time ( near sighted) .  If I use my glasses at the eyepiece, the focus is at point A. If I take them off, then I can see only blurs in the eyepiece, and have to focus to point B. If the scope was "always in focus", how would that explain what I see each time I use my scopes?

 

Your host was not correct..that is why a scope has a focuser that can correct for far ssighted and near sighted eyes.  I suspect the real reason was that the host did not want people touching his scope. 

 

Mike


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#7 Alex McConahay

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Posted 18 March 2019 - 10:01 AM

I do lots of outreach. I wear reader glasses at 2.0. I put them on before focusing at an outreach to make my vision "normal." 

 

When I am observing alone, I do not use the glasses to focus. 

 

I allow others to adjust focus to their preference. But after they focus, I refocus using my glasses back to normal. 

 

If you have old eyes, and just use readers, there is no reason to use your glasses to focus. Just focus as you like. 

 

If you are focusing for others (and use readers) use the readers as you focus to make your focus proper for "normal" eyes. (Realizing that not everybody has normal eyes.) 

 

If you have astigmatism or other eye problems and need corrective lenses beyond simple readers, use your glasses to observe.

 

If, however your question is about star party etiquette, remember that if the scope owner says not to adjust, you do not adjust. He or she is wrong about the "focus point is the same" but it is his or her scope. 

 

Alex


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#8 EricCCD

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Posted 18 March 2019 - 10:02 AM

I am nearsighted but view without my glasses, so of course my focus point is different from most anyone else.

 

My favorite personal story regarding this was showing off the Moon to a guest through a scope in our backyard. I focused for my eyes and instructed her how to play with the focuser. She looked through the eyepiece and fiddled slightly with the focuser but pretty much just gave a polite "that's nice". I felt something was off, so I refocused the scope, this time with my glasses on, and had her take another look.

 

"OH MY GOD!"

 

Precious flowerred.gif

 

My least favorite story regarding this was at a public star party. Someone had his Questar aimed at some daytime targets. I took my glasses off, looked through the eyepiece and reached for the focuser. The fellow practically tore my head off as he yelled me away from touching his scope and demanded I keep my glasses on. Not pleasant (and that's being polite).

 

Eric


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#9 lee14

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Posted 18 March 2019 - 10:06 AM

If someone is that disinclined to allow a viewer at a star party to refocus their telescope for themselves, they ought to consider not bringing it to such an event. When I did outreach, which included lots of children and first timer viewers, I always asked how the image appeared (i.e. pinpoint stars?) and explained how to refocus. Most people will need to tweak the focus a bit.

 

Lee


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#10 Ken Sturrock

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Posted 18 March 2019 - 10:28 AM

As others said, there is no perfect focus for everyone.

 

The behavior that you saw at the star party is, unfortunately, not unusual. I do understand the attitude because I've seen members of the public do horrific things to telescopes at outreach events, but it's just part of the game. Don't bring out your precious heirloom. Another issue is that, if you've got a long line of people, allowing each one to adjust focus takes time. Again, though, it's just part of the game.

 

I volunteer with my club at a local historic observatory. While many of our telescope operators don't actively encourage the viewer to re-focus the instrument, I don't know of any of us who discourage it.


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#11 csrlice12

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Posted 18 March 2019 - 10:37 AM

Been to a few of those Ken.  I pretty much tell the person to use the focuser knobs...otherwise, what's the point of outreach?


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#12 Mike G.

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Posted 18 March 2019 - 10:39 AM

at outreach the first thing I show people is where to look through (EP pupil), then I show them the focus knob and make sure they can find it with their eye at the EP - "put your eye here and your hand here.  turn the knob back and forth until it is clear and sharply defined".

 

I consider anything less as a disservice to those who traveled and made the effort to look through a telescope.


