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A Pensioner's Focusarater
  
 
Doctorbird
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p.1 #1 · A Pensioner's Focusarater


Occasionally, one suspects that something is awry with the focusing of his equipment even after taking great care in the preparation of the shots. Such was the case some months ago when I mounted a newly acquired 85mm f/1.2 on the 5DIII. In order to make a convincing case to the service folks at Canon I decided to construct my own contraption to test focus - not original but modeled after others that I had seen in the past. I used mostly scrap wood and other items laying around but still had to purchase a few of the pieces.

One result from doing this is that the Imaging Sensor Assembly in the 5D III was replaced by Canon after I presented the test images to them. The irony is that I thought it was the 85mm that was the front focusing culprit, since I had been using the 5D III for months before that and hadn't pixel peeped enough to notice this. It was my failed attempt to get some shallow depth of field shots with the new lens that alerted me to it. Needless to say the subsequent performance of the 5D was quite improved. The lens was OK.

A few images of the contraption, my 'focusarater', are attached here.

Some aspects:

It's collapsible and adjustable with the aid of 2 cabinet hinges and 2 lid stays.

The angle of the steel ruler that with the index marks is adjustable within a range of about 30 - 45 degrees.

The ruler is only spring clamped and can be adjusted to line up a convenient index mark precisely with the target.

There is a mirror which can be flipped down, using yet another hinge, in front of the focus target to aid in ensuring near parallelism between the target and the sensor plane of the camera.

In the example here the face of the target is aligned with the 30 cm mark on the steel rule. It clearly shows that the 5D/85mm combo suffers from front focusing. [It got worse as the target distance was increased].

This may seem like a bit of overkill but once constructed it's easily set up to test other configurations. It certainly already paid dividends for me.

[The next iteration of this could be contrived to make the mirror flip up automatically in synch with the reflex mirror in the camera. ]

Db







Steel ruler at about 45 degrees

  Canon EOS 5D Mark III    28-300mm lens    50mm    f/9.0    1/320s    400 ISO    +1.0 EV  







Ruler set at about 30 degrees

  Canon EOS 5D Mark III    EF24-70mm f/2.8L II USM lens    63mm    f/5.6    1/800s    800 ISO    0.0 EV  







Mirror assembly.

  Canon EOS 5D Mark III    EF24-70mm f/2.8L II USM lens    70mm    f/5.6    1/400s    800 ISO    +0.7 EV  







Result from the 5D/85mm setup showing front focusing.

  Canon EOS 5D Mark III    EF85mm f/1.2L II USM lens    85mm    f/1.4    1/800s    400 ISO    +1.3 EV  







It can be folded flat for storage.

  Canon EOS 5D Mark III    28-300mm lens    55mm    f/9.0    1/160s    400 ISO    +1.0 EV  



Edited on Mar 01, 2014 at 07:43 PM · View previous versions



Feb 28, 2014 at 07:32 AM
lowa2
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p.1 #2 · A Pensioner's Focusarater


Nicely done! Would you mind explaining more how your mirror helps in getting you lined up?

Charles



Feb 28, 2014 at 10:52 AM
jcolwell
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p.1 #3 · A Pensioner's Focusarater


lowa2 wrote:
Nicely done! Would you mind explaining more how your mirror helps in getting you lined up?

Charles


If you can see "yourself" (i.e. the centre of the lens), you're lined up correctly.



Feb 28, 2014 at 11:06 AM
jcolwell
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p.1 #4 · A Pensioner's Focusarater


Hi Db,

Nice gizmo. You must have a decent pension. I mean, you're flying United, right?

I have a suggestion, if you replace the focus target with a "known" test target like the USAF 1951 test chart, then you can actually calculate the lens+camera resolution (lines per mm, lpmm) from an in-focus image of the focus target; two tests in one.

