Focusing Tests: Lens or Camera?

lpj8 · 23rd of July 2008 (Wed)

I've taken a couple thousand pictures with my XT now and I've always felt that something was "off". Things just didn't look sharp. I'm probably a pixel peeper, and I know that my equipment is somewhat limited; however my results just looked fuzzy!

So I decided to conduct two focusing tests with the two lenses I own: The Kit 18-55 F3.5-5.6 NONIS and the 50mm 1.8. Test was used with a Tripod with the mirror lock enable. Images were shot RAW and converted to JPEG using DPP.

The first test looks like this

Here is this test using the 50mm
100% crop
1/80Sec
F1.8
ISO 100
50.0 mm

Here is the test using the 18-55mm Kit. The kit is 5.6 at 50; so I shot it at 24 to achieve F3.5 to control DOF.

1/15Sec.
F3.5
ISO 100
24.0 mm

Wow. That looks off to me!

Next test was the battery test. The batteries and measuring tape are set at a 45 degree angle from the camera. For all pictures, I focused on the center portion of the middle battery. I'll start with the nifty fifty again:

1/60Sec.
F1.8
ISO 400
50.0 mm

100% crop:

And now for the 18-55 Kit. I had to bump up the ISO to get a faster shutter speed.

1/30Sec.
F5.6
ISO 1600
55.0 mm

And now the 100% crop

It seems that it is time to replace/upgrade my walk around lens! This is the data I needed to justify the expense to myself....and my wife.

strobe monkey · 23rd of July 2008 (Wed)

Your kit lens looks like its backfocusing.

lpj8 · 23rd of July 2008 (Wed)

Quote:

Originally Posted by strobe monkey

Your kit lens looks like its backfocusing.

Definitely! Picture after picture it consistently backfocused. This helps explain, at least in part, some of the results I've had.

ALaS · 23rd of July 2008 (Wed)

Your Kit lens is back focusing. The 50 seems like it has a slight front bias, but it's certainly within spec. It could also just be your rebel, but it's fine. Send that kit lens in! My Xti was doing the same thing, but it was definitely the body. Canon fixed it under warrany.

nicksan · 23rd of July 2008 (Wed)

Yep, back focusing.

ef2 · 23rd of July 2008 (Wed)

May be off topic but how do you accurately keep your camera at a 45 degree angle

TheMadMule · 23rd of July 2008 (Wed)

What exactly is "backfocusing"?

Mark_Cohran · 23rd of July 2008 (Wed)

Quote:

Originally Posted by TheMadMule

What exactly is "backfocusing"?

Backfocus occurs when the camera/lens actually focuses behind the point of focus. Front focus is just the opposite.

lpj8 · 23rd of July 2008 (Wed)

Quote:

Originally Posted by ef2

May be off topic but how do you accurately keep your camera at a 45 degree angle

Well for the first test I used a tripod and used a protractor to measure the angle. I took a ruler (any straight object would do) to make sure the barrel of the lens was positioned to hit the chart at 45 degrees.

The second test was a lot easier to accomplish. You set your camera perfectly level and then you put the batteries at a 45 degree angle on a flat surface.

LeeSC · 23rd of July 2008 (Wed)

A large carpenter's triangle also does the trick!

TheMadMule · 23rd of July 2008 (Wed)

Quote:

Originally Posted by Mark_Cohran

Backfocus occurs when the camera/lens actually focuses behind the point of focus. Front focus is just the opposite.

Thanks! I always learn a thing or two a day from this site.

DC Fan · 23rd of July 2008 (Wed)

Quote:

Originally Posted by lpj8

It seems that it is time to replace/upgrade my walk around lens! This is the data I needed to justify the expense to myself....and my wife.

It doesn't have to be a large expense. The recently-released 18-55mm IS lens is a very good and reasonably priced upgrade from the older 18-55mm lens. Otherwise, consider the Tokina 17-55mm f/2.8.

ef2 · 23rd of July 2008 (Wed)

Quote:

Originally Posted by lpj8

Well for the first test I used a tripod and used a protractor to measure the angle. I took a ruler (any straight object would do) to make sure the barrel of the lens was positioned to hit the chart at 45 degrees.

The second test was a lot easier to accomplish. You set your camera perfectly level and then you put the batteries at a 45 degree angle on a flat surface.

LOL I wish I had a protractor...I have to guestimate with the tripod and a ruler...

lpj8 · 23rd of July 2008 (Wed)

Quote:

Originally Posted by ef2

LOL I wish I had a protractor...I have to guestimate with the tripod and a ruler...

