[6BQ5]

Do big aperture full frame lenses overwhelm APS sized sensors with too much light? Today I tried shooting with a Jupiter 9 lens (85mm, f/2) wide open and I got a horribly overexposed image. Granted, this was in broad daylight. Does the full frame spot size produce too much light for the smaller APS sensor cavity? Is light bouncing around all over?

I was able to get better exposures when I stopped down the aperture to f/4 or more.

[jsherman999]

No.

It's a manual-everything lens, so it can't even cause 'over exposure.' You just didn't select an adequate shutter speed when you were shooting wide-open, or the green button failed you for some reason.

I shot quite a bit with the J-9 on my K20d - very fun lens.

.

[SpecialK]

Nope. You may have hit your shutter speed limit, or had a funny meter (spot metering?)

[carrrlangas]

Boris, I´ve seen many of your threads (recognize them because of your unique avatar) and I think you are confused about how lenses and different formats work together. Focal length, crop factor, Depth of field control, diffraction, exposure. All of them are interesant topics that you can take advantage of knowing about. I see you are very curious so I strongly suggest to go through the tutorials on this website:
Cambridge in Colour - Photography Tutorials & Learning Community

You won´t be disspointed. Hope they help.

Regards,
Francisco

[johnyates]

A full frame lens covers an area much bigger than an APS-C sensor, so there is a great deal more image-forming light entering the camera. This shouldn't cause over exposure, but it does have the potential to cause lack of contrast due to flare. That's why a sufficiently long lens hood is a necessity for best image quality.

[kh1234567890]

A full frame lens covers an area much bigger than an APS-C sensor, so there is a great deal more image-forming light entering the camera. This shouldn't cause over exposure, but it does have the potential to cause lack of contrast due to flare. That's why a sufficiently long lens hood is a necessity for best image quality.

In my experience fast (f/1.4) full frame lenses on APS sensors can give this sort of hazy flare when used wide open :




A deep hood does not really help (unless so deep as to effectively reduce the aperture), stopping down the lens a touch does. I don't really have a comparison with what these lenses would do on a full frame sensor - in the days when I used to shoot film I could not afford them. I'd put it down to stray light from outside the sensor area, but it is just a conjecture.

As for overall overexposure - I've never had that problem.

[TOUGEFC]

Nope. You may have hit your shutter speed limit

or your ISO was probably too high

[vanyagor]

I do not have any overexposure problems with my J-9. Others have already suggested possible explanation, posting an image with full EXIF may help find the problem

[interested_observer]

I might be a bit confused here, but I really do not understand the use or need of a wide open aperture. I only see the need for a wide open aperture for a couple of cases 1) low light; and 2) thin depth of field for subject isolation. Other than those two situations its better to go to something like f8 - usually the sweet spot in the lens for the sharpest and best image quality.

In full sunlight, again using a low iso will certainly increase image quality through the reduction of sensor noise. Also, using a metering mode that averages across the sensor rather than one single spot should give better overall exposure control. Using Av or M modes for manual lenses along with the green button to set the shutter speed, should produce excellent overall images.

[Lowell Goudge]

Do big aperture full frame lenses overwhelm APS sized sensors with too much light? Today I tried shooting with a Jupiter 9 lens (85mm, f/2) wide open and I got a horribly overexposed image. Granted, this was in broad daylight. Does the full frame spot size produce too much light for the smaller APS sensor cavity? Is light bouncing around all over?

I was able to get better exposures when I stopped down the aperture to f/4 or more.

I think you are confusing several points here. There are many full frame lenses still manufactured for Pentax cameras including many sigma and tamron lenses. There is, in general no issue with exposure, other than the invariable inaccuracies in any lens design and manufacture. Others have explained lenses are designed to give uniform exposure over the frame (assuming uniform lighting of subject) and the difference in sensor size simply determines how much of this uniform light (per square mm) hits the sensor.

