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Thread started 15 Jan 2018 (Monday) 07:48
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Does FoCal work

 
anitaw2
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Jan 17, 2018 13:52 |  #31

digital paradise wrote in post #18543169 (external link)
It is in the DT video. Guess that is why why deleted a forum post about it. Did you watch the 18 minute video? About minute 13.

Yes I did. But I am wondering something. He said that if always shoot at a certain distance (like 15 feet) you should tune the lens at that distance. When I shoot, I like the "3D" look so I shoot from far at 1.8. I focus on the face from far. should I go in Live view, click on the little magnifying glass button and make sure the focus is actually on the face? I look through the eye piece. Maybe what I think is in focus is not actually what the camera sees.


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Jan 17, 2018 13:59 |  #32

anitaw2 wrote in post #18543177 (external link)
exactly...I think you realized the same thing I did.

Well, I think DP is on to something with your lens.

Just as a trial, you could try a simple focus test. Set up three cereal boxes or similar items (flat things with fine detail on them), staggering their distance from the camera. Put one 2 or 3 inches forward, and the other a bit behind. Then in good light, take a pic of them with the lens wide open, focusing on the middle one. Which box is sharpest?

Now change the MFA setting. Make a big change - like from 0 to +10 or +20 - and repeat the test.

You should soon discover if the needed MFA setting is within the range of the camera. If it is, then keep repeating, but with smaller increments, until you get it real close. This is way more time-consuming than doing Dot-tune, but has a chance of rescuing the lens when dot-tune is not working well. Even if it is out of the camera's range, setting it to +20 might make the lens very usable.


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digital ­ paradise
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Jan 17, 2018 15:12 |  #33

anitaw2 wrote in post #18543181 (external link)
Yes I did. But I am wondering something. He said that if always shoot at a certain distance (like 15 feet) you should tune the lens at that distance. When I shoot, I like the "3D" look so I shoot from far at 1.8. I focus on the face from far. should I go in Live view, click on the little magnifying glass button and make sure the focus is actually on the face? I look through the eye piece. Maybe what I think is in focus is not actually what the camera sees.

Pretty shallow DOF. With MFA set to zero put the focus point on an eye ball and even use spot focus. Open it with DPP and verify the AF point. Zoom to 50 and 100% and see what you are getting.

Also try this. Tape a dollar bill to the wall. With tripod and remote of you have it take 10 shots in a row and defocus between shot. Use mirror lock up and take your time between shots. Then take a few in LV and compare the 10 and see if there is a lot of deviation. Pick the best few and compare to the LV shots.


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Jan 17, 2018 15:45 |  #34

Might be worth checking out.
https://photography-on-the.net …/showthread.php​?t=1489004


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Wilt
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Post edited over 1 year ago by Wilt. (3 edits in all)
     
Jan 18, 2018 12:12 |  #35

Archibald wrote in post #18543188 (external link)
Well, I think DP is on to something with your lens.

Just as a trial, you could try a simple focus test. Set up three cereal boxes or similar items (flat things with fine detail on them), staggering their distance from the camera. Put one 2 or 3 inches forward, and the other a bit behind. Then in good light, take a pic of them with the lens wide open, focusing on the middle one. Which box is sharpest?

Now change the MFA setting. Make a big change - like from 0 to +10 or +20 - and repeat the test.

You should soon discover if the needed MFA setting is within the range of the camera. If it is, then keep repeating, but with smaller increments, until you get it real close. This is way more time-consuming than doing Dot-tune, but has a chance of rescuing the lens when dot-tune is not working well. Even if it is out of the camera's range, setting it to +20 might make the lens very usable.

The technique described does get you to the adjustment value...the technique I would refine with this comment...
Each time you adjust, set HALF the value between the best pair, in order to arrive at the optimal setting faster (that is, fewer test iterations to perform).

Let us assume you fundamentally need + value adjustment.


  1. So your highest choice is +20...set that and see how it compares to +0
  2. Next, set +10, and compare that result to +0 and +20 tests

    Assuming that it seems the optimum is between +0 and +10, set +5 and test and compare that to the +0 and +10 test results
    Or if it seems the optimum is between +10 and +20, set +15 and test and compare that to the +10 and +20 test results

  3. Again (depending upon the 'better' of the comparison, again set HALF (for example, half way between +5 and +10 is a setting of about +7, and half way between +7 and +10 is about +8.


So you see it takes a maximum of 4 iterations of tests to arrive at the 'optimum' value for MFA, because with each iteration you eliminate half of the possible MFA values. For example

Test Iteration 1: 0 to 20 (middle value 10)
Test Iteration 2: 10 to 20 is best pair (middle value 15)
Test Iteration 3: 10 to 15 is best pair (middle value 12.5)
Test Iteration 4: 10 to 12.5 is best pair (middle value 11)
...and it should be possible to see the best of pair (10 or 11), simply choose that as your MFA setting

Not sure about current recommendations, but at one time Canon suggested test distance for MFA was 50 * FL
And to ensure that your camera is perfectly parallel to your test focus plane, set your camera so that when you look thru the viewfinder you find that your camera is aimed at its own reflection in the mirror, then afix your focus target to that mirror!


