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06-06-2016, 12:55 PM - 1 Like   #1
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Full frame lenses on APS-C bodies

I have tried searching the forums and could only see a thread regarding lenses designed for APS-C bodies used on full frame body. I am sure this has to do with the release of the K1 full frame. As I am personally an amateur photographer buying a full frame body is out of the question: I cannot validate the expense knowing I have so much to learn. Having said that, I am very interested in the new full frame lenses, primarily the 28-105 f3.5-5.6 and the 24-70 F2.8. I am seriously considering a purchase of the 28-105 due to the positive reviews. After doing some research, I came across this video (see below):


essentially, the recommendation is that, if maximum sharpness is your criteria, it is likely not the best idea to buy full frame lenses and use them on an APS-C body: the zoom and focal length both get multiplied by the crop factor! I knew about the zoom, but certainly did not expect that the variable aperature would be affected.

I am looking for recommendations. Should I consider the 16-85 mm APS-C designed zoom lens? I am looking for a zoom due to the convenience and I also would like to improve my image quality in that zoom range (currently I own the 18-55 mm kit lens purchased with my K10D). I have a newer K5II body that is my primary body. Thank you in advance for any suggestions

06-06-2016, 01:11 PM   #2
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QuoteOriginally posted by weaponx525 Quote
I have tried searching the forums and could only see a thread regarding lenses designed for APS-C bodies used on full frame body. I am sure this has to do with the release of the K1 full frame. As I am personally an amateur photographer buying a full frame body is out of the question: I cannot validate the expense knowing I have so much to learn. Having said that, I am very interested in the new full frame lenses, primarily the 28-105 f3.5-5.6 and the 24-70 F2.8. I am seriously considering a purchase of the 28-105 due to the positive reviews. After doing some research, I came across this video (see below):

Should you use Full Frame Lenses on Crop Bodies? Yes and No... - YouTube

essentially, the recommendation is that, if maximum sharpness is your criteria, it is likely not the best idea to buy full frame lenses and use them on an APS-C body: the zoom and focal length both get multiplied by the crop factor! I knew about the zoom, but certainly did not expect that the variable aperature would be affected.

I am looking for recommendations. Should I consider the 16-85 mm APS-C designed zoom lens? I am looking for a zoom due to the convenience and I also would like to improve my image quality in that zoom range (currently I own the 18-55 mm kit lens purchased with my K10D). I have a newer K5II body that is my primary body. Thank you in advance for any suggestions
The actual aperture doesn't change. Its both f/5.6 on FF as well as on APS-C. However, with the crop factor of the smaller sensor, the image gets "zoomed" in more and the effect is that the depth of your focus zone appears larger. That is, its harder to get really thin planes of focus than on FF. However, the light gathering ability and settings needed for proper exposure are not changed.
06-06-2016, 01:12 PM   #3
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The only issue with using FF lenses on an APS-C sensor is that you lose the wide end. So if you buy the 28-105 your widest focal length will be 28mm. Put your current 18-55 on 28mm and consider if that will be wide enough for you. I used a lot of FF lenses on APS-C with no problems, so don't believe everything you read on the internet

For APS-C though I would get the 16-85. The only way the 28-105 would make sense is if you also had the DA 12-24. Then you would have 12-24 and 28-105 which would be a fine combination.
06-06-2016, 01:16 PM   #4
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Breathe deeply and repeat after me. "Crop factors are confusing. "

The Crop Factor Unmasked - Articles and Tips | PentaxForums.com

Yes equivalent depth of field and aperture effects are similar to multiplying by crop factor - but that happens on apsc lenses and full frame lenses just the same.

The difference is cost and size etc. that 28-105 is going to be a normal lens to short telephoto with no wide angle. The 16-85 is a very wide angle through short telephoto.