You could also fold a sheet of paper so that it makes a 45 degree angle =)

arzir · 23rd of July 2008 (Wed)

uff at least they look worst than mine, i dont know if its a relief... as i was testing the 17 55 is and it should perform better:

http://photography-on-the.net/forum/...d.php?t=539178

23rd of July 2008 (Wed)	#1
lpj8 Member Join Date: Jun 2006 Location: Tampa, FL Posts: 244 IMAGE EDITING OK	Focusing Tests: Lens or Camera? I've taken a couple thousand pictures with my XT now and I've always felt that something was "off". Things just didn't look sharp. I'm probably a pixel peeper, and I know that my equipment is somewhat limited; however my results just looked fuzzy! So I decided to conduct two focusing tests with the two lenses I own: The Kit 18-55 F3.5-5.6 NONIS and the 50mm 1.8. Test was used with a Tripod with the mirror lock enable. Images were shot RAW and converted to JPEG using DPP. The first test looks like this Here is this test using the 50mm 100% crop 1/80Sec F1.8 ISO 100 50.0 mm Here is the test using the 18-55mm Kit. The kit is 5.6 at 50; so I shot it at 24 to achieve F3.5 to control DOF. 1/15Sec. F3.5 ISO 100 24.0 mm Wow. That looks off to me! Next test was the battery test. The batteries and measuring tape are set at a 45 degree angle from the camera. For all pictures, I focused on the center portion of the middle battery. I'll start with the nifty fifty again: 1/60Sec. F1.8 ISO 400 50.0 mm 100% crop: And now for the 18-55 Kit. I had to bump up the ISO to get a faster shutter speed. 1/30Sec. F5.6 ISO 1600 55.0 mm And now the 100% crop It seems that it is time to replace/upgrade my walk around lens! This is the data I needed to justify the expense to myself....and my wife. __________________ Canon 5D Mark III 24-105 F/4L; 70-200 F/4L; 85 F/1.8

23rd of July 2008 (Wed)	#2
strobe monkey Senior Member Join Date: Apr 2008 Location: Other side of the pond! Posts: 1,072 IMAGE EDITING OK	Re: Focusing Tests: Lens or Camera? Your kit lens looks like its backfocusing. __________________ Canon Supremacy

23rd of July 2008 (Wed)	#4
ALaS Goldmember Join Date: Aug 2007 Posts: 2,200	Re: Focusing Tests: Lens or Camera? Your Kit lens is back focusing. The 50 seems like it has a slight front bias, but it's certainly within spec. It could also just be your rebel, but it's fine. Send that kit lens in! My Xti was doing the same thing, but it was definitely the body. Canon fixed it under warrany. __________________ Best Regards, -Ericson. flickr \| Gear - Canon 1Ds Mark II, 50L & 28mm f/1.8 for SALE!

23rd of July 2008 (Wed)	#5
nicksan Man I Like to Fart Join Date: Oct 2006 Location: NEW FRIGGIN' YORK Posts: 23,891 IMAGE EDITING OK	Re: Focusing Tests: Lens or Camera? Yep, back focusing. __________________ NYC Wedding Photographer \| Blog \| facebook \| Galleries \| Flickr \| Gear My 5D Mark III Review

23rd of July 2008 (Wed)	#6
ef2 Senior Member Join Date: Jan 2008 Location: Pittsburgh Posts: 1,136	Re: Focusing Tests: Lens or Camera? May be off topic but how do you accurately keep your camera at a 45 degree angle __________________ 5D Mk III Canon 580EX Canon 16-35mm f/2.8L \| 24mm f/3.5L \| 50mm f/1.4 \| 100mm f/2.0 \| 100mm f/2.8 Macro \| 135mm f/2.8 SF \| 70-200mm f/2.8L IS \| 70-300mm f/4.5-5.6 DO Sigma 50mm f/1.4 EX

23rd of July 2008 (Wed)	#7
TheMadMule Member Join Date: Jun 2008 Location: San Jose/Orange, CA Posts: 42	Re: Focusing Tests: Lens or Camera? What exactly is "backfocusing"? __________________ Figured out that a clunky DSLR isn't my sort of thing. Sold the XSi and continuing the journey with a S95!

23rd of July 2008 (Wed)	#10
LeeSC Member Join Date: Apr 2007 Location: Camden, South Carolina Posts: 816 IMAGE EDITING OK	Re: Focusing Tests: Lens or Camera? A large carpenter's triangle also does the trick! __________________ GEAR

23rd of July 2008 (Wed)	#15
arzir Junior Member Join Date: Mar 2008 Location: London Posts: 20	Re: Focusing Tests: Lens or Camera? uff at least they look worst than mine, i dont know if its a relief... as i was testing the 17 55 is and it should perform better: http://photography-on-the.net/forum/...d.php?t=539178

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