"Fine Tuning" Auto Focus?
Feb 25, 2018 16:48:58 #
What exactly is “fine tuning” auto focus? I have never done this or knew it needed to be done. I am shooting Olympus E-M1, and several Olympus lenses. Can't find anything in the manuals on the topic. Is this something I need to know? Thanks!
Feb 25, 2018 16:50:49 #
flashbang wrote:
What exactly is “fine tuning” auto focus? I have never done this or knew it needed to be done. I am shooting Olympus E-M1, and several Olympus lenses. Can't find anything in the manuals on the topic. Is this something I need to know? Thanks!
In the world of camera lingo this one is pretty self-explanatory. Check an on line manual for say, a Nikon D500 for procedure related to that camera.
Feb 25, 2018 17:52:59 #
Sometimes for a lens, camera combination, the autofocus of the camera is not 'dead on'.
The error is usually referred to as either front focus or back focus depending on whether the focus point is in front or in back the subject.
Fine tuning the autofocus allows you to correct the error by moving the focus point forward or backward from its initial point.
The camera remembers this correction and the lens it goes with and applies it whenever that lens is attached.
I hope I said all of that correctly.
The error is usually referred to as either front focus or back focus depending on whether the focus point is in front or in back the subject.
Fine tuning the autofocus allows you to correct the error by moving the focus point forward or backward from its initial point.
The camera remembers this correction and the lens it goes with and applies it whenever that lens is attached.
I hope I said all of that correctly.
Feb 25, 2018 18:28:12 #
Ltgk20
Loc: Salisbury, NC
I think what you're referring to is the process of microadjusting the focusing on DSLRs or other cameras where the autofocus sensor is not on the imaging sensor. In this case the length of the light path can sometimes be slightly different as it travels to the AF sensor vs. the imaging sensor. This microfocus adjustment allows an offset to be input to correct for the difference.
Mirrorless cameras focus off of the imaging sensor (using CDAF or PDAF) and don't need this type of adjustment.
Mirrorless cameras focus off of the imaging sensor (using CDAF or PDAF) and don't need this type of adjustment.
Feb 25, 2018 18:53:21 #
Feb 26, 2018 08:23:20 #
This is a great topic. It appears to me that perhaps some camera manufacturers have a way of adjusting that sharpness level to recognize the lens attached to the camera to provide the best sharpness for those optics. This should be available to the camera owner as well in assigning a value through the software in the camera.
Any comments welcomed.
Don
Any comments welcomed.
Don
Feb 26, 2018 09:42:30 #
With phase detection AF errors made by the operator are common. Most AF errors are operator's errors.
Back of front focus require adjustment when they happen but in my book I want a reputable technician or the importer to fix the problem since they have the instruments to make fine calibrations in camera.
I have never recommended to anyone to do a fix on his or her own.
Back of front focus require adjustment when they happen but in my book I want a reputable technician or the importer to fix the problem since they have the instruments to make fine calibrations in camera.
I have never recommended to anyone to do a fix on his or her own.
Feb 26, 2018 10:41:17 #
These explanations were very good. Normal depth of field will compensate some. The larger the aperture the more important it becomes. It would be very useful if someone showed a graphical demonstration of the concept. It would really clear up the concept for everyone. It would be useful if someone named the cameras where the front & rear focus points could be changed & how. These focus errors would be hard to see in a snap shot but would show up more in blowups.
There is a concept seldom reported in 4x5 & 8x10 lenses where one focuses at say F4.5 for maximum light on the grounds glass then typically or often uses F16 for max depth of field (in particular when using a tripod-F16 is not the sharpest F stop either). Enlargements were less with 4x5 films compared to say 35mm film so fewer error & grain showed up. With many of these 4x5 & 8x10 lenses at F16 there is a focus shift very hard to see on a dim ground glass. Sometimes it's beyond your focal point & sometimes in front of your focal point. You need to determine it. Sometimes it's a possible advantage & sometimes it's not. If you are initially focused on infinity, any focus point beyond infinity at F16 serves no useful purpose--it ruins the picture. But if the focus shift is closer than infinity now at F16 the average fore ground in focus is increased. F16 depth of field will still keep infinity reasonably sharp & often unnoticed unless it is fine print & you also took a shot at F11 for comparison. Fewer comparisons were made due to time consumptions, developing time, negative drying & cost in particular to the digital camera ease of them & quick computer blow up comparisons. Objects from say 15' to 200' are easier to tell if they might be out of focus some compared to 200' & beyond. Large negatives are so easy to work with compared to 35mm. 120 negs often don't need a magnifying glass. I often regret I didn't start using a Hasselblad sooner. What got me started with the 120mm adaptor for the 4x5.
