Focus is driving me mad! - DPChallenge Forums

Canon EF 24-70mm f/2.8L USM

08/02/2007 10:30:09 PM · #1

I recently bought a Sigma 70-200 2.8 APO DG MACRO HSM. It had focus problems, but after 3 months and complete system board upgrade, it is back, the same as ever!

Shots look fine through the viewfinder, but the actual photos are terrible! It's worst at the extreme macro range, wide open, but noticeable in almost every shot if you look hard enough. At f6+, shots normally look pretty good, but I didn't buy this lens to shoot at f6! Here's some examples...

These are full size images, not cropped, just resized, so that gives you an idea of how bad the problem is. Through the viewfinder, both images looked pretty much perfect, without the horrible haze.

I don't understand. This is supposed to be a really good lens, but it's making absolute rubbish photos. Is there something wrong with my camera? Is the 400D just not able to use good lenses?

Message edited by author 2007-08-02 22:32:16.

violinist123

Canon EOS-6D

08/02/2007 10:34:54 PM · #2

Are you checking with the dof preview button when you say 'through the viewfinder'? That shot with the twigs, portions of those twigs look in focus. Look like it can focus, just maybe still not focusing wher eyou want it to.

boysetsfire

08/02/2007 10:36:55 PM · #3

perfect :)

08/02/2007 11:09:46 PM · #4

Originally posted by routerguy666:

Are you checking with the dof preview button when you say 'through the viewfinder'?

Photos are taken at f2.8, so the DOF preview does nothing. :)

Originally posted by routerguy666:

That shot with the twigs, portions of those twigs look in focus. Look like it can focus, just maybe still not focusing wher eyou want it to.

Nope, there's nothing there that's in focus. It's not a matter of front or back focusing, it's a matter of no focus at all.

Here's a 100% crop of the twig, the pseudo focus point is definitely somewhere in this photo, but nothing is in focus. Compare this with the same shot (also 100% crop) from the kit-lens...

and the kit lens ->

And just for comparison, here is also a f5.6 crop from the Sigma. Certainly better, and almost on par with the kit lens at f5.6. I'd expect much better from a lens that costs roughly 10 times as much.

Message edited by author 2007-08-02 23:11:58.

SamDoe1

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

08/02/2007 11:14:05 PM · #5

Originally posted by surfdabbler:

I don't understand. This is supposed to be a really good lens, but it's making absolute rubbish photos. Is there something wrong with my camera? Is the 400D just not able to use good lenses?

Doubt it's a problem with your camera if it works just fine with the kit lens. And as far as the 400D not being able to use good lenses...my 350D works just great with the 70-200mm f/4L and worked great with the f/2.8L as well. :) I think it's an issue with the lens itself. Call Sigma and complain. Also, run a focus test (google it) and verify if the focus is landing where it should. You can use this to tell Sigma that it's not just back focusing or front focusing and that there are bigger issues at hand.

Edit to add: Look inside the lens, does it appear different to you? Is there a haze, fog, or anything else that shouldn't be there?

Message edited by author 2007-08-02 23:14:49.

trevytrev

Canon EF 16-35mm f/2.8L USM

08/02/2007 11:18:10 PM · #6

Just a question, are you using AF or manual focus?

boysetsfire

08/02/2007 11:18:27 PM · #7

Auto or manual focus?

08/02/2007 11:32:44 PM · #8

Yep, I've done the focus test. Was intermittently slight front-focusing before I sent it in the first time, but it's pretty spot-on now.

I'm mostly using auto-focus, centre point focus. Tried a few shots on MF, and same result.

Lens looks fine inside, no haze or fog. Images look fine through the viewfinder, but not the photo. The haze that comes in the photo is not in the viewfinder.

Message edited by author 2007-08-02 23:33:56.

SamDoe1

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

08/02/2007 11:34:35 PM · #9

Have any other lenses you can use to test out? And just so I'm understanding this right, the kit lens does work just fine on the body? If the image looks just fine through the viewfinder, there isn't a problem with the lens, cause what you're seeing is what the lens is seeing and what would be put onto the sensor... Although the 400D VF is not very good for judging what's good and what isn't since it's small and dark. My 350D is the same, I hate it.

08/02/2007 11:53:38 PM · #10

I've only got the kit lens, and I've never seen this problem with the kit. Unfortunately, I don't have another 70-200 to test. :) A friend has a 300D body that I might be able to borrow to test.

Yes, I know what you mean about the 400D VF. It's a little small, and it's about at the limit of my ability to see properly, but I'm fairly sure that what's in the view finder is not what's coming out on the final image.

SamDoe1

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

08/02/2007 11:58:26 PM · #11

Hmm...I'm stumped then. Until the lens can be tested on another body, I think you're kinda dead in the water with that one. Either test it again or send it back again. I'd wait for

kirbic to find this thread, I'm sure he can give you some more suggestions/reasons than I can.

