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Melaka
12th June 2011, 02:54 PM
It being a wet day and not having anything better to do I thought I'd get out some long lenses and see if they are suffering from front or back focus. I was prompted partly by my own experience and partly by posts from other 300mm users.

I used the chart from here http://focustestchart.com/focus21.pdf not being keen on splashing out fifty quid for a more sophisiticated device. I mounted the lens on a tripod and put the diagram on the floor at a distance roughly equal to the height of the tripod, thus giving an angle of incidence of about 45 degrees. The centre of the diagram was just over 6ft away which meant that the 300mm and 90-250mm were close to minimum focus. Coupled with the use of f2.8 and with the 90-250mm at the long end it gave a very narrow DOF. This I found useful and on the whole had little difficulty in identifying the actual point of focus. I used centre spot auto focus. The focus check was done on the LCD screen which was fine with the E5 and E620 but not very good with the E3.

I didn't change the distance for the 35-100mm so even at full aperture and zoomed to the long end the DOF was relatively wide. That made checking focus more difficult. I also tried with the 50-200mm (with and without the EC14) but got no significant focus errors on either camera or on the E3 (which doesn't have AF adjust). The E3 gave back focus with the 90-250mm but was about right with the 300mm.

The 35-100mm and the 50-200mm are fitted with a filter but the two longer lenses are not. I didn't try the EC with the 35-100 since that seemed rather pointless in my circumstances.


With the E5 I found I had to make the following adjustments

300mm +9 I'd always had some concerns about focus with this lens so wasn't too surprised.

300mm with EC14 +0 Slightly surprised at that as it was with teleconverters that I thought I had the biggest problem.

300mm with EC20 +0 As above.

35-100mm +12 Wow, why should that be?

90-250mm -2 I've only just acquired this lens and have insufficient experience to know if this is realistic.

90-250mm with EC14 +0 As above.

90-250mm with EC20 +3 As above.


I then tried with the E620, the only other body I have that has AF adjust

300mm +0 Significantly different from the result with the E5.

300mm with EC14 -2 Closer to the E5 result.

300mm with EC20 +0 The same as the E5 result.

35-100mm +5 A lot but not as much as with the E5.

90-250mm -1 Not quite as much correction in these three results as with the E5.

90-250mm with EC14 -2

90-250mm with EC20 +0


I'd welcome observations from Ian and from others who have tried this exercise or done it with an E30. I note that the lens is registered with the camera by its serial number (as is the EC) but that the 90-250mm, despite having a serial number on it, showed s/n 00000.

I was interested that there are differences between the figures for the E5 and the E620. Presumbly this means that front or back focus is a function both of the camera and lens. I seem to recollect an earlier post where it was said that the 300mm could be adjusted to focus correctly with an E3 but might then not focus correctly with an EC attached.

I now need to see how the new settings work in the field.

peak4
12th June 2011, 07:39 PM
David, I've not got as far as making any E-620 or E-5 adjustments yet, but I have been playing this afternoon with a badly behaved 50-200mm.
In This post (http://e-group.uk.net/forum/showthread.php?p=120278#post120278) I mentioned that it was front focussing by about 10cm in 4m on a variety of bodies.

How do the + & - adjust numbers relate to actual distance in your experience?

Melaka
12th June 2011, 09:04 PM
Your post on the 50-200mm and your fine piece of kit were amongst the things that prompted me to do my test. I suspect my test kit is less sophisticated/accurate than yours and that my results may, in consequence, be less reliable. Time will tell. Depending on where the focus fell compared to the central line I either wound on or wound off a few notches of adjustment until I got what looked to be right. It was largely guesswork. Then I did another shot to check. In many cases I found that the texture of the paper, which came out very well with the better lenses, was a more reliable guide than the actual printed letters. The snag with my rig was that changing the setup to accommodate the shorter lenses would have meant altering both the tripod and the position of the test paper and I was too idle to do that. That's why I got a relatively deep DOF with the 35-100mm and the 50-200mm because they were well beyond the minimum focus distance. The key seems to be to keep the DOF, and hence the distance, as small as possible.