I've attached a screen shot of the central part of the USAF 1951 chart. You figure out which is the smallest set of "line triplets" that's 'resolved' in your test image, and then you can calculate lpmm from the "set group" label, the lens focal length, and the distance from the target. I can send you a spreadsheet to do this, if you like.

Here's some focus target and resolution chart links. Snapsy's new crosshatch focus target is wicked good for accurate focus, but I don't know how to calculate lpmm from it.


USAF test chart pdf http://photo.net/learn/optics/USAF1951.pdf
- (from http://photo.net/learn/optics/index)

ISO 12233 test chart http://www.graphics.cornell.edu/~westin/misc/ISO_12233-reschart.pdf

snapsy's new focus grid http://www.testcams.com/DotTune/CrossHatch_Target.png
- (from http://www.fredmiranda.com/forum/topic/1187247/20#12140517 )

FM thread on 'testing lens resolution...' http://www.fredmiranda.com/forum/topic/1261919/0#12017003
FM thread on 'guides for comparative testing' http://www.fredmiranda.com/forum/topic/1255884/0#11957157







Feb 28, 2014 at 11:42 AM
PetKal
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p.1 #5 · A Pensioner's Focusarater


Fine work there, Db, I have lottsa respect for people who are still able to fashion nice, useful and good objects with their own hands.

What is that talk about "pensioner's" ? Have you joined the retirement ranks of the likes of Petkal, Mitesh, Arbitrage, Colwell etc ?



Feb 28, 2014 at 12:43 PM
schlotz
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p.1 #6 · A Pensioner's Focusarater


... there are more


Feb 28, 2014 at 01:43 PM
mitesh
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p.1 #7 · A Pensioner's Focusarater


PetKal wrote:
What is that talk about "pensioner's" ? Have you joined the retirement ranks of the likes of Petkal, Mitesh, Arbitrage, Colwell etc ?


Retirement? I'm afraid that's a good 30 years away for me, Peter. In the meantime, I'm trying to learn from you as an example of what NOT to do

Excellent work, DB




Feb 28, 2014 at 02:03 PM
Jon Joshua
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p.1 #8 · A Pensioner's Focusarater


That's pretty cool. Looks easy to make. Any chance of providing a cut list for all of the pieces?


Feb 28, 2014 at 05:30 PM
Imagemaster
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p.1 #9 · A Pensioner's Focusarater


I have no idea why you would go to all this trouble when you can simply use Dot-Tune:

http://www.fredmiranda.com/forum/topic/1187247/0



Feb 28, 2014 at 06:14 PM
burningheart
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p.1 #10 · A Pensioner's Focusarater


Very nice design and manufacture. Excellent job.

Beware of the venture capitalists they will be knocking on your door to mass market it. Of course they will want 90% of your business profits in return for a their small $25 investment.



Feb 28, 2014 at 06:16 PM
 

Search in Used Dept. 



Doctorbird
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p.1 #11 · A Pensioner's Focusarater


lowa2 wrote:
Nicely done! Would you mind explaining more how your mirror helps in getting you lined up?

Charles


I guess Jim explained it very tersely below. View the mirror through the camera's viewfinder and adjust for straight on viewing.

Db



Feb 28, 2014 at 10:05 PM
Doctorbird
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p.1 #12 · A Pensioner's Focusarater


jcolwell wrote:
Hi Db,

Nice gizmo. You must have a decent pension. I mean, you're flying United, right?

I have a suggestion, if you replace the focus target with a "known" test target like the USAF 1951 test chart, then you can actually calculate the lens+camera resolution (lines per mm, lpmm) from an in-focus image of the focus target; two tests in one.

I've attached a screen shot of the central part of the USAF 1951 chart. You figure out which is the smallest set of "line triplets" that's 'resolved' in your test image, and then you can calculate lpmm from the "set
...Show more

That's a lot of good suggestions Jim. And thanks for the links. I do have one or two of your charts but haven't yet thought on using them in a more quantitative manner. Just wanted something with some contrasty lines to get focus. and added the United luggage tag in the mix. (Alas, it was from an economy flight, and only a pensioner's one at that ).

