Nov 24, 2011, 18:04
I experimented using Matthews D700 with my Samyang 8 mm fisheye, which is specifically designed for an APS-C sensor under low light, high contrast situation.
There are several issues I wished to examine in this experiment. One had to do with the coverage of the sensor and the other with noise/image quality under moderately low light, high contrast situation. The experiment was not well thought through, so there will be some arm waving.
1) D700 shows in the viewfinder the coverage one is to expect from an APS-C sensor lens. it is a "wire frame" similar to the one you get in a rangefinder for a telephoto. The actual coverage of the Samyang was much larger and covered about 1/2 way the distance between the wire frame and the full image size. So far so good. However, the image quality (resolution) appeared low in this "extra" space.
2) I set the camera to ISO 3200. DXO sensor tests suggest that D700 beats D300 sensor by about 1.5 f-stops in terms of light sensitivity and dynamic range. On the other hand, I heard from a number of photographers that in practice, D700 performed a lot better than that. I therefore hoped that 2 f-stops higher than my usual cut off for a tolerable photo (ISO 800) should be doable. At this point, I should say that under high contrast situations, I usually expose for highlights (underexpose to the point where my highlights are just not blown and i bring up the shadows in software). Sometimes I use GNDs and sometimes HDR/multiple images. In this instance, I have been exposing for highlights. This is tough on image quality, because of the combined effect of the noise from high ISO AND an augmentation of this issue by boosting the shadows in post-processing. As I said, this methods works up to ISO 800 with D300.
At ISO 3200 with D700, the noise in the shadows was slightly greater than with D300 at ISO 800 (not based on any measurement - based on my experience). I found that in order to get a relatively low artifact image, I had to do sufficiently radical noise reduction that the image appeared smeared. Not much, but more so than I usually get with D300 at ISO 800. The difference was not large, but it was noticeable. I would guess that as far as shadows were concerned, DXO - based estimate of about 1.5 f-stop gain from D300 to D700 is about right. Midtones and highlights looked fine at ISO 3200 and required no cleanup, confirming what the happy owners were telling me about shooting at high ISO with D700. I am guessing that 2 factors conspire. High ISO on its own tends to exaggerate noise, but the problem is minor or field irrelevant with full frame sensor if the image is correctly composed and the image is not overly contrasty and does not require too much manipulation. Similarly high contrast photos shot at low ISO are much more resistant to noise. It is the common situation however, that the low light situation contain elements with high contrast and so this relationship between high ISO and contrast is very relevant. Furthermore, dynamic range decreases with increasing ISO.
Combination of noise and general softness in the areas outside of the APS-C frame on D700 makes this are ill suited for placing there subject where resolution matters. Unfortunately, I usually place at least a part of my main subject in that area.
The answer - There is no free lunch. But in some situations, you could get a worthwhile improvement in low light conditions shooting with full frame cameras and APS-C lenses, trading resolution for light sensitivity. This trade may be less painful as the number of pixels seem to grow rapidly in anounced or rumored cameras
There are several issues I wished to examine in this experiment. One had to do with the coverage of the sensor and the other with noise/image quality under moderately low light, high contrast situation. The experiment was not well thought through, so there will be some arm waving.
1) D700 shows in the viewfinder the coverage one is to expect from an APS-C sensor lens. it is a "wire frame" similar to the one you get in a rangefinder for a telephoto. The actual coverage of the Samyang was much larger and covered about 1/2 way the distance between the wire frame and the full image size. So far so good. However, the image quality (resolution) appeared low in this "extra" space.
2) I set the camera to ISO 3200. DXO sensor tests suggest that D700 beats D300 sensor by about 1.5 f-stops in terms of light sensitivity and dynamic range. On the other hand, I heard from a number of photographers that in practice, D700 performed a lot better than that. I therefore hoped that 2 f-stops higher than my usual cut off for a tolerable photo (ISO 800) should be doable. At this point, I should say that under high contrast situations, I usually expose for highlights (underexpose to the point where my highlights are just not blown and i bring up the shadows in software). Sometimes I use GNDs and sometimes HDR/multiple images. In this instance, I have been exposing for highlights. This is tough on image quality, because of the combined effect of the noise from high ISO AND an augmentation of this issue by boosting the shadows in post-processing. As I said, this methods works up to ISO 800 with D300.
At ISO 3200 with D700, the noise in the shadows was slightly greater than with D300 at ISO 800 (not based on any measurement - based on my experience). I found that in order to get a relatively low artifact image, I had to do sufficiently radical noise reduction that the image appeared smeared. Not much, but more so than I usually get with D300 at ISO 800. The difference was not large, but it was noticeable. I would guess that as far as shadows were concerned, DXO - based estimate of about 1.5 f-stop gain from D300 to D700 is about right. Midtones and highlights looked fine at ISO 3200 and required no cleanup, confirming what the happy owners were telling me about shooting at high ISO with D700. I am guessing that 2 factors conspire. High ISO on its own tends to exaggerate noise, but the problem is minor or field irrelevant with full frame sensor if the image is correctly composed and the image is not overly contrasty and does not require too much manipulation. Similarly high contrast photos shot at low ISO are much more resistant to noise. It is the common situation however, that the low light situation contain elements with high contrast and so this relationship between high ISO and contrast is very relevant. Furthermore, dynamic range decreases with increasing ISO.
Combination of noise and general softness in the areas outside of the APS-C frame on D700 makes this are ill suited for placing there subject where resolution matters. Unfortunately, I usually place at least a part of my main subject in that area.
The answer - There is no free lunch. But in some situations, you could get a worthwhile improvement in low light conditions shooting with full frame cameras and APS-C lenses, trading resolution for light sensitivity. This trade may be less painful as the number of pixels seem to grow rapidly in anounced or rumored cameras