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11-28-2008, 02:28 PM   #16
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Whilst the 3300K and 4800K light sources are Panasonic highest grade high frequency desklamps which are specified to have 10,000 Hz of refresh rate, per second. So, they will not flicker at 50Hz afterall (and neither the tungsten as they are just like continuous light owing to the slow deaddown time, even they are 50Hz).[/QUOTE]

Panasonic isn't "highest grade" and "specifications" are just specifications.


If you research this just a little I think you'll find the visual flicker you mentioned isn't the issue.

.... more importantly, it's not sensible to confuse the issue by using any sort of fluorescent light since the notions being discussed are DAYLIGHT and TUNGSTEN, both of which abound globally.

"Tungsten" refers to the glowing filament in quartz or other incandescent lights.
Daylight...well, you know...

Why not use proper light sources? If you want an alternative to daylight, you've always got flash...and close focus flash isn't a challenge, given our technology.


Last edited by janosh; 11-28-2008 at 02:50 PM.
11-28-2008, 03:38 PM   #17
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"If you want an alternative to daylight, you've always got flash"

You can't focus using flash.
11-28-2008, 06:01 PM   #18
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QuoteOriginally posted by NorrisTudor Quote
Ok here is pics to show the case:

To me perfect. 1/3 front, 2/3 behind.

So still the question is will a colour correction filter change the situation. Not sure what to get to try this yet.
But the most important thing is, as I have told, a "45 degree" test won't tell you the truth.
11-28-2008, 06:07 PM   #19
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Huh?

QuoteOriginally posted by janosh Quote

Panasonic isn't "highest grade" and "specifications" are just specifications.
Well, do I mean Panasonic = highest grade?

QuoteQuote:
"Tungsten" refers to the glowing filament in quartz or other incandescent lights.
So, I did use real tungsten for the tungsten test, so?

QuoteQuote:
Why not use proper light sources? If you want an alternative to daylight, you've always got flash...and close focus flash isn't a challenge, given our technology.
And, you could properly change the light sources to "proper" ones each times our DSLRs would mis-focus before we shot! (whilst my film Pentax SLRs will have no problem!)

11-28-2008, 08:10 PM   #20
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QuoteOriginally posted by NorrisTudor Quote
"If you want an alternative to daylight, you've always got flash"

You can't focus using flash.
Try this one: Use an extremely bright tungsten source as in a 500w halogen. Let me know how that tests out.
One thing I've often wondered is the IR portion and AF since the dimmer the tungsten the more proportional IR you probably get. The AF module can focus w/ a visible light cut filter as far as I know. And IR focuses in a different plain. I suppose putting a hot mirror filter might work as well. Anyways try a bright tungsten source first...

In regards to color and the AF module, found this interesting:
That aside, in very low light situations, I often get more "keepers" without the filter, simply because an 80A has more than a 2 stop effect on an AF system (although the sensors do respond to red, green, or blue, the camera manufacturers don't typically filter them aggressively, so the red sensitivity is higher than the green or blue.
http://forums.dpreview.com/forums/read.asp?forum=1021&message=21655735

Last edited by jeffkrol; 11-29-2008 at 04:41 PM. Reason: Just adding a link
12-02-2008, 03:03 AM   #21
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QuoteOriginally posted by jeffkrol Quote
Try this one: Use an extremely bright tungsten source as in a 500w halogen. Let me know how that tests out.
One thing I've often wondered is the IR portion and AF since the dimmer the tungsten the more proportional IR you probably get. The AF module can focus w/ a visible light cut filter as far as I know. And IR focuses in a different plain. I suppose putting a hot mirror filter might work as well. Anyways try a bright tungsten source first...

