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12-18-2008, 10:54 PM   #1
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Front Focus - could it be this bad???

I just did the angled chart test:

Nikon D70 Focus Chart

to my shock, I was front focusing badly.
DA* 50-135 is -6
DA* 16-50 is -10
FA 50 1.4 is -10

Again, this really is a shocker since I've gotten tack sharp photos from the 50-135 adn the 50 1.4 in the past.

These were all done in tungsten lighting with flash. I really need a -12 on the 16-50.

I then tested against a bookshelf in the same room. To my shock, these severe focus corrections yielded the sharpest pics. I'm stunned.

Should I risk sending the camera body in after the holidays? I'm concerned it will come back with more issues.

12-18-2008, 11:09 PM   #2
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QuoteOriginally posted by laissezfaire Quote
These were all done in tungsten lighting with flash. I really need a -12 on the 16-50.
Tungsten lighting always causes FF. If you adjust for that, you may start getting BF in better light.
12-19-2008, 06:46 AM   #3
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You've missed the key words..

QuoteOriginally posted by Marc Sabatella Quote
Tungsten lighting always causes FF. If you adjust for that, you may start getting BF in better light.
Tungsten lighting always causes Front Focusing for Pentax DSLRs. if you adjust for that with Pentax DSLRs, you will start getting Back Focusing in Daylight.
12-19-2008, 06:59 AM   #4
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-6, -10, this is nothing.

On one of my bodies I needed +130 for one lens, +30 on another and -40 on the third one.

12-19-2008, 07:12 PM   #5
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QuoteOriginally posted by awo425 Quote
-6, -10, this is nothing.

On one of my bodies I needed +130 for one lens, +30 on another and -40 on the third one.

How do you get such extreme adjustments? mine only goes up to +/- 10

Ok, so I read all of the posts, it appears to be a tungsten light issue, so what are we to do if half of our pics are in tungsten lighting?
12-19-2008, 07:32 PM   #6
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QuoteOriginally posted by laissezfaire Quote
Ok, so I read all of the posts, it appears to be a tungsten light issue, so what are we to do if half of our pics are in tungsten lighting?
The actual *amount* of the tungsten-induced FF isn't normally enough to take a subject that was in focus and throw it completely out of focus, although it might be enough to move the main focus from the eyes to the nose if you are shooting a very large aperture with a very small DOF. But when dealing with DOF that thin and trying to place focus that precisely, you pretty much need manual focus anyhow.

At apertures of, say, f/2.8 or smaller, you won't notice the difference. Mostly, it's something that affects focus test charts but not the real world.
12-19-2008, 08:32 PM   #7
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QuoteOriginally posted by laissezfaire Quote
How do you get such extreme adjustments? mine only goes up to +/- 10

Ok, so I read all of the posts, it appears to be a tungsten light issue, so what are we to do if half of our pics are in tungsten lighting?
Those high numbers are from the K10D debug mode. The K20D has +/- 10 as you say.
12-19-2008, 08:54 PM   #8
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QuoteOriginally posted by Marc Sabatella Quote
Tungsten lighting always causes FF. If you adjust for that, you may start getting BF in better light.

yes, but the only time I'm using large apertures (f/1.4 - 2.8) is in tungsten lit indoor situations. outdoors, I'm at f/8+, if possible, and unless I'm wrong, FF or BF is not a problem at those small apertures.

Given my use of the camera, I think I'll correct at tungsten and live with the backfocus outdoors.

What do you think?

12-19-2008, 11:23 PM   #9
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I think with a response like that RH just confirmed his nomination in the New Year Awards thread.
What IS your problem RH
12-19-2008, 11:46 PM   #10
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QuoteOriginally posted by Marc Sabatella Quote
Tungsten lighting always causes FF. If you adjust for that, you may start getting BF in better light.
Hmm... this has me thinking... I sometimes do shoots in tungsten lighted areas. If my AF is confused, does that mean I need to manual focus? or...?

I sometimes get back focus on my DA*16-50, but usually more on complex items (completely black case with a reflective surface, etc.)
12-20-2008, 05:21 AM   #11
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QuoteOriginally posted by RiceHigh Quote
Tungsten lighting always causes Front Focusing for Pentax DSLRs. if you adjust for that with Pentax DSLRs, you will start getting Back Focusing in Daylight.
What does this statement imply to you?

Cutting-Edge Autofocus. High performance with 3.9 fps continuous shooting, new shutter with a durability of 150,000 cycles and improved weather-resistant body.

The EOS 5D Mark II has a sophisticated AF system consisting of 9 user-selectable AF points, along with a total of 6 additional vertical and horizontal AF assist points. The central AF point is cross-type, and is sensitive to vertical lines at an aperture of f/2.8, horizontal lines at f/5.6. The AF system is also sensitive to its light source, and can compensate for focus errors that can occur when multiple sources illuminate a scene. AF points can be chosen by the photographer using the 5D's multi-controller or preferred control dial. Plus, the EOS 5D features a dedicated AF ON button.

