[PDL]

If the aperture stays the same at f/2.8, the image will not be darker. Exposure remains the same. The photos will be somewhat different, due to the difference in depth of field (see above for detail).

The major difference will be the FOV between the bodies.

[swanlefitte]

And back to 1 everybody and action.

[BruceBanner]

Still

So a 50mm 2.8 on a full frame K1. Will produce , exactly the same photo as a

35mm2.8 on a KP 1.5 crop body or

will the image on the KP be darker?

No, they will be different.

a 35mm 2.8 on a KP will look more like a 52/4.2 on FF, only in terms of FoV and DoF, exposure will be the same, no loss of exposure.

[2B1]

If the aperture stays the same at f/2.8, the image will not be darker. Exposure remains the same. The photos will be somewhat different, due to the difference in depth of field (see above for detail).

So a 2.8 on crop is same as 2.8 full frame.....OK

---------- Post added 12-20-19 at 03:19 PM ----------

No, they will be different.

a 35mm 2.8 on a KP will look more like a 52/4.2 on FF, only in terms of FoV and DoF, exposure will be the same, no loss of exposure.

Ok ..Bruce .

Cheers

[Wasp]

The major difference will be the FOV between the bodies.

Exactly.


To "compensate" you can shoot the 35mm at f/2.8 on crop and the 50mm at f/4 (or f/4.5, YMMV) on FF. If you frame the shots the same and adjust the shutter speed or ISO for the same exposure, there will be little difference between the two.

---------- Post added 2019-12-21 at 16:19 ----------

So a 2.8 on crop is same as 2.8 full frame.....OK

---------- Post added 12-20-19 at 03:19 PM ----------


Ok ..Bruce .

Cheers

Uhm. No. See above.

[stevebrot]

If you frame the shots the same

The position of the lens' front nodal point should also be the same as well as the orientation of the lens' primary principal plane.* Both are required to maintain relative size and shape of objects within the frame. The second is easier to accomplish than the first and even then, the equivalent focal length for the plane of focus may also be problematic depending on lens design. Framing the shots the may defeat nodal point position.

There are very good reasons to avoid overthinking these things.


Steve

* One might also add positions of primary and secondary nodal/primary points and position/orientation of focal plane and media (think tilt/shift lenses and cameras with movements). Of course people using these tools for pictorial work seldom aim for equivalence (duh).

[RGlasel]

There are very good reasons to avoid overthinking these things.

Definitely worth repeating.

[BruceBanner]

The position of the lens' front nodal point should also be the same as well as the orientation of the lens' primary principal plane.* Both are required to maintain relative size and shape of objects within the frame. The second is easier to accomplish than the first and even then, the equivalent focal length for the plane of focus may also be problematic depending on lens design. Framing the shots the may defeat nodal point position.

There are very good reasons to avoid overthinking these things.


Steve

* One might also add positions of primary and secondary nodal/primary points and position/orientation of focal plane and media (think tilt/shift lenses and cameras with movements). Of course people using these tools for pictorial work seldom aim for equivalence (duh).

Ya think?

Ok, so me being the OP, I opened this thread up to gain some clarity. It's really common knowledge to do the 1.5x thing for the FL but hardly anyone mentions the 1.5x thing for the aperture. Even right now in Facebook land someone else is asking a similar question and people are chiming in with their responses and no one is mentioning the aperture aspect. Of course I understand in part why this is, exposure is still going to be the same, but this user right here I always felt something was 'off', and now I know why. Aperture is not just about light and exposure, for me aperture's most apparent (and endearing) feature is DoF. People say 'the biggest difference will be FoV' and of course that is true (and hardly needs mentioning), but no one ever says 'and also be aware that your aperture will appear more stopped down than what FF will give"... I kinda think this is a really big deal.
I guess it's the kinda photography you're doing, perhaps DoF junkies (*raises hand up in the air) becomes a bigger talking point than Landscapers or users that tend to look for optimum sharp shots at prefer the f4-8 apertures...

So many posts in this thread have went over my head with crazy maths, 'overthinking'? I dunno man... I just tripodded up quickly and demonstrated with 5mins of shooting what I see to being significant differences in images and aperture would be the defining difference to the shots. I don't get into this 'nodal point' or whatever, I just focused on something close to the lens for the shots (off centre) so we could judge the oof areas easier (whilst still observing the focused object for IQ/Sharpness). So please, if all of this is overthinking then I'd like to know where I have overthought this process, because the examples here were rushed, non scientific yet still I feel make a solid point and should be something made more apparent to users. Just recently we had someone ask the question on a Facebook post about upgrading from a crop to a ff camera and not ONE member in about 50 comments actually mentioned any of this stuff, everyone just harping on about IQ and sharpness, no one talking about the additional benefit of enhanced DoF. F2.8 or F1.8 is going to take on a whole other meaning for that member who has only experienced f1.8-2.8 on their crop bodies... How is this thought of as being a small thing, hardly worth mentioning is beyond me, these aperture ranges can change the entire intent of a picture.