Exposure with manual lenses , like the Jupiter 9 may have a differ issue depending on the camera you use. Although not discussed much any more, when the K10 and K20 were first released there was a long debated issue about exposure inaccuracy related to the native aperture of the lens. See the attached graph



The metering is calibrated(my opinion) to match the way the bodies behave with a manual lens, for open aperture metering. With manual lenses the camera does not know what aperture is selected, and therefore there is no calibration applied. You can see that F4-5.6 is the sweet spot for manual lenses and this is because most lenses have an aperture in this range.

The only way to successfully use (again my opinion) manual aperture lenses is to test your lens/camera combination at each aperture using a uniformly lit surface like a block wall or paved roadway, and then measuring the greyscale on the histogram for linearity across all apertures. Once you know how a lens/camera perform you will able to make ese corrections and continue to get great shots

[Canada_Rockies]

Personally, with manual lenses I find quite often that Sunny 16 and its derivatives are the best exposure meters out there. No batteries required, either. There are occasions with the 400 that spot metering is useful, but generally speaking, the little piece of paper that used to come with the roll of film is really quite good.

[Kozlok]

In bright sunlight at f2, your maximum shutter speed is just too slow. It seems I can never shoot below 2.8, or even 4, when it is a very bright day. If you want f2 in full sunlight, you need an ND filter (maybe a 2 or 3 stop). Sometimes a CPL (circular polarizer) is enough to get me to f2.

[1r0nh31d3]

Always amazed at how friendly the pentax forum is. These are some very gracious responses. Most of these responses responses have hit the nail on the head. bottom line, it's not your lens.

[6BQ5]

Thanks to everyone for their responses! I really appreciate the help here.

I do use spot metering. It's late evening as I type this so I can't experiment right now. I'm planning to take another lunch time walk tomorrow and I will try capturing a few pictures to post here. As I capture the pictures I'll be sure to take careful notes on my lens settings. It may take me a day or two to collate all the pictures and notes for posting.

Sometimes I would try exposure compensation but I would get haze very similar to what kh1234567890 showed.

[stevebrot]

Hi Boris,
Like jsherman99 (Jay) above, I have a lot of experience with the Jupiter-9 (J-9) on my K10D. IIRC, you shoot with a K-30. With the J-9 you have the choice of using M-mode with the green button and getting reasonably accurate metering or using Av mode and getting fairly inaccurate metering (the degree of inaccuracy is dependent on aperture, tends toward gross underexposure at wider apertures, and is not a simple bias). I would suggest M-mode.

The flow in M-mode:

• Frame your shot and focus
• Stop the lens down to the shooting aperture. This is requires some forethought with pre-set aperture lenses like the J-9.
• Press the green button to meter (camera will set the shutter speed)
• Press the shutter release

A few other points:

• With all lenses lacking the "A" contacts you will be limited to center-weighted average metering. You will not have spot or matrix metering.
• Your J-9 will benefit immensely from having a hood attached
• With the J-9, lower contrast and less sharpness are the rule when shooting wide-open
• In M-mode you will not be able to use exposure compensation. Instead...shoot, chimp, adjust shutter speed/aperture, shoot again. Once you determine the appropriate exposure for your subject you don't need to re-meter until either the light changes or you choose a different subject.
• As noted in the point above, chimping (evaluating the photo in the rear LCD screen) is your friend if you are not sure about exposure

Now...having said all the right things, I have to ask a silly question. When your Jupiter-9 is mounted to the camera does the display show F-- as the aperture? If so, everything is great. If not, we have a problem. The reason I ask is that my camera does that every so often with mated to my Jupiter-9. Does that mean that the lens fairy has magically gifted my lens with "A" contacts? I don't think so. What I do know is that I put an ohmmeter to the base of my lens and was surprised to find that the paint is mildly conductive to electricity. For some reason this sometimes fools the camera into thinking that it can set the aperture on a lens with no aperture coupling. The result is completely random green button metering based on the program line.


Steve


(...link to a few of my J-9 shots...)