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07-05-2017, 08:49 AM   #1
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What is the Size of the DA* 60-250 on Fullformat

Hello

What will be the corrected Size for the SMC DA* 60-250, designed for APS-C, when you connect it to the K-1?
80-300 or 50-200?

Gérard


Last edited by Gerard_Dirks; 07-09-2017 at 01:57 AM.
07-05-2017, 08:53 AM   #2
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It'll be 60-250. I assume you mean K-1 and not "K2".
07-05-2017, 08:57 AM   #3
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Size? or Focal Length? Obviously size won't change.
Focal length is always a spec for 35mm full frame format regardless of the compatibility with APS-C only or FF. So from focal length perspective it is still 60-250mm FF or not but the crop factor of 1.5 kicks in for APS-C bodies. Its only a matter of the image circle which may or may not offer FF coverage. 60-250 mods are published and popular. So once modified the image circle serves FF sensor too.

Hope this helps.
07-05-2017, 10:11 AM   #4
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@pres589, i mean K-1 ;-)

@shardulm. I am really confused. When we talk about the 20 year old "SMC Pentax-FA 28-200mm F3.8-5.6 AL [IF]" the focal length will be 42-300mm when you use this lens on an APS-C.

Reverse, the SMC DA* 60-250mm designed for APS-C should be lower when use it on the K-1! e.g. 40-166mm ?? Who can confirm this or is their something wrong with my thinking ?!?! :-(


Last edited by Gerard_Dirks; 07-05-2017 at 10:14 AM. Reason: error
07-05-2017, 10:16 AM   #5
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QuoteOriginally posted by Gerard_Dirks Quote
@pres589, i mean K-1 ;-)

@shardulm. I am really confused. When we talk about the 20 year old "SMC Pentax-FA 28-200mm F3.8-5.6 AL [IF]" the focal length will be 42-300mm when you use this lens on an APS-C.

Reverse, the SMC DA* 60-250mm designed for APS-C should be lower when use it on the K-1! e.g. 40-166mm ?? Who can confirm this or is their something wrong with my thinking ?!?! :-(
Nope. The "effective" focal length on APS-C for the 60-250mm is 90-375mm. Pentax lists the actual focal length, regardless of the sensor size. DA* 60-250mm is 60-250mm on full frame.
07-05-2017, 10:20 AM - 1 Like   #6
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Focal length will be 60-250.
QuoteOriginally posted by shardulm Quote
Focal length is always a spec for 35mm full frame format
Actually focal length is a property of the lens and has nothing to do with the format of the film or sensor it is used on. Angle of view however, does change with the sensor or film size.
A 645 28-45 is still 28-45 whether it is used on the 645z, the K-1, the K-3 or m4/3 or even on the Q. However the angle of view will be dramatically different, from very wide angle on the 645 to long telephoto on the Q.

QuoteOriginally posted by Gerard_Dirks Quote
What will be the corrected Size
The focal length has nothing to do with being designed for APS-C or any other format. The critical point is whether the image circle of a particular lens covers the sensor or film of the camera it is mounted to. In this case, the 60-250 has an internal baffle that restricts the image circle to APS-C size. It works on FF mostly but with a strong vignette at some focal lengths. Remove the baffle and it becomes fully usable on FF.
See here: DA* 60-250 mod for FF - PentaxForums.com

Last edited by jatrax; 07-05-2017 at 10:28 AM.
07-05-2017, 10:35 AM - 1 Like   #7
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When speaking about effective focal length full frame is always the reference. Otherwise the confusion will be endless. To get the range the 60-250 gives you on aps-c you would need a 90-375mm zoom on the K-1. The range that the DA* 60-250 will give you on the K-1 is comparable to a 40-167 mm lens on aps-c so it would act as a more versatile version of the DA*50-135 on aps-c on full frame. See how confusing it gets?
07-05-2017, 11:58 AM   #8
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QuoteOriginally posted by D1N0 Quote
The range that the DA* 60-250 will give you on the K-1 is comparable to a 40-167 mm lens on aps-c
D1N0 I believe is answering the OPʻs intended question above. As a film and digital teacher since the early 90ʻs, I am often asked questions that really twist my brain to understand. Itʻs like a digital student taking a film class and asking "if dodging blocks the light, wouldnʻt it get make the print darker?" Or how do motion picture film cameras eliminate rolling shutter?

Living in a predominantly APS-C native world now, it is confusing as the world was once FF native. Everyone posted above is correct: 60-250mm on ANY format would be 60-250mm. But if you only know what fov 60-250mm does on APS-C, the OP wanted to understand what equivalent focal length would look (fov) on APS if he was using the 60-250mm on FF.

Of course, if heʻs a Canon shooter, then itʻs 1.6x, not 1.5x...so more like 37-156mm.

07-05-2017, 02:33 PM   #9
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QuoteOriginally posted by Gerard_Dirks Quote
I am really confused. When we talk about the 20 year old "SMC Pentax-FA 28-200mm F3.8-5.6 AL [IF]" the focal length will be 42-300mm when you use this lens on an APS-C.
The focal length never changes based on the camera body. See this article for a full explanation:

https://www.pentaxforums.com/articles/photo-articles/table-of-equivalent-focal-lengths.html

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07-05-2017, 03:01 PM - 1 Like   #10
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QuoteOriginally posted by Gerard_Dirks Quote
@pres589, i mean K-1 ;-)

@shardulm. I am really confused. When we talk about the 20 year old "SMC Pentax-FA 28-200mm F3.8-5.6 AL [IF]" the focal length will be 42-300mm when you use this lens on an APS-C.
You're confusing the focal length, which doesn't change with different formats, vs. field-of-view, which has an apparent change only because the image circle is cropped more in smaller formats.