In regards to color and the AF module, found this interesting:
That aside, in very low light situations, I often get more "keepers" without the filter, simply because an 80A has more than a 2 stop effect on an AF system (although the sensors do respond to red, green, or blue, the camera manufacturers don't typically filter them aggressively, so the red sensitivity is higher than the green or blue.
Would you believe...: Nikon D3 - D1 / D700 Forum: Digital Photography Review
I think I will try and get an IR filter and see if that does the trick.
12-02-2008, 12:54 PM   #22
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QuoteOriginally posted by NorrisTudor Quote
I think I will try and get an IR filter and see if that does the trick.
hot mirror filters are pricey I guess.......
58mm Hot Mirror Filter - 58SHM - Buy.com
http://www.enggadgets.com/Tiffen-62MM-SHM-Standard-Hot-Mirror-Screw-in-Infra...lection-Filter
12-02-2008, 02:01 PM   #23
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seen this which might be better...
Amazon.com: B + W 58mm UV/IR Blocking #486 Glass Filter for Blocking Ultra Violet and Infrared Radiation: Camera & Photo
(although the example photo is wrong - its using an IR pass filter)

problem is I don't really want to spend that kind of money on a test.

12-02-2008, 09:21 PM   #24
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QuoteOriginally posted by NorrisTudor Quote
seen this which might be better...
Amazon.com: B + W 58mm UV/IR Blocking #486 Glass Filter for Blocking Ultra Violet and Infrared Radiation: Camera & Photo
(although the example photo is wrong - its using an IR pass filter)

problem is I don't really want to spend that kind of money on a test.
Neither did I.
BTW: I doubt that, contrary to a few naysayers, this is a Pentax only problem:
I never heard of that before, but I just read this in the 50D preview. I wonder if all the Canon cameras have focusing problems in different light sources...

Interestingly, the 50D now includes the ability to detect the light source (including the color temperature and whether or not the light is pulsing), and then take these into account and microscopically shift the focus as necessary.

30D backfocusing under fluorescent light - FM Forums
OR:
50L back-focus and light dependent AF (boring technical :): Canon SLR Lens Talk Forum: Digital Photography Review
I should first stress that this is not about the focus-shift, it’s about back-focus (wide open), a kind of back-focus that Canon seems to have problems in detecting and fixing. My 50L is still back-focusing after three trips to service. It seems like other people have had a similar experience.

What I have observed with the cameras that I have tried (copies of 400D, 40D & 5D) is that their AF system focuses differently depending on the present light.

For example, the focus in incandescent light seem to commonly end up slightly in front of that obtained in daylight (and fluorescent light). It’s not much; but at f/1.2 it’s about half a DOF (at least for closer shots), so it becomes a real problem when added to the focus-shift.

Apparently it's primarily a camera body issue, but a crucial thing here is that whereas my 24L is apparently calibrated to produce best focus in daylight (and fluorescent light), my 50L is obviously giving best focus in incandescent light. The latter means that in daylight and fluorescent light (i.e. the majority of situations) it will back-focus.

Perhaps, this could at least partly explain why they seem to have such difficulty to find and fix this back-focus? They reportedly use a special light during calibration. Maybe some aberration in the 50L lens will “filter” this light differently than other lenses, resulting in a calibration that is more suitable for incandescent light than for daylight and fluorescent light…?
Comments are welcome. Regards, Bjorn

And on and on..........
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 ligh

Not that common that I know of. One nice canon tech explained - and demonstrated its effect to me in real time (tech lab has different lighting installed). Not sure about possible solution except perhaps using external flash as af assist, but I haven't tried this one yet.
XSi / 450D focus problem solved !!!: Canon EOS 1000D / 450D - 300D Forum: Digital Photography Review
http://forums.dpreview.com/forums/read.asp?forum=1031&message=6797351
Let's not leave sony out....
this oddity only happens with my room's tungsten ceiling light. with or without built in flash as long as the tungsten light is switched on, i'll get backfocus. This doesn't happen in daylight or when all the lights are off and i rely fully on the built-in flash. It's funny as with manual focus I can get sharp focus, and even though the assist lamp is on even in tungsten conditions, whatever the tungsten lighting is doing to confuse the AF is overriding the AF assist lamp.

I use spot focus and single shot AF. I've tried automatic too and I've chosen objects that big enough to fill the entire circular AF area and not just the tiny rectangle middle focus.

