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12-23-2011, 01:18 PM   #1
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Pentax A 1.7 or Pentax M 1.4?

They are roughly the same price and I want to buy one but I'm not sure which to go for.

Does the Auto-aperture just mean I can use Av mode and change the aperture through the camera?

Which would you guys prefer ? :S

12-23-2011, 01:25 PM   #2
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QuoteOriginally posted by userage Quote
Does the Auto-aperture just mean I can use Av mode and change the aperture through the camera?
Yes. For the same price I would get the A f/1.7 so you can use the camera controls. There is some debate on which is sharper the 1.7 or the 1.4 with lots of different opinions. I think that, unless you are really trying to shoot with narrow DOF then there is not much difference. And in that case go with the 'A' every time.
12-23-2011, 01:33 PM   #3
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Would there be a big difference between 1.7 and 1.4 in low light shooting? Roughly what shutter speeds would you get, if anyone knows >.<?
12-23-2011, 01:36 PM   #4
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Refer to your manual for a list of functions not available with older lenses. Among other issues, flash will be limited to max output with M lenses and SR will have to be pre-set.

12-23-2011, 01:42 PM - 1 Like   #5
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QuoteOriginally posted by userage Quote
Would there be a big difference between 1.7 and 1.4 in low light shooting?
That is a 1/2 stop difference. Not really a big deal for low light especially with newer cameras where you can adjust the ISO quite a bit. Impossible to say what the shutter speed would be without knowing the light available and the ISO you are using. But the difference between the two lenses is still 1/2 stop, which means 1/2 of a shutter speed setting as well. It is all related.

So for example if you have the 1.4 at 1.4 and the speed setting for proper exposure is 1/125 then the 1.7 at 1.7 would need a speed of maybe 1/100 to achieve the same exposure. Changing the ISO by a 1/2 stop achieves the same thing so if you needed the speed to be 1/125 then at 1.7 you bump the ISO up a half stop and you can keep the speed at 1/125.

I think the big difference will be in the DOF achieved because nothing you can do will make the 1.7 act like the 1.4 in that specific case. For exposure, you can change other settings to achieve the same thing.
12-23-2011, 01:44 PM   #6
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Don't see what camera you are using so how much the difference between 1.4 and 1.7 will matter is a bit harder to determine. Not much difference except when you need a faster shutter in very low light (or a very fast shutter in mediocre light). If I had to choose between the two at the same cost I'd choose the A myself as others have said - faster camera use overall IMHO. Good luck.
12-23-2011, 01:58 PM   #7
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Thanks for responses

I'm more shifted towards the A at the moment, would be nice to have a faster lens though
12-23-2011, 02:15 PM   #8
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A50/1.7 is a fine lens. Auto aperture is useful.

12-23-2011, 02:55 PM   #9
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I own both the A 50/1.7 and the M 50/1.7.
  • The lenses are the same optically
  • The M's build and "feel" is superior to the A's (the A is made of plastic, the M is made of metal)
  • Most A 50/1.7 have defective aperture rings making use off the "A" setting almost impossible
  • The sole advantage to the A 50/1.7 is the higher compatibility on Pentax dSLR bodies and that is a huge advantage in my book. The "A" position allows full aperture control by the body to support program and shutter-priority exposure automation.


Steve
12-23-2011, 03:33 PM   #10
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QuoteOriginally posted by userage Quote
They are roughly the same price and I want to buy one but I'm not sure which to go for.

Does the Auto-aperture just mean I can use Av mode and change the aperture through the camera?

Which would you guys prefer ? :S
I would buy the 'A1.7'. Practically speaking, they're quite similar from f1.7/1.8 and up, and quite sharp (from what I hear), and as others have said, you lose half a stop, which means either +50% shutter speed (for instance 1/30 -> 1/20) or an equivalent change in ISO, but it's hard to focus at f1.4 (or f1.7) lens well enough to make frequent use of of the extra glass. The extra compatibility, however, is worth a lot. In-camera aperture control (and the correspondingly instant exposure calculations) are totally worth it. It also makes it much more compatible with flashes.

(I own M1.7, M28, A28, and FA1.7)
12-23-2011, 03:37 PM   #11
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QuoteOriginally posted by stevebrot Quote
I own both the A 50/1.7 and the M 50/1.7.
The lenses are the same optically
The M's build and "feel" is superior to the A's (the A is made of plastic, the M is made of metal)
Most A 50/1.7 have defective aperture rings making use off the "A" setting almost impossible
The sole advantage to the A 50/1.7 is the higher compatibility on Pentax dSLR bodies and that is a huge advantage in my book. The "A" position allows full aperture control by the body to support program and shutter-priority exposure automation.
My wife has the A 1.7 & I have the M 1.4. Ditto all this stuff, except her "A" setting works just fine. I personally like the M 1.4, but you can't go wrong with either.

Cheers,
Bobbo :-)
12-23-2011, 04:20 PM   #12
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have all the lenses mentioned above, including m2.0, a2.0, m1.4, m1.7, and a screw mount m1.4 and hands down, the m1.4 produces the best image quality.
12-23-2011, 04:43 PM   #13
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Get the A lens because there are so many advantages to having the auto aperture function where aperture is controlled from the camera body.

- multi segment metering
- P (hyper program) mode
- Sv (sensitivity priority) mode
- Tv (shutter priority) mode
- A (aperture priority) mode
- TAv (shutter & aperture priority) mode
- M (hyper manual) mode
- P-TTL auto flash
- Exif info
12-23-2011, 05:37 PM   #14
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OK, let me really set the dogs loose on this thread.

Get the A50/1.4 and/or the M50/1.7. The prices are what they are (comparatively) for a reason.

M50/1.7 is wonderful for flat field of view and razor sharp. A50/1.4 has all the A-setting advantages and doesn't suffer from the plastic detent aperture ring failure so common on the A50/1.7.
12-23-2011, 08:15 PM   #15
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I can't imagine trading my M 50 1.4 for an A 50 1.7. But I recognize that an A lens would be a lot more convenient for general use.

In low light the extra half stop is enough to make focusing slightly easier.
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