[BrianR]

he did state: "I can see a point in the future when I may go FF"

Yes of course, but he also seemed mostly concerned about today (ok, he mostly seemed to be making a point) ... what impact will the choice one or the other have when used his k-30? If little to none, and the cost is similar than the FA version would make more sense if a K-1 might be possible down the road (of course the DA50 functions pretty well on FF as it is), and this is the scenario I understand to OP is considering.

Maybe you can help, when converting focal length from the k30 to the k30, I can never remember if I should divide by the crop factor or multiply? We'll get to the bottom this.

so if equivalence doesn't matter, why did pentax rate the lens for aps-c use?

To save on ink... "DA" is cheaper than "DFA" to print.

[GUB]

The DA 50mm is practically a full frame lens, for what it's worth. Just a bit more vignetting wide-open than with the FA.

Yeah but still a valid example -- I would choose the FA 50mm now with the K1 in mind for the future. And it was just an example of what I felt the OP was meaning.

[osv]

Maybe you can help, when converting focal length from the k30 to the k30, I can never remember if I should divide by the crop factor or multiply? We'll get to the bottom this.

lol... i suspect that people have already reached the bottom of this discussion, you can't make it any worse.

and no, for the record the ink cost argument isn't very convincing

[talkskiwon]

actually there are potential issues with FF lenses on crop sensor bodies, largely due to potential for reduced contrast due to an excessive amount of light entering the mirror box area. light in the mirror box area, which is not hitting the sensor, needs to be absorbed or it will result in images that are foggy, may have odd reflections, or greatly reduced contrast.

additionally, and again not fully appreciated, is that lens hoods for full frame lenses ARE NOT optimized for the field of view of a cropped sensor. as a result, light outside of the field of view can enter the lens and lead to flair, especially if it is a bright light or the sun specifically.

so while FF lenses may have some benefits, you need to be ware that there are also drawbacks

Thanks for the heads up!

[Rondec]

that's what i gave him, disadvantages with putting ff glass on a crop sensor... 1)the focal length is wrong, 2)the aperture numbers are wrong, 3)the point of visible diffraction doesn't match the aperture number, etc.

The Opening Poster owns a crop camera. He doesn't own a full frame one, as far as I know. For him, there are no particular disadvantages to mounting a full frame compatible lens on a crop camera, except that maybe the lens will be a little larger, as it will cover a larger image circle than is necessary for his crop sensor. The rest of it is not true. The focal length is not wrong it is what it is and doesn't change just because you have cropped part of the image circle out.

You learn what a lens is capable of on your particular camera. I shot only APS-C for 10 years. It didn't kill me and I certainly didn't struggle with (1) wrong focal length (2) wrong apertures and (3) some kind of weird diffraction. If I mounted a 55mm lens on a K5, I knew what field of view it would give me and where its sweet spot was with regard to aperture. No down side to it, as far as I am concerned.

[newmikey]

You seem to have it covered with the possible exception of the decreased effectiveness of dedicated lenshoods when using a FF lens on APS-C. Sigma seems to be the only company who very thoughtfully have added an APS-C extender to the lenshood for use on APS-C cameras on their formidable 85mm/f1.4 (sometimes dubbed "the beast" in my household due to its siz when both hood and extender are attached.)

[Lowell Goudge]

The Opening Poster owns a crop camera. He doesn't own a full frame one, as far as I know. For him, there are no particular disadvantages to mounting a full frame compatible lens on a crop camera, except that maybe the lens will be a little larger, as it will cover a larger image circle than is necessary for his crop sensor. The rest of it is not true. The focal length is not wrong it is what it is and doesn't change just because you have cropped part of the image circle out.

It is a myth that full frame lenses MUST be larger to cover a larger image circle.

While this MIGHT be true on some cases, please note, the barrel diameter of the lens is largely determined by the l ns mount. So if you are considering interchangeable mounts and use of legacy glass, the K mount designed in the full frame era, was carried over to cropped sensors, and as a result determines the lens barrel diameter.

