[bxf]

I don't really belong in this forum, as I have no great pangs for FF (at least until it can be miniaturized). But, I suspect this is as good a place as any to ask my question.

"Every time" someone on one of the other forums mentions FF vs APS-C lens comparison, somebody will come up with something like "you need an f1.1 lens to produce the same image with APS-C that you'd get with an f1.8 with a FF". So, here is the question:

You are in a situation where you want to take a photo, and you've determined that with your FF gear, you will use a 50mm lens at f1.8, ISO 100. Due to the nature of the subject, DOF is not an issue.

What lens and setting do I need in order to obtain the "same" (in practical terms) image with my APS-C camera. Do I need your theoretical f1.1 lens, or will a 31mm/35mm f1.8 do? If the latter, does it not mean that this constant obsession with equivalence is exaggerated, in the sense that it is not always applicable?

[ldj4549]

I am not qualified to answer your question what-so-ever. But, I respectfully pose this in reply - are you an artist or a technician? If you are an artist, then who who cares!

[Ole]

On an APS-C camera you'd use a 35mm lens (or 31mm if you have that one) at F1.8, ISO 100. It's that simple.

[starjedi]

I don't really belong in this forum, as I have no great pangs for FF (at least until it can be miniaturized). But, I suspect this is as good a place as any to ask my question.

"Every time" someone on one of the other forums mentions FF vs APS-C lens comparison, somebody will come up with something like "you need an f1.1 lens to produce the same image with APS-C that you'd get with an f1.8 with a FF". So, here is the question:

You are in a situation where you want to take a photo, and you've determined that with your FF gear, you will use a 50mm lens at f1.8, ISO 100. Due to the nature of the subject, DOF is not an issue.

What lens and setting do I need in order to obtain the "same" (in practical terms) image with my APS-C camera. Do I need your theoretical f1.1 lens, or will a 31mm/35mm f1.8 do? If the latter, does it not mean that this constant obsession with equivalence is exaggerated, in the sense that it is not always applicable?

1) If you want to create the "identical" picture (focal length, exposure and DOF) in FF (50mm F1.8 ISO 100), APS-C need to use 35mm F1.1 with ISO 50 assuming FF and APS-C camera have the number of pixels.
2) If DOF is not the issue as you mentioned, 35mm lens F1.8 ISO 100 will be enough.

The difference between FF and APS-C is not dramatic unlike the difference between a cheap point-and-shoot camera and any DSLR. A lot of other factors in photography are far more important than this factor. Unfortunately, people simply tends to exaggerate this difference because of tranditional high pricing of FF and legacy 35mm lens. The lens manufacturers have adapted to build good FF lens for years and APS-C market is got less supported (Pentax might be the exception :-)). That's why the sigma APS-C adapted 18-35mm F1.8 made a lot of people exciting this year.

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Last edited by starjedi; 12-27-2013 at 09:19 PM.

[bxf]

On an APS-C camera you'd use a 35mm lens (or 31mm if you have that one) at F1.8, ISO 100. It's that simple.

1) If you want to create the "identical" picture (focal length, exposure and DOF) in FF (50mm F1.8 ISO 100), APS-C need to use 35mm F1.1 with ISO 50 assuming FF and APS-C camera have the number of pixels.
2) If DOF is not the issue as you mentioned, 35mm lens F1.8 ISO 100 will be enough.

The difference between FF and APS-C is not dramatic unlike the difference between a cheap point-and-shoot camera and any DSLR. A lot of other factors in photography are far more important than this factor. Unfortunately, people simply tends to exaggerate this difference because of tranditional high pricing of FF and legacy 35mm lens. The lens manufacturers have adapted to build good FF lens for years and APS-C market is got less supported (Pentax might be the exception :-)). That's why the sigma APS-C adapted 18-35mm F1.8 made a lot of people exciting this year.

The emphasis in my question was intended to be on whether or not "this constant obsession with equivalence is exaggerated". From your responses, it appears to confirm that the answer is YES. And all this ignores the fact that sometimes greater DOF is desirable.

I understand that there are situations in which FF can do something that cannot be done with APS-C, but I just wish that people would stop this persistence with equivalence, as if these theoretical lenses were an essential requirement in the majority of situations.

