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11-15-2010, 09:58 AM   #76
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QuoteOriginally posted by blende8 Quote
I don't understand.
What does this help?
this modification shorts the pin that determines whether a lens is in A mode or not.

it enables matrix metering, and perhaps lets the P-TTL flash fire at other than full power. although you need to make sure the flash and lens are set where you want them

11-15-2010, 12:19 PM   #77
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Hmm ...
But the disadvantage is that you always have to set the camera to the same aperture as the lens aperture ring. Otherwise you will get over- or underexposure. Right?
11-15-2010, 02:12 PM   #78
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QuoteOriginally posted by blende8 Quote
Hmm ...
But the disadvantage is that you always have to set the camera to the same aperture as the lens aperture ring. Otherwise you will get over- or underexposure. Right?
I use this for pre-set lenses (not M lenses - I have no K mount lenses with an aperture lever, but I have quite a few pre-set lenses with a K bayonet and no aperture lever: m42's, modified nikon, soligor, rokinon, bellows, etc...).

The advantages to me are that P-TTL works & exposure is correct for all my lenses (and I have only A type and pre-set lenses.)

If the camera were not tricked this way, exposure would be ok in M mode using the green button, but P-TTL would not work.

Aperture is set on the lens & the green button sets correct exposure; I don't change the e-wheel aperture setting from F2.8 (therefore it is wrong in exif*). Setting aperture on the camera and a different aperture on a M type lens might work to correct the aperture linearity problem but I think it not worth the trouble & confusion.

Dave

*with the camera mount modified to think all lenses are A type & using pre-set lens, correct data can be written to exif in M mode if: (1) the exposure time is set with the green button while the e-wheel aperture is at F2.8, then (2) the e-wheel aperture is changed to match that of the lens.

Last edited by newarts; 11-15-2010 at 03:03 PM.
11-15-2010, 08:43 PM   #79
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QuoteOriginally posted by newarts Quote
No messing with the lens, just a small, reversible modification to the camera's mount.

This modification is easily reversible & increases the utility of my pre-set lenses (Macro-Tak 50:4, MIR 65:3.5 tilt/shift, bellows, Pentax 135:2.5, among others) a bit.

Dave
so you are telling me if i put the foil on the camera pin it will think i have an A lens on when using a K or M lens right and it will auto apature for me right?

11-15-2010, 08:45 PM   #80
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anouther thing is what f: stop do i leave the lens set to for it to work wide open i would think but not sure?
11-15-2010, 09:11 PM   #81
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Douglas:
So that was my problem? The camera won't meter automatically in Av mode with K and M lenses and then stop down based on the lens ring? You have to do it? I thought that since the k7 was so advanced it'd do that on it's own. But I was getting funky
11-15-2010, 09:13 PM   #82
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results! That's really lame the old top model 35mm models could do that sort of thing but a fancy digital with all the bells and whistles can't. Especially when Pentax brags about how it can use its old mounts.
11-16-2010, 05:02 AM   #83
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QuoteOriginally posted by lguckert79 Quote
so you are telling me if i put the foil on the camera pin it will think i have an A lens on when using a K or M lens right and it will auto apature for me right?
I said, "I use this for pre-set lenses (not M lenses - I have no K mount lenses with an aperture lever, but I have quite a few pre-set lenses with a K bayonet and no aperture lever: m42's, modified nikon, soligor, rokinon, bellows, etc...)."

I suspect using K mount lenses with an aperture lever would be a pain in the neck at least with the K-x body. When in M mode with an A lens (and it would think the M lens is an A lens), the K-x green button does not close the aperture at metering time - it calculates what the brightness will be & the calculation will be wrong: therefore it would close the aperture to the wrong place at exposure time.

To get around this for M type lenses one might use a different e-wheel aperture setting for each lens aperture setting - probably a big pain in the neck.

Other model cameras may behave differently; perhaps the K-r or K100D closes the aperture to meter when in M mode? If so, using M type lenses the camera thinks are A type would be easy. I just don't know.

QuoteQuote:
anouther thing is what f: stop do i leave the lens set to for it to work wide open i would think but not sure?
With my K-x and pre-set lenses (no aperture lever) I set the lens aperture to whatever I want and set the e-wheel aperture to a constant value (F2.8 for my Macro-Takumar 50:4 for example) - then I press the Green Button which sets the correct exposure time.

