Focal Reducer Pentax-M 28mm Element Collision

Lazmarr · 03-20-2020, 03:26 PM

I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity.

Is there anyway that I can increase the distance ever so slightly to prevent this collision?

I had tried one of the extension tubes I have, but it alters the minimum focusing distance so much so that it becomes a macro lens.

Any help is appreciated!

stevebrot · 03-20-2020, 03:44 PM

Originally posted by Lazmarr

I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity.

Is there anyway that I can increase the distance ever so slightly to prevent this collision?

I had tried one of the extension tubes I have, but it alters the minimum focusing distance so much so that it becomes a macro lens.

Any help is appreciated!

Aside from not focusing to near infinity, probably not.

It is unlikely that there is a way to allow you to increase the distance of the rear element from the reducer that would preserve infinity focus. Have you contacted the maker of the reducer for their suggestions? Is it safe to assume that the reducer is native K-mount on the lens side and not stacked with other adapters?

Steve

photoptimist · 03-20-2020, 03:50 PM

Not without some surgery on the focal reducer. You would need to increase the thickness of the mount on the lens side (to add space) and decrease the thickness of the mount on the camera side by an amount proportional to the reducer factor (to reduce space and enable infinity focus). For example, if you have a 0.7X reducer, you might add 2 mm on the lens side and take-off 0.7 * 2 mm = 1.4 mm on the camera side. It should work, but the image quality might be a bit lower.

**UncleVanya** · 03-20-2020, 08:07 PM

Originally posted by Lazmarr

I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity.

Is there anyway that I can increase the distance ever so slightly to prevent this collision?

Do you need infinity? If not you may be able to adjust the main lens to stop short of infinity without hitting the glass.

Wasp · 03-21-2020, 12:34 AM

Anything you put between the lens and focal reducer will reduce the ability to focus to infinity.

03-20-2020, 03:26 PM	#1
Lazmarr New Member Join Date: Mar 2017 Posts: 7	Focal Reducer Pentax-M 28mm Element Collision I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity. Is there anyway that I can increase the distance ever so slightly to prevent this collision? I had tried one of the extension tubes I have, but it alters the minimum focusing distance so much so that it becomes a macro lens. Any help is appreciated!

03-20-2020, 03:50 PM	#3
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,122	Not without some surgery on the focal reducer. You would need to increase the thickness of the mount on the lens side (to add space) and decrease the thickness of the mount on the camera side by an amount proportional to the reducer factor (to reduce space and enable infinity focus). For example, if you have a 0.7X reducer, you might add 2 mm on the lens side and take-off 0.7 * 2 mm = 1.4 mm on the camera side. It should work, but the image quality might be a bit lower. Last edited by photoptimist; 03-20-2020 at 05:08 PM.

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03-20-2020, 03:44 PM	#2
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Lazmarr I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity. Is there anyway that I can increase the distance ever so slightly to prevent this collision? I had tried one of the extension tubes I have, but it alters the minimum focusing distance so much so that it becomes a macro lens. Any help is appreciated! Aside from not focusing to near infinity, probably not. It is unlikely that there is a way to allow you to increase the distance of the rear element from the reducer that would preserve infinity focus. Have you contacted the maker of the reducer for their suggestions? Is it safe to assume that the reducer is native K-mount on the lens side and not stacked with other adapters? Steve

03-20-2020, 08:07 PM	#4
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	Originally posted by Lazmarr I purchased a Pentax-M 28mm f2.8 for some wide angle photos, and have just found out that the rear elelment collides with the focal reducer's elelment near infinity. Is there anyway that I can increase the distance ever so slightly to prevent this collision? Do you need infinity? If not you may be able to adjust the main lens to stop short of infinity without hitting the glass.

03-21-2020, 12:34 AM	#5
Wasp Pentaxian Join Date: Mar 2017 Location: Pretoria Photos: Gallery Posts: 4,660	Anything you put between the lens and focal reducer will reduce the ability to focus to infinity.

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