New focus test

Tim Jackson · Jun 24, 2004

STOP! If you don't care about focus / back focus / front focus then move right along to another thread.

To those of you still here, I have once again updated my notorious focus test chart document.

There's now a LOT more information included on the AF system:

+ How the AF system works
+ Why the test chart works (in spite of rumours to the contrary)

+ Simple exercises for you to try out yourself which will greatly help you in your understanding of how the AF system works.

Find it here: http://md.co.za/d70

Tim
--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

Raydar · Jun 24, 2004

Great piece of work Tim
I will be trying that tomorrow.

Thanks heaps
Ray

aecom · Jun 24, 2004

You made it to simple for me not to try to see if I suffer, well you know fromt he dreaded BF problemmm thanks.

--
http://www.pbase.com/aecompaul/nikon_d70_work

Iliah Borg · Jun 24, 2004

apart from
http://travel.howstuffworks.com/autofocus3.htm

What we have is essentially the same as split-screen. 2 arrays of sensors look at the target through opposite fragments of front lens (providing the nessessary base; the bigger is that distance, the more difference is in signals when the subject is OOF). Focus is achived when the phase of both readings from arrays is matched.

--
no text

aceattorney · Jun 24, 2004

--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

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

aceattorney · Jun 24, 2004

Tim, I keep getting 10mm backfocus...is this within the range of normal acceptability? BTW, I'm getting this result with the kit lens.

Thanks

--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

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

ThomasBricker · Jun 24, 2004

Thanks again Tim.

I keep hoping my focus issue will go away like a bad dream some day.
Probably wont though... : (

aceattorney · Jun 24, 2004

Tim, check it out please:

I focused on the middle focus line:

Here, I drew a line 10mm in front of the focus line and focused on it:

You may check out large crops of the original here:

http://ImageEvent.com/aceattorney/focustest

Thanks again, Tim!

--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

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

Tim Jackson · Jun 24, 2004

Most ingenious!

I like that idea. I woulda covered the original line with a piece of white paper just in case the AF system got confused but it clearly worked without a problem the way you did it.

I'd say your BF problem is not lkely to cause you a problem in normal photography. The focus line is almost perfectly in focus and, as soon as you're furhter away from the subject and/or using a smaller aperture it will be within the depth of field.

I know I would want it fixed but that's because I always want everything to be just right. As I said though, it's not likely to cause any real world problems.

Tim

--
=============================
At the time of posting this message, the latest
focus test chart is V2.1 (Dated 24 June 2004)
Get it here: http://md.co.za/d70
=============================

aceattorney · Jun 24, 2004

Yeah, I'm going to have to send it in for that 10mm fix...thanks again, Tim!

--
Proud owner of a Nikon Coolpix 5700!
Proud owner of a Nikon D70!

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

TMacaw · Jun 24, 2004

Incredible timing! Your older posts went back a bit so I decided to make the new "thank-you post" and this pops up!

I will probably not be satisfied without playing with this chart, but you can see that the older one produced a pretty good result.

Never got any type of response to clarify what was replaced. Only a "laundry" list of items done to clean and adjust.

A knowledgeable source told me the US$271. charge is a "standard" amount for opening the dslr and is probably reported to most D70 owners.
No matter, I guess, if all comes out ok.
You can see from my pic that I have not fiddled with the styrofoam cup yet!
Many thanks.
TMc

Spannie · Jun 24, 2004

Ace,

What is acceptable depends totally on you.

It also depends on the distance of the shot and the focal length. I had a consistent 10-15mm back-focus at 20 inches distance at 70mm FL. This was not acceptable to me!!

I sent the camera and lens back to Nikon for calibration, and it came back perfect for AF. Unfortunately my MF was still way off, and I resorted to calibrating the MF myself (sucessfully - thank goodness!).

Good luck!

Tip: if you send it back, don't ask them to check possible backfocus - ask them to calibrate the focus OPTIMALLY. This prevents them from merely checking the focus and say that it is within acceptable limits.

Spannie

--
Spannie

Spannie · Jun 24, 2004

... with some help from the NIkon service center

--
Spannie

Lenwoodbluz · Jun 24, 2004

thanks...I'm gonna give this a try tonight at work...of course I'll wait until all my work is done and I'm on my break...(just incase my boss is reading this)....LOL

--
LENWOODBLUZ........NO REGRETS

See My Not-So-Hot pics at

http://www.pbase.com/lenwoodbluz

I Be Using The F828.......AND I LOVE IT...DON'T KNOW HOW TO USE IT.....BUT I LOVE IT!!!!!

I also be using the D70...This, as well, I don't know how to use. But I LOOOOOOOVE IT!!!!

1stAde · Jun 24, 2004

Tim

Forgot to reply to your email from the other week, but thanks. I will get to complete that blog on the subject, but you seem to have covered it so well I guess there's less urgency.

