K (non-A) lens and *ist DS

Hi,

I am seeking advice on the use of a fully manual Pentax K lens on *ist DS. There is a previous post on this topic but I’ve been unable to find it.
The gist of it was to:

1. firstly set 2 menu Custom Settings to allow the use of manual lenses,
2. switch to MF, and dial to M on the camera body,
3. followed by selecting an f-stop, then compose and focus.
4. Half press the shutter release button and press AE-L button, which sets the shutter speed.
5. Fully press the shutter release button and take the shot.

I used a Pentax K 100mm Macro lens on a tripod-mounted *ist DS for this exercise, aperture settings were f4 through to f22. The test was performed indoors (it’s brass monkeys outside), WB set to tungsten lamp, table-top subject(s) at about 1.5m to 2.5m distance from the camera.

The resulting exposures, using in-camera ‘judgement’ for shutter speed (from Step 4), deteriorate as the aperture is stopped down; ie. there was an increasing underexposure using AE-L button. Although one can obviously compensate by manually increasing the shutter speed, it kind of defeats the object.

As a reference I used the histogram to approximate Ev consistency throughout, as I manually changed the aperture on the lens and took shots.

The correlation to achieve comparable exposure (ie. histogram) at reducing apertures is approximately:

Increase 1full f-stop => increase 2 shutter speeds
Eg. f5.6 => 0.2 s (baseline histogram)
f8 => 1 s (should be 0.5s ?)
f11 => 4 s

I need to emphasise the above values are approximate but the smaller the aperture opening, the more I needed to increase the shutter speed to achieve comparable exposed shots (histograms).

Is the methodology and my method correct ?

Thanks, Colin

If you set the body to M that means "Manual" and hence as you stop down the lens the light is reduced, but the shutter speed stays the same. hence increasing under-exposure as you stop down. If the camera was set to A then the shutter speed would change to compensate.

Macro shots benefit from the use of a tripod, so the lengthening of the shutter speed will not result in camera shake. Also it will be easiere to focus precisely - essential where depth of field is limited.

To keep the exposure constant, shutter speeds and apertures work together, so, for example the following combinations allow through the same amount of light:
1/125 s f8
1/60s f11
1/30s f16

At very long shutter speeds this relationship starts to break down (reciprocity failure) so 1 sec may need to be 2 sec, 4 sec may need to be 20 sec or whatever.....The longer the exposure the worse it gets. This is true for film, haven't checked it out with a CCD.

Hope that helps!

Hi John,
Thanks for the reply and, yes, it helps.

The lens I used does not not have an A setting. I don't understand why the shutter speed remains the same when I stop down, as you describe. Will a power On/Off help ?

You are spot on with limited depth of field !

I understand the constant exposure, ie shutter speed & aperture relationship. It is the fact that it doesn't work here that is perplexing.

Reciprocity failure is a phrase I know but don't really understand. However, comparing our explanations does seem to point to it as being a possible cause. Perhaps the use of a macro lens is not helping either.

Maybe someone else has explored this with CCD cameras.

Regards, Colin

Just did a quick test with a SMC-M 50mm F1.7 on my DS.

Camera set to M, aperture set on the aperture ring. Focus manually then press the AE-L button. Camera stops down and sets what it thinks is the shutter speed for correct exposure. Changing the aperture setting and then pressing the AE-L button again causes the camera to stop down again and work out the correct shutter setting for that aperture.

On my camera this works very well, except for one slightly odd thing, which is that the camera never works out a shutter setting of more than 1.5 seconds. For example for the test I just did in my study:

F1.7 - 1/20s
F4 - 1/4s
f8 - 1s
f16 - 1.5s
f22 - 1.5s

The first 3 result in a correct exposure but the last two don't. In fact if I put the lens cap on and press the AE-L button a shutter speed of 1.5 seconds gets set no matter what the aperture is.

Regards
Steve

Was this the topic you were thinking of?

https://www.pentaxuser.com/forum/viewtopic.php?t=1634&highlight=lens

Maybe it's just me, but I had a terrifically hard time following that topic. Does the *ist D operate differently than the Ds, I don't know?

I use the following method of metering when using an SMC-M lens on my *ist Ds:

I set the exposure mode to M
I set the camera focus mode to MF

When I want aperature priority operation I chose a desired f stop on the lens. I then operate the DOF preview and simultaneously operate the thumbwheel to chose a shutter speed and the EV compensation figures in the viewfinder act as a match-needle meter. If I want any exposure compensation I can see it at that point.

When I want Shutter priority operation I first use the thumbwheel to chose the desired shutter speed then turn the lens aperature ring to match-needle as above. I also use this procedure for flash pictures by chosing a flash sync shutter speed and then chosing the appropriate aperature based on the flash guide number and distance.

I tried using the AE-L button method you describe above and I also could not get it to chose a shutter speed slower than 1.5 seconds. Maybe it has limitations I don't know about but using my method I can get any combination of settings I chose and it seems as intuitive to me as an old match-needle manual camera. Give it a try.

Regards Drew

PS: John, doesn't reciprocity failure only apply to film? Let me know if I am wrong.

I don't know - I just mentioned it to complete the answer - I can't recall seeing anywhere any comment on this with regards to digital cameras, and i haven't tried it.

