Focusing questions

[david_pidcock]

<p>This came up recently with 35MM film camera but I think it applies to medium format also, both single lens reflex.<br>

I need 200 + readers to read a book plus distance vision is not so hot either.<br>

If I use my naked eye, doesn't the lens focus the image I see in the finder, and it should come out focused when printed? Or do I need to use my readers to see the focused image as I need them to read?<br>

Kind of confused. I thought the camera / lens would take over and my poor vision otherwise would not affect the final image. In some of the images I just made, I used the distance scale on the lens barrel but not sure what that did.<br>

Thanks for your thoughts,<br>

David</p>

[Matthew Currie]

<p>As far as I have ever known....</p>

<p>Remember there used to be many viewfinder cameras with no focus coupling to the rangefinder. The only way to focus was by using the distance scale on the lens. </p>

<p>If the distance scale is accurate and you use it right, or if the image is focused in and SLR viewfinder (not broken or maladjusted) the image is focused as far as the camera is concerned, but in the latter case, to be sure it's so you must be able to focus your eyes on the focusing screen. That's why there are viewfinder diopters and high eyepoint finders for glasses wearers. </p>

<p>It's much easier on old fashioned film SLR's with a circle and or other focusing aids, because if you can see those things clearly you know whether or not your eyes are seeing the finder well. </p>

<p> </p>

[christopher_ward2]

<p>David,<br>

Most of the better cameras offer diopters that screw into the eyepiece. I use +2 reader glasses and my old Nikon F2 slr finder is at +1, so I added a +1 diopter and the finder information is now sharp. I still need my glasses to see the controls on the outside.<br>

Chris</p>

[SCL]

<p>Hi David - Most SLR cameras, 35mm or Medium format (such as Hasselblad, Bronica, etc), have a focusing screen which when you look thru the viewfinder show the image the lens is focused on, but the optics which allow YOU to see the focus screen itself, where the image is formed, are set up for near vision, generally as if you were focusing on an object in the 12-36 inch range. So, not only does your camera's lens need to focus properly on the screen, but so do your eyes, which is why manufacturers produce either a variable diopter in the camera viewfinder itself, or you may need to add one to the eyepiece (so you can see the screen itself clearly, with your glasses (if you wear them during photography), or without (if that is your normal shooting technique). It is a little annoying, until you get it all adjusted, but once you get it nailed down...everything is great!. As the previous poster mentioned, if your camera has a well adjusted focusing scale, AND you use a sufficiently stopped down aperture, you can also scale focus....my first two cameras worked that way, and I just bought one a couple of weeks ago which works that way. Perhaps if you mention the camera/s you are working with, especially if you don't have an instruction manual, we can provide additional guidance.</p>

[david_pidcock]

<p>Thanks, Stephen. The medium format is the RB 67 Pro S. The 35 MM is Nikon F body.<br>

David</p>

[SCL]

<p>David - here is the site for a manual for your cameras (I use it as a lookup, and yes I did pay him courtesy $3 when I downloaded a manual - the guy has done a great service by providing thousands of manuals online for free). Nikon routinely has a slightly negative diopter in many of their camera viewfinders (see details) http://support.nikonusa.com/app/answers/detail/a_id/639/~/viewfinder-diopter-adjustment . I found I needed to fiddle around a little with some earlier cameras which didn't have built in diopter correction knobs, and ended up with a "0" lens which did the trick so I could focus with my eyeglasses on. You may need to read the details in the RB67 Pro S manual for the specifics there. As an aside, over the years I've collected a couple of used diopter eyepieces in odd prescriptions (like 1/2 diopters) which sort of generically fit a number of cameras, so that as my eyes shift a little here and there, I can substitute the necessary ones.</p>

[Matthew Currie]

<p>If the Nikon F is a Photomic or has the later round eyepiece, the diopters are not hard to find. I use about a 2 1/2 power reading glass, but a +1 diopter is quite sufficient. Even though you'd expect the diopter amount to be similar to your reading glass, it's not. I tried +3 and +2, but could not focus on the screen at all with them.</p>

[david_pidcock]

<p>Thanks much Stephen. I'll look and figure it out.<br>

David</p>

[david_pidcock]

<p>Thanks Matthew.</p>

[bebu_lamar]

<p>When you need 2.00 glasses for reading and you typically read at ta distance of 12-18". The focusing screen appears to be about 1 meter or 39 inch from your eye. So you need a lens that would help you see well at that distance. That would mean a +1 diopter lens. However, Nikon call this lens as the 0 diopter lens because the camera without any diopter attached is considered to be -1.</p>

[david_pidcock]

<p>Thanks, BeBu.</p>

[Alan Marcus]

<p>Hi David,<br>

The camera lens focuses an image of the outside world onto the film, which is stretched flat like a miniature movie screen. The viewfinder system of the SLR (Single Lens Reflex) uses a mirror, a ground glass screen and a pentaprism (five sided) and eyepiece lens. The mirror turns (reflex) the image forming rays so they can play on a ground glass focusing screen instead of the film. This image is upside down and inverted. The pentaprism reverses and normalizes the image. The SLR design affords eyelevel viewing. This places the view screen only inches from the observer's eye. To allow the observer to see and focus upon the image on the screen, a powerful magnifier eyepiece is required. The eyepiece lens causes the exiting rays to leave the camera viewfinder collimated (parallel). This is called an afocal system.</p>

<p>The camera operator, peering into the viewfinder is now able to focus sharply on the close at hand screen. The parallelism of the rays fools the eye into believing the view is coming from an infinity position (as far as the eye can see). This allows the eye lens to remain relaxed avoiding eyestrain. Those with severe vision problems will likely be unable to focus on the ground glass screen image. As a counter measure, most modern viewfinders allow limited adjustments that correct for an observer with minor eye defects (near or far sited). Unfortunately, this adjustment is far too limited to help if the eyesight defect is severe. Perhaps as a countermeasure, an optician can fabricate a supplemental correction lens and mount it at the rear of the eyepiece.</p>

<p>Some late film cameras with optical viewfinders (no ground glass) had a viewfinder interconnected to the camera lens and presented a view that allowed the operator to focus the system much like a telescope. These models functioned poorly because people with good vision were able to accommodate (involuntary change in the power of the human eye). This made focusing the camera extremely difficult. I had such a camera and complained to the maker. Eventually I deposited the camera on the counter at the camera's North American repair service and never returned. </p>

[bob_sunley]

<p>An easy way to determine the + diopter you need it to head down to a store that sells reading glasses and bring a tape measure with you. Stand about 3 ft from a sign on the stand and use your tape measure to put the tip of your nose 38" from the sign on it. Now try various pairs of glasses until you can see the sharpest detail on the sign. The diopter number you need is on the glasses. :)</p>

<p>If you are at all handy, you can grind down a lens from a dollar store pair of glasses to fit in the eyepiece on the camera.<br /> This also works when you are using the distance part of your bi/tri focals to look thru the viewfinder and you want to determine which diopter you need so you can wear your glasses and see the viewfinder clearly. Just hold the reading glasses in front of your regular ones when reading the sign.</p>

 

[david_pidcock]

<p>Thanks for all the input, really.<br>

Just to make sure I understand:<br>

If I need +200 glasses from the drug store to read at, say, 18 inches. Would that equate to +2 diopter for the waist level finder on my RB 67? Which would also mean if I needed +100 glasses is +1 diopter in the same finder?<br>

Thanks once again,<br>

David</p>

[david_pidcock]

<p>Or, just use the drug store glasses, which are bi-focals, +200, when I shoot?<br /> David</p>