[redrockcoulee]

I suggest Pentax/Ricoh release a ff asap and let us find this out for ourselves NOW!!!

There are lots of full frame abet film Pentax cameras out here now

[Ash]

Unfortunately what you describe is not possible. In its simplest form aperture is not related to image circle at all, no extra light that comes into a lens can be recovered and used to increase brightness of image. Aperture especially on a tele lens is the focal length divided by front element diameter. Just look at a K300/4 and the DA300/4. Both use 77mm filters. The bigger the front element the more light gathered. That's all. To put elements behind the lens, and put more light on the image would require a retro focus element / group, reducing the focal length.

You can also achieve this in a limited manner with a close up lens. These effectively shorten the focal length of the lens, and since the diameter is not changing the F-number gets smaller (bigger aperture)

I understand. I put forward no argument for the benefits of trying to 'squeeze in' the FF image circle into an APS-C sensor. But is 'light gathering ability' limited only by the size of the front element? The DA 12-24 takes a 77mm filter, and granted the front element doesn't span the entire 77mm, but it is rather large and is only f/4. The DA 15 is smaller and also f/4. The FA 31 is 58mm and f/1.8. I figure there's more to maximum aperture than just front element size - lens design otherwise, including rear element size and optical properties of the elements, would play a part in it (cf. FA 50/1.4)

[Ash]

There are lots of full frame abet film Pentax cameras out here now

Yes, but then we'd have to return to the inability to chimp, and work without a histogram, and have to scan images/negatives (which degrades IQ), and spend more on film and processing, and not be able to shoot 7fps, and, well you get the idea.

[Lowell Goudge]

I understand. I put forward no argument for the benefits of trying to 'squeeze in' the FF image circle into an APS-C sensor. But is 'light gathering ability' limited only by the size of the front element? The DA 12-24 takes a 77mm filter, and granted the front element doesn't span the entire 77mm, but it is rather large and is only f/4. The DA 15 is smaller and also f/4. The FA 31 is 58mm and f/1.8. I figure there's more to maximum aperture than just front element size - lens design otherwise, including rear element size and optical properties of the elements, would play a part in it (cf. FA 50/1.4)

Wide angle lenses all include already retro focus elements and groups because the regestry distance exceeds the focal length. The front element on wide angle lenses may or name not be the limit, like they we on tele photos, and you need to look at the physical placement of the aperture relative to the retrofocus group to know where the physical limit is.

For the F A 31 look at the true element diameter, at F 1.8 it should and likely is in the order of 17 mm. The wide filter is more to do with angle of view and vignetting. Don't consider the filter as the front element especially on a UWA lens

[ElJamoquio]

I understand. I put forward no argument for the benefits of trying to 'squeeze in' the FF image circle into an APS-C sensor. But is 'light gathering ability' limited only by the size of the front element? The DA 12-24 takes a 77mm filter, and granted the front element doesn't span the entire 77mm, but it is rather large and is only f/4. The DA 15 is smaller and also f/4. The FA 31 is 58mm and f/1.8. I figure there's more to maximum aperture than just front element size - lens design otherwise, including rear element size and optical properties of the elements, would play a part in it (cf. FA 50/1.4)

You can limit the light somewhere else - e.g. by using apertures. In some lenses some of the light is going to 'fall by the wayside' and be absorbed by the matte-black-finish inside the lens.

Front lens element is a good way to figure out apertures for longer focal lengths, but for shorter focal lengths other stuff is going on.

[Rondec]

I think these sorts of discussions are a little silly. Basically, if I take a photo with a 135 mm lens at f2.8 and iso 100 on APS-C, I will have the same photo (roughly) as if I took the same photo with a 200mm lens at f2.8 and iso 100 on a full frame camera, but with one more stop of depth of field. Since iso and aperture are "relative," they end up scaling by the format and my shutter speed will be exactly the same. If the "amount of light getting to the sensor" was truly different, then my shutter speed would be faster on full frame, but it isn't.

I find these discussions frustrating, in general, because there ends up being an assumption that the goal of photography is narrow depth of field. There are certain situations where this is helpful in producing a pleasing effect, but it can be over used and in many types of photography (landscape, macro), it can be a distinct negative. Even in portraiture, there are plenty of examples of too little depth of field.

[lytrytyr]

The lens resolves the same on a lp/mm basis

It's more complex than that.
Lenses may outresolve a sensor,
but that won't show up in the image captured by the sensor.
(In fact it's even more complicated because of the AA filter,
but let's not go there.)

but the mm is so much higher on the FF sensor, that on a lp per picture height basis, excellent on a CX is on par with 'poor' or so on FF.

That's backwards.

At the extreme,
the Nikkor is "excellent" on FF,
but at best only "good" on CX.

[lytrytyr]

. . . there ends up being an assumption that the goal of photography is narrow depth of field.

Maybe not the goal,
but a way to rescue a badly composed photograph
by blurring a distracting background.

