What is Focal length, Sensor size in photography and why is it matters?

The intention of this article is to dig out the relationships between focal length of the lens and the camera’s sensor sizes and how does the both affects the framing independently.

I have made a simple illustration diagram below, which depicts how does the light enters from the scene to the sensor/film.

Focal Length-Photography-Sensor-Light entryImage a. – Light travelling path inside a lens and camera body from the scene. x is the height of the sensor(part of the camera), b is the focal plane(principal)- this always happens inside the lens, z is height of the frame (photograph’s vertical measurement in landscape mode), y is the focal length which is usually mentioned on the lens.

Focal length(y) is the distance between the sensor (a) and the focal plane (b) where the light rays converge to form a sharp image of an object to the digital sensor.

Now, the frame you see via the viewfinder will change, if you adjust the Focal length which is possible in zoom lenses. The same is not possible in prime lenses since the focal length has been set in the factory itself while manufacturing, in such a way that it cannot be changed. The prime lenses are made purposely for high quality at a lesser price comparatively with a zoom lens in that focal length.

Conversely, it is also possible to change the frame by changing the size of the sensor. But the sensor has been fit inside the camera while manufacturing in the factory itself and it cannot be changed by wish on the field. But you can use two different cameras having different sensor sizes as one may wish.

Now we have understood that, if we change the size of the sensor (x) or the focal length (y), in both the ways the frame will get changed.

The ranges of available lenses in the market with different focal lengths are beyond listing thus I am not getting into that.

Sensor sizesImage b – Scale of the other smaller sensors with respect to the Full frame sensor. The FF sensor size is 36mm × 24 mm. For the sake of understanding, we here discuss about the vertical  measurement(x).

The smaller the sensor sizes, the field of view gets narrower. That is, if “x” gets smaller, “z” also becomes smaller Assuming that the “y” is same in both the cases. Conversely, if “x” gets bigger the field of view (z) also gets wider.

The advantages and disadvantages of choosing which sensors (cameras) have been briefly explained here in my earlier article.

The crop ratio has been established in the industry with reference to the 35mm film sensors. 35mm width sensors are the reference one and the crop factor for those sensors is 1.00. Other sensors are classified by the crop factor with respect to 35mm sensors (1.00).

Crop factor is the ratio of the dimensions of a given sensor’s imaging area compared to the 35mm sensor’s imaging area (full frame sensors in common). If a sensor’s crop factor is more than 1(APS-C sensors), the image area will be less by that ratio. Conversely, if the crop factor of the camera is less than 1(medium format cameras), the image area will be more by that ratio.

For instance, if a camera’s crop ratio is 1.60 and you have mounted 85mm prime lens, what the camera sees is the view of 136mm (85mm × 1.60) not what is written on the lens. If the same 85mm lens been mounted on a medium format camera with 0.50 crop factor, what you will be seeing is 42.5 mm (85mm × 0.50) focal length view.

Sensor sizesImage c – Dimensions of the different sensors fixed in different cameras and the respective crop ratios.

The focal length written on the lens is true, only if it is mounted on 1.00 X crop factor sensors (full frame cameras). If you are mounting it on non-full frame cameras, you should multiply the crop factor of that camera to get the actual focal length.

I hope, I have covered all the necessary topics which are required to understand the focal length, sensor sizes and how does both affects what you see in the viewfinder. Have I missed something? or the article been helpful to you, do drop a comment and let me know.

Cheers & Happy Photographing.

The power of Alphabets in Lr 5


Not having any specific title, but the intention is to post one article today. After some amount of nail biting, decided to write about the most helpful list of shortcuts in Lr. Despite the amount of information spread across the internet in out of seconds of googling and a dedicated Lightroom shortcut display in each module in just one click (Ctrl + ‘), the smart list of keyboard shortcuts is still a scarce. Here is one, which you will use it day in and day out for sure.
 
I have maintained no order with respect to either the modules or the list of tools/functions. The only thing I kept in mind is the one which we will use often. The pdf file of the same can be easily downloaded, the link is at the bottom of this article.

