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What does 2mm backfocus mean?!

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Csaba Ónody

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Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on 50/1.8 what would that mean in the photos? Is it a visible backfocus on portrait photo? What would that mean on a telephoto (70-300) lens.

Thanks and regards,

Csaba
 
Hello,

When you're talking about a few mm of front/backfocus, it really doesn't mean anything. Especially with a lens such as the 50mm 1.8, even the slightest backfocus will be visible in the test charts and still not affect your real life shots. My 50mm 1.8 has 25 mm frontfocus on my D70 - verified on test charts - but I cannot see any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
 
Hello,

This is what 25mm frontfocus looks like in real life:



50mm 1.8, 1/40 sec, f/5. In-camera sharpening set to Normal, resized for web, slight USM applied to compensate loss of details in the resizing process.

Regards
Thomas
Mimoid said:
When you're talking about a few mm of front/backfocus, it really
doesn't mean anything. Especially with a lens such as the 50mm 1.8,
even the slightest backfocus will be visible in the test charts and
still not affect your real life shots. My 50mm 1.8 has 25 mm
frontfocus on my D70 - verified on test charts - but I cannot see
any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
Click to expand...
 
I have a 50 1.4 which frontfocuses as well.

Using apertures larger than 2.8, focusing for head shots is a hit&miss affair but is OK with smaller apertures. Just need to know the strengths and weaknesses of each lens.
Mimoid said:
This is what 25mm frontfocus looks like in real life:



50mm 1.8, 1/40 sec, f/5. In-camera sharpening set to Normal,
resized for web, slight USM applied to compensate loss of details
in the resizing process.

Regards
Thomas
Mimoid said:
When you're talking about a few mm of front/backfocus, it really
doesn't mean anything. Especially with a lens such as the 50mm 1.8,
even the slightest backfocus will be visible in the test charts and
still not affect your real life shots. My 50mm 1.8 has 25 mm
frontfocus on my D70 - verified on test charts - but I cannot see
any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
Click to expand...
Click to expand...
 
Hi,

Do you really? The Nikon tech center rep told me that they had never encountered focus errors with a prime before.

My D70 has been calibrated twice now and focuses perfectly with every other lens - except my 50mm 1.8. Still, I am not too sure I would care having the lens sent in for exchange, I have yet have to find one shot ruined by this frontfocus. At f/2 or f/2.2, the DOF is so narrow that even the slightest movement of my subject will shift the focal plane a lot more than the focus error.

Regards
Thomas
Buckrogers said:
I have a 50 1.4 which frontfocuses as well.
Click to expand...
 
Cute Kid, your son ?
Mimoid said:
This is what 25mm frontfocus looks like in real life:



50mm 1.8, 1/40 sec, f/5. In-camera sharpening set to Normal,
resized for web, slight USM applied to compensate loss of details
in the resizing process.

Regards
Thomas
Mimoid said:
When you're talking about a few mm of front/backfocus, it really
doesn't mean anything. Especially with a lens such as the 50mm 1.8,
even the slightest backfocus will be visible in the test charts and
still not affect your real life shots. My 50mm 1.8 has 25 mm
frontfocus on my D70 - verified on test charts - but I cannot see
any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
Click to expand...
Click to expand...
 
I have not detected any focusing errors on my Nikkor 18-70, Tamron 28-300, Nikkor 70-300G. But on a test set-up with the 50 1.4, the focal plane is around 5mm in front.

In real-life shooting, any of the acceptably sharp 1.4 pics are probably due to "errors".

I cannot say for certain that my camera only front-focuses with the 50 - it is possible that the deeper DOF with the other lenses can cover-up any inaccuracies.
Mimoid said:
Do you really? The Nikon tech center rep told me that they had
never encountered focus errors with a prime before.

My D70 has been calibrated twice now and focuses perfectly with
every other lens - except my 50mm 1.8. Still, I am not too sure I
would care having the lens sent in for exchange, I have yet have to
find one shot ruined by this frontfocus. At f/2 or f/2.2, the DOF
is so narrow that even the slightest movement of my subject will
shift the focal plane a lot more than the focus error.