For long lenses, the size /diameter of the objective is determined by the desired FStop a 300F4 must be 75 mm in diameter. Format does not change this fact.

So let's get off the myth that full frame lenses must be larger than crop format lenses, it is BS as far as I am concerned

[TER-OR]

Certainly it's a myth. Look at the M40 pancake.

I have a couple Full-Frame lenses. The Sigma 28mm f1.8 macro is probably huge because it's f1.8. A 77mm filter thread makes the thing look like a coffee mug. Nice lens, though.
The FA100 f2.8 macro isn't all that big. The Promaster 28-105 is pretty compact. The rubber lens hood does make it a bit bigger, though.

I guess I don't have a point.

There have been no contrast issues I can see with either lens, and I have used both for insect macro.

[Rondec]

It is a myth that full frame lenses MUST be larger to cover a larger image circle.

While this MIGHT be true on some cases, please note, the barrel diameter of the lens is largely determined by the l ns mount. So if you are considering interchangeable mounts and use of legacy glass, the K mount designed in the full frame era, was carried over to cropped sensors, and as a result determines the lens barrel diameter.

For long lenses, the size /diameter of the objective is determined by the desired FStop a 300F4 must be 75 mm in diameter. Format does not change this fact.

So let's get off the myth that full frame lenses must be larger than crop format lenses, it is BS as far as I am concerned

Obviously it depends on (a) the registration distance (b) the mount size (c) the focal length and (e) the image circle needed to be covered. A lens like the DA 40, which has been mentioned in this thread (or its earlier version the M 40) is so small because its focal length is close to the registration distance, it is relatively slow at f2.8, and the image circle is pretty weak on full frame. It may have been OK in film days, but it isn't great now.

Anyway, I have a feeling that a DA 15 f4 would have been bigger if it covered a full frame image circle.

[Lowell Goudge]

Obviously it depends on (a) the registration distance (b) the mount size (c) the focal length and (e) the image circle needed to be covered. A lens like the DA 40, which has been mentioned in this thread (or its earlier version the M 40) is so small because its focal length is close to the registration distance, it is relatively slow at f2.8, and the image circle is pretty weak on full frame. It may have been OK in film days, but it isn't great now.

Anyway, I have a feeling that a DA 15 f4 would have been bigger if it covered a full frame image circle.

as i said, there are some cases where and specific examples where there could be an optimum arrangement that favors one format over another, but in general, given 1 mount, and one registration distance , generally format does not determine size especially in longer lenses

not sure how a 15mm would fare today in full frame, but clearly the DA 15/4 is smaller 66mm dia x 40mm long compared to the A 15/3.5 at 80mm dia 81mm long and ligher at 217 grams compared to 595 grams, but look at how much advancement today is available in materials. that could reduce the size even with full frame.

[Rondec]

as i said, there are some cases where and specific examples where there could be an optimum arrangement that favors one format over another, but in general, given 1 mount, and one registration distance , generally format does not determine size especially in longer lenses

not sure how a 15mm would fare today in full frame, but clearly the DA 15/4 is smaller 66mm dia x 40mm long compared to the A 15/3.5 at 80mm dia 81mm long and ligher at 217 grams compared to 595 grams, but look at how much advancement today is available in materials. that could reduce the size even with full frame.

Hard to argue either way. My impression would be that it would take less glass to cover APS-C sensor making lenses like the DA 15, 35, 40, and 70 smaller than if they had to cover a full frame image circle (which most do not do a great job of covering). As to how much of an increase in size/weight it would be, I have no way of knowing.

