Are all copies of SMC Pentax-FA* 28-70mm F2.8 AL soft at 70 mm f 2.8?

naomi.mavro · 10-08-2015, 12:05 PM

Hi there,

My lens is very soft at 70 mm f 2.8, I would say unusable and I want to know If it is a bug and might be fixed or all copies of SMC Pentax-FA* 28-70mm F2.8 AL are the same.... I attached some photos so you can see how bad is it....

Thank you in advance for your reply
Naomi

Attached Images

View Picture EXIF

View Picture EXIF

Jonathan Mac · 10-08-2015, 12:11 PM

It's certainly very soft. Are you sure it's properly focused?

naomi.mavro · 10-08-2015, 12:24 PM

Originally posted by Jonathan Mac

It's certainly very soft. Are you sure it's properly focused?

The focus should be on the kid eye

**grahame** · 10-08-2015, 12:26 PM

It looks the focus point is closer to the objects.
Try adjusting the focus, or using live-view focusing to test the lens again.

naomi.mavro · 10-08-2015, 12:36 PM

If I use a tripod and also central point of focusing the result is the same, no improvement....

**grahame** · 10-08-2015, 12:43 PM

Originally posted by naomi.mavro

f I use a tripod and also central point of focusing the result is the same, no improvement....

Did you use live-view (CDF) focusing? Or focus manually by enlarge the image in screen?

naomi.mavro · 10-08-2015, 12:47 PM

The softness is very pronounced only at 70 mm f 2.8, if I go below the problem disappears...see photo...

---------- Post added 10-08-15 at 07:51 PM ----------

Originally posted by grahame

Did you use live-view (CDF) focusing? Or focus manually by enlarge the image in screen?

Why would I do that ...I shoot mainly people (handheld) and it is irrelevant because nobody have the patience to wait for me to focus in live view...

Attached Images

View Picture EXIF

**pasorro** · 10-08-2015, 12:56 PM

wich camera do you use, it is a k 5?

naomi.mavro · 10-08-2015, 01:09 PM

Originally posted by pasorro

wich camera do you use, it is a k 5?

K3 is my camera

JinDesu · 10-08-2015, 01:10 PM

Originally posted by naomi.mavro

The softness is very pronounced only at 70 mm f 2.8, if I go below the problem disappears...see photo...

---------- Post added 10-08-15 at 07:51 PM ----------

Why would I do that ...I shoot mainly people (handheld) and it is irrelevant because nobody have the patience to wait for me to focus in live view...

You would do that to test if it is an autofocus issue where the lens front focuses (as it appears to be, possibly) or if it literally is just soft at 70mm F2.8.

In fact, I'm almost certain it's front focusing. Look at the two pictures of your kid in his blue sweater vest. Look at the sweater vest where it sits closer to the camera than his face - it looks sharp there.

naomi.mavro · 10-08-2015, 01:14 PM

Originally posted by JinDesu

You would do that to test if it is an autofocus issue where the lens front focuses (as it appears to be, possibly) or if it literally is just soft at 70mm F2.8.

In fact, I'm almost certain it's front focusing. Look at the two pictures of your kid in his blue sweater vest. Look at the sweater vest where it sits closer to the camera than his face - it looks sharp there.

Indeed is quite sharp there... is it possible to be front focus only at the long end of the lens and not at the rest of it?

JinDesu · 10-08-2015, 01:17 PM - **1 Like**

Yep, many zoom lenses have different focusing characteristics throughout their range. My Tamron 70-200 backfocuses at 70mm, is neutral near 135mm, and front focuses at 200mm. I set it to correct for front focusing because the backfocusing at the short range is not that pronounced.

Your solution may be to test the focusing characteristics and see if adjusting it for slight front focus may help at 70mm and may not affect 24-69mm - or you could keep it in mind and just aim further behind your targets when at 70mm.

stevebrot · 10-08-2015, 01:52 PM

Originally posted by naomi.mavro

Why would I do that ...

You would do that because you asked for help on this forum. The user was attempting to walk you through a diagnostic flow to determine if the problem is with the PDAF (viewfinder AF), lens AF mechanism, or an optical problem.

Here is how it works:

Acceptable focus using AF(CDAF) in live view?
- If yes, tuning the PDAF may help.
- If no
  - Acceptable manual focus in live view (use magnified live view, see manual)?
    - If yes, there may be a mechanical issue with the lens AF linkage
    - If no, an optical issue is likely

Either of the last two points will require a service visit. Before fiddling with lens calibration is is best to establish that the lens is capable of sharp results. Manual focus using magnified live view is the gold standard.

Steve

**sholtzma** · 10-08-2015, 03:04 PM - **1 Like**

Short answer to your title question...no, not all copies are soft at 70mm f2.8, though that does tend to be the weakest point of this lens' performance. I just took out mine (on a K-5iis), took a shot of my cat 3-4 ft away (with flash to reduce hand shake and subject movement), and it was quite sharp. Did the same with my cat at 6-7 ft away with same results. Went outside, used LiveView to magnify a small flower 4 ft away, and the shot of it was very sharp. All ISOs at 80. If you wish, I can post the shots....

naomi.mavro · 10-08-2015, 10:38 PM

The test: first picture is without LiveView and the second is with....

