medium format Archives - Infrared Conversions, IR Modifications & Photography Tutorials

IR Fireworks

What to do on the 4^th of July… Humm… Grill? Done. Catch up with family? Done. Relax? Done. Watch fireworks? Wait a second… How many of you have photographed fireworks? I’m guilty. But who’s photographed fireworks in IR? I’ve never done that, and probably few have. Let’s give it a try.

I climbed on the roof of my house to get a better vantage point and set-up my full spectrum 5D Mk II with a 720nm filter.

I use a Hoodman Loupe for focusing my 5D, since the filter blocks the visible light and makes the viewfinder useless. This technique works quite well for me and is what I’ve been using for more than 5 years. I wrote a blog on the topic.

I knew about where to look for the fireworks. So I installed my Pentax 67 55mm medium format lens and prefocused before it turned dark. It’s more difficult to focus once it is dark. I connected my shutter release and then waited…

At 9 o’clock on the dot, the fireworks began. I was shooting exposures from about 3-10 seconds at ISO 400 and f/5.6. This seemed to work well. Adjustments in framing, focusing and exposure need to be done quickly, as the fireworks continue. I continued to shoot until my memory card was full. It was close to 9:30, which is when the firework show typically ceases. A quick back of the camera indicated that I had captured some interesting shots.

So where were the trouble spots? First, I noticed that the 55mm lens had some significant internal reflections. I’m not sure if this was caused by the filter, or the basic lens design itself. My EF24-70mm f/2.8 has a similar issue with super-contrasting scenes. I’ll have to set-up an experiment to test my lenses under these conditions. I’ll share the results here. The three photos below, though still interesting show the effect of the internal reflection.

Releasing the shutter release mid explosion halts the motion of the firework and provides a truncated look. Note also a second shell climbing to altitude.

The other problem I encountered was the wind. I was standing on my roof and at times needed to grip the tripod to insure that it didn’t take a tumble. Interestingly, the wind also had an effect of blowing the fireworks. Many didn’t have the traditional firework shape, but rather a skewed , wind-swept look. This was also interesting.

Finally, as with any long exposures on digital cameras, there are some required management of hot pixels. Most modern DSLR’s have internal noise processing, But this requires an equal-length dark exposure for each light exposure. So I prefer to do this off-line using the technique outlined here . Since the exposures were fairly short, the hot pixels are manageable, even by manual removal methods.

I did very little post processing of these images. I set the camera with a custom white balance on a green subject. Most images were posted after a little cropping and re-sizing for the blog format, but not much more than that. I did process several in B&W, since that’s my favorite IR medium. Some photos have a bit of an abstract look to them.

By the time the fireworks show was over, the mosquitoes had found me. So I gathered up my tripod, camera bag, loupe and flashlight and headed off the roof. It all ended well and I enjoyed the experience. I hope you’ll give it a try next year.

Happy 4^th of July…

Medium Format Lenses – Part II

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!

Diffraction and IR Photography

A few years after I began my photography adventure I took a photography class that came free with my first SLR camera. I thought I knew a lot about photography. After taking the class I thought I knew all there was to know about photography. Funny thing is that all these years later I’m still learning, almost on a daily basis. One photography class take away for me were all the details about depth of field and aperture. When I went to any action event, I’d shoot at high f/numbers so everything was in focus (before the days of auto focus). Some years later while working on my undergraduate degree, I became interested in optics. I was hired to work in an optics research lab (see my holography post). It was then I started learning about the wave nature of light and how diffraction occurs. I mostly worked with lasers. So most of my diffraction experience was with monochromatic light (one color). Below is a shot of textbook linear laser diffraction through a small opening. This is the effect on light as it passes through small openings. This also occurs in photography with all the colors diffracting different amounts, but occurring simultaneously.

My interest in photography began to mesh with what I had learned about optics. I had always wondered about white light diffraction, especially in camera optics. It turns out that diffraction can be a fairly significant issue with camera lenses. You can shoot everything at f/22 and have great depth of field and focus. But there’s a trade-off. As the aperture size decreases, diffraction increases and becomes more visible. There is diffraction at all f/numbers though its more pronounced at smaller apertures.

I like to understand where all my lenses are sharpest and where they are soft. So when I added another medium format lens to my fleet, I decided to do a little more testing. Interestingly, my 165mm f/4 LS medium format lens has a minimum aperture of f/32. At this aperture diffraction makes the image quite soft. It is so evident that it’s even evident in the live-view display.

I shoot IR almost exclusively with medium format lenses. Check out my blog topic on medium format lenses. They are huge, but I really like using them. Here’s a comparison to a 50mm f/1.4 Minolta manual focus lens that I bought with my 35mm SLR. These are the lenses I included in my testing for this blog (except for the Minolta lens).

Left to right in the rear: Pentax 67 55mm f/4, Pentax 67 75mm f/4.5, Pentax 67 165mm f/4. Front row: Minolta MD 50mm f/1.4

I found some level of diffraction in all three of the lenses I tested. On this particular test subject (my neighbor’s palm tree), diffraction is much less evident in the 55mm and 75mm lens, but very clear in the 165mm lens. This is partially due to the minimum aperture size of f/32. The animations below are all 740nm IR photos, shot with a custom white balance. No other processing was done.

Pentax 67 55mm at f/4, f/11 and f/22

Pentax 67 75mm at f/4.5, f/11 and f/22

Pentax 67 165mm at f/4, f/11 and f/32

Diffraction is inversely proportional to aperture diameter. So diffraction is less visible as the aperture diameter increases. Unfortunately, diffraction is proportional to the wavelength of the light being shot. This means more diffraction at longer IR wavelengths. For those of us shooting IR, we will likely have to use a slightly larger aperture vs. when shooting the same equipment in color. If you shoot IR around 740nm, diffraction will be about 30% worse than at the center of the visible spectrum (about 550nm). That seems significant but doesn’t seem to affect my images much. However, you should keep this in mind if you’re planning to shoot IR at small aperture diameters (large f/numbers).

You may have noticed something else that is evident when shooting at small apertures. Any dust or streaks that happen to be on the lens, filter or sensor become much more evident at smaller apertures. Take a look at the speck to the upper right of the bird in the 165mm image above. The dust spec is invisible in the f/4 image, but very clear in the f/32 shot. Yet another reason to open up those apertures.

First