[ComputerControlled]

Given the 1.5x crop factor, what size lens equates to a 50mm on my K100DS? I'm assuming it works out to a proper 50mm equals a 75mm? If this is true, then i'm guessing a 25mm equates to a 50mm? Though i don't there exists a 25mm lens =o] I guess 35 is best thing then.

[Adam]

The field of view of a 50mm on APS-C digital is the same as that of a 75mm on a film camera. Similarly, the field of view of a 50mm lens on film is the same as that of a 33mm an APS-C digital. So yes, get a 35mm



Details here: https://www.pentaxforums.com/forums/pentax-lens-articles/90477-crop-factor-fo...ield-view.html

[ComputerControlled]

Cool, so basically, i was right =o] I guess for now i can keep my 35-70 on the 35mm setting until i can find a 35mm prime.

[MDegri]

The DA SMC Pentax-DA 35mm F2.4 AL is awesome especially for the price I love mine.
SMC Pentax-DA 35mm F2.4 AL Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

[ComputerControlled]

Hmm, thanks for that. I think it might be my best bet.

[Mike Cash]

25 x 1.5 doesn't equal 50.

[ComputerControlled]

Ya, my math was wrong. Don't know what i was thinking...

[RXrenesis8]

Angle of View Calculator

[Marc Sabatella]

Given the 1.5x crop factor, what size lens equates to a 50mm on my K100DS? I'm assuming it works out to a proper 50mm equals a 75mm? If this is true, then i'm guessing a 25mm equates to a 50mm? Though i don't there exists a 25mm lens =o] I guess 35 is best thing then.

Just to be clear - whther the lens is manual of not has nothing to do with anything. all 35mm lenses have the exact same FOv or they wouldn't be 35mm lenses. And when you say, "what size lens equates to a 50mm on my K100DS", I assume you mean, "what focal length lens on K100DS would equate to a 50mm lens on some other camera I haven't actually mentioned but presumably own that happens to use a larger format like 135". In which case, the answer is that a 35mm lens - manual or not, doesn't matter - on your K100DS will give the same FOV as a 50mm lens on this mystery camera you are preaumably comparing to. Because if you mean what you really asked - what focal length lengths equates to 50mm on your K100DS, the answer is simple: all 50mm lens will behave exactly the same on your K100DS.

[ComputerControlled]

I initially assumed that all the new lenses made for DSLRs had this crop factor built into the lenses. So a 35mm lens made for a DSLR would actually be 35mm. Not a hair under 50mm. That makes more sense to me, to show what equivalent size is on the lens. Rather than make people guess. Mythical camera? Take your pic of any Pentax 35mm film camera, though i happen to have the MX. Though i'm now sure how that's important, because, AFAIK, all 50mm lenses will look the same on any SLR.

Anyway, my question has been answered.

[Lowell Goudge]

I initially assumed that all the new lenses made for DSLRs had this crop factor built into the lenses. So a 35mm lens made for a DSLR would actually be 35mm. Not a hair under 50mm. That makes more sense to me, to show what equivalent size is on the lens. Rather than make people guess. Mythical camera? Take your pic of any Pentax 35mm film camera, though i happen to have the MX. Though i'm now sure how that's important, because, AFAIK, all 50mm lenses will look the same on any SLR.

Anyway, my question has been answered.

Without beating a dead horse, you don't want to show equivalent focal length on the lens. This is done on P&S cameras because 1) the lenses don't come off, and 2) every P&S has a different sized sensor, so to keep every one sane, they put the real focal length and the equivalent to 35mm on the camera. For interchangeable lens cameras, this would add confusion because it would only apply to one sensor.

[ComputerControlled]

That makes sens.

[Marc Sabatella]

I initially assumed that all the new lenses made for DSLRs had this crop factor built into the lenses.

Crop factor is way of comparing the field of view created by a lens on two different cameras. But it does not and cannot ever change the actual focal length of the lens. All 50mm lenses produce exactly the same field of view *when used on the same camera*. But the same 50mm lens will produce an entirely different FOV on your MX versus on your K100D.

In short - crop factors are ocassionally useful for comparing the same lens pn different *cameras*, but they have nothing to do with comparing different *lenses*.

So a 35mm lens made for a DSLR would actually be 35mm.

And so it is. Again, all 35mm lenses - whether new or old, manual or AF, made fo film or digital - have *exactly* the same focal length, and hence they have *exactly* the same FOV when used on any given camera.

That makes more sense to me, to show what equivalent size is on the lens.

that makes no sense whatsoever. A lens has no idea what type of camera it is goong to be mounted to. again, any given 35mm lens has an entirely different FOV depending on what *camera* it is mounted to, but all 35mm lenses have the same FOV pn any one given camera. If they are going to go around putting crop factors on anything, it could only be on cameras, not on lenses, because again, crop factors are only useful as a means of comparing cameras, not of comparing lenses.

Rather than make people guess.

there is no guesswork. Again, all 35mm lenses - digital or film, manaul or AF, Pentax or Sigma, black or silver, macro or non-macro, meta or plastic - they all have the exact same FOV on your K100DS. If you are wondering what focal length lens would produce the same FOV on your MX, you multiply by the crop factor *for the K100DS*, and again, you do this exactly the same way regardless of what 35mm lens you are talking about. there is nothing that could be possibly be written on the lens, or done to the lens, or changed about how the lens is described, that changes this.

AFAIK, all 50mm lenses will look the same on any SLR.

On any *one* SLR, yes. But a 50mm lens mounted to your MX has an entirely different FOV than that same 50mm mointed to your K100D.