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05-21-2017, 10:40 AM   #16
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QuoteOriginally posted by pschlute Quote
You should increase the distance from camera to chart as you use a longer lens. The important thing is to have the spot focus point cover the "focus here" point exactly.

Looking at your Flickr pictures at 100% I can see:

The 21mm failed to achieve focus at all. You need to redo the tests.

The 50mm is still exhibitting slight backfocus

The 100mm is exhibitting very very slight backfocus, not that you would notice it in practice.

The important thing about this test is that you are able to do say 10 tests with the same lens and get a good percentage at correct focus (not front or back focus). You will not get 10 correct ones....autofocus is not that good ! Only use widest aperture, there is no point in stopping down. + adjustment corrects backfocus
Thanks for the feedback, will try some more later today.

So, here i have a 100% zoom on the 50mm, which as you say is slight backfocus, is this because the 20mm (circled green) is more in focus/sharper than the 20mm circled red which is obviously softer?


This results in the term 'backfocus' and if things were the other way around it would be termed frontfocus? If I'm suffering from backfocusing which direction should i tinker the adjustment in the AF Fine Tuning? + or -?

Please note, I realise I have not conducted this test properly yet, I am simply reaching out for advice as I am setting up and conducting, no tinkering of the AF has taken place yet!

It's interesting that you say the 21mm didn't manage to focus at all, because obviously I did 'focus' the 21mm on the tripod using the spot centre focus point (red box comes up, grid flashes red to say 'yep... in focus' etc), this is the result it gives, an out of focus shot (as you point out). This is not a one off, at 3.2 this is a very typical shot I derive from the 21mm. What gives?

So, later today I shall conduct more tests with different distances from camera to sheet with the appropriate lens etc. What should I be aiming for, each lens when taking the picture has the chart pretty taking up most of the frame? Like perhaps there is a small gap visible between the top and bottom of the chart on the viewfinder? (but obviously not focusing via the viewfinder)

Cheers,

Bruce

05-21-2017, 01:52 PM   #17
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Yes it is backfocussing and you can make a + adjustment to correct it. I can actually see the 6/10/14 and the 20mm marker points clearer behind the focus point too. You are aiming once adjusted for the sharpest point to be the "focus here" point and for each set of numbers behind and in front to be equally less sharp.

For the 21 mm how far is the camera from the test chart? Can it never focus ? Use a distance so that the centre AF spot is going to be able to pick up the black line easily. In your example i think you are too far away with the 21mm

You say "but obviously not focusing via the viewfinder". What do you mean ? i hope you are not using Live view for these tests?
05-21-2017, 02:20 PM   #18
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QuoteOriginally posted by pschlute Quote
Yes it is backfocussing and you can make a + adjustment to correct it. I can actually see the 6/10/14 and the 20mm marker points clearer behind the focus point too. You are aiming once adjusted for the sharpest point to be the "focus here" point and for each set of numbers behind and in front to be equally less sharp.
Gotcha

QuoteOriginally posted by pschlute Quote
For the 21 mm how far is the camera from the test chart?
So, initially i set the sheet on the table, 45 degree angle and then placed the tripod on the floor and mounted the K-1 and then swapped all 3 lenses one at a time with the same distance to the sheet (never moving the tripod or sheet closer), The camera isn't mounted currently to the tripod but I have just taken a measuring tape and measured the distance from the Arca swiss plate on the tripod to the black focus line of the focus sheet and it's 95cm in distance (so a little less than that once the k-1 and a lens is mounted).

QuoteOriginally posted by pschlute Quote
Can it never focus ?
It always says it has focused (ie gives the feedback that every other lens gives when in AF mode, ie the whirring of the lens as it tries to focus on the spot area yer aiming at, and then the red box blinks red as does the grid lines around it etc. Usually when i hear the words 'can it never focus' that's more like the lens whirrs back and forth struggling entirely to capture what yer focusing on (such as the 100mm does occasionally in tricky situations) and never gives a redbox or red gridlines to tell you it's successfully locked on, this definitely isn't the case here. It's just at it's widest (3.2) it (the DA21) does a horrible job imo (as you can see from that sample), increasing to say f8 and it becomes a lot more acceptable. I shall try to also demonstrate this difference later on today, this is one of the reasons I created this thread in the first place, I find the DA21 to be almost useless at it's wider settings, really it feels like this is a f8 lens and upwards which then becomes a pretty darn expensive prime for such a limited aperture :/

QuoteOriginally posted by pschlute Quote
Use a distance so that the centre AF spot is going to be able to pick up the black line easily. In your example i think you are too far away with the 21mm

You say "but obviously not focusing via the viewfinder". What do you mean ? i hope you are not using Live view for these tests?
Yeah nah of course not, i simply meant that if checking the framing/distance and whatnot to the focus sheet with the viewfinder, should I be aiming to have the distance of such with each lens that the focus sheet top to bottom (of the piece of paper) almost touches the edge of the viewfinder screen (not physically touching, perspective wise)? (but then of course switching to optical view and using spot centre focus point to focus on the black line). Sorry i just explain myself terrible bad

