Monday, October 27, 2008

You thought you couldn't use any DA/DA* lenses on future full frame DSLRs from Pentax? Well...think again. (See Update) By: Yvon Bourque

Dear Pentaxian friends,

The DA/DA* series of lenses were designed specifically for the Pentax APS-C sized Digital Cameras. The Pentax APS-C sensor is 23.5mm x 15.7mm, and the DA/DA* lenses have an image circle big enough to cover the diagonal length of the sensor. We don't actually know the image circle of every lens that Pentax designed for the DSLRs currently equipped with the APS-C sized sensors. What we know is that if the image circle is smaller than the diagonal of a FF sensor, vignetting will occur.

Click on the picture to the above right to find out more about APS-C/FF

Although my lenses are comprized of more FA and C lenses, I have been building my DA/DA* lenses arsenal since my first Pentax DSLR, the *ist D. Currently I have the DA 10-17mm, the DA 18-55mm II, the DA 16-45mm, the DA 50-200mm, the DA 70mm Limited, the DA* 200mm and the DA* 300mm.

Last week, I decided to get a roll of 35mm film, have it developed in prints as well as on CD, and try all my DA/DA* lenses on an older 35mm SLR, the Pentax PZ-10. I chose the PZ-10 because it was the only old SLR in my very humble collection that had a working battery. Because the DA/DA* lenses have no aperture rings, I could only go by shutter priority. So my examples do not necessarilly compare the 35mm results with the K20D results, as I am not certain of what the aperture was on the PZ-10. However, it's a good reference to determine which lens will produce images acceptable on future FF DSLRs and which will produce too much vignetting. (Of course, you can always crop the vignetting portion) The film I used was Fujifilm Superia @ ISO 400. I took a picture with each lens attached to the PZ-10 and then did the same with my K20D set at ISO 400 in shutter priority (Sv). There was a few days between the shots with film and the shots with the K20D. So basically, I focused on a US flag we have in the parling lot at work, and stood approximately at the same place. The left photos were taken with the K20D and, of course, the right photos were taken with the PZ-10 .

So here are the results. I probably don't have to add many words, the pictures should speak for themselves. Here goes:

Pentax K20D ***************** Full Frame

DA 10 - 17mm @ 10mm

DA 10 - 17mm @ 17mm

DA 18 - 55mm II @ 18mm

DA 18 - 55mm II @ 55mm

DA 16- 45mm @ 16mm

DA 16- 45mm @ 45mm

DA 50- 200mm @ 50mm

DA 50- 200mm @ 200mm (I guess the aperture must have been very small on the PZ-10 here.) There should be less vignetting at 200mm!

DA 70mm Limited @ 70mm

DA* 200mm @ 200mm

DA* 300mm @ 300mm

So...you can see that some of the lenses will be very compatible with FF DSLRs and some seem to have vignetting, specially in the wide angle portion.

Thank you for reading,

Yvon Bourque

UPDATE 10/18/2008 @ 7:10 P.M. Pacific Time.

I just realized that this topic is hitting home for many. If I get enough requests, I will go ahead and purchase a used Pentax AF 35mm SLR from EBay with the capability of selecting the aperture from the camera (I'm not sure which model does that). Following that, I will test every DA & DA* lenses in both formats, 35mm/FF and APS-C size. I will test each lens at all available aperture, using a tripod positioned exactly at the same place for all shots (35mm and K20D), and show the results here. Let me know your thoughts in the comments at the bottom of the post.

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