So a 28-200mm lens designed for FF is still a 28-200mm on APS-C, but with APS-C it may LOOK the equivalent of a 42-300mm on FF.
07-05-2017, 03:02 PM   #11
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It's a sort of 'rite of passage' that has to be passed on the journey towards gaining the complete knowledge of all things photographic

Here's another way to consider the specific situation you're asking about .... Say you had a K5 and a K1, and you stayed standing in the same place. On the K5 you put the 60-250mm lens .... Zooming and looking through the viewfinder gives you a certain amount of view coverage ...(the borders of the image frame), so you can see a certain amount of the view in front of you.

Now if you next picked up the K1, if you wanted to replicate the exact same series of views and amount of coverage that was visible through the K5, then you would need to fit a zoom with a longer starting and ending focal length. My maths is terrible, but it's about 90-350mm......someone will correct me.....

Last edited by mcgregni; 07-05-2017 at 03:19 PM.
07-05-2017, 06:33 PM   #12
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QuoteOriginally posted by Gerard_Dirks Quote
@pres589, i mean K-1 ;-)

@shardulm. I am really confused. When we talk about the 20 year old "SMC Pentax-FA 28-200mm F3.8-5.6 AL [IF]" the focal length will be 42-300mm when you use this lens on an APS-C.

Reverse, the SMC DA* 60-250mm designed for APS-C should be lower when use it on the K-1! e.g. 40-166mm ?? Who can confirm this or is their something wrong with my thinking ?!?! :-(
All lenses' focal lengths are specified for full frame (35mm). A 60-250mm is a 60-250mm on any body FF, APS-C or mft.
What changes is the FOV (field of view) based on the sensor size. What that means is how much part of the image circle is captured by the sensor. In case of a FF 100% of the image circle (rectangle of course) is captured. With APS-C it is a smaller rectangle and with mft it is even smaller a rectangle. This is similar to what you would get when you crop a FF image by 50% or 25% in the center. The smaller the rectangle of the sensor the more (cropped) zoomed-in you are (smaller FOV) into the image. But the zoom-in is not because of the lens but because of the size of the sensor. This phenomenon is often mis-stated as an increased FL (200mm becomes 300mm on APS-C for ex because of the 1.5x crop factor between the FF sensor size and APS-C sensor size OR 400mm on mft 2x and so on). The focal length does not really change here because of the optics. . It's the FOV that changes because of the sensor size.
Now for 60-250 lens when used on APS-C body the FOV will be equivalent to an FOV from a lens specified at 90-375mm.

To give you another example the DA*50-135mm on APS-C body will give you similar FOV range that is offered by D-FA*70-200 on K-1 (FF). And so will a da*16-50 on an APS-C will give you a similar FOV range that is offered by D-FA24-70 on K-1 (FF).

Last edited by shardulm; 07-05-2017 at 06:52 PM. Reason: Competed post
07-05-2017, 06:41 PM - 1 Like   #13
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QuoteOriginally posted by D1N0 Quote
When speaking about effective focal length full frame is always the reference.
...and that is why use of the the term "effective focal length" should be taboo. Most people currently doing digital photography have never touched a 35mm film canister. Even those who have, usually have a poor intuitive sense of what to expect of a 28mm or 135mm lens when shooting to the 24x36mm frame. Strangely, this has been a non-issue with users of the multiple formats* supported with 120 roll film during its long history. Similarly, large format shooters don't agonize over whether they will be able to replicate a 35mm frame exposed with a 70mm lens. Most know the basics of what to expect of their gear and have larger technical demons to battle before the exposure is made.

The most useful advice is to leave focal length alone and frame the lens choice discussion in terms of camera position (perspective), composition, and amount of enlargement required to bring the desired crop to final viewing size. If a user must know, tell them that the 24x36mm format provides a field of view that is half again wider on the diagonal than APS-C.


Steve

(...if one crops a K-1 image to 7360x3200, does that change the DOF in the final print?)

* 6x12cm, 6x9cm, 6x7cm, 6x6cm, 6x4.5cm, and 6x3cm. FWIW, effective focal length calculations sort of fall apart the further one moves from the 3:2 aspect ratio.

Last edited by stevebrot; 07-05-2017 at 07:16 PM.
07-05-2017, 07:26 PM - 2 Likes   #14
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QuoteOriginally posted by stevebrot Quote
If a user must know, tell them that the 24x36mm format provides a field of view that is half again wider on the diagonal than APS-C.
Probably more helpful for a new FF shooter is a short table of common applications:
  • Ultra-wide: 20mm and shorter
  • Very-wide: 24mm
  • Wide: 28mm
  • Moderate wide (street photography): 35mm or 40mm
  • Normal: 45mm through 58mm
  • Short tele (portrait) 75mm through 90mm
  • Medium tele: 100mm through 150mm (some use up to 135mm for portrait)
  • Long tele: 150mm through 250mm
  • Ultra-long tele: 300mm and longer
In context of the original post for this thread, the DA* 60-250 covers the range of normal through long-tele subjects.


Steve
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