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#13 WarmWeatherGuy

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Posted 18 March 2019 - 10:49 AM

Being old I have presbyopia which means I have a fixed focal point. My eyeglass prescription is -1.0 diopter which means I focus at one meter. -2.0 would focus at 1/2 meter,  -3.0 would focus at 1/3 meter etc.. When I focus the scope then everyone who can see things clearly at one meter should be able to see it in focus. The only time people need to turn the focus knob is when they can't see things clearly at one meter. This often happens when they take off their glasses.

 

People often ask if they should use their glasses or not. I tell them it is better without glasses as long as they don't have much astigmatism and I show them the focus knob.



#14 TOMDEY

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Posted 18 March 2019 - 10:58 AM

at outreach the first thing I show people is where to look through (EP pupil), then I show them the focus knob and make sure they can find it with their eye at the EP - "put your eye here and your hand here.  turn the knob back and forth until it is clear and sharply defined".

 

I consider anything less as a disservice to those who traveled and made the effort to look through a telescope.

Ditto that! I've noticed that most walk-ups, many having never even looked thru an astronomical telescope, are completely unaware that you focus it (to your own preference)... and are terrified of touching anything. Even to the point of having to be encouraged to ge closer, closer, closer to the eyepiece! (Some start feet or inches back and are amazingly reluctant to even "address" the telescope... possibly fearing that they will either break something or burn their eye out) Some don't even know that you use one eye, not two.

 

So, absolute opposite of what the ~expert~ was saying... encourage everyone to get their eye comfortably placed and rotate this knob, right here, so the stars look comfortable and sharp.

 

And agree, if you are entertaining guests, and don't want anyone even touching your precious telescope... just go to the event, but leave your scope at home, or in the trunk!    Tom 


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#15 TOMDEY

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Posted 18 March 2019 - 11:05 AM

PS: There are, of course, the opposite kinda walk-ups: Kids and adults who immediately grab the telescope and start swinging it around like a playground ride. I've found palm prints on my 36-inch telescope PM (at NEAF, last year) and one guy yanked one of the truss poles right out of its mooring! No kidding! Fortunately, we had a ~surrogate PM~ in the scope, anticipating that sorta abuse, and the scope is now fully-operational in my private observatory dome.

 

When guests come over... that's the nice 100mm binos, out on the deck behind the house. Only experienced observers get to share in use of the 36-incher!    Tom


Edited by TOMDEY, 18 March 2019 - 11:06 AM.

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#16 Alex McConahay

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Posted 18 March 2019 - 11:30 AM

Oh, by the way, I know this is not about imaging, but with an imager, there is one and only one focal point. Of course, where the focuser is positioned to get to that point may be different depending on how the camera is mounted. But, unlike the eyeball, which can adjust its own focus, the sensor in a camera cannot change. 

 

Alex



#17 sg6

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Posted 18 March 2019 - 12:13 PM

Everyone's eye's will be slightly different, maybe not by a lot. Even if you have glasses you will find they do not deliver the same a someone who had perfect sight. They add a component in to the lens to make them more "general". My last prescription they added in a bit too much.

 

What often happens is they determine infinity. Since most things are not at infinity they add in (or take out I suppose) an amount to place your far point at around 80-100 feet away. That way you can see TV OK and see distance OK.

 

So even with glasses I would expect that you would have to tweek a focuser. All the tweeking does is to set the image at your rest point, that may or may not be infinity. It is where your eyes will naturally observe an object at when they are nice and relaxed and doing close to nothing. Basicall at rest, and comfortable.

 

Another factor is that everyone just wants to find out if they can get that little extra out of the view by changing the focus, and often end up back at exactly where they started out.

 

Person at the star party just didn't want people playing with their equipment. After my last experience I can half understand it. Had for some reason 3 kids that wanted to feel/touch the front corrector of an SCT. No idea why and has not occurred other times, so why this one night I have no idea.

 

Had similar experience myself as you did, person convinced that no one knew what a scope was and so even less on how to use a scope.



