How to check focus on a v wide angle lens?


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Kanski

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Nov 4, 2007
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Hi,

I've tried searching for this on here plus dpreview, but was wondering if anyone could point me towards or post advice on this?

I'm going to buy a Tokina 11-16mm f2.8 in Hong Kong. But I'm not sure how to test if the focus is accurate (if there are any other tips on checking out the lens I'd be grateful to hear those too).

Surely the depth of field is too big to use a focus chart?

I know real world pictures are best but I won't have much time there.

Thanks for your time,

James
 

night86mare

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go close to something relatively moderately sized with words, and then af lor

when you are focusing very close with any lens, the dof is razor thin comparatively

something like this is a good example of what i am talking about, but please use a more appropriate item



then check focus to infinity, i think that should be it
 

Kanski

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Thanks for the advice, I didn't know about the close focus thing.

I think the lens focuses from 1 foot away.

Normally I'd line up targets different distances from each other and chose something in the middle.

Ok, using a dof calc: my D80, 11mm, 1 ft away, at f2.8: gives a dof of 0.28 ft Cool!

Umm, how do I check focus to infinity? Do I take a pic of something very far away and looks at it on a computer monitor?

thanks,

James
 

night86mare

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Thanks for the advice, I didn't know about the close focus thing.

I think the lens focuses from 1 foot away.

Normally I'd line up targets different distances from each other and chose something in the middle.

Ok, using a dof calc: my D80, 11mm, 1 ft away, at f2.8: gives a dof of 0.28 ft Cool!

Umm, how do I check focus to infinity? Do I take a pic of something very far away and looks at it on a computer monitor?

thanks,

James
based on slrgear.com, closest focus (at max wide) should be 0.3m / 11.8 in. so yes, that should be about a foot.

you can probably do the same thing, if you shoot wide open at f/2.8.

you don't have to use computer monitor, just zoom in and check if it is reasonably sharp

just in case though, it is good to note that i am a relatively suka buyer.. if you want to really make sure spot on, i personally do not really care since the idea is that you will be shooting at f/8 most of the time, and it is rare that you would even experience depth of field problems even with wider apertures.
 

Kanski

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Nov 4, 2007
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Thanks for taking the time to reply. The hours I've spent gazing at your photos makes me a big fan of your work.

I agree I'll mostly be at f8. Though the reason for buying this lens and not the Sigma 10-20 f4 was to try and use it for low light situations (and play around with the dof:) ). I actually prefer the HSM of the Sigma.

I guess I just want to make sure I've not got a dud, as I'm a bit wary of 3rd party lenses.

Cheers,

James

p.s. what is a 'suka buyer'? I know suka suka means 'like'
 

night86mare

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#6
Thanks for taking the time to reply. The hours I've spent gazing at your photos makes me a big fan of your work.

I agree I'll mostly be at f8. Though the reason for buying this lens and not the Sigma 10-20 f4 was to try and use it for low light situations (and play around with the dof:) ). I actually prefer the HSM of the Sigma.

I guess I just want to make sure I've not got a dud, as I'm a bit wary of 3rd party lenses.

Cheers,

James

p.s. what is a 'suka buyer'? I know suka suka means 'like'
between you and me, i think the f/2.8 might help in low light, especially when you do not have SR. wide angles are very resilient to hand shake compare to normal or telephoto.. but even then it will help.

as for play of dof - some others had approached me on this, to be frank i do not think you are going to get very shallow dof for most situations where it is required unless it is the right place, right time, i.e. subject is very far away from background.

yes, for 3rd party best to check. other than focus just remember to check that you've gotten a reasonably sharp copy. remember, shooting at wide open will be soft no matter what lens you use, especially when zoom in. but the lens should be really sharp (bar hand shake or any other obscure factor) when at f/8 to f/11.
 

KY1977

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Jan 3, 2008
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#7
go close to something relatively moderately sized with words, and then af lor

when you are focusing very close with any lens, the dof is razor thin comparatively

something like this is a good example of what i am talking about, but please use a more appropriate item



then check focus to infinity, i think that should be it
Cute toy
 

Kanski

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Nov 4, 2007
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#8
between you and me, i think the f/2.8 might help in low light, especially when you do not have SR. wide angles are very resilient to hand shake compare to normal or telephoto.. but even then it will help.

as for play of dof - some others had approached me on this, to be frank i do not think you are going to get very shallow dof for most situations where it is required unless it is the right place, right time, i.e. subject is very far away from background.

yes, for 3rd party best to check. other than focus just remember to check that you've gotten a reasonably sharp copy. remember, shooting at wide open will be soft no matter what lens you use, especially when zoom in. but the lens should be really sharp (bar hand shake or any other obscure factor) when at f/8 to f/11.
Thanks for your reply. I'm really looking forward to this lens. I can just imagine all the light that is going in at 11mm and 2.8 :cool:

I just hope that the CA correction in NX is up to the job and that I don't miss the HSM of the Sigma- but the huge DOF will help.

I'm not quite sure how to check whether the lens is sharp enough at f8 though, as I'm not thinking of bringing the laptop. Still, I guess I'll compare it to my 105mm f2.8 which is reasonably sharp.

Cheers,

James
 

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