[lakeshore]

I'm just starting to experiment using my M Series lenses on my K50. So far I have only been using my M 20/f4 and have noticed that the colour rendering seems less saturated than with my DA 35/2.4 and it is more prone to blowing out highlights. I had the dynamic range settings turned off, as recommended on PF for the settings on a K50.

My question is: When using M Series or other legacy glass, is it recommended to compensate somehow for the older lens coatings or other aspects of these old beauties?

[mattt]

IMO Sunny 16 is your friend.

I shoot it in manual and typically under expose a touch as shadows are easy to pull up and blown highlights can be difficult to recover. I really like M 20/4.. so compact.

[KC0PET]

I do most of my corrections in post processing with vintage lenses. As mattt pointed out, underexposing helps with blown out highlights (shadows are easier to recover). I also tend to use auto bracketing when shooting manual. I don't have the M20 (yet ), but some vintage lenses have better color rendering than others, but nearly always I can get a look I like in PP.

Here's one taken with the M50mm f/1.7 (very fine lens by the way). Just a little bit of tweaking in PS and really pulled the colors out.

[stevebrot]

I'm just starting to experiment using my M Series lenses on my K50. So far I have only been using my M 20/f4 and have noticed that the colour rendering seems less saturated than with my DA 35/2.4 and it is more prone to blowing out highlights. I had the dynamic range settings turned off, as recommended on PF for the settings on a K50.

My question is: When using M Series or other legacy glass, is it recommended to compensate somehow for the older lens coatings or other aspects of these old beauties?

Stop-down metering on current AF dSLRs is not particularly reliable. The full explanation would take me an hour or more to type out and perhaps I should craft a "sticky" one day with the full information, but not today. Here are the high points:

• Meter readings (measured EV) may be non-linear within certain aperture ranges. Most common is wide open down to about f/4 and from f/11 to minimum. The result is over or underexposure (sometimes severe) with the actual behavior varying between lenses.
• This problem is not limited to Pentax-brand cameras
• Live view metering is not affected and should be linear throughout the aperture range

As noted in the last point above, live view metering is the easiest solution. A hand-held meter may also be used. If those are impractical, then I suggest a flow similar to the steps below when using K or M series lenses:

• For a particular subject and lighting, do a test exposure using green button metering in M mode.*
• Review the image and using the histogram as a reference, adjust the exposure to suit your intent for the subject
• Shoot at that setting (or equivalent EV) until either the light or the subject changes

Steve

[stevebrot]

I do most of my corrections in post processing with vintage lenses. As mattt pointed out, underexposing helps with blown out highlights (shadows are easier to recover).

Assuming that exposure variance is fairly mild. I have a couple of lenses that will underexpose about 4 stops wide open.


Steve

[KC0PET]

Assuming that exposure variance is fairly mild. I have a couple of lenses that will underexpose about 4 stops wide open.

Steve

Good point. Some lenses and/or some situations can be off the mark with green button metering. Hence why I find myself using bracketing quite a bit. So I guess to clarify, when a good exposure is found (and your steps above are good), then leaning to underexposure can help when trying to recover blown out highlights. I still find myself frustrated quite a bit with manual lenses with blown out highlights because I did not take the time to make sure I had the right exposure.

[leekil]

Meter readings (measured EV) may be non-linear within certain aperture ranges. Most common is wide open down to about f/4 and from f/11 to minimum. The result is over or underexposure (sometimes severe) with the actual behavior varying between lenses.
This problem is not limited to Pentax-brand cameras

This seems somewhat weird. More reason for Pentax to have a mechanical aperture connection for the older lenses.

FWIW, I had the same experience today with the same lens as the OP, and it was outside of the two common ranges cited (it was f/8).

[wombat2go]

Some of the old -M lenses in my collection here had slow aperture stop-down due to old lubrication problems.
That can cause inconsistent exposure.
To check, hold the stop down lever open with a fingernail and let the lever suddenly free.
The aperture should stop down instantly with audible "clack".
If if closes visibly slowly or the aperture blades can be seen moving near smallest f/- , or without a "clack", it may need service.

Edit: Forgot to mention to set minimum aperture (f/16 ~22 etc) before doing the above check.

[lakeshore]

Variation using green button metering: I noticed that today. When I
I pressed the green button the shutter speed was 1/750. I pressed it again and it was 1/180. I thought I was doing something wrong! I'll check my lens using the above noted method. Thanks for the information and tips.

I have a number of M lenses from my film days - 50/f1.7, 28/f2.8, 35/f2.0, 100/f2.8, 40-80 zoom and 80-200 zoom. Lots of lenses to try out.

[KC0PET]

I have a number of M lenses from my film days - 50/f1.7, 28/f2.8, 35/f2.0, 100/f2.8, 40-80 zoom and 80-200 zoom. Lots of lenses to try out.

Nice set of lenses! I also have the M100 f/2.8 and it is another very fine lens. Here are couple taken with that lens.

[lakeshore]

Some of the old -M lenses in my collection here had slow aperture stop-down due to old lubrication problems.
That can cause inconsistent exposure.
To check, hold the stop down lever open with a fingernail and let the lever suddenly free.
The aperture should stop down instantly with audible "clack".
If if closes visibly slowly or the aperture blades can be seen moving near smallest f/- , or without a "clack", it may need service.

Edit: Forgot to mention to set minimum aperture (f/16 ~22 etc) before doing the above check.

I performed this test on all my M lenses and they are all working well except for the 35/f2.0 and the 20/f4. The aperture doesn't stop down with a "snap." The 20/f4 is the worst of course.

What's involved in servicing these lenses for this problem?
Is it a DIY fix?

Any advice would be appreciated.

---------- Post added 09-17-16 at 11:55 AM ----------

Nice set of lenses! I also have the M100 f/2.8 and it is another very fine lens. Here are couple taken with that lens.

Great shots!

Luckily my 100/f2.8's aperture seems to stop down properly. Can't wait to try it out.

[reh321]

I performed this test on all my M lenses and they are all working well except for the 35/f2.0 and the 20/f4. The aperture doesn't stop down with a "snap." The 20/f4 is the worst of course..

So, the next question is whether the ones that don't "snap" also give mediocre green-button metering.

[lakeshore]

So, the next question is whether the ones that don't "snap" also give mediocre green-button metering.

So far I've only tired out the 20/f4 and yes, the green button metering is erratic.

Should I try cleaning the lenses myself or am I likely to ruin them. I have visions of parts flying out or the lens being made totally useless by me. I do not want to spend money having them repaired at this time.

[Dlanor Sekao]

So far I've only tired out the 20/f4 and yes, the green button metering is erratic.

Should I try cleaning the lenses myself or am I likely to ruin them. I have visions of parts flying out or the lens being made totally useless by me. I do not want to spend money having them repaired at this time.

In a simple solution.....One Word.....Eric Hendrickson ! The original Pentax Guru will fix them right up !
I wouldn't attempt a self repair on the 20mm ever. If you don't want to do it now ....... just remember that name for future use.

[KC0PET]

In a simple solution.....One Word.....Eric Hendrickson ! The original Pentax Guru will fix them right up !
I wouldn't attempt a self repair on the 20mm ever. If you don't want to do it now ....... just remember that name for future use.

+1 on that. I have tried repairing some lenses with only limited success. Without the experience, the right tools and a stash of parts it is difficult at best. Fortunately I tried this on lenses that were basically junk anyway. And of course another practical consideration is the cost of a good replacement vs the repair cost. And I have had success selling lenses for repair/parts so there is some value in the junkers.