I tested both cameras on one lens and the ECs before changing to the next lens. Interestingly, but not surprisingly, when I changed from the E5 with HLD to the E620 without (I have one but it wasn't fitted) the whole rig tilted forward slightly with the changed weight and I had to adjust accordingly. I suppose the other lesson I learned (thank goodness!) was that when you pay top money for a top lens you get across the board quality even wide open whereas IQ falls off slightly even with the Pro series lenses. Certainly the IQ of the Pro lenses wide open did not compare favourably with that of the Top Pro. In particular the texture of the paper was much less discernible with the cheaper lenses.

peak4
12th June 2011, 09:16 PM
Thanks David, I don't think your method is any less accurate or reliable. It's just that I wanted something repeatable that doesn't blow about in the wind.
I have used the same pdf as you previously, but I printed it onto some sticky back polyester paper and mounted it on a rigid plastic panel. In retrospect, it probably wasn't the best choice, because, as you say, the grain of the paper can be quite useful.

I'll have another go before I send the lens off at a closer distance to minimise DOF even further. I'm sure I could use the adjustment on the E-5/620, but I still couldn't use the lens on other bodies for close up work in its current state.

Tordan58
12th June 2011, 10:30 PM
Hi,

Do you know how to transform mm to the scale available on the camera? (+/- 20, no unit specified).

Thanks,
Tord

Reprint of the E-620 user manual. p 105:
-------------------------
AF FOCUS ADJ.
You can use the AF sensor to fine-adjust the focusing position to a range of 20 steps
(: closer, +: toward )). Normally, there is no need to change this.
[SET AF DATA]
Fine-adjust the AF default value and register the setting. You can also register the
setting according to the lens.
[OFF]
AF focus adjustment is not performed.
[DEFAULT DATA]
Registers and applies all lens AF adjustment
values not registered individually.
[LENS DATA]
Fine-adjusts the AF for each lens. You
register the adjustment values for up to 20
lenses.

David M
12th June 2011, 11:11 PM
It's threads like this that remind me why I still haven't swapped my OMZ 350mm f2.8 for the ZD 300mm f2.8.

Melaka
13th June 2011, 08:37 AM
Hi,

Do you know how to transform mm to the scale available on the camera? (+/- 20, no unit specified).

Thanks,
Tord



I think it's roughly one notch per millimetre. I did it by trial and error. I adjusted a few notches in the right direction and then took another shot. It's easy enough on the E5 and E620 LCDs to see where the focus falls. No individual adjustment took more than five minutes. I saved each combination in the camera so, in theory, every time I fit that lens/EC I should get the right focus. Now the weather has cleared up I intend to go out and see if it works in real life.

Melaka
13th June 2011, 08:42 AM
It's threads like this that remind me why I still haven't swapped my OMZ 350mm f2.8 for the ZD 300mm f2.8.

The OMZ gives you some extra reach and I can see why you would want that. The cost/benefit analysis of switching to the 300mm would be a difficult issue in your circumstances. However you have to adjust the focus and aperture for every shot. If what I did yesterday is right it's a one off exercise that should last the life of the lens and camera.

Tordan58
13th June 2011, 09:01 AM
I think it's roughly one notch per millimetre. I did it by trial and error. I adjusted a few notches in the right direction and then took another shot. It's easy enough on the E5 and E620 LCDs to see where the focus falls. No individual adjustment took more than five minutes. I saved each combination in the camera so, in theory, every time I fit that lens/EC I should get the right focus. Now the weather has cleared up I intend to go out and see if it works in real life.
Thanks,

I plan to apply this test on my telephoto lenses and E620.
/Tord

Tordan58
13th June 2011, 10:46 AM
Hi

I read the document and the author recommends to have the calibration sheet fill the camera frame. (Not sure why he recommends that). Anyhow, as a modest contribution to this interesting topic I calculated the distance required from the camera sensor to the centre of the calibration sheet. It could be useful to know how much free space you need in front of the camera before rigging up the tripod.

