SMC Pentax 28mm f/2 minimum focus distance?

**.a.t.** · 05-14-2022, 11:44 AM

Originally posted by Lowell Goudge

Maybe the is a difference between minimum focus distance and minimum working distance.
Minimum focus is to the film plane minimum working is to the front element.
. . .

I hadn't thought about that. When I re-checked my lens just now, minimum focus distance is approx. 30.5cm and working distance is approx. 19cm.

Originally posted by gofour3

I have the first 1976 version, same as yours, it has 0.3 as well for the MFD.

Phil.

Thank you, Phil.

LennyBloke · 05-14-2022, 02:48 PM - **1 Like**

Originally posted by pschlute

Is that on all of them John ?

Peter - I only have the one copy now with a tiny 'ding' on the filter ring, I can't remember who I sold my perfect copy to

**dkpentax** · 05-15-2022, 11:16 PM

also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.

Jonathan Mac · 05-16-2022, 07:04 AM

Originally posted by dkpentax

also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.

That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer?

**.a.t.** · 05-17-2022, 10:40 PM

Originally posted by dkpentax

also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.

The few pieces of official Pentax literature I've seen all list the MFD as .3m. But measuring stopped down is an interesting idea.

I've never thought about that before: Do claimed MFD ratings apply to a lens when shooting wide open?
My own eyeballed measurements were taken with my lens at f/2.8.

Originally posted by Jonathan Mac

That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer?

When I tried a quick measurement at f/22, MFD seemed about 27cm. But it was difficult to distinguish sharp and unsharp at f/22, so there's probably a bit of wiggle room.

Using default criteria, DOFMaster claims a near depth of field limit of 24.3cm at f/22 with a subject distance of 30cm for a 28mm lens using 35mm film format.

Ole · 05-03-2023, 12:42 PM

Originally posted by .a.t.

According to the Pentax Forums Lens Review Database and the Pentax K-Mount Page reference site, the SMC Pentax 28mm f/2 has a minimum focus distance of .25m. So when my recently purchased copy arrived I was surprised to see it had a MFD of .3m.

Looking around on the internet I've seen only .3m MFD copies. And my circa 1977 Pentax lenses booklet also lists the MFD at .3m.

Were there differing versions of this lens? Does anyone here own a K 28mm f/2 with a MFD of .25m?

Attachment 572887

Attachment 572888

I agree that 30 cm must be the correct value. It matches my 1979 lens brochure. I have correcrted the database entry. Thanks for catching this.

**.a.t.** · 05-04-2023, 09:39 AM

Originally posted by Ole

I agree that 30 cm must be the correct value. It matches my 1979 lens brochure. I have correcrted the database entry. Thanks for catching this.

My pleasure, Ole. Thank you for your time and effort.

zapp · 05-06-2023, 06:03 AM

The easiest solution often is correct. A typo in the table…

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05-14-2022, 11:44 AM	#16
.a.t. Site Supporter Join Date: Mar 2011 Location: yesterday Photos: Gallery Posts: 1,261 Original Poster	Originally posted by Lowell Goudge Maybe the is a difference between minimum focus distance and minimum working distance. Minimum focus is to the film plane minimum working is to the front element. . . . I hadn't thought about that. When I re-checked my lens just now, minimum focus distance is approx. 30.5cm and working distance is approx. 19cm. Originally posted by gofour3 I have the first 1976 version, same as yours, it has 0.3 as well for the MFD. Phil. Thank you, Phil.

05-14-2022, 02:48 PM - 1 Like	#17
LennyBloke Pentaxian Join Date: Aug 2008 Location: Worcestershire, UK Photos: Gallery Posts: 677	Originally posted by pschlute Is that on all of them John ? Peter - I only have the one copy now with a tiny 'ding' on the filter ring, I can't remember who I sold my perfect copy to

05-15-2022, 11:16 PM	#18
dkpentax Site Supporter Join Date: Jun 2020 Posts: 132	also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely.

05-16-2022, 07:04 AM	#19
Jonathan Mac Pentaxian Join Date: Apr 2009 Location: Madrid, Spain Posts: 10,897	Originally posted by dkpentax also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely. That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer?

05-17-2022, 10:40 PM	#20
.a.t. Site Supporter Join Date: Mar 2011 Location: yesterday Photos: Gallery Posts: 1,261 Original Poster	Originally posted by dkpentax also, Pentax may consider the minimum focus distance to include the additional depth of field from not only maximum lens focus on the scale, but also from stopping down the lens completely. The few pieces of official Pentax literature I've seen all list the MFD as .3m. But measuring stopped down is an interesting idea. I've never thought about that before: Do claimed MFD ratings apply to a lens when shooting wide open? My own eyeballed measurements were taken with my lens at f/2.8. Originally posted by Jonathan Mac That would be a bit cheeky... and at minimum focus would the DoF really bring the minimum focus distance appreciably closer? When I tried a quick measurement at f/22, MFD seemed about 27cm. But it was difficult to distinguish sharp and unsharp at f/22, so there's probably a bit of wiggle room. Using default criteria, DOFMaster claims a near depth of field limit of 24.3cm at f/22 with a subject distance of 30cm for a 28mm lens using 35mm film format.

05-03-2023, 12:42 PM	#21
Ole Administrator Join Date: Sep 2006 Location: Copenhagen, Denmark Photos: Gallery \| Albums Posts: 4,408	Originally posted by .a.t. According to the Pentax Forums Lens Review Database and the Pentax K-Mount Page reference site, the SMC Pentax 28mm f/2 has a minimum focus distance of .25m. So when my recently purchased copy arrived I was surprised to see it had a MFD of .3m. Looking around on the internet I've seen only .3m MFD copies. And my circa 1977 Pentax lenses booklet also lists the MFD at .3m. Were there differing versions of this lens? Does anyone here own a K 28mm f/2 with a MFD of .25m? Attachment 572887 Attachment 572888 I agree that 30 cm must be the correct value. It matches my 1979 lens brochure. I have correcrted the database entry. Thanks for catching this.

05-04-2023, 09:39 AM	#22
.a.t. Site Supporter Join Date: Mar 2011 Location: yesterday Photos: Gallery Posts: 1,261 Original Poster	Originally posted by Ole I agree that 30 cm must be the correct value. It matches my 1979 lens brochure. I have correcrted the database entry. Thanks for catching this. My pleasure, Ole. Thank you for your time and effort.

05-06-2023, 06:03 AM	#23
zapp Pentaxian Join Date: Jul 2011 Posts: 2,385	The easiest solution often is correct. A typo in the table…