[uintaangler]

I recently became aware of a Pentax adaptor for using Pentax 67 lenses on the 645D
I am new to all things Pentax and trying to learn about Pentax glass now that I have a 645D to play with
With the 25mm lens offered with the 645D being so expensive and me being primarily a landscape shooter - it would be great to discover that there is a ultra-wide 67 lens that worked well on the 645D
Thanks,
Bob

[Adam]

This is the widest 6x7 rectilinear lens:
SMC Pentax 67 / SMC Pentax-6x7 45mm F4 Reviews - 67 Wide-Angle Primes - Pentax Lens Reviews & Lens Database

On the 645D it would give you a FOV of about 54 degrees, which is about the same as a 24mm on APS-C and a 35mm on film.

[uintaangler]

Hi Adam,
Thanks for responding
* What is the focal length conversion factor for the 645D? In other words for the FA 35mm 645 F/3.5 lens I already own - how would it compare to using a 35mm Nikon lens on my Nikon D800?
* How do the Pentax 67 lenses compare to the ( is it 5? ) lenses available for the 645D: 24, 35, 55, 120, 300? Is it worth picking up an adaptor and buying some of the 67 lenses?
Bob

[Bob from Aus]

This chart from Ricehigh might help. He has a reputation for very strong opinions.
RiceHigh's Pentax Blog: What is/are the Meaning(s) of a Cropped Digital System Now?

[Adam]

Hi Adam,
Thanks for responding
* What is the focal length conversion factor for the 645D? In other words for the FA 35mm 645 F/3.5 lens I already own - how would it compare to using a 35mm Nikon lens on my Nikon D800?
* How do the Pentax 67 lenses compare to the ( is it 5? ) lenses available for the 645D: 24, 35, 55, 120, 300? Is it worth picking up an adaptor and buying some of the 67 lenses?
Bob

It's full frame is a 1.2x crop vs the 645D.

Here's a table showing you what focal lengths match up:


Adapted lenses are fine since Av mode is supported. No stop-down metering is needed.

[uintaangler]

Adam,

I appreciate you posting the table, but I don't know how to interpret it

I go to f/ 35 and it says 64.3 degrees for the 645D - what I want to know is what that means in terms of equivalent focal length
In other words, when I put a 35mm lens on my 645D - is it a wide angle lens in terms of coverage or a normal lens
I guess the problem is that I don't know how to convert horizontal degrees into focal lengths???

Also, on the table, is 24 x 36 the sensor on a full frame Nikon like my D800?

Thanks,
Bob

[Douglas_of_Sweden]

As Adam says, the adapter is great since it has full mechanical aperture control for the 67 lenses on the 645/645D. I use some 67 lenses on my 645N for that reason and is planning to pick up some more.
How about the Pentax 67 35mm fisheye. On the crop of the 645D I doubt you would see much distortion since you would just use only the center. And then you would reach nearly to comparable to 28mm on 24x36mm.
It is a hefty piece of glass. I've played with it on the 645N, since it is wider than the A45mm 645 lens I have, and then of course I get a lot of distortion.

[Douglas_of_Sweden]

Adam,

I appreciate you posting the table, but I don't know how to interpret it

I go to f/ 35 and it says 64.3 degrees for the 645D - what I want to know is what that means in terms of equivalent focal length
In other words, when I put a 35mm lens on my 645D - is it a wide angle lens in terms of coverage or a normal lens
I guess the problem is that I don't know how to convert horizontal degrees into focal lengths???

Also, on the table, is 24 x 36 the sensor on a full frame Nikon like my D800?

Thanks,
Bob

You will have to go down to 35mm in the 645D column and find the angle, and then locate the same angle in the 24x36 column (of course you need to interpolate since it doesn't have all values). In this case you end up somewhere between 31 and 28mm, closer to 28mm, so lets say 29mm approximately.

[uintaangler]

Thanks Douglas

[672]

unitangler, there is no real good 67 wide angle for the 645D. The 35mm for 645 is the best wide angle lens if we dont want to buy an expensive 25mm . The 67 35mm and 45mm dont give very good image quality on the 645D for some reason. I am sure we can find someone to disagree with me , but in general , most 645D user on this forum have found similiar wide angle experiences.

[Smolk]

* How do the Pentax 67 lenses compare to the ( is it 5? ) lenses available for the 645D: 24, 35, 55, 120, 300?

The number of lenses available depends on where you look, and whether you want new lenses only or also used. New lenses include the 2.8/90mm which appears to be of very high quality.
Used lenses here in the UK are available, at FFordes for example. There is the FA 45-85mm zoom, the FA 150mm, etc, see Pentax 645 Medium Format Lenses - Pentax Lens Reviews & Lens Database

[donesteban]

unitangler, there is no real good 67 wide angle for the 645D. The 35mm for 645 is the best wide angle lens if we dont want to buy an expensive 25mm . The 67 35mm and 45mm dont give very good image quality on the 645D for some reason. I am sure we can find someone to disagree with me , but in general , most 645D user on this forum have found similiar wide angle experiences.

Indeed, the 67 45mm needs quite a lot of stopping down to provide good sharpness on the 645D. Although it is achievalbe at f/11, it doesn't make sense buing this lens for the 645D. The 45-85mm gives similar quality, the SMC-A 35mm is wider and a lot better.
The 67 45mm is good for useing it on the 6x7 cameras. Then it is a real wide angle.

[uintaangler]

The number of lenses available depends on where you look, and whether you want new lenses only or also used. New lenses include the 2.8/90mm which appears to be of very high quality.
Used lenses here in the UK are available, at FFordes for example. There is the FA 45-85mm zoom, the FA 150mm, etc, see Pentax 645 Medium Format Lenses - Pentax Lens Reviews & Lens Database

Is it safe to assume that ALL Pentax 645 lenses will be completely compatible with the 645D?
With no adaptor required?

[Silent Street]

Indeed, the 67 45mm needs quite a lot of stopping down to provide good sharpness on the 645D. Although it is achievalbe at f/11, it doesn't make sense buing this lens for the 645D. The 45-85mm gives similar quality, the SMC-A 35mm is wider and a lot better.
The 67 45mm is good for useing it on the 6x7 cameras. Then it is a real wide angle.

Gosh, I wouldn't dream in a fit of sacrificing the sterling image quality of the 67 45mm on 645 or ~D. It's false economy. As donesteban states, stopping the lens down to f11 is not going to bring up the best out of that particular lens because of the format. Better lenses specificallly for the 645D are available and should be investigated.

[Smolk]

Is it safe to assume that ALL Pentax 645 lenses will be completely compatible with the 645D?
With no adaptor required?

Yes, all are compatible, but of course the A lenses do not autofocus or imprint the focal length on the film / exif... And their performance varies, as the digital goddess demands in ways different from film.