The focal lengths are obtained from the portfolio of Olympus lenses, either as is or combining with the EC14/EC20. (I may have missed some combinations). To calibrate lenses with FL above 200 mm you will need a platform of some sort. Calibrating super telephoto

Distances below refer to horizontal and vertical (same distance since the test is performed at 45 degree angle).

Focal length / Distance to sheet for full frame (meters)
600 4,36
420 3,05
300 2,18
280 2,04
250 1,83
200 1,48
180 1,33
150 1,12
100 0,76
90 0,65
70 0,51
60 0,46
54 0,40
50 0,38
40 0,30
35 0,27
22 0,17
18 0,14
17 0,13
14 0,11
12 0,10
11 0,09
9 0,08
7 0,06

David M
15th June 2011, 09:30 AM
The OMZ gives you some extra reach and I can see why you would want that. The cost/benefit analysis of switching to the 300mm would be a difficult issue in your circumstances. However you have to adjust the focus and aperture for every shot. If what I did yesterday is right it's a one off exercise that should last the life of the lens and camera.

Having spent 30+ years focusing manually I don't have a problem with that and I very rarely change the aperture.

The other thing that makes me stay with the 350mm is all the complaints I see about using the EC20 with the ZD 300.

Who's_E
15th June 2011, 08:10 PM
Dad,

Just looking at this method of focus testing and I am sure you have covered the answer in the test but how do you tell whether you have the mid-point of your depth of field?

I can see how you can tell whether the focus is in the right ballpark but I am sure that there must be a depth of field here that is greater than the thickness of the paper. If you are adjusting the focus to start being sharp at the piece of the paper, then surely you run the risk of moving the depth of field point?

I know that you do a lot of bird photography and tend to select the eye as your focus point so wouldn't you want the depth of field to extend a bit in front of the bird to sharpen the bird's beak and a bit behind to cover the rest of it's head? Maybe the diagonal approach used by peak4 would be better for this adjustment.

I will call to talk about it tomorrow. And do a rain dance!

Nick

Tordan58
17th June 2011, 11:11 AM
Hi

I set up and conducted the test with 70-300, 50-200 SWD, EC14 and EC20. With a distance to target about two meters I used a focal length around 170mm to fill the frame vertically.

The target was secured by adhesive tape on the floor and I paid high attention in focusing on the central line using the camera centre focus point.

Before drawing conclusions by inspecting the sharpness of the mm scale using the LCD, I had a second look in Olympus Master 2. With a larger screen I noticed anomalies in the sharpness manifested as non-symmetrical sharpness L/R and also U/D. It varied somewhat from frame to frame.

Defective lens? No. The root cause is that the paper sheet had warped (as result of taping it). Not much, close inspection revelealed something like 2mm at most but that was enough to clearly bias the result.

Will have to redo the test...

Kiwi Paul
17th June 2011, 12:46 PM
Does the correction at close focus also apply at longer distances. For instance if you calibrate a lens at say 10 feet will it still need the same adjustment factor at say infinity?
I did calibrate all my lenses a while ago at a fixed distance (about 15 feet I think) and they do seem to work ok from close focus to infinity. But I don't think it's a given that the same correction can be used at all distances.
The only way I could think to calibrate at longer distances is to use a corrugated wall or picket fence with the camera on a tripod at about 45 deg to the wall or fence. Place a mark to focus on and adjust accordingly.

Paul

Tordan58
17th June 2011, 01:29 PM
Does the correction at close focus also apply at longer distances. For instance if you calibrate a lens at say 10 feet will it still need the same adjustment factor at say infinity?
I did calibrate all my lenses a while ago at a fixed distance (about 15 feet I think) and they do seem to work ok from close focus to infinity. But I don't think it's a given that the same correction can be used at all distances.
The only way I could think to calibrate at longer distances is to use a corrugated wall or picket fence with the camera on a tripod at about 45 deg to the wall or fence. Place a mark to focus on and adjust accordingly.

Paul

Hi Paul

This also struck my mind, actually. If that is true then it is bad, since the feature has a limited value...

What I also have been wondering about is if the method provides different results for different zoom levels. Can we rule out any correlation between focus and zoom level?