If you send it back again, this time tell them to keep it and send your money back instead. This time get the 70-200mm f/4L, you won't be disappointed with that one. :)

Retroesque

Canon EOS-5D Mark II

Canon EF 85mm f/1.8 USM

08/03/2007 12:07:09 AM · #12

Originally posted by boysetsfire:

perfect :)

You beat me to it - GRIN!

violinist123

Canon EOS-6D

Canon EF 24-70mm f/2.8L USM

08/03/2007 12:08:32 AM · #13

Some crops off test patterns would be helpful to see. I still see portions of those twigs that are in focus. Soft like you would expect from a third part non-L lense wide open, but in focus nontheless. Could be trickiness of the subject though. A plain grid might make it more readily apparent.

hankk

Sigma 24-70mm f/2.8 EX Aspherical DF for Canon

08/03/2007 09:27:48 AM · #14

How far away from the subject are you? There is a minimum distance where you can focus, what is it for your lens?

Camabs

Canon EOS-20D

Canon EF 35mm f/2.0

08/03/2007 09:44:05 AM · #15

Originally posted by surfdabbler:

Originally posted by routerguy666:
Are you checking with the dof preview button when you say 'through the viewfinder'?

Photos are taken at f2.8, so the DOF preview does nothing. :)

Close focus at f/2.8, that gives you a VERY VERY shallow DOF. Maybe even so shallow that nothing seems in focus

albc28

Canon EOS-50D

Canon EF 50mm f/1.8 II

08/03/2007 09:54:17 AM · #16

I need to keep an eye on this thread. Sometimes I have a similar issue with my 50mm f/1.8

Prof_Fate

08/03/2007 11:54:24 AM · #17

It's not the lens...it's the user.

Every new lens takes some getting used to, and I can't tell you how many times I want to blame the new lens, when it turns out it's me.

You're shooting what? Macro at 2.8? that's your first problem. You want ANY DOF in when shooting macro get to F8 or better. And use a tripod and a solid subject - a flower on a stem outdoors will move too much. You're trying to do the impossible and not succeeding - not surprising.
//www.dofmaster.com/dofjs.html

Next, you're shooting wide open with a third party lens and expecting sharp results - nope. That's what you have to pay L lens prices for, sorry. There are a few exceptions (tamron's 28-75 2.8SP being one). Put in on a tripod (using the lens collar and a stout tripod -the $10 Big Lots ones are too weak to solidly hold a heavy lens). Use mirror lockup too. Eliminate as many variables as possible.
Now shoot a subject at 2.8 to 5.6 at 1/3 stop increments and examine them in PS. You'll probably find by 5.6 it's razor sharp, and softer as it gets more wide open. there will probably be one frame extra soft.

You can do this with one focus, or focus each time, or de-focus and focus each time and check the results against eachother.

Long lenses don't focus well in low light - not their fault. The camera has difficulty with contrast in low light, add in the extra distance involved when using a long lens and you're gonna have issues. My 30D is fine upto about 15 feet, then forget it, focusing becomes iffy (i'm talking ISO 1000 at 1/30 at 2.8 type of darkness, and with a 580 for focus assist). So keep than in mind as well.

Message edited by author 2007-08-03 11:55:34.

Samsung Galaxy S24, S24+, S24 Ultra

08/04/2007 01:35:39 AM · #18

Thanks Prof for your post. Yes, I think the user might be the problem. I've had trouble with him before, and apparently he can't be fixed, and they won't take him back. :)

I've been 'focussing' (ha ha) on the most problematic scenario (wide open closest focus, longest zoom), and judging the lens by that. I will give this lens some time, try it out more seriously in a variety of situations, and see how I get used to it.

(Just for the record, I tried it with another camera body today, and the result was the same.)

Bear_Music

Sony 24-70mm f/4 Vario-Tessar T* FE OSS

08/04/2007 02:00:11 AM · #19

Have I got this right? You're HAND HOLDING at f/2.8 and shooting macro outdoors? Geeze, my hands are incapable of holding a focus point reliably in that scenario, and I've done a LOT of it. I have to click off many frames and choose the one that actually has all the elements in the correct plane. Check out my Flowersx30 gallery, nearly all of them are f/2.8... But that's with Canon's REALLY GOOD macro lens, so it is actually very sharp wide open. Your lens can't possibly be that sharp wide open, I don't think.

So, as prof fate said, take her down to f/5.6 or f/8...

If you want to see if it's really got focus problems, you need a tripod and a yardstick, for a simple setup. Put the yardstick on a table, shoot it at a 45 degree angle, and focus on a specific mark on the stick. Do this at various apertures, maybe with a post-it in each shot with the aperture written on it for reference.

This will tell you two things: is the lens focusing where you tell it to, or is it showing front/rear focus shift? And how is the overall sharpness at the various apertures? Plus you can see the various DOF ranges...

R.

ShannonLee

08/04/2007 02:14:47 AM · #20

Originally posted by boysetsfire:

perfect :)

hah nick beat me to it. seriously though. join the funnnn!

Mr_Pants

SiPix Blink

08/04/2007 02:30:29 AM · #21

Originally posted by Bear_Music:

It's sort of possible, though an attempt is here.

Not a 100% crop, though.

I have seen Sigma lenses that look soft when wide open (the 18-50 f/2.8 being one example). If it were me, I'd try some test shots first in more 'normal' conditions, e.g on the street, at a zoo etc. and see how sharp the lens is wide open. You could also perhaps check out the lens forums at DPReview.