What Are Your Experiences with 28mm Lenses?

**richard0170** · 04-17-2021, 04:05 AM

Some time has been spent doing some extensive testing of my F 28 and A 28mm's, as 1. I have been puzzled by the difference in results despite the same optical formula and 2. I really would like an A 28mm to perform as well as the F model, preferring MF lenses and physically the A is such a sweet one.

What I have found is that the A can be as sharp as the F at all apertures, but your focusing has to be bang on. It appears the AF of the F is more reliable than my eyes and manually focusing, at least when using a standard screen. My K3 has a Focusscreens.com cut down Canon micro-prism screen installed and the keeper rate as far as focusing goes is much higher now. I still experience unreliable exposures with the A though.

As a self confessed 28mm junkie on APSC, all this experimentation has convinced me to think that I need (Ha! Ha!) a M 28mm f3.5. Unfortunately they seem to have become quite rare and relatively expensive. Hopefully supply issues will improve as lockdowns start to end.

**GUB** · 04-17-2021, 05:14 AM

Originally posted by richard0170

Some time has been spent doing some extensive testing of my F 28 and A 28mm's, as 1. I have been puzzled by the difference in results despite the same optical formula and 2. I really would like an A 28mm to perform as well as the F model, preferring MF lenses and physically the A is such a sweet one.

What I have found is that the A can be as sharp as the F at all apertures, but your focusing has to be bang on. It appears the AF of the F is more reliable than my eyes and manually focusing, at least when using a standard screen. My K3 has a Focusscreens.com cut down Canon micro-prism screen installed and the keeper rate as far as focusing goes is much higher now. I still experience unreliable exposures with the A though.

As a self confessed 28mm junkie on APSC, all this experimentation has convinced me to think that I need (Ha! Ha!) a M 28mm f3.5. Unfortunately they seem to have become quite rare and relatively expensive. Hopefully supply issues will improve as lockdowns start to end.

Try Live view and see if you miss focus. (focus peaking on) Easy-as with a 28mm.

**richard0170** · 04-17-2021, 05:57 AM

Originally posted by GUB

Try Live view and see if you miss focus. (focus peaking on) Easy-as with a 28mm.

Already tried that - no joy, and to my mind negates the point of an OVF.

**TwoUptons** · 04-17-2021, 02:29 PM

Originally posted by richard0170

Already tried that - no joy, and to my mind negates the point of an OVF.

Do you need to calibrate your camera's AF?
It will change where the focus confirmation light calls it good.
As my eyes age, I'm more reliant on that than I'd like to admit...

-Eric

trixtroll · 04-17-2021, 07:02 PM

Originally posted by richard0170

Already tried that - no joy, and to my mind negates the point of an OVF.

I recently picked up a Pentax-A 28mm and have also had a terrible time with the manual focus.

Focusing to 0 feet, then slowly focus towards infinity and stopping as soon as the red assist light flashes works well for me.

It’s not quick, but it netted more keepers today.

**MSL** · 04-17-2021, 08:12 PM

I have also found the A28 challenging to use. The issues that I find most difficult are the short focus throw that makes it hard to nail focus and this is particularly bad towards infinity. In talking with others I get the impression that this lens works better as a walk around street lens than it does for landscapes for example.

**GUB** · 04-18-2021, 04:45 AM

I am sorry but I don't understand these issues. I find the A28 and the Tak Bayonet 28mm the easiest of lenses to focus.
Have you checked that your lenses are achieving infinity?
Have you checked that they are not stopping past infinity. (my A50 1.7 does).
If they are stopping nicely at infinity how hard can it be to take a landscape shot?
Even at f4 anything more than say 40 meters (arguably) can be considered infinity so just smack the lens to the end.
I tend to use my 28mm lenses at the open end and maybe that is the difference?
In Liveview with these sharp lenses used open the focus peaking is strong and obvious.

**UncleVanya** · 04-18-2021, 05:44 AM

Originally posted by trixtroll

I recently picked up a Pentax-A 28mm and have also had a terrible time with the manual focus.

Focusing to 0 feet, then slowly focus towards infinity and stopping as soon as the red assist light flashes works well for me.