Regards
Thomas
Buckrogers said:
I have a 50 1.4 which frontfocuses as well.
Click to expand...
Click to expand...
 
Hi,

Thank you! My 1 yo daughter actually - nowadays the only person not running away screaming whenever I come around with my D70.

"I was athinkin', maybe we should get that 85mm 1.4 to be able to keep filling the family album with shots like this......"

Hm, I'll have to keep practising on this phrase.

;)

Regards
Thomas
 
Thanks a lot it is goods news. I realized on the test charts that I have 1-2mm front focus on 50/1.8 and same amount but backfocus on the kit lens. That made me dissappointed but as it looks everybody has a slight front or back focus on either of lens and 2mm is not as huge as I expected.

Thanks for your reply and congratulations to your lovely daughter
Mimoid said:
When you're talking about a few mm of front/backfocus, it really
doesn't mean anything. Especially with a lens such as the 50mm 1.8,
even the slightest backfocus will be visible in the test charts and
still not affect your real life shots. My 50mm 1.8 has 25 mm
frontfocus on my D70 - verified on test charts - but I cannot see
any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
Click to expand...
 
Mimoid said:
Hi,

Thank you! My 1 yo daughter actually - nowadays the only person not
running away screaming whenever I come around with my D70.

"I was athinkin', maybe we should get that 85mm 1.4 to be able to
keep filling the family album with shots like this......"

Hm, I'll have to keep practising on this phrase.

;)

Regards
Thomas
Click to expand...
 
My story: Had 3cm/5mm@24/120 backfocus with 24-120 VR . Enough to get blurred focus at wide open, acceptable when stopped down to f8-f11. OK with 70-300 ED. OK with cheapo 28-80 G. Sent to Nikon UK, it took a month, ("not a pro camera") bless them, but it's fine now. They adjusted both the lens and body for focus. 70-300 and the other one still OK. While the camera in service I found a 50/1.4 non-D secondhand. Surprise surprise (is there a pattern?) it has 5mm frontfocus@50cm At f1.4 DOF ±3mm , so forget close-ups at wide open . DOF rises with distance but so does the frontfocus. Here I have a photo with the 50/1.4@f2. I focused on the face and its OK but the hands are the sharpest . The pic is unprocessed BTW with no in-camera sharpening. Actually I like it more this way but the fact is I didn't focus on the hands but the face.

The thing is it all depends on your expectations. For a pro 1-2mm back/front focus with a pro lens would be unacceptable. Cue Ken Rockwell. Us mortals, we stop down.

 
Hello,

Actually, your photo is brilliant, I particularly like the focus on the hands.

But you are right about the 50 mm 1.8 frontfocusing after D70 backfocus recalibration. Mine constantly frontfocuses, as long as I shoot various test targets. It never frontfocuses with real life photos. For what reason I do not know, but I guess the AF system of the D70 is more complex than what appears at first sight.

I was initially shocked to find that I have 25mm frontfocus with my 50mm and I thought the lens would be unusable. But in real life, I end up with just as many backfocused photos as frontfocused ones (obviously my mistakes), while the majority of the photos turn out with focus exactly spot on. I have no idea why my test rig shots look different from my real life photos but they do.

Here's a shot of Felix the Cat: 50mm 1.8, f/2.8, 1/60. 100% crop. Focused very carefully on the eyes, Guess what, eyes turned out sharp, not tip of the nose or the ears. And no, the cat wasn't moving. Maybe I was, I didn't use a tripod.



Regards
Thomas
 
Snap...mine is the old 1.4 as well - have no idea why it would FF.

