lunar module wrote:
Eating popcorn. Enjoying the show.
Thank you Fred for the exposition. Very helpful and informative.
I think the wording in your final example may be a tiny bit confusing to some (count me in!). If I understand what you are saying, if you START with an A7R3 and the 24mm 1.4 GM @ f1.4 at ISO 400 and you push the crop button, you will END UP with an image equivalent to 36mm f2.1 ISO 1000. The actual images themselves will not be "similar". Right?
I think that is what I understand as well. Fred did a great job and I never knew those calculations before. I appreciate Fred a lot for saving me the $$$ of 35/2.8.
So: when I push the button, the image comes out as it was from Sony 36mm f2.1 GM at ISO 1000 and A7R3 Mini 18.5 MP at ISO 1000 ?
lunar module wrote:
Eating popcorn. Enjoying the show.
Thank you Fred for the exposition. Very helpful and informative.
I think the wording in your final example may be a tiny bit confusing to some (count me in!). If I understand what you are saying, if you START with an A7R3 and the 24mm 1.4 GM @ f1.4 at ISO 400 and you push the crop button, you will END UP with an image equivalent to 36mm f2.1 ISO 1000. The actual images themselves will not be "similar". Right?
You're welcome!
Yes, not similar! My last sentence was not clear and I just updated it.
IzelPhotograph wrote:
But you're also only trying to cover half the area.
If at FF you're 1.4 exposure @1.4 is 1/125, ISO100 then changing to crop mode your exposure [email protected] is 1/125, ISO100. Effectively (in crop mode), you're not reducing the amount of light, your reducing the amount of space the light can fall onto. It doesn't alter the speed of the lens.
If you print a picture and then trim a couple of inches off the side of it, the image that remains still has the same intensity as it did before you trimmed it.... it doesn't fade because less ink is visible.
Now, this will alter the depth of field but it has zero impact on the exposure. ...Show more →
I'm not getting that.
I use S35 constantly for video, as soon as I crop, my exposure changes, I always have to add light, since I can't increase my shutter speed (I always adhere to the 180 degree rule), I open up my iris. I just tried this again on a scene I'm filming right now (it's morning tea break).
Let's agree to disagree, unless a Sony engineer can chime in with actual data to support either one of our tests, it's going to be a long drawn out argument. I go by my waveforms.
So you are saying that when you crop in post (stills or video), your image darkens and you have to turn up the gain to get exposure equivalent to the uncropped image?
Melindra wrote:
I'm not getting that.
I use S35 constantly for video, as soon as I crop, my exposure changes, I always have to add light, since I can't increase my shutter speed (I always adhere to the 180 degree rule), I open up my iris. I just tried this again on a scene I'm filming right now (it's morning tea break).
Let's agree to disagree, unless a Sony engineer can chime in with actual data to support either one of our tests, it's going to be a long drawn out argument. I go by my waveforms.
Shooting with A7RIII + 24/1.4 GM wide open at ISO 400 (42MP) in "APS-C crop mode" will yield an image equivalent to ~35/2 ISO 1000 (18.6MP) when both images are equalized.
42/1.5/1.5 = 18.66 MP
24 x 1.5 = 36mm
f/1.4 x 1.5 = f/2.1
ISO 400 x (1.5 square) = 400 x 2.5 = ISO 1000
I guess and to be pedantic the last formula should read
ISO 400 x (1.5 square) = 400 x 2.25 = ISO 900
and to add, the perspective is still the perspective of 24mm focal length, as Guy shows it in his pictures of the nose of a truck with scaled CV21 vs Sony 24mm.
darrellc wrote:
So you are saying that when you crop in post (stills or video), your image darkens and you have to turn up the gain to get exposure equivalent to the uncropped image?
In their latest and current issue the german photo magazine "Color Foto" published a test of the Sony GM 1,4/24mm with absolutely excellent results. Exceptionally good indeed. The run lens tests at a magnification of 1:50 on a flat board and evaluate only the jpeg files.
Melindra wrote:
I'm not getting that.
I use S35 constantly for video, as soon as I crop, my exposure changes, I always have to add light
Cropping into an image or video alone cannot make it darker, everything else being equal. Maybe you're changing the frame rate, which changes the shutter speed. Something else changes. No matter how much you crop, the overall exposure remains the same. Half the image size requires half the amount of light. An f/1.4 lens gives the same general exposure in medium format as in a tiny phone camera. Not to mention cropping in Photoshop doesn't change the exposure, either.