R – Crop tool

     O – after pressing “R” will displays the rules of composition overlay in cyclic mode
     Shift + O – will make different versions of the current compositional overlay
     X – Rotate crop
     Pressing Ctrl will activates the level tool
G – Grid view in Library module
D – Develop module
E – Loupe mode in library module
P – Set select flag
X – Set reject flag
U – Unflag
J – Highlights and Blacks clipping
F – Full screen view
T – Display Tool bar
V – Convert the current image to B & W, press again to back
Q – Activates Spot removal tool
M – Activate graduated filter tool
L  – Lights dim/Out in cyclic mode
W – Activates White balance selection tool
K – Activates Adjustment brush tool
     O – Show/Hide paint overlay
     H – Show/Hide adjustment pins
     [ – Make your brush size smaller
     ] – Make your brush size bigger
     A – after pressing “K” for auto mask on & off
Y – View before and after side by side
     Alt + Y – View before and after up and down
C – Compare mode
N – survey mode
Z – Zoom view
Library
Ctrl + Alt + A – Select all flagged
Ctrl + Shift + E – Export window opens up
Ctrl + Shift + I – Import window opens up
Ctrl + D – Select none
Ctrl + A – Select all
Ctrl + , – Create virtual copy
Ctrl + ‘ – Display the key board short cuts pertains to the particular module
Ctrl + L – Library filters on
Ctrl + U – Auto tone
Ctrl + Shit + U – Auto White balance
Ctrl + Backspace – Delete all rejected flagged photographs (a dialog box will open up and ask whether to delete the images or just remove them from the catalog)
Ctrl + S – Save metadata to file
Tab – Hide side panels
Shift + Tab – Hide all panels
Backslash (\) in Library module – Library filter bar on & off
Backslash (\) in Develop module – before view
(/) Slash in develop module – deselect active photo
Develop
Shift + F – Full screen working space cyclic
Shift + M – Activates radial filter
0 – No star ratings
1-5 – respective 1 star to 5 star rating
6-9 – colour labeling
F5 – Show Module picker
F6 – Show Film strip
F7 – Show Left module
F8 – Show Right module
= = Increase grid size
– = Decrease grid size
Hope this article helps to save your valuable time and the pdf file can be downloaded by clicking here. If you have got any other smart shortcuts, share it in the comments section.
Cheers and Happy photographing. 🙂

Ultraaaa wide

Recently I have been commissioned for to shoot for a dental hospital. It has surgical facility and all the associated laboratory facilities. Any person coming to the hospital with a dental problem can get all his needs attended to under a single roof.

To get on to the theme of this topic, this type of indoor shoot sessions need to be preplanned and made execution-ready with a certain thoroughness and seriousness. This would apply to all shoots that need to backed by a weighty commitment. I fixed an appointment with the client a week ahead, to firm up on the schedule and locations of the shoot. I also had a long discussion with the client about how they want the photographs, and for what purpose they want, in an attempt to understand what are their intentions/ideas are and the use the photographs are going to be put to. I came to know during the conversation that they are putting up a website to show to the world the facilities/competencies they have. It was, at this point of time, important to understand the level of lighting that needs to be maintained at the time of the shoot session. The choice/trade-off was between using auxiliary/sophisticated lighting at extra cost or use existing lighting/minimal equipment and bring out the best possible pictures under the circumstances. Needless to say, the customer wants pictures that would be used in a marketing showcase, be it in digital form or print form(web, brochures etc.).

I surmised that the shoot can be done only by ultra-ultra wide lenses and I selected Canon 16-35mm f2.8 L II as my boy along with Canon EOS 5D M III as my recorder and Canon 50mm prime f1.8 for few portraits of the staffs. This shoot is not really an artistic portrait, you don’t have to look out for exotic views or angles as the photographs are meant for the general public (patients too). Simplicity and neatness are the key elements.

Simplicity

During the shoot I stick with one rule “Either keep the room’s vertical lines parallel with the vertical lines in the frame or horizontal lines in the room parallel with horizontal lines in the frame, if possible keep both. But definitely not without either, which will make something extraordinary or ugly. Even when you shoot this cautiously you will end up with a  noticeable amount of both barrel and pincushion distortions .

Lightroom comes in to rid the pictures of all the distortions and it does automatically if you select Auto for most of the lenses. Manual intervention is required for all the ultra-ultra wide lenses for manual correction might be necessary because automatic correction based on lens profiles are not very accurate when distortion levels are too high.  It is necessary to be careful while making corrections for distortions. You have to careful while correcting though.

Both of the photographs here have been corrected in Lightroom. Here is a quick peek into Lr Lens Corrections. The Lens correction panel has been further divided in to Profile, colour and Manual. The first sub panel “Basic” is the front control of the next two panels. If you check the check box all the auto correction will be applied by Lr. Even after the auto corrections, if you feel to fine tune it you have to click the respective panels. When shooting jpeg some older cameras might not provide lens information in the image file and in such cases we have to remember the lens used and later choose it in Lightroom’s Profile subpanel,  if it is present there and then Lightroom will apply the relevant corrections to the image.

