[zapp]

The Rokinon does not have smooth manual focus - results are great at f/2. K1 has no interchnagebale focusing screen. I tried the Rokinon on K3 and it was difficult to focus due to a stiff focus ring. On K1 hitting correct focus would be a pain in my opinion. I am happy with the DFA* 70-200 at all apertures. Different size, dimension, zoom, weather sealing... If you want to single focus tele photo with low footprint Rokinon would do the job. If a zoom is fine for you, go Pentax - the 70-200 is still the only D-FA* for K1 :-)

[sjwoodworth]

Backing up what Class A said, this applet might be helpful [it includes the formula for depth of field, so it's easy to isolate all the variables]:

depth-of-field - Digital Photography

If you take the K1 and put it in crop mode then you've made the allowable circle of confusion smaller --- there are less sensor pixels that still need to fill the same size frame (4"x6" or 4000 x 6000 screen pixels or whatever) --- and so less DOF. [This has more to do with resolution though than with format size per se. Notice that format/sensor size isn't a variable in DOF equation.. only indirectly through circle of confusion. I hadn't thought this through before --- thanks Class A!]

On the other hand once the K1 is in crop mode you'll want to get as close as possible to the original composition (though of course perspective will changed). Once you back up subject distance is farther so DOF increases. (Or you could change from crop to non-crop, and then you'll move forward... subject distance decreases and so too DOF.) That's what people mean when they say that the same lens will produce a shallower depth of field on a larger format... it's because they're assuming that subject distance has changed so that a head and shoulders shot on FF is being compared to a head and shoulders shot on APSC.

[sylvainp]

@CLASSE A

Sorry for the delay of my answer but I don't put too much time on things like that anymore. I know the paper you are referring too and you will see in the inclusion of "non ideal" camera and lens and then making sure that all variables been the same. He doesn't include the sensor density, generation (iso perf etc) and AF performance but focus on the physic. It's exactly my point anyway. The pentax K1 and some nikon are the best example of a camera able to show you the end results and get close to the ideal camera. A telephoto lens like the da 300mm f4 is close to be a ideal lens to show this since been a long telephoto they generally are not designed with compromised diameter.

So you can read that paper you site or you can take a K1 with a long telephoto, take a picture in FF mode then in apsc mode then taking that same picture in apsc mode but moving back so the fov match the original photo in FF and then compare all the pics in lightroom.

In the end when you crop with K1 a D810 or a D850 in apsc mode what it does is the same exact thing as cropping the FF photo in lightroom. Nothing else. It doesn't make a 300mm f4 lens a 450mm f5.6 lens. It gives you a zoom in the image and the paper explain this. Then you can compose the image to get same fov and dof will be changed. Yet the light is still from a F4 lens.

A much more helpful question is what the difference between two images is that are shot on

1. K-1 in FF mode with a 300mm lens at f/4.
2. K-1 in crop mode with a 200mm lens at f/2.8.

The answer is (practically) none (let's ignore ISO settings here). I'm writing "practically" because technically the f-ratio should be f/2.67 for the 200mm lens, not f/2.8.

Your example of a 200mm f2.8 compared to a 300mm f4 doesn't work. You had to exclude ISO yourself to try to fix the comparison. The 200mm f2.8 will bring more light so you will have to adjust iso and then you will get more noise and also the AF system will have a harder time. This mean the 200mm f2.8 bring more light in FF than a 300mm F4 in apsc mode. try it with you K1. Remember when I said you will have to add variables to justify equivalency on f-stop to "work" ? you did it by telling us to ignore iso in you comparison.

The paper you linked never said it make sense to adjust F-stop in equivalency. It say that given same everything fov and dof will change regarding sensor size. It something Tony N. and many don't seems to understand.

It does, however, make a ton of sense to refer to a 50/1.8 APS-C lens as a "75/2.8 FF-equivalent" lens. Why? Because to all purposes and intents, the APS-C lens will allow you to take the same images that a 75/2.8 lens will allow you to take on FF.

If you only factor dof and fov after adjusting composition. Emphasizing dof that much is a recent thing in the evolution of photography. When using a ovf you see instantly that these are two different lenses just by the brightness level.

You can blame the industry's convention to label lenses with their focal length instead of with their AOV. If a 50mm lens were labelled "46.79°" then it would have been possible to simply state "This 46.79° FF lens, will look like a 32.17° lens on APS-C". This would have avoided unhelpful responses like "50mm = 50mm" and "f/2.8 = f/2.8" because no one challenges the fact that the AOV changes when one crops. What most people do not seem to understand is that the idea is not to claim that a 50mm "becomes" a 75mm lens. As a matter of fact, it is correct that the focal length doesn't change. However, it is 100% valid to say that the 50mm lens on APS-C is equivalent to a 75mm lens on FF. So the correct wording is that it is an "75mm FF-equivalent" lens.

