Full frame - I'm confused

Grendel

Grendel

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Paul
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At the risk of appearing silly I wonder if you can help me to understand something :shrug: . Most sensors on DSLRs have a crop factor. 1.6 on my Canon 400D. So a 300mm lens on my camera equates to 480mm, a 50mm equates to 80mm etc. If I understand correctly, if I put the same lens on a full frame camera I would get the true focal length of the lens - 300mm = 300mm, 50mm = 50mm. So my question is this: What's the benefit of buying a full frame camera if I'm effectively going to loose focal length from my lenses :thinking:
 
The focal length of the lens does not change, what you see in a crop camera is a proprtion of the view of the lens. This equates to the same area you sould see on a full frame if you zoomed in 1.6 times

The benifit of full frame is a much brighter and bigger viewfinder, Higher quality redition of the image and less noise at higher ISO's. However. A full frame is not so forgiving on lenses as it uses more of it.

So, if your lenses are not high quality, the benifit may be lost.

Well thats as I see it, someone will be along in a min to show how wrong I am

Steve
 
The_old_man said:
The focal length of the lens does not change, what you see in a crop camera is a proprtion of the view of the lens.
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Quite correct..:thumbs:



The_old_man said:
Well thats as I see it, someone will be along in a min to show how wrong I am

Steve
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No sir, You explained it very well.:)

I read all over the place people talking about the crop factor giving a better reach. Not true..:nono:
 
Well the effect of the 1.6 conversion is that you DO get an effective better reach. Although it's a 10Mp crop you see.

Other than perhaps wanting a little lower noise, I'm happy with the 1.6x crop factor. I hace lenses from 10mm - 300mm (16mm - 480mm equiv) so other than noise I'm happy. Also a benefit is that I have an 8mp image from the 1.6 crop. The 5D has effectively less resolution for the same image when cropped.

I'll not be upgrading for a while and if I do it would likely be for a 1dMkIIN.
 
Might be easier in a picture

Inside the white box is what a crop sensor will see, all of the image is what a full size sensor will see.

Now if you take an image with a 12.8mp full sensor camera and crop it to the same as you see in a crop sensor you will get about 8mp. So a full frame 5D cropped to show the same image as a 30D gives about the same resolution

eos_5d_beauty_hires_02_Small_.jpg
 
Except that the full framers have larger pixels and therefore lower noise and higher IQ in that 'crop'
 
If four of us stood side by side, but using 1.5, 1.3, 1.6 and full frame cameras respectively, but all using the same focal length lens we'd all record the same size image of our actual subject (let's say it's a Robin) on the sensor.

The problem is with long lenses anyway, the bigger the sensor the more you'd crop to get a decent size image of your Robin. So that's the real problem.... full frame sensors are great if you can really fill the frame with your subject and take advantage of that large sensor, but that means getting very close or using very expensive monster lenses, and even then it's difficult to fill that full frame.

For landscape and less extreme telephoto work though, the benefits are more obvious. :)
 
Just a note to finish with

The quality difference you will see on a normal PC screen or tft, or if you print at normal sizes will hardly be noticable by anyone but a pruist. If you are going full frame, remember its a lot more money. The camera is more and the cheaper lenses will look "bad"

I am going to buy a full frame in the next few weeks. The reason I am doing this is that I wish to go higher quality. Its a personal thing. Unless you have a real good reason for a full frame or a lot of money in your pocket I cannot see the benifit.

Steve
 
If you look at the sensor size and pixels then the 20D/30D has 156pixels per mm compared to the 5Ds 122 pixels per mm. Not a big difference right enough but I've still not got a big enough reason to upgrade.

The 400D has 175 pixels per mm which is the highest of any Canon dSLR. I understand though that more pixels sqeezed into the smaller spaces = more noise but my 20D seems great in this respect.

Maybe next generation may entice me!
 
FWIW, I've been using the 20D quite alot with the 500mm,in preference to the 1DMk2n, particularly with longer shots, as it just means less cropping. :shrug:
 
Thanks very much for all the very informed answers guys. I understand this issue a whole lot better now :thumbs:
 
Ok, you've all lost me completely now. :bang:
 
Simple

Option 1
Very high quality everyday use, portrait and landscape = 5D with high quality lenses. So it costs a lot

Option 2
High quality everyday, wildlife, portrait and landscape = 20D and good lenses. So it costs a lot, but not as much as option 1

However, if money is not a problem then get the 1Dn and the 1Ds

There you go, nice and simple...... NOT
 
Jason said:
Ok, you've all lost me completely now. :bang:
Click to expand...

This is an uncropped shot at 700mm on the 1DMk2n.

700mmRobin1.jpg


I'd want to crop this quite a bit to show the bird larger in the frame. If I'd used the 20D with the same lens, I'd have got exactly the same size image on the sensor but with a less wide view of the robin's surroundings (due to the smaller sensor), so I'd have to crop quite a bit less.