There is a concept seldom reported in 4x5 & 8x10 lenses where one focuses at say F4.5 for maximum light on the grounds glass then typically or often uses F16 for max depth of field (in particular when using a tripod-F16 is not the sharpest F stop either). Enlargements were less with 4x5 films compared to say 35mm film so fewer error & grain showed up. With many of these 4x5 & 8x10 lenses at F16 there is a focus shift very hard to see on a dim ground glass. Sometimes it's beyond your focal point & sometimes in front of your focal point. You need to determine it. Sometimes it's a possible advantage & sometimes it's not. If you are initially focused on infinity, any focus point beyond infinity at F16 serves no useful purpose--it ruins the picture. But if the focus shift is closer than infinity now at F16 the average fore ground in focus is increased. F16 depth of field will still keep infinity reasonably sharp & often unnoticed unless it is fine print & you also took a shot at F11 for comparison. Fewer comparisons were made due to time consumptions, developing time, negative drying & cost in particular to the digital camera ease of them & quick computer blow up comparisons. Objects from say 15' to 200' are easier to tell if they might be out of focus some compared to 200' & beyond. Large negatives are so easy to work with compared to 35mm. 120 negs often don't need a magnifying glass. I often regret I didn't start using a Hasselblad sooner. What got me started with the 120mm adaptor for the 4x5.
Feb 26, 2018 12:07:44 #
ken glanzer wrote:
With many of these 4x5 & 8x10 lenses at F16 there is a focus shift very hard to see on a dim ground glass. .
40+ years of studio large format work and I have never had this happen. Stopping down increases the depth of field, not the focus itself. General rule of thumb is that what ever that increase, it will be about 1/3 in front of the focus point and 2/3 behind it. Usually you could see this on the ground glass with a good loupe. Then the Goddess of Photos gave us Poloroids!
Feb 26, 2018 12:16:56 #
Large Format for me was 11X14 film. Loading the film holders in the dark was really fun.
Sounds as if you and I must have similar backgrounds. 65 years for me. went digital 6 years ago.
Don H
Sounds as if you and I must have similar backgrounds. 65 years for me. went digital 6 years ago.
Don H
Feb 26, 2018 13:16:18 #
Officially, just over 50 for me, not counting shooting for Theodore Roosevelt High School's newspaper, where I learned that as school photographer I could get out of classes!
Feb 26, 2018 13:26:26 #
As an Industrial Photographer I had many differing assignments , Here is a link to some of my past photography jobs.
One winter I did the Santa Clause thing for S. Kline Dept Store 3 locations. I will never forgive myself.
http://1-donald-hill.artistwebsites.com/
Don
One winter I did the Santa Clause thing for S. Kline Dept Store 3 locations. I will never forgive myself.
http://1-donald-hill.artistwebsites.com/
Don
Feb 26, 2018 13:57:17 #
Flashbang check out Jeffery Friedl's blog.You can download his test chart. Sorry I don't have his web address.
Feb 27, 2018 01:30:33 #
flashbang: As I said I've had Focus Shift at F16 on 4x5 & 8x10 lenses. Your lenses may not have shifted @F16. On some lenses it goes forward & sometimes backward. Since it is seldom reported it's seldom caught or even looked for. I didn't mention I also had it with a 50mm Nikon lens but only @F8. It retained the focus point on all the other F stops. I noticed this when I was running lens resolution tests on each F-Stop. I checked the focus setting at each F stop & had to refocus @F8. At all other F Stops it didn't change. This was the first time I did that. I was testing a friends lens & he saw the shift also. This really shook him up as he remembered some of his F8 pictures weren't in focus where he remembered he focused at! I'm going to try it with my Hasselblad lenses next. My Leica Collapsible F2 lens was in focus at each F Stop. It had the maximum resolution of any 35mm lens I ever tested @F4 using Kodak High Contrast Copy Film of 240 lines/mm. They used a Slide Rule to design it. The WWII German Binoculars I have were always better than the American Binoculars also. Sharper, wider field of view & longer eye relief!
