Check your new lenses!

[simpo two]

My Sigma 20-40mm f2.8 arrived yesterday.

While I was idly sitting in the settee photographing the nearest object, a TV remote control, I looked at the monitor and thought ' That's funny, I focused on that button but the one in front of it looks sharper...'

Further tests revealed that at close range it focuses 20mm too close!!

Hence it will be going back to Warehouse Express for a swap.

Head-on:



Oblique, focusing on the word 'FILM':



As (1) but with Nikkor 18-70mm:

[406tm]

Now what was it I said about only buying Nikon lenses

[beano500]

406tm said:

Now what was it I said about only buying Nikon lenses

What?! that you get free Bob Hope movies?

[simpo two]

406tm said:

Now what was it I said about only buying Nikon lenses

Yep but at £969 it's a non-starter mate. Sigma are fine if you get a good one
Actually reading some reviews there were some questions asked about their QC. I hope they're not going the way of Vivitar.

[beano500]

Damn!

They've pinched the name for our new photography business!

[HankScorpio]

Do a proper test and let us see the results...

http://md.co.za/d70/chart.html

(print superfine on good paper for best results)

[cirks]

interesting test with the magazine..Something for me to try as a test of my Canon's and possibly the 10-22 Sigma (if/when I get it).

[poah]

simpo two said:

My Sigma 20-40mm f2.8 arrived yesterday. While I was idly sitting in the settee photographing the nearest object, a TV remote control, I looked at the monitor and thought ' That's funny, I focused on that button but the one in front of it looks sharper...' Further tests revealed that at close range it focuses 20mm too close!! Hence it will be going back to Warehouse Express for a swap. Head-on: Oblique, focusing on the word 'FILM': As (1) but with Nikkor 18-70mm:

not really a great subject to test it on. how many times did you press the focus button?

[simpo two]

It's perfectly good enough to test a lens that's 20+mm out of whack. It's not scientific but I can tell the difference between sharp and not sharp.

[poah]

just for comparison this from sigma's 30mm f1.4 @ f1.4 attachd to my 20D

this is a resized imaged

http://img75.imageshack.us/img75/392/14fs8nf.jpg



this is a 100% crop.

http://img75.imageshack.us/img75/314/14crop6zv.jpg

[cirks]

poah said:

just for comparison this from sigma's 30mm f1.4 @ f1.4 attachd to my 20D this is a resized imaged http://img75.imageshack.us/img75/392/14fs8nf.jpg this is a 100% crop. http://img75.imageshack.us/img75/314/14crop6zv.jpg

Whatever is written on the paper is as clear as mud to me but at least it's sharp and in focus

[simpo two]

Here are links to four shots of the test card via Hank's link (about 1.8Mb each)

Studio conditions, 40mm, 1/400th sec at f2.8.

www.autograph.uk.com/Pix/6.JPG
www.autograph.uk.com/Pix/7.JPG
www.autograph.uk.com/Pix/8.JPG
www.autograph.uk.com/Pix/9.JPG

It's not a well bunny is it?

[ThatPhilBrettGuy]

Welcome to the world of front/back focusing. I hate to say it, but sometimes it's a camera / lens interaction. I've seen lenses that are miles out on one body that are fine on another (of the same type).

I hope yours is just the lens else you're in for a world of pain.

[_dobbo_]

poah said:

just for comparison this from sigma's 30mm f1.4 @ f1.4 attachd to my 20D this is a resized imaged http://img75.imageshack.us/img75/392/14fs8nf.jpg this is a 100% crop. http://img75.imageshack.us/img75/314/14crop6zv.jpg

Doesn't really help unless you say where you were focusing.

[simpo two]

ThatPhilBrettGuy said:

Welcome to the world of front/back focusing. I hate to say it, but sometimes it's a camera / lens interaction. I've seen lenses that are miles out on one body that are fine on another (of the same type). I hope yours is just the lens else you're in for a world of pain.

All my other lenses are OK, including the Sigma 70-200 f2.8. Hence I have to say it's the lens. I guess they dropped it or something...

[ThatPhilBrettGuy]

simpo two said:

ThatPhilBrettGuy said: Welcome to the world of front/back focusing. I hate to say it, but sometimes it's a camera / lens interaction. I've seen lenses that are miles out on one body that are fine on another (of the same type). I hope yours is just the lens else you're in for a world of pain. All my other lenses are OK, including the Sigma 70-200 f2.8. Hence I have to say it's the lens. I guess they dropped it or something...

If only it was that simple! One chap I knew had 3 lenses. One spot on, the other 2 back focused. They adjusted the lenses AND the body.

I suspect there's a closer link to the lens and the body than you'd believe.

Oh, and before the comments come, all the kit was from the same manufacturer.

Does sound like the lens in this case though I'd agree...

[joust]

Pardon me being stupid, but how is this happening?

Surely the focusing is a closed loop feedback from the light entering the lense, going to the focus sensors, and then the lense being moved in/out of focus until the sensor 'sees' it's in focus.

Given the light hitting the sensor should have travelled the same distance as when it hits the film/sensor, I fail to see how the lense can create this? Surely if it's out of focus on the sensor point you chose, then that would relate to a missalignment of the lense optics that is different for the film sensor than it is for the autofocus sensor, but given the AF sensor is normally in the same path I'm lost as to how that can happen???

Confused I am!

J

[Bee_Jay]

joust said:

Pardon me being stupid, but how is this happening? Surely the focusing is a closed loop feedback from the light entering the lense, going to the focus sensors, and then the lense being moved in/out of focus until the sensor 'sees' it's in focus. Given the light hitting the sensor should have travelled the same distance as when it hits the film/sensor, I fail to see how the lense can create this? Surely if it's out of focus on the sensor point you chose, then that would relate to a missalignment of the lense optics that is different for the film sensor than it is for the autofocus sensor, but given the AF sensor is normally in the same path I'm lost as to how that can happen??? Confused I am! J

My thoughts exactly, but it still happens and I am confused to hell as to why.

I have found on my 20d that unless I switch off, change lens then switch back on again some lenses will not focus exactly - very strange.

[cirks]

John,
just noticed on FredMiranda that a few other people seem to have had probs with this lens including another WHX supplied one.

[simpo two]

cirks said:

John, just noticed on FredMiranda that a few other people seem to have had probs with this lens including another WHX supplied one.

Aha - link?

RRP £600+
WH £350 (a fair saving you'll aaree)
Then suddenly, special offer this month only, £250. Odd

Frankly I'd get better results from a LensBaby, possibly even a milk bottle bottom!

>> Edited by simpo two on Thursday 1st December 14:53