[retired2007]

i have a k20d with the 1.4 converter i use with my 300 f4 and am happy. my question is can i use the adapter with my k1? without doing any damage, i want to use the 300 f4 and the 100 f2.8 macro with the converter on the k1. thanks

[boriscleto]

It will not do any damage, but there may be vignetting in FF mode.

[UncleVanya]

i have a k20d with the 1.4 converter i use with my 300 f4 and am happy. my question is can i use the adapter with my k1? without doing any damage, i want to use the 300 f4 and the 100 f2.8 macro with the converter on the k1. thanks

If this 1.4x is the Pentax HD DA 1.4x it will seriously vignette at more stopped down f stops. Wide open it will have some heavy darkened corners but at f8 it will show a black circle.

If using a different 1.4x please provide the specific model in use.

[mlag]

My understanding: all generations pentax k-mount lenses , including convertors, can be used on all bodies, either full frame or aps-c. The mechanical mount is compatible.

The only exception are Ricoh lenses (one might argue it aren’t pentax lenses) with the infamous ricoh pin, which can block the lenses when mounted on the camera.
However, functionality might be with restrictions:
Aps-c lenses (DA series) have smaller image circle and will produce vignetting (dark corners) , might vary with aperture. Cropped mode on k1 is a way out...
Full Frame (FA) lenses work on aps-c but are bigger/heavier than required for aps-c lenses, so it is bit unused extra weight in your bag. Sometimes they avoid the corner unsharpness , because aps-c uses only the center part of lens.
Newest lenses can be mount on older bodies but you might lack aperture ring A setting or camera screwdrive autofocus when it is only electrical controlled in the lens (some latest KAF4 mount variants), it becomes a manual focus lens (if focusring is present) working on max aperture opening in worst case .

Some older lenses might be less sharp on newest high resolution digital bodies, glas and coatings have evolved over time.

There are some third party lenses with issues, but consult the lens database on the forum before buying less common lenses... I remember parts hitting new electrical contacts lens to body on certain mixes of new to older items, thick (mirror?) lens barrels hitting the body or protruding flash of body, autofocus of old lens might be less reliable on new bodies...

[UncleVanya]

My understanding: all generations pentax k-mount lenses , including convertors, can be used on all bodies, either full frame or aps-c. The mechanical mount is compatible.

The only exception are Ricoh lenses (one might argue it aren’t pentax lenses) with the infamous ricoh pin, which can block the lenses when mounted on the camera.
However, functionality might be with restrictions:
Aps-c lenses (DA series) have smaller image circle and will produce vignetting (dark corners) , might vary with aperture. Cropped mode on k1 is a way out...
Full Frame (FA) lenses work on aps-c but are bigger/heavier than required for aps-c lenses, so it is bit unused extra weight in your bag. Sometimes they avoid the corner unsharpness , because aps-c uses only the center part of lens.
Newest lenses can be mount on older bodies but you might lack aperture ring A setting or camera screwdrive autofocus when it is only electrical controlled in the lens (some latest KAF4 mount variants), it becomes a manual focus lens (if focusring is present) working on max aperture opening in worst case .

Some older lenses might be less sharp on newest high resolution digital bodies, glas and coatings have evolved over time.

There are some third party lenses with issues, but consult the lens database on the forum before buying less common lenses... I remember parts hitting new electrical contacts lens to body on certain mixes of new to older items, thick (mirror?) lens barrels hitting the body or protruding flash of body, autofocus of old lens might be less reliable on new bodies...

Kaf4 adds electronic aperture control and a non-compatible body like the K-5 series will not be able to control f stop and the lens will remain wide open at all times.
A film SLR without aperture control from the body will not be able to control a DA or DFA lens aperture and it will remain stopped down fully all the time (exceptions being D FA 50 and D FA 100 which both have an aperture ring - not true with the D FA 100 WR).
Some lenses that are not autofocus still support full communication protocols and report f stop and aperture etc via the communication rather than passively via the A series method. These are all 3rd party only.

---------- Post added 03-30-22 at 10:16 PM ----------

Another bit to add:

The 1.4x HD DA does have some lenses (not bodies) that are not recommended to be used with it due to potential for damage:
Scroll down and read the notes on lenses...

HD PENTAX-DA AF REAR CONVERTER 1.4X AW / Converter / AF Lens Adapter / K-mount Lenses / Lenses / Products | RICOH IMAGING