It’s not quick, but it netted more keepers today.

That’s odd since the red light isn’t for focus confirmation. It only shows where focus is being attempted. The green hexagon is what shows if you are focused. However the red light does light up earlier than the green hexagon so maybe for your lens that’s a more reliable indicator of focus?

trixtroll · 04-18-2021, 06:44 AM

Originally posted by AgentL

I'm interested in getting an inexpensive 28mm lens for the KP, as I think that gets me closest to 40mm equivalent, which is a focal length I really like. I like small primes, but I'm willing to experiment with anything if it's inexpensive. Do you have experience with a 28mm that you like, and why?

I guess I never really answered your question on my previous post.

I’ve had two 28mm primes and agree that it’s a very nice focal on the KP.

My first was a Sears 28mm F2.8 and they look to be around $30 on eBay. It provided very nice images when shooting on Tri-X 400, but not so much on digital. I tried it on my (former) K10 and the contrast and colors were always poor.

I currently have a Pentax-A 28mm F2.8 mounted on my KP and the images are much nicer, but I’m struggling with manual focus. That could entirely be a user error or lack of calibration. I paid $59 and the aperture control contact makes it so much nicer to use.

**AgentL** · 04-19-2021, 10:09 AM

Originally posted by trixtroll

I guess I never really answered your question on my previous post.

I’ve had two 28mm primes and agree that it’s a very nice focal on the KP.

My first was a Sears 28mm F2.8 and they look to be around $30 on eBay. It provided very nice images when shooting on Tri-X 400, but not so much on digital. I tried it on my (former) K10 and the contrast and colors were always poor.

I currently have a Pentax-A 28mm F2.8 mounted on my KP and the images are much nicer, but I’m struggling with manual focus. That could entirely be a user error or lack of calibration. I paid $59 and the aperture control contact makes it so much nicer to use.

Thanks, I did try an M 28mm for a bit, but didn't find the IQ to be particularly good - it reminded me why I don't typically like to manually focus with modern digital cameras. The focus confirmation in the KP is nice, but I find I've turned slightly past by the time my brain registers the green light is on.

AH11 · 04-19-2021, 12:06 PM

I had the Pentax K 28mm f3.5. It was a decent manual focus lens but very difficult to focus properly. I hardly ever used it and had to let go of it.

**GUB** · 04-19-2021, 01:46 PM

Cmon guys if you apply a circle of confusion (coc) of .005mm to a 28mm at f4 and focus at 40 metres then everything between 20 metres and infinity has a maximum coc of .005mm . This is the size of a K-1 or K5 pixel and is actually 1/6 of the standard coc applied to full frame.
The issue is more - how can you miss focus?
Time to find another reason for soft images - not just focusing.

**robbiec** · 04-19-2021, 04:06 PM

Save your money and save for a FA31, it'll work out cheaper in the long run. @rparmar had a massive thread years ago on the various Vivitar 28s - some were pretty good but none got really close.

**MSL** · 04-19-2021, 05:37 PM

Originally posted by GUB

Cmon guys if you apply a circle of confusion (coc) of .005mm to a 28mm at f4 and focus at 40 metres then everything between 20 metres and infinity has a maximum coc of .005mm . This is the size of a K-1 or K5 pixel and is actually 1/6 of the standard coc applied to full frame.The issue is more - how can you miss focus?Time to find another reason for soft images - not just focusing.

Everything in that range may be in focus, but it doesn't mean everything in that range will be sharp.

**GUB** · 04-19-2021, 08:40 PM

Originally posted by MSL

Everything in that range may be in focus, but it doesn't mean everything in that range will be sharp.

Then it is not focusing that is the issue.

04-17-2021, 07:02 PM	#125
trixtroll Pentaxian Join Date: Sep 2009 Location: Dayton, OH Posts: 403	Originally posted by richard0170 Already tried that - no joy, and to my mind negates the point of an OVF. I recently picked up a Pentax-A 28mm and have also had a terrible time with the manual focus. Focusing to 0 feet, then slowly focus towards infinity and stopping as soon as the red assist light flashes works well for me. It’s not quick, but it netted more keepers today. Last edited by trixtroll; 04-17-2021 at 07:08 PM.

