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Thread: Achieving Critical Focus

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    Senior Member Tesselator's Avatar
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    Achieving Critical Focus

    Today I received a PM here at GetDPI which read:

    You need to write and publish an article on achieving critical focus. I've been reviewing a bunch of your images on the forums and also the samples on your FTP server. Only a small part of the apparent sharpness is the lens and the rest is something you are doing when focusing. I sure wish you'd share it with the rest of us.
    For those of you who haven't read many of my posts here I almost exclusively use manual focus lenses or if the lens is an AF model I switch it off and use it in MF mode. I currently don't own any of the native 4/3 lenses anyway so everything is just MF all the time no matter what.

    As you can tell from the folder listing on my website I tend to favor film models from the 70's and early 80's with a few models reaching back into the 60's. I don't know if that's relevant here but that time range does represent the period during which SLR MF lens design rose, peaked, and declined in favor of the AF types. I don't follow old Ned's philosophy directly but I am a Luddite to the extent that I have little interest in AF lenses. Correctly or incorrectly I believe that in order to get an AF system which can compete with my usual MF style I would need to spend over $4,000 for the camera body alone or compromise on modern features which I'm not willing to give up. The Canon 1D Mark II (1DsII, and IIn) all have an excellent AF system at an affordable $500 to $700 however there is no sonic sensor cleaning, and no live view to name but two such features. Additionally I've become somewhat addicted to the adaptability that mirrorless camera models offer. Pretty much any lens ever made can be fitted to my camera (The GH1 currently) just by purchasing an $8 ~ $25 adapter.

    AFAIK, I'm not doing anything special when focusing though. I use the camera with the LCD turned in on itself - almost always - unless I'm shooting video or it's otherwise impossible to look through the EVF (Electronic View Finder) for whatever reason. My form and stance is not optimal or even scientific. Often my elbows are pointed out like an awkward bird discovering his wings for the first time. If there is anything special it's in the constant use of the zoomed MF assist viewing mode. I enter this mode for almost every shot I take. And as you can see my continual button pressing has worn off the decal almost completely. And that is my third copy of the camera with all previous copies showing the same wear. I'm currently on my 4th copy of the GH1 and fully expect it to wear in the same fashion.

    I like to discover how a lens performs at it's widest aperture. Almost every lens is sharp stopped down but the character and quality of wide open lenses is something I enjoy noting and distinguishing. I guess I'm a bit of a nerd in that sense! My technique if one can call it a technique, is probably no different than most other people's when trying to achieve the sharpest focus possible at a lenses widest aperture. I guess these steps will look familiar to almost everyone here:

    1. Identify a scene or subject I think might be photogenic,
    2. Switch on the camera,
    3. Raise it up to my right eye,
    4. Press it firmly against my eyebrow,
    5. Generally focus for the scene,
    6. Check composition and identify the focus subject,
    7. Enter the MF assist zoom view positioned on that subject,
    8. Rock the focus plane in front and behind of the peak point to find the middle,
    9. Decide on the middle - most perfect - focus setting,
    10. Remove my fingers from the focus barrel,
    11. Half press the shutter release button to exit MF assist zoom,
    12. Double check composition and exposure settings,
    13. Breathe in and exhale slowly (A);
    14. Press the shutter button all the way down.
    15. Click.

      (A) - If the shutter speed is lower than the focal length divided by one.

    Steps 3 and 4 are omitted when using a tripod of course and step 13 is replaced by using the timed shutter of 2 or 10s. But that's about it. I guess everyone is doing something similar if not the exact same things?

    On the use of tripods I use them whenever I can! Like my lens collection I prefer older pods from the 60's and 70's but with a modern ball or gimbal head. If the lens is on the heavy side I like gimbals, if light; the ball head works best. Gimbal heads are also better for tracking while focusing too - for like, birds in flight and etcetera.

    I'm probably just rambling at this point but the reason my tripods like most of my lenses, are from a previous age is because I want to feel the history of the equipment and the nostalgia of the photographic process. Hehe, I'd probably be using film if it weren't inferior on several different levels - as well as more expensive. I like the older Linhof tripods myself!

