[striker_]

The camera doesnt stop down the aperture blades until the pic is taken because it will be hard to see through the viewfinder if you are shooting with a small aperture. You can check it by looking through the viewfinder using both lenses and the 50mm will be brighter.

[paulh]

Quote:
What I do not understand is why Pentax did not give the user the opportunity to dial the aperture into the camera when using manual lenses. As long as the number dialed into the camera matched the aperture selected on the lens aperture ring, the camera should be able to perform the necessary calculations.
That would be ideal. I could set it to f8 or whatever and leave it and let it autocheck the light without pushing the button..do any of the other model cameras do that? or is that the same across the line?

You need an A - type manual lens for this. It has the electrical contacts that communicate with the body, so you can use all modes (Av, Tv, etc) automatically. You still have to manually focus. The M & K series lenses have no communication with the body, so you can only use M-mode, and must use stop-down (green button) metering for the camera to make a calculation.

[striker_]

You need an A - type manual lens for this. It has the electrical contacts that communicate with the body, so you can use all modes (Av, Tv, etc) automatically. You still have to manually focus. The M & K series lenses have no communication with the body, so you can only use M-mode, and must use stop-down (green button) metering for the camera to make a calculation.

or using green button in M mode works as well but it doesnt meter perfectly every time (not for me).

[vonBaloney]

This is where screw-mounts can be advantageous in some cases. If you had a manual m42 lens on there, and you put the ring on f8, it would really be on f8 (and would be darker in the viewscreen, so you might find yourself moving the ring back and forth for focusing). But you can use Av without pressing any buttons. Once you get into the groove using the green button (or =/-), it isn't so bad. But a 'A' lens would be most ideal, obviously.

This is the effect of the "crippled" part of the K-mount on DSLRs, right? With the same lens on a K1000, it knows the aperture. (Of course, it doesn't have Av mode.)

But going back to your original query, once you get the metering worked out, you will probably find that the 50 *does* let in a little more light than the zoom and so you can use slightly faster shutter speeds (on the same aperture), but not the big difference you were seeing.

[paulh]

or using green button in M mode works as well but it doesnt meter perfectly every time (not for me).

The K10D & K20D have a well-known problem with green button metering accuracy. My older bodies (istD, K100D) are very accurate, and I understand the models from the past couple years are also fairly accurate.

[kswier]

You need an A - type manual lens for this. It has the electrical contacts that communicate with the body, so you can use all modes (Av, Tv, etc) automatically. You still have to manually focus. The M & K series lenses have no communication with the body, so you can only use M-mode, and must use stop-down (green button) metering for the camera to make a calculation.

Correct. You do need and A lens for this with Pentax's current implementation. But I do not understand why it has to be this way.

With just a bit of extra code, I think that Pentax could have had the user input the aperture of the lens (the lens and body are not communicating, but the body knows the aperture because you dialed it into the body). This would make m-lenses a lot more functional. It seems like the camera could ask you to enter the wide open aperture of the lens (just like it asks you for the focal length for manual lenses), and then allow you to dial in the aperture you are using. From this information, figuring out the metering is a piece of cake. You could make an menu option to turn off the feature for those who do not want it.

Anyway, just a feature I wish Pentax had implemented to increase the functionality of manual lenses. I am unsure if they did not think of it, thought it would be too complicated for users, or wanted to protect new lens sales. Or, it is possible I am missing something.

[paulh]

Correct. You do need and A lens for this with Pentax's current implementation. But I do not understand why it has to be this way.

With just a bit of extra code, I think that Pentax could have had the user input the aperture of the lens (the lens and body are not communicating, but the body knows the aperture because you dialed it into the body). This would make m-lenses a lot more functional. It seems like the camera could ask you to enter the wide open aperture of the lens (just like it asks you for the focal length for manual lenses), and then allow you to dial in the aperture you are using. From this information, figuring out the metering is a piece of cake. You could make an menu option to turn off the feature for those who do not want it.

Anyway, just a feature I wish Pentax had implemented to increase the functionality of manual lenses. I am unsure if they did not think of it, thought it would be too complicated for users, or wanted to protect new lens sales. Or, it is possible I am missing something.

A bit of info here: https://www.pentaxforums.com/forums/pentax-dslr-discussion/165273-crippled-k-mount.html

[vonBaloney]

h just a bit of extra code, I think that Pentax could have had the user input the aperture of the lens (the lens and body are not communicating, but the body knows the aperture because you dialed it into the body). This would make m-lenses a lot more functional. It seems like the camera

They wouldn't need you to input the information -- the position of the aperture control on the lens moves as you as turn the ring -- the lenses ARE transferring information, but mechanically not electrically. Pentax bodies *USED* to read the aperture setting from M lenses this way but they disabled it. (i.e. the crippled mount) So if they brought it back, they should just bring back that capability. Don't hold your breath -- they are in the lens business too, after all.

[rbefly]

) is there some larger problem with my stock lens? I'll be honest when I put it on, I felt it looked a little dark in comparison to the 50mm prime I'd just had on there. It doesn't look dirty

Hi Crossmr,
The solution to this is because you're looking through the 50mm f1.7 at f1.7. The fastest (widest) you could look through the 18-55mm lens is f3.5 (wide open).
The zoom, at its widest setting, is two full stops slower (darker) than the f1.7 wide open.
Ron

[kswier]

They wouldn't need you to input the information -- the position of the aperture control on the lens moves as you as turn the ring -- the lenses ARE transferring information, but mechanically not electrically. Pentax bodies *USED* to read the aperture setting from M lenses this way but they disabled it. (i.e. the crippled mount) So if they brought it back, they should just bring back that capability.

Interesting...I was just reading about that on the link that paulh posted. I never knew that these lenses provided aperture information. I agree that adding in a mechanical sensor would be ideal. A software solution may be less expensive though (I feel like I could write the code in less than a day fairly easily...and I am no expert programmer).

Don't hold your breath -- they are in the lens business too, after all.

Yep agreed...These darn businesses...always trying to make money

Anyway...I need to stop hijacking this forum. Thank you all for the information and listening to my random idea.

[epqwerty]

or using green button in M mode works as well but it doesnt meter perfectly every time (not for me).

I found that center weighted and/or spot meterring provide much more accurate results over the other type the full meterring one. Which generally underexposes the image.

[manacho2005]

The camera doesnt stop down the aperture blades until the pic is taken because it will be hard to see through the viewfinder if you are shooting with a small aperture.

...but it would feel a bit nostalgic. Brings back memories shooting my k1000. :-)

[vonBaloney]

...but it would feel a bit nostalgic. Brings back memories shooting my k1000. :-)

The K1000 doesn't stop down until you take the picture either (it uses the mechanical method described above to transmit aperture info to the meter), although strangely enough I remembered it the same way until the crippled mount bit was explained to me.

[manacho2005]

The K1000 doesn't stop down until you take the picture either

I guess I had an older model, either that or there was a hidden dof preview switch stuck somewhere

[vonBaloney]

I guess I had an older model, either that or there was a hidden dof preview switch stuck somewhere

Pretty sure they were all the same. If you were using a Takumar or something other than a Pentax-M lens then maybe, but otherwise only the needle moved up and down.