#18 barbarosa

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Posted 18 March 2019 - 12:19 PM

When I read the bit about not refocusing I had to stop and think about the why, so I looked it up, and yes those of us with less than perfect eyes need in effect to defocus the scope to get an image that our imperfect eyes can bring to focus.

 

I'm not a star party guy, but I've been to a couple just to see different scopes in action. The presenters  bring out scopes and EPs that vary greatly in value and some of them do ask you not to touch anything. That is fine with me and I do not see why it wouldn't be fine with others. Not every child is well behaved or every adult for that matter, nor do they all have a delicate touch. What normally works is to politely ask for permission or assistance. The grouchiest presenter I encountered was  a nice white haired guy making his first appearance with his brand new Celestron 8 SE. He had a little talk prepared and he was nervous. When someone walked up and picked up the hand control, his reaction was a bit sharp. So what?

 

So let thank rather than censor those who offer up their scopes of whatever value if some of them are fussy or over cautious, or grouchy or a bit abrupt. It never hurts to ask permission first and can start a good conversation. We are guests at these affairs and guests have obligations too.



#19 stargazer193857

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Posted 18 March 2019 - 07:33 PM

Most young people can focus with their eyes, making the scope work for most people.

However, someone with glasses might take them off for the scope to adjust, and leave it there. Then everyone else will see it blurry.

#20 Jon Isaacs

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Posted 18 March 2019 - 07:59 PM

Eyepieces are designed so that the field stop is in sharp focus for someone whose natural gaze rests at infinity. For someone wearing distance glasses,  this would also be their natural gaze and I consider this the standard focus. Someone who is near sighted would need to refocus. 

 

My own 71 year old fixed focus,  presbyotic eyes somehow managed to zero their focus in on infinity and so when I am at an outreach event,  I zero the focus between observers as a starting point.  I provide a short couple of sentences on how to focus and have the individual tell me what they're seeing and if I think they are not in reasonable focus,  I will try to help them. 

 

I agree that many are intimidated by a telescope . I tell them there's no way they can break the telescope and if the bang it or move it , I can find and center the object in a few seconds. 

 

One of the senior members needs to take this fellow aside and explain these basics. 

 

Jon


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#21 WarmWeatherGuy

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Posted 18 March 2019 - 08:25 PM

I have a goto scope. If someone moves it I have to shut it off and realign it. That means nobody gets to look through the telescope for several minutes.



#22 Ken Sturrock

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Posted 18 March 2019 - 09:10 PM

Yeah. I've never had anyone throw off alignment by normal handling & focusing, but I have had a few tripod kicks in the dark that did the trick. Some nights you just can't win. I pretty much stick to low tech for the masses anymore.

 

My "favorite" was doing a solar gig at a public event where the kids came to look at the sun right after getting their faces painted. Fortunately, I could rinse the Kellner off in the bathroom sink without feeling too guilty.

 

This post sounds like an equipment malfunction, but it is still terrible.



#23 nimitz69

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Posted 18 March 2019 - 09:48 PM

Absolutely nothing wrong with someone asking folks not to touch their scope during outreach.  However, not understanding the basics of how optics work is not helpful to newcomers or worse, if they are just making up a story so no one touché their stuff is even worse.    



#24 Alex McConahay

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Posted 18 March 2019 - 10:21 PM

>>>>. If someone moves it I have to shut it off and realign it.

 

You know, if all they did was move it, and the tripod stayed in the same place, you might just use the handpaddle to move (with the directional buttons, not the goto function) back to a recognizable target (like a bright star), center it (with the buttons, not goto), and then do a "synch." If your mount is capable of that, you do not need to turn off and realign. Yes, it still wastes time, but not all that much. 

 

Alex


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#25 gnowellsct

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Posted 28 March 2019 - 09:05 PM

If I have 50 people lined up at my scope I focus it with my glasses on and let them look. If I have 5 people I'll teach them how to focus.


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