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05-24-2020, 10:06 AM   #1
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645Z Cropping numbers

Can't hike with every 645Z lens. Figure the gap between lenses, especially teles, can be larger and the difference can be made up by cropping. Some questions about crop sizes.
1. How many megapixels are left when 645Z is cropped 1.5x (like K-1 to APS-c)?
2. When cropping the 645Z to roughly match the K-1, how many megapixels are left?

I'm looking at telephotos for the Z and trying to figure out what is needed. Would love to carry a 300 and 400 but that's too much weight for me to hike with. Leaning towards the 645 300 5.6 but it won't work with the 1.4x teleconverter.

Thanks,
barondla

05-24-2020, 11:03 AM - 3 Likes   #2
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1. 51.4 divided by 1.5 twice is 22.8 MPix

2. Cropping the 33x44 mm 645Z sensor to the 24mm x 36mm frame of the K-1 yields 30.6 Mpix
05-24-2020, 11:05 AM - 2 Likes   #3
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Hi barondla,
QuoteOriginally posted by barondla Quote
1. How many megapixels are left when 645Z is cropped 1.5x (like K-1 to APS-c)?
8256*6192/(1.5^2)=22720512 pixels ~22.7 megapixels.
QuoteQuote:
2. When cropping the 645Z to roughly match the K-1, how many megapixels are left?
As a rough number, you can multiply 645Z pixel count with the square of the ratio of the crop factor of 645Z sensor to that of K-1 (but K-1's crop factor is supposed to be 1). That would be the pixel count when you crop such that the diagonal length of the cropped part on the 645Z sensor is equal to the diagonal length of the K-1 sensor.

8256*6192*0.79^2~31.9 megapixels.

If you crop so the resulting field of view becomes the same as on K-1 using a lens of the same focal length, the pixel count would be that of 645z multiplied by the ratio of the physical sensor area of K-1 to 645Z. The result is somewhat different from the crop factor based number due to different aspect ratio of the two sensors, but not overly so.

8256*6192*((35.9*24 mm^2)/(43.8*32.8 mm^2)) ~ 30.7 megapixels.

[Edit]
photoptimist, you beat me to it!
05-24-2020, 11:53 AM - 1 Like   #4
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You can of course resample and retain the same MP count

The real question is what do you do with your images ? If you want to print large then you need to employ a sherpa to carry all your 645 lenses. For web posing no problem, just resize

05-24-2020, 11:58 AM - 1 Like   #5
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QuoteOriginally posted by barondla Quote
Can't hike with every 645Z lens.
---well, no. That would require a burro, which is what Anselm Adams used on occasion.

QuoteQuote:
I'm looking at telephotos for the Z and trying to figure out what is needed. Would love to carry a 300 and 400 but that's too much weight for me to hike with. Leaning towards the 645 300 5.6 but it won't work with the 1.4x teleconverter.

Thanks,
barondla
So, your post has me scratching my head a bit. Maybe you could be more specific? As in, how many lenses/which ones; what sort of tripod and head; and what else is in the pack; and then, what pack? Also, what is a "hike": how far, elevation gain, time of year, location, & etc. Finally, do you also have physical constraints?

I ask because I have hiked with a sizeable kit and done ok, and I'm 64 and no triathlete be any stretch....
05-24-2020, 07:44 PM - 1 Like   #6
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I’ve hiked with the 400–the FA 400 is noticeably lighter than the A* 300–much more plastic in the barrel. Bulk is the issue.

I’ve hiked with a 35, 45-85, 200, and 1.4, which is a compact and effective combo that all fit in a waist pack.

I’ve also hiked with a 35, 55, 200, and 400, all on a waist belt. (The 55 in case it started raining).



Now, it might be the 28-45, 45-85, and the 80-160. Or the 28-45, 45-85, and 200.

There are so many things to photograph the I just choose subjects and compositions that fit what I have.

Rick “who used to hike with a much heavier 4x5 kit in a Kelty external-frame expedition pack” Denney
05-25-2020, 01:20 AM - 1 Like   #7
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Hi barondla,

although the crop factor is a factor that's represented by one single value, it's IMO kind of weird to compare the Z sensor area with the K-1's since you compare different image ratio's - 4:3 vs. 3:2. That means different visual image appearances. So, IMO you should only have a look at the 645Z with its 4:3 ratio.

