New to RF: Focusing fast lenses

[bessasebastian]

Coming from an SLR background with some years experience I´m having a little trouble focusing a rangefinder with that tiny superimposed image.

Wide angles seem to be less of a problem, stopped down anyway. But when using a fast lens wide open - let´s say a 50mm f1.4 - how do you make sure you get the focus right?

 

[cmogi10]

I use a 1.25 or 1.35 magnifier on my M8 to help me focus my fast and longer lenses.

 

[ferider]

See also here:

http://www.rangefinderforum.com/forums/showthread.php?t=34185

Things that help:

- long EBL (including magnifier, etc)
- well-calibrated camera/lens combo
- prefocus, then move to focus
- focus bracketing

50/1.4 shouldn't be too difficult. 90/2 and 135/2.8 are harder.
The closer the more difficult.

Best,

Roland.

 

[cmedin]

Jenni: True, but you have more playroom with the slower lenses / smaller apertures. With say an 85/1.2 even the smallest focusing error will be very noticeable, while with say a 25/4 you have a significant 'fudge factor' since your acceptably sharp depth of field is so great.

 

[cmedin]

Agreed on that, though none of us ever get it PERFECLY right. 🙂 Like bessasebastian though, I seem to do better on SLRs than on RFs for some reason.

 

[waileong]

Actually, SLR's don't focus perfectly either. The key thing is to find a vertical line in the subject and use it to line up the rangefinder images.

 

[cmedin]

Don't think anybody claimed SLRs focus perfectly. Some find them easier than rangefinders, some find rangefinders easier.

 

[telenous]

Wide angles seem to be less of a problem, stopped down anyway. But when using a fast lens wide open - let´s say a 50mm f1.4 - how do you make sure you get the focus right?

If you are working from a distance to your subject then superimposing the secondary image on the rangefinder patch should suffice, even at f/1.4. In close distance photography you will have less slack for error. A 'trick' that works for me in portraits is trying to superimpose a catch light on the eye in the coincident image with that on the viewfinder. It's usually bright enough to let you get the focus on the eyes right in the dimmest of lights. But you 're right, the longer the lens the harder it gets.

 

[thomasw_]

I use a 1.25 or 1.35 magnifier on my M8 to help me focus my fast and longer lenses.

carl, where did you get a 1.35x magnifier? was it megaperls?

 

[waileong]

The question is not about difficulty of focusing due to bad eyesight, it's about how to focus in a RF vs SLR. The key thing about RF is learning to line up the images. Even if one added a 1.35 magnifier, it's still about lining up the images.

 

[rxmd]

Lining up the images is learned with practice, I'd say. Just don't worry. After your first five films or so with a rangefinder you'll feel pretty comfortable about it.

In theory focusing difficulty is independent of lens aperture, because you have to align the images no matter what. If you can do that precisely with an 21/4, you can also do it precisely with a 85/2. Precision largely depends on your eyesight, the effective baselength of the camera and the haptics of the lens. Aperture figures in the equation only in so far as slower lenses and/or larger apertures are a bit more forgiving in this respect - but only as long as you don't print crops or very large prints.

 

[rxmd]

You are mistaken about enlarging. DOF does not change because the print size changes. DOF changes with the ratio of print size to viewing distance. In that case, no matter the size of the print, DOF will vary with viewing distance.

Well no matter if you say that DOF changes with print size or with viewing distance, you are both making assumptions about the viewer's behaviour and hence you're both somehow right. My personal viewing behaviour works like this that I look at larger prints from a somewhat, but not proportionally larger distance; e.g. I (try to) keep an album of prints, and while I may look at an 18x24 print in there from a somewhat larger distance than a 13x18 print, the book is still more or less on my lap, and hence 18x24 prints are more critical regarding DOF. Hence for me personally at least it is more useful to describe DOF in terms of print size and enlargement ratio.

Also if you relate DOF to viewing distance, it becomes difficult to describe DOF behaviour in partial crops, because you get the viewing distance of a small print coupled with the enlargement ratio of a large one. In this case it makes much more sense to talk about DOF in relation to enlargement factor.

Philipp

EDITed to correct grammar in some sentences which no verb.

 

[Finder]

Well no matter if you say that DOF changes with print size or with viewing distance, you are both making assumptions about the viewer's behaviour and hence you're both somehow right. My personal viewing behaviour works like this that I look at larger prints from a somewhat, but not proportionally larger distance; e.g. I (try to) keep an album of prints, and while I may look at an 18x24 print in there from a somewhat larger distance than a 13x18 print, the book is still more or less on my lap, and hence 18x24 prints are more critical regarding DOF. Hence for me personally at least it is more useful to describe DOF in terms of print size and enlargement ratio.

Also if you relate DOF to viewing distance, it becomes difficult to describe DOF behaviour in partial crops, because you get the viewing distance of a small print coupled with the enlargement ratio of a large one. In this case it makes much more sense to talk about DOF in relation to enlargement factor.

Philipp

EDITed to correct grammar in some sentences which no verb.

It is not an either/or statement. It is both viewing distance AND print size. Enlargement factor does not alter the change and so it does not matter about cropping - keep the relationship the same between the viewing distance and print area and the print DOF remains constant. The practical upshot is that changing print size does not affect print DOF.

 

[rxmd]

Enlargement factor does not alter the change and so it does not matter about cropping

Take a picture of a diagonal row of telegraph poles, sticks, pencils, trees, whatever, at a low aperture, on high-resolution film. Print to 8x10". Crop the central 10% and print to 8x10". View from the same distance. DOF will look different. The enlargement factor is important because you project the negative's circles of confusion when creating a print from a given negative. If you enlarge them more, DOF behaviour will be affected.

