front focus?

mikerigel · 11-25-2006, 07:02 AM

Does it make a difference what focusing distance you're doing the test ? do you use the minimal, as close as you can be with your lens, or not ?
It appear I have a very slight front focus on mine.... I have to do a better test though..

**jfdavis58** · 11-25-2006, 08:15 AM

There's lots about this test that one should know before attempting it. Two items near the top of such a list: it's not an optical bench (with sub micrometer tools and fancy dedicated computers) that you will be using to perform the test, and your camera is a manufactured device-it's operating parameters are judged statistically to be in or out of spec when it was last inspected.

This test-either with the Jackson pdf and chart or via the book index page-is thought to work best at closest focus to the camera, wide open aperture. And herein lies another thing to know (posed as a question): will you regularly use the camera/lens in a similar fashion? With auto-focus-(FYI: I usually do my macro work with manual focus.)

Tony · 11-28-2006, 01:41 PM

When i use the fa 50 1.4 with my K100D at very large apertures i always select the bottom right focus point to get a focus lock and then recompose the pic. It is the only way i can be sure i wont get a front focus issue. The focus points on my camera are not aligned right and if i use the spot focus i get front focus. I have got so used to this it does not bother me one bit and was thinking you may have misaligned focus points too that are only evident when using very large apertures that have narrow depth of field

roscot · 11-28-2006, 05:50 PM

This is a new one for me. I don't ordinarily do testing, unless I suspect I've got a problem, but out of curiosity, I decided to try Sam's test with K10. I had interesting results. I tested a FA35 f2.0, FA50 f1.4, FA77 lmt, and a FA135 f2.8. Just for kicks I added the FA28-105 f3.2-f4.5 @ 50mm to the Mix.

This of course is not the most accurate test, it is just to get a general idea. It seems I have a little front focusing, at minimum focus distance with both the 35 and the 50. It's not to bad though. If I backed off some, the situation improved. Both the 77 and the 135 were dead on. Oh, and I got the shock of my life when I pixel peeped at the 135, wide open. I always new this is a very good lens, but this thing is not just tack sharp, it's razor sharp. I'm going to have to use this lens more often.

My off the cuff conclusion is the body is fine, and I probably have had the same FF issues with the 35 and 50 on my DS all along, but never noticed, because I'm usually stopped down a stop or 2, and DOF is covering it.

Sam, I'm glad you were able to resolve your issues. You obviouly had one that was out of calibration. Now go out and have fun with it.

Cheers
-Alan

11-25-2006, 08:15 AM	#17
jfdavis58 Site Supporter Join Date: Nov 2006 Location: 13 S 0357397-3884316 Photos: Gallery Posts: 887	Auto-focus testing There's lots about this test that one should know before attempting it. Two items near the top of such a list: it's not an optical bench (with sub micrometer tools and fancy dedicated computers) that you will be using to perform the test, and your camera is a manufactured device-it's operating parameters are judged statistically to be in or out of spec when it was last inspected. This test-either with the Jackson pdf and chart or via the book index page-is thought to work best at closest focus to the camera, wide open aperture. And herein lies another thing to know (posed as a question): will you regularly use the camera/lens in a similar fashion? With auto-focus-(FYI: I usually do my macro work with manual focus.)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
K-5 Manual Lens Front Focus & Focus Beep woes fixed	kneonx	Pentax K-5 & K-5 II	14	04-12-2014 03:47 PM
Front focus and back focus K-5	allantois	Pentax K-5 & K-5 II	48	03-31-2012 09:21 PM
Front focus far away, back focus up close	hjb981	Pentax K-5 & K-5 II	14	05-05-2011 01:28 AM
Trying to understand front focus/back focus thing	41ants	Troubleshooting and Beginner Help	16	08-31-2010 08:42 AM
front focus, back focus or other?	imfinetoday	Pentax SLR Lens Discussion	23	07-08-2010 11:49 AM

11-25-2006, 07:02 AM	#16
mikerigel Veteran Member Join Date: Sep 2006 Location: Florida Photos: Gallery Posts: 354	Does it make a difference what focusing distance you're doing the test ? do you use the minimal, as close as you can be with your lens, or not ? It appear I have a very slight front focus on mine.... I have to do a better test though..

11-28-2006, 01:41 PM	#18
Tony New Member Join Date: Sep 2006 Location: Hertfordshire UK Posts: 24	When i use the fa 50 1.4 with my K100D at very large apertures i always select the bottom right focus point to get a focus lock and then recompose the pic. It is the only way i can be sure i wont get a front focus issue. The focus points on my camera are not aligned right and if i use the spot focus i get front focus. I have got so used to this it does not bother me one bit and was thinking you may have misaligned focus points too that are only evident when using very large apertures that have narrow depth of field

11-28-2006, 05:50 PM	#19
roscot Veteran Member Join Date: Sep 2006 Location: Virginia Beach VA USA Photos: Gallery Posts: 1,363	This is a new one for me. I don't ordinarily do testing, unless I suspect I've got a problem, but out of curiosity, I decided to try Sam's test with K10. I had interesting results. I tested a FA35 f2.0, FA50 f1.4, FA77 lmt, and a FA135 f2.8. Just for kicks I added the FA28-105 f3.2-f4.5 @ 50mm to the Mix. This of course is not the most accurate test, it is just to get a general idea. It seems I have a little front focusing, at minimum focus distance with both the 35 and the 50. It's not to bad though. If I backed off some, the situation improved. Both the 77 and the 135 were dead on. Oh, and I got the shock of my life when I pixel peeped at the 135, wide open. I always new this is a very good lens, but this thing is not just tack sharp, it's razor sharp. I'm going to have to use this lens more often. My off the cuff conclusion is the body is fine, and I probably have had the same FF issues with the 35 and 50 on my DS all along, but never noticed, because I'm usually stopped down a stop or 2, and DOF is covering it. Sam, I'm glad you were able to resolve your issues. You obviouly had one that was out of calibration. Now go out and have fun with it. Cheers -Alan

Thread Tools	Search this Thread
	Search this Thread: Advanced Search