Which of my lenses do what?

[AVALANCHE]

You are correct, the field of view changes, not the focal length of the lens. Whilst you may not have appreciated the reply, your original comment: "Well, given the 550D is a cropped sensor your lenses actually have different focal lengths", is not correct and did need clarifying/correcting.

A lens doesn't magically become a different focal length cause it is on a crop sensor body. A 50mm lens is a 50mm lens, whether it is on a crop body, a full frame body, or sitting on a kitchen bench. What changes is the field of view:

That diagram is handy and very straight-forward, thanks. I'll save it to my desktop.

...and sure, there are ways to go about correcting someone though, I don't think;

NO NO NO NO NO NO NO NO !!!!!!!!!
DO NOT PERPETUATE A LIE!!!!

...is this the right way to go about it. Call it over-sensitive, and I don't think this type of behaviour should be accepted. In fact, it is in the rules:

YOUR RESPONSIBILITIES

[8] Members should be treated with respect and courtesy. Members are requested not to insult or make personal attacks on other members. Members are requested not to make lewd comments on the content of photos posted for critique. Remarks deemed to be libellous, defamatory, slanderous or offensive will be deleted, "Flame bait" postings, identical or similar repeat postings will also be deleted.

With that said, I am leaving it at that.

- - - Updated - - -

For Avalanche:

The reason we like to keep to a certain level of correctness with respect to lens focal lengths and crop factors, is because of the differences in DOF.

So if you shot at 35mm on APS-C and 50mm on full frame, you will certainly have very similar FOV in both images, but the 50mm lens image will naturally provide a shallower DOF if the image is focused at the same point and the aperture remains the same.

Similarly with your question about cropping the fullframe shot to suit the FOV of an smaller sensor image.... the DOF rendering is going to be shallower, so while the image may appear to be similar, it will look different to an actual shot from an APS-C camera. The output size of the respective images will determine whether you can see those differences or not.

ps. angle of view is not entirely set for any specific focal length either.
The angle of view is related to the sensor size.

That is, you can get two different lenses at 15mm that can give you two different fields of view!! One could be set to 90° on a 35mm frame .. the other could be as much as 180° if the lens designer wants it to be.

Also! a 50mm lens gives you a FOV equivalent to about 50° on a 35mm frame, but that may also equate to a 60° FOV on a medium format frame .. or even a 90° on MF too! But then again the lens may only privide a 42mm radius imaging circle, and hence only give you only 55° FOV on medium format .. irrespective of what MF size is used.... etc, etc.

It's not really as simple as you may think it is!



So this should read: the angle of view stated for this lens on one format size will be different for another format size!(ie. not focal length).

Thanks, I had to re-read that a few times haha. All part of the learning.

[arthurking83]

.......


Thanks, I had to re-read that a few times haha. All part of the learning.

LOL!

See my last post in this thread too about this annoyance of focal length/crop factor too:

HERE


It's a difficult concept to just visualise without first hand experience.

But if you shoot with a 50mm lens, your DOF will be the same no matter what sensor format you've chosen.

Because full frame 35mm and APS-C are quite close in size, the differences are not quite as obvious.

For a more clear understanding of these differences, you need to look at extremes of the sensor scale.

That is, look at how a superzoom image captured by even a bridge camera, but more clearly seen with a more compact camera is rendered compared to an equivalent image captured by a proper tele lens on a full frame camera.

Some of those small compact cameras apparently have an 400-600mm equivalent(to 35mm format) lens, and you place a 500mm lens on a full frame camera and getting any depth of focus in the scene is nigh on impossible! That's because the compact superzoom lens is really only something like 27mm, as compared to 500mm on the larger format! No need to descibe the differences in DOF between those two focal lengths!

[William W]

Arthur, I have carefully read both and yet I remain confused by both of your posts -

DoF is a concept, which is predicated on the “Circle of Confusion.
The Circle of Confusion changes with the Format size of the camera.
The DoF at any aperture, also changes with the SD (Subject Distance).

I therefore don’t understand how we can discuss the “DOF of a Lens at a given Aperture”, without ALSO referring to:

• the camera’s format and therefore include the change of the Circle of Confusion
• the SD.

In light of the above points, would you please explain what you mean by the statement:

But if you shoot with a 50mm lens, your DOF will be the same no matter what sensor format you've chosen.

WW

[fess67]

You guys!! You are not making AP look good with this 'my knowledge is better than yours' crap.

The OP wanted to know what his lenses could do. He is a beginner with a few posts under his belt. Please treat the topic in that manner and give information that is relevant to the question and experience level.

My view is this: When my son asks me a question I answer it as best I can but within his sphere of knowledge and understanding. Sure I have a degree and could give him the university level answer but that will not really help, in fact it may even harm because it is not what he needs. He needs a base to build his knowledge on, then we can introduce more advanced ways of looking at the question.

This thread was started by a question about what lenses do what. At a beginner level it requires a generalist response and does not (IMO) need to descend into the nitty gritty of the xyz of focal lengths, camera formats, ....blah blah blah.

You want to beat your chests about how much you know, take it into a darkroom somewhere and live the dream, but please don't alienate members with this tit for tat style blogging.

</rant>

[William]

Gets back to my thinking , The KISS method of learning for a beginner works , To much knowledge sometimes is not good , And an overload

[William W]

Speaking for myself only: I asked a question, because I don’t understand something which was written in this thread and also in the other thread, to which there was a link provided.
I would like an explanation, as, I sincerely believe that member “Arthur King” has the best interests of the Site and also its Members, in mind – but I really don’t understand what he is meaning to say.

On another point – I don’t understand why being “a beginner” at The Craft, automatically subjugates one into a sub group of NOT being able to understand or keep up with a logical flow of conversation.

Thirdly, the analogy with (assumed) a Child, is flawed as we are (assumed) discussing the capacities of an Adult’s: learning; thinking and understanding skills: not a Child.

Fourthly, included in answering specific questions to benefit any particular OP, I would expect that general learning and exchange across the Site’s Membership is a part of the raison d'être.

And on a final point – the technical issues of a lens actually do pertain to what lenses “can do” which is what the thread is about.
On the other hand “ranting” at other members, however is off topic: not that I mind personally, but just establishing this point - because going “off topic” was brought into the conversation as the primary reason for the rant.

WW