Noise might overwhelm any effect on digital anyway.

Has anyone actually investigated this?

Steve,
You pretty much confirming my findings.
This weekend I'll do some testing on three manual K lens I have and report back.

Regards, Colin

Drew,
Thanks for your input:
I will try both methods on three manual K lens at the weekend and publish findings here.


Regards, Colin

ps What's a match-needle ?!

Ya, you're right...I'm old

Intersting read this thread, I've been using my 50 1.4 for portraits, with studio lights and a handheld meter, and no problems. I definately am tucking some of this info into a dark dusty crevice somwhere in the depths of my twisted mind filed under "good to know..."

Testing manual focus lens on the *ist DS

Well, here are my findings from the testing of my manual focus lens. Apologies, but my http code isn't good; ie. I couldn't format my data in columns here after copying from my original Excel spreadsheet:

Conditions Sunny day, light wind , slight cloud which had minimal affect on exposure readings.

Subject Garden sun-dial from @ 20m, constant sensor to subject distance throughout, except for 400mm. This beast was tripod mounted, hence moved the camera sensor back about 80mm.

Camera Pentax *ist DS, meter on Spot Correct Exposure achieved using Aperture priority : f-Stop and Shutter Speeds

External meter Sekonic L558 1 Degree Spot, used as a reference for continuity throughout the test while attaching different lens to camera. I only took single spots on the sun-dial.

Test Results

Method 1 Camera MF, Dial M, Set aperture on lens, Half-press shutter and press AE-L for shutter speed.

Method 2 Camera MF, Dial M, DOF preview lever and thumbwheel to obtain 0.0 on camera exposure meter for shutter speed.

Note N/A means Not Availablle on the lens under test.

• Zenitar MC 16mm Fisheye
  (f2.8-f22) f1.7 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f45
  Method 1 N/A 4000 2000 1000 500 250 180 90 N/A N/A
  Method 2 N/A 4000 2000 1000 500 250 180 90 N/A N/A
  Sekonic L558 (1deg Spot) N/A 4000 2000 1000 500 250 125 60-125 N/A N/A

• Pentax A SMC 20mm
  (f2.8-f22) f1.7 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f45
  Method 1 N/A 1000 500 250 125 60 30 15 N/A N/A
  Method 2 N/A 4000 500 250 125 60 30 15 N/A N/A
  Sekonic L558 (1deg Spot) N/A 4000 500 250 125 60 30 15 N/A N/A
  Lens on A and Camera on Av N/A 4000 500 250 125 60 30 15 N/A N/A

• Pentax A SMC 50mm
  (f1.7 f22) f1.7 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f45
  Method 1 4000 2000 1000 500 250 125 60 30 N/A N/A
  Method 2 Out of Range 4000 1500 750 250 125 60 30 N/A N/A
  Sekonic L558 (1deg Spot) 4000 4000 2000 1000 500 250 125 60 N/A N/A
  Lens on A and Camera on Av Out of Range 4000 2000 1000 500 250 125 60 N/A N/A

• Pentax M SMC 100mm Macro
  (f4-f32) f1.7 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f45
  Method 1 N/A N/A 3000 1500 750 250 125 60 20 N/A
  Method 2 N/A N/A 3000 1500 750 250 125 60 20 N/A
  Sekonic L558 (1deg Spot) N/A N/A 4000 1 to 2000 500-1000 250 125 60 15 - 30 N/A

• Pentax M SMC 400mm Tele
  (f5.6-f45) f1.7 f2.8 f4 f5.6 f8 f11 f16 f22 f32 f45
  Method 1 N/A N/A N/A 1500 1000 500 250 125 90 30
  Method 2 N/A N/A N/A 1500 1000 500 250 125 60 30
  Sekonic L558 (1deg Spot) N/A N/A N/A 1000 500 250-500 125-250 60-125 30-60 15-30

Observations

1. Using an outside subject, in daylight, both the Methods 1 and 2 corroborated well with the Sekonic meter, particualry the M-Series lens.

2. The A-Series lens seemed to perform with more consitency, as compared with the Sekonic meter, when set to A. The aperture Av was then set in-camera.

Any views or constructive criticism welcome.

Very thorough test there Colin.

It is interesting to see the consistency of all methods but also curious to see the 2 stop difference between method 1 and 2 when using the Pentax A SMC 20mm at f1.7. It would seem that the method 1 figure would be correct by the progression but all the other methods at that f stop jump from 500 to 4000 in one f stop. Any theories?
Did you notice in the *ist Ds manual P. 179 that the chart indicates that when you use Method 1 that an "exposure error may occur". I'm not sure what they mean by that (maybe because it won't go below 1.5 sec...who knows, they don't explain) but it was why I originally chose to use method 2 when I first tried Manual Mode so I stuck with it. ( I make enough errors without the camera introducing any) Also I liked method 2 because I can pick either aperture priority or shutter speed priority. I disagree with the chart in P. 133 that says in Manual mode exposure compensation isn't possible. Using method 2 it is clearly possible and it is evident in the viewfinder.
Anyway, thanks Colin for the great research you have done. Obviously there doesn't seem to be any glaring differences between methods and no "exposure errors" to speak of so I am going to start using Method 1 when I want a faster way to expose using a manual lens and want aperture priority.

Thanks again

Drew