Focus to infinity problems on a D70s

[Just_John]

Heya guys and gals,

I apologize in advance if this isn't where i should have started this topic, but i couldn't find a more suitable one. I searched the forum (and the entire Internet, as a matter of fact), but i couldn't find a similar topic.

So, i seem to have a problem with my D70s: as the distance to the subject increases, the camera doesn't seem to be able to focus correctly.. Noticed this when trying to shoot a few hundred crows that keep hovering daily around our city: i've set the focus to manual, and to infinity on my 18-70 (actually, past the infinity marker, to where the focusing ring stopped), and took some shots. They were all incredibly out of focus, so i later tried to shoot some buildings from my apartment at the 10th floor (those i was aiming at were at least 2km away): same result, with both the 18-70 and the 75-150 at both f4.5/f3.5 and f8 (only tested with the tele end, 70mm and 150mm respectively).

So i'm pretty sure the problem is within the camera. I posed a question at the local Nikon distributor, but all they said was "bring the camera". I would, except i don't know how much it'll cost, and i'm not ready to pay maybe more than a SH D70s would cost for something that i am unsure of.

Have any of you heard of this, or even encountered this phenomenon? If so, would you happen to know of a "cure"?

Much obliged,
John

[Sterling]

Sorry, I can't help with your focus issue. But I'd like to thank you for this sentence:

"Noticed this when trying to shoot a few hundred crows that keep hovering daily around our city:"

It made my morning.

[dcclark]

Have you tried letting the camera autofocus on a distant subject, taking a photo, and then taking a photo with your lenses manually focused at infinity? Are the results same, or is the autofocused one correctly in focus?

Those lenses you mentioned (I think both of them) don't have a "hard" infinity stop on the focus ring -- which is why you could go past infinity. That's because the infinity focus point actually moves around as the glass in the lens warms/cools. So, often you really can't tell where "infinity" is unless you are very good at manual focus, or let the camera do it for you.

[Almond.Butterscotch]

it sounds like to me that you're trying to get stuff in the far distance in focus by focussing on infinity.

That's not what's going on, is it?

[Just_John]

Sorry for the late reply, but my work schedule is not exactly forgiving..

Originally Posted by Sterling

It made my morning.

Glad to be of service! If i can get the darn thing to focus, i'll even show them to you!

Originally Posted by dcclark

Have you tried letting the camera autofocus on a distant subject, taking a photo, and then taking a photo with your lenses manually focused at infinity? Are the results same, or is the autofocused one correctly in focus?

Those lenses you mentioned (I think both of them) don't have a "hard" infinity stop on the focus ring -- which is why you could go past infinity. That's because the infinity focus point actually moves around as the glass in the lens warms/cools. So, often you really can't tell where "infinity" is unless you are very good at manual focus, or let the camera do it for you.

I'm quite new, very inexperienced in photography, so i'm not exactly sure what to tell you. I would appreciate it you could tell me exactly what tests i should do to make sure there is indeed a problem, and it's not some sort of human error! Yes, both lenses appear to have a "dead zone", meaning that the dial pushes the infinity sign past the marker; could this be the problem? the lens can focus beyond infinity?? Isn't that like.. dividing by zero, somehow?

I'll try to get some more shots tomorrow, while setting the marker directly at the infinity mark, and also some shots using autofocus, and hopefully i'll have a more detailed report about the results..

Originally Posted by Almond.Butterscotch

it sounds like to me that you're trying to get stuff in the far distance in focus by focussing on infinity.
That's not what's going on, is it?

As i said, i'm only a beginner, and quite a realist, so i thought the infinity marker kind of started where it was actually drawn, and still going until the focusing ring actually stops. So i think it's safe to say that i was trying to focus the buildings ~2km away by setting the manual focus to infinity (or beyond it, regarding the enlightenment brought by dcclark's response.
Since i sense in your reply that what i've done is very wrong, could you please tell me how to manually focus on those buildings? I took just a guess, and went for it, my mediocre eyesight (with the glasses on, even) do not provide me with enough certainty as to whether i would focus correctly that far (the rather dim viewfinder isn't of much help, either, unless there are good lighting conditions).

Thank you all again, hopefully it was just human error, and i won't have to take the camera to the doc!

[dcclark]

As I mentioned, you can go "past" infinity, because "where" infinity really is will change, as the lens elements heat and cool.

Here's an example: let's say you start out on a cool day, and focus at "infinity". Then, as the day warms up, some of the glass in the lens will expand slightly. This changes the optical properties of the glass, causing it to focus slightly differently. Now, your level of focus has changed slightly -- you're focused a little closer than you were originally. So, to get back to "infinity", you need to move the focus ring again. That's why you can't just peg it at infinity and hope it'll work all the time.

I highly recommend just using autofocus. Point the focus point you've chosen at what you want to focus on, let it focus, and call it good.

If you really want to run tests, do the following:

1. Set the lens to autofocus. Focus on a distant, stationery object (like a building). Take a photo.
2. Set the lens to manual focus. Focus at infinity, pointing the camera at the same object. Take a photo.

Compare the results and see if one is in focus and the other isn't. Then let us know what the results were.

[Almond.Butterscotch]

Well, for glasses wearers (like myself), one of the nifty features often overlooked on the camera is the diopter- look for a sliding switch on the viewfinder that (i'm not sure how it physically does what it does) moves the viewfinder back and forward- it'll help you see everything in your viewfinder with the added separation of your glasses.

as for focussing on buildings 2000m away, there's really no "correct" amount to turn the focus ring by- as dcclark said, even if it were marked, it'd change slightly, and at distances that far, fractions of a millimeter make a great deal of difference- it mostly comes down to trial and error, i guess.

[Just_John]

Originally Posted by dcclark

As I mentioned, you can go "past" infinity, because "where" infinity really is will change, as the lens elements heat and cool.

I highly recommend just using autofocus. Point the focus point you've chosen at what you want to focus on, let it focus, and call it good.

Well, today i was finally able to make the tests (and to examine more closely the lenses), and i saw why i've been so confused: the 18-70 indeed does go 3-5mm beyond the infinity mark, but the 75-150 and the 50 hit the infinity at max (the focusing ring just stops there). The pictures i took were much sharper than those seen last week, and it's also true that the 18-70, taken beyond the infinity mark loses focus (the sharp picture was still about 1mm beyond the infinity mark). So this difference between the lenses must've been confusing enough for an amateur like me to believe his camera's got problems..

As for the autofocus function: gladly, but the 75-150E (which i got because it's price was more than affordable [went on the idea of "not much to lose, maybe a lot to win" deal]) is an old Ai or Ai-S lens, which does not focus automatically on my D70s - the main reason why i wanted to learn to focus manually in the first place.

Originally Posted by Almond.Butterscotch

Well, for glasses wearers (like myself), one of the nifty features often overlooked on the camera is the diopter- look for a sliding switch on the viewfinder that (i'm not sure how it physically does what it does) moves the viewfinder back and forward- it'll help you see everything in your viewfinder with the added separation of your glasses.

I'm aware for the diopter slider, and i tuned it to best fit my eyes (which means max minus reduction), but since it's been about a year from the last time i got my eyes checked, this setting only works when using the glasses, so it's kind of a let-down. Still, getting the proper glasses will mean i should be able to tune the diopter optimally (although i hate sticking the viewfinder's rubber cup on the glasses, i would rather this diopter had a wider range, so i wouldn't have to use my glasses at all).

Thank you all for your replies, it would seam it was all due to human error. I have learned the error of my ways, hopefully i'll still get a few good-ish shots of my 18-70 before switching to the Tamron 17-50.