Sigma 30mm f1.4 and focusing issues

[Marshy]

Please excuse the large amount of photographic duffery that I'm about to exhibit in this post, but some opinions would be welcome.

I've become enamoured by the idea of a large aperture fixed focus lens for low light photography, primarily of bands in small clubs. My simpleton rationale is that if the aperture is that much bigger, camera shake isn't such an issue as it would be with the stock 18-55 kit lens, and I can trade the lack of zoom for being able to crop an inherently sharper picture down to get the results I want. As such, the Sigma 30mm f1.4 blah blah looked like a good lens for my 300D. Certainly the most aperture per buck I could see.

This lens looks to have been out since about mid 2005, and early reviews did seem to point out that quality control was an issue with many people talking about auto focus issues down at f1.4, and others having no problems. Some people seem to have got the lens swapped out, solving their issue.

I bought one yesterday, thinking that these issues ought to have been solved after a year and a half on the market. Seems not... Many test shots at f1.4 (using center weighted metering/focusing) are just plain out of focus, with the lens seeming to focus somewhere much closer than the object I've got the camera pointed at. Is this what people mean when they talk about "front focusing"?

Have I just got a duffer then? Here's an example photo taken earlier. I focused on the text on the big spikey grave thing. The most in focus object is actually the gravestone on the left. Seems plain wrong...

[poah]

they seem to be indifferent when focusing on far objects. whats it like close up?

[Marshy]

"Indifferent"

So: low light, close up (about 50cm away):-


Much more light:-


Another example - I was standing by the wing of the mondeo (perhaps obviously), focusing on the back of the fester (the pic is cropped, btw):-


Again the question ('cos I really am at the duffer end of the scale): am I expecting too much? Would (say) a Canon 50mm f1.8 perform better in terms of focusing on (comparatively) distant objects at f1.8? Certainly I'd get some coin back going for one of those - they're cheap as chips...

Thanks

Edited by Marshy on Sunday 28th January 13:25

Edited by Marshy on Sunday 28th January 13:26

[GetCarter]

'ello mate - I know nout about canons or that lens, but If I was focussing on the Fiesta and that's what turned up - I'd throw the lens into the sea.

[Marshy]

Right, off back to t'shop then.

Meh.

[Andy M]

Marshy said:

Right, off back to t'shop then.

Meh.

Is it by the sea?

How much did you pay for the lens?

Edit: all photo's taken in: www.pistonheads.com/gassing/topic.asp?t=349826&f=109&h=0 are with Canon's version of the 35 1.4 - a lens I highly recommend

Edited by Andy M on Sunday 28th January 14:20

[poah]

I find mine focuses in poor light but thats the camera not the lens (20d)

if its really focusing badly then exchange it. the lens is very sharp though

[mr noble]

That is a pretty massive distance for it get wrong!

Are you sure that your camera is set to the centre point focus both it the selector field and in the menus. You may find that you have the focus menu set to "closest subject" or something similar which will adversly affect your focusing.

Also, check the camera is set to fix the focus (and normally beep) when you press the shutter button halfway. If you press it halfway and then move the cam to be centered on another close subject does the camera refocus or not?

I got a Sigma 30mm f1.4 on Thursday and so far have been very pleased with it. It really does give a good few stops advantage. I'm yet to stretch its legs though.

HTH
G

[Marshy]

Andy M said:

Marshy said:

Right, off back to t'shop then.

Is it by the sea?
How much did you pay for the lens?
Edit: all photo's taken in: www.pistonheads.com/gassing/topic.asp?t=349826&f=109&h=0 are with Canon's version of the 35 1.4 - a lens I highly recommend

The shop is not by the sea, although if predictions for sea level rise and its effects on Cambridge are true, then it won't be long! I paid two hundred-and-mumble for the lens, about 40 quid over eBay price. But, that gets me the thirty day no quibble return policy which might just be handy in this case...

It's interesting that you recommend the Canon - is it the 50mm f1.4 USM or the 35mm f2? They're getting the f1.4 in for me to try ("try" being the operative word: something I should have done first... hey ho...)

poah said:

I find mine focuses in poor light but thats the camera not the lens (20d)
if its really focusing badly then exchange it. the lens is very sharp though

20d. Damn. Short on coinage for that sort of stuff :/

mr noble said:

That is a pretty massive distance for it get wrong!

That's what I thought.

mr noble said:

Are you sure that your camera is set to the centre point focus both it the selector field and in the menus. You may find that you have the focus menu set to "closest subject" or something similar which will adversly affect your focusing.Also, check the camera is set to fix the focus (and normally beep) when you press the shutter button halfway. If you press it halfway and then move the cam to be centered on another close subject does the camera refocus or not?

It's set to centre focus in the selector field, but there is no menu option relating to focusing: one of the cut downs of the 300D? I don't have the beep turned on, but there's a focus lock indicator in the viewfinder. It doesn't continually refocus as long as the shutter is half-pressed.

mr noble said:

I got a Sigma 30mm f1.4 on Thursday and so far have been very pleased with it. It really does give a good few stops advantage. I'm yet to stretch its legs though.

I've still got it at the moment, until a couple of Canon lenses come in for me to check it against. I'll see how I go...