Neatness

If you are not satisfied with the Lr’s Chromatic Aberration correction, you can do it manually by clicking the eye dropper directly on the image where the CA appears. You can easily find it out by viewing the image on 1:1 and for further fine tuning there are sliders. Finally the manual adjustments for lens distortion correction. The distortion slider fixes the pincushion distortion if you move the slider towards left, it fixes the barrel distortion if you move towards the right side. The vertical and horizontal slider fixes or adjusts any vertical/horizontal perspective correction if any, you wish. Rotate slider is to use it for any level correction or slight distortion too. Scale slider is to either stretch out or to squeeze in the image for any reason which may be because of the distortion correction you have applied or too much of perspective correction applied. Aspect slider is to enlarge or squeeze the image in one axis for some creative purposes and can be useful to fix images from certain heavily distorting lenses that stretches the image along one axis causing it to look skewed. Finally Constrain crop, I keep it checked all the time, so you don’t need to see the portion which is not going to be part of the photograph due to the corrections being applied. On a lighter note once the “Constrain crop” is checked here, the “Constrain to Warp” in crop tool is also being checked automatically.

It is not advisable to use the vignette here and I don’t use for the following reasons – a. The controls here are minimal – only Amount & Midpoint, these controls are  required to eliminate only the vignetting produced by the lens,  and so it is not very flexible when we want to create artistic vignetting effects b. If you have cropped the photograph and you have applied some vignette, you are not going to get the full result rather you might get some unimaginable result, because the vignette you apply here is for the full image, it won’t consider the crop you have made via crop tool.  I suggest you to use the Effects panel and use post crop vignette where you have more controls.

Heading back to Lens corrections in the Basic sub-panel at the lower level there are Level, Vertical, Full, Auto and off options. They are to correct the perspective corrections which I am not using because of following reason – I do my crop as my first correction in the develop module, while I crop I have to do the level corrections and if any perspective issue I switch to the Manual section in Lens correction panel as for the above photographs. So I am in no need to use the auto function, but I have heard from my friends that Auto does a neat job in most cases.

If you are interested in reading more about CA click here and have you heard about mustache / complex distortion or if you want to read more about distortion click here and write your thoughts in the comments section.

Cheers, Happy photographing.

Full frame & APS-C sensors why and why not.

Full frame is derived directly from 35mm films. The sensor size is 35mm width as in films.

The advantage of having a full frame is

a)    You have got around 2.5 times more surface area on the sensor than in an APS-C sensor; it means more photo sites in the sensor which directly leads to capturing more details.

b)    By the very nature of the sensor you can shoot up in high ISO without any significant noise.

c)    The lens focal length will shoot what exactly it shows when it is mounted on a full frame sensor. (details below)

d)    You want to take a shot at f 1.8 in a full frame; you get 1.8, but in APS-C you get 2.88 and so on. (details below)

For instance you shoot in 200 mm zoom on a full frame camera you get exactly what it is in 200 mm, but in a APS-C (1.6 crop factor) actually you get 320mm zoom (1.6*200), it could be an advantage of using APS-C for some zoom shots. When you want to take a wide angle shot you actually zoom in a bit. In that case you definitely need a full frame camera and that too, too many details in a wide angle shot, without a doubt you need it.

The shot you take on f 22 in a full frame is not the same when you take the very shot in f 22 in APS-C. To get the shot equivalent to f 22 in FF you have to change the f no. to 14 in APS-C.

Image

Advantages of APS-C sensors

a)    You zoom in according to the extra crop factor, say if the crop factor is 1.6 multiply your focal length by 1.6 (as mentioned above), without any extra zoom lens.

b)    The cost of the APS-C sensor/camera is far less than FF. (Details below)

c)    A very good one for starters.

Why a FF sensor does cost much than an APS-C?

Sensor is made of Silicone wafer with other technical parts in it. The silicon panel comes in a size where APS-C sensors can be cut without much wastage. Whereas lots of wastages in cutting in to FF sensors. So the manufacturers want to make the lost money in wasting the wafers. (I strongly believe they will be recycling the waste portions)

Conclusion

a)    If you are a starter you do not have to buy a FF camera, APS-C is far better for learning.

b)    If you are a wildlife photographer, you buy an APS-C high end camera (say canon 7D) you get 1.6 converter attached to it by its very nature.

c)    If you are high end fashion photographer and your photographs are going to print often, better you own a FF apart from having some L lenses.

d)    If you are a night bird; you have to take a FF camera. APS-C cameras are very bad for lowlight, night photography.

e)    This above list is not exhaustive.

Thanks for reading, If you find useful do comment and share. If you find mistake do notify, will modify it. I do make mistakes.

Navaneethan

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