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08-12-2018, 09:08 AM   #1
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Do I account for crop factor when selecting the focal length for manual lenses?

Hello!

I just got my K-5 yesterday and have been messing around with it.
All of my lenses are manual, so I have to input the focal length of the lens when I boot the camera up.

Should I account for crop factor when I give it an input?
All of my lenses are full-frame from my K1000.

So, if I put my 50mm lens on my K-5, should I tell it that the focal length is 50mm or 75mm?

I'm assuming this is only to tell the camera how to use it's image stabilization motors and whatnot, right?

08-12-2018, 09:10 AM - 2 Likes   #2
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no, focal length is the focal length...

50 = 50
08-12-2018, 09:16 AM   #3
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QuoteOriginally posted by pepperberry farm Quote
no, focal length is the focal length...

50 = 50
So, is it just the field of view that's affected by the crop factor?
08-12-2018, 09:23 AM - 1 Like   #4
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I'm not sure what you mean with this second question, but it is only to tell the camera what kind of lens it needs to stabilize. An added bonus is that you'll see the focal length in your postprocessing software even when the lens will not transmit any exif data, allowing easier identification of the lens used. BTW, don't forget to turn SR off when using a tripod. The camera will not ask for local length anymore when SR is turned off.

---------- Post added 08-12-18 at 09:24 AM ----------

Oh Yeah, before I forget: enjoy your K5!

08-12-2018, 09:27 AM - 2 Likes   #5
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QuoteOriginally posted by Ropuchy Quote
So, is it just the field of view that's affected by the crop factor?
Yes - the crop is like putting a mask over the photo. Imagine you have an 18x24 print made from a FF negative. Then you put a 12x16 mask over it. the resulting field of view is from the crop - the image remains the same. If you adjust your position to get the same framing as the original (which you likely do) your image will have slightly different perspective and background elements etc. The shorthand about focal length is just a heuristic way of looking at it and getting a basic idea of the change in field of view.
08-12-2018, 09:31 AM   #6
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QuoteOriginally posted by HoutHans Quote
I'm not sure what you mean with this second question, but it is only to tell the camera what kind of lens it needs to stabilize. An added bonus is that you'll see the focal length in your postprocessing software even when the lens will not transmit any exif data, allowing easier identification of the lens used. BTW, don't forget to turn SR off when using a tripod. The camera will not ask for local length anymore when SR is turned off.

---------- Post added 08-12-18 at 09:24 AM ----------

Oh Yeah, before I forget: enjoy your K5!
Alright.
Yeah, thanks! It's been a lot of fun so far!
08-12-2018, 09:32 AM - 1 Like   #7
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You just input the actual focal length to the camera. "Field of view" might be one way of looking at crop factor. "Field of view" usually applies to optical instruments like binoculars and telescopes where different eye lenses can deliver different "field of views" given the same objective (strictly due to the eye lens construction).

If you compare a given camera to one that is full frame, essentially the field of view is changed for a given FL lens but it is due to the sensor being smaller than a FF sensor so the word "crop" more correctly applies. The camera is doing a crop on what would be a FF view. The shake reduction doesn't really care what crop exists. It just needs to know actual focal length to do its work by moving the sensor to compensate for shake, since the image "jitter" is a function of camera movement and FL.
08-12-2018, 09:32 AM   #8
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QuoteOriginally posted by UncleVanya Quote
Yes - the crop is like putting a mask over the photo. Imagine you have an 18x24 print made from a FF negative. Then you put a 12x16 mask over it. the resulting field of view is from the crop - the image remains the same. If you adjust your position to get the same framing as the original (which you likely do) your image will have slightly different perspective and background elements etc. The shorthand about focal length is just a heuristic way of looking at it and getting a basic idea of the change in field of view.
Ok, thanks for clarifying!
So it wouldn't affect what value I input, right?

---------- Post added 08-12-18 at 09:34 AM ----------

QuoteOriginally posted by Bob 256 Quote
You just input the actual focal length to the camera. "Field of view" might be one way of looking at crop factor. "Field of view" usually applies to optical instruments like binoculars and telescopes where different eye lenses can deliver different "field of views" given the same objective (strictly due to the eye lens construction).

If you compare a given camera to one that is full frame, essentially the field of view is changed for a given FL lens but it is due to the sensor being smaller than a FF sensor so the word "crop" more correctly applies. The camera is doing a crop on what would be a FF view. The shake reduction doesn't really care what crop exists. It just needs to know actual focal length to do its work by moving the sensor to compensate for shake, since the image "jitter" is a function of camera movement and FL.
Ok, that makes sense.
Thanks!

08-12-2018, 09:38 AM - 2 Likes   #9
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What you do need to do is understand the crop factor's affect on APS_c cameras if you are coming from a full frame or film.
You input the value on the lens, a 24mm lens is 24mm, but if you are used to FF or film, remember, 24 of FF is the same field of view as 16 on APS-c.