[Ole]

The field of view of the lens depends on sensor size. So a 75 mm lens on a FF camera has the same FoV as a 50mm lens on an APS-C camera. The light level transmitted is not affected. F1.8 is F1.8 no matter what.

The depth of field increases as the focal length decreases.

So FF (or a larger format like 645) may be advantageous if you want a narrow depth of field, and APS-C (or smaller) may be preferable if you want a large depth of field.

Wide angle lenses are easier (and cheaper) to make for FF, whereas telephoto lenses for APS-C are smaller and lighter.

So there you have it. No format is "better", it's all about trade offs.

Should Pentax launch an FF camera I'll use it for wide angle and keep my APS-C for telephoto.

[Asama]

I am not qualified to answer your question what-so-ever. But, I respectfully pose this in reply - are you an artist or a technician? If you are an artist, then who who cares!

IDJ4549,......Hahahahaha, that has to be the funniest reply I have read on this forum.

Being an Artist myself & having studied The History of Art, we learnt that most of the Great in Art became great,precisely because they couldn't give a rats ass about the "official accepted " technique of the time......think Vincent Van Gough, Monet, Gaugan & Picasso!

So on the one hand you are absolutely right,great photographs have been taken with the most basic equipment....let's not forget that!
However,try painting a big broad landscape with tiny brushes! If big broad brushes are available then the technology helps produce a better picture!

I still believe that for Pentax users, we of all people could use FF, precisely because Pentax has complete backwards lens capability,MORE than any of the big boys!
FF means all my old M lenses & Takumars will work perfectly as with my 35mm film SLR's.

Bring it on Pentax!

[bxf]

I am not qualified to answer your question what-so-ever. But, I respectfully pose this in reply - are you an artist or a technician? If you are an artist, then who who cares!

Your point is well taken. However, if this question were to be the primary criterion in these forums, then most of the posts herein would not (need to) exist

[TomB_tx]

I've done tests focusing on a foreground object with a detailed background a distance off, using both a Leica M9 with 50mm f2.0 and K-5 with 35mm f2.0 so the field of view (from the same spot) matched closely. Yes, the background blur with the M9 was greater than with the K-5 (as expected with the larger sensor), but both were pleasing pictures.
IMHO the preoccupation with thin DOF is a passing fad. Just learn to get the best results with the tools you have.
My only reason for wanting a Pentax FF dSLR is for a larger, sharper viewfinder for manual focus, and to give the same FOV on all my legacy M lenses. Still longing for a digital LX...

[jogiba]

I've done tests focusing on a foreground object with a detailed background a distance off, using both a Leica M9 with 50mm f2.0 and K-5 with 35mm f2.0 so the field of view (from the same spot) matched closely. Yes, the background blur with the M9 was greater than with the K-5 (as expected with the larger sensor), but both were pleasing pictures.
IMHO the preoccupation with thin DOF is a passing fad. Just learn to get the best results with the tools you have.
My only reason for wanting a Pentax FF dSLR is for a larger, sharper viewfinder for manual focus, and to give the same FOV on all my legacy M lenses. Still longing for a digital LX...

People forget that you need the motor drive and bulk film back on the LX to use it like todays compact full frame cameras with SDXC card.

[jsherman999]

..

You are in a situation where you want to take a photo, and you've determined that with your FF gear, you will use a 50mm lens at f1.8, ISO 100. Due to the nature of the subject, DOF is not an issue.

What lens and setting do I need in order to obtain the "same" (in practical terms) image with my APS-C camera. Do I need your theoretical f1.1 lens, or will a 31mm/35mm f1.8 do? If the latter, does it not mean that this constant obsession with equivalence is exaggerated, in the sense that it is not always applicable?

To get the same photo, you would need about a 33mm f/1.1 lens on aps-c. Note that the image would in most cases be just as 'good' if you shot it with a 35mm f/1.8 wide-open. Think of it this way: FF in a lot of cases just expands your options with DOF control.

Why would you want to shoot something like a 33mm f/1.1? One reason is it lets you completely obliterate a messy kitchen in the background while shooting from 'normal' distance

50mm @ f/1.8 == 33mm f/1.1 on aps-c


Or a messy neighbor garage area in the background of a short telephoto shot...

