[wes k]

Reading reviews of the DA 35mm F/2.4, a lot of people were pointing out that this is in fact 53mm because of the Pentax APS-C format, but in my head I'm thinking - but all Pentax DSLR'S are aps-c, and DA range is only for dslr's, so surely if it says 35mm, then it is 35mm.
Then I read the item description, on a well-known, recently re-imagined British camera stores website which backed up their theory, so now I'm questioning myself.
who's right?

[GabrielFFontes]

Reading reviews of the DA 35mm F/2.4, a lot of people were pointing out that this is in fact 53mm because of the Pentax APS-C format, but in my head I'm thinking - but all Pentax DSLR'S are aps-c, and DA range is only for dslr's, so surely if it says 35mm, then it is 35mm.
Then I read the item description, on a well-known, recently re-imagined British camera stores website which backed up their theory, so now I'm questioning myself.
who's right?

It is EQUIVALENT to a 53mm on fullframe.
The optics are of a 35mm, but, since the sensor isn't fullframe, you'll be cutting it a bit, and therefore you'll get the field of view equivalent of a 53mm lens.

[crewl1]

The focal length is 35mm, exactly like a vintage 35mm lens from the film SLR days.
In APSC format, the image capture area is a little smaller than a film frame, so the edges are cropped off and the picture that you end up with is similar to what you would get if you put a 50mm lens on that film camera.
If you need the picture to display on APSC what you would see on a film SLR with a 35mm lens, you need to use a 21mm lens to be able to fit the image into the smaller area.
Or take a few steps back and recompose the shot

[calculator01]

A 35mm lens is a 35mm lens regardless of sensor size.

However, if that 35mm is on a cropped sensor, APS-C is a crop of about 1.5, then it is the equivalent field of view as a 53mm on a full frame camera.

If you have the FA 43mm, it is a full frame lens, so yes, the field of view is a 43mm on a full frame. If you put it on a APS-C, then it is 43mm* 1.5 = 64.5mm

Basically, using a 35mm on a APS-C is like using a 53mm on a full-frame. Using a 50mm on a full frame, is like using a ~31mm on a APS-C.

Hopefully that's not too confusing

Also, the DA 35mm f2.4 will accommodate full frame, it is just labeled a DA.

[jatrax]

Reading reviews of the DA 35mm F/2.4, a lot of people were pointing out that this is in fact 53mm because of the Pentax APS-C format, but in my head I'm thinking - but all Pentax DSLR'S are aps-c, and DA range is only for dslr's, so surely if it says 35mm, then it is 35mm.
Then I read the item description, on a well-known, recently re-imagined British camera stores website which backed up their theory, so now I'm questioning myself.
who's right?

35mm is 35mm the math is right. The focal length of a lens is a physical property that cannot be changed.

There is a difference in angle of view when using a lens on both Full Frame (35mm film or sensor) and on an APS-C sensor. But unless you use both cameras and switch back and forth please just ignore all the 'crop sensor' BS. That angle changes depending on the sensor (or film size) used and this property is also true of m4/3 sensors and medium format backs.

Quite a number of sellers promote the 'crop factor' of APS-C as "extending the range" or "acting like a longer lens" but that is mostly hype, not entirely untrue from some ways of looking at it but not really true either.

If all you have is APS-C cameras then just consider 35mm = 35mm and ignore all the hype.

[Jean Poitiers]

... Also, the DA 35mm f2.4 will accommodate full frame, it is just labeled a DA.

True, there's a thread about which DA's will function on a FF .. J

[jatrax]

quick confirmation for me re: DA lenses

Was that quick enough? 4 posts in 3 minutes, I have to save out the answer to this question in a file so I can copy and paste it in, it takes too long to type it in each time.

[Na Horuk]

35mm means 35mm, its a property of the lens and it doesn't matter what sensor you put it on. But if your sensor is smaller (like, ASPC) then you are cutting off a part of the frame, which makes it look like a 53mm on a film camera. If you put this lens on a 645, it would appear to be even wider than 35mm on film. But because it is not made for 645, its image circle isn't that big, so the corners would be unsharp and dark. Most crop lenses have an image circle too small for film (full frame), but the DA 35mm is kind of an exception - it was tested on film, and it performed adequately.
So it is 35mm, as it says, but if you are using a crop sensor, it will appear like 53 on film. If you put this lens on a Q (even smaller sensor) it will appear to have a FoV of a 175mm (I think) on film. The only reason people even talk about "FF equivalent" is because this helps out old photographers who used film for decades and already know how a 50mm and 35mm looks like on film and would be surprised if they used it on a crop. So, don't worry, just buy the lens. Check the sample photos, look at the plastic wonder thread, its a nice lens. Feel free to buy it from japan in a funky colour, like pink

[Gerbermiester]

Here's a picture to help explain.
The lens will always project the same sized image circle into the camera, regardless if the camera is fullframe or aps-c. In the picture below, the image that the lens projects into the camera is the grey area.