If you use auto exposure, and you crop in to something bright, the automatic metering system might make that area darker to compensate. That's a metering issue. Yes, cropping can affect automatic metering. But if you're in fully manual mode, and you simply crop in, and don't change anything else, the exposure cannot change. Now if your light is flickering, and your shutter speed is very short, you may randomly get a different result, depending on whether you catch a dark phase or a light one. It's like a rotor moving in front of you -- it may or may not block your view at the moment, depending on its current position.
I'm not sure what your camera does, but if it just crop a part of the image, its exposure is unaffected.
Also cropping in could change the way you think about exposure. If I have a landscape with a small shadow, it's not the main subject. But as soon as I crop in, the shadow area becomes the main subject, so it needs more light. That's an artistic choice. Changing the composition might require you to add light because the scene changes. But that's not the crop itself that causes it. It's how our mind reacts to a change of composition. When I look at something dark, my brain automatically adjusts to it, and I see it brighter, but that's just a mental image. The physical image didn't change, only its perception. Similarly, the histogram can change drastically when you crop into a brighter or darker area. But if you shoot something middle gray, and you crop in significantly, it'll stay middle gray. There's no need to add more light due to the cropping alone.
cppguy wrote:
Cropping into an image or video alone cannot make it darker, everything else being equal. Maybe you're changing the frame rate, which changes the shutter speed. Something else changes. No matter how much you crop, the overall exposure remains the same. Half the image size requires half the amount of light. An f/1.4 lens gives the same general exposure in medium format as in a tiny phone camera. Not to mention cropping in Photoshop doesn't change the exposure, either.
If you use auto exposure, and you crop in to something bright, the automatic metering system might make that area darker to compensate. That's a metering issue. Yes, cropping can affect automatic metering. But if you're in fully manual mode, and you simply crop in, and don't change anything else, the exposure cannot change. Now if your light is flickering, and your shutter speed is very short, you may randomly get a different result, depending on whether you catch a dark phase or a light one. It's like a rotor moving in front of you -- it may or may not block your view at the moment, depending on its current position.
I'm not sure what your camera does, but if it just crop a part of the image, its exposure is unaffected....Show more →
I tried it again today, in video, exposed for 0.0, cropped to S35, got -0.7EV.
Studio lighting, so no ambient fluctuations.
Back to FF, 0.0, crop, -0.7
I'm not super savvy with the technicalities, but cropping on our 7R's with real world scenes results in a lower exposure everytime. My boss puts it down to less light funneling its way to the sensor, as do I.
If I'm wrong I'd be happy and interested to hear an explanation of what is happening.
That shows you are paying attention!
Yes, perspective does not change, only FOV.
BokehBeauty wrote:
I guess and to be pedantic the last formula should read
ISO 400 x (1.5 square) = 400 x 2.25 = ISO 900
and to add, the perspective is still the perspective of 24mm focal length, as Guy shows it in his pictures of the nose of a truck with scaled CV21 vs Sony 24mm.
Also, this image is cross-posted from the FE image thread as I wanted to make a separate note that wasn't purely image based.
The shot below was with the EyeAF actuated in AF-C while my daughter was erratically jumping up and down. Oddly enough, it did pretty well in this sequence with regard to speed and accuracy.
However, there are times when the subjects are relatively static and at varying distances where the EyeAF will not engage right away. Still trying to figure out if I can see a pattern or recurring set of conditions present when it doesn't engage so as to identify how to mitigate or work-around. Not a crazy big deal for my uses but still stirs my curiosity. The leaves need to fall - GM 24 by John Dizzo, on Flickr
Ordered one of these from Adorama today, because of the pics in the Images thread.
Just received the Sigma 24mm F1.4 Art in FE mount. While it's a nice lens in and of itself, it doesn't live up to the rest of the Art line, IMO, so I found it somewhat lacking anyway.
It's going back, and hopefully Adorama fills their backorders quickly.
I've always loved my Batis 25, probably my most used lens...But, I gotta say, I like the 24GM better, it's VERY sharp, AF is really fast and the bokeh is smoooooth and interesting and the form factor and build seem to be just about perfect, add to that the 1.4 aperture and there's just a lot to like about this lens. Definitely a keeper.
I've always loved my Batis 25, probably my most used lens...But, I gotta say, I like the 24GM better, it's VERY sharp, AF is really fast and the bokeh is smoooooth and interesting and the form factor and build seem to be just about perfect, add to that the 1.4 aperture and there's just a lot to like about this lens. Definitely a keeper.
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