04-19-2021, 01:46 PM	#132
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760	Cmon guys if you apply a circle of confusion (coc) of .005mm to a 28mm at f4 and focus at 40 metres then everything between 20 metres and infinity has a maximum coc of .005mm . This is the size of a K-1 or K5 pixel and is actually 1/6 of the standard coc applied to full frame. The issue is more - how can you miss focus? Time to find another reason for soft images - not just focusing. Attached Images

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04-17-2021, 04:05 AM	#121
richard0170 Site Supporter Join Date: Feb 2017 Photos: Gallery \| Albums Posts: 2,032	Some time has been spent doing some extensive testing of my F 28 and A 28mm's, as 1. I have been puzzled by the difference in results despite the same optical formula and 2. I really would like an A 28mm to perform as well as the F model, preferring MF lenses and physically the A is such a sweet one. What I have found is that the A can be as sharp as the F at all apertures, but your focusing has to be bang on. It appears the AF of the F is more reliable than my eyes and manually focusing, at least when using a standard screen. My K3 has a Focusscreens.com cut down Canon micro-prism screen installed and the keeper rate as far as focusing goes is much higher now. I still experience unreliable exposures with the A though. As a self confessed 28mm junkie on APSC, all this experimentation has convinced me to think that I need (Ha! Ha!) a M 28mm f3.5. Unfortunately they seem to have become quite rare and relatively expensive. Hopefully supply issues will improve as lockdowns start to end.

04-17-2021, 05:14 AM	#122
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760	Originally posted by richard0170 Some time has been spent doing some extensive testing of my F 28 and A 28mm's, as 1. I have been puzzled by the difference in results despite the same optical formula and 2. I really would like an A 28mm to perform as well as the F model, preferring MF lenses and physically the A is such a sweet one. What I have found is that the A can be as sharp as the F at all apertures, but your focusing has to be bang on. It appears the AF of the F is more reliable than my eyes and manually focusing, at least when using a standard screen. My K3 has a Focusscreens.com cut down Canon micro-prism screen installed and the keeper rate as far as focusing goes is much higher now. I still experience unreliable exposures with the A though. As a self confessed 28mm junkie on APSC, all this experimentation has convinced me to think that I need (Ha! Ha!) a M 28mm f3.5. Unfortunately they seem to have become quite rare and relatively expensive. Hopefully supply issues will improve as lockdowns start to end. Try Live view and see if you miss focus. (focus peaking on) Easy-as with a 28mm.

04-17-2021, 05:57 AM	#123
richard0170 Site Supporter Join Date: Feb 2017 Photos: Gallery \| Albums Posts: 2,032	Originally posted by GUB Try Live view and see if you miss focus. (focus peaking on) Easy-as with a 28mm. Already tried that - no joy, and to my mind negates the point of an OVF.

04-17-2021, 02:29 PM	#124
TwoUptons Loyal Site Supporter Join Date: Nov 2015 Photos: Albums Posts: 4,213	Originally posted by richard0170 Already tried that - no joy, and to my mind negates the point of an OVF. Do you need to calibrate your camera's AF? It will change where the focus confirmation light calls it good. As my eyes age, I'm more reliant on that than I'd like to admit... -Eric

04-17-2021, 08:12 PM	#126
MSL Site Supporter Join Date: Feb 2012 Location: Greater Toronto Area Photos: Gallery \| Albums Posts: 4,749	I have also found the A28 challenging to use. The issues that I find most difficult are the short focus throw that makes it hard to nail focus and this is particularly bad towards infinity. In talking with others I get the impression that this lens works better as a walk around street lens than it does for landscapes for example.

04-18-2021, 04:45 AM	#127
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760	I am sorry but I don't understand these issues. I find the A28 and the Tak Bayonet 28mm the easiest of lenses to focus. Have you checked that your lenses are achieving infinity? Have you checked that they are not stopping past infinity. (my A50 1.7 does). If they are stopping nicely at infinity how hard can it be to take a landscape shot? Even at f4 anything more than say 40 meters (arguably) can be considered infinity so just smack the lens to the end. I tend to use my 28mm lenses at the open end and maybe that is the difference? In Liveview with these sharp lenses used open the focus peaking is strong and obvious.