I think I could move the sheet or tripod a lot closer to the focus sheet for the DA21mm as it has a pretty decent close focus distance. In my examples above it looks like perhaps the FDA100mm is shot too close to the focus sheet and the DA 50mm a tad too far away, and obviously the DA21mm far far too far away.
I have a small job or two to do this morning but will definitely upload more examples in the next 12hrs
05-21-2017, 02:45 PM   #19
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For distance between camera and chart aim for about 50 times the focal length...so for the 21mm you are about right. Even at f3.2 it must be in focus somewhere.

05-22-2017, 12:39 AM   #20
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Alrighty... whose up for geeking out over some amateur Focus Sheets! YAY!...

I added the dng files to LR and exported them as jpgs, other than this absolutely no post processing, and then zipped up to rar files and have placed them below in case anyone would actually like to see the set of series of pics;

100mm 2.8

50mm 1.7

21mm 3.2


For anyone with bad net and too lazy to dl the pack (understandable, I am super lazy and have super awful net speeds), please find below an example crop from each set which actually represents quite an accurate finding among the rest of the shots in the set;

100mm 2.8, cropped to 1:2 in LR


50mm 1.8, cropped to 1:2 in LR


21mm 3.2, cropped to 1:2 in LR


Cropping in LR to 100% (or any specific %) is annoying as hell! There seems to be no way to actually do it. I just tried cropping and then toggled the 1:2 view and kept cropping till it didn't really toggle much at all... I also decided cropping to 1:2 was easier to see the results that 1:1.

Ok, so this time, before just rushing and doing my own thing I actually read the pdf file that had the focus sheet provided earlier (it's amazing what answers are given to all my questions had I just bothered to READ the preceeding pages to the focus sheet... sigh).

1) I couldn't put the paper flat and arch my tripod down to 45 degrees as I wasn't sure how I could manage that feat accurately. Instead I folded a piece of A4 paper to create a 45 degree angle and then used that as a rough guide to help angle the focus sheet mounted to cardboard and propped up to a similar angle.

2) I then followed the advice given and tried to fill the focus sheet to frame, shooting 50x the focal length seemed WAY to far away from the sheet to accurately critique. Your thoughts?

3) The distance varied for each lense type, the 50mm 1.8 essentially as close as it could be before not being able to focus properly, and the 21mm 3.2 pretty much as close to the sheet as possible with tripod legs touching the table on which the sheet was standing on (hence it's a little further away than the other two shots).

4) I used a 2 sec timer, Av mode, shot at widest aperture for each lens, shot around 9-10 times each lens, and between each shot stuck my hand between the lens and sheet to give it something else to focus on before having to refocus itself for the focus sheet.


From the results I conclude the following;

1) The 100mm is slightly back focusing, it's probably acceptable but I am going to try adjusting the AF Finetune by a few and retry
2) The 50mm is bang on, I can't see either values above or below more or less blurry than one another, the only thing is perhaps the focus is 'too close', I may try again with a couple inches back incase it was struggling to get a good focus on the sheet.
3) The 21mm is back focusing the worst, the 20mm and 30mm marks are quite different entirely as well as the above text being legible and the bottom barely! This may very well be the issue I've been having since day one with the 21mm, magnified and made worse when being used in hand and not in timer mode and tripod (ie compounded by operator error). I think this lens may need adjustment the most, or sold on and put down to not being very compatible with the K-1...

Do my findings sound about right?
05-22-2017, 04:49 AM   #21
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Sounds spot on. One suggestion...put a couple of rulers or something similar on the paper so that the test sheet is as flat as you can get it.
05-27-2017, 01:08 AM   #22
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Thought I'd leave some feedback here.
So after spending quite a while trying to fine tune my lenses after using the focus sheet set up in the manner I have mentioned previously, I have come to the conclusion that my setup is inadequate for such a test.
Even making adjustments with a lens (say +7), then moving the tripod back a few inches, and then trying again, I found that +7 was no longer suitable, that essentially any adjustment I made was suitable for that lens at that exact distance to the sheet, moving the camera back and resetting things up again made the adjustments either not required or of a different value.
This was confirmed more in the field, I have now reset all values to 0.

I either need to get the focus sheet stuck absolutely flat down on a level table (no air bubbles) and then figure out a way to have my camera pointing down exactly level and 45 degrees... or perhaps come up with another method of proping the focus sheet at a 45 degree angle. I noticed you can buy plastic kinda ones etc.
Because at this point in time, im not sure if focus sheets are a bit of a nonsense, because the distance between the camera and the sheet actually gives different tweaks necessary, or if that is a result of my bad testing (more likely). It could also be that K-1 + AF is just not that good, perhaps I'm better at really using manual focus as much as possible...
05-28-2017, 02:03 AM   #23
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To be honest either your camera is broken or your tecnique is incorrect. I have calibrated all my lenses with the K1 and they work fine at all focussing distances.

