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11-09-2017, 06:28 AM   #16
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QuoteOriginally posted by Sandy Hancock Quote
If you have the DA*300 already, just shoot it in full frame mode. It is officially designated by Pentax as full frame compatible.

Put the K-1 in crop mode if you use the HD DA 1.4x Rear Converter with the DA*300 though. The DA*420/5.6 is definitely a crop lens
The 1.4 doesn't vignette that badly. You can crop the corners vertically or horizontally. I prefer to shoot in FF and crop in post. It just gives you more options. Many times the crop you get is the same as what you would have cropped even without the vignetting, and is still bigger than APS-c.

11-09-2017, 10:18 AM   #17
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QuoteOriginally posted by pschlute Quote
Damn crop factors again ! The single most useless invention of the camera industry.
What he said ^^^^

QuoteOriginally posted by clackers Quote
This 'equivalence' crap has to stop!

The aperture doesn't change. The focal length doesn't change. The exposure doesn't change. The depth of field doesn't change.

What you get is the middle fifty percent of the FF frame, that's actually what 'crop' means, a reduced field of view.
I almost, but not quite entirely, fully agree with you.
The depth of field should be impacted by cropping and subsequent enlarging. Of course, a theory pretending that DoF is determined by the aperture is a fraud.
11-09-2017, 10:28 AM   #18
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QuoteOriginally posted by Kunzite Quote
What he said ^^^^


I almost, but not quite entirely, fully agree with you.
The depth of field should be impacted by cropping and subsequent enlarging. Of course, a theory pretending that DoF is determined by the aperture is a fraud.
In photography yes....in optics, it's a little different.
QuoteQuote:
The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane.[2] If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. A wide aperture admits uncollimated rays, resulting in a sharp focus only for rays coming from a certain distance.
Aperture - Wikipedia

In photography you have fixed ƒ-stops at known intervals (quite arbitrarily assigned for the sole purpose of defining light intensity for the purpose of exposure.) where each f-stop is half or double thrones on either side of it. Thus, the Aperture is a set of numbers designed to help in exposure. If they were designed to double or halve Depth of Field, they'd be a photographic measurement of some value perhaps, but they aren't They were conceived and implemented as a standard to be a simple method of understanding exposure values. If at some point some guy like Northrup decides they are going to be a DoF value, the system is going to have to be completely reworked for that purpose.

The biggest problem with the way Northrup uses it, is Aperture used to describe DoF values, doesn't tell you what the DoF is. It only tells you what it is compared to some other system, for which you also don't know what the DoF is, 1 stop of Aperture, does not double or halve the DoF and it's not the same across all focal lengths. It's not a constant measure of anything, and it changes from focal length to focal lentgth. The DoF on a 50mm lens is not the same as the DoF of a 100mm lens at the same Aperture. But ƒ2.8 is ƒ2.8 for exposure regardless of focal length or sensor size. Aperture is simply not adequate as a description of DoF. Only a DoF table does that. Then you have all parameters, where does the DoF start, where does it stop, what distance does it cover. A single variable like Aperture is simply not adequate to describe it. At best Aperture describes the size of the hole, but it's different sizes on different focal lengths, so it doesn't even accomplish that adequately and there are many more parts to the equation.

If Northrup had a clue what he was talking about, he would have had to know he needs to explain all this when he says these things. His presentations present a lack of context , which suggests he doesn't himself understand the context.

If you understand the context, then you know these kinds of statements about Aperture and DoF are misleading. But if you don't understand the context, you don't even understand that you're making a mistake.

Last edited by normhead; 11-09-2017 at 11:15 AM.
11-09-2017, 12:47 PM   #19
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I'm talking about the DoF in its photographic sense involving a print or another display method - where "acceptable focus" depends on things like the viewing distance and visual acuity. And, of course, subject magnification - which you influence by a simple crop and resize.

Yes, "equivalence" can be resumed as: "if this long list of conditions are met, you can get similar images with two different formats". It doesn't help you take the images in the first place - with the visualization process discussed by Ansel Adams. It doesn't help you when - and it's a when, not an if - the real life conditions are different, and your goals are different than that of the "equivalence".
My pet peeve with it is that it's an awfully confusing theory to the less experienced people, and that it detracts them from learning photography. They're led to learn "inter-format comparison in theoretical conditions" instead.

11-09-2017, 12:59 PM   #20
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QuoteOriginally posted by Kunzite Quote
I'm talking about the DoF in its photographic sense involving a print or another display method - where "acceptable focus" depends on things like the viewing distance and visual acuity. And, of course, subject magnification - which you influence by a simple crop and resize.