The EOS 5D Mark II has a rugged new shutter designed to withstand 150,000 exposures. Combined with its impressive build quality, this new shutter ensures that the EOS 5D Mark II will thrive in challenging shooting environments.

Canon EOS DSLR Digital Cameras - 5D Mark II 50D XS XSi XTi XT 5D 40D 1Ds Mark III 1D Mark-III EOS 3 EOS 1V - Vistek Calgary Toronto Edmonton Mississauga Ottawa
Now as to other systems:
Sony/Minolta seems to have it as well...
Yes, colour of light does affect results, Minolta/Sony used a calibrated source supposedly round 5800K with minimal spectrum spikes. The cameras will generally backfocus in tungsten light or when aimed at red targets, and front focus if aimed at a blue pattern (or used in blue light, which is not common).
http://www.photoclubalpha.com/forum/viewtopic.php?f=27&t=561&p=2309&hilit=tungsten#p2309

Last edited by jeffkrol; 12-20-2008 at 06:27 AM.
12-20-2008, 10:45 AM   #12
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QuoteOriginally posted by jeffkrol Quote
What does this statement imply to you?
that instead of watching porn, RH uses 5D advertisements to assist in his "endeavors"?
12-20-2008, 01:09 PM   #13
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Even more fun with light and AF

This time UV or ?????
Mr. Borg results w/ a Canon 1D MkII and long lenses.



Re: Now that is just weird...: Open Talk Forum: Digital Photography Review




I use regular slim MRC Schneider 010 type. The experiment was quite simple: a resolution target lit by sun, 50 shots AF on with filter, 50 shots AF on without filter. Lens was focused to infinity manually between shots. Resolution was consistently higher on the shots with the filter. Shots without filter exhibited slightly erratic focus behaviour, with 20% of shots being 8% lower resolution and 40% being 4% less resolution then the shots with the filter on. Only 10% of shots without the filter were of the same resolution then the peak resolution obtained with the filter. 70% of shots with the filter achieved maximum resolution; 20% of shots with the filter were 4% less then maximum resolution, 10% of shots with the filter were 8% less them maximum resolution. On the contrary, 10% of the shots without the filter resolved 30% less then maximum.

I hesitate to attribute this to the effect of UV on the AF system. I started with a hot mirror because the reports were that AF misses were mostly under hot outdoor conditions. Getting better AF behaviour with hot mirror I decided to recheck with a simple UV blocking filter, and it turned out AF improvement with UV filter was nearly the same as with hot mirror filter. My colleague used a Tiffen clear glass filter on his Canon camera with the same AF improvement results.


One more for our resident troll...........
http://forums.dpreview.com/forums/read.asp?forum=1031&message=29245803
Well at least for me the mystery is solved... it's all about the light.

I have both an XTi and XSi and for a long time had been unhappy with inconsistent focusing (mostly only using primes at wide aperture). From both real life shooting and AF test charts, it seemed at first that the XTi was pretty good (although inconsistent) and the XSi was front focussing pretty badly.

Then on another day it seemed that the XSi was absolutely perfect and the XTi was backfocussing. I couldn't figure it out and assumed I was doing something wrong or it was just the limits of the AF system.

But then I figured it out.... it was the light! Not the amount of light, but the TYPE of light. My shooting had been mostly indoors under incandescent light and this massively affects the Canon AF system. For me it's 100% reproducable. There is no question that my XSi is absolutely bang-on perfect in daylight, but front-focuses under incandescent light. (Note I'm only talking cm, but with primes at wide apertures, this is all the difference!)

The lightwaves from the incandesent light globes in my house cause the AF to front focus way more. Maybe some globes are worse than others. Note I'm not saying your camera will front focus under this light, but it will front focus more than in natural daylight. Especially if the incandescent light is quite intense. So you could have a perfectly focusing camera under incandescent light which will then back-focus slightly in daylight (which was my XTi).

Sorry about the rant if this was already obvious, but I've never seen this mentioned before.

For those struggling with AF and doing all those lens chart tests, I highly recommend doing all your tests in daylight. (or at least doing a comparison)
Is this common knowledge? Am I way off the mark? Is there a solution?
...............
I am using Canon primes wide open: 35L, 50 1.4, 85 1.8.

At distances less than 10m there isn't much DOF wide open, so I notice the difference. I guess if you're shooting at F4 or above you'll never see it.

I have even tried with all the lights turned on, so it's fairly bright and still the same result. Of course I can't get it as bright as during the day, but certainly not dim.

For example at a distance of about 4m, the 85-1.8 nails it in daylight. Perhaps 1-2cm or so forward if I wanted to be really picky. Still good enough to be tack sharp.

But under indoor light it's sometimes about 10cm forward. That's too much to be sharply in focus at F1.8.

Last edited by jeffkrol; 12-20-2008 at 05:48 PM.
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