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New to 'adapting'; confused re: LTM 39 to E mounts

AlwaysOnAuto

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No, you're not confused. A 50 on APS-C with a crop factor of 1.5 = FOV of a 75 on a full frame. The lens is still a 50 no matter which camera it is on, full frame or crop sensor. The field of view is what 'changes'.
 

Petrochemist

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No, of course. Yet it gives the equivalent of a roughly 75; the standard computation of a ff lens on aps-c is 1.5, is it not? Or is this another thing I'm confused about?:blush:
For Nikon, Sony, Fuji, Pentax, yes the field of view (FOV) is the full frame equivalent to 1.5x focal length
With Canon it's 1.6x, my old sigma is 1.7x (both also described as APS-C).
But in each case it's only the FOV that changes not the focal length. Focal length is important when calculating the effects of extension or combination with diopters etc. so it's not just that I'm being pedantic.
Too often the 'equivalent' is quoted without being clear about which bit is equivalent. I found many photographers end up getting confused thinking an adapted FF lens will work out different than a native crop lens of the same focal length...

If you only shoot APS-C the need for a FF frame of reference is nearly non existent. Just get familiar with what each focal length looks like on your body. Even though I use 3 sensor sizes regularly I tend to know the right lens for a shot without applying crop factors. I do find them useful when chatting with photographer friends or when considering more gear.
 
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xavyr

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Sorry; tied up in phone calls.
Again, I have expressed myself poorly - of course, I was not meaning to say that the magnification changed but simply the view - that the crop is that as it would be with a 75 rather than 50.
Dashing off again - back this evening doubtless!
 

bdbits

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Most lens makers - even 3rd-party ones - have a naming convention that will tell you if it is an APS-C or full-frame lens. For example, with Sony, FE in the lens name means it is full-frame, just an E means APS-C.

I don't remember the other conventions off-hand, but if you look at the lens names on the vendor's site you can often see the naming pattern fairly readily.
 

Petrochemist

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Most lens makers - even 3rd-party ones - have a naming convention that will tell you if it is an APS-C or full-frame lens. For example, with Sony, FE in the lens name means it is full-frame, just an E means APS-C.

I don't remember the other conventions off-hand, but if you look at the lens names on the vendor's site you can often see the naming pattern fairly readily.
Nikon have FX & DX, Canon EF & EF-S, then Sigma & Tamron have their own codes all different.

With Pentax I believe its DA for APSC digital & DFA for full frame digital, while the earlier film series all cover FF. However there are DA lenses that have been found to cover FF perfectly well (released while Pentax didn't make a FF body). Likewise some of the lenses designed for the 110 film cover APSC and more.

Things get really complicated with c-mount lenses - most lenses above 35mm focal length will cover MFT, some 50mm lens will cover APSC, but I have one zoom that's only manages to cover half the MFT sensor even at 100mm. The film formats c-mount lenses are designed for varying from about 15mm diagonal ('super 16mm' format) to under 6mm (standard 8mm format) CCTV sensors probably went significantly smaller.

Lenses will often cover more than their designed format (usually at lesser quality) but quite a few will show significant vignetting in the corners as they don't fully cover the sensor. A bit of research will usually tell what a lens was designed to cover, but you only really get to find out when you give it a try.

Many of the lenses I've collected weren't designed for cameras so coverage is a complete lottery, fortunately about a dozen manage to cover 5"x4" often with room to spare for movements. I don't have anything needing more than that - but it would be nice to have that coverage in something less than 100mm focal length :)
 

xavyr

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But in each case it's only the FOV that changes not the focal length. Focal length is important when calculating the effects of extension or combination with diopters etc. so it's not just that I'm being pedantic.
Oh, Lord forbid, Petro; by all means, please explicate away. I am here, after all, specifically to get a bit of pedantry. It increaseth understanding. Mixing so-called crop sensor cameras with "full-frame" lenses is quite a new thing for me; as you point out, there is more to it than a simple shift of FOV.
 

xavyr

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Meanwhile, back at the adapter, considering separation of the components and installation of a permanent shim between them, side-lighted close-ups show the distinctive allen key hex:

SM-N960U    ---    4mm    f/2.4    1/120s    ISO 200


Found my very small allen wrenches, and would have sworn that the smallest was no bigger than a cat's whisker, but it's too large for these.
 