The basic hole in my knowledge boils down to this: should a short lens like this be able to focus on objects off in the distance? I'm assuming so, since it does have an infinity marking on the distance chart thingumy, but I don't know if infinity has a special meaning when it comes to lenses. Damn, I need more time than I have to learn. (Day job: about to install a million quid's worth of global data network. Next passion: band. Some way down the list of things I get to do: take pictures...)

Edited by Marshy on Sunday 28th January 16:17

[poah]

this was taken with my sigma 30mm

[brightside]

Here are a couple taken this afternoon, as you can see the one's taken at F1.4 have a greater DOF.


F1.4

F1.4 focused on the second upright

F3.5 focused on the second upright

I hope this helps as a comparison, the camera focused with no problem and so far (3days) i'm pleased with the lens.

Iain

[Andy M]

Marshy said:

It's interesting that you recommend the Canon - is it the 50mm f1.4 USM or the 35mm f2? They're getting the f1.4 in for me to try ("try" being the operative word: something I should have done first... hey ho...)

It's the Canon 35mm f1.4 as seen here: www.fredmiranda.com/reviews/showproduct.php?product=24&sort=7&cat=2&page=2

I can't recommend it highly enough

brightside said:

F1.4 focused on the second upright

Something's a bit wrong there IMO. If I focused my Canon lens @ f1.4 at the 2nd upright, the rest would be lost in a creamy bokeh.

You sure it was at 1.4?

[brightside]

Andy, details as taken this afternoon

2007:01:28 15:44:28
30mm
1/1250 sec, f/1.4
Mode: Av
Metering: Evaluative
ISO: 200
AF mode: AI Focus AF
Drive: Single frame shooting
White balance: Auto
Flash: Off
File size: 2,875KB
Image size: 2336 x 3504
Color space: sRGB
Saturation: Normal
Sharpness: 3
Contrast: Normal
Picture Effect: Normal
Sharpness level: 3
Custom Functions:
Default settings

Just took a couple in auto as a reference.

Iain

[RobDickinson]

Marshy you 100% sure you have selected a single focal point and the center one at that?

Done the half press to focus on the right place then shifted the camera to frame the picture?

I know sigma can have focusing issues but the fiesta one looks to me far to badly out of whack to be a lens issue. Sigma often have issues focusing close up, distance focusing isnt usualy an issue.

Make sure you have one single focus point and thats firmly focused on the distance you want as the center of the DOF.

f1.4 can give a very shallow DoF , especialy when close focused.

Alternativly download a focus chart, use a tripod and do some tests instead of real world shots where things can get inthe way.

BTW I think the tailing shot could be f1.4, focus point is soem distance away from the camera and at low focal lengths you get bigger DoF anyhow.

[RobDickinson]

Marshy said:

The basic hole in my knowledge boils down to this: should a short lens like this be able to focus on objects off in the distance?

Focal length of the lens shouldnt alter its ability to focus on a specific point at all. my sigma 10-20mm focuses just fine (on a 350d).

[GetCarter]

IMHO: In every reasonably lit condition, if you autofocus on a part of the frame - that part of the frame should be in focus - regardless of lens or apature. If it isn't you should seek the sea or the shop you bought it from (unless your camera is crap or bust of course).

[Marshy]

RobDickinson said:

Marshy you 100% sure you have selected a single focal point and the center one at that?
Done the half press to focus on the right place then shifted the camera to frame the picture

Yes to both. The shot of the fiesta has the fiesta's arse dead centre before the crop. I've selected only centre focus point and that's the only thing that shows the little red dot in the viewfinder too.

Rob said:

f1.4 can give a very shallow DoF , especialy when close focused.

I know that - and it's one of the things that appeals. I just expected it to be capable of stuff more than 40cm away, that's all

Rob said:

Alternativly download a focus chart, use a tripod and do some tests instead of real world shots where things can get inthe way.

Just so happens that I've just done that. (Hang on a sec...)

Now, this isnt' like for like, since the std Canon lens only goes down to f5.6, but to preclude the body being totally shagged...

The standard Canon 18-55mm jobby at f5.6:-


The Sigma at f1.4:-


Next question: do I need to throw more light at that test?

[Marshy]

GetCarter said:

IMHO: In every reasonably lit condition, if you autofocus on a part of the frame - that part of the frame should be in focus - regardless of lens or apature. If it isn't you should seek the sea or the shop you bought it from (unless your camera is crap or bust of course).

The sea it is then. Hell, I need an excuse to get out to the coast...

Thing is, I "hand set" the tripod to 45 degrees a.k.a. it doesn't have a scale on it. Who the hell owns protractors these days? That said, I was focusing on the bit that says "focus here" so it shoulnd't be *that* far out of whack. Bah.

And thanks - everybody - for advice and comments so far. Very useful and educational.

[RobDickinson]

Aer they tripod mounted shots? Sigma looks like its front focused a little but also very soft (should be as good as the kit wide open or better - somewhere), more light would definatly help, the 300d isnt the best focusing in low light.

Try setting up a more real world test of bottles on a table spaced about 1ft apart focus on each as you go.

Also try a manual focus shot or two.

[Marshy]

Drinking and photography - great idea.

And yes, they were tripod shot using the timer.