Notwithstanding the above my computation says crop factor of the 645Z compared to K-1 is ~0.82 - a 55mm lens on 645Z will roughly offer the diagonal angle of view of an 45.1mm lens attached to the K-1.

I guess this isn't really what you want to know.

What about how to crop a 645Z image to get the angle of view of a longer focal length on the 645?
Here are the results of specific computations based on a computer program I developed some time ago. Hope the examples do help you to get an impression of scenarios.

Let's assume you use a 35mm lens on the 645Z.

Then to get the angle of view of a 55mm lens (i.e. equiv. 45mm on K-1 FF) you have to crop the image to 5260 x 3940px = 20.72 Megapixel.

If you'd like to get the angle of view of a 300mm lens you have to crop the image to 964 x 722px, only 0.7 Megapixel! ... not that much

To get something usable, you have to change your lens. Let's say you choose a 200mm lens. Then you have to crop to 5510 x 4128px (22.75 Megapixel). Much better and usable.

If you use a 300mm lens you get the angle of view of a 400mm lens cropping to 6199px x 4644px (28.79 Megapixel) and 500mm by cropping to 4959 x 3715px (18.42 Megapixel).

Does this make sense to you and does it help to decide which focal length to purchase?

regards, acoufap
05-25-2020, 05:22 AM - 1 Like   #8
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I too struggle with the question. I occasionally do 1:4 ratio crops (this is the 'longest' I can easily get printed commercially). In this case the, K-1 provides more pixels than my D due to the ratio difference - I'd still probably prefer using the D.

Hiking is dependent on many factors, not least the bag/backpack arrangement. As long as I've got the space (more correctly don't need space for 'hiking' gear), bulk isn't a problem. Weight can be offset by a backpack with a very good harness, my LowePro Trekker 400AW... has such a harness (proper hiking rig with weight bearing waist belt). The bag weighs 3kg empty but more than makes this up in comfort.

Lenses wise, once you get to 300 or longer, your tripod/head and how you carry them become issues. If I wanted to get to 300 I'd probably limit myself to just my FA33-55 and A*300, otherwise probably FA33-55, FA45-85, DFA55 (WR) and late 67 200 (if going a long way the FA45-85 might be left behind).

05-25-2020, 06:33 AM - 1 Like   #9
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Original Poster
QuoteOriginally posted by texandrews Quote
---well, no. That would require a burro, which is what Anselm Adams used on occasion.

So, your post has me scratching my head a bit. Maybe you could be more specific? As in, how many lenses/which ones; what sort of tripod and head; and what else is in the pack; and then, what pack? Also, what is a "hike": how far, elevation gain, time of year, location, & etc. Finally, do you also have physical constraints?

I ask because I have hiked with a sizeable kit and done ok, and I'm 64 and no triathlete be any stretch....
At the moment my 645 kit is a DFA645 55MM, A 120 macro, and a FA80-160. Have a DFA645 35 3.5 on the way (if Auspost ever figures out how to actually ship it). I will end up purchasing a 300 or 400. Tripod is an old Gitzo Reporter with medium size Linhof ball head.

I'm 60, in decent health, but heavier than optimal. Hikes depend on how far it is to get to the site. I rarely hike for fun. To the south land is flat and relatively easy to hike. N,E,W are hilly to major hilly with numerous ravines that greatly impacts distance of hike.

I don't own a proper backpack. For APS-c always carried the little Domke with 3 to 4 lenses (mostly small, none of that f2.8 madness). Getting back into medium format snuck up on me. I will now have to learn about backpacks, which I've always hated. Compared to a Domke working from a backpack is a pia.

So the 300 5.6 is looking like the best alternative for me. I love 300mm on FF or APS-c. and worry that it will be a little short on MF. Hence the crop questions. Thanks for the help.

---------- Post added 05-25-20 at 08:38 AM ----------

QuoteOriginally posted by acoufap Quote
Hi barondla,

although the crop factor is a factor that's represented by one single value, it's IMO kind of weird to compare the Z sensor area with the K-1's since you compare different image ratio's - 4:3 vs. 3:2. That means different visual image appearances. So, IMO you should only have a look at the 645Z with its 4:3 ratio.

Notwithstanding the above my computation says crop factor of the 645Z compared to K-1 is ~0.82 - a 55mm lens on 645Z will roughly offer the diagonal angle of view of an 45.1mm lens attached to the K-1.