I would like to have your spread sheet. It may prove useful once everything is all adjusted properly.

Db






Feb 28, 2014 at 10:17 PM
Doctorbird
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p.1 #13 · A Pensioner's Focusarater


PetKal wrote:
Fine work there, Db, I have lottsa respect for people who are still able to fashion nice, useful and good objects with their own hands.

What is that talk about "pensioner's" ? Have you joined the retirement ranks of the likes of Petkal, Mitesh, Arbitrage, Colwell etc ?


Well Peter,

We all know what happens if idle hands aren't put to good use.

And, yes I've joined your exclusive rank. How else can one afford to play with such foolishness as Super Teles, Focusaraters, and what not.



Db


Edited on Feb 28, 2014 at 11:43 PM · View previous versions



Feb 28, 2014 at 10:23 PM
Doctorbird
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p.1 #14 · A Pensioner's Focusarater


Jon Joshua wrote:
That's pretty cool. Looks easy to make. Any chance of providing a cut list for all of the pieces?


Jon:

It was fun putting it together. I'd be happy to do so. But what exactly is a 'cut list' ?

Db



Feb 28, 2014 at 10:38 PM
Doctorbird
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p.1 #15 · A Pensioner's Focusarater


Imagemaster wrote:
I have no idea why you would go to all this trouble when you can simply use Dot-Tune:

http://www.fredmiranda.com/forum/topic/1187247/0


I guess I'm just old fashioned.

Db



Feb 28, 2014 at 10:39 PM
Doctorbird
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p.1 #16 · A Pensioner's Focusarater


burningheart wrote:
Very nice design and manufacture. Excellent job.

Beware of the venture capitalists they will be knocking on your door to mass market it. Of course they will want 90% of your business profits in return for a their small $25 investment.


Thanks Burningheart!

I will take your advice to heart. Hopefully, the initial IPO will be sufficient to satisfy all.

Db



Feb 28, 2014 at 10:43 PM
jcolwell
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p.1 #17 · A Pensioner's Focusarater


Doctorbird wrote:
I would like to have your spread sheet. It may prove useful once everything is all adjusted properly.


Hi Morrell,

It's not "my" spreadsheet. It was developed and shared online by Rob Studdert, through his website DI Studio (Digital Imaging). This site is no longer online, but he seems to still be an active semi-pro photographer in Australia.

old link, Rob Studdert DI Studio, http://home.swiftdsl.com.au/~distudio/publications/

We'll swap email addresses by PM, and I'll send it to you.

Cheers,
Jim



Mar 01, 2014 at 12:03 AM
jimbob
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p.1 #18 · A Pensioner's Focusarater


Thank you Db for this thread and sharing your ideas. I have lots of wood and hinges and screws and time. I'll be right on it after I do the laundry and the dishes and peeling the potatoes and the snow shovelling and and. I am into my 29th year of retirement. There is no money in it but the freedom is nice.
Regards
jimbob



Mar 01, 2014 at 03:29 PM
PetKal
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p.1 #19 · A Pensioner's Focusarater


jimbob wrote:
I am into my 29th year of retirement. There is no money in it but the freedom is nice.
Regards
jimbob


Jimbob, the way I look at it is as follows: can we put a price on our freedom ? I do not think so, I think freedom is practically priceless, or it is very very expensive to buy or earn.
Any money with no or limited freedom is really not worth much. The only thing that compares to freedom in value is our health. That's the way I see it.



Mar 01, 2014 at 04:29 PM
Jon Joshua
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p.1 #20 · A Pensioner's Focusarater


Doctorbird wrote:
Jon:

It was fun putting it together. I'd be happy to do so. But what exactly is a 'cut list' ?

Db


A list of measured pieces that I would need to cut to make my own.



Mar 01, 2014 at 04:30 PM
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