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03-23-2010, 01:34 PM   #1
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Advice required

Hi all,
I got my new Sigma 50-150 f2.8 today and suspect it may be slightly front focusing. Can someone advise me on how to test this properly please?
Thanks

03-23-2010, 02:02 PM   #2
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QuoteOriginally posted by Naim Khan Quote
Hi all,
I got my new Sigma 50-150 f2.8 today and suspect it may be slightly front focusing. Can someone advise me on how to test this properly please?
Thanks
A simple way, IMO, is to use 3-5 AA batteries. Alighn them at an angle, say 30 degrees, to your lens, then focus the middle one, take photos and check where the sharpest area is.

Last edited by ddhytz; 09-01-2010 at 08:07 PM.
03-23-2010, 02:15 PM   #3
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QuoteOriginally posted by ddhytz Quote
A simple way, IMO, is to use 3-5 AA batteries. Alighn them at an angle, say 30 degrees, to your lens, then focus the middle one, take photos and check where the sharpest area is.
Do it outside in good light..

03-23-2010, 02:17 PM   #4
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QuoteOriginally posted by ddhytz Quote
A simple way, IMO, is to use 3-5 AA batteries. Alighn them at an angle, say 30 degrees, to your lens, then focus the middle one, take photos and check where the sharpest area is.
Thanks ddhytz - that looks straight forward enough. I'll try it tomorrow.

03-23-2010, 02:27 PM   #5
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QuoteOriginally posted by JeffJS Quote
Do it outside in good light..

That may be a problem - it's going to rain for the next 2 or 3 days. I am living in sunny England after all!!
03-23-2010, 02:29 PM   #6
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Hey Jeff, completely off topic but can you tell me how you and a lot of others have the camera label as part of your signature. I want the K20 sign.
03-23-2010, 02:35 PM   #7
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QuoteOriginally posted by Naim Khan Quote
Hey Jeff, completely off topic but can you tell me how you and a lot of others have the camera label as part of your signature. I want the K20 sign.
https://www.pentaxforums.com/forums/other-pentax-related-topics/67605-pentax-...tags-more.html
03-23-2010, 02:40 PM   #8
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Hey Adam thanks.
Note the signature

03-23-2010, 04:47 PM   #9
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QuoteOriginally posted by Naim Khan Quote
That may be a problem - it's going to rain for the next 2 or 3 days. I am living in sunny England after all!!
Inside with a strong lamp then, I guess. But don't complain:

My electric bill was $287 last month in sunny Florida because of air conditioning, even though that was a COOL month.

Either that or I'm just being ripped off, but what else is new? And my place is small.
03-23-2010, 05:35 PM   #10
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QuoteOriginally posted by Ira Quote
My electric bill was $287 last month in sunny Florida because of air conditioning, even though that was a COOL month.
Either that or I'm just being ripped off, but what else is new? And my place is small.
Time to relocate. Zacatecas, and Guanajuato a bit south of there, are both glorious, incredibly photogenic, World Heritage Sites, and temperate. Downtown Guanajuato (which looks rather like a colonial city inside a 1/5-scale Yosemite Canyon) is at 6500 feet; the heart of Zacatecas (not far from a Corona brewery about the size of the VAB at Cape Canaveral) is at 8500. No hurricanes. No AC needed. Low cost; in Zacatecas, WalMart is the expensive big box.

Wait, this was supposed to be about back-focusing. My only problem there is if I back up while focusing and fall off the edge. Try to avoid that in Guanajuato.
03-24-2010, 12:19 AM   #11
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QuoteOriginally posted by Naim Khan Quote
That may be a problem - it's going to rain for the next 2 or 3 days. I am living in sunny England after all!!
QuoteOriginally posted by Naim Khan Quote
Hey Jeff, completely off topic but can you tell me how you and a lot of others have the camera label as part of your signature. I want the K20 sign.
You already have your answer for the sig pics. I actually just stole the ones for the cameras I have and built a single pic for the 3 cameras.

WRT to strong light for your tests, ok, pick the one day out of the year the sun actually shines to do it.. It seems that many people try doing these focus tests especially with the charts, in poor light and then they are surprised when they get wonky results and can't make suitable adjustments. You don't really want to use a flash either, again, especially with the charts.

03-24-2010, 04:46 AM   #12
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OK guys, I have done what ddhytz told me to do. Below is the result - the focus is on the middle battery (long live Costco!!!). Image stabilisation was set to 'OFF'. What do you think? Do you think it's OK?
03-24-2010, 02:47 PM   #13
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Given the angle we are looking at, I would say you are focused just in front of the Kirkland on the middle battery. I'm seeing some light blooming on the D in the middle battery and on the K on the one shown to the left of it. I suspect that if the photo weren't shot at an angle, one or the other would be dead nutz on and I would guess that point to be closer to the center battery, just in front of the Kirkland label. That's what I see anyway.

Maybe a slight adjustment is in order but I wouldn't go very far with it.

03-24-2010, 02:56 PM   #14
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Thanks Jeff for you input. I took some pictures with the lens a little while ago and they seemed pretty sharp to me. I agree with you that if the lens needs some adjustment, it is very little and my gut feeling is that I should keep it as it is. I am not sure how I would make the adjustment but it would involve sending the lens to Sigma (or is there a DIY method of doing so?).
Cheers.
03-24-2010, 03:35 PM   #15
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QuoteOriginally posted by Naim Khan Quote
Thanks Jeff for you input. I took some pictures with the lens a little while ago and they seemed pretty sharp to me. I agree with you that if the lens needs some adjustment, it is very little and my gut feeling is that I should keep it as it is. I am not sure how I would make the adjustment but it would involve sending the lens to Sigma (or is there a DIY method of doing so?).
Cheers.
Exif reports you have the K20d.. You can do minor individual AF adjustments for up to 20 different lenses. IIRC, the option is in the custom menu. You just go in there, select single lens and make your adjustment. The only issue with storing the adjustments is if the camera thinks another sigma lens is the same lens, the adjustment will apply to that one as well.

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