[fnflying]

I have a couple of medium format lenses I use on my sony A7 that I want to use on my K3II. Does anyone know the aps-c equivalent of the lens? I know the 35mm equivalent was roughly 70%. They are mamiya 645 lenses. Thanks, Frank

[redrockcoulee]

The do called equivalent is the same as any other lens. A 75mm medium format will give you the same field of view as a 75 mm 35mm on your Pentax. Focal length is focal length, FOV changes with the area of film or sensor being exposed.

[fnflying]

The do called equivalent is the same as any other lens. A 75mm medium format will give you the same field of view as a 75 mm 35mm on your Pentax. Focal length is focal length, FOV changes with the area of film or sensor being exposed.

I guess I wasn't clear...FOV equivalent is what I am looking for, for medium format to aps-c. My mamiya 55mm is equivalent to roughly a 38mm F.F. What would it b for APS-C sized sensors? Thanks

---------- Post added 02-07-16 at 10:23 PM ----------

I found my answer(s)...https://www.pentaxforums.com/forums/54-pentax-lens-articles/93714-field-view-...d-645-6x7.html

[stevebrot]

I guess I wasn't clear...FOV equivalent is what I am looking for, for medium format to aps-c. My mamiya 55mm is equivalent to roughly a 38mm F.F. What would it b for APS-C sized sensors? Thanks

---------- Post added 02-07-16 at 10:23 PM ----------

I found my answer(s)...https://www.pentaxforums.com/forums/54-pentax-lens-articles/93714-field-view-...d-645-6x7.html

Your 55mm Mamiya is still 55mm regardless of what camera it is mounted on and is exactly equivalent to 55mm FF when mounted to your A7. On your K-3II it will have exactly the same FOV as the Pentax-DA* 55/1.4 which is about 2/3rds that of a 55mm lens on your A7.


Steve

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Last edited by stevebrot; 02-07-2016 at 10:56 PM.

[tuco]

As already noted, a medium format 55mm lens mounted on an APS-C camera = (55mm) x 1.5 = 82.5mm equivalent with a large image circle.

[redrockcoulee]

I guess I wasn't clear...FOV equivalent is what I am looking for, for medium format to aps-c. My mamiya 55mm is equivalent to roughly a 38mm F.F. What would it b for APS-C sized sensors? Thanks

---------- Post added 02-07-16 at 10:23 PM ----------

I found my answer(s)...https://www.pentaxforums.com/forums/54-pentax-lens-articles/93714-field-view-...d-645-6x7.html

Your 55 mm Mamiya lens mounted on your 645 would give an equivalent of approximately 38mm lens on a FF camera. But you would have to put a 25mm lens on a cropped sensor camera to give the coverage that you are getting on a your 645. But putting the 55m lens on a FF camera instead of wide angle it is a normal lens and if you mounted it onto a APS-C camera it is a short telephoto lens but regardless it is always going to be actaully a 55 mm lens.

[fnflying]

Thanks everyone...one other issue I have with putting any kind of manual lens on the K-3II...I cannot seem to get the light meter to work, any ideas or is this the way it is?

[stevebrot]

Thanks everyone...one other issue I have with putting any kind of manual lens on the K-3II...I cannot seem to get the light meter to work, any ideas or is this the way it is?

Lenses lacking electrical contacts on the mount face (so-called A-contacts) have limited meter support on a Pentax dSLR. The reasons are a little complicated and shrouded by the dust of history and are not real pertinent. To use lenses lacking the contacts, stop-down metering or an external (hand held) meter or estimating exposure are your options.

Here is a link to a sticky on the topic:

https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html


Steve

[stevebrot]

stop-down metering

I will explain a little further. Modern cameras typically meter with the aperture wide open. The is accomplished either through a mechanical link between the aperture ring on the lens or by having the body control the aperture independent of the aperture ring. If neither mechanism is available, there is a third route; that being metering with the lens stopped down so that the meter "sees" the amount of light that will actually strike the sensor during exposure. This is called stop-down metering and was common on TTL metered cameras in the 1960s through to the early 1970s. A good example would be the Pentax Spotmatic. Stop-down metering is supported on many modern cameras and allows for use of legacy lenses as well as bellows and other accessories.

With your K-3II, you have three basic options for stop-down metering. If using an M-42 (screw mount) lens, the aperture diaphragm must be in full manual mode for any of the below. For all lenses lacking the A-contact the menu item to enable aperture ring must be set to On.

• M mode using green button: With press of the button, the body will take a momentary light reading and adjust the shutter speed to match. If a K-mount lens is mounted the lens is stopped down prior to the reading.
• M mode using optical DOF preview: In this view there is an EV scale in the viewfinder that allows for manual adjustment of shutter speed. This is a very cool and not commonly used feature.
• Av mode:* Works best with M-42 lenses and provide continuous metering. Shutter speed will float according to the setting on the aperture ring. K-mount lenses are limited to shooting wide open at maximum aperture.

The rule of thumb is to use M mode with K-mount lenses.


Steve

* When an A-contact lens is not detected, most modes (Green, P, Tv, Sv, TAv) will default to Av. Similarly, auto-ISO is disabled for all modes. P-TTL flash automation is available, though with some features disabled.