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View Full Version : Infinity questions (not an infinity of questions...;))



macandal
23-Sep-2014, 09:10
At times, this is a bit puzzling to me. I started thinking about it this past weekend when my friend and I went shooting at night. Long story short, I could not focus. It was hard. We tried pointing light at the subject (when this was feasible) and I could not do it. So I decided that I would set my camera at infinity and shoot that way. Some questions:


How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm.
If one sets one's camera at infinity the subject will be sharp, right?
How far does the near subject have to be in order to get a sharp image? Is there an easy way to figure this out or is it complicated? Using my past experience as a reference, I was using an 180mm lens, how far did I have to be from the subject in order to get a sharp image?

Thanks.

I love night photography, but for me, because I've always had bad eyesight, it's so damn hard.

djdister
23-Sep-2014, 09:47
How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm. You should calculate this (focus on an object more than 100 ft away) during daylight, and make an infinity mark if your camera doesn't have infinity stops (most field cameras do). Setting the distance between the lens and rear standard may not equal the infinity focal point. For example, a retrofocus or telephoto lens will not focus on infinity at the marked focal length.

If one sets one's camera at infinity the subject will be sharp, right? Depends where your subject is.

How far does the near subject have to be in order to get a sharp image? Is there an easy way to figure this out or is it complicated? Using my past experience as a reference, I was using an 180mm lens, how far did I have to be from the subject in order to get a sharp image? You should get a table (or calculate it) of the hyperfocal distances for your particular lens. That way you would know for example that shooting at f/22 will yield everything from 8 feet to infinity as "reasonably sharp." If your camera doesn't have a ruler scale on the side, get one, because it will make setting the focus at the proper hyperfocal distance settings easier at night.

drew.saunders
23-Sep-2014, 10:01
How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm.
If one sets one's camera at infinity the subject will be sharp, right?
How far does the near subject have to be in order to get a sharp image? Is there an easy way to figure this out or is it complicated? Using my past experience as a reference, I was using an 180mm lens, how far did I have to be from the subject in order to get a sharp image?


You could use the flange-back measurement (see http://www.ebonycamera.com/articles/lenses.html) to get the distance from the front of the lensboard to the film plane. The problem is that it's not always easy to find the exact film plane. I find it easier to focus at "infinity" (a.k.a. a building that's at least 400m/yards from my front yard) during daylight and then measure the distance from the front of the front standard to the rear of the rear standard and mark it down. That way I have two easy to measure points that will get me to infinity focus. For my 180mm Xenar and my Ebony the measurement between those two points of reference is about 149mm. For the 165 Zeiss Tessar in my avatar, that distance is 134mm. Your camera may have a scale on it that you could mark.

Then, using the thin lens equation (http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html), you can figure out extension for some common distances and make a note. Using that equation, you can determine that you'll need 1.6mm extension for 20m, 3.3mm for a 10m subject, 6.7mm for a 5m subject, and anything closer you may not want to bother with for night photography, and just extend the bellows accordingly. That's 1/180 - 1/20,000 = 1/181.635; 1/180 - 1/10,000 = 1/183.3; 1/180 - 1/5000 = 1/186.722 etc.

From here (http://www.dofmaster.com/dofjs.html) determine the DOF at those distances for various f stops to get your hyperfocal distance range. You could pre-calculate a couple options and have a chart with you.

Enjoy!

Drew

macandal
23-Sep-2014, 10:10
I should have mentioned that I use a Sinar F2 (monorail). It has a lot of numbers all over the camera, some of which I don't know what they are, so, my camera may have some of the markings you guys are talking about.

Also, there must be an app for this, right? Recommendations?

Thanks.

Jac@stafford.net
23-Sep-2014, 10:17
How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm.

Not so good. Did you measure from the lens board to ground glass or from the lens rear element? There are other concerns.


If one sets one's camera at infinity the subject will be sharp, right?

Only if the subject is at infinity. Infinity is very far away. An approximation using a typical .11mm CoC, 180mm normal lens, F/16 puts infinity at ~95 yards. (opinions will vary)

If you cannot focus the view camera to infinity at night, then stick a mm rule on the focusing rails, set the aperture you will use, then focus on something a mile away in daylight. Mark the ruler against a prominent part of the front standard, lens board. Use that mark at night. That gets you close enough. Factors that make this suggestion vulnerable include atmospheric clarity, profound differences in ambient temperature.

Drew Wiley
23-Sep-2014, 10:27
I'd never trust some marking. There are lots of movements on a Sinar and most other view cameras which only need to be a little bit off to spoil correct focus. I'd always check the groundglass with a good loupe. Certain large format cameras generally termed technical cameras were designed for optional handheld shooting with
rangefinder focus etc, with cams and inifinity stops. Sinar is not one of these, but does have a greater range of movements than a technical camera. Your f2 has scales
for determining yaw-free setting on things like tabletop photography. This takes a bit of explanation, but has relatively little to do with your question.

Jim Noel
23-Sep-2014, 13:07
How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm. You should calculate this (focus on an object more than 100 ft away) during daylight, and make an infinity mark if your camera doesn't have infinity stops (most field cameras do). Setting the distance between the lens and rear standard may not equal the infinity focal point. For example, a retrofocus or telephoto lens will not focus on infinity at the marked focal length.

If one sets one's camera at infinity the subject will be sharp, right? Depends where your subject is.

Correction: Most field cameras do not have infinity stops! Graphics have them,but they are not field cameras. Other makes which resemble a Graphic may have them.