180mm @ f/2.8 == 120mm f/1.8 on aps-c



Or just allows you to very subtly remove a subject from it's environment just a tad more, pull it out, highlight it, if there's a quiet moment to be seen amidst chaos:

180mm f/2.8 == 120mm f/1.8 on aps-c:


When it comes to aesthetics, sometimes a small difference can make an outsized impression. Artists will be the first to tell you that


It also allows you to get sharper at the plane of focus while maintaining an option for DOF control. For instance, you could shoot your 50mm at f/2.8, nearing the lens's probable sweet spot for sharpness, and get the same subject isolation you'd need to shoot a 35mm f/1.8 wide-open to get - and a 35mm is probably not going to be as sharp wide-open and may show more CA.

To your subsequent angry comments about equivalence ; 'equivalence' just describes a relationship between formats, so you can know what to expect if you're shooting a 50mm lens on micro 4/3, or aps-c, or FF, or Medium format. It's still a 50mm lens, but will behave much differently across formats, in FOV and DOF. 'equivalency' provides you a method to determine how it will perform, what it will show you on other formats. Getting mad at equivalence is like getting mad at a mathematical equation.

.

[DavidSKAF3]

Is a portrait shot a good way to start exploring the range and effect of depth of field variables?

[RonHendriks1966]

Why would you want to create the same thing? You can make excellent images with various sensor-format camera's but they are different in many ways. While all the above images are very nice, there is no pressing need to have that thin DOF in images to make them exceptional.

[bxf]

To get the same photo, you would need about a 33mm f/1.1 lens on aps-c. Note that the image would in most cases be just as 'good' if you shot it with a 35mm f/1.8 wide-open. Think of it this way: FF in a lot of cases just expands your options with DOF control.

Why would you want to shoot something like a 33mm f/1.1? One reason is it lets you completely obliterate a messy kitchen in the background while shooting from 'normal' distance

50mm @ f/1.8 == 33mm f/1.1 on aps-c


Or a messy neighbor garage area in the background of a short telephoto shot...

180mm @ f/2.8 == 120mm f/1.8 on aps-c



Or just allows you to very subtly remove a subject from it's environment just a tad more, pull it out, highlight it, if there's a quiet moment to be seen amidst chaos:

180mm f/2.8 == 120mm f/1.8 on aps-c:


When it comes to aesthetics, sometimes a small difference can make an outsized impression. Artists will be the first to tell you that


It also allows you to get sharper at the plane of focus while maintaining an option for DOF control. For instance, you could shoot your 50mm at f/2.8, nearing the lens's probable sweet spot for sharpness, and get the same subject isolation you'd need to shoot a 35mm f/1.8 wide-open to get - and a 35mm is probably not going to be as sharp wide-open and may show more CA.

To your subsequent angry comments about equivalence ; 'equivalence' just describes a relationship between formats, so you can know what to expect if you're shooting a 50mm lens on micro 4/3, or aps-c, or FF, or Medium format. It's still a 50mm lens, but will behave much differently across formats, in FOV and DOF. 'equivalency' provides you a method to determine how it will perform, what it will show you on other formats. Getting mad at equivalence is like getting mad at a mathematical equation.

.

You provide examples and discussion pertaining to DOF, even though I specifically said "Due to the nature of the subject, DOF is not an issue".

I am sufficiently aware of the fact that with FF it is possible, under some circusmtances, to obtain DOF that is thinner than what may be achievable with APS-c. My annoyance with equivalence is not that it exists, but rather because people repeatedly make statements that imply that you must have (for example) a 35mm f1.1 to achieve the same results you'd obtain with a 50mm f1.8, while apparently failing to take into consideration the fact that this is true only some, and not even necessarily most, of the time.

[wildman]

If you are an artist, then who cares!

The artist cares because the the artist has no choice.
The artist is no different then anyone one else - he must live within the same mundane constraints of the real physical world as the rest of us.
The artist must have a certain level of understanding of his medium of expression or no expression is possible at all.

However, having said that I think the following post is also essentially true - most of the gear questions on the forum have little practical relevance to the final image and much to do with technical navel gazing.

most of the posts herein would not (need to) exist