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05-26-2020, 02:31 PM   #1
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Crop Factor

I recently shot a pic of a ship in the harbor with the Tamron 500mm mirror lens on a Sony A7 II and then on the Q-S1. And at 2300mm on the Q-S1 it gets really up close and personal with that ship. However, if I enlarge the 500mm image from the Sony a few times I wind up with the approximate same magnification and detail. So the question is why not just use the Sony and crop out the center? This seems essentially what the Q-S1 is doing. Someone help me out here.

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05-26-2020, 02:43 PM   #2
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If you have both indeed, why not.
05-26-2020, 02:45 PM - 5 Likes   #3
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My absolute best advice for for crop factor questions is to forget you ever heard the term. There is no such thing.
Learn become attuned to how your lenses render on your format(s) and use whatever best suits the situation and gives you the result you're looking for.
Let me explain that a bit.
Let's say you have in front of you a hot dog, a bottle of ketchup, and a bottle of mustard. How mustard and ketchup taste on a hamburger is completely, totally irrelevant.
05-26-2020, 02:54 PM - 5 Likes   #4
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QuoteOriginally posted by boojum Quote
I recently shot a pic of a ship in the harbor with the Tamron 500mm mirror lens on a Sony A7 II and then on the Q-S1. And at 2300mm on the Q-S1 it gets really up close and personal with that ship
You shot both images with a 500 mm lens, no 2300mm lens exists.

The magnification the 500mm lens produces "at the sensor" is identical on both cameras.

Your Q-s1 has a smaller physical sized sensor, so takes a smaller bite out of your 500mm lens image circle.

If you crop the larger sensor image to the same size as the Q-S1 you will get the "same" image.....except quality will depend on pixel density and other factors.

05-26-2020, 02:56 PM   #5
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QuoteOriginally posted by boojum Quote
... So the question is why not just use the Sony and crop out the center? This seems essentially what the Q-S1 is doing. Someone help me out here.


Why not indeed! If you're getting the same amount of pixels in your final image the results should be very similar. For display on a screen that's probably all you need. However, if you're intending to print the results on paper, the more pixels you start with the bigger you'll be able to print the picture and retain an acceptable degree of detail and sharpness.


Don't confuse yourself with "equivalent focal lengths". A 500mm lens is a 500mm lens whatever you bolt it onto. An old 500mm lens that was originally designed with the limitations of film in mind will quite possibly have noticeable limited resolution capability on modern high-density digital sensors. That doesn't make it a bad lens, just a bad choice for that job


Edit : Obviously I managed to cross-post with several like-minded individuals! The fact that I was last in the list simply demonstrates how much slower I am at typing than they are

Last edited by kypfer; 05-26-2020 at 03:01 PM.
05-26-2020, 03:02 PM - 1 Like   #6
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You crop before you take the picture or after you process the picture. Take your pick.

Just a thought. Whenever i take a shot and do any cropping in pp i am going to start calculating how much I crop so i can give lens mm equivalence.😀 "I shot this with my 100mm but I cropped 20% so my lens is really a 120mm!" On the back end it really looks silly.

Last edited by swanlefitte; 05-26-2020 at 03:10 PM.
05-26-2020, 09:14 PM   #7
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QuoteOriginally posted by pschlute Quote
You shot both images with a 500 mm lens, no 2300mm lens exists.

The magnification the 500mm lens produces "at the sensor" is identical on both cameras.

Your Q-s1 has a smaller physical sized sensor, so takes a smaller bite out of your 500mm lens image circle.

If you crop the larger sensor image to the same size as the Q-S1 you will get the "same" image.....except quality will depend on pixel density and other factors.
QuoteOriginally posted by kypfer Quote
Why not indeed! If you're getting the same amount of pixels in your final image the results should be very similar. For display on a screen that's probably all you need. However, if you're intending to print the results on paper, the more pixels you start with the bigger you'll be able to print the picture and retain an acceptable degree of detail and sharpness.


Don't confuse yourself with "equivalent focal lengths". A 500mm lens is a 500mm lens whatever you bolt it onto. An old 500mm lens that was originally designed with the limitations of film in mind will quite possibly have noticeable limited resolution capability on modern high-density digital sensors. That doesn't make it a bad lens, just a bad choice for that job


Edit : Obviously I managed to cross-post with several like-minded individuals! The fact that I was last in the list simply demonstrates how much slower I am at typing than they are
QuoteOriginally posted by swanlefitte Quote
You crop before you take the picture or after you process the picture. Take your pick.

Just a thought. Whenever i take a shot and do any cropping in pp i am going to start calculating how much I crop so i can give lens mm equivalence.😀 "I shot this with my 100mm but I cropped 20% so my lens is really a 120mm!" On the back end it really looks silly.
OK, thanks to you all. I have been kicking this around all afternoon and have come up with a similar answer. So the question now is who has the better sensor? Sony, hands down. Also in the Sony I have better image stabilization software/firmware so it looks like the Tamron will be on the Sony more than the Pentax.

Downside is the Sony will not fit in my jacket pocket. ;o)

Thank you all for the help.
05-26-2020, 10:17 PM   #8
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QuoteOriginally posted by boojum Quote
Downside is the Sony will not fit in my jacket pocket.
Does Tamron with Pentax Q fit?

05-27-2020, 01:02 AM - 1 Like   #9
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QuoteOriginally posted by boojum Quote
Downside is the Sony will not fit in my jacket pocket. ;o)

Thank you all for the help.