Dave

11-16-2010, 05:45 AM   #84
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QuoteOriginally posted by newarts Quote
I suspect using K mount lenses with an aperture lever would be a pain in the neck at least with the K-x body. When in M mode with an A lens (and it would think the M lens is an A lens), the K-x green button does not close the aperture at metering time - it calculates what the brightness will be & the calculation will be wrong: therefore it would close the aperture to the wrong place at exposure time.
But wouldn't this be the same with an M42 lens?
Here, too, the camera would think it is an A lens and would not do an actual measurement.
11-16-2010, 06:58 AM   #85
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QuoteOriginally posted by newarts:
I suspect using K mount lenses with an aperture lever would be a pain in the neck at least with the K-x body. When in M mode with an A lens (and it would think the M lens is an A lens), the K-x green button does not close the aperture at metering time
QuoteOriginally posted by blende8 Quote
But wouldn't this be the same with an M42 lens?
Here, too, the camera would think it is an A lens and would not do an actual measurement.
A M42 lens (for example) is already stopped down to wherever you turned the aperture ring so the camera measures the correct light level for the exposure: the shutter speed is set correctly by the green button and the camera cannot change the len's aperture because there is no aperture lever.

The result is a correct exposure, and p-ttl flash, matrix metering, multi-point focusing, etc can be used.

Dave
11-16-2010, 07:07 AM   #86
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BTW ... in case someone would insist on doing that, it seems that there is an easy way to use an M/K lens as an M42 (with insulated base): just isolate body pin #2 (counting from the bottom). :-) (Seems to work with the k-x at least).
11-16-2010, 07:13 AM   #87
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I have the feeling that for some reason my brain is not working properly today.

I cannot test this atm, since I have the camera not with me.

The camera thinks that it is an f1.2/22 lens, because all contacts are shortened.
It assumes that the lens is in the A-position.
It thus assumes that the lens is fully open (F1.2).
It then will take the f-reading from the camera (which you have set with the back wheel) and will calculate the speed.
This will happen independent of there being an aperture lever or not.
Or does the camera recognize that there is no aperture lever?
11-16-2010, 07:36 AM   #88
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QuoteOriginally posted by blende8 Quote
I have the feeling that for some reason my brain is not working properly today.

I cannot test this atm, since I have the camera not with me.
that's OK
QuoteQuote:
The camera thinks that it is an f1.2/22 lens, because all contacts are shortened.
yes
QuoteQuote:
It assumes that the lens is in the A-position.
yes becayse the mod to the camera shorted pin 3 to th elens mount
QuoteQuote:
It thus assumes that the lens is fully open (F1.2).
yes
QuoteQuote:
It then will take the f-reading from the camera (which you have set with the back wheel) and will calculate the speed.
yes but it will get it wrong because it is assuming that the open aperture is F1.2 and not what ever the lens is that you have mounted
QuoteQuote:
This will happen independent of there being an aperture lever or not.
I am not sure of what you mean by aperture lever here, do you mean the activation lever , or the aperture coupling lever on K mount bodies that tells the camera what the aperture is set to.
The activation lever holds the aperture open until the shutter is tripped, The coupling lever is the one deleted when they went to the FA-J mount.
QuoteQuote:
Or does the camera recognize that there is no aperture lever?
again, the digital camera does not know about the aperture coupling lever because the camera side coupling is missing.

I am not sure you are aware that there were, on K and M lenses 2 aperture levers, one that coupled the aperture ring setting to the metering, and a second that opens and closes the aperture (aperture activation lever).

All K mount lenses have the activation lever, and no DSLR bodies have the coupling lever,

I think part of the confusion also comes from the use of M42 lenses that are stopped down before shooting, these will meter OK in AV mode but P-TTL flash is not easy because the camera does not understand what open aperture is, vs the preset aperture.
11-16-2010, 07:54 AM   #89
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Lowell, what I want to find out is this:
Dave said that he can put his M42 lens on his A-modified body and it meters correctly. I am questioning this based on the above reasoning.
Dave said that that the difference is that M42 lenses do not have a "diaphragm actuator" (as Bojidar calls it here) or "activation lever" as you call it. But is this detected by the camera?




QuoteOriginally posted by jolepp Quote
BTW ... in case someone would insist on doing that, it seems that there is an easy way to use an M/K lens as an M42 (with insulated base): just isolate body pin #2 (counting from the bottom). :-) (Seems to work with the k-x at least).
Really? Strange.
You mean r2?
r2 appears to be just a pin for the aperture encryption.
And what do you mean by "insulated base". If it is already insulated, why again insulate it?

11-16-2010, 08:10 AM   #90
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If you're interested only in AV mode you may remove the aperture lever (if reversible) or don't completly mount the lens and the camera will give you an accurate metering with full manual aperture control. (note that if you stop down to f16 the viewfinder will darker)

If you need matrix metering and P-TTL short the pin on the body also. (blende8 is the * on the picture)
The drawback is that your picture exif will show always f1.2 and you can't select the f-stop on the body.

Keeping the situation above in mind, if you use a K50 1.2 and put f4 on body and stop down the lens at f4 your picture will'be severly over exposed because the body will read the light that is passing trough the lens at f4 thinking it is fully open.

All of the above can be done easily without arming or modifing the mount on the lens.
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