crop factor on older lenses

Started Jun 6, 2014 | Questions thread
Kim Letkeman
Kim Letkeman Forum Pro • Posts: 33,428
Re: crop factor on older lenses

hindesite wrote:

Kim Letkeman wrote:

hindesite wrote:

mbower wrote:

Ok, my next question -

I understand crop factor and that my 45mm lens is equivalent to a 90mm lens in the 35mm world.

That is correct. But why is it of interest, really? If you are using m4/3 as your system, you only need to know what the focal length means as it applies to the system, ie 14mm is wide angle, 45 is good for portraits, etc.

It is a little like moving to the metric system; there is no need to convert back to imperial to grasp what a dimension means, if you get used to thinking in metric.

I don't think people used to think about crop factors when they used large format cameras and SLRs together, (I know I didn't) they just built up an understanding of what each lens did for them on each format.

But how do I calculate the crop factor for an older lens? I have the adaptor that lets me attach my Nikon 35mm prime to my M43s body.

My own personal opinion, is that crop factor is irrelevant.

That would be hugely wrong.

Well, I'd disagree; as I said, this is my personal opinion.

Pretty much everything on these forums is someone's personal opinion. The debate generally centers around aligning opinions with facts or at least with plausible assertions.

We have to communicate with photographers across many different systems,

Nope, I don't. I'm selfish and only think about what I am doing when I'm taking photos. I don't see how I communicate other than with the finished product.

You are taking the time to communicate right now. And I don't see any finished products here ...

and the way we do that is to use the current defacto standard ... 35mm equivalence.

Doesn't look like a defacto standard. Very few people in this forum ever quote their lens equivalent FL in 35mm FF, they generally use the actual FL of the lens. Everybody understands this, and to do otherwise would just be tedious and confusing

When discussing the lens itself, you identify it by its FL, obviously.

When discussing how it behaves in the hand, the EFL is much more useful for framing, bokeh and for its useful shutter range ...

This is not really supposed to be a complex topic.

(and frankly, a little precious).

Frankly, I think you are trying that one on yourself

So I am always aware of what EFL I am using. My Tamron 500mm mirror on the Nikon G adapter is 1000mm EFL. A small telescope.

My 100-300 is 200-600 EFL, thus requiring that I use excellent technique to get anything close to sharp.

The problem with ignoring crop fact is that you have to relearn everything like the 1/FL rule etc ... much easier to just understand the crop factor of the system you use.

The rule is just a very rough guide,

Not at all. It takes into account the effective magnification that has everything to do with subject and camera movement. There is little about it that is "rough" ... however, obviously people have different levels of steadiness and different skills. Some can compensate for shake much better than others. Some have much better technique than others. But they all are affected equally by the EFL.

and the best way is to build up experience and know what speeds work best on your system. Some people are capable of holding a lens steadier than others may be. Or not. Some subjects and conditions may require some deviation from the rule.

Yes, and yet if you don't know or understand the rule, you don't know or understand what it is you are trying to deviate from ...

You actually made my point for me there.

That lens generally behaves like any lens of its focal length, if its focal length is actually 35mm, on m4/3 it corresponds to the longer end of most kit lenses; to think how it looks on m4/3 just set a kit lens to the same focal length.

What is the general crop factor that should be applied when one uses older lenses?

It is 2x for 35mm (most SLR) cameras.

You should be clear that you mean film cameras, and yes, I know that SLR is distinguished from dSLR cameras, but with dSLR being about a decade old now, many shooters have never thought about film cameras and thus do not automatically go there when you say "SLR" ...

Then many of those same people also have no idea or experience with so called "FF" cameras anyway. Many people coming to m4/3 from P&S probably had no idea about FF and crop factors until they started following this forum.

That's a specious argument. Of course they learn about FF and crop factors when they come here, because they come here to learn about why their keeper rates are changing so much as they move up into better cameras or down into smaller cameras.

They have to make sense of the EFL difference -- whether they know it exists or not -- before they can figure out why their images are always blurred. Once they have the epiphany they are set and can manage it themselves from that point on.

Compacts are sold by EFL.

APS-C dSLRs outsell everything else by a wide margin in the world and one learns quickly to see that FLs are not doing what they expect from their compact experience. And then they move to mirrorless and all heck breaks loose because the 100-300 can't make a sharp image to save their life. Until they learn that they are shooting at 600mm EFL that is .... then they learn to treat it with the respect it deserves.

You would be better to say 2x to full frame / 35mm equivalence.

But I never think wow, I'm using a (600mm FF equivalent) when I'm using my 100-300 zoom. I never think that I'm using a 18-36mm FFE lens when using my ultrawide angle Olympus.

Your choice, but it is a good thing to bear in mind that 300mm is 600mm EFL and not easily hand held.

That is kind of my point, exactly. Isn't it better to bear in mind that 300mm is 300mm and not easily handheld? 600mm doesn't even come into it unless you make it.


The answer should be obvious, but I will repeat it here.

Many people are coming to mirrorless from small dSLRs. Those dSLRs are generally APS-C. The classic 70 to 300mm lens is actually quite easy to hand hold when you own a small dSLR because it is only 450mm EFL, much less effective magnification.

So they get to m4/3 and they pop their 100-300 on there and change nothing in their technique. Yet their rate of keepers drops. They wonder why on earth their keepers are so low and they end up crapping all over the 100-300 lens for not being sharp.

Note: We have had this exact thread several times in recent weeks and it caused me to order the tripod collar for the 100-300, which of course makes a massive difference.

So once someone explains to them that they have to treat this 300mm entirely differently from the 300mm they were used to on their (for example) Nikon D3100, they have the epiphany that crop factors matter and they start paying attention to it so they can translate between what they were used to and what they now own.

You want to believe that people should be willing to go to any new system as a "green field" and learn all the focal lengths from scratch again. But you forget or ignore that people are natural pattern matchers and will very quickly start aligning the behaviours they see with what they were used to on their last camera. Once they start thinking that way, they quickly understand the difference in terms of crop factor and everything gets easier.

Those used to shooting a 50mm 1.8 on an APS-C camera will, for example, understand that there is no equivalent in the m4/3 system. Those used to the 85mm 1.8 will realize quickly that the Sigma 60mm 2.8 is usable for the same kinds of images. Of course, a Canon shooter might prefer the Oly 75 1.8, since the 1.6CF of Canon adds a bit more EFL. Those used to the 35mm 1.8 will soon understand that the 25 1.8 is close enough.

Of course, then they start wondering why they are getting very differing amounts of subject isolation, despite having equivalent EFLs, and this is also a crop factor related issue. Their wonderful 60mm 2.8 is really a 120mm 5.6 versus the 85 1.8 on their APS-C Nikon, which is really a 128mm 2.7, a difference that is going to be pretty noticeable in the background blur they achieve. Hence, the search for ever faster lenses on mirrorless systems.

There is no substitute for this understanding when making decisions of what to buy and how to shoot it. People know what they like to use and understanding the equivalent inside this system allows them to go straight there without wasting money on the wrong focal lengths and without wasting time gnashing their teeth over differences they see but do not understand ...

Now, you have admitted to being selfish, but I think in fact you are self-deluding here. You probably have a deeply entrenched understanding of the mapping of focal lengths and apertures onto what you have always liked to shoot, so you no longer pay attention to it.

But others should and do ...

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