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11-08-2017, 06:05 AM   #1
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K-1 Crop Function

As a new K-1 user, I have a question about the effect of the Crop function. If I mount a DA* 400mm on the K-1 in Crop mode, will I have an effective 600mm lens?

Thank you.

---------- Post added 11-08-17 at 07:09 AM ----------

Correction: will the DA*300mm give me an effective 450mm lens?

11-08-2017, 06:22 AM   #2
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If you select the APS-C crop, you will get the field of view of a 450 mm lens, yes.

But I'd suggest you record the full frame and then crop as needed in post.
11-08-2017, 06:24 AM - 1 Like   #3
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No. Cropping, either in an image processing software, by using a camera with a smaller sensor or with a pair of scissors cutting the borders of a print does not change the focal length of your lenses.
11-08-2017, 06:28 AM   #4
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QuoteOriginally posted by cpoteet Quote
As a new K-1 user, I have a question about the effect of the Crop function. If I mount a DA* 400mm on the K-1 in Crop mode, will I have an effective 600mm lens?

Thank you.

---------- Post added 11-08-17 at 07:09 AM ----------

Correction: will the DA*300mm give me an effective 450mm lens?
It makes no difference to your images.

Field of view is measured as an angle. On APS-c that would be 5.4 horizontal and 4.6 which would be the equivalent of 450mm is it were a full frame image.

The 300 on full frame will be approximately the equivalent FoV of a 200mm lens on APS-c. The DA* 200 on APS-c is 8.1 and 6.9. But only the FoV changes. The resolution and image is the same, there is just less of it. So, it's not the same as a 150--450 in full frame mode, because you've cropped so much of the sensor.

SO it's not the same as 450 in full frame mode, you've lost a lot of resolution, but it's a lower res 450 FF image.

So really, unless you have large file issues with your computer, shoot in FF mode and crop to suit.


Last edited by normhead; 11-08-2017 at 07:14 AM.
11-08-2017, 06:29 AM   #5
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As far as I know, there is no DA * 400mm, but the simplified answer is yes.
If my math is right, 400mm f/5.6 at ISO100 on APS-C or crop mode is roughly like using 600mm f/8.5 at ISO400 on FF on full mode.

EDIT: and 300/4 on crop is like 450/6 on FF.
11-08-2017, 06:58 AM   #6
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QuoteOriginally posted by cpoteet Quote
As a new K-1 user, I have a question about the effect of the Crop function. If I mount a DA* 400mm on the K-1 in Crop mode, will I have an effective 600mm lens?

Thank you.

---------- Post added 11-08-17 at 07:09 AM ----------

Correction: will the DA*300mm give me an effective 450mm lens?
It will give you the same field of view as a 450mm on a 36mm x 24mm sensor ("full" frame). However, when prints are made, the image from the APS-C ("crop") sensor will have to be enlarged much more than the image from the full frame sensor to get the print to the same size as from the "full" frame, thus rendering the image fuzzier than the image from the "full" frame sensor. If you want a really long effective focal length, mount the telephoto on a Pentax Q. Of course, the resulting images will have to be greatly enlarged to view them at the same size as the prints from a "full" frame sensor.
11-08-2017, 07:16 AM   #7
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QuoteOriginally posted by pete-tarmigan Quote
Of course, the resulting images will have to be greatly enlarged to view them at the same size as the prints from a "full" frame sensor.
Or less reduced, depending on the size of the print.
11-08-2017, 08:49 AM   #8
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Damn crop factors again ! The single most useless invention of the camera industry.

---------- Post added 11-08-17 at 04:01 PM ----------

QuoteOriginally posted by topace Quote
If my math is right, 400mm f/5.6 at ISO100 on APS-C or crop mode is roughly like using 600mm f/8.5 at ISO400 on FF on full mode.

EDIT: and 300/4 on crop is like 450/6 on FF.
Take the DA* 300mm lens. The magnifying/telephoto properties of that lens produces an image circle of a certain resolution. Whether the OP then uses either crop-mode on the K1 to produce a cropped image, or shoots in FF mode and crops the photo in pp he still ends up with identical images, identical resolution.

Now if he slaps a D-FA 150-450 on his k1 at 450mm in FF mode his lens is producing a more magnified/larger image of his subject on the sensor. If he now crops this image to the same proportions as the 300mm images (ie the bird he is photographing fills the frame to the same extent) he will be using more pixels and achieve higher resolution because the image was recorded by a larger amount of pixels in the first place.

These two examples show that using the 300mm lens in K-1 crop-mode is nothing like using a 450mm lens on the same camera.

11-08-2017, 07:25 PM   #9
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It will take the same image as full frame with the sides cut off.

The advantage of this mode is a faster frame rate. That is what I use it for.

That and saving disk space when shooting a stationary object that fits into the smaller frame.

Last edited by derekkite; 11-08-2017 at 07:32 PM.
11-08-2017, 10:31 PM   #10
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A 300mm lens on a Pentax APS-C camera give's you a image equivalent, or fills the sensor the same as a 450mm lens would on a full frame camera. You multiply the lens by 1.5 when fitted to a Pentax APS-C camera.

But as stated, your better off when using the K1 to shoot in full frame mode and crop as desired later.
11-08-2017, 10:58 PM - 3 Likes   #11
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This 'equivalence' crap has to stop!

The aperture doesn't change. The focal length doesn't change. The exposure doesn't change. The depth of field doesn't change.

What you get is the middle fifty percent of the FF frame, that's actually what 'crop' means, a reduced field of view.
11-08-2017, 11:16 PM   #12
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If you have the DA*300 already, just shoot it in full frame mode. It is officially designated by Pentax as full frame compatible.

Put the K-1 in crop mode if you use the HD DA 1.4x Rear Converter with the DA*300 though. The DA*420/5.6 is definitely a crop lens
11-09-2017, 02:28 AM   #13
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QuoteOriginally posted by Craig66 Quote
A 300mm lens on a Pentax APS-C camera give's you a image equivalent, or fills the sensor the same as a 450mm lens would on a full frame camera
A 300mm lens on aps-c camera (or K-1 in crop mode) gives the same "field of view" as a 450mm lens on K-1 in FF mode. What it does not do is give an "equivalent image". The magnifying/telephoto properties of a 450mm lens is 1.5 times that of the 300mm.

You will not achieve the same resolution or "reach" using the 300mm in crop mode on the K1 as using a 450 mm lens in FF mode. The same is true for using the 300mm on an aps-c sensor camera, although output quality depends on other factors such as pixel pitch too.

The OP asks if the 300mm in crop mode gives him an "effective" 450mm lens? Apart from field of view the answer is no. I expect when folk ask this question they are more concerned with "reach", magnifying ability, call it what you wish, rather than field of view.
11-09-2017, 03:56 AM   #14
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These kind of questions are easy to answer and understand when you also put the image size on the equation.

So the DA*300 on the K-1 will give you in FF mode a 36.4Mpxl frame which if you crop it in PP to the APS-C size, there will be 15Mpxl remaining in the resulting image.
If you shoot in APS-C mode with the DA*300 you will get exactly the same frame of the previous cropped image with exactly 15Mpxl, so you gain nothing at all, but the higher frame rate and smaller files in your SD cards.
11-09-2017, 03:59 AM - 1 Like   #15
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Cropping changes the angle of view of a lens, it doesn't really do anything else. If you can get closer to your subject or can afford a longer lens, you are probably better doing that. That said, even fifty percent crops from K-1 images still look good. There is just no particular benefit (other than file size and frame rate) to doing it in camera versus doing it after the fact.
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