If on the other hand I'd used a full frame camera (I don't got one anyway) I'd still have got the same size image of the robin, but quite substantially more of his surroundings too, so I'd have to crop even more of the image to frame the shot as I'd like.

In other words I'd be getting no image quality advantage from that full fame sensor at all.

For landscapes, wedding work and portraits though where you can easily fill the frame with your subject, there are real advantages in the full frame format, but you'd need to print very large images to see the improvement in quality.

Hope that helps. :)
 
The crop factor also effects the DOF by increasing it throughout the range.
 
Thanks CT, i think i've got it now.
 
And I've just discovered today that digital lenses don't work very well with full frame film cameras :bang: I have 36 beautifully composed landscape shots....that are all circular :'( They were my best shots of the day too :(

Because my Sigma 10-20mm lens is designed for my D70, there is some severe vignetting going on.
 
But Nikon don't do a FF dSLR?
 
whitewash said:
yeh i took a couple of shots with a digital (18-50mm DC sigma) on my eos5, saves time and effort on putting a border on the image.....
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But I can't use any of the shots for my college project now - they have to be proper 'negative' shaped!
 
EOS_JD said:
But Nikon don't do a FF dSLR?
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No, they don't. It confuses me (doesn't take much :lol:), but I think you can use film lenses ok on digi cameras, but sometimes digi lenses (esp wideangle) used on film cameras give vignetting. If this is wrong, I'm sure someone will put me straight!
 
You're spot on - some 'digital' lenses are built for smaller sensors (1.3 / 1.5 / 1.6 crops) and so project a smaller image. On full frame this doesn't touch the sides and leaves an extra large vignette.
 
Mohain said:
The crop factor also effects the DOF by increasing it throughout the range.
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I don't see how that could be as the lens focal length does not change. Got a link to an explanation?
 
I won't and can't even claim to understand why it is, but it is. I'll put it down to either black magic or how the optic gathers light....
 
Joe T said:
Cropping an image can not possibly affect DOF! Surely???
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It isn't the cropping itself which reduces DOF Joe, but the fact that you crop to enlarge usually. There's a widely held belief that sharpness in a shot extends from the near to the far limits of dof which isn't the case. A shot is only actually really sharp in the very narrow plane in which you focused.. either side of that it becomes increasing unsharp, although it may still be judged to be acceptably sharp to the viewer.

What is a pin point of detail in your print at the plane of actual focus gradulally becomes an increasingly diffused disc either side of that plane of focus. At moderate printing/viewing sizes it's not apparent, but the more you enlarge the image, the more that diffusion becomes apparent and looks unacceptably sharp. It's known as the 'Circle Of Confusion'

So when we look at a landscape which we deem to be sharp from the foreground to the mountains in the distance, it in fact isn't... it's only sharp at the actual plane of focus, no matter even, how small an aperture we use.

So instead of saying "That's a good sharp shot Joe!" we should really be saying "That's very acceptably unsharp Joe!" :D

Read Bob Atkins, he explains it betterer than what I can. ;)
 
Without any scientific explanations you can do a test and see for yourself with a compact and your SLR. Set them both to the same f-number and take the same shot with each camera.

One of the biggest gripes I have with my Fuji s9500 is the difficulty in getting a narrow DOF due to it's tiny sensor.
 
Mohain said:
Without any scientific explanations you can do a test and see for yourself with a compact and your SLR. Set them both to the same f-number and take the same shot with each camera.

One of the biggest gripes I have with my Fuji s9500 is the difficulty in getting a narrow DOF due to it's tiny sensor.
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That would be using a different focal length, which is my query.
 
I tells ya - it be black magic!!
 
Joe T said:
I think thats only true because you need a different focal length for the same angle of view.
Click to expand...

Exactly, Bob says...

Bob Atkins said:
If you use the same lens on a small-sensor camera and a full-frame camera and crop the full-frame image to give the same view as the digital image, the depth of field is IDENTICAL
Click to expand...
 
In an effort to put this one to bed..

If you take a pic of a given subject with a full frame sensor and then with a crop sensor at the same camera to subject distance, DOF in both images will be identical.

However, if you now move back from the subject with your crop sensor camera to obtain the same field of view as you would with a full frame sensor, you've increased the camera to subject distance, and because DOF increases with subject distance, the shot will have greater DOF than the identically framed shot with a full frame sensor. It's therefore true in one sense that DOF increases with the smaller sensor, but somewhat misleading without the realisation that the same FOV is required for this to be correct.

It's also true what Steep and Bob Atkins are saying - that cropping an image reduces DOF as it necessitates a greater enlargement because of the crop. It's the extra enlargement which shows up that circle of confusion discussed earlier. :)
 
Just tried to read Bob Atkins Going to lay down my single brain cell has collapsed and just keeps repeating hu Its too much for me yet prefer simple replies on here
Bob:thinking:
 
also forgot to mention that although you get the 1.6 crop. you also loses the the wide angle. i want the 16 - 35 mm to be that. not 24 - 50
 
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