Of course if you step back by the same amount as your enlargement factor grows, DOF is not affected, but if you enlarge more to a print of the same physical size - such as when cropping - DOF behaviour changes.

Keep the relationship the same between the viewing distance and print area and the print DOF remains constant. The practical upshot is that changing print size does not affect print DOF...

...assuming that as your prints get larger, the viewer steps backwards. Nobody is denying that, but it's an assumption which is highly dependent on how and where the images are viewed.

For example, Soviet lenses have comparatively generous DOF scales. At f/16 my 35/f2.8 Jupiter-12 indicates DOF from infinity to 1m, my Skopar 35/f2.5 roughly from infinity to 1.3m, that's a 1 stop difference. My 1949 Kiev has a DOF scale for 50mm lenses (which might well be a German part) that, at f/16, indicates infinity to 1.7m; my 1984 Canon 50/f1.4 lens has a DOF scale which gives the same range only for f/22. The reason is precisely because the typical Soviet picture was a 7x10 in an album held in your lap. After the war viewing behaviour changed - primitively speaking the average print size got bigger, so DOF was becoming more critical, but peoples' albums and laps were still at the same distance because people didn't grow as their prints did.

It's true of course that the two are interrelated, but judging from my own viewing habits I find it not very useful to use viewing distance as my metric and much more useful to use print size and enlargement factor (which again are interrelated of course). I can do so precisely because they are interrelated. Also this approach makes it much easier to compare DOF behaviour between 35mm and medium or large format prints.

Philipp

 

[Finder]

Take a picture of a diagonal row of telegraph poles, sticks, pencils, trees, whatever, at a low aperture, on high-resolution film. Print to 8x10". Crop the central 10% and print to 8x10". View from the same distance. DOF will look different. The enlargement factor is important because you project the negative's circles of confusion when creating a print from a given negative. If you enlarge them more, DOF behaviour will be affected.

Of course if you step back by the same amount as your enlargement factor grows, DOF is not affected, but if you enlarge more to a print of the same physical size - such as when cropping - DOF behaviour changes.

You are complicating what was a simple statement - print size changes print DOF. Take that cropped image and print it any size you want and print DOF is not changing.

I am not talking about the print DOF in comparing a full frame image and a section cropped from it printed at the same size.


[/quote]...assuming that as your prints get larger, the viewer steps backwards. Nobody is denying that, but it's an assumption which is highly dependent on how and where the images are viewed. [/quote]

Right. That is why print size in and of itself makes no difference.

For example, Soviet lenses have comparatively generous DOF scales. At f/16 my 35/f2.8 Jupiter-12 indicates DOF from infinity to 1m, my Skopar 35/f2.5 roughly from infinity to 1.3m, that's a 1 stop difference. My 1949 Kiev has a DOF scale for 50mm lenses (which might well be a German part) that, at f/16, indicates infinity to 1.7m; my 1984 Canon 50/f1.4 lens has a DOF scale which gives the same range only for f/22. The reason is precisely because the typical Soviet picture was a 7x10 in an album held in your lap. After the war viewing behaviour changed - primitively speaking the average print size got bigger, so DOF was becoming more critical, but peoples' albums and laps were still at the same distance because people didn't grow as their prints did.

It's true of course that the two are interrelated, but judging from my own viewing habits I find it not very useful to use viewing distance as my metric and much more useful to use print size and enlargement factor (which again are interrelated of course). I can do so precisely because they are interrelated. Also this approach makes it much easier to compare DOF behaviour between 35mm and medium or large format prints.

Philipp

I never intended this to be an exhaustive discussion on DOF. I was simply discussing the statement that print size affects print DOF. Regardless of your viewing habits (while people's habits can be different, they are also consistant), the statement is not true.

 

[Nikon Bob]

If you are used to an SLR with a split image focusing screen you should be able to get a similarly good focus with the patch on an RF by lining up on a vertical element in a scene or superimposing two clearly defined edges. Is your RF new or used as the condition of the patch may not be as good as it should be in an older used model RF. Then again RF alignment can get knocked out/drift out of place and there maybe nothing wrong with your focusing method. If you do a search here on the forum there are many threads on how to check RF alignment.

Bob

 

[peter_n]

Coming from an SLR background with some years experience I´m having a little trouble focusing a rangefinder with that tiny superimposed image.

Wide angles seem to be less of a problem, stopped down anyway. But when using a fast lens wide open - let´s say a 50mm f1.4 - how do you make sure you get the focus right?

Sebastian, first you need to always have your lens set at infinity. Look for a vertical in the plane of focus in the scene. You always turn the focus ring in one direction only and stop when the two verticals snap together in the VF patch.

Do not roll the focus ring past the plane of focus and rock it back and forth slightly as you would with an SLR.


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edit: whoops! one "focus" too many and took it out... 🙄
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[principe azul]

Peter's right. It's different from focusing an SLR, and it might just take a bit of getting used to, nothing to worry about.

People who've only used autofocus have taken shots with my RF and asked me how to focus. "That's cheating!" one of them said. She couldn't believe it was so simple. But if you've been used to turning the lens back and forth and checking the ground glass for sharpness, you might have to unlearn some of that on your RF.

 

[wintoid]

Do not roll the focus ring past the plane of focus and rock it back and forth slightly as you would with an SLR.

I'm not being provocative, just genuinely curious..... why not rock it?

I'm someone who still has problems with accurate focus of very wide apertures at close distance, and would like to improve this. I do generally rock the focus.

 

[principe azul]

why not?

Mind over matter... 😉