[Fogel70]

Fogel hasn't been debating depth of field with me. I have been clear from the beginning that I have been talking about exposure which comes down to shutter speed, aperture and film/sensor sensitivity. Furthermore, I also the FOV and angle of view difference is due to the sensor size. That is basic photography. Where things get murky is when people want to start using equivalency in terms of aperture relative to depth of field which misleads folks into think it effects exposure.

Yes, what I have been trying to debate is the below statement. But I might not have been using the correct terms for everything I try to prove, or maybe I totally misunderstood you.

For example, an FA 77/1.8 at f1.8 lets the same amount of light to the aps-c sensor at ISO 100 as it does to a roll of ISO 135 film.

If using the same lens, with same aperture and ISO, half the light (photons) is collected by the APS-C sensor, than with a FF sensor if using the same shutter speed on both. With a FF lens on a APS-C camera half of the light that enter the lens will fall outside the APS-C sensor and will not be used for exposure of the image.

[Rondec]

Yes, what I have been trying to debate is the below statement. But I might not have been using the correct terms for everything I try to prove, or maybe I totally misunderstood you.



If using the same lens, with same aperture and ISO, half the light (photons) is collected by the APS-C sensor, than with a FF sensor if using the same shutter speed on both. With a FF lens on a APS-C camera half of the light that enter the lens will fall outside the APS-C sensor and will not be used for exposure of the image.

But I think the point is that if you keep your iso and aperture the same, your shutter speed will be the same as well on both formats in order to give you a well exposed image. And isn't that the goal?

[Ben_Edict]

Ben, I believe the thought stemmed from the possibility of creating a reverse teleconverter - allowing FF lenses to be used on APS-C format, only with the ability to encapsulate the complete FF image circle concentrated onto an APS-C sensor, thereby increasing incident light intensity per sensor area. This effectively makes the FF lens 'faster' than it innately is. I mentioned earlier that I found little practical utility in this as extra glass naturally implied a degradation in IQ - we may as well just have DA lenses for APS-C created with larger apertures (if that is the intention of having such a reverse TC), which means larger lenses (not what Pentax would be wanting to create anyway).

To me, let FF lenses be put on a FF camera (we're waiting, Pentax), and finally we can have a camera that will use the full image circle from the lenses and put an end to this madness!

It doesnt - simply because the definition of aperture is a simple relationship based on the fundamental lens properties, i.e. focal length and the diameter of the entrance pupil (aka "max. aperture"). What you suggest is a device very well known as "focal reducer". And it lives up to its name, by shortening the focal length (thus cramming the larger image circle of the lens onto the smaller sensor). If the FL is getting shorter, but obviously the glass elements stay the same, you will get a faster aperture. It is not soemthing "equivalent", it is pure, well-knwon lens properties.

By the way: this concept is very old and used day by day by astrophotographers around the world. Focal reducers are hard to design and very expensive, if they shall work on different lenses and not being dedicated to one signle lens model. I don't know of any of those, which would work on the already comparetively fast lenses, we use in photography - and by any means, reducers also reduce the back focal length of a lens, thus, you can't focus to infinty anymore. If you want to keep infinity focusing, you need to add a relay system to the reducer and thus you create a big, bulky and expensive piece of equipment, which is a hefty compromise in termy of image quality anyway...

Ben

[ElJamoquio]

I find these discussions frustrating, in general, because there ends up being an assumption that the goal of photography is narrow depth of field.

My assumption is that someone (me, you) want a certain given DOF level, regardless of whether I'm shooting with a D600 or a K-5.

[Ben_Edict]

If using the same lens, with same aperture and ISO, half the light (photons) is collected by the APS-C sensor, than with a FF sensor if using the same shutter speed on both. With a FF lens on a APS-C camera half of the light that enter the lens will fall outside the APS-C sensor and will not be used for exposure of the image.

No, that is wrong and part of the misconception behind many (not all) statements related to the "equivalency modell".

The light "wasted" outside the sensor area does not contribute to the brightness of the image area ON the sensor, it is simply part of the lens' image circle, that will not be recorded as it is outside the sensor's boundaries. By the way: If you use a long tele lens, its image circle is usually vast and exceeds by far even the 35mm format. It is artificially cropped by the lens barrel and often by a mask at the rear of the lens (the old Pentax K 300/4 is a very prominent example). Do you think, this is "wasted light"?

If you aim to concentrate that additional light onto the sensor, you need in effect shorten the focal length of the lens, thus creating a wider lens. You could simply swap lenses, to achieve the same.

Ben

[ElJamoquio]

It's more complex than that.
Lenses may outresolve a sensor,

True, but I was speaking from a lens-only frame of reference.

That's backwards.

At the extreme,
the Nikkor is "excellent" on FF,
but at best only "good" on CX.

I think you've misinterpreted what I said.

What is the best-possible on a CX is (at most) mediocre on FF.

Speaking of resolution only, of course.

[Ben_Edict]

My assumption is that someone (me, you) want a certain given DOF level, regardless of whether I'm shooting with a D600 or a K-5.

Then simply chose the appropriate lenses on both systems and here you go.

Ben