I guess this isn't really what you want to know.

What about how to crop a 645Z image to get the angle of view of a longer focal length on the 645?
Here are the results of specific computations based on a computer program I developed some time ago. Hope the examples do help you to get an impression of scenarios.

Let's assume you use a 35mm lens on the 645Z.

Then to get the angle of view of a 55mm lens (i.e. equiv. 45mm on K-1 FF) you have to crop the image to 5260 x 3940px = 20.72 Megapixel.

If you'd like to get the angle of view of a 300mm lens you have to crop the image to 964 x 722px, only 0.7 Megapixel! ... not that much

To get something usable, you have to change your lens. Let's say you choose a 200mm lens. Then you have to crop to 5510 x 4128px (22.75 Megapixel). Much better and usable.

If you use a 300mm lens you get the angle of view of a 400mm lens cropping to 6199px x 4644px (28.79 Megapixel) and 500mm by cropping to 4959 x 3715px (18.42 Megapixel).

Does this make sense to you and does it help to decide which focal length to purchase?

regards, acoufap
Makes sense to me. Thanks.

---------- Post added 05-25-20 at 08:39 AM ----------

QuoteOriginally posted by photoptimist Quote
1. 51.4 divided by 1.5 twice is 22.8 MPix

2. Cropping the 33x44 mm 645Z sensor to the 24mm x 36mm frame of the K-1 yields 30.6 Mpix
Thanks this helps a lot.

---------- Post added 05-25-20 at 08:42 AM ----------

QuoteOriginally posted by kwb Quote
Hi barondla,

8256*6192/(1.5^2)=22720512 pixels ~22.7 megapixels.
As a rough number, you can multiply 645Z pixel count with the square of the ratio of the crop factor of 645Z sensor to that of K-1 (but K-1's crop factor is supposed to be 1). That would be the pixel count when you crop such that the diagonal length of the cropped part on the 645Z sensor is equal to the diagonal length of the K-1 sensor.

8256*6192*0.79^2~31.9 megapixels.

If you crop so the resulting field of view becomes the same as on K-1 using a lens of the same focal length, the pixel count would be that of 645z multiplied by the ratio of the physical sensor area of K-1 to 645Z. The result is somewhat different from the crop factor based number due to different aspect ratio of the two sensors, but not overly so.

8256*6192*((35.9*24 mm^2)/(43.8*32.8 mm^2)) ~ 30.7 megapixels.

[Edit]
photoptimist, you beat me to it!
Great info, thanks

---------- Post added 05-25-20 at 08:45 AM ----------

QuoteOriginally posted by rdenney Quote
I’ve hiked with the 400–the FA 400 is noticeably lighter than the A* 300–much more plastic in the barrel. Bulk is the issue.

I’ve hiked with a 35, 45-85, 200, and 1.4, which is a compact and effective combo that all fit in a waist pack.

I’ve also hiked with a 35, 55, 200, and 400, all on a waist belt. (The 55 in case it started raining).



Now, it might be the 28-45, 45-85, and the 80-160. Or the 28-45, 45-85, and 200.

There are so many things to photograph the I just choose subjects and compositions that fit what I have.

Rick “who used to hike with a much heavier 4x5 kit in a Kelty external-frame expedition pack” Denney
Great to know about the 400. May end up with 300 & 400 but only take 1 on hike.

---------- Post added 05-25-20 at 08:46 AM ----------

QuoteOriginally posted by acoufap Quote
Hi barondla,

although the crop factor is a factor that's represented by one single value, it's IMO kind of weird to compare the Z sensor area with the K-1's since you compare different image ratio's - 4:3 vs. 3:2. That means different visual image appearances. So, IMO you should only have a look at the 645Z with its 4:3 ratio.

Notwithstanding the above my computation says crop factor of the 645Z compared to K-1 is ~0.82 - a 55mm lens on 645Z will roughly offer the diagonal angle of view of an 45.1mm lens attached to the K-1.

I guess this isn't really what you want to know.

What about how to crop a 645Z image to get the angle of view of a longer focal length on the 645?
Here are the results of specific computations based on a computer program I developed some time ago. Hope the examples do help you to get an impression of scenarios.

Let's assume you use a 35mm lens on the 645Z.