Everyone loves the DA 15/4, I never gravitated towards it, I was effectively seeing a 22.5/6 response from the lens (in my minds eye), it's just natively too stopped down for my tastes, a one trick pony meant for landscaping really. I'm not saying it cannot do portraits, it can, any lens can, but it definitely has its limits. Comparing that lens with say the FA20/2.8 or FA24/2... huge difference in terms of applications. What's interesting to me is I could actually accept things the other way around. The DA 15 needed to be 2.8, and the FA 20 and 24 could be f4's, I could work with that, but somehow the crop lenses are getting more stopped down apertures, which I think makes for the worst compromise of all because the intent is a crop sensor... , I'm guessing stopped down glass is better for size of lenses? And that Pentax thinks people want small lenses for their small crop bodies? I guess the DA 15/4 would still be sitting in my bag if it had WR... (I guess you can tell I am not a huge fan of it ). haha.

But no seriously, the geeky sciency talk is interesting at all, but I think I'd need some images accompanied to these posts if you're going to make a case of me overthinking this stuff. I can now look back at shots I have taken with the HD DA 20-40 in FF mode on the K-1 and understand better the reasons for the 3D pop and better focused subject isolation, Examples;

FF Mode, 23mm @2.8


This shot would not have been possible with the HD DA 20-40 on the KP, it can't go as wide as 23mm, instead I would have to use 30mm, stand further back and get f4.2 DoF, which means a drastically different image, even if framed the same, goodbye gorgeous bokeh and subject isolation.

Same again here. 23@2.8


This one's interesting as it's taken at 30mm with f3.5 in FF mode;

I might be able to get something close to this on the KP if I set it to 20mm and use f2.8, but it will still be a little more stopped down than this.

Anyway, love to see some images from other people in demonstrating any of this stuff to being 'overthinking' and that in certain scenarios or whatever the differences are minimal etc. Would genuinely like to see that.

[swanlefitte]

Bruce,
Pretty sure not talking about you. What you mentioned about Facebook is the heart of it. Equivalence confuses.
You dive in and figure your stuff out with and despite forum help. Good on you.

[swanlefitte]

I wonder how many people have only apsc cameras and still convert their lenses to FF equivalence.

[BruceBanner]

I wonder how many people have only apsc cameras and still convert their lenses to FF equivalence.

Well that's kinda it isn't it. Doesn't history go something like;

Film 35mm (most popular and common camera)
Digital Age arrives, crop sensors rule, things are different now, is everyone converting?
Digital Age continues and FF sensors arrive, YAY! We're back 35mm equivalence, things make sense again at long last?

For me, I didn't do Film at all, I started with a K-50 for 24 months, then sold it, bought a K-1 and then a little later a KP as a backup body. K-1 got the most use so everything I use and see through the OVF and the results I have come to think of as 'standard' (that and as well as marketing sites showing equivalence of lenses in FF). Yet up to only recently, when choosing what glass to buy for a KP (and hoping it has some uses for the K-1), I was only 1.5x the FL and never the aperture that I calculated. I got a great deal on a DA 12-24/4 which I couldn't pass up it's proving to be quite cool on the K-1 at 19-24mm, and at f4 it has decent enough subject isolation for some portrait work, however I never really considered that on the KP it's effectively offering a f6 DoF, that's practically meant ruling it out of any portrait work on the crop body, its a landscape lens for crop. These things are important to me, I can see now why 11-18/2.8's are really a big deal for crop bodies. I just try to fill gaps in my lens line up between two bodies is all. As previously stated, the FA77 on KP becomes a little like a DFA100/2.8 on K-1, not obviously in terms of macro capability but in terms of FoV and DoF similarities and capabilities, or uses even. Thinking that I can buy a DFA100 and place it on the KP and get a 150mm/2.8 is not how it will pan out, I will be getting something more like a 150/4.2...

Education. It's important, can help better purchasing decisions. Not at any time have I ever wanted to purposefully recreate identically the same scene with two different sensor cameras with either the same or lens or different glass, that's really not what this is about at all.

[Dartmoor Dave]

I wonder how many people have only apsc cameras and still convert their lenses to FF equivalence.

Naah. When I'm shooting with my favourite Takumar 20mm on APS-C, I only ever think about how much (actually how little) depth of field I'd get with the equivalent 210mm on an 8"x10" view camera. The difference that another miniature format like FF would make is too insignificant to bother thinking about.

[Dartmoor Dave]

I got a great deal on a DA 12-24/4 which I couldn't pass up it's proving to be quite cool on the K-1 at 19-24mm, and at f4 it has decent enough subject isolation for some portrait work, however I never really considered that on the KP it's effectively offering a f6 DoF, that's practically meant ruling it out of any portrait work on the crop body, its a landscape lens for crop.

Personally I prefer to shoot portraits of people in an environment that reveals something about their personality, and I like to have the background pretty much in focus.

[Dartmoor Dave]

Darn, and I'd sworn to myself that I was never going to get involved in an equivalence thread ever again. . .:lol:

[Wasp]