It wouldn't make sens. I use my lenses on different format. When I use my 300mm f4 on my K1 I don't expect the box to say 450mm F 5.6 (APSC) 300mm F4 (FF) or should it be 450mm f4 (apsc) 300mm f3.5 (FF) or else XX degrees on this sensor XX degrees on this sensor and in the case of canon a third XX degrees on the aps-h. They can give examples or a table of conversion if they want they need a proper description of the lens.

They describe the lens the best way possible, a 300mm F4 is a proper physical description of what it is. ok maybe T-stop could be more useful and that's another subject.

Dof at the widest aperture doesn't have to be written anywhere. It's a results of decision taken from the photographer including the camera he will use and if he will crop ... it's not a physical parameter of the lens.

The lens is a 300mm f4 and you do what you want with it. My olympus 300mm f4 is sharper including wide open than my pentax 300mm f4 and it has nothing to do with the sensor size inside the camera. They are of similar optical size and lenght when you factor one include stabilisation and better focusing system. You implied that my olympus is sharper because it's easier to build than my pentax da f4 which doesn't make any sense been both telephotos. The end result is similar optic size, similar ratio and similar light. The olympus could had been smaller if it wasn't a telephoto lens. If it was a 50mm lens instead of 300mm it would make sens to reduce the glass size considering the lens was designed to be used on a m43 sensor. At 300mm it's not the case anymore.

The above assumes that both images will be looked at the same size. If you were to enlarge both by the same factor, you'd get images of different sizes which, again, would make comparisons difficult. You didn't specify the viewing conditions for your thought experiment, but the only fair comparison is to assume that both are printed at the same size or that they are viewed at different magnifications on a screen.

True, it hold up until you lack resolution for the end results. Someone that need to do large banner seen from couple of feet will have to take decision based on that. I compare in a 4k 27" ips lcd or printed on my canon pro-10 13"x19" seen up close generally.

Photography has been influenced a lot by videographer in the recent year (5dmkII played a role and I've seen a shift in the way people select and compare lenses after that) and the use of shallow dof to center on a subject has taken a big part of the conversation apparently.

I see so many comparing F-Stop between sensor size for light and noise, you don't and I appreciate it. If you tell me this lens, when used on this body will give you a fov and dof similar to this lens on this other body I can't say you are wrong. I still find it a form of noise in the conversation but you don't refer to some made up concept like "total light" to try to justify the light of a F2.8 lens magically become different when used on a different sensor size.

Again, sorry for the delay of my answer.

BTW : if your name refer to amplifier design, I design and build tube classe A amplifiers as a hobby.

---------- Post added 03-18-18 at 05:15 PM ----------

I am not trying to be rude or adversarial, but I can learn more myself when people show me what they're seeing and as it is not uncommon to find people making negative comments about gear (and fair enough if there's a problem) most people don't post examples so the value that can be placed on those comments are comparatively diluted.

Hope the above clarifies that I'm not seeking an argument.

Tas

Op asked a question and I think I gave him some useful informations instead of just telling him it's super sharp wide open. If I was in his shoes I'd rather have some informations regarding a little bit of softness at f2.8 and 200mm and that it suffer from focus breathing. Finding photos of the lens wide open on google is a matter of seconds.

I have to say that since my 70-200mm came back I've put in on the side and didn't had lot's of time for this.

Anyway at this point it is safe to say the op has move on.

yesterday I went out and took some shots with my olympus 300mm f4 and mc-14 teleconverter or 2.95 degrés. If it's of any interest I dumped some here : A cold and windy Saturday at Saint-Bernard Island | Flickr

In a perfect world I would had taken the same exact shots with my pentax system but it's not a easy task to bring all this weight hiking. I never bring two different body on a hike as you may understand.

I could find a static subject and shoot both system including the 70-200mm 300mm f4 from pentax etc and post the results. I did it on test charts but it's boring. If I was to post those test I would put them on the lens section and I'm not really sure if member of the forum would appreciate it.

