Pentax 645 MF lens on Canon XSi body

[charles_wood]

<p>I recently purchased an adapter to use my collection of Pentax MF 645 lenses on my Canon bodies. My preliminary results confirmed them to be sharper edge to edge and free from the CA that seem to be common with my wider Canon lenses.<br>

I'm posting this nine frame stitch I shot at The Wave last Saturday. The picture itself is fairly unremarkable due to midday light and lack of interesting sky. However if you examine it closely you'll see no CA artifacts. I used a Pentax 645 35mm non-autofocus lens. It is significantly superior to my 17-40mm F4L Canon lens in terms of the completed results.</p><div></div>

[dogbert]

<p>Sorry are you saying that a nine frame stitch is superior to a single wide shot taken with the 17-40 f4 L or are you saying that for the same single shot the Pentax 645 lens produces superior results to the 17-40 f4 L?</p>

[charles_wood]

<p>Yes, it's superior on both counts. Viewed single frame it's sharper edge to edge with no CA. My 17-40 is soft at the edges even though I'm using it on a APS sized sensor. I have to set the 17-40 to approximately 26-28mm to eliminate softness and minimize CA. Overall, I prefer the Pentax.<br>

The stitching was done to create a file size for a very large print. The net file size was approximately 450 megs, after stitching nine 69 meg 16 bit files.</p>

[mike_earussi1]

<p>Actually the Pentax 35mm lens for 645 has extremely high CA, but only on the edges, which you, of course, aren't using. Nor should it be too surprising that its sharpness is even across the relatively tiny APS-c sensor, since the lens is designed to cover a full 645 frame. But I'm glad it works for you and is as sharp as the Canon L you were using. I imagine it's also a lot cheaper. So who knows, you may start a trend.</p>

[sarah_fox]

<p>That's a nice looking photo! :-)</p>

<p>It would be wonderful to see comparison shots between the 17-40 and the 645 35! The 17-40 does have some falloff in corner sharpness, but are you seeing better sharpness in the MF lens even in the center of each frame? (That would surprise me.)</p>

[chrisjb]

<p>Ditto Sarah, but fair, 35mm at normal aperture for a scene as this, f8? Also may I ask what software used for stitchin this size file ?. Nicely done. I compared my ef 50mm 1.8 a while back with hassy 50 f4 and noticed better contrast and sharper edges, no suprize the hassy cost 5500aud. but that was 20d. might try again on the 5d see what happens :) </p>

[charles_wood]

<p>I have to think my 17-40L is a bad example. I see far less CA on my 645 35mm at the extremes of the frame than I do on my 17-40L. <br>

I stitched the RAW files before converting the image to a TIFF, and subsequently a JPG, using Photoshop CS4. I don't have an identical comparison but I'm attaching a four frame stitch, wider view of the same scene shot with the 17-40. If you download it and take it to 100% or so you'll see red fringing around rock detail in the upper left part of the frame and blue/purple fringing along the skyline where the mountain image merges with the blue sky. That simply doesn't exist with the 645 35mm lens. As for costs, the 645 35mm was about the same price as the 17-40 back in the heyday of film medium format. On the other hand, the use of the MF lenses requires a bit more planning and post processing work. But I'm pleased so far.</p><div></div>

[sarah_fox]

<p>Your 17-40 image does appear somewhat soft. That said, I'm astounded how sharp your MF lens is. Maybe it's just a prime vs. zoom thing. While it's true you're only using its sweet spot, the lens is also optimized over a much larger image circle, so compromises unnecessary for 35mm format would have been made to the design, so as to achieve such a wide angle of view. I would expect the center sharpness of a 35mm format lens to be greater than that of an MF lens when used with a 35mm format. But maybe I'd be wrong! ;-) Interesting stuff. Thanks!</p>

[anthony_hicks]

<p>Did you try your Pentax 55mm this time Charles?</p>

[charles_wood]

<p>I did some shots this morning with the Pentax 645 55mm, Canon 70-200 F4L and Canon 18-55IS kit lens. I did not include the Canon 17-40F4 L because of it's limited range and because my particular example seems to be not much better in most respects than my 18-55IS kit lens.</p>

<p>The Pentax MF 55mm and Canon 70-200F4L are very close but I'd give a slight edge to the Pentax in terms of absolute sharpness. I had an opportunity yesterday to shoot some frames with my 70-200 on a 5DmkII and I now find it's edge sharpness is soft at 70mm with CA on the left side of the frame. Disappointing.</p>

<p>Obviously impossible to exactly match focal lengths in these comparisons but you can get a feel for the three lenses. i've also enclosed a full resolution JPG frame of a group of cacti shot with the Pentax 55 at 240dpi.</p>

<p>The amazing thing about the Pentax 645 55mm is that it can be had nowadays for about $125-150 on the used market. An adapter for EOS bodies is about $70.</p><div></div>

[charles_wood]

<p>The same image with Canon 70-200F4L lens.</p><div></div>

[charles_wood]

<p>The same image with Pentax MF 645 55mm lens Pentax to EOS adapter. Infinity focus just short of infinity mark on adapter.</p>

<p>All focus settings for all shots were done with live view full magnification. 10 sec timer mirror up.</p>

[charles_wood]

<p>Previous attachment attempt failed...will try again.</p>

[charles_wood]

<p>Not sure what is going on here...once more.</p><div></div>

[charles_wood]

<p>Finally, a shot of cactus, reflected light with the Pentax 55mm. Extremely uniform sharpness across the entie frame.</p><div></div>

[anthony_hicks]

<p>Thanks for those Charles. Looks like I might be forking out for an adapter!</p>

[yuri_huta]

<p>Thanks for posting all of these Cahrles! What would you say is the equivalent field of view on a 35mm system for the Pentax 35mm and 55mm lenses?<br>

Also, which adapter did you get? I had one for $60 (not top quality craftsmanship, but I did not expect it for $60) but sold it as the lenses would too often get stuck and would require considerable force to pry them off the mount. It seemed that it was not uniformly machined and went on easily at first, but the last few millimeters were tough and subsequently getting the lens off was really tough.</p>

 

[charles_wood]

<p>The field of vision of the Pentax 645 lenses (35mm and 55mm) match almost identically my Canon lenses set at 35mm and 55mm. I've posted a side by side comparison of the full frame captured by the Pentax 35mm lens and the Canon 17-40/F4 L lens also set for 35mm. The framing is virtually identical except the Canon seems of deliver an off center image which may account for part of the soft focus it exhibits on the left sideof the frame and the right lower corner. Although the bushes in the foreground are not in sharp focus, when you look at both images up closely, you can see the Pentax is much sharper.<br>

Both images were derived from RAW files. I made only level matching corrections, with no color corrections and .3 pixel of sharpening. The Pentax has a slightly different color/contrast balance compared to the Canon, directly from the RAW file. Color temp for both images was 5700 degrees K.<br>

If you examine the upper left corner of both frames where the ridge line of the mountain in the background meets the sky, you will see far more CA abnormality from the Canon. The blue fringing is extremely evident whereas the Pentax exhibits far less CA. If I was using the 17-40 on a full frame body I would be very disappointed in it's performance. Perhaps it's time to send back to Canon and ask them to try aligning it again or perphaps I simply have a lemon.<br>

My adapter is a no-name Chinese made device imported by Fotodiox USA. www.fotodiox.com</p>

 

[charles_wood]

<p>My apologies, I forgot to flatten images in CS4 before posting. Here it is.</p>

[charles_wood]

<p>Sorry all, I'm not sure why my JPG attachment does not display. If you have any suggestions let me know.</p>