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Forum: Pentax SLR Lens Discussion
11-11-2017, 05:04 PM
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Agreed. No argument with that from me. I think, though, that most amateurs concerned about equivalence (and I include myself, back when it bothered me) aren't considering, or even aware of, the details of a lens' optical performance in this situation... they just want a broadly equivalent field of view and depth-of-field on the format they're using. They most likely don't even fully understand what they want - and that's no criticism of them, but simply an observation based on my own journey :)
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Forum: Pentax SLR Lens Discussion
11-11-2017, 04:01 PM
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At the risk of extending an equivalence discussion I've already intervened in (!), and one that is verging off-topic from the original post, I feel I have to say my piece :D
I agree that, generally, it's a waste of time to worry about equivalence... Shoot with the lenses that give you the results you want on the sensor format you have available. That's all that really matters.
That said...
Some owners of APS-C format cameras want to be able to reproduce what they see from full-frame photographers. That's quite understandable. I've been in that situation, and so have plenty of others here.
The main issue, as I see it, is one of subject isolation using limited depth-of-field.
If someone shoots an image on a full-frame camera with an 85mm f/1.4 lens at - say - f/2, it will have a particular field of view and depth-of-field relative to the subject. To recreate that same image with an APS-C camera, I would need to shoot at the same distance with a 56mm lens at f/1.3. No such lens exists, so - clearly - I couldn't recreate that shot *exactly*. I could, perhaps, use a 50mm f/1.4 lens wide open to get a similar field of view and depth-of-field, but (at best) it would be an approximation (and suffer from the imperfections of a lens used at maximum aperture).
The situation becomes even more difficult if we consider an image from that same full-frame camera plus 85mm lens shot wide open at f/1.4. To reproduce that with my APS-C camera, I'd have to use a 56mm lens at f/0.93. Again, no such lens exists. Indeed, there isn't even a 50mm lens I know of that has such a large maximum aperture - so, in this case, I simply couldn't take the *same* shot with my APS-C camera. This is one area where the APS-C format is potentially limited compared to full-frame (if you look at it that way)... shallow depth-of-field for a given field-of-view is limited by the maximum aperture of available lenses at the necessary focal lengths.
Of course, there are plenty of benefits to using APS-C too. For example: If greater depth-of-field is my priority, I'm laughing. If a full-frame photograph is taken using a 300mm lens at f/5.6, I can take an almost-equivalent shot from the same distance, using my APS-C camera and a 200mm lens at f/3.5 to f/4. I'll get very similar depth-of-field and, as a bonus, for the same shutter speed I can use a lower ISO.
But I return to my opening agreement with some of what has already been said... it's a waste of time to worry (too much, at least) about lens equivalence between sensor formats... Shoot with lenses that give you the results you want on the sensor format you have available. That really is all that matters :)
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Forum: Pentax SLR Lens Discussion
11-11-2017, 03:20 PM
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Ok, fellas - breathe :p Relevant discussion, but please let's keep it friendly and not personal. Thank you :) |
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Forum: Pentax SLR Lens Discussion
11-10-2017, 03:07 PM
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Okay fellas, enough on the DPR bashing - we've been here before and it didn't end well! :p
Thank you :) |
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Forum: Pentax SLR Lens Discussion
11-07-2017, 05:44 AM
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Absolutely.
A few related observations (straying off the thread's purpose, I accept):
- Lab tests and test charts might measure optical performance, but they don't measure character (witness the FA43)
- Even so-called weak lenses can have their charms; sometimes, it's those very weaknesses that give them their unique character and creative appeal (my Helios 40-2, for example)
- There are, IMHO, relatively-few truly weak lenses that offer nothing creatively regardless of the sensor format they're used on
:)
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Forum: Pentax SLR Lens Discussion
11-06-2017, 03:10 PM
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LOL :lol:
I have the DA70 and I like it, though I don't use it all that often. The colours and contrast are lovely, it's sharp, and the out-of-focus rendering is really nice. I haven't used the FA77 but from what I've seen, it's excellent. I'd be delighted to own one, but couldn't justify it given on what the DA70 is capable of and my own creative / artistic limitations right now. If I was moving to full-frame on Pentax, maybe I'd be tempted... but then, it would be a different experience altogether, given the wider field of view :)
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Forum: Pentax SLR Lens Discussion
11-06-2017, 09:47 AM
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Right. This goes back to my earlier point - that sensors with similar pixel density, regardless of format, will give very similar results for the same lens. The sensors in the K-1 and - for example - the K-5IIs have very similar pixel densities (I think?), so the same lens on both cameras should give very similar results, if the K-1 image is reproduced such that the APS-C crop portion is the same physical size as the K-5IIs image.