The Leica F2 lens only resolved 100 lines/mm (most lenses topped out at 100 lines/mm) with Panatomic film with the 25 ASA. It resolved 400 lines/mm with Kodak's 649 Spectroscopic Film. The film was rated to resolve 1000 lines/mm. It actually made good looking pictures using the Tech Pan Type Developer. I think it would have made Billboard Pictures. I couldn't see any grain in the negs with my microscope. It was a bit slow of film speed. I took a 25 ASA light meter reading & increased the exposure 10 times. If I figured it right that's about a .02 +/- ASA. It's not exactly hand held.
I used this camera lens in my Leica Focolmat Enlarger also which I still have. They even had an adaptor for it. It made very sharp enlargements across the picture when I used about 60% of the neg. When I used the full width neg I had to use F8. It's one of the best enlargers ever made. It had a stay in focus design also once set. Lenses have always been far better than the film normally used. I had box seats at Safeco Field in Seattle & I took a shot with a medium priced 70-300mm lens across the field about 350' mounted on my D2X & was amazed at the 8x10 picture resolution with that lens. I'd like to try it with the N850 now.
There is a trick where you can check resolution just using a 10X Hasting magnifier held in the image area on any lens or binocular for quick comparisons. You can put a magnifying glass on your focus window also for precise focusing. It's handier if you use a mount of some kind to hold it there or in the lens image.
I used the Standard Air Force Resolution Chart at a "certain distance" about 3' or so & had 3-3"x3" charts set right behind each 1", one set in the center, at the 4 corners, top & bottom middle & the sides middle. Focusing on the center chart I could check if the focus field moved in or out on the edges also on every F Stop also. I used a microscope to quickly view the negs for the resolution values. I had a frame I pulled the negs through to keep the film centered & the same distance away from the microscope lens. It was always in focus & quick to use. When I used High Contrast Copy film I had to move the chart back at 2 or 3 times the distance as I remember. The chart only went to 100 lines/mm. You can use a newspaper with different size print for comparison checks at any distance for lenses or binoculars.
The Leica F2 lens only resolved 100 lines/mm (most lenses topped out at 100 lines/mm) with Panatomic film with the 25 ASA. It resolved 400 lines/mm with Kodak's 649 Spectroscopic Film. The film was rated to resolve 1000 lines/mm. It actually made good looking pictures using the Tech Pan Type Developer. I think it would have made Billboard Pictures. I couldn't see any grain in the negs with my microscope. It was a bit slow of film speed. I took a 25 ASA light meter reading & increased the exposure 10 times. If I figured it right that's about a .02 +/- ASA. It's not exactly hand held.
I used this camera lens in my Leica Focolmat Enlarger also which I still have. They even had an adaptor for it. It made very sharp enlargements across the picture when I used about 60% of the neg. When I used the full width neg I had to use F8. It's one of the best enlargers ever made. It had a stay in focus design also once set. Lenses have always been far better than the film normally used. I had box seats at Safeco Field in Seattle & I took a shot with a medium priced 70-300mm lens across the field about 350' mounted on my D2X & was amazed at the 8x10 picture resolution with that lens. I'd like to try it with the N850 now.
There is a trick where you can check resolution just using a 10X Hasting magnifier held in the image area on any lens or binocular for quick comparisons. You can put a magnifying glass on your focus window also for precise focusing. It's handier if you use a mount of some kind to hold it there or in the lens image.
I used the Standard Air Force Resolution Chart at a "certain distance" about 3' or so & had 3-3"x3" charts set right behind each 1", one set in the center, at the 4 corners, top & bottom middle & the sides middle. Focusing on the center chart I could check if the focus field moved in or out on the edges also on every F Stop also. I used a microscope to quickly view the negs for the resolution values. I had a frame I pulled the negs through to keep the film centered & the same distance away from the microscope lens. It was always in focus & quick to use. When I used High Contrast Copy film I had to move the chart back at 2 or 3 times the distance as I remember. The chart only went to 100 lines/mm. You can use a newspaper with different size print for comparison checks at any distance for lenses or binoculars.
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