[Rondec]

My copy of the DFA 70-200 is very nice. I think the hard part about the Olympus comparison is that which Class A has stated. Assuming the same framing and equivalent focal length, you have more depth of field with an f2.8 lens on micro four thirds than with an f2.8 lens on full frame. This overall gives a feeling that the image is less sharp than the full frame comparison. In addition, the images should be viewed at the same size (not pixel peeped). This does put more of a strain on the four thirds images in comparison to the full frame ones. The tendency is to pixel peep both.

I don't shoot micro four thirds, but I do have a K3 and it is harder to get pixel sharp images with it as compared to the K-1, particularly at other than base iso.

[sylvainp]

My copy of the DFA 70-200 is very nice. I think the hard part about the Olympus comparison is that which Class A has stated. Assuming the same framing and equivalent focal length, you have more depth of field with an f2.8 lens on micro four thirds than with an f2.8 lens on full frame. This overall gives a feeling that the image is less sharp than the full frame comparison. In addition, the images should be viewed at the same size (not pixel peeped). This does put more of a strain on the four thirds images in comparison to the full frame ones. The tendency is to pixel peep both.

I don't shoot micro four thirds, but I do have a K3 and it is harder to get pixel sharp images with it as compared to the K-1, particularly at other than base iso.

When I read what you said I'm inclined to think you mean the subject seems sharper if everything else is out of focus. The subject is not sharper but more isolated.

I personally don't find the image sharper on FF or on apsc or m43. Generally I find that the best lenses give the sharpest results as long as you respect and understand the tools you have to work with and the end result you aim at. Not having a AA filter help also.

The image certainly don't get soft when shooting apsc compared to FF on the k1 as long as you don't lack resolution for your print. Maybe the technology involved in the K1 compared to the k3 is the reason you get this.

[Rondec]

When I read what you said I'm inclined to think you mean the subject seems sharper if everything else is out of focus. The subject is not sharper but more isolated.

I personally don't find the image sharper on FF or on apsc or m43. Generally I find that the best lenses give the sharpest results as long as you respect and understand the tools you have to work with and the end result you aim at. Not having a AA filter help also.

The image certainly don't get soft when shooting apsc compared to FF on the k1 as long as you don't lack resolution for your print. Maybe the technology involved in the K1 compared to the k3 is the reason you get this.

I think the point is that you will get similar results between a 50-135 f2.8 on APS-C and a 70-200 f4 on full frame. My 70-200 is quite a bit sharper at f4 on a K-1 than my 50-135 is wide open on my K3. Comparing them both wide open gives significantly different results.

[sylvainp]

I think the point is that you will get similar results between a 50-135 f2.8 on APS-C and a 70-200 f4 on full frame. My 70-200 is quite a bit sharper at f4 on a K-1 than my 50-135 is wide open on my K3. Comparing them both wide open gives significantly different results.

Have you tried using the k1 in aps-c and ff mode to test this ? been the same photo sites for both modes, the aps-c mode won't be limited by the lens. In aps-c a smaller portion of the lens is used but the resolution is reduced according to the sensor's surface used. In this mode I can't find lost of sharpness cropping on the k1. When using a FF lens on a k3 you will give a hard time to the lens trying to to get all your 24 mpixel in a smaller portion instead of 36 mpixel in the whole lens.

With smaller sensor you need better glasses there is no way around this.

[Pål Jensen]

I think the point is that you will get similar results between a 50-135 f2.8 on APS-C and a 70-200 f4 on full frame. My 70-200 is quite a bit sharper at f4 on a K-1 than my 50-135 is wide open on my K3. Comparing them both wide open gives significantly different results.

The missing point is that you don't want similar result. You want better result with a larger format. Thats why you buy it.

[normhead]

The missing point is that you don't want similar result. You want better result with a larger format. Thats why you buy it.

And yet, when shooting with the K-1 and K-3 for wildlife, if I put the images from a shoot in the same folder, I have to look at the exif to see which is which in many cases. If you want better results with the K-1 then you are going to have to buy bigger longer lenses. That will do for about 10 seconds with a K-1, until you realize you can put the same lens on a K-3.

The larger format is for those occasions when it's not a disadvantage to use it, like when the subject is close enough you won't have to crop. If you have to crop, the smaller format will probably be better using the same lens.

Even when the K-1 images fill the frame, now you have DoF problems.

When everything works out, you get better images ith the larger format.
K-1 image.


K-3 image


The K-1 is better if you have great opportunity, the K-3 is better at distance. There's not a lot to pick and choose from whichever you use. There's just not that much difference IMHO.

[Rondec]

The missing point is that you don't want similar result. You want better result with a larger format. Thats why you buy it.