What the camera actually 'sees' is dependent on the sensor size. Larger, fullframe sensors, will see more. Smaller Aps-c sized sensors, will see less. Essentially, the Aps-c camera is only receiving the middle of the image, thus it appears to be more zoomed in, relative to the Fullframe sensor.
This translates into images that look like this: (Aps-c on the left, fullframe on the right).


So, what does it all mean to you?
If used on a APS-C sized sensor, your images taken with the Da 35mm f/2.4 lens would appear to have been shot with a 52.5mm lens. If you put the same 35mm lens on a fullframe camera, you would get images that appear to be taken on a 35mm lens. (This 35mm vs 52.5mm apparent focal length difference is known as equivalence. A 35mm on APS-C is equivalent to a 52.5mm lens on fullframe sensor.

Right now, in 2013, Pentax only makes APS-C dslrs that can mount K-mount lenses. You might be asking yourself, "So, why do people bother saying that it is a fullframe lens at all?"
Well, some lenses, such as the Sigma 30mm f/1.4 have a smaller image circle (grey area), and thus can't be use on fullframe sensors, only APS-C sized sensors. Lenses like the Sigma wouldn't project light to the corners of the Fullframe sensor (because the image circle is too small to do so, and you'd get images that look like this:
\

If Pentax does choose to make Fullframe DSLRs in the future, your 35mm lens can be used on that new camera, and the images it makes will cover the entire sensor. That 35mm lens you have will project an image circle (the grey area in the first picture) large enough to be used on both fullframe and APS-C.

I guess you could say that buying a Fullframe lens for a APS-C DSLR is 'future proofing' in a sense. But, nobody knows for sure what the future holds for Pentax Fullframe. My advice: get the lens you want for today, not for tomorrow. The DA 35mm f/2.4 is a great little wide angle on Fullframe and a great little Normal lens on APS-C.

[Driline]

Here's a picture to help explain.
The lens will always project the same sized image circle into the camera, regardless if the camera is fullframe or aps-c. In the picture below, the image that the lens projects into the camera is the grey area.

What the camera actually 'sees' is dependent on the sensor size. Larger, fullframe sensors, will see more. Smaller Aps-c sized sensors, will see less. Essentially, the Aps-c camera is only receiving the middle of the image, thus it appears to be more zoomed in, relative to the Fullframe sensor.
This translates into images that look like this: (Aps-c on the left, fullframe on the right).


So, what does it all mean to you?
If used on a APS-C sized sensor, your images taken with the Da 35mm f/2.4 lens would appear to have been shot with a 52.5mm lens. If you put the same 35mm lens on a fullframe camera, you would get images that appear to be taken on a 35mm lens. (This 35mm vs 52.5mm apparent focal length difference is known as equivalence. A 35mm on APS-C is equivalent to a 52.5mm lens on fullframe sensor.

Right now, in 2013, Pentax only makes APS-C dslrs that can mount K-mount lenses. You might be asking yourself, "So, why do people bother saying that it is a fullframe lens at all?"
Well, some lenses, such as the Sigma 30mm f/1.4 have a smaller image circle (grey area), and thus can't be use on fullframe sensors, only APS-C sized sensors. Lenses like the Sigma wouldn't project light to the corners of the Fullframe sensor (because the image circle is too small to do so, and you'd get images that look like this:
\

If Pentax does choose to make Fullframe DSLRs in the future, your 35mm lens can be used on that new camera, and the images it makes will cover the entire sensor. That 35mm lens you have will project an image circle (the grey area in the first picture) large enough to be used on both fullframe and APS-C.

I guess you could say that buying a Fullframe lens for a APS-C DSLR is 'future proofing' in a sense. But, nobody knows for sure what the future holds for Pentax Fullframe. My advice: get the lens you want for today, not for tomorrow. The DA 35mm f/2.4 is a great little wide angle on Fullframe and a great little Normal lens on APS-C.

We should just make a "sticky" of your explanation Professor Gerbermiester. That has to be the best and most easily understood explanation with pictures for those of us who require visual aids that I have ever seen.

[jatrax]

We should just make a "sticky" of your explanation Professor Gerbermiester. That has to be the best and most easily understood explanation with pictures for those of us who require visual aids that I have ever seen.

+1, very nice explanation!

[ismaelg]

It has already been explained but I wrote an article in spanish on this topic for our local forum. This is a common topic I get asked frequently. This is one of the charts I use to explain it:



Thanks,

[Kerrowdown]

A 35mm lens is a 35mm lens regardless of sensor size.

Absolutely spot on, it's an old chestnut this one, but it's been well explained again in this thread.

[lytrytyr]

Reading reviews of the DA 35mm, a lot of people were pointing out that this is in fact 53mm.

If you're mathematically dyslectic?

[wes k]

That's great guys, but I already understand crop factor, and wasn't actually what I asked, but i've got an answer so, thank you.
I should probably have asked - "do Pentax compensate for the crop factor when labelling their DA lenses?" (this might sound strange to you all, but makes sense to me)