AlwaysOnAuto

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The smallest hex key I have in my tool box measures 0.0505" across the flats. I'm sure that's way too big for that screw.
Canon PowerShot SD1000       6mm    f/2.8    1/30s    ISO 200
 

xavyr

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My Lord, whose tiny digits grasped these things, and with what? I wonder how many of them the assembler accidentally inhaled?
 

AlwaysOnAuto

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My google fu shows there are two sizes smaller than my 0.050", so I guess the screws could be one of those sizes.
Yeah, sometimes the assembly of some of these optics amazes me. Luckily my adapter uses straight bladed screws. But they are very weak I've discovered.
 

xavyr

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Well, drilling them out is not really an option, so I guess I gotta go for laying a shim layer "collar" around the rear of the lens as before
 

bdbits

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Those are really tiny. I have a set of very small allen wrenches, I don't even remember where I got them, but they could still be too big.

I wonder if maybe they are assembled by or with a machine of some sort. Otherwise, you would think that would be a significant assembly cost to be avoided.
 

AlwaysOnAuto

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So now the problem, as I see it from here on the now sunny west coast, is how to cut the aluminum foil nicely so it stays unwrinkled and fairly flat.
I think it's going to start with making a sandwich to hold the aluminum foil. Then the problem becomes what diameter to cut it to and do you make the ID cut first or the OD cut?

(As you can tell I've been giving this some thought, well, maybe you can't, but I have.)
 

xavyr

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I have been, now and then.
First off, I'm still not sure about shim materials. I took a moment to put the micrometer on some heavy duty foil and it seemed a lot thinner than I'd thought.
Gonna check the 'net for the specs on self-adhesive copper foil and look around at plastics, other things perhaps...
Cut-out technique will challenging, true...
 

dbmiller

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Oh, Lord forbid, Petro; by all means, please explicate away. I am here, after all, specifically to get a bit of pedantry. It increaseth understanding. Mixing so-called crop sensor cameras with "full-frame" lenses is quite a new thing for me; as you point out, there is more to it than a simple shift of FOV.
The APS-C (or smaller) vs FF debate has gone on forever. There are two camps: A lens is physical and doesn't change when you adapt it to FF. The other camp says you have to need to find equivalent framing and equivalent DoF, and so you should take the crop factor into account. Both camps are right, but for various reasons.

Let's use the A6000, A9, and A7R4 as three example cameras.

Now stick a prime lens on each, say a 55mm1.8. stand in one spot and take a picture of the same object with each camera. Shoot an extra shot in crop mode on both of the FF cameras. Compare images at the same size and distance.

You should see that the cropped images from FF look the same as the one from the A6000. And the one from the A7R4 is nearly the same image size.. You could manually crop the FF images yourself for the same result. The lens acted the same, gathered the same amount of light and cropping results in the same image, same DoF, albeit different image sizes.

But viewing the full sensor images you obviously have a different field of view.

Now put a 16-70/4 on the A6000 and a 24-105/4 on the FF cameras.

At 16mm, you get the same framing as the 24mm on FF when taken from the same distance. And while f/4 measured the amount of light hitting the sensor, the depth of field is different because the focal length is different. To get the same DoF, that 16-70 needs to be slightly better than f/2.8. or drop the FF to as close as you can get to f/6.

Now go back to your prime lens. To get the same framing on APS-C as FF, you could just move further (1.5x) back with the A6000. Now the image matches the A9 and has the same 24mp, but your distance is different so the DoF is again different.

So focal length doesn't change. The light gathering ability doesn't change. A lens is a lens. Sensor size doesn't magically change the lens. But how you use them together affects the end result of what you capture.
 

Petrochemist

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The smallest hex key I have in my tool box measures 0.0505" across the flats. I'm sure that's way too big for that screw.
That works out at close to 1.3mm which I'm sure must be the size of your allen key.
I suspect it's about twice the size needed (very probably 0.7mm).
Some of my adapters have come with the appropriate allen key so I must have several around - even so I can never find the blighters when I want them!
 

bdbits

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Not to be pedantic, but aperture is normally a measurement of the size of the opening in the lens (in photography anyway). The amount of the light hitting the sensor is measured in t-stops, which you will sometimes see listed for cine lenses. Two lenses with the same aperture i.e. f-stop can actually have different t-stop values, but they are normally close enough that lens makers do not often bother measuring t-stops.

And dbmiller is right, equivalency arguments have filled countless discussion pages on the internet. In the end, our WYSIWYG wonders will to a large degree mitigate the theoretical discussions and we just need to learn what works so we can set it up properly.
 
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