Help for getting better results with close-focus AF for an f1.8 20mm Sigma on the K1

pimpim · 01-13-2023, 02:11 AM

Originally posted by pschlute

Are you aware that a 20mm 1.8 lens at a distance of 8 inches has a DOF of less than half an inch ? How much do you sway or your kids move between AF lock and the shutter trigger ?

Even with on-camera flash this is what you can do. K-1II + DFA 21mm at f11 ISO 200. Diffused single flash......... ps..I hazard a guess that my 6 month old Spaniel can out-run your kids

Those dogs have beautiful hair

Flash would be an issue though, would create a lot of excitement in the room

Also don't want to get too much DOF because there's usually some bunch of toys in the background I'd like to hide in the out of focus areas

I think I start doing the fine tuning and also will crank up the aperture a bit. I also have a 28mm f1.8 Sigma that creates a bit more usable focusing distance.
In my personal opinion the 20mm look works well on young kids because any distortion it creates somehow fits the playful setting.

Because these bright f1.8 wide angle AF lenses were all developed for the analog era I do wonder what kind of results people got with them with the analog cameras from the era. Maybe combined with a grainy high iso black and white film it wouldn't matter too much to get the focus completely right, and you would be able to get at least some photos in very difficult light conditions.

Good to hear the modern Pentax lenses could actually boost my AF accuracy for these kind of focal lengths, but my photography related funds all went into the K1

and I like the image rendering of these older lenses.

One thing I picked up from all feedback here is that the combination of these older lenses with APS-C bodies is likely a more easy-going way to use this old glass and suffer a bit less from their disadvantages concerning alignment and/or AF issues. I previously thought going native full frame would be the way to go, but maybe instead of the K1 the K3iii is a better fit for my goal of using Pentax for vintage AF glass.

---------- Post added 13-01-23 at 02:16 ----------

Originally posted by AstroDave

Yeah, but you've got his attention!!!

With my toddler I have an additional challenge as she wants to use the camera herself

I already sometimes let her press the shutter and handle the cameras, she tries to look through the viewfinder and loves all the mechanical sounds of the motor drive and mirror and shutter. I am already looking for a cheap 35mm plastic da or the small 21mm so she could actually play around with a relatively light K-R.

pschlute · 01-13-2023, 02:22 AM - **1 Like**

Originally posted by pimpim

Good to hear the modern Pentax lenses could actually boost my AF accuracy for these kind of focal lengths

To be honest I never use AF at all when using a lens of 20mm or thereabouts on FF. My picture above was pre focussed on a spot on the carpet before I brought my dogs (I mean models !) into the room. I use the DOF scale that is etched on the lens to ensure all I want to be in focus will be.

Originally posted by pimpim

my goal of using Pentax for vintage AF glass

I love using old Pentax glass, and do so a lot. Manual focus on the older primes takes a bit of technique but is not difficult and you can use the AF confirmation to help too.

pimpim · 01-13-2023, 02:49 AM

Originally posted by pschlute

I love using old Pentax glass, and do so a lot. Manual focus on the older primes takes a bit of technique but is not difficult and you can use the AF confirmation to help too.

I'm getting some really nice keepers using catch-in focus with an old Sigma filtermatic 24mm (this has a very precise focus throw!) at f2.8 on a K-X, where the 12MP and grain are quite forgiving ...

.. but it drives my wife crazy so I need the AF as well

**mikesbike** · 01-13-2023, 11:45 AM

Originally posted by pres589

A 20mm on full-frame has a certain ring to it but I don't know if I'd use it for photographing kids.

Same here. I would likely be using a zoom lens, or if a prime, something far less wide. And I agree with those questioning shooting at f/1.8, though it would provide more shutter speed for moving subjects indoors without flash, at the same time, your DOF would be very shallow, even with such a WA lens. Also, with most ultra-WA lenses, AF is more touchy even if working well, because objects appear much smaller in the VF and many are then harder for the AF points to pick up and zero in on. The reduced indoor lighting doesn't help the AF system either.

Try a less-WA lens, reduced AF points to include only a central area, and practice to improve your panning skills!

Last edited by mikesbike; 01-13-2023 at 11:51 AM.

