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4 Days Ago - 1 Like   #1
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What is the "crop factor" of the 645Z

I've been shooting Pentax since 1976 and think focal lengths in the 35mm format. Still not used to APS-C conversions, but getting there. I purchased a 645Z the other day and now need some new lenses. To help me decide what to get, it would be helpful to know the crop factor for the 645Z. There are various numbers running around, which vary widely from each other. Can someone point me to the accurate conversion number?

(The one number I've been using is 0.62075, but nobody else seems to be using that number. 0.62075 translates the 75mm "normal" to be 46.5 in the 35mm world.)

Thanks for any help. I've gone from 35mm to APS-C to the Q. About time to go experiment the other way and try medium format.

4 Days Ago - 4 Likes   #2
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One of the hurdles is that they have different aspect ratios, the cropped 645 is 44x33mm and 35mm is 35.9x 24mm. How many come up with for crop factor is by using the diagonal dimension .

cropped 645 55mm and 35mm as 43.18

43.18/55=0.785 crop factor
If you are going to use the full width let's say your final image is 16 by 9 aspect, then 35.9/44= 0.815 crop factor
4 Days Ago - 2 Likes   #3
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The crop factor of the 645Z relative to the K-1 is 0.78

The FA645 75/2.8 gives a similar angle of view on the 645Z as a 58mm lens would on the K-1, whereas the DFA645 55/2.8 equates roughly to 43mm as Ian points out above

Last edited by Sandy Hancock; 4 Days Ago at 11:55 PM.
4 Days Ago   #4
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Thank you, Ian and Sandy. Since I posted the above, I went into the picture thread and looked at the EXIF data for those pictures where it was available. It confirms what you said. After recalculating my chart, I'm in better shape than I initially thought. I have a D FA 55/2.8, a FA 75/2.8, a FA* 300/4, a FA 80-160/4.5, and a Rear Converter-A 2x coming in the mail from various sources. To fill the gaps, I'll start hunting up a 35/3.5 of any vintage and a FA 200/4, probably from B&H as they are heavily discounted right now. There are a lot of Rear Converter-A 1.4x available from Japan through eBay.

4 Days Ago - 1 Like   #5
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QuoteOriginally posted by volosong Quote
Thank you, Ian and Sandy. Since I posted the above, I went into the picture thread and looked at the EXIF data for those pictures where it was available. It confirms what you said. After recalculating my chart, I'm in better shape than I initially thought. I have a D FA 55/2.8, a FA 75/2.8, a FA* 300/4, a FA 80-160/4.5, and a Rear Converter-A 2x coming in the mail from various sources. To fill the gaps, I'll start hunting up a 35/3.5 of any vintage and a FA 200/4, probably from B&H as they are heavily discounted right now. There are a lot of Rear Converter-A 1.4x available from Japan through eBay.

congratulations on joining the 645 club....

be sure to keep an eye out for a deal on the 120 Macro, also....
3 Days Ago - 1 Like   #6
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QuoteOriginally posted by volosong Quote
Thank you, Ian and Sandy. Since I posted the above, I went into the picture thread and looked at the EXIF data for those pictures where it was available. It confirms what you said. After recalculating my chart, I'm in better shape than I initially thought. I have a D FA 55/2.8, a FA 75/2.8, a FA* 300/4, a FA 80-160/4.5, and a Rear Converter-A 2x coming in the mail from various sources. To fill the gaps, I'll start hunting up a 35/3.5 of any vintage and a FA 200/4, probably from B&H as they are heavily discounted right now. There are a lot of Rear Converter-A 1.4x available from Japan through eBay.
You are going to be in hog heaven my friend. Had my Z since it first came out, early adopter. Still totally in love with it. One interesting thing: the aspect ratio on the Z makes wides seem wider to me, such that my real wides don't get tons of use, while the 35 and 55 get a lot. Especially the DFA 55, which I love---yet on 35FF it's not an FL I use much.
3 Days Ago   #7
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Thanks for the welcome. Ordered a FA 200 and a 1.4x converter from Japan this morning. Almost sprung for a 400, but decided to wait. The FA 35 can wait too. If I really miss that focal length, I'll think about hunting one up. I should probably investigate a more heavy duty tripod too.

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The 645 FA 200 mm f/4 : one of the best lenses anyone could hope for !



2 Days Ago - 1 Like   #9
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QuoteOriginally posted by volosong Quote
Thank you, Ian and Sandy. Since I posted the above, I went into the picture thread and looked at the EXIF data for those pictures where it was available. It confirms what you said. After recalculating my chart, I'm in better shape than I initially thought. I have a D FA 55/2.8, a FA 75/2.8, a FA* 300/4, a FA 80-160/4.5, and a Rear Converter-A 2x coming in the mail from various sources. To fill the gaps, I'll start hunting up a 35/3.5 of any vintage and a FA 200/4, probably from B&H as they are heavily discounted right now. There are a lot of Rear Converter-A 1.4x available from Japan through eBay.
Nice set-up!
I'm also a late adopter, got my 645z less than a year ago.
Since then, I've tried many of the lenses, and finally settled on A35, FA45-85, FA120, FA*300, and A*600.
Two tripods, a lighter one with geared head, and a heavier one with gimbal head for the two long telephotos.
I'm delighted with the IQ and the ergonomics!
Marco
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