However thanks for your help, I finally have a great camera. My original was returned with the kit lens. The next 3 bodies and kit lenses tested (they weren't mine - just tested out) all clearly behaved the same, but when I put on another lens (24-85 typically) there wasn't the problem, so I've simply been waiting for a supply of body onlys to arrive in London.

Much to my delight - got one today with a second hand 24-120 VR and the photos are much better immediately. It just proved to me that the 10mm of backfocus demonstrated in your tests was ruining the sharpness of many photos that I had taken.

Of course it could be a change in manufacture/quality control, but I still think avoiding the kit lens has been the secret of my current satisfaction.

Again thanks for the help. Its now about time I finally posted some photos!

Adrian.

djmckay · Jun 24, 2004

Tim, I like your tests and technical explanations.

In my case I found that some of my lenses focussed perfectly at distances up to approx. 2 metres, but at 4 metres and beyond the had terrible back focus.
So I think people should also check at longer focus distances.

I realise that the above seems very strange.

I have had a lifetime as a medical and general photographer and would never have believed the above possible.

Also people should not forget the 1/3 in front 2/3 behind DOF rule.

My 80mm to 200mm f2.8D was the only lens that the camera focussed well.
All tests were made at wide apertures.

It took me a long time to convince myself that the camera was at fault, and not me.
I found a good quick test was to photograph my wifes face.

Her glasses and hair was plenty good enough for the auto focus latch on to, but the focus was always about her ear or neck.

Focus good now after Nikon service.

MR173848 · Jun 24, 2004

Spannie:
Some questions:
Where did you send your camera to? CA or NY?
What did you send along with the camera, lens, battery, etc?
Did you send a letter explaining the BF problem?
How long did it take to get calibrated?
Hope you can help me.
Thanks

--
Newbee

THomasAdams · Jun 24, 2004

Hello Tim,

I too have seen the many debates over this test, I am printing it out right now as I type and clearing off my table. I appreciate you hard work, and continued devotion to keeping things updated, I have read the first portions explaining many things to do with the focusing which I find very interesting, I wish there was a way to tell exactly where the actual focusing areas were with in the focus guides : P

I have one question, as I have been reading many post on this website, I ran across one earlier. It has to do with hyperfocal distance. A phenomenon where centering on a focal point, at a focal distance of infinity would mean that 1/3 in front of the focal plane, and the 2/3's directly behind the focal plane, are in focus. Or simply, if I manually

adjust my focus to infinity, then move the camera so that the tip of an eraser was in focus. And took a photo, there would be 2/3 more focus on the backside of the focus point (the eraser) and only 1/3 in front of this.

A Top down view:
Lens at infinity.

O
O
O
O
O

Original post I ran across:

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9285911

Which directed me here:

http://www.vividlight.com/articles/2314.htm

I found this post to be very informative in regards to DOF, hyperfocal distance, CoC (circles of confusion), and several other bits of important information.

My question is, to what degree would this phenomenon play a part if a user was to manually focus, or Auto focus into this focal area of the lens, would that not explain some users getting back focus? If this was a particular user’s setup, whether intentionally or unintentionally could this explain some back focus issues? Does this phenomenon only happen at infinity, or is it possible to occur elsewhere within a particular focal length of a lens? If the focal point is in focus, would some degree of backfocus be acceptable, as long as your focal point is in focus?

Thank you very much,
Best regardsm
Thomas Adams

--
http://www.280dgamingclan.com/ThomasAdams/gallery/

msport · Jun 24, 2004

And I found it to be very sensitive to the vertical aim, as mentioned before, which can affect the results.

I can repeatedly "make" my camera/kit lens front OR back OR dead-on focus by making tiny adjustments to the vertical aim of my camera. Roughly 10-15 mm BF at 70 mm, wide open, close range. Or about the same front focus! Or ~ zero back or front focus! This repeats for the same camera positions and indicates a marked sensitivity to the vertical aim.

When I do the test with a parallel target (as Nikon does and would do to any camera they test/calibrate) I get good focus.

I can get a rough idea of the AF sensor position relative to the viewfinder markings I suppose by comparing the results from these tests, but there are better ways to do this.

My concern is that the average D70 owner does not know exactly where his AF sensors are located, but obviously can see the center rectangle on the viewfinder. This means that different good-focussing cameras but which have slightly differently positioned AF sensors (compared to the markings) will show differences in focus on your type of test. I think we agree that the AF sensors are seldom perfectly positioned and lined up with the guide markings.

This is part of why it may make sense to eliminate that possible variation and test just ONE thing at a time if we'd like to have a credible test.

msport · Jun 24, 2004

http://forums.dpreview.com/forums/read.asp?forum=1034&message=9306145

New focus test

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