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08-07-2014, 06:38 PM   #1
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What gives??

A couple of nights ago, I joined the Pentax forum since I am a Pentax System owner, but still a film camera holdover (I have never own a digital camera). I just recently decided that I should get on the digital era already , and I have been researching about cameras, mostly FF digital, since I am so familiar with the format (film).

The thing is... after reading so much about the Pentax K3, I have been kind of lured to it, but, it being an APS-C format, the lenses available for it are O.K for general photography. To my surprise, after searching at B & H, Adorama, etc., I came empty with the one lens I was hoping to find specifically made for Digital cameras: an 85mm f/1.4 1.8 or 2.8 maximum aperture equivalent to a FF, I found none. This is my favorite lens for portraiture which is what I mostly do with my film system. The closest find was the Pentax 55mm f/1.4 which translates to an equivalent 82.5mm f/2.1, but at a so-so .17x (1:6) magnification.

Now, since I am not a digital connoisseur my question is: am I missing/misunderstanding something that I do not know about cameras/lenses for digital systems?; since no other lens was available (according to me) to match exactly an 85mm equivalent to a FF with an acceptable equivalent maximum aperture of 2.8 or less. Would the above mentioned Pentax 55mm f/1.4, .17X claimed magnification factor translate into a magnification equivalent factor in a FF, or would the magnification remains the same in both formats?, sorry, I hope I'm making sense. Thanks!!!

08-07-2014, 06:52 PM   #2
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QuoteOriginally posted by Robert_1 Quote
Pentax 55mm f/1.4 which translates to an equivalent 82.5mm f/2.1
No, it translates to a 82.5mm F1.4 Aperture is a constant - I think that's what you're misunderstanding. The 55mm's field of view is roughly equivalent to a 85mm lens on film, so the DA* 55mm is the lens you should get.

A lens's maximum magnification is related to the minimum focusing distance and it has nothing to do with the format being used. 0.17x is actually pretty good, since most 85mm's (such as the Sigma 85mm F1.4) have a minimum focusing distance of 85cm, which is longer than that of the 55mm. The aformentioned Sigma has a max. magnification of 0.11x, which means it's actually less versatile for close-up shooting.

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08-07-2014, 07:06 PM   #3
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"Magnification" refers to the maximum size of the image cast on the sensor at the minimum focus distance. It's a measure of macro capability more than anything else.

Yes, the DA* 55mm has only 1:6 maximum magnification. That's related to its 45cm minimum focus distance. You'll never want to get that close for portraits so don't worry about the magnification. (citing my math so others can fact-check. An APS-C sensor is approximately 23mm wide. At 1:6 magnification, 23mm * 6 = 138 mm = 5.4 inches. An object 5 inches wide would fill the entire frame.)

For comparison purposes, the older D-FA (or even older FA) 50mm macro is similar to the DA* 55mm focal length. Both lenses will give near the same size image at the same distance from the subject. The macro lens, though, let's you move much closer before it becomes impossible to focus; the 19.5cm minimum focus distance yields 1:1 magnification.

Last edited by DeadJohn; 08-07-2014 at 07:13 PM.
08-07-2014, 07:14 PM   #4
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QuoteOriginally posted by Adam Quote
No, it translates to a 82.5mm F1.4 Aperture is a constant - I think that's what you're misunderstanding. The 55mm's field of view is roughly equivalent to a 85mm lens on film, so the DA* 55mm is the lens you should get.

A lens's maximum magnification is related to the minimum focusing distance and it has nothing to do with the format being used. 0.17x is actually pretty good, since most 85mm's (such as the Sigma 85mm F1.4) have a minimum focusing distance of 85cm, which is longer than that of the 55mm. The aformentioned Sigma has a max. magnification of 0.11x, which means it's actually less versatile for close-up shooting.
@ Adam: Thanks. Sorry, I am somehow confused translating equivalents from one format to another. After reading your reply, I check the source of my equivalent measurements, and I am realizing that the equivalency the article was talking about for F-numbers was in relation to "depth of field". This means to me that the Pentax K3 + the 55mm f/1.4 would be the camera system to get. Thanks again. If after Photokina, Pentax does not come through with a FF camera, I will definitely get the Pentax system, if I decide not to go with a FF Nikon system (kind of a lot of money for a new system).