We've had this discussion many times. Sometimes I want the same result (but with better image quality), sometimes I want different. In a perfect world, a K-1 gives me 36 megapixels of high quality pixels with excellent dynamic range, perfect to begin post processing. There are plenty of times that I want the depth of field I would get with APS-C, I just want a little better image to work with. The K-1 gives me that in many situations.

There are times when stopping down your full frame camera will require bumping iso, but there are plenty of times when there is enough light that you can stop down without having to go up on your iso.

People, for some reason, focus on depth of field a lot when discussing the differences in formats, but I appreciate a lot more having better dynamic range (particularly in higher iso situations) and having a little better resolution. APS-C is more than capable of shallow depth of field photography for me and more often than not, I am stopping down to match APS-Cs depth of field.

[Pål Jensen]

We've had this discussion many times. Sometimes I want the same result (but with better image quality), sometimes I want different. In a perfect world, a K-1 gives me 36 megapixels of high quality pixels with excellent dynamic range, perfect to begin post processing. There are plenty of times that I want the depth of field I would get with APS-C, I just want a little better image to work with. The K-1 gives me that in many situations.

There are times when stopping down your full frame camera will require bumping iso, but there are plenty of times when there is enough light that you can stop down without having to go up on your iso.

People, for some reason, focus on depth of field a lot when discussing the differences in formats, but I appreciate a lot more having better dynamic range (particularly in higher iso situations) and having a little better resolution. APS-C is more than capable of shallow depth of field photography for me and more often than not, I am stopping down to match APS-Cs depth of field.

Few would disagree with this but the problem is the insistence of having the same output when comparing formats. That is ridiculous; it is like comparing a Pentax 67 with 1600ISO with an LX with 50 ISO. This is not how cameras are chosen or used. We choose the format that fits our needs and economy and use them to the best of their abilities in whatever situations we encounter..

[Rondec]

Few would disagree with this but the problem is the insistence of having the same output when comparing formats. That is ridiculous; it is like comparing a Pentax 67 with 1600ISO with an LX with 50 ISO. This is not how cameras are chosen or used. We choose the format that fits our needs and economy and use them to the best of their abilities in whatever situations we encounter..

I don't think that's the question at all. The question for me is which gives me better iso 100 when I am on a tripod. That's all.

[normhead]

Few would disagree with this but the problem is the insistence of having the same output when comparing formats

And I'd say the problem is the insistence on ignoring the fact that better output doesn't always happen or isn't always necessary. Higher resolution only makes a better image when the smaller sensor for some reason can't resolve part of the image, and what it resolves adds something to the photograph. Sometimes obscuring detail adds something to the photograph.

In one of the few actual comparisons of real prints the blind tester looking at the same image produced by a K-5 and D800 said "I prefer some parts of one image, and other parts of the other image, overall, I can't choose between them."

Understanding that is the key to this part of the discussion. You can expect to get images you like as much from the smaller sensor, unless the photographer is adept at getting the most out of the larger sensor.

The insistence isn't on haveing exactly the same output, it's about having equally enjoyable output. That is certainly possible for all but a few images.
Back when I was shooting 8x10s in the studio, my instructor used to show us images from his throw away cameras with the plastic parabolic lenses. The fact that there is such a thing as 8x10 film view cameras in no way diminishes the images you get with your point and shoot. A good picture is just a good picture.

[Pål Jensen]

I don't think that's the question at all. The question for me is which gives me better iso 100 when I am on a tripod. That's all.

And thats what I'm saying.

[Rondec]

Equivalence is just a formula that lets you compare different formats. This is not necessary if you are only shooting one size sensor, but it is helpful if (as I did) you go from shooting APS-C to full frame. I learned pretty quickly that I had to stop down my landscapes more with full frame to get adequate depth of field for them. It wasn't that I was exactly trying to reproduce my APS-C photos, but I do like having things sharp from foreground to background and at f8 on a K-1 it wasn't happening.

It makes sense that at a given iso and image size, a bigger sensor will tend to perform better. It also makes sense that the easiest way to make lenses smaller is to make their apertures slower. Particularly if you are shooting stopped down a lot, this isn't necessarily a bad thing.

The problems come when people say equivalence says that a give format is good or bad. It doesn't do anything of the sort. Not everyone needs super fast lenses and in point of fact, I very much enjoy shooting with lenses like the DA 15 and DA 40 precisely because they are small lenses, but I enjoy shooting with f1.4 lenses too. In the end, the most important thing is that a photographer understands how to get the framing they desire and maximize the camera gear they have.