How far does the near subject have to be in order to get a sharp image? Is there an easy way to figure this out or is it complicated? Using my past experience as a reference, I was using an 180mm lens, how far did I have to be from the subject in order to get a sharp image? You should get a table (or calculate it) of the hyperfocal distances for your particular lens. That way you would know for example that shooting at f/22 will yield everything from 8 feet to infinity as "reasonably sharp." If your camera doesn't have a ruler scale on the side, get one, because it will make setting the focus at the proper hyperfocal distance settings easier at night.

Drew Wiley
23-Sep-2014, 15:48
Hyperfocal theory is relative to the amt of enlargement on the final print etc. I have done well ignoring hyperfocal doctrine altogether. It's like imitation ice milk concerning focus technique. Having used an f2 for many years I can certainly attest that it is fairly easy to get one setting or another a bit out of whack, at least if you carry the camera around - swing or tilt or fine adjustment. I guess one could make a mark or machine a custom stop on the rail just for quick setup. But that just takes a few seconds anyway, visually, sliding the standards into position. After that, you still need to do your fine focus thru a loupe. Otherwise you give up a lot of the precision this camera is capable of. Rarely does one use a view camera this way anyway - at least not me. Almost always I find myself using tilts, so there would be no point in having infinity stops in the first place - they'd be useless. And even a lens as short as 180 on 4x5 film is likely to require movements in most situations, otherwise they is little sense using a view camera at all, or its ability to control plane of focus through tilts. Maybe you just need some time to practice
with this kind of equipment until it becomes instinctive to you.

Vaughn
23-Sep-2014, 15:53
Not for infinity, but when using a flashlight and if you can get to your subject, prop the flashlight at the subject, point the flashlight at the camera, then focus on the bright flashlight.

Jac@stafford.net
23-Sep-2014, 17:11
I'd never trust some marking.[...]

Most excellent point. If one is going to photograph under the circumstances comsidered here, then a Technical Camera helps. In in my modest experience, tactile zero detentes is critical. Each to his own. Thanks for that.

.

macandal
23-Sep-2014, 17:23
Hyperfocal ...Drew, just sent you an email through this site. Your PM box is full.

ic-racer
23-Sep-2014, 20:07
Two lenses together can make a collimator which can be used to set any camera to infinity. Otherwise focus on the moon.

http://www.kyphoto.com/classics/collimator.html

Regular Rod
24-Sep-2014, 01:59
How does one set the LF camera (4x5 for me) to infinity? For example, that evening, I had an 180mm lens, so I made sure that the distance between the lens and the rear standard was 18 cm. You should calculate this (focus on an object more than 100 ft away) during daylight, and make an infinity mark if your camera doesn't have infinity stops (most field cameras do). Setting the distance between the lens and rear standard may not equal the infinity focal point. For example, a retrofocus or telephoto lens will not focus on infinity at the marked focal length.

If one sets one's camera at infinity the subject will be sharp, right? Depends where your subject is.

How far does the near subject have to be in order to get a sharp image? Is there an easy way to figure this out or is it complicated? Using my past experience as a reference, I was using an 180mm lens, how far did I have to be from the subject in order to get a sharp image? You should get a table (or calculate it) of the hyperfocal distances for your particular lens. That way you would know for example that shooting at f/22 will yield everything from 8 feet to infinity as "reasonably sharp." If your camera doesn't have a ruler scale on the side, get one, because it will make setting the focus at the proper hyperfocal distance settings easier at night.

This advice is spot on. Here's a tool you can make in few minutes that will help you. Tick the tick box for a hyperfocal chart to be included.

http://tomchuk.com/misc/rf/

RR

Struan Gray
24-Sep-2014, 08:45
If you don't mind risking your night vision, there are a couple of tricks if you have a flashlight with a small bulb/LED or a laser pointer.

The first is to place a mirror against the front rim of the lens. Put the light source up against the ground glass, and an inch or so off center. Focus the image of the light source which appears on the opposite side of the optic axis (gg centre if you have no movements). This is a form of autocollimation.

Cruder, but still better than measuring and setting without something like a Vernier caliper, is to put the light source at the centre of the ground glass and look into the lens. Infinity is when the source appears to be infinitely large. Focus back and forth to find the position where the light spot is least distinct (it also inverts, which can be see if it has any structure). This is also a form of autocollimation, but uses your eye as one of the collimating lenses.

The second method works whether you have your eye up against the lens (like a loupe) or far back from it. It's less good if you manage to put your eye one focal length from the lens' optical centre - then you can get odd results.

Drew Wiley
24-Sep-2014, 09:25
Just cleared my mailbox. Thanks. My approach to this is PRACTICAL. A Sinar f2, deliberately designed for portability and breakdown, simply will not hold hard settings
if bounced around a bit. I like the Sinar monorail design a lot better than technical cameras like the Technika or Horseman FA because I gravitate toward long lenses
and want a full range of movements, and I did modify one once with hard carbon fiber inserts which essentially turned it into a point n' shoot infinity box camera for distant road quick shots, where a modest focal length lens and hyperfocal theory are applicable (though I tend to use 6x7 more for that kind of convenience stuff). But otherwise, it's a waste of time - correct theory or not. I currently use a Sinar Norma instead of the f2, which is a little more rigid, but I'd say exactly the same thing about it. Maybe a P2 would keep its settings if you kept it in a heavily padded case and had an elephant around to lug the entire apparatus.