06-06-2016, 01:21 PM - 1 Like   #5
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Camera bodies come and go. Lenses... that's a different story. My opinion is to always invest in quality glass first. Whether or not it's designated FF or not is a different story. Being FF or not only matters in one scenario: You get into enough and later on you want to upgrade... so you could just buy a new camera body (that gets swapped out every few years anyway) and be all set. If you have crop only lenses you basically have to buy all new lenses too. (more or less)

The main difference you will see (forget focal length for a minute) is the FIELD OF VIEW. That means how wide and how tall of a view do you actually get. This is the only real difference you will experience. You do not get more zoom. That' is garbage.

Imagine if you will looking at a photo of something. That is the full frame of the shot. Now take a pair of scissors and cut a one inch margin off the edges of that picture. That is the crop.

You do not lose zoom and you do not gain zoom. What you see is what you get. All this confusing stuff you read about boils down to people that are used to say shooting with a 28mm lens on a FF camera and then putting that same lens on a crop camera. Just know that all the edges are going to be cut off so you in effect have to get back a few more feet to get everything in. It can in ways change the dynamic of how someone would otherwise shoot, but rest assured none of that matters as to the content and quality of a shot.

One downside to a new FF zoom being used on a crop sensor is that you lose a lot on the wide end, whereas if you go with the 16-85mm you have a tremendous range of focal lengths and a very wide range of FIELD OF VIEW.

Sharpness will not be an issue regardless of what format the lens is. A good lens is a good lens. Likewise a bad lens is a bad lens.

I have the 16-85mm and I think that lens is just stellar. I took it on a 5 country around the world trip and it was on the camera 95% of the time. Plus it's WR. It is in fact a stellar lens.

If I was doling out advice I would say that is an excellent place to start. 16-85mm + a crop camera and you can learn the ropes.
06-06-2016, 01:32 PM   #6
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QuoteOriginally posted by weaponx525 Quote
essentially, the recommendation is that, if maximum sharpness is your criteria, it is likely not the best idea to buy full frame lenses and use them on an APS-C body: the zoom and focal length both get multiplied by the crop factor! I knew about the zoom, but certainly did not expect that the variable aperature would be affected.

This is complete nonsense. What you wrote there. That guy in the video might have said it and implied it but he's wrong. You need to erase this notion from your memory banks. It won't do anything but cause you trouble and confusion.
06-06-2016, 01:36 PM   #7
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QuoteOriginally posted by weaponx525 Quote
did not expect that the variable aperature would be affected.
Ignore Mr. Northrup. Constant aperture compared to variable aperture is a red herring, Northrup's point about the amount of light hitting the sensor with different image sizes is just plain wrong. My A 70-210 f4 lens is not f6 on my K-30, other than depth of field if comparing to photos taken with the same lens on a FF body, using a FF lens on an APS-C camera doesn't affect the image within the APS-C field of view. The light hitting each pixel doesn't change. That's what the camera has to expose for.

A FF lens has to cover a larger sensor with the same registration distance (flange focal distance) as an APS-C only lens on the same mount; depending on the focal length, the FF lens may need to have a bigger diameter and a different combination of glass elements, which will tend to make FF lenses heavier, larger and less convenient to handle than a lens designed to work only with APS-C sensors. That's why the FF 28-105 has similar dimensions to the APS-C 18-135 lens, even though the focal length range is shorter. By the way, the aperture range of the 28-105 is the same as the 18-135 over their respective focal length ranges. If Northrup was right, why wouldn't the 28-105 have an aperture range of f2.3-3.7?
06-06-2016, 01:37 PM   #8
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To agree further... Every lens of the same focal length does more or less the same thing on a given camera as far as focal length and aperture (assuming both are the same speed). So a 50mm f1.4 full frame may be a bit heavier than a crop only theoretical 50mm f1.4 but both would give similar results in the cropped camera. The same is true of the reverse if you only look at the center of the picture - the edges could be blacked out or very fuzzy on the full frame when using a da only lens.