[Lowell Goudge]

Hard to argue either way. My impression would be that it would take less glass to cover APS-C sensor making lenses like the DA 15, 35, 40, and 70 smaller than if they had to cover a full frame image circle (which most do not do a great job of covering). As to how much of an increase in size/weight it would be, I have no way of knowing.

i think it comes down to the optical design. what i have seen, is especially for wide angle lenses is 2 approaches, i will use my tamron 24 and 28mm lenses on one side, both of which are full frame lenses and very simple optical design with very small front elements consistent with diameter = focal length / fstop. i.e. front element of roughly 12 and 14 mm respectively and on the other side, look at the kiron (also vivitar) 24mm and 28mm F2 lenses which have front elements in the 40mm range,

it really is based upon how the lens designers approach the solution.

the front element of my samyang 14/2.8 is absolutely massive at about 60 mm in diameter.

this is much more of the case for wide angle over telephoto. and i think related to the concept of incident light being close to perpendicular to the element in some designs

[redrockcoulee]

The only possible disadvantage I can think of is that the FF lens may be larger than its APS-C counterpart for example the DA 70 and FA 77 or the FF lens may be older and therefore heavier than a modern lens with lots of plastic. It ssems to me that size is a bigger difference in zoom lenses than in most primes.

Otherwise I see no disadvantage to using them on a cropped sensor camera. In my camera bag I only have two lenses that are not FF capable and I currently have no interest in FF digital camera. 8f you are thinking of going the K1 route you may wish to include that in your decision.

[reh321]

One thing I find curious about pentax camera and lenses as a beginner in photography is that many people use FF lenses on their crop sensor bodies. And, I believe there is no disadvantages of FF lens on crop-body because the image coming through the lens is perfectly covering the sensor and there is no problems on picture image. In fact, because FF lenses are shooting bigger images than the sensor itself to the sensor, the corner contrast and sharpness issues we see from APS-C lenses on APS-C body is not present on the FF lens on APS-C body. Does this make sense? and is there any disadvantages of using FF lens on crop bodies? I think this could help me making right choices for lens purchases. Thanks!

I see that this thread has degenerated into the usual squabble over "equivalency" theory. All I have to offer is experience. As I have said many times at this forum, I was surprised to discover that the Pentax-A 50mm f/1.7 lens, which was kitted with the Super Program I purchased 32 years ago, is probably the sharpest lens I've ever used on my K-30. I have purchased several other film-era lenses recently, and they've worked just fine on the K-30 also. If I had any thought of all of purchasing a K-1, any lens I added to my group would be a "FF" lens; from my experience, I'm confident that it would work at least as well as the "APS-C" lens that I would have purchased otherwise.

[redrockcoulee]

wrong... you need to read the link i posted.

---------- Post added 07-07-16 at 08:41 AM ----------



i agree that the lens itself doesn't change, but the effect is not the same, as you admitted, the fov is different, and i'm here to tell you that the aperture numbers on the aperture ring are therefore also effectively wrong.

you claim no disadvantage, then admit that there is a difference, and argue semantics about what the word "disadvantage" really means.

if you want to claim that everything being wrong is not a disadvantage, you are certainly welcome to your opinion... i do agree that with ff lenses on crop, we get used to everything being wrong, but my point is, lets not lose sight of what the truth really is.



that's another contradiction, and it's not correct because the total light falling on different sensor sizes is different... you can't have it both ways... "Saying "f/2 = f/2 = f/2" is like saying "50mm = 50mm = 50mm". Just as the effect of 50mm is not the same on different formats, the effect of f/2 is not the same on different formats... Total Light = Exposure x Effective Sensor Area, and it is the total amount of light falling on the sensor, as opposed to the exposure, which is the relevant measure."

that's why the aperture numbers are wrong.

If I understand you correctly if I am shooting at 50mm with my 18-50 and I want to shoot with a larger aperture I can not use my F50 1.7 because it 8s the wrong focal length? If I had the FA 35 instead of the DA 35 I could use that instead as that would give approximately 50mm equivalence.

I think my full frame 50 gives the same focal length as 50mm on the zoom, or close enough. I have no reason to need a crop only 50 when I own a FF 50. When I pit the DA 70 on my film camera it is a 70 etc. Of course the 70 has narrower FOV on the one camera compared to the other but that has nothing to do with selecting a lens to use. When I put the 50 on my K5iis I do not even think about what it would be like on my film camera or a 50 on the Hasselblad or anything else. I put the 50 on theK5iis because it is the one I want to use.