Then to get the angle of view of a 55mm lens (i.e. equiv. 45mm on K-1 FF) you have to crop the image to 5260 x 3940px = 20.72 Megapixel.

If you'd like to get the angle of view of a 300mm lens you have to crop the image to 964 x 722px, only 0.7 Megapixel! ... not that much

To get something usable, you have to change your lens. Let's say you choose a 200mm lens. Then you have to crop to 5510 x 4128px (22.75 Megapixel). Much better and usable.

If you use a 300mm lens you get the angle of view of a 400mm lens cropping to 6199px x 4644px (28.79 Megapixel) and 500mm by cropping to 4959 x 3715px (18.42 Megapixel).

Does this make sense to you and does it help to decide which focal length to purchase?

regards, acoufap
Thanks for the extra math. It makes things clearer for me.

Thanks everyone,
barondla

Last edited by barondla; 05-25-2020 at 06:48 AM.
05-25-2020, 06:47 AM   #10
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QuoteOriginally posted by rdenney Quote
I’ve hiked with the 400–the FA 400 is noticeably lighter than the A* 300–much more plastic in the barrel. Bulk is the issue.

I’ve hiked with a 35, 45-85, 200, and 1.4, which is a compact and effective combo that all fit in a waist pack.

I’ve also hiked with a 35, 55, 200, and 400, all on a waist belt. (The 55 in case it started raining).



Now, it might be the 28-45, 45-85, and the 80-160. Or the 28-45, 45-85, and 200.

There are so many things to photograph the I just choose subjects and compositions that fit what I have.

Rick “who used to hike with a much heavier 4x5 kit in a Kelty external-frame expedition pack” Denney
Hey, like that photo. Good promo photo for Pentax! Noting the bear bell (been in serious bear country w/o one, and felt like an idiot/dinner...). Also noting the crampons on less than heavyweight boots---how did that work out?
05-25-2020, 07:04 AM - 2 Likes   #11
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QuoteOriginally posted by barondla Quote
At the moment my 645 kit is a DFA645 55MM, A 120 macro, and a FA80-160. Have a DFA645 35 3.5 on the way (if Auspost ever figures out how to actually ship it). I will end up purchasing a 300 or 400. Tripod is an old Gitzo Reporter with medium size Linhof ball head.

I'm 60, in decent health, but heavier than optimal. Hikes depend on how far it is to get to the site. I rarely hike for fun. To the south land is flat and relatively easy to hike. N,E,W are hilly to major hilly with numerous ravines that greatly impacts distance of hike.

I don't own a proper backpack.
And there we have it...which is why I asked the questions. BTW, you should love the DFA 35.

So, I think consider several things. You don't say exctly which model of Gitzo, but I think there are better options for you now. Also, I recommend an Acratech head for the best combo of strength/quality/weight. I have 2 of them, the macro one and the one that converts to a pano head. They really are great. I have an older Feisol that I use when needing to hike in, a 3224 I think, which at the time had the best weight/height/sturdiness/cost combination. Since I bought it there are other good options, though. I also have a big Leofoto, their largest, that I can walk under fully extended, and I have actually hiked with it. I'd use the Feisol if I had to go more than a couple of miles.

And then there's the Backpack. Personally, I'd say this is the real issue. If you're going to go any distance, there just is no good option other than a good pack. I use a Mindshift 30L, and it has been super---the best I've tried. It can be worn multiple ways, can swing around so that you can access the lower gear compartment w/o taking it off, and hold a ton of stuff. The shoulder straps are excellent, as is the waist belt---and the waist belt is at least as important as the shoulder straps. The pack itself is among the lightest available (some packs are weirdly heavy by themselves), has other great features. One feature I like best: it doesn't look like it, but it conforms to overhead bin regulations for air travel.

If you're going to hike with more than just the camera and a lens, you just gotta have the pack.

Finally, like you my weight is not optimal, but unlike you I looooove to hike. That's your final hurdle, learning to like that. It's actually wonderful, and a lot better with the proper gear. Good luck with your decisions!
05-25-2020, 08:11 PM - 1 Like   #12
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QuoteOriginally posted by texandrews Quote
Hey, like that photo. Good promo photo for Pentax! Noting the bear bell (been in serious bear country w/o one, and felt like an idiot/dinner...). Also noting the crampons on less than heavyweight boots---how did that work out?
The boots were a mistake, of course. But the black toenails had grown out after a...year. The real problem with those boots emerged when hiked up to Mount Marathon Bowl (actually, when coming back down).