If I can be certain that a new 1.4D or 1.8D would have spot-on focus I'd replace the old 1.4...but otherwise, it would be a lens just for fun whereas the 18-70 would be the main lens.
d_light said:
My story: Had 3cm/5mm@24/120 backfocus with 24-120 VR . Enough to
get blurred focus at wide open, acceptable when stopped down to
f8-f11. OK with 70-300 ED. OK with cheapo 28-80 G. Sent to Nikon
UK, it took a month, ("not a pro camera") bless them, but it's fine
now. They adjusted both the lens and body for focus. 70-300 and the
other one still OK. While the camera in service I found a 50/1.4
non-D secondhand. Surprise surprise (is there a pattern?) it has 5mm frontfocus@50cm At f1.4 DOF ±3mm , so forget close-ups at
wide open . DOF rises with distance but so does the frontfocus.
Here I have a photo with the 50/1.4@f2. I focused on the face and
its OK but the hands are the sharpest . The pic is unprocessed BTW
with no in-camera sharpening. Actually I like it more this way but
the fact is I didn't focus on the hands but the face.
The thing is it all depends on your expectations. For a pro 1-2mm
back/front focus with a pro lens would be unacceptable. Cue Ken
Rockwell. Us mortals, we stop down.

Click to expand...
 
Thanks for your comments,

Cs
d_light said:
My story: Had 3cm/5mm@24/120 backfocus with 24-120 VR . Enough to
get blurred focus at wide open, acceptable when stopped down to
f8-f11. OK with 70-300 ED. OK with cheapo 28-80 G. Sent to Nikon
UK, it took a month, ("not a pro camera") bless them, but it's fine
now. They adjusted both the lens and body for focus. 70-300 and the
other one still OK. While the camera in service I found a 50/1.4
non-D secondhand. Surprise surprise (is there a pattern?) it has 5mm frontfocus@50cm At f1.4 DOF ±3mm , so forget close-ups at
wide open . DOF rises with distance but so does the frontfocus.
Here I have a photo with the 50/1.4@f2. I focused on the face and
its OK but the hands are the sharpest . The pic is unprocessed BTW
with no in-camera sharpening. Actually I like it more this way but
the fact is I didn't focus on the hands but the face.
The thing is it all depends on your expectations. For a pro 1-2mm
back/front focus with a pro lens would be unacceptable. Cue Ken
Rockwell. Us mortals, we stop down.

Click to expand...
 
The test charts may give you some indication that you MIGHT have backfocus, but the true test is to photograph a subject to see whether you really have backfocus.

I thought I had a 10mm backfocus, but when I did testing on real, three-dimensional subjects, my camera focused just fine.
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

My Hummingbird gallery - continuously updated!
---> http://ImageEvent.com/aceattorney/hummingbird

My latest: Dragonfly Eating a FLY!
---> http://ImageEvent.com/aceattorney/dragonflyenjoyingmeal
 
D70 can front and back focus with stlye! congrats
Mimoid said:
This is what 25mm frontfocus looks like in real life:



50mm 1.8, 1/40 sec, f/5. In-camera sharpening set to Normal,
resized for web, slight USM applied to compensate loss of details
in the resizing process.

Regards
Thomas
Mimoid said:
When you're talking about a few mm of front/backfocus, it really
doesn't mean anything. Especially with a lens such as the 50mm 1.8,
even the slightest backfocus will be visible in the test charts and
still not affect your real life shots. My 50mm 1.8 has 25 mm
frontfocus on my D70 - verified on test charts - but I cannot see
any impact on my real life photos. None whatsoever.

Regards
Thomas
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
Click to expand...
Click to expand...
--
D70 Bites.

 
I have tried it in the "real" life and in closeups the difference can be seen just in the posted picture. It is not a big trouble but it is annoying.
Thanks for your comments.
aceattorney said:
I thought I had a 10mm backfocus, but when I did testing on real,
three-dimensional subjects, my camera focused just fine.
Csaba Ónody said:
Hi!

If a I have 2mm backfocus on my kit lens and 1mm front focus on
50/1.8 what would that mean in the photos? Is it a visible
backfocus on portrait photo? What would that mean on a telephoto
(70-300) lens.

Thanks and regards,

Csaba
Click to expand...
--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

My Hummingbird gallery - continuously updated!
---> http://ImageEvent.com/aceattorney/hummingbird

My latest: Dragonfly Eating a FLY!
---> http://ImageEvent.com/aceattorney/dragonflyenjoyingmeal
Click to expand...
 
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