I'm not too bothered by this, I'm just wondering if anyone else has experienced this quirk............................ (new response next)
It is not really a case of low light. It is tungstung light, no matter how bright, that causes this.

Even with enough lamp light to hand hold the camera with a wide angle at 200 iso (for instance 1/60 at 2.8, no flash) there is a backfocus problem. Switching of the lights to make the AF assist lamp to come on solves the backfocus problem.
It seems to be more related to color temperature than to light levels.

Peter

http://forums.dpreview.com/forums/read.asp?forum=1037&message=29085885

Shhh... don't tell anyone that Canon and Sony does this as well. Of course this is all hearsay.......... someone may start a blog...
apparently this is the same sort of discussion in russian(?)
http://www.penta-club.ru/forum/index.php?showtopic=44847&hl=
https://www.pentaxforums.com/forums/pentax-dslr-discussion/36630-back-focus-myth-real.html

Last edited by jeffkrol; 12-02-2008 at 09:59 PM.
12-03-2008, 03:14 AM   #25
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I really appreciate your research.

Obviously Canon having the same issue, gives me some ammunition against my mate who has a 400d, and thinks I am just a geek with a problem camera. proven by my flickr as its covered in test charts.

More importantly though it just reassures me that the camera is solid, and there are no problems with it.

On the different light source question...I'm sure that if Canons have the same problem..an easy fix like an IR filter is not the solution.
12-03-2008, 07:33 AM   #26
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QuoteOriginally posted by NorrisTudor Quote
I really appreciate your research.

Obviously Canon having the same issue, gives me some ammunition against my mate who has a 400d, and thinks I am just a geek with a problem camera. proven by my flickr as its covered in test charts.

More importantly though it just reassures me that the camera is solid, and there are no problems with it.

On the different light source question...I'm sure that if Canons have the same problem..an easy fix like an IR filter is not the solution.
One of the interesting "rumors" out of all this is that Canon (and maybe others) actually measured the color temp and threw in an automatic "fudge factor" to correct for it. On a side note, sending the camera in for recalibration may just allow the techs to adjust for it a bit in a sort of compromise way. What I've learned is basically these systems are way more complicated then they appear on the surface and usually involve much more then hardware and simple control software.
12-03-2008, 08:35 AM   #27
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Wow you're right mine's front focusing too in tungsten light!

I tried out my K20D in the focusing chart here: Pentax DSLRs: PART-1. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35

(I prefer it to the one you used here)

So when I tried it out, I found all my lenses had to be adjusted about -9. So I did some tests on some objects in the room that had a flat plane and yes the shots were sharper with the -9 dialled in. But when I went to the other rooms here at home the shots were backfocusing!

I was really stumped and now I've read this it confirms it! The other rooms had flourescent lighting and the room I did the initial test is using tungsten lighting.

So I took some photos of photos (haha) on the walls (flat plane) in 1 room with tungsten and 1 with flourescent, shots with the focusing adjusted and shots with no adjustment. I used flash so I didn't need to kill camera shake.

So in the rooms with tungsten the adjustment had sharper shots and in the flourescent room having no adjustment yielded sharper shots.

This sucks. What should I do?

Can anyone else try it out?

Last edited by soccerjoe5; 12-03-2008 at 08:51 AM.
12-03-2008, 08:56 AM   #28
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Check dpreview under my sig and I was just tearing my hair out 2 years ago when i got the 50/1.4 and tried to use it indoors under tungsten.

Every knuckle headed fanboy argued it was somehow my fault then about 4,000 other members starting posting images with severe front focus using the 50/1.4.

What made it so infuriating was that outdoors it was fine so as a newbie I was utterly lost.
12-03-2008, 09:18 AM   #29
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Hmm I just had a thought: maybe my camera backfocuses with flourescent instead of frontfocuses with tungsten.

I'll try tomorrow morning (it's midnight here) with daylight.
12-03-2008, 11:45 AM   #30
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Now we just need someone with a 49mm IR Cut filter to test with and without to see if its the IR thats confusing the AF sensors.
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