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06-25-2011, 01:44 AM - 3 Likes   #1
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Pentax D-FA 645 25mm f/4 AL (IF) AW Review



(1) At First Glance

The build quality of this lens is exceptional, everything feels very solid and well engineered. The entire body and even the lens cap are made
of aluminum (except for rubber/plastic rings, the knob and the dial). It's definitly on the heavier side at 1070g but understandable for its size.

(2) View Angle (82.70 horizontal / 66.85 vertical / 95.46 diagonal)

Corresponding to approximately 19.5mm on a 35mm full frame sensor, the view angle is good enough for most wide angle landscape shots.
Except for a handful of unusual occasions (i.g. Horseshoe Bend, AZ), I personally hardly go any wider than 16mm (on 35mm FF). Since this
lens will convert to a 15.5mm (on a 35mm FF) super-wide angle with a full-frame 645 sensor, I think this will remain as the wide end of my
work range.





(3) Optical Performance

The D-FA 645 25mm shows very impressive resolution across the frame, although it remains to be seen how it performs with a full-frame 645
sensor. With the current cropped sensor of 645d, even the extreme corners look very sharp and contain fine details. I would love to compare
this lens to Rodenstock Digaron-S 23mm, both of them seem to boast exceptional performances, but I am personally curious about how the
state-of-the-art 645 full-frame retro-focus superwide angle lens can stack up against high quality short-focus superwide angle lenses.

(4) Chromatic Abberations

This lens shows a substantial amount of CA, which can mostly be fixed by using any lens correction software. Although Pentax has not
announced the newest version of RAW converter or a correction profile for ACR, you can still use lens correction filters of Photoshop to partially
correct them.


100% crop from raw sample #4.

A brief test reveals that the longitudinal CA is not an issue even at f/4, (as can be seen from the image of the focus test chart, no color cast
in the out of focus areas). At f/10-13, which is the typical aperture range for landscape photography, longitudinal CA is almost non-existent
(due to smaller aperture) and most of the CA is lateral and therefore correctable.


Focus test chart can also show longitudinal chromatic abberation in natural light.

I have no idea why Pentax didn't use any low-dispersion elements for a $5000 lens. I've yet to carry out tests at wider apertures, but I don't
think it would matter that much to a landscape photographer like me since I hardley shoot any wider than f/8.


(5) Filter Compartment

Creating an internal filter compartment in the mid-section of the lens was a fantastic idea and it works perfectly. Using the plastic dial, a polarizer
can be easily rotated and this saves you the trouble of purchasing a large (and very expensive) polarizer and sacrificing one slot of your filter
holder. You can also separately purchase a 40.5mm ND8 filter from Hoya, which can be very useful for shutterspeed control.



(6) Using GND Filters - Custom Filter Holder

Since nobody has manufactured a dedicated filter holder for this lens, I had to fabricate one from a cheap abs pipe and Cokin z-pro filter holder.
At Home Depot, I picked up a small end cap hub that has a slightly smaller diameter than the front section of the lens, cut off the cap part,
converted it into a short cylinder and glued it to the back side of the Cokin Z-pro filter holder. I had to bore the cylinder a bit for a proper
tolerance and lined it with black velvet. FYI, after wasting a fortune on a number of different materials, I settled down on fake adhesive velvet
that I picked up from Daiso. After cutting and grinding, spray painting is a must and now you have a custom filter holder. You can use one 4X6
rectangular filter without vignetting.





(7) Custom Focus Mirror

I also fashioned a custom focus-mirror that can be attached to the lens. For precise DOF control, I find myself focus-stacking quite often,
and if your camera is on your eye level and you are shooting horizontal, there is no good way of quickly changing the focus. So I purchased
a small inspection mirror at a hardware store, took off the handle and screwed it to a reusable rubber twist tie. This can also be used with
different lenses for the same purpose.

Mirror :
Amazon.com: General Tools 557 2 1/4-Inch Diameter Inspection Mirror: Home Improvement

Tie :
Amazon.com: Nite Ize GT18-2PK-01 Gear Tie Reusable 18-Inch Rubber Twist Tie, 2-Pack, Black: Home Improvement



(8) A Sample Image and 100% Crop (Processed with ACR, Sharpening : 75/1/50/30)



Alamere Falls, Point Reyes National Seashore, Bolinas, California




100% Crop #1


100% Crop #2


100% Crop #3


100% Crop #4

(9) More Samples
It has been a slow season for landscape photography, so I haven't got a chance to utilize the full-potential of this lens. I will add new pics
as soon as they are available.