04-18-2021, 05:44 AM	#128
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,401	Originally posted by trixtroll I recently picked up a Pentax-A 28mm and have also had a terrible time with the manual focus. Focusing to 0 feet, then slowly focus towards infinity and stopping as soon as the red assist light flashes works well for me. It’s not quick, but it netted more keepers today. That’s odd since the red light isn’t for focus confirmation. It only shows where focus is being attempted. The green hexagon is what shows if you are focused. However the red light does light up earlier than the green hexagon so maybe for your lens that’s a more reliable indicator of focus?

04-18-2021, 06:44 AM	#129
trixtroll Pentaxian Join Date: Sep 2009 Location: Dayton, OH Posts: 403	Originally posted by AgentL I'm interested in getting an inexpensive 28mm lens for the KP, as I think that gets me closest to 40mm equivalent, which is a focal length I really like. I like small primes, but I'm willing to experiment with anything if it's inexpensive. Do you have experience with a 28mm that you like, and why? I guess I never really answered your question on my previous post. I’ve had two 28mm primes and agree that it’s a very nice focal on the KP. My first was a Sears 28mm F2.8 and they look to be around $30 on eBay. It provided very nice images when shooting on Tri-X 400, but not so much on digital. I tried it on my (former) K10 and the contrast and colors were always poor. I currently have a Pentax-A 28mm F2.8 mounted on my KP and the images are much nicer, but I’m struggling with manual focus. That could entirely be a user error or lack of calibration. I paid $59 and the aperture control contact makes it so much nicer to use.

04-19-2021, 10:09 AM	#130
AgentL Site Supporter Join Date: Sep 2020 Location: Seattle Photos: Albums Posts: 1,756 Original Poster	Originally posted by trixtroll I guess I never really answered your question on my previous post. I’ve had two 28mm primes and agree that it’s a very nice focal on the KP. My first was a Sears 28mm F2.8 and they look to be around $30 on eBay. It provided very nice images when shooting on Tri-X 400, but not so much on digital. I tried it on my (former) K10 and the contrast and colors were always poor. I currently have a Pentax-A 28mm F2.8 mounted on my KP and the images are much nicer, but I’m struggling with manual focus. That could entirely be a user error or lack of calibration. I paid $59 and the aperture control contact makes it so much nicer to use. Thanks, I did try an M 28mm for a bit, but didn't find the IQ to be particularly good - it reminded me why I don't typically like to manually focus with modern digital cameras. The focus confirmation in the KP is nice, but I find I've turned slightly past by the time my brain registers the green light is on.

04-19-2021, 12:06 PM	#131
AH11 Junior Member Join Date: Jan 2011 Location: Los Angeles, CA Photos: Gallery Posts: 38	I had the Pentax K 28mm f3.5. It was a decent manual focus lens but very difficult to focus properly. I hardly ever used it and had to let go of it.

04-19-2021, 04:06 PM	#133
robbiec Site Supporter Join Date: Feb 2009 Location: Cork Photos: Albums Posts: 1,882	Save your money and save for a FA31, it'll work out cheaper in the long run. @rparmar had a massive thread years ago on the various Vivitar 28s - some were pretty good but none got really close.

04-19-2021, 05:37 PM	#134
MSL Site Supporter Join Date: Feb 2012 Location: Greater Toronto Area Photos: Gallery \| Albums Posts: 4,749	Originally posted by GUB Cmon guys if you apply a circle of confusion (coc) of .005mm to a 28mm at f4 and focus at 40 metres then everything between 20 metres and infinity has a maximum coc of .005mm . This is the size of a K-1 or K5 pixel and is actually 1/6 of the standard coc applied to full frame.The issue is more - how can you miss focus?Time to find another reason for soft images - not just focusing. Everything in that range may be in focus, but it doesn't mean everything in that range will be sharp.

04-19-2021, 08:40 PM	#135
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,760	Originally posted by MSL Everything in that range may be in focus, but it doesn't mean everything in that range will be sharp. Then it is not focusing that is the issue.