Frankly, I think all of this is essentially moot. Full frame lenses work great on APS-C cameras. Differences due to sensor pixel density - whilst apparent when pixel peeping - can and should be ignored. If the field of view is appropriate and the lens renders nicely, that's all the reasons we need to justify its use on crop.
A related side note: As I recall, the FA77 Limited beat (only just) the DA70 Limited when the two were tested side by side on an APS-C body, right here on these very forums :)
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Forum: Pentax SLR Lens Discussion
11-06-2017, 08:53 AM
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I see where you're coming from... My point is, that's not due to the lens performing any differently on one sensor than the other. It's simply a physical scaling issue. If the images are viewed / printed in proportion to the crop factor, there will be no difference. The lens isn't part of the equation, agreed?
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Forum: Pentax SLR Lens Discussion
11-06-2017, 04:32 AM
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I don't know if the DA35 f/2.4 has any poly-carbonate elements - it wouldn't surprise me if that's the case, though. A few modern Pentax lenses (and plenty of third party models) have poly-carbonate bonded aspheric elements.
That said, the resolution performance from this lens will be exactly the same on sensors of different formats that are otherwise equal (i.e. same pixel density, same AA filtering etc.), if you limit comparison to the relevant area of the image circle, and view that area at the same physical dimensions.
To prove that in a non-technical way, we can simply use a lens on the K-1 in both full frame and crop modes. The sensor remains the same - we're just using a smaller part of it by cropping. The lens doesn't perform any differently as a result of the crop.
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Forum: Pentax SLR Lens Discussion
11-05-2017, 02:52 PM
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I do see the limitations in the borders and corners on full-frame, but not to a degree that bothers me. For center and mid-frame performance (frame-wide on crop), I'm quite happy with it wide-open after AF fine adjustment, for certain types of shot - though I agree it benefits hugely from being stopped down to f/4, where I think it really shines :)
I can understand that, for sure. I've just found that, for most of my own shooting, 28mm on APS-C is usually as wide as I want to go - in fact, I'd say 28 to 50mm is my preferred range, though it's nice to have a little more headroom for certain situations. I guess I'm a little uncommon in that respect... I certainly wouldn't recommend 28-75 on APS-C as a walk-around combo for most, but it works really well for me :p I do have wider-angle lenses I enjoy using too (the DA21 on crop is a favourite), but I rarely find myself wanting to go wider. My DA15 is, sadly, my least-used lens, though I love the IQ :o
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Forum: Pentax SLR Lens Discussion
11-05-2017, 01:26 PM
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I came to this one pretty late, and everything has already been said...
I quite like Tony Northrup, but this really is one of his more misleading and less helpful videos. @stevebrot is probably right - Tony would likely avoid the subject or (hopefully) change his tune nowadays.
Full frame glass works just fine on any size sensor, whether it's (so called) full frame, APS-C, micro 4/3 or even smaller. A 24-70mm f/2.8 lens will let in the same amount of light and - when shot at the same distance - will produce the same depth of field on any sensor. The field of view will, of course, differ depending on the size of that sensor (if the sensor is cropped, the field of view will be cropped accordingly) and that will determine the appropriate use-cases for the lens and camera combination. Furthermore, the greater the pixel density of the sensor (a combination of sensor size and resolution), the more demanding it will be of a lens' resolving capabilities. Fit a poorly-performing lens to a high-res 24 megapickle APS-C camera, and you'll notice the deficiencies more than you would on a slightly-lower-resolution 16 megapickle APS-C camera. On a (by today's standards) relatively-low-res 12 megapickle full-frame camera, you'll notice those deficiencies less still. But, if you shoot full-frame and APS-C cameras with same pixel density sensors side by side, with the same lens, you're going to get exactly the same performance from the lens.
The glass I have most fun with is old Soviet stuff intended for use on 35mm film cameras. Some of those lenses are sharp, some less so; some produce weird bokeh (occasionally nice, often distracting), others have contrast or flare issues. I use them on my Sony full-frame and Pentax / Samsung APS-C cameras with no obvious difference in results, save for the different field of view based on sensor size. My full-frame cameras use 24Mp sensors, and I have APS-C cameras with everything from 6 to 24Mp sensors.
One of my favourite - and most used - lens / camera combinations is the full-frame Tamron 28-75 f/2.8 on the 10Mp Samsung GX-10 (Pentax K10D). The focal length / field of view range on APS-C is perfect for much of what I do. I have the same lens in Sony A-mount for my full frame gear, and it gets used much less - purely because of the field of view.
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