---------- Post added 08-07-14 at 10:23 PM ----------

QuoteOriginally posted by DeadJohn Quote
"Magnification" refers to the maximum size of the image cast on the sensor at the minimum focus distance. It's a measure of macro capability more than anything else.

Yes, the DA* 55mm has only 1:6 maximum magnification. That's related to its 45cm minimum focus distance. You'll never want to get that close for portraits so don't worry about the magnification. (citing my math so others can fact-check. An APS-C sensor is approximately 23mm wide. At 1:6 magnification, 23mm * 6 = 138 mm = 5.4 inches. An object 5 inches wide would fill the entire frame.)

For comparison purposes, the older D-FA (or even older FA) 50mm macro is similar to the DA* 55mm focal length. Both lenses will give near the same size image at the same distance from the subject. The macro lens, though, let's you move much closer before it becomes impossible to focus; the 19.5cm minimum focus distance yields 1:1 magnification.
@DeadJohn: Thank you for the clarification, this helps clear my confusion!!!

08-07-2014, 07:30 PM   #5
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QuoteOriginally posted by Robert_1 Quote
@ Adam: Thanks. Sorry, I am somehow confused translating equivalents from one format to another. After reading your reply, I check the source of my equivalent measurements, and I am realizing that the equivalency the article was talking about for F-numbers was in relation to "depth of field".
It's a contentious issue around here.

Two sets of comparisons:

1) APS-C at 55mm, F/1.4, and say 1/100s, and 36x24 (FF) at 84mm*, F/1.4 and 1/100s... the FF picture will have less depth of field, and less image noise, assuming the same sensor technology is used in both (like the D800 and the D7000).


2) APS-C at 55mm, F/1.4, and 1/100s, vs. 36x24 at 84mm F/2.1 and 1/100s... the FF picture will have the same depth of field and the same image noise, assuming the same sensor technology.




Personally, when deciding between two systems, I find it much easier to compare on equivalent focal length and equivalent aperture, and go from that baseline. Others vehemently disagree with me.



*I used 84mm as the crop factor is ~1.52 for the K-5. Don't know what it is for the K-3.
08-07-2014, 07:31 PM   #6
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And don't forget: if you already own film-era K-mount lenses, they will work perfectly fine on APS-C Pentax DSLRs.
My kit currently consists of 2 APSC-zooms and 4 Full Frame primes!
I use the primes on both my film bodies and the K-5IIs.
Also I am waiting for a FF DSLR from Pentax, to use them even more :-)

Tamron AF 17-50mm F2.8
Pentax SMC DA 55-300mm F4-5.8
Sigma AF 15/2.8 EX DG FISHEYE
Pentax SMC FA 31 F1.8 Limited
Pentax SMC M-50 F1.4
Pentax SMC FA* 85mm F1.4
08-07-2014, 07:32 PM   #7
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QuoteOriginally posted by Robert_1 Quote
If after Photokina, Pentax does not come through with a FF camera....
Welcome to Pentaxforums. People have been saying the above for about (someone help me) how many years?
08-07-2014, 09:29 PM   #8
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Also, don't forget about the FA77 f1.8 - I have the da*55 and it's a stellar lens, but there's something about the FA77 that's pretty special. Of course the fov is around 115mm but it's a pretty magical lens. I forget why the designer of this lens chose 77mm (and 43mm and 31mm for that matter) for the focal lengths...

08-08-2014, 06:57 AM   #9
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43 was a normal lens.
08-08-2014, 07:41 AM   #10
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For a "manual focus" film shooter with a large collection of Pentax-M lenses, I found the dSLR offerings frustrating. The image quality is fine, but the cameras are poor for manual focus, even after changing the focus screen. Plus all my old wide-angles cropped too much. The K-5 would really require me to buy new lenses, even though I was happy with my old ones.
So for me the answer was to think outside of the (Pentax) box, and I found the Sony A7 with K adapter is a much better solution for my Pentax-M lenses for the way I like to shoot. Even my 20mm SMC-M is stellar with its full ~95 deg angle of view, and the 85 f2.0 SMC is still a fine portrait lens. The A7 is much easier to manual focus - just by judging viewfinder sharpness - than any of the Pentax offerings.
08-08-2014, 07:57 AM   #11
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Hm, yeah the A7 seems to be the go-to solution for people who can cope with MILC and want to use Pentax glass. Enjoy :-)
I personally found the handling of the camera really not practical, which is why I will have to wait for a DSLR in K-mount... or a different style of MILC in FF.
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