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01-13-2023, 02:11 AM	#16
pimpim Senior Member Join Date: Sep 2010 Location: Mainz Photos: Albums Posts: 253 Original Poster	Originally posted by pschlute Are you aware that a 20mm 1.8 lens at a distance of 8 inches has a DOF of less than half an inch ? How much do you sway or your kids move between AF lock and the shutter trigger ? Even with on-camera flash this is what you can do. K-1II + DFA 21mm at f11 ISO 200. Diffused single flash......... ps..I hazard a guess that my 6 month old Spaniel can out-run your kids Those dogs have beautiful hair Flash would be an issue though, would create a lot of excitement in the room Also don't want to get too much DOF because there's usually some bunch of toys in the background I'd like to hide in the out of focus areas I think I start doing the fine tuning and also will crank up the aperture a bit. I also have a 28mm f1.8 Sigma that creates a bit more usable focusing distance. In my personal opinion the 20mm look works well on young kids because any distortion it creates somehow fits the playful setting. Because these bright f1.8 wide angle AF lenses were all developed for the analog era I do wonder what kind of results people got with them with the analog cameras from the era. Maybe combined with a grainy high iso black and white film it wouldn't matter too much to get the focus completely right, and you would be able to get at least some photos in very difficult light conditions. Good to hear the modern Pentax lenses could actually boost my AF accuracy for these kind of focal lengths, but my photography related funds all went into the K1 and I like the image rendering of these older lenses. One thing I picked up from all feedback here is that the combination of these older lenses with APS-C bodies is likely a more easy-going way to use this old glass and suffer a bit less from their disadvantages concerning alignment and/or AF issues. I previously thought going native full frame would be the way to go, but maybe instead of the K1 the K3iii is a better fit for my goal of using Pentax for vintage AF glass. ---------- Post added 13-01-23 at 02:16 ---------- Originally posted by AstroDave Yeah, but you've got his attention!!! With my toddler I have an additional challenge as she wants to use the camera herself I already sometimes let her press the shutter and handle the cameras, she tries to look through the viewfinder and loves all the mechanical sounds of the motor drive and mirror and shutter. I am already looking for a cheap 35mm plastic da or the small 21mm so she could actually play around with a relatively light K-R.

01-13-2023, 02:22 AM - 1 Like	#17
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,210	Originally posted by pimpim Good to hear the modern Pentax lenses could actually boost my AF accuracy for these kind of focal lengths To be honest I never use AF at all when using a lens of 20mm or thereabouts on FF. My picture above was pre focussed on a spot on the carpet before I brought my dogs (I mean models !) into the room. I use the DOF scale that is etched on the lens to ensure all I want to be in focus will be. Originally posted by pimpim my goal of using Pentax for vintage AF glass I love using old Pentax glass, and do so a lot. Manual focus on the older primes takes a bit of technique but is not difficult and you can use the AF confirmation to help too.

01-13-2023, 02:49 AM	#18
pimpim Senior Member Join Date: Sep 2010 Location: Mainz Photos: Albums Posts: 253 Original Poster	Originally posted by pschlute I love using old Pentax glass, and do so a lot. Manual focus on the older primes takes a bit of technique but is not difficult and you can use the AF confirmation to help too. I'm getting some really nice keepers using catch-in focus with an old Sigma filtermatic 24mm (this has a very precise focus throw!) at f2.8 on a K-X, where the 12MP and grain are quite forgiving ... .. but it drives my wife crazy so I need the AF as well

01-13-2023, 11:45 AM	#19
mikesbike Site Supporter Join Date: Dec 2016 Location: Southeastern Michigan Posts: 4,558	Originally posted by pres589 A 20mm on full-frame has a certain ring to it but I don't know if I'd use it for photographing kids. Same here. I would likely be using a zoom lens, or if a prime, something far less wide. And I agree with those questioning shooting at f/1.8, though it would provide more shutter speed for moving subjects indoors without flash, at the same time, your DOF would be very shallow, even with such a WA lens. Also, with most ultra-WA lenses, AF is more touchy even if working well, because objects appear much smaller in the VF and many are then harder for the AF points to pick up and zero in on. The reduced indoor lighting doesn't help the AF system either. Try a less-WA lens, reduced AF points to include only a central area, and practice to improve your panning skills! Last edited by mikesbike; 01-13-2023 at 11:51 AM.