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Jan 18, 2018 14:24 |  #36

Old Wilt is still there! :-)




  
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Perfectly ­ Frank
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Jan 24, 2018 04:11 |  #37

Does FoCal work with large lenses?
Before my next air show in March, I want to MFA my Canon 300 f2.8 with the 1.4x & 2x extenders.

As Wilt says, Canon recommends a distance of 50 x FL. That means a distance of 49' bare lens and up to 98' with the 2x attached. I think at that distance a printed target would not be useable.

Up to this point I've used a method that is okay, but time consuming...

Camera on tripod, mirror lock, IS off, 10 sec timer set. Find a target with good contrast & detail at a distance I expect to shoot at when I'm at an air show. Take 11 shots with MFA set from 0 to +10, then again from -1 to -10. I slew the focus ring each time to force the camera/lens to re-focus with each shot. This is what takes the most time.

Go home, load the photos in my pc, kick back and crack open a beer. View the photos and find the sharpest one, noting the MFA value. Just don't crack open too many beers or they will all look blurry.


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Jan 24, 2018 05:10 |  #38

Perfectly Frank wrote in post #18547854 (external link)
Canon recommends a distance of 50 x FL.

I don't know who's righter, but FoCal recommends 7.5 m (25 ft) for a 300 mm lens and 12 m (40 ft) for a 600 mm lens. You'd need the Pro version to do more than 400 mm.

In any case, unless I'm missing something, if the target is at 50 x FL, its image should be the same size regardless of focal length (I think).


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Jan 24, 2018 06:22 |  #39

Pippan wrote in post #18547867 (external link)
Perfectly Frank wrote in post #18547854 (external link)
Canon recommends a distance of 50 x FL.

I don't know who's righter, but FoCal recommends 7.5 m (25 ft) for a 300 mm lens and 12 m (40 ft) for a 600 mm lens. You'd need the Pro version to do more than 400 mm.

In any case, unless I'm missing something, if the target is at 50 x FL, its image should be the same size regardless of focal length (I think).

Ok, that makes sense. Thanks.


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Jan 24, 2018 08:39 |  #40

I think Canon suggests 50X to cover themselves. FoCal describes when a lens settles down here. Page 2.

http://s449182328.webs​itehome.co.uk …20Test%20Distan​ce_1.1.pdf (external link)


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Jan 24, 2018 09:18 |  #41

As the pdf in the link DP posted suggests, the micro adjustment saturates after a certain distance, so the practical difference between 20X and 50X is negligible. So, you can actually do MFA your long telephoto in your backyard instead of looking for a parking lot.


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Jan 24, 2018 09:38 |  #42

Actually I have some Canon documents that say 50X and some say at the location/same distance you normally shoot at. The manual warns it is normally not necessary and may effect AF.

The link is the latest one I have found and the first that includes both. Also the first I believe to say that precision will be effected when your shooting distance is significantly different from where you MFA. We already knew that, Canon just finally said it.

This is also the first time Canon has hinted about lighting conditions. Page 5

http://www.learn.usa.c​anon.com …roAdjustGuide_d​esktop.pdf (external link)

Now to throw another wrench in the works Liquidstone who is a member here and a respected birder MFA's a MFD. You can't argue with success.

A few years ago another member stated that a company in Europe MFA'd long primes at something like 21 ft which would be similar to Liquidstone's approach. MFD for a 600mm F4 II is about 15 ft. I asked for the name of the company but this member never came back to any forums.

My initial complaint when MFA was introduced was it was all over the place. That latest document I linked to is the most comprehensive to date IMO.


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Jan 24, 2018 09:43 |  #43

Scrumhalf wrote in post #18547952 (external link)
As the pdf in the link DP posted suggests, the micro adjustment saturates after a certain distance, so the practical difference between 20X and 50X is negligible. So, you can actually do MFA your long telephoto in your backyard instead of looking for a parking lot.

Parking lots are also subject to atmospheric distortion. The further the target the more it can effect results.

http://arihazeghiphoto​graphy.com …ment-is-it-always-needed/ (external link)


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Jan 24, 2018 09:54 |  #44

digital paradise wrote in post #18547960 (external link)
Parking lots are also subject to atmospheric distortion. The further the target the more it can effect results.

http://arihazeghiphoto​graphy.com …ment-is-it-always-needed/ (external link)

Good point. I always try to do it early in the morning to minimize this very thing.


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Jan 24, 2018 10:16 |  #45

Scrumhalf wrote in post #18547967 (external link)
Good point. I always try to do it early in the morning to minimize this very thing.

Call me crazy but I may lose the indoor space that just makes the minimal FoCal distance for 560mm. If that day comes and I get a new longer lens I can rent a large photo studio downtown for 2 hours for $50. I'm already using daylight balanced studio CFL's to light my target so I'm set and ready to go.

The last time the developer of Dot Tune chatted at FM he said infinity gave him the best results. I was able to hit it but I couldn't repeat it. Too much wind, etc. Waiting for the right day or time is frustrating. I always get consistent results working indoors.


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