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10-20-2015, 07:42 PM   #1
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Pentax 645 lens to FF

Well, Im really exciting to use 645 lens to FF if Pentax make an AF adaptor for 645 lenses. (I don't have any adaptor yet)

I have 645 macro 120mm lens.

If I use this lens on FF, what's the focal length?

10-20-2015, 07:48 PM - 1 Like   #2
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120mm
10-20-2015, 08:07 PM   #3
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https://www.pentaxforums.com/forums/48-pentax-medium-format/133518-crop-factor-645d-2.html

An old topic that covers this in great detail. Essentials to remember. Focal length does not change. Equivalent focal length is just mental shorthand to give a comparison frame of reference. Crop factor is hard to compare in 645d vs ff of apsc since the ratio of height vs width isn't the same but a rough estimate is that your lenses would act as though they were 1.27x longer than they are in your current frame of reference. In other words the 120mm on FF gives the same field of view as a 152mm lens on the 645d.

Another way of looking at this is that a 95mm lens on FF gives the same field of view as a 120mm on a 645d/z.
10-20-2015, 08:22 PM   #4
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Pepperberry Farm is quite right, Sunshine.


The focal length will still be 120mm, the FoV will be about that of a 150mm lens.


There is a 645 to K-mount adaptor already, no?

10-20-2015, 08:30 PM   #6
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I mean the adaptor with AF function.
10-20-2015, 08:36 PM   #7
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QuoteOriginally posted by sunshine7913 Quote
I mean the adaptor with AF function.
And which one is that?
10-20-2015, 08:51 PM   #8
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QuoteOriginally posted by sunshine7913 Quote
I mean the adaptor with AF function.
There aren't any.


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10-21-2015, 12:37 AM   #9
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Worth the effort?

Is the quality of 645 lens good enough to justify adapting to K-3? I have A55mm, A200mm, and A80-160mm.
10-21-2015, 03:09 AM   #10
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I asked a similar question a while back:

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/301113-m42-vs-645-a.html


there are adapters for 645 to K; all make the 645 lenses fully manual.... I am still debating the question I posed in the topic...
10-21-2015, 06:16 AM   #11
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QuoteOriginally posted by sunshine7913 Quote
Well, Im really exciting to use 645 lens to FF if Pentax make an AF adaptor for 645 lenses. (I don't have any adaptor yet)
QuoteOriginally posted by clackers Quote
There is a 645 to K-mount adaptor already, no?
QuoteOriginally posted by sunshine7913 Quote
I mean the adaptor with AF function.
QuoteOriginally posted by jatrax Quote
And which one is that?
QuoteOriginally posted by Adam Quote
There aren't any.
QuoteOriginally posted by pepperberry farm Quote
there are adapters for 645 to K; all make the 645 lenses fully manual....
The way I read this was that OP posed the question with the hope that Ricoh would create a 645 AF adapter. I don't think the first post was meant to be a question as to the existence of an adapter with AF capabilities.

I'm not sure what such an item might cost but I suspect it would be cost prohibitive for most people and only really appeal to those with a stable of lenses for their 645.
10-21-2015, 08:01 AM   #12
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QuoteOriginally posted by UncleVanya Quote
posed the question with the hope that Ricoh would create a 645 AF adapter.
Missed that. Agree it would be cool but also cost prohibitive.

Over in this thread there is a rumor showing a slide that mentions a 645 adapter. Looks quite fake to me & most others but who knows.
10-21-2015, 09:18 AM   #13
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QuoteOriginally posted by ivanvernon Quote
Is the quality of 645 lens good enough to justify adapting to K-3? I have A55mm, A200mm, and A80-160mm.
I don't have any of those lenses but among my lenses (33-55, 75, 120Macro, 150-300) only the 120mm is worth using on 35mm.
10-21-2015, 09:32 AM   #14
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QuoteOriginally posted by clackers Quote
Pepperberry Farm is quite right, Sunshine.


The focal length will still be 120mm, the FoV will be about that of a 150mm lens.


There is a 645 to K-mount adaptor already, no?
120 times 1.5 = 180 !!!
10-21-2015, 11:04 AM   #15
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QuoteOriginally posted by RuiC Quote
120 times 1.5 = 180 !!!
But the crop factor in question depends on frame of reference. From a 645d or z the crop factor is only 1.27x.

This chart and article helps.
The Crop Factor Unmasked - Articles and Tips | PentaxForums.com
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