So if you're considering a K-1000 50, you need to be considering an APS-c 35 for the same field of view. And in my post processing software it will actually tell what the FF field of view is. That K-5 is still great camera by the way. Still top 50 on DxO after all these years. MY wife is still using hers and has almost 70,000 actuations on the shutter.
08-12-2018, 09:51 AM - 1 Like   #10
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QuoteOriginally posted by normhead Quote
What you do need to do is understand the crop factor's affect on APS_c cameras if you are coming from a full frame or film.
You input the value on the lens, a 24mm lens is 24mm, but if you are used to FF or film, remember, 24 of FF is the same field of view as 16 on APS-c.

So if you're considering a K-1000 50, you need to be considering an APS-c 35 for the same field of view. And in my post processing software it will actually tell what the FF field of view is. That K-5 is still great camera by the way. Still top 50 on DxO after all these years. MY wife is still using hers and has almost 70,000 actuations on the shutter.
Alright.
So, using a 50mm lens on my K-5 will give me the same field of view as using a 75mm lens on my K1000?

Thanks, I'm glad I got it!
Oh, nice! I got mine with only about 6000 actuations on the shutter.
08-12-2018, 09:58 AM - 1 Like   #11
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QuoteOriginally posted by Ropuchy Quote
So, using a 50mm lens on my K-5 will give me the same field of view as using a 75mm lens on my K1000?
Exactly.
08-12-2018, 10:27 AM   #12
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QuoteOriginally posted by normhead Quote
Exactly.
Ok, thanks!
08-12-2018, 10:40 AM - 1 Like   #13
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QuoteOriginally posted by Ropuchy Quote
Alright.
So, using a 50mm lens on my K-5 will give me the same field of view as using a 75mm lens on my K1000?

Thanks, I'm glad I got it!
Oh, nice! I got mine with only about 6000 actuations on the shutter.
Right. So now a fast-aperture 50mm lens will be a very good choice for a portrait lens, for instance. A K-5 with only about 6000 shutter actuations, if in undamaged perfect condition, is essentially like a new camera! Good for you! The K-5 is still an exceptionally fine camera.
08-12-2018, 11:08 AM - 1 Like   #14
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as has been said, input the actual focal length of the lens

as far as " crop " sensor:

The Crop Factor Unmasked
Field of View vs Focal Length on various formats
By PF Staff in Articles and Tips on Jul 23, 2014

Many of us have cameras with different sensor sizes; this raises the question of which lenses need to be used to get the same field of view on two different formats. Below we provide a table listing focal lengths with equivalent Field of View (FoV) across several sensor sizes. . . . .

Note that the focal length of a lens (say 50 mm) is an optical property of the lens and remains the same no matter what sensor size camera the lens is mounted on.
In other words, an smc Pentax-A 50mm F1.7 lens as shown to the right is a 50 mm lens when mounted on a Pentax Q7 (1/1.7 inch sensor size), on a Pentax K-3 (APS-C sensor size), or on a Pentax film SLR (aka 24 x 36 mm or full frame). The focal length does not change with the camera. But the field of view which the lens captures does change. And so does depth of field, but that is for another article. . . .


Read more at: The Crop Factor Unmasked - Articles and Tips | PentaxForums.com
08-12-2018, 11:17 AM   #15
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QuoteOriginally posted by mikesbike Quote
Right. So now a fast-aperture 50mm lens will be a very good choice for a portrait lens, for instance. A K-5 with only about 6000 shutter actuations, if in undamaged perfect condition, is essentially like a new camera! Good for you! The K-5 is still an exceptionally fine camera.
I have 2 SMC 50mm 1:2 lenses, actually!

And yeah, it's practically new! Came with all the straps and cords.
Hopefully I'll be able to make good use of its abilities!

---------- Post added 08-12-18 at 11:18 AM ----------

QuoteOriginally posted by aslyfox Quote
as has been said, input the actual focal length of the lens

as far as " crop " sensor:

The Crop Factor Unmasked
Field of View vs Focal Length on various formats
By PF Staff in Articles and Tips on Jul 23, 2014

Many of us have cameras with different sensor sizes; this raises the question of which lenses need to be used to get the same field of view on two different formats. Below we provide a table listing focal lengths with equivalent Field of View (FoV) across several sensor sizes. . . . .

Note that the focal length of a lens (say 50 mm) is an optical property of the lens and remains the same no matter what sensor size camera the lens is mounted on.
In other words, an smc Pentax-A 50mm F1.7 lens as shown to the right is a 50 mm lens when mounted on a Pentax Q7 (1/1.7 inch sensor size), on a Pentax K-3 (APS-C sensor size), or on a Pentax film SLR (aka 24 x 36 mm or full frame). The focal length does not change with the camera. But the field of view which the lens captures does change. And so does depth of field, but that is for another article. . . .


Read more at: The Crop Factor Unmasked - Articles and Tips | PentaxForums.com
Alright, thanks for clarifying!
I'll check into that article.
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