Are you setting the AF fine adjustment for individual lenses or using the global adjustment ?

And yes the paper needs to be flat, how can you expect correct results otherwise? Have the camera level and the chart propped up at 45 degrees.


ps... Are you using USER modes at all when testing/calibrating ?

05-28-2017, 02:51 AM   #24
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QuoteOriginally posted by pschlute Quote
To be honest either your camera is broken or your tecnique is incorrect. I have calibrated all my lenses with the K1 and they work fine at all focussing distances.

Are you setting the AF fine adjustment for individual lenses or using the global adjustment ?

And yes the paper needs to be flat, how can you expect correct results otherwise? Have the camera level and the chart propped up at 45 degrees.


ps... Are you using USER modes at all when testing/calibrating ?
No to user modes, just manual, or aperture priority (so that i can set the aperture wide ok shutter speed (even tho im obviously tripodding) and auto iso (tho obviosuly not wanting anything past 1600 etc).

AF Fine adjustments for individual confirmed, no to global.

I think the camera is fine, this is purely error/technique at fault. I just meant to say that getting the paper FLAT on a piece of cardboard (which also may not be purely flat but have a slight bend in it) is difficult to obtain, I tried twice with two printouts and I could still see a bubble pop up etc, or that when looking on the left and right side of the focus sheet the focus was not equal (which suggests a bad set up).

So we have;

1) printout (focus sheet) is difficult to obtain perfectly flat mounted onto something like cardboard (I'll have to try something else next time like a binder, just didn't have one lying around). Whatever it needs it has to be also level and not one side dipping more than the other, this also factored in when propped up.

2) Even if you manage to get the paper perfectly flat onto the harder backing, it then needs to be orientated 45 degrees on both sides, that can also be tricky to manage (ie not squint), as this was I'm sure why on one side the focus was different to the other side slightly, which side to you go by etc? Neither in this case because you need both sides to be exactly the same focus, even if they are fwd or back focusing.

3) mounting the camera on the tripod and getting level and trying your best to aim the spot centre focus point at the centre of the focus sheet is incredibly hard, you might have the air bubbles of the tripod guage as perfect as possible, and the camera sensor telling you everything is straight and perfect, but again its still hard, and even if slightly off (or a combination of this point and point number 2) means things aren't focusing on each side equally on the chart

4) In theory perhaps making the focus adjustment at one range of distance should be enough, but the fact that you try and do it all over again from a few inches back with different results just proves how inaccurate and untrustworthy this process is (imo).

5) I even noticed that when I was taking my EYE to the optical viewfinder, depending upon how and what angle I came at to the optical viewfinder gave a different perspective as to whether I felt I had the centre focus point directly on the 'Focus Here' center point of the focus sheet, or slightly above or below! It really feels as tho I'd need a laser guidance (no joke) so that you actually make sure the centre focus IS on the centre of the sheet and not slightly above or below, because at such wide apertures it makes a big difference!



In summary, I'm not saying this is a complete waste of time, I am saying it needs incredible time and patience to set things up right, which I am not convinced as of yet instructions that meet my satisfaction. I shall indeed investigate this matter more.
05-28-2017, 05:32 AM   #25
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This is what I do.........

get the focus chart on a sheet of metal and use two magnetic rulers to hold it in place. Then I use a kitchen cookery book stand to hold it at an angle, it does not have to be exactly 45 degrees. But you can prop up a large hardback book and place a couple of plastic or wooden rulers to hold it flat. If you have taken it direct from your printer there won't be any unevenness in the paper.

Level the camera on the tripod using the cameras level tools. You will then be able to see if your chart is aligned properly by looking at the corners through the viewfinder.

Then position the tripod so that the "focus here" point is in the centre of the viewfinder, dont look for the focus confirmation red square....the AF sensor point is bigger than that.

Now do the test procedures.
05-28-2017, 12:53 PM   #26
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QuoteOriginally posted by pschlute Quote
This is what I do.........

get the focus chart on a sheet of metal and use two magnetic rulers to hold it in place. Then I use a kitchen cookery book stand to hold it at an angle, it does not have to be exactly 45 degrees. But you can prop up a large hardback book and place a couple of plastic or wooden rulers to hold it flat. If you have taken it direct from your printer there won't be any unevenness in the paper.

Level the camera on the tripod using the cameras level tools. You will then be able to see if your chart is aligned properly by looking at the corners through the viewfinder.

Then position the tripod so that the "focus here" point is in the centre of the viewfinder, dont look for the focus confirmation red square....the AF sensor point is bigger than that.

Now do the test procedures.
Thanks Peter, good advice, I do have magnetics lying around, I like that idea. I shall attempt to repeat the tests again later on in the week.
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