Ano Nuevo State Park, Pescadero, California


Memorial Church, Stanford University, Palo Alto, California


Near Pigeon Point Lighthouse, Pescadero, California


Gray Whale Cove, Montara, California


Schwabacher Landing, Grand Teton National Park, Wyoming


Sutro Baths, San Francisco, Caifornia

(10) Samples for Download (RAW)

http://www.harkleephotography.com/D-FA_645_25mm/Pentax_D-FA_645_25mm_Sample_01.PEF
http://www.harkleephotography.com/D-FA_645_25mm/Pentax_D-FA_645_25mm_Sample_02.PEF
http://www.harkleephotography.com/D-FA_645_25mm/Pentax_D-FA_645_25mm_Sample_03.PEF
http://www.harkleephotography.com/D-FA_645_25mm/Pentax_D-FA_645_25mm_Sample_04.PEF

(11) Latest Work (With Other Lenses)


Grotto Geyser, Yellowstone National Park, Wyoming


Lake Tahoe, California


Bay Bridge from Yurba Buena Island, San Francisco, California


Bonsai Rock, Lake Tahoe, Nevada


Garrapata State Beach, Carmel, California


Zephyr Cove, Lake Tahoe, Nevada


Lake Tahoe, California


Thanks for looking, you can comment or PM with any questions and I would be happy to answer them. Thanks.

- Hark


Last edited by harklee; 06-30-2011 at 05:14 PM.
06-25-2011, 04:05 AM   #2
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Very nice review- and this looks like a stellar lens. I'll also have the opportunity to test the 645D next month and it really sounds like this lens is something worth trying!

By the way, is it OK if we move your review to the lens review database? We'll just need a numerical score for the lens from 1 to 10

Pentax-D FA 645 25mm F4 AL [IF] SDM AW Reviews - 645 Wide-Angle Primes - Pentax Lens Reviews & Comprehensive Database

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06-25-2011, 05:55 AM   #3
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Hi Hark:

Thank you for all the effort in this post. Very nice images. I downloaded two of your files (listed with PEF extension in your post) They download as TIFs and I am unable to open them with Photoshop (wrong kind of document)
You mentioned in an earlier post that you sometimes use ISO 100. What are the advantages?

Tom
06-25-2011, 06:14 AM   #4
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Excellent review harklee, I too was disappointed to note the omission of lower dispersion glass types in this new lens especially considering it's price. But I will point out neither the hasselblad or the mamiya 28mm lenses are without fault, they exhibit similar characteristics in terms of chromatic aberrations - and from the samples you have provided I will say that it's possible the Pentax 645 25mm f/4 AL [IF] lens may outperform the Carl Zeiss 28mm f/4 - which cannot be used on full frame 645 format - the image circle is too small. From my use of the Zeiss 28mm f/4 lens on a hasselbald H3D I have noted it is prone to veiling flare which is rather curious, Carl zeiss lenses for the Hasselblad H system are made by fuji - which apply their highly regarded EBC coating to these lenses. Perhaps pentax has finally caught up to and surpassed fuji EBC coatings?

QuoteOriginally posted by harklee Quote
I would love to compare this lens to Rodenstock Digaron-S 23mm, both of them seem to boast exceptional performances, but I am personally curious about how the state-of-the-art 645 full-frame retro-focus superwide angle lens can stack up to high quality short-focus superwide angle lenses.
not even remotely a fair comparison IMO, the diagron-S being symmetrical lens design Vs a retrofocual lens design. However I do recall from several MFDB users comment that even without any camera movements used the diagron-s 23mm has a green colour cast around the edges along with vignetting, which I surmise is because of the high incident angle of the light hits the sensels in the corners of the sensor - which is typical for such an extreme wide angle lens. however I do not recall Michael Reichman encountering such a limitation when he used a retrofocus Canon 24mm f/3.5L Version II T/S lens on a Phase one P45+


Last edited by Digitalis; 06-25-2011 at 06:35 AM.
06-25-2011, 08:30 AM   #5
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And I had just about convinced myself I did not "need" the 25mm. It looks like a fine lens and fine performance considering the focal length/angle of view. Thanks for your time and effort in doing this.
06-25-2011, 10:53 AM   #6
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Harklee, the Zephyr Cove, Lake Tahoe, Nevada is a beautiful image. Which lens did you use?
06-26-2011, 06:47 AM   #7
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Hi Harklee,

As others have stated, lovely images and really appreciate your posting them as well as your preliminary users report. Generally for landscape work, the new 25mm which is effectively 19.5mm on the 645D (related to 35mm full frame) is not as easy to use as say the FA 35mm lens (which has an effective focal length of 28mm on the 645D is full frame 35mm terms)...but you did a superb job.

