Confused about focal length

NabilY

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Hi!

I used to have a SONY DSC-HX50V camera and now I have a Sony A7 II. I want to buy a lens for my new camera with a similar zoom.

The DSC-HX50V states it has a (F=35MM) 24-720mm focal length, does that mean I would need a lens with up to about 720mm for my Sony A7 II? The standard length says 28-70.

In short: What focal length is needed for my Sony A7 II (35 mm full frame cmos sensor) to get the same zoom as the SONY DSC-HX50V?

Specs for the DSC-HX50V:
https://www.sony.com/electronics/cyber-shot-compact-cameras/dsc-hx50-hx50v/specifications


Thanks!
 

gondo

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Lets try to explain this. Your old compact HX50V had a CMOS sensor much smaller than the older 35mm cameras. Your new A7 II has a full frame sensor the same size as the old 35mm cameras. The old sensor is exactly 5.6 times smaller (diagonally) than the new full frame one. This 5.6 is known as the crop factor.

So here is what you need to know. The smaller sensor of the old HX50V camera that is 5.6 times smaller captures way less light and works poorly in dim conditions. The new camera has a very large sensor and captures the best quality images and gathers the most light. Hense the large size of the camera and the high price.

However when you look at the physics of it, the 5.6x smaller sensor has an effect of making the image appear zoomed in 5.6 times. This is known as the crop factor. The lense is the same size, but because the sensor can only see 5.6 times less of the image it appears zoomed in. Imagine using the same lense and looking at a tree with both cameras. With a full frame camera you see the whole tree. With the small sensor you see 5.6 times less so you see the middle part of the tree or some branches. Essentially like it's zoomed in. You sensor is so small it can only see part of the image.

So the old camera had exactly a focal length of 4.3mm-129mm. Not very much, which explains the small size of the compact camera. But because of the small sensor and the 5.6x crop factor it was virtually like having a 24-720mm lense on a full frame sensor camera. Just multiply the 4.3mm and 129mm by 5.6. So the advantage of a cheap small sensor is you instantly get telephoto lenses. What most people don't realize though is that the quality is way less than with a full size sensor. You could take the same picture with a full frame camera, crop the image on a computer in photoshop and make it look like it's zoomed it and it'll probably have better quality than the original zoomed in picture on the cheaper camera.

That 30x optical zoom you mention is just the high end of the lense divided by the low end. So 129/4.3 or 720/24. Optical zoom means nothing. It just tells you the ratio of the high end of the zoom to the low end. You could have a 1000-30,000mm lense and it's still 30x optical zoom, but it's 30,000mm which is 42 times better than the 720mm. It's all advertising and means nothing.

Just remember your old camera had a sensor 5.6 times smaller. Way less quality, way less light. Forget shooting indoors in low light, or at night. Your new full frame can gather light and quality like a beast. It's great for night photography, night sky shots, city streets at night, and indoors dim shots like wedding receptions. Give your new camera a good lense and you'll be in heaven.

As for the lense. Your old one was exactly a 129mm, but virtually looked like a 720mm when looking through it due to the small sensor. So if you put a 129mm on your new camera it'll gather a similar quality image of the tree, if you put the image in photoshop and crop it to only see the branches. Or you could get a 720mm lense and get the same photo straight out of the camera, but the image quality will blow the old one out of the water.

Another thing to look at is the aperture or speed of the lense. The F value. The smaller the number the bigger the diameter of the lense and more light it gathers. If you get for example an F/2.8 lense for your new camera it would have been equivalent to a much higher F number because of the small sensor gathering so little light. You'll notice that F2.8 and lower lenses are considered high end and designed for night shots. They are very large, heavy, and expensive. Going above F2.8 results in much lower quality but a more affordable lense. F2.8 seems to be the value between quality and price. F1.8 is more for enthusiasts and pros. If you want very good without breaking the bank look at 2.8.

The aperture or F value of the lense is a much more important thing to look for than the focal length.

Google F stop values and read up on it. Also google crop factor and sensor sizes and read up fast on that. If you really want to zoom in look at digiscoping. basically using a small spotting scope or land telescope on a tripod and using an adaptor to hook your camera to it. The gives you 1000mm territory without spending a fortune. You can do it for under $1000 whereas an actual camera lense would cost over $10,000.