No problem ... get a new jacket
05-27-2020, 09:49 AM - 1 Like   #10
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QuoteOriginally posted by boojum Quote
OK, thanks to you all. I have been kicking this around all afternoon and have come up with a similar answer. So the question now is who has the better sensor? Sony, hands down. Also in the Sony I have better image stabilization software/firmware so it looks like the Tamron will be on the Sony more than the Pentax.

Downside is the Sony will not fit in my jacket pocket. ;o)

Thank you all for the help.
The Q will have better image quality than the Sony cropped. Cropping the Sony down to Q size won't provide anywhere near the 12mp resolution of the Q. Look at the comparision here on PentaxForums. Adam compared Q to cropped Nikon 810. Q beat the 32mp camera.

Are you sure the Sony has better image stabilization? The Q sensor is much smaller, and must be easier to position than a heavy full frame sensor.
Thanks,
barondla
05-27-2020, 02:39 PM - 2 Likes   #11
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If you do the math, the little 12mp sensor in the Q has such a fine pixel pitch, that a full-frame sensor would have to have about 350mp to match it. Well, original Q anyway, the QS-1 and Q7 would be a bit less.


So the Q cameras should win hands down when it comes to looking for ultimate resolution.

Unfortunately, the limiting factor here isn't the megapixel resolution, but the Tamron lens. It's only got so much sharpness to offer. On full frame when looking at the full image, it's pretty decent (unless you compare it to big buck prime telephotos). But on the Q that takes that tiny bite out of its image and shows it to you up close, the softness is evident. There's also the fact that the Q is diffraction limited by around f4.5, so an f8 mirror lens is well into diffraction on such a high resolution sensor as the Q as well.


Very few 35mm format lenses perform well on the Q. They've got to be top notch to look even half decent on a Q (like a macro lens). The Q-specific lenses are very high resolution in comparison, but they've only got a tiny sensor to cover.

So, yes, the Tamron cropped right down on the Sony full-frame might look just as sharp as what you can get out of it on the Q.
05-27-2020, 06:49 PM   #12
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QuoteOriginally posted by jumbleview Quote
Does Tamron with Pentax Q fit?
That's a time when "deep pockets" has a new meaning.
05-27-2020, 07:18 PM - 1 Like   #13
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QuoteOriginally posted by barondla Quote
The Q will have better image quality than the Sony cropped. Cropping the Sony down to Q size won't provide anywhere near the 12mp resolution of the Q. Look at the comparision here on PentaxForums. Adam compared Q to cropped Nikon 810. Q beat the 32mp camera.

Are you sure the Sony has better image stabilization? The Q sensor is much smaller, and must be easier to position than a heavy full frame sensor.
Thanks,
barondla
I am assuming the Sony has better image stabilization for two reasons: 1) more recently developed, and 2) it is five axes (Full-frame camera with 5-axis image stabilization | a7 II | Sony US) which pretty much covers it all. I believe the Zeiss lens also has built-in stabilization. I do not believe that Q-S1 is so gifted. The Sony is the better camera, the Pentax is the more convenient and fun.

I also believe the Sony has better color and detail. But I am talking a more expensive camera with a more expensive Zeiss lens, 55mm f1.8, which is a very, very good lens (Zeiss FE 55mm f/1.8). Each camera has its place.

Regard: first photo is from the Q-S1, second from the Sony. Sony focus is off because I did not reset it from center point to grid. The Pentax is grid so it is in focus. I make it a point now to carry the Pentax. It is just so easy to slip into a pocket and punches so far above its weight. Comparison will be difficult as the both images are compressed for uploading.

Sorry to have been so long-winded but I did want to lay out the what and why vis a vis the Pentax and the Sony.

Cheers
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Last edited by boojum; 05-28-2020 at 02:57 AM. Reason: Added a thought
06-03-2020, 01:27 AM - 2 Likes   #14
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Hi boojum, others already gave you good answers but let me try anyway.

When we say Q-S1 sensor could in principle capture "more details" than A7RII, we're not necessarily talking about sharpness, we're talking about digitizing resolution. Pixels of A7RII sensor are huge, each is roughly 10 times as large in area as Q-S1's. If the lens is projecting fine details that are too small for the A7RII sensor, a finer-pitched sensor like Q-S1's could more faithfully digitize that.

Let me show you a comparison between Q7 (same sensor as Q-S1) and Pentax KP shooting the moon with 480mm f/6 telescope on the same night. These are shot RAW, I only adjusted white balance and exposure in lightroom to make them look similar, everything else is according to the default setting. Pixels in KP's 24Mpix crop sensor are more densely packed than your A7RII, but it's still only ~2.7Mpix inside the footprint of Q7 sensor (for A7RII it's about 1.2Mpix).

If you look at 1:1 crop of the same field of view (left is Q7, middle top is KP) the difference is apparent. All finer details are with better contrast using Q7 (e.g. look at two tiny mountains in the big crater), some of fine structures are so small they're almost completely invisible using KP (e.g. fine wrinkles of the ground outside of the crater, multiple ridges visible in the left inner slope of the crater).

If you scale down Q7's picture to the same size as KP's (middle bottom), it looks very similar to KP. In general you want to look at 1:1 crops without scaling down for accurate comparison though I suspect that not-too-large prints (e.g. letter size) will also expose the difference.

Just to give you a very rough idea, I also scaled down Q7's picture to show how it might look with A7RII.

I won't worry too much about f/8. An ideal f/8 lens can still project details that are too small for A7RII sensor (the threshold for that is at around f/18, that's eighteen) and that's what matters. Even though that's not too small for Q-S1 sensor (the threshold for Q-S1 is at around f/6), that doesn't mean that Q-S1 doesn't have an advantage. That's not to say that your f/8 lens is almost as good as an ideal f/8 lens, though, that's a different question.
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