The downhill walk on that hike revealed just how poorly the boots were securing my feet. I retightened the laces at least 50 times.

But when you find Size 15 boots on sale, you buy them. Sometimes, you get more than what you pay for. Sometimes, you don't. The heck of it is that my old REI boots are still great and would have been a much better choice, but I really wasn't expecting the heavy hiking on this trip. I had just lost a bunch of weight in a crash diet and was in the midst of a cancer scare--now, I'm 18 months after the (successful) cancer surgery, another 20 pounds lighter, and back into regular workouts. My wife's hiking club was supposed to be doing the hiking, while I poked around with my camera on my own. But I'm an old endurance triathlete, and dropping the weight made the hikes too tempting to pass up, especially when I found I was as fit a hiker as nearly everyone in our group.

But on the day we spent on the Root Glacier, my big toes had stopped hurting and the boots were no problem at all. Not that much steepness, just a lot of ice, and some of it had a layer of water on it and was slippery as could be. The crampons were necessary just for safety. But those boots have not been on my feet since that trip.



Here's another view of what I was carrying on the Root:


The backpack was lunch and water, not photo stuff. All the photo stuff was on the belt. No tripod, though. Notice how I was using the neck strap as a stabilizer for the shot--a strap under sufficient tension is a structural member. Here's the photo I was making:



The moulin was at least a couple of hundred feet deep.

Somewhere, I have a picture of myself down in the Maze at Canyonlands NP, with a large Kelty backpack loaded with a Cambo SC (not exactly optimized for the backcountry!), three lenses (for the OP--90mm, 121mm, and 210mm--nearest to the 35, 45, and 75 on the 645z), ten film holders, a Pentax light meter, and a disgustingly heavy Bogen 4030 tripod that I still use with my Sinar. That picture was the only interesting picture I got out of that trip--all the large-format film was fogged for reasons I never discovered. I've never mastered the art of traveling with a large-format camera, and quickly learned that lesson. That's when I switched to medium format in addition to 35mm. Were it not for COVID-19, I would today be driving from Antelope Slot Canyon back to Moab, after having spent a week in the Escalante Basin. Maybe September, or next year.

By the way, I didn't just have the bear bell. Notice the bear spray on my belt? I'm mighty glad I didn't need either. The closest I've come to a bear in Alaska was running across (very) fresh scat on a hike my wife and I took back to Humboldt Glacier about 20 years ago.

Rick "sorry for the off-topic excursion" Denney

Last edited by rdenney; 05-25-2020 at 08:41 PM.
05-26-2020, 02:55 AM - 1 Like   #13
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I always bring my FA 150-300 mm f/5.6 along but sometimes I feel it lacks a "little reach" or "magnification" despite permitting great versatility in image framing. That's when I appreciate my FA 400 mm f/5.6 the most, although both lenses are voluminous but not so massive and really quite light. I have the 1.4X converter and it is usable on the 400 mm too. When you visit a new place for the first time and you don't know what to expect (visually I mean), bring the zoom. If you estimate the place requires a longer focal length, simply return there with the 400 mm + converter.


Regards !
05-26-2020, 07:42 AM - 1 Like   #14
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QuoteOriginally posted by RICHARD L. Quote
I always bring my FA 150-300 mm f/5.6 along but sometimes I feel it lacks a "little reach" or "magnification" despite permitting great versatility in image framing. That's when I appreciate my FA 400 mm f/5.6 the most, although both lenses are voluminous but not so massive and really quite light. I have the 1.4X converter and it is usable on the 400 mm too. When you visit a new place for the first time and you don't know what to expect (visually I mean), bring the zoom. If you estimate the place requires a longer focal length, simply return there with the 400 mm + converter.
The 400 is not particularly heavy, as you say. But the tripod you'll need for the 400 plus the 1.4x converter might make up for that.

Rick "whose lightweight Gitzo worked well enough with high shutter speeds, but that required higher ISO settings" Denney
05-26-2020, 08:41 AM - 1 Like   #15
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True, you need a tripod with the 400 mm but it's the second time you get there, so you know better what to expect ... lol ! Bring your llama, like Ansel Adams thought of doing.

Regards !
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