The calibration sheet is designed in such way that it should fill the frame. A zoom lens offers you a range of distances within which you can use the method and apply one notch compensation per mm out of focus. From practical point of view you would likely want to use distances in the order 1-2 meters, not 5 (unless you have access to a platform...) If you have a fixed focal length you have to resort to the distance specific for that lens.

/Tord

Kiwi Paul
17th June 2011, 01:37 PM
The E5 allows you to calibrate at minimum zoom and full zoom and it uses in between corrections for middle zoom ranges.

Paul

Melaka
20th June 2011, 09:29 AM
Now the weather is better I hope to get out to see if the adjustments I made are correct. For those interested in the methodology this link is useful http://fourthirdsphoto.com/images/E-30_AF_FOCUS_ADJ_Instructions_EN.pdf

Wreckdiver
20th June 2011, 09:41 AM
Thanks for the link David, very well timed as I was just about to calibrate my E-30 *chr

Steve

Melaka
20th June 2011, 10:06 AM
Please let us know how you get on.

PeterD
20th June 2011, 11:52 AM
Hi Paul

This also struck my mind, actually. If that is true then it is bad, since the feature has a limited value...

What I also have been wondering about is if the method provides different results for different zoom levels. Can we rule out any correlation between focus and zoom level?

The calibration sheet is designed in such way that it should fill the frame. A zoom lens offers you a range of distances within which you can use the method and apply one notch compensation per mm out of focus. From practical point of view you would likely want to use distances in the order 1-2 meters, not 5 (unless you have access to a platform...) If you have a fixed focal length you have to resort to the distance specific for that lens.

/Tord

Thinking about this issue.... The offsets being made are to the original factory offsets before the camera is released for sale. If there is an issue in setting up with a given focal distance and/or zoom then this would likely be accounted for in a lookup table within the firmware. If this is the case then, this lookup table would still be used after you put in your offsets. In this case, we could still optimise everything if we knew the factory set-up conditions.

Ian
20th June 2011, 12:02 PM
I haven't yet found the need for critical focus adjustment on any of the lenses I use. It may simply be that a) I'm not that demanding! or b) I'm lucky and my style of photography doesn't depend on critical focus.

Ian

CallaWolf
20th June 2011, 01:26 PM
The E5 allows you to calibrate at minimum zoom and full zoom and it uses in between corrections for middle zoom ranges.

Paul

Paul

Does the E5 record 2 settings per lens, to correspond with minimum & full zoom?

I've done some half-hearted calibration work and I know I need to bite the bullet and do it sometime soon.

Wreckdiver
22nd July 2011, 03:57 PM
Finally got around to check the AF performance of my E-30 and the Sigma 150mm f/2.8 macro lens.

Took 41 shots at all AF adjust values from -20 through 0 to +20 to get an idea of the range of the focus adjustments and to see where the lies was optimum. Well, I looked and looked ...... and looked again at all the shots and could I see any difference between any of them? Even comparing the -20 and +20 I could not detect the slightest difference in focus. I have rechecked just to make sure I was actually viewing two different shots on the computer screen.

Surely you would expect to see SOME difference :confused:

Steve

Tordan58
25th July 2011, 08:31 AM
Finally got around to check the AF performance of my E-30 and the Sigma 150mm f/2.8 macro lens.

Took 41 shots at all AF adjust values from -20 through 0 to +20 to get an idea of the range of the focus adjustments and to see where the lies was optimum. Well, I looked and looked ...... and looked again at all the shots and could I see any difference between any of them? Even comparing the -20 and +20 I could not detect the slightest difference in focus. I have rechecked just to make sure I was actually viewing two different shots on the computer screen.

Surely you would expect to see SOME difference :confused:

Steve
Hi Steve,

It may be a long shot - could it be that AF Focus adjust is not supported for third party lenses?

/Tord

Wreckdiver
25th July 2011, 08:38 AM
Hi Tord,

The Sigma 150mm lens is recognised by camera and shows up on the cameras display during calibration. There are several people on this forum who have calibrated this lens successfully.

Steve