Several months ago, I wrote a blog about using medium format lenses on DSLR. I wanted to continue this series with a little more information. In my experience, one of the most understood characteristics of using non-standard lenses with different film/sensor size is crop factor. Before going into this, let’s get a little background on what crop factor is and why it’s relevant to this blog.
When you use a lens that is intended for a different sensor size or film format, the lens can overfill or under-fill the sensor/film. Using a full format (35mm) lens on a DSLR with a crop sensor (APS-C, Micro Four Thirds, etc), the lens will project an image that is larger than the sensor size. This overfills the sensor. In other words the smaller sensor is sitting in the center of a larger image on the film plane. When this happens, the sensor is only seeing a portion of image on the film plane. This gives the appearance that the image is zoomed, when compared to the same image on a full format sensor. The image below represents a full frame DSLR image (35mm format). The inset square represents the crop factor of an APS-C sized sensor.
It’s important to note that there is no magnification or change in focal length. It is merely a characteristic of the image size and the sensor/film size. This is called crop factor. The most common is when using a full format lens on an APS-C sensor camera. This gives a crop factor of 1.6. This is simply the ratio of the smaller image size vs the larger one. Since different sensors have different aspect ratios (height to width) I prefer to use the diagonal distance for crop factor calculation, as it accounts for both height and width. A full frame sensor is nominally 36mm x 24mm, which is 43.3mm diagonally. An APS-C sensor is 22.4mm x 15mm or 27.0 mm. So 43.3mm/27.0mm=1.6X.
The exact same situation occurs when we use a medium format lens on a DSLR. I’m currently using Pentax 67 lenses on my full spectrum Canon 5D Mark II. There is a big difference in film/sensor size. So there is a significant crop factor. The film size of a 6×7 is about 6 x 7cm, however the actual size is about 56.0 x 72.0mm, depending on camera format. Using lenses for medium format on a full frame DSLR provides a crop factor of over 2X. Using these lenses on an APS-C sensor provides a crop factor of over 3.4X. In terms of what was discussed earlier, a 6×7 lens on a full frame DSLR over fills the sensor area by more than 2 times. It over fills an APS-C sensor by 3.4 times.
A 55mm lens is a 55mm lens. It won’t matter if this lens is used on a full frame camera or a medium format camera. The focal length does not change. Only the field of view changes. But if you take a photo with a medium format camera and then use the same lens on a full frame DSLR, the DSLR photo will appear to be zoomed by 2X. But remember, it’s just seeing less of the full image. I did an experiment to validate this and took several Canon L lenses (intended for full frame sensors). These were compared with images shot with my medium format lenses. I overlaid them in Photoshop to make comparisons. With these, it’s easy to see that the medium format lenses have the same field of view as the Canon lenses.
It turns out that crop factor is one of the best characteristics of using a medium format lens on a DSLR. Most lenses are clearest in the center. It’s toward the edge of the frame that aberrations occur. Using the medium format lenses on DSLR’s uses sees the image through the best part of lens, the center.
I love shooting IR with the medium format lenses. They are hefty and manual focus, but are superb for IR. They fit the way I shoot IR and provide superb results. I hope this information helps understand how crop factor affects the field of view and that there is no magic happening when you use medium format lenses on a DSLR. I also hope it encourages you to do some experimentation of your own. Happy shooting!
Latest articles by Eric Chesak (see all articles)
- IR Fireworks - July 14, 2018
- Medium Format Lenses – Part II - December 11, 2017
- Bracketed Exposures for IR photography - July 19, 2017
Eric Chesak is a physicist, engineer, photographer, and general technophile. He has always been interested in cameras, photography, and optics with several patents and scientific publications on the subject. He’s a full-time consultant, after a successful career in Engineering and R&D management. Eric has been enjoying photography for more than 40 years and began shooting with his grandfather’s rangefinder, 35mm Zeiss Ikon camera. His life-long passion for astronomy and astrophotography spun off to IR photography which developed into a full-blown obsession.
Eric's images are published in Astronomy & other magazines, many websites and on the artwork on a classical music CD. He has also written for several engineering trade magazines and received numerous awards for technical excellence. In addition to his photography hobbies, he enjoys metalworking, machining, and mechanical design and is experienced with CNC machining equipment. In fact, he designs and fabricates some of his own equipment for astrophotography and photography.
You can view more of Eric's IR and Astrophotography at his online gallery.
Eric currently shoots with custom, full-spectrum modified Canon 50D and 5DmkII -- and learns something new every time he shoots a photo.