Yes, "equivalence" can be resumed as: "if this long list of conditions are met, you can get similar images with two different formats". It doesn't help you take the images in the first place - with the visualization process discussed by Ansel Adams. It doesn't help you when - and it's a when, not an if - the real life conditions are different, and your goals are different than that of the "equivalence".
My pet peeve with it is that it's an awfully confusing theory to the less experienced people, and that it detracts them from learning photography. They're led to learn "inter-format comparison in theoretical conditions" instead.
I doubt that will ever be a real course at an accredited school.

Look at Audiobombers math above, now do that for every F-stop, for every lens you own and one's you'd like at every distance from the lens. You have a practically infinite number of scenarios You're going to have to write them down to remember all your results, you'll have a book thicker than a phone book. What I do is look at the scene say "that looks like ƒ3.4 (based on my experience), I'll probably shoot ƒ4 and ƒ8m maybe ƒ11 just to be sure.

How is calculating the DoF based on distance from the camera, ƒ stop and focal length of lens for different formats a practical work flow. If I do that for more than one format it will take twice as long. I'd say a theoretical understanding of equivalence and how it applies to each scene would definiteatezy be an impediment to your photographic career, not a help. Experience working with the equipment is more valuable. Experience enables you to do instantly calculations that would take minutes to hours using equivalence tables. There is not benefit to using equivalence theory that would actually speed up your photography, or even make you a better photographer. It's internet argument or click bait fodder, nothing more.

Last edited by normhead; 11-09-2017 at 01:10 PM.
11-09-2017, 04:57 PM   #21
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QuoteOriginally posted by normhead Quote
The 1.4 doesn't vignette that badly. You can crop the corners vertically or horizontally. I prefer to shoot in FF and crop in post. It just gives you more options. Many times the crop you get is the same as what you would have cropped even without the vignetting, and is still bigger than APS-c.
I didn't know you had the DA*300 Norm. It's a pretty significant vignette in my opinion. With other lenses it is not so bad.

Anyway, shooting in crop mode gives you more room on the card, AF points nearly all the way to the edges, and quicker burst shooting, so there are some advantages.
11-09-2017, 06:08 PM   #22
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QuoteOriginally posted by Sandy Hancock Quote
I didn't know you had the DA*300 Norm. It's a pretty significant vignette in my opinion. With other lenses it is not so bad.

Anyway, shooting in crop mode gives you more room on the card, AF points nearly all the way to the edges, and quicker burst shooting, so there are some advantages.
I was talking about the HD DA 1.4 TC which is also an APS-c piece of equipment.
11-09-2017, 06:25 PM   #23
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QuoteOriginally posted by normhead Quote
I was talking about the HD DA 1.4 TC which is also an APS-c piece of equipment.
Yeah, but it performs quite differently with different lenses. With the DA*300 specifically, it vignettes significantly on the K-1 in full frame mode. That was all I was claiming.

Using my computer screen as an evenly lit light source, one at infinity focus and one at MFD:

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11-09-2017, 08:03 PM   #24
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My mistake. I should have said, " your focal length does not change in any way. It is still a 300mm lens. In terms of "equivalent", the resulting crop would give you a narrower field of view that is equivalent to what a 450mm lens would give on a K1 full-frame camera"

Shoot and enjoy the power of the Pentax K1 full frame sensor with a DA*300mm lens. Crop as desired......
11-09-2017, 10:19 PM   #25
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QuoteOriginally posted by Kunzite Quote
What he said ^^^^


I almost, but not quite entirely, fully agree with you.
The depth of field should be impacted by cropping and subsequent enlarging. Of course, a theory pretending that DoF is determined by the aperture is a fraud.
Please don't tell me you've turned into DPR's Richard Butler, Kunzite!

If you crop to an APS-C sized frame, there's no way that when only one eye was in focus, the other one suddenly becomes sharp too.

As for enlarging, this is the digital age, that metaphor doesn't work.

The sensor pixels are the same size between the K-5 and the K-1, and an output device would still be 300 ppi whether it's fed an APS-C image or a FF one. There isn't any upscaling involved in that example until you print larger than 11" by 14".
11-09-2017, 10:46 PM   #26
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It's the other way around - if I crop and print to the same size (enlarge), the other eye might appear less sharp.

Pixel data in a RAW file doesn't have dimensions, but the image projected on the sensor does.
11-13-2017, 11:24 AM   #27
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I think the guy asking the question ran away after the second answer :-)
11-13-2017, 05:04 PM   #28
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QuoteOriginally posted by zapp Quote
I think the guy asking the question ran away after the second answer :-)

cant blame him really.
11-13-2017, 05:20 PM   #29
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A very entertaining thread, with some posters tying themselves in knots over this. I can see certain words and certain concepts meaning different things to different people, some people coming at it from a film background, some from an APS-C background, and some from a FF background, all at cross-purposes. But keep it going guys, it's fun
11-13-2017, 08:34 PM - 1 Like   #30
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Thank You

I asked the original question and I have read every answer. It is most appreciated that so many would take time to try to elucidate the answer. Thank you for your most generous responses.
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