[ChrisPlatt]

My macro lens is an Auto Promaster MC 1:2.8 50mm. Marked on the side of the lens is an indicator: Macro 1:10, 1:8, 1:5, 1:4. Would extension tubes still allow autofocus (this is not a killer issue)? Also, I always shoot in AE mode (I'm not much of a photographer), the lens doesn't have an electrical contact. How would aperture priority function?

Your Pentax Program Plus is a manual focus camera, not AF.
Can your Promaster lens be physically mounted to camera?

Any Pentax-K mount lens can be used with aperture priority AE on the Program Plus.
Electrical contact and "A" setting on aperture ring are required for Program AE only.

Chris

[WLubarsky]

Your Pentax Program Plus is a manual focus camera, not AF.
Can your Promaster lens be physically mounted to camera?

Any Pentax-K mount lens can be used with aperture priority AE on the Program Plus.
Electrical contact and "A" setting on aperture ring are required for Program AE only.

Chris

I always manually focused, no problem. The Promaster lens first has no electrical contact so I can't use AE, and it although it is marked on the front 1:28, the barell
markings don't go lower than 1:4. I can't get close enough for detail and remain in focus

[ChrisPlatt]

1:2.8 refers to the maximum (widest) aperture;
1:4 is the reproduction ratio, or magnification.

At 1:4 object will appear 1/4 actual size on negative at closest focus.
A true macro lens will do 1:2 without extension; some go to 1:1.

Using your Pentax Program Plus body aperture-priority autoexposure
(you set aperture manually, camera sets shutter speed automatically)
should work with any Pentax K-mount lens, even if it has no contacts.

Lens with electrical contacts and "A" setting on aperture ring is required only
for Program AE (camera sets both aperture and shutter speed automatically).

Suggest you re-read your camera manual and look for a film-era macrophotography primer.

Chris

[WLubarsky]

1:2.8 refers to the maximum (widest) aperture;
1:4 is the reproduction ratio, or magnification.

At 1:4 object will appear 1/4 actual size on negative at closest focus.
A true macro lens will do 1:2 without extension; some go to 1:1.

Using your Pentax Program Plus body aperture-priority autoexposure
(you set aperture manually, camera sets shutter speed automatically)
should work with any Pentax K-mount lens, even if it has no contacts.

Lens with electrical contacts and "A" setting on aperture ring is required only
for Program AE (camera sets both aperture and shutter speed automatically).

Suggest you re-read your camera manual and look for a film-era macrophotography primer.

Chris

I am going to need Program AE, which means looking for a replacement lens, a true macro lens. Photography is not a never will be my hobby. This is all so I can record and share my plants.

[ChrisPlatt]

I am going to need Program AE, which means looking for a replacement lens, a true macro lens.
Photography is not a never will be my hobby. This is all so I can record and share my plants.

As mentioned my wife has the SMC Pentax-A 50mm f/2.8 Macro lens.
It's a terrific lens for general photography and macrophotography.

This model goes to 1:2 and will work in Program AE mode on your camera.
Nice used copies can be purchased for under $200.

I am also sending you via PM a link to an eBay auction for the Sigma 50mm f/2.8 1:1 Macro lens I mentioned.

Chris

[WLubarsky]

As mentioned my wife has the SMC Pentax-A 50mm f/2.8 Macro lens.
It's a terrific lens for general photography and macrophotography.

This model goes to 1:2 and will work in Program AE mode on your camera.
Nice used copies can be purchased for under $200.

I am also sending you via PM a link to an eBay auction for the Sigma 50mm f/2.8 1:1 Macro lens I mentioned.

Chris

I went and bought the Sigma lens, it arrived this afternoon. It looks to be exactly what I was looking for, however I will have to wait until my current roll of film is developed to see just what is what. The light intensity from my plant lights keeps the exposure time quite short even with ASA 800 film.