06-06-2016, 01:45 PM   #9
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QuoteOriginally posted by RGlasel Quote
Ignore Mr. Northrup.
^^^THIS^^^

That guy is notorious for doling out terrible information.

Again, erase the bull**** you just 'learned' from him from your mind and memory banks. It's just flat out incorrect.
06-06-2016, 02:04 PM   #10
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It doesn't matter what format the lens is designed for. Just look at the focal length

That main disadvantage of the lenses you're considering is that they're not as wide as walkaround lenses designed for APS-C. That said, you'd be using their "sweet spot", so you can generally expect better corner performance and less vignetting.

There are plenty of users who like the 24-70mm on crop, but as I said before, bear in mind that 24mm is a lot narrower than 16mm or 18mm.

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06-06-2016, 02:31 PM   #11
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QuoteOriginally posted by Adam Quote
There are plenty of users who like the 24-70mm on crop
I shouldn't speak for D FA 24-70 owners, but I think the main advantages of it over the 17-70 APS-C zooms is a faster aperture at the long end and better bokeh. When you are wider than 24mm, f2.8 and creamy bokeh aren't big selling points. Now that a DA 70 Ltd is on its way to me, I'll probably won't consider the 24-70, but if I didn't have fast 35mm, 50mm and 70mm primes, it would definitely be attractive to me.
06-06-2016, 02:36 PM   #12
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QuoteOriginally posted by weaponx525 Quote
Should I consider the 16-85 mm APS-C designed zoom lens?
I suspect that for most people, the DA 16-85 would be a better choice on an APS-C camera than the DFA 28-105 — but that's not because the former is an APS-C lens and the latter FF. The 16-85 simply offers a more attractive range for most APS-C shooters than the 28-105. However, if you expect that you would find the 85-105 range more useful than the 16-28 range, then you'd be better off getting the 28-105 for your APS-C camera. The fact that the 28-105 is an FF lens is really neither here nor there, it's what focal range you most need that counts.
06-06-2016, 02:44 PM - 1 Like   #13
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Yep, ignore Northrup.

You get apparent zoom with an APS-C camera when you print APS-C and full-frame images of the same view AT THE SAME PHYSICAL SIZE.

Your DOF difference is because of the field of view - you have to back further away to get the same subject in frame, and longer distance = deeper DOF.

For exposure, f/4 (or whatever) is f/4 whether on crop or on FF.

To make the math simple: when you put a 100mm full-frame lens on a crop-sensor camera, you get the same field of view that a 150mm lens (Nikon, Pentax) or 160mm lens (Canon) would give you on the full-frame body, but as already stated above, the magnification is an illusion caused by viewing the picture at the same physical size as the full-frame one. The illusion is compounded by newer APS-C cameras having more pixels per square millimetre so they can stand the expansion without losing detail. This is why K-3 users transitioning to the K-1 are losing out with their crop lenses, as the crop square has not quite as many pixels per square mm as the K-5, so their ability to make larger prints from the crop zone has taken a step back. Users of the K-5 and earlier APS-C DSLRs, of course, don't take as much of a hit (if any).
06-06-2016, 03:13 PM   #14
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The 16-85 is a higher specification lens than the 28-105 as it covers the same field of view as 24mm-125mm on Full Frame(and is excellent optically). Thats why it is more expensive. The 17-70 focal length is the most similar. Then there are the f2.8 APS-C lenses that are much cheaper and lighter than the 24-70/2.8 in Full Frame.
06-06-2016, 03:48 PM   #15
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Thanks to all the replies. That YouTube video threw me off and I immediately went on these forums for opinions. I am glad I did. The reason I decided that the 28-105 may be more suitable for me is that I do own the DA12-24 (what a difficult lens to use, keeping horizon straight and avoiding pincushion effects!) and I figured that if I do upgrades body's in the future, it would be a FF no question, and I would be good to go with the 28-105. Out of curiosity, I suppose the other lens thread will inform me, but what are the opinions of the 16-85 on a FF body?
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