In terms of simply optical performance (resolution etc.) how would you compare the new 25mm with the FA 35? (I know its a bit like comparing apples to oranges). I too was surprised to see the level of CA in this lens but like most, hope that efficient post processing will eliminate most issues with it.

I hope to be testing out the new 25mm soon. Again thanks for posting samples nd your imprtession of the lens...extremely helpful!

Dave (D&A)
06-26-2011, 09:38 PM   #8
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You shouldn't be posting stuff like this. I can't afford the camera, but this makes me want it even more!

Great work

06-27-2011, 05:00 AM   #9
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QuoteOriginally posted by Yamanobori Quote
Harklee, the Zephyr Cove, Lake Tahoe, Nevada is a beautiful image. Which lens did you use?
Sorry

Excellent report by the way !
06-27-2011, 07:00 AM   #10
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QuoteOriginally posted by fs999 Quote
Sorry

Excellent report by the way !
Why is this funny? From the 11th image, Harklee posts his lastest work with other lenses. I assume you read the caption. Why asking about the optics is strange?
06-27-2011, 07:11 AM   #11
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QuoteOriginally posted by Yamanobori Quote
Why is this funny? From the 11th image, Harklee posts his lastest work with other lenses. I assume you read the caption. Why asking about the optics is strange?
Oops so sorry !
I overlooked that the other shots where taken with other lenses. I thought it was a crop...
06-27-2011, 07:20 AM   #12
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You can read it in the exifs when passing on or loading the pictures/properties, for example the last one is taken at 55mm, probably the kit lens.
06-27-2011, 08:33 AM   #13
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QuoteOriginally posted by Zygonyx Quote
You can read it in the exifs when passing on or loading the pictures/properties, for example the last one is taken at 55mm, probably the kit lens.
I am not able to do that or at least I have not figured that out on my Mac.
06-28-2011, 09:04 AM   #14
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Thank you all for the comments.

QuoteOriginally posted by Adam Quote
By the way, is it OK if we move your review to the lens review database? We'll just need a numerical score for the lens from 1 to 10
Thanks Adam, I will go ahead and type in the numbers. : )

QuoteOriginally posted by Thomas Quote
I downloaded two of your files (listed with PEF extension in your post) They download as TIFs and I am unable to open them with Photoshop (wrong kind of document)
You mentioned in an earlier post that you sometimes use ISO 100. What are the advantages?
Tom, that's strange. The files download fine on my computer, you may try right-click and 'save as'? Or you can simply try changing the extension to PEF and try opening them with the newest verion of ACR or Pentax RAW converter.

QuoteOriginally posted by Digitalis Quote
not even remotely a fair comparison IMO, the diagron-S being symmetrical lens design Vs a retrofocual lens design. However I do recall from several MFDB users comment that even without any camera movements used the diagron-s 23mm has a green colour cast around the edges along with vignetting, which I surmise is because of the high incident angle of the light hits the sensels in the corners of the sensor - which is typical for such an extreme wide angle lens. however I do not recall Michael Reichman encountering such a limitation when he used a retrofocus Canon 24mm f/3.5L Version II T/S lens on a Phase one P45+
Digitalis, thanks for the detailed comment, yeah, Nikon 14-24mm and Canon 24mm II have really changed my perception of retro-focus type wide angle lenses and I just thought it would be an interesting comparison. : )

QuoteOriginally posted by Yamanobori Quote
Harklee, the Zephyr Cove, Lake Tahoe, Nevada is a beautiful image. Which lens did you use?
Thanks for the compliment, Yamanobori, that was taken with A 645 35mm f/3.5.

QuoteOriginally posted by DandA Quote
In terms of simply optical performance (resolution etc.) how would you compare the new 25mm with the FA 35? (I know its a bit like comparing apples to oranges). I too was surprised to see the level of CA in this lens but like most, hope that efficient post processing will eliminate most issues with it.
DandA, I think A 35mm has a slight edge over FA 35mm (at least with the current sensor size of 645d), and D-FA 25mm beat them both in resolultion. If it wasn't for CAs and price, I would give this lens a 10.

QuoteOriginally posted by Zygonyx Quote
You can read it in the exifs when passing on or loading the pictures/properties, for example the last one is taken at 55mm, probably the kit lens.
Zygonyx, that was taken with the FA 45-85mm zoom. : )

Last edited by harklee; 06-28-2011 at 10:52 AM.
06-28-2011, 10:51 AM   #15
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Here are two more sample pics from a weekend trip to Yosemite. Both pics were taken with D-FA 25mm and the weather was almost too clear for landscape shots.


Tioga Lake, Yosemite National Park, California



Dog Lake, Yosemite National Park, California
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