10-08-2015, 01:52 PM	#13
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by naomi.mavro Why would I do that ... You would do that because you asked for help on this forum. The user was attempting to walk you through a diagnostic flow to determine if the problem is with the PDAF (viewfinder AF), lens AF mechanism, or an optical problem. Here is how it works: Acceptable focus using AF(CDAF) in live view? If yes, tuning the PDAF may help. If no Acceptable manual focus in live view (use magnified live view, see manual)? If yes, there may be a mechanical issue with the lens AF linkage If no, an optical issue is likely Either of the last two points will require a service visit. Before fiddling with lens calibration is is best to establish that the lens is capable of sharp results. Manual focus using magnified live view is the gold standard. Steve

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Pentax FA* 28-70 F2.8 vs Tokina ATX Pro 28-70 F2.6-2.8 The showdown	discharged	Pentax SLR Lens Discussion	11	01-30-2017 07:02 PM
For Sale - Sold: SMC Pentax-FA* 28-70mm f/2.8 AL- Now AUD900	KeiChoi	Sold Items	3	03-19-2013 12:23 PM
For Sale - Sold: Pentax FA* 28-70mm f2.8 AL lens + F 135mm f2.8 (Worldwide)	Fleafly	Sold Items	3	04-27-2010 02:47 PM
For Sale - Sold: SMC Pentax-FA* 2,8 28-70mm AL	jcm	Sold Items	7	01-26-2009 03:16 AM

10-08-2015, 12:11 PM	#2
Jonathan Mac Pentaxian Join Date: Apr 2009 Location: Madrid, Spain Posts: 10,894	It's certainly very soft. Are you sure it's properly focused?

10-08-2015, 12:24 PM	#3
naomi.mavro New Member Join Date: Jun 2013 Location: Bucharest-Romania Posts: 24 Original Poster	Originally posted by Jonathan Mac It's certainly very soft. Are you sure it's properly focused? The focus should be on the kid eye

10-08-2015, 12:26 PM	#4
grahame Loyal Site Supporter Join Date: Aug 2011 Photos: Albums Posts: 2,041	It looks the focus point is closer to the objects. Try adjusting the focus, or using live-view focusing to test the lens again.

10-08-2015, 12:36 PM	#5
naomi.mavro New Member Join Date: Jun 2013 Location: Bucharest-Romania Posts: 24 Original Poster	If I use a tripod and also central point of focusing the result is the same, no improvement....

10-08-2015, 12:43 PM	#6
grahame Loyal Site Supporter Join Date: Aug 2011 Photos: Albums Posts: 2,041	Originally posted by naomi.mavro f I use a tripod and also central point of focusing the result is the same, no improvement.... Did you use live-view (CDF) focusing? Or focus manually by enlarge the image in screen?

10-08-2015, 12:56 PM	#8
pasorro Site Supporter Join Date: May 2010 Posts: 132	wich camera do you use, it is a k 5?

10-08-2015, 01:09 PM	#9
naomi.mavro New Member Join Date: Jun 2013 Location: Bucharest-Romania Posts: 24 Original Poster	Originally posted by pasorro wich camera do you use, it is a k 5? K3 is my camera

10-08-2015, 01:10 PM	#10
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Originally posted by naomi.mavro The softness is very pronounced only at 70 mm f 2.8, if I go below the problem disappears...see photo... ---------- Post added 10-08-15 at 07:51 PM ---------- Why would I do that ...I shoot mainly people (handheld) and it is irrelevant because nobody have the patience to wait for me to focus in live view... You would do that to test if it is an autofocus issue where the lens front focuses (as it appears to be, possibly) or if it literally is just soft at 70mm F2.8. In fact, I'm almost certain it's front focusing. Look at the two pictures of your kid in his blue sweater vest. Look at the sweater vest where it sits closer to the camera than his face - it looks sharp there.

10-08-2015, 01:14 PM	#11
naomi.mavro New Member Join Date: Jun 2013 Location: Bucharest-Romania Posts: 24 Original Poster	Originally posted by JinDesu You would do that to test if it is an autofocus issue where the lens front focuses (as it appears to be, possibly) or if it literally is just soft at 70mm F2.8. In fact, I'm almost certain it's front focusing. Look at the two pictures of your kid in his blue sweater vest. Look at the sweater vest where it sits closer to the camera than his face - it looks sharp there. Indeed is quite sharp there... is it possible to be front focus only at the long end of the lens and not at the rest of it?

10-08-2015, 01:17 PM - 1 Like	#12
JinDesu Veteran Member Join Date: Jun 2011 Location: New York City Photos: Gallery Posts: 5,638	Yep, many zoom lenses have different focusing characteristics throughout their range. My Tamron 70-200 backfocuses at 70mm, is neutral near 135mm, and front focuses at 200mm. I set it to correct for front focusing because the backfocusing at the short range is not that pronounced. Your solution may be to test the focusing characteristics and see if adjusting it for slight front focus may help at 70mm and may not affect 24-69mm - or you could keep it in mind and just aim further behind your targets when at 70mm.

10-08-2015, 03:04 PM - 1 Like	#14
sholtzma Site Supporter Join Date: Sep 2007 Location: Salisbury, NC Photos: Gallery Posts: 1,043	Short answer to your title question...no, not all copies are soft at 70mm f2.8, though that does tend to be the weakest point of this lens' performance. I just took out mine (on a K-5iis), took a shot of my cat 3-4 ft away (with flash to reduce hand shake and subject movement), and it was quite sharp. Did the same with my cat at 6-7 ft away with same results. Went outside, used LiveView to magnify a small flower 4 ft away, and the shot of it was very sharp. All ISOs at 80. If you wish, I can post the shots....

Thread Tools	Search this Thread
	Search this Thread: Advanced Search