[plunkstar]

In some ways the Pentax 50/1.7 formula is better than the 50/1.4. It is generally sharper. Unless you particularly want that extra 1/3 stop of speed and or the slightly thinner depth of field at max aperture, consider a different focal length for your next lens.

I have the SMC-A 135/2.8 winging its way to me from Poland as we speak.

The slightly thinner depth of feel could come in use and I have heard the bokeh is more pleasant on the 1.4, presumably helped by the extra diaphragm blades, 8 as opposed to 6?

[monochrome]

In some ways the Pentax 50/1.7 formula is better than the 50/1.4. It is generally sharper. Unless you particularly want that extra 1/3 stop of speed and or the slightly thinner depth of field at max aperture, consider a different focal length for your next lens.

Better is a subjective standard. The 1.4 is different from the 1.7. The 1.4 was designed to produce images with the subject centered and isolated by softness at the edges. The 1.7 was designed for flat work -sharp across the frame. Desired image values are different today, in which edge sharpness and micro contrast are more desired than sharp subject isolation with soft edges.

[stevebrot]

I have heard the bokeh is more pleasant on the 1.4, presumably helped by the extra diaphragm blades, 8 as opposed to 6

The number of blades affects the shape of the aperture shadow, but is only part of what determines good bokeh, overall. It should be noted that bokeh has only been part of the lens evaluation vocabulary for about a decade. Before then reviews may have mentioned distracting or harsh OOF rendering, but that was about as far as it went.


Steve

[plunkstar]

Better is a subjective standard. The 1.4 is different from the 1.7. The 1.4 was designed to produce images with the subject centered and isolated by softness at the edges. The 1.7 was designed for flat work -sharp across the frame. Desired image values are different today, in which edge sharpness and micro contrast are more desired than sharp subject isolation with soft edges.

So it appears there are benefits to holding onto the 1.7 as well as the 1.4 until I settle on which suits me better then.

[monochrome]

So it appears there are benefits to holding onto the 1.7 as well as the 1.4 until I settle on which suits me better then.

i can't tell you what you should do, but I have 1.7's and 1.4's.

Many. Of both.

[boriscleto]

i can't tell you what you should do, but I have 1.7's and 1.4's.

Many. Of both.

Many of us do. It's the mark of LBA. Though I'm looking to get rid of some of the 1.7s...in fact most of them. Too close to the 55 1.8s

[aoeu]

i can't tell you what you should do, but I have 1.7's and 1.4's. Many. Of both.

I usually carry a short zoom, 50mm Macro and 100 mm Macro. Modern Pentax DSLRs have gotten fast enough that very fast lenses might not help much. I also carry a flash unit.
If I have a particular pic in mind I might carry a custom kit.
As a general rule I carry A lenses or later. PTTL is better than nothing and pre A lenses don't support it well.

[Paleo Pete]

I have the K 50 f1.4, the M 50 f1.7 and the A 50 f1.4.

The K 50 f1.4 has a slight bit of fungus I've never been able to completely eliminate, but it still gets very good shots. I used the A 50 quite a lot until I decided to pull out some other lenses and play wit them a little, the M50 f1.7 has been my go to lens ever since. It seems to be the sharpest of the bunch, the K 50 might match it, but the bit of fungus bothers me so I don't use it often, even though I don't see any detrimental affect on the pictures it gets.

I still pull out and use the A 50 now and then, but the M 50 f1.7 is the one I grab almost all the time. I rarely shoot wide open so I don't really know how either one does...

[ldj4549]

I don't have an A version, however, I have both the M 1.4 and M 1.7. Without going into technical details, the M 1.7 wins hands down. It has an certain quality that can't be defined which the 1.4 lacks, and it is somehow way easier to use - don't know how to explain it just is what it is. Hope this helps!

[plunkstar]

Thank you for your comments everyone. They are all very helpful.

I am going to stick with the A f1.7 for now and get the M f1.4 to play with. The 1.7 has done me well to date (below is an example image I snapped in a rare moment of quite!). If the f1.4 suits me I will consider investing in the A version.

