Problems using aperture ring

Hi all,

Just having a play with my Pentax-A 28mm f2.8, using the aperture ring to select aperture rather than using the camera on "A" setting (doing it to get some practice in advance of receiving a Pentax-M 135mm f3.5 I've purchased off the classifieds).

Firstly, using the aperture ring set at "A", and in Av mode I lined up a shot at f2.8 and made a note of the shutter speed (and other settings) the camera suggested. I then went to M mode, used the settings I had noticed and took a picture. Picture looked good, all exposed properly.

Then, changing the aperture ring to 2.8, I used the same settings as previous, but the shot looked very different, not necessarily underexposed, but just more yellow.

Here are the pictures (don't judge me , they are very quick and rough for testing only!):

[IMG]http://i659.photobucket.com/albums/uu319/rob_davies/IMGP2221.jpg[/IMG]

[IMG]http://i659.photobucket.com/albums/uu319/rob_davies/IMGP2222.jpg[/IMG]

I then tried a longer exposure on the second picture but it began to look a bit glarey and overexposed.

Does anyone have any idea what is wrong/what I'm doing wrong?

Kris, you're a gentleman and a scholar.

White balance was indeed the issue, when I switched off Auto White Balance to any other setting the results were almost identical between camera and lens based aperture selection.

The only issue seems to be now that only AWB on the "A" setting gives a result that actually looks like what I'm looking at!

More experimenting methinks.

By the way, tweezers worked brilliantly, replacement screen in and going well. I'll pop them back in the post to you. Cheers again.

I wonder why on earth taking the lens off "A" would mess-up the white balance: Sounds like an "undocumented feature" to me

K.

Cheers Kris,

Advice was spot on, works a treat now!

Regards

Rob

Could be just coincidence if something else triggered the change, like a slightly different framing of the subject. Sometimes it only takes the slightest change to make auto WB flip from one setting to another.

The shots are not framed the same with the first shot you have some purple and with the second shot that purple is almost white and the white is to yellow.
Probably it tried to make the purple white in the last shot

It has nothing to do with the aperture.

I do recall that the advice when using an "A" lens is to leave the aperture on "A" and not try and select it manually.

It is a while since I used an "A" lens on my K10, but it may be that you will lose the aperture fuctionality...ie your shots will all be at wide open. I don't know what camera you are using, and it may well be that my advice is not appropriate , but it is worth you investigating

The shots won't be wide open it will stop down, the problem is that the camera does not know the aperture you've selected so it simply meter it wide open without any correction for the aperture you've the ring on.

Yes, it's more convenient with digital cameras to leave the lens on "A" all the time. You can still use Manual mode if you wish. Just select the aperture via the camera.

Stefan

According to my K10 manual, an "A" lens with the aperture set to anything other than "A", will work in Av mode but any exposure will be wide open irrespective of the aperture setting on the lens.

You must use manual exposure to get the lens to stop down.

This may differ from the OP's camera of course.

Yeah you're right, just tried it with the DFA 100mm, the funny thing is that it does close the aperture down but only after the exposure

I tried it on numerous occasions (more than just the two examples given above) and every time there was the same marked difference.

Also no "non-auto" white balance setting when using the aperture ring gives anywhere near the picture as evidenced using the "A" position and AWB.

Kris' suggestion of manually setting white balance addressed the issue, but I'm a little confused as to how it arose?

I'm also concerned that an M lens will suffer the same problems.

Stefan, no one has said it is a problem with aperture. But it is a problem which is occurring when I use the aperture ring in anything other than the A position.

I took numerous shots and the difference was marked every time.

My understanding (which could be wrong) was that as long as I enabled the camera to use the aperture ring, set the camera to M mode, adjusted the aperture using the ring, metered (which will be metering at the aperture I've selected, not wide open), then things should at least be comparable to when using the "A" setting, and certainly not this different.

My concern is that when using an M lens that these problems are going to arise (as I obviously won't have the A setting).

Although I've only posted two pictures above, I took numerous different pictures using the two settings, and for some reason every time I wasn't on the A setting the AWB went a bit funny (technical speak).