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07-18-2013, 02:11 PM   #1
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Question on FA77/DA70 focal lengths

Sorry for the dumb question, but hopefully this is quick to answer.

I see a lot of comparisons on the FA 77 vs. the DA 70, and I'm wondering about equivalent focal lengths. Since the FA is film format and the DA is APS-C format, don't they end up with different equivalent focal lengths? So:

- wouldn't the DA 70 be equivalent to 105 on a full frame, while the FA is 77 on a full frame?
- and is it true that the DA 70 cannot be used on full frame?

So when comparing lenses would one be looking at both of these for the same purpose? And yet I see a lot of head-to-head comparisons of these two. Or is that there's something about the physical focal lengths that makes them both highly regarded and naturally comparable; i.e.: why not compare DA 70 to FA 100?

Thanks for clarification.

07-18-2013, 02:15 PM   #2
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They are both adjusted on APS-C so the 70 is~105 and the 77 is ~115.5mm.

You want to read this In Depth review:
https://www.pentaxforums.com/reviews/da-70mm-vs-fa-77mm-limited-comparison/introduction.html
07-18-2013, 02:20 PM   #3
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QuoteOriginally posted by Docrwm Quote
They are both adjusted on APS-C so the 70 is~105 and the 77 is ~115.5mm.

You want to read this In Depth review:
DA 70mm vs FA 77mm Limited - Comparison: Introduction - PentaxForums.com
Ah. For some reason I was thinking the DA lenses were labeled differently. Like I said, dumb question.

Thanks!
07-18-2013, 02:23 PM   #4
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QuoteOriginally posted by Takumar55 Quote
Ah. For some reason I was thinking the DA lenses were labeled differently. Like I said, dumb question.

Thanks!
No dumb questions. That's a common one, but that means that there is a lot of confusion on it. The In-Depth comparison I linked to is a very good review. Enjoy.

07-18-2013, 03:01 PM   #5
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QuoteOriginally posted by Docrwm Quote
They are both adjusted on APS-C so the 70 is~105 and the 77 is ~115.5mm.
Just to avoid any misunderstandings: The FA 77 was built for FF. It fills the frame fully and, with 77 real millimetres, is what you might call a portrait lens, with a 50% longer FL than a standard lens.

AFAIK the 70 is for APS-C only (that's why it is so small). I don't own one but I suspect that on FF the corners would be pretty dark (beyond recovery).
07-18-2013, 03:26 PM   #6
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QuoteOriginally posted by Pentaxosaurus Quote
Just to avoid any misunderstandings: The FA 77 was built for FF. It fills the frame fully and, with 77 real millimetres, is what you might call a portrait lens, with a 50% longer FL than a standard lens.

AFAIK the 70 is for APS-C only (that's why it is so small). I don't own one but I suspect that on FF the corners would be pretty dark (beyond recovery).
I've mounted my 70 to my SF-1 and the image in the 100% FF viewfinder is fine. Of course only the emergence of an actual Pentax FF dSLR would make this a meaningful issue.
07-18-2013, 03:34 PM   #7
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The DA is a 70mm lens and the 77 a 77mm lens regardless of format. However, the 77 is designed to cover the 35mm format (FF) whereas the 70mm to cover APS. If you want to know these lenses focal lenghts are in 35mm format equivalents you multiply their focal lenghts with 1.5. Ie you need an 115,5mm lens on an FF camera to get same angle of view as the 77 on an APS camera.
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