See All Articles by Eric Chesak
Try not use Kipon or Fotodiox those adapters cause very flare . I Sold My Kipon and chinese adapters all of them .and i Bought ” Hartblei adapters” (are the best of my adapters tests)
Thanks for your comments. These appear to be good adapters, but I do not see a solution for Canon EF to P67. Each camera set up will have its own perfect solution. For my set-up, I have excellent results with the Kipon. No flare, solid construction and the shift adapter is fantastic for Pano’s. See my Panorama posts.
I believe I understand, but I would like to clarify. I have the same Pentax 67 55mm lens you have on the Canon at the top of this post. I put it on an IR Nikon APS-C sensor camera and I am seeing the same image as I see when I use a Nikkor 55mm lens on the camera. This jives with what you are saying. But for some reason I got turned upside down with the crop factors and going from 35mm to APS-C and now from P67 to APS-C. I suppose that if I actually owned a full size sensor DSLR or perhaps a medium format camera, I would have understood better (as in learn by examples).
For some reason, I was expecting my 6×7 55mm lens to provide me with a 42mm equivalent focal length (because of the crop factors). Fooled me!
Anyway, I am very, very pleased with the Pentax 67 55mm lens on my IR camera.
Like the example I used, you can calculate the crop factor by using the diagonal length of each sensor format. Using the diagonal distance accounts for the aspect ratios of the different formats. This is the crop ratio and is only the ratio of the different sensor sizes. The lenses give a different apparent focal length because of the size of the sensor that is being illuminated by the lens.
There are some really superb 6×7 format lenses out there. I have the 165mmLS, 150mm Takumar f/2.8, 75mm f/4.5, and the absolutely flawless 55mm f/4. There are also some good 645 lenses at decent prices.
Thanks Eric,
For non IR photography, I shoot Nikon. D500, D850, D810. Do you have any issues with infinity focus?
Fotodiox has a shift adapter called a Tilt Rokr.
https://www.amazon.com/Fotodiox-Adapter-Pentax-Camera-TLTROKR-P67-NikF/dp/B0792MBLBR/ref=sr_1_1?s=electronics&ie=UTF8&qid=1530128244&sr=1-1&keywords=Fotodiox+TLT+ROKR+tilt-shift+lens+adapter
They are under $200.00 Any recommendations on adapters that work good? and Pentax lenses/apertures/focal lengths?
Thanks again,
Ray
Ray,
That adapter should work OK. But if you’re not in need of the tilt/shift features, you can probably save some money on the adapter. I use Kipon and Fotodiox, both with good results. Just be sure to get a decent adapter as the lenses are heavy.
If you haven’t already, read my blog here:
https://www.lifepixel.com/photography-gear/medium-format-lenses-dslr
But also do reviews on the lenses. Just like today’s lenses, not all are created equal. With medium format, I shoot from 55-165mm and that covers my range pretty well.
Hope that helps,
Eric
Thanks Eric,
I will check out the blog!
Ray
I have 2 Sony a6000 cameras converted. 720 and 590.
As they are aps-c, will medium format lenses and adapters work?
Thanks,
Ray
Ray, If you can find an adapter, they would work fine. I use them on my full spectrum 50D (APS-C) with superb results.
Eric
Sure, I understand all that, but I am at a loss as to why it seems to be such an issue.
It appears to be a telephoto only if you compare it to a standard lens image. I shoot mostly FX lenses or old film lenses on my DX and I don’t know the difference by looking at the image, nor do I care. Kinda like pixel peeping.
But I digress. I recently bought a Kipon adapter and two Pentax 6X7 lenses. A later 200 mm and an older 45 mm. I don’t have my full spectrum Nikon D7100 back from LifePixel yet.
So I have taken a few test shots, with another D7100. I am very pleased with the results. And this set up may just take over my landscape stuff. I want to try it with my 35mm film cameras, and my Standard color filter D200
Of course I had known about doing this for years, but after seeing Eric’s photos, I knew I had to do it. I only live 500 miles east of him, so I will have much of the same landscape.
Thanks Eric, for the great photos, ideas and inspiration. I know I will eventually have to get a 6×7 body. But, hey, I already have the lenses so might as well, right?
It is kind of sad that lenses and cameras that used to cost thousands can now be had for less than $100. Medium format adapters and lenses were expensive and hard to come by, before the internet.
I’m nearly 80 and I buy nearly everything over the internet. I think Amazon has me on speed dial.
Thanks Barry. I have a thing for ultra-sharp images. Shooting through the sweet spot of these larger lenses is just the ticket. I too use them sometimes for non-IR applications, where there is time to properly focus. Glad you enjoyed the article and the use of MF lenses. I’d enjoy seeing some of your photos sometime. My website address is in the Author Bio at the end of the article. There’s contact link there.