What's the difference between this A lens and the same M lens - ?

Michael Piziak · 10-02-2021, 04:20 PM

What's the difference between the smc Pentax-A* 300mm green star f4 lens and the smc Pentax-M 300mm green star f4 lens - what's the difference in the A (automatic) and M (manual) since they are both primes (and the A couldn't auto focus)?

I should have probably put this in the beginner section...

bertwert · 10-02-2021, 04:24 PM

The 'A' designation means that the lens has electronic contacts to communicate it's aperture to the camera. When the aperture ring is set to 'A', you control the aperture in camera using the e-dials (as you would a modern lens), whereas with an M (or K) series lens you're stuck with stop down metering: How to Use Manual Lenses on Pentax DSLRs - Tutorial Videos | PentaxForums.com

Personally, I find 'A' lenses much more convenient to shoot with, but it's not too big a hassle with M lenses either.

ZombieArmy · 10-02-2021, 04:38 PM

If you're shooting an older K mount film camera the M lenses will have proper metering with a half press of the shutter. It's pretty cool.

stevebrot · 10-02-2021, 04:52 PM - **2 Likes**

The KMP page is an excellent resource for this sort of thing:

Pentax Extreme Telephoto Prime Lenses | The K-Mount Page

Click the entries for each lens and see the spec's and link to the optical diagram!

The KMP is a hugely useful resource. It's where we go to answer your questions. Bookmark it for future reference.

The K-Mount Page | Information about Pentax technology

Steve

**K-Three** · 10-02-2021, 05:34 PM

Optically the same lens, just the difference in aperture operation

kypfer · 10-03-2021, 05:42 AM

Originally posted by ZombieArmy

If you're shooting an older K mount film camera the M lenses will have proper metering with a half press of the shutter. It's pretty cool.

… and by some sophisticated jiggery-pokery the K-3iii can use an M lens in (some) auto modes as well … that is also pretty cool

10-02-2021, 04:20 PM	#1
Michael Piziak Closed Account Join Date: Dec 2013 Location: West Virginia Posts: 2,815	What's the difference between this A lens and the same M lens - ? What's the difference between the smc Pentax-A* 300mm green star f4 lens and the smc Pentax-M 300mm green star f4 lens - what's the difference in the A (automatic) and M (manual) since they are both primes (and the A couldn't auto focus)? I should have probably put this in the beginner section...

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10-02-2021, 04:24 PM	#2
bertwert Veteran Member Join Date: Jun 2015 Location: Golden, BC Posts: 15,173	The 'A' designation means that the lens has electronic contacts to communicate it's aperture to the camera. When the aperture ring is set to 'A', you control the aperture in camera using the e-dials (as you would a modern lens), whereas with an M (or K) series lens you're stuck with stop down metering: How to Use Manual Lenses on Pentax DSLRs - Tutorial Videos \| PentaxForums.com Personally, I find 'A' lenses much more convenient to shoot with, but it's not too big a hassle with M lenses either.

10-02-2021, 04:38 PM	#3
ZombieArmy Pentaxian Join Date: Jun 2014 Location: Florida Posts: 3,210	If you're shooting an older K mount film camera the M lenses will have proper metering with a half press of the shutter. It's pretty cool.

10-02-2021, 04:52 PM - 2 Likes	#4
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	The KMP page is an excellent resource for this sort of thing: Pentax Extreme Telephoto Prime Lenses \| The K-Mount Page Click the entries for each lens and see the spec's and link to the optical diagram! The KMP is a hugely useful resource. It's where we go to answer your questions. Bookmark it for future reference. The K-Mount Page \| Information about Pentax technology Steve

10-02-2021, 05:34 PM	#5
K-Three Loyal Site Supporter Join Date: May 2014 Location: Pugetopolis, WA Photos: Gallery Posts: 937	Optically the same lens, just the difference in aperture operation

10-03-2021, 05:42 AM	#6
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,588	Originally posted by ZombieArmy If you're shooting an older K mount film camera the M lenses will have proper metering with a half press of the shutter. It's pretty cool. … and by some sophisticated jiggery-pokery the K-3iii can use an M lens in (some) auto modes as well … that is also pretty cool

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