    These are the models I like the most and/or have owned:

    Oh, look, here's a shot of me standing next to my favorite and most used Linhof now:

    Yep, that ancient bearded biker looking fellow is me about 3 years ago. Anyway, tripods, hmm, yes.

    These Linhof pods may look heavy but they are as light or lighter than the newer carbon fiber models costing $450 and under! There are however a few CF models costing between $500 and $1k which are lighter tho. The Linhofs I've owned were all made of a special alloy comprised of titanium and aluminum which is virtually impervious to scratches yet is very lightweight and incredibly sturdy at the same time. It's not uncommon to find a linhof from the early 50's looking like it just came off the assembly line - and usually the number on the price-tag is quite reasonable <$250 or so. There are also aluminum and wooden Linhof tripods but I've not used any. My wooden tripod is from a different maker.

    Tripods are pretty important pieces of equipment in photography. There's a reason that you'll almost always see the camera mounted on a tripod when you step into a studio. Think about it; even though the studio is equipped with enough lights to blind the son of Zeus the tripod is still mostly used. Even though I often break it myself my own rule for requiring a tripod is simply focal length. Anything over 200mm on the GH1 and I have to use a tripod - period. I also hope to use a pod anytime the shutter speed is the same or less than the focal length of the lens being attached to the GH1. So if it's a 100mm and the exposure calls for 1/100 or less I want a pod. It seems to go all the way down and all the way up an still apply too. So with a 12mm lens if the exposure is 1/12th or less and with a 500mm lens if the exposure values call for a speed of 1/500th or less.

    I've done quite a few comparison tests from 28mm on up through 300mm with fast shutter speeds using tripods versus shooting hand-held and even the very best hand-held shots I think I've nailed show some subpixel blur; With the tripod too but much less often. Sometimes we don't mind or even want some blur but when I'm trying show the properties of a lens for whatever reasons, it's not a good idea to allow blur or atmospherics to affect anything.

    Atmospherics are another factor in critically focusing your optical system! I learned this again in a most startling way in my Moon Thru A $10 Lens thread at another site.

    Same lens, same camera, same technique, slightly different RH:

    There's an easier way of testing this than shooting the moon on nights of differing RH (Relative Humidity) tho. Pick a nice contrasty subject and shoot it in room light on a tripod. Then pop up your flash and shoot it again with the flash. Now compare the pixels at 200% to 400% in your RAW converter. While this is a slightly more complex and different phenomena than atmospherics alone it can be used to demonstrate the difference between good light and poor light - which might be due to poor atmospherics. So the conditions in which you shoot the shot can also drastically affect the clarity and apparent sharpness of a photograph. I try to take this under consideration when I shoot to show off a particular lens's attributes - or lack thereof.

    The final point I'll mention is also the final step in image creation and presentation. The PP (Post Processing) step. Every camera seems to have a different method of producing JPegs suitable for electronic transfer. They all seem to produce different results too. Some are great but mostly they suck nuggets! Well, to me they do anyway. I've been editing and producing electronic images since the first 8bit computers were introduced even before there were such things as GDAs (Graphic Display Adapters). This has given me the confidence justified or false, to think I'm better than the camera is at converting RAW images into JPegs. True or not I'm certainly slower for sure! While time consuming, converting your own RAWs in something like LR, ACR, DxO, Capture One, or ACR+PS almost always produces better and more self-styled images than camera converting engines do. I'll save the details of this part of the topic for a second post but the main idea is to shape up the data without adding or removing any observable pixel information. We want to modify the existing pixels so we can see them better but not add halos and other false-detail data. It's not too hard. It just takes some time and paying attention to the results different tools and tool-values produce.

    So I'll leave it here and if there's any interest I'll detail the steps I take in post both for lens samples and for just posting "pretty pictures".
    Last edited by Tesselator; 17th March 2012 at 05:04.
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