Merry Christmas everyone.

[digital029art]

You are a small bit mistaken. Yes, you can do stop-down metering with the M-series lenses, but the meter is limited to center-weighted averaging only and may not be fully reliable as compared to open-aperture reading with the A-series lens equivalent.

The advantages of A-series over M-series on a Pentax dSLR go like this:

• All exposure modes fully supported*
• Better meter accuracy**
• All three meter modes supported (matrix, center-weighted, and spot)
• P-TTL flash support***
• Exif includes set aperture

I shoot with both A-series and M-series lenses and would choose A-series over M-series for general shooting. That being said, I also would not pay a high premium just to get the "A" contacts. Some consider stop-down metering an inconvenience and I generally concur, though I learned on and currently own several stop-down meter film cameras. In practice, I swing both ways fairly easily.


Steve

* When "A" contacts are not present, all modes except M, B, and X default to Av mode at maximum aperture only.
** The reasons for this are complex, but stop-down metering with even current model Pentax dSLRs is not fully linear with most lenses nor will there be consistent agreement with a wide-open reading for the same subject. This is a general problem across dSLR brands.
*** P-TTL support for A-series lenses is not as good as for AF lenses, but at least works for most subjects.

This has me thinking. As previously stated, I received an eBay A50/1.7 however it has the rear flange from an A50/1.4 installed (verified by contact pattern and opening for larger rear element) for some unknown reason (why/who would do this??).
I have an M50/1.4, so I'm thinking of swapping the two flanges to get *some* 'A' style functionality. What would I get? Anybody have any experience transplanting A and K flanges?? Thx!

[osv]

The 1.7 has done me well to date (below is an example image I snapped in a rare moment of quite!)

shirley temple!

that's a great pic

[baro-nite]

This has me thinking. As previously stated, I received an eBay A50/1.7 however it has the rear flange from an A50/1.4 installed (verified by contact pattern and opening for larger rear element) for some unknown reason (why/who would do this??).
I have an M50/1.4, so I'm thinking of swapping the two flanges to get *some* 'A' style functionality. What would I get? Anybody have any experience transplanting A and K flanges?? Thx!

Should work, assuming you are successful at also transferring the "A" pin, but keep in mind that the M and older lenses have a different ratio of diaphragm actuator distance to aperture change. In other words, the farther from wide open, the less accurate the exposure will be.

[Just1MoreDave]

Pentax changed the way the aperture lever worked from M to A lenses. Moving the lever say 0.5mm moves the aperture blades one stop, for its full range of motion. The contacts tell the camera what the lens's aperture range is. For example the Pentax-A 135mm f2.8 opens to f2.8 and stops down to f32. Then the camera knows how to set each aperture precisely through that range.

Older lenses don't have to have a precise aperture lever. The lever just moves the blades between wide open and wherever the aperture ring is set. The older cameras could see the position of the aperture ring and use that for metering. Those cameras have an arm that moves the lever, but it always moves the lever 100%, not in tiny increments like recent cameras.

If you swap mounts, the camera will see an A lens and expect the A aperture arm movement. Metering will be right sometimes, wrong at other times. Maybe you'll get lucky. The conventional wisdom is that it's not worth the trouble.

I had some photos of each lens so I include them:


A50/1.7:


A50/1.4:


M50/1.4

[digital029art]

Thanks J1MD!
Looking at this more in depth:
I used to think that if the aperture lever moved in an arc (it would be angled in relation to the mount from open to close) was an M or K lens.
Conversly, I used to think that if the lever just moved straight up/down it would be an A lens.
Now I look at a few lenses and see combinations that nullify the above .. for instance the M50/1.4 moves straight up/down and say the A28/2.8 moves in an arc. Very strange!

I wonder does the linear operation of the aperture depend on the linkage or the way the iris blades are attached? I really don't want to dig in too deep, just wondering if anybody's figured out the actual physical difference(s)?