 

kanewolf

Splendid
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You can't get a 30X zoom lens for a DSLR. Most DSLR long (200mm+) are 3X or 4X There are some expensive lenses that are 10X (35mm-350mm) but you can't duplicate what a video camera does with a single lens on a DSLR.

If they say that the video camera has a 35mm equivalent of 24 - 720 then, yes you would have to get a 800mm lens to duplicate it.
 

gondo

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Lets try to explain this. Your old compact HX50V had a CMOS sensor much smaller than the older 35mm cameras. Your new A7 II has a full frame sensor the same size as the old 35mm cameras. The old sensor is exactly 5.6 times smaller (diagonally) than the new full frame one. This 5.6 is known as the crop factor.

So here is what you need to know. The smaller sensor of the old HX50V camera that is 5.6 times smaller captures way less light and works poorly in dim conditions. The new camera has a very large sensor and captures the best quality images and gathers the most light. Hense the large size of the camera and the high price.

However when you look at the physics of it, the 5.6x smaller sensor has an effect of making the image appear zoomed in 5.6 times. This is known as the crop factor. The lense is the same size, but because the sensor can only see 5.6 times less of the image it appears zoomed in. Imagine using the same lense and looking at a tree with both cameras. With a full frame camera you see the whole tree. With the small sensor you see 5.6 times less so you see the middle part of the tree or some branches. Essentially like it's zoomed in. You sensor is so small it can only see part of the image.

So the old camera had exactly a focal length of 4.3mm-129mm. Not very much, which explains the small size of the compact camera. But because of the small sensor and the 5.6x crop factor it was virtually like having a 24-720mm lense on a full frame sensor camera. Just multiply the 4.3mm and 129mm by 5.6. So the advantage of a cheap small sensor is you instantly get telephoto lenses. What most people don't realize though is that the quality is way less than with a full size sensor. You could take the same picture with a full frame camera, crop the image on a computer in photoshop and make it look like it's zoomed it and it'll probably have better quality than the original zoomed in picture on the cheaper camera.

That 30x optical zoom you mention is just the high end of the lense divided by the low end. So 129/4.3 or 720/24. Optical zoom means nothing. It just tells you the ratio of the high end of the zoom to the low end. You could have a 1000-30,000mm lense and it's still 30x optical zoom, but it's 30,000mm which is 42 times better than the 720mm. It's all advertising and means nothing.

Just remember your old camera had a sensor 5.6 times smaller. Way less quality, way less light. Forget shooting indoors in low light, or at night. Your new full frame can gather light and quality like a beast. It's great for night photography, night sky shots, city streets at night, and indoors dim shots like wedding receptions. Give your new camera a good lense and you'll be in heaven.

As for the lense. Your old one was exactly a 129mm, but virtually looked like a 720mm when looking through it due to the small sensor. So if you put a 129mm on your new camera it'll gather a similar quality image of the tree, if you put the image in photoshop and crop it to only see the branches. Or you could get a 720mm lense and get the same photo straight out of the camera, but the image quality will blow the old one out of the water.

Another thing to look at is the aperture or speed of the lense. The F value. The smaller the number the bigger the diameter of the lense and more light it gathers. If you get for example an F/2.8 lense for your new camera it would have been equivalent to a much higher F number because of the small sensor gathering so little light. You'll notice that F2.8 and lower lenses are considered high end and designed for night shots. They are very large, heavy, and expensive. Going above F2.8 results in much lower quality but a more affordable lense. F2.8 seems to be the value between quality and price. F1.8 is more for enthusiasts and pros. If you want very good without breaking the bank look at 2.8.

The aperture or F value of the lense is a much more important thing to look for than the focal length.

Google F stop values and read up on it. Also google crop factor and sensor sizes and read up fast on that. If you really want to zoom in look at digiscoping. basically using a small spotting scope or land telescope on a tripod and using an adaptor to hook your camera to it. The gives you 1000mm territory without spending a fortune. You can do it for under $1000 whereas an actual camera lense would cost over $10,000.


 

NabilY

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Aug 6, 2017
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Thanks for a wonderfully thorough answer! This surely clears things out for me and I feel a lot smarter already. I'll look those things up. So many new terms to get familiar with. Photography is science!

Although kanewolf's answer was more direct and answered my question perfectly fine (as asked), it would feel unfair to not give the correct answer to the very detailed answer. I thank both of you.
 

NabilY

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Instead of creating a new thread I'd like to know if this one is decent:

Sony E 55-210/4,5-6,3 OSS (for Nex)

It's a rather cleap lens. Would it have bad quality (considering the high F-number)?

Also, can any Sony E-mount use the Nex?
 

gondo

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The Sony A7 II uses the E mount lenses. You can get E mount in 2 different sizes...APS-C or Full Frame. Basically the size of the hole in the back of the lense. You have a full frame sensor so with a full frame lense you get the full 24mp of your camera. Your camera can also use APS-C lenses but it will only use a portion of the sensor equivalent to APS-C size and the resulting picture will be about 10-12MP or so depending on if you shoot in 3:2 or 16:9 mode. The A7 II has a crop mode setting for using APS-C lenses. The Sony has a crop factor of 1.5x so that 55-210mm lense would be equivalent to 83-315mm.

If you can, go for a full frame lense and take advantage of your $1800 camera.

The bad news is there isn't much support for E-Mount yet. E-Mount was designed for Sony mirrorless cameras that are light, compact, and have DSLR quality. Take a DSLR Canon lense for example and Sigma can do a minor tweak and make it Nikon or Pentax compatible. An E-MOunt lense requires a whole new design. That's why there is not much from Tamron, Sigma, and Rokinon/Samyang in the E-Mounts.

That being said Sony has a 70-200mm F4 full frame Emount that is around $1600. An F 2.8 version is over $3000. Those are pro level lenses that match up quite well with the pro level of your $1800 camera. With an $1800 camera it's expected that you will invest many times that amount in lenses. Lenses can last a user 30+ years while some people upgrade camera bodies every 2-3 years. It's not uncommon for pros to have a $1000 camera with over $10,000 in lenses. Using a $400 lense with an almost $2000 full frame camera seems kind of pointless but it's possible.

So I checked all the Sigma, Tamron, Rokinon stuff and there isn't much. Sony has that 55-210mm in APS-C format as you said. It's small, light, portable, and the picture quality is not terrible. Not great but not terrible. It's a great value. But if you can swing it that 70-200mm F4 is a great lense. Being F4 it'll allow about 3 times more light than the F6.3 of the cheaper lense which would be better. You can compensate by upping the ISO which results in grainier pictures, or reduce the shutter speed with induces blur or requires a tripod. F 2.8 is when you enter the realm of night photography such as city streets at night or indoors like at a club, concert, wedding reception where it's dark. You can also see how expensive it is.

The F2.8 is 1480g, The F4 is 840g. The F4-6.3 is 345g. You can see the big difference here. The F2.8 is over 4 times heavier. the F2.8 is also almost twice as long. So you can see the advantage of the cheaper lense as a walkaround lense. The full frame lenses are also weather resistant to match your camera body.

Hope this helps you out without you getting too discouraged with E-Mount stuff :) Great cameras but not quite as common as Nikon/Canon stuff. The only reason Nikon and Canon sell soo many cameras is they had tons of lense options and people who own thousands of dollars worth won't get rid of it all to change camera brands. Build the lenses and people will buy your cameras.

 

gondo

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To clear things up, when Sony first released mirrorless cameras in 2010 they had APS-C size sensors. The cameras where called the NEX series. If you see a Nex series lense it's APS-C format. It's still E-Mount though but designed for that sensor size.

Full Frame E-Mount lenses are listed as Full Frame. They are also sometimes called FE mount or full frame e-mount.

Your camera can use either but with the APS-C remember the crop factor of 1.5x and you need to set your camera into crop mode.
 

gondo

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Looking around there are some Sony telephotos in the $1000 range. Also some Sigmas around $1000. The Sigmas include an adapter to convert their Canon lense to E-Mount but it maintains image stabilization and auto focus.

In the 18-50mm range I saw some fast primes of F1.8 for under $400. But for telephoto that 55-210mm for $350 is it. After that you jump into $1000 territory. Keep in mind the $1000 lense will be weather proof and full frame.

I think I would go for the Sony FE 70-300mm f/4.5-5.6 G OSS for $1200 or the 70-200mm F4 for $1500. Those are good values for performance without getting too crazy.

Also no matter which lense you choose, don't underestimate getting a polarizer filter. it can make a big difference in reducing glare so you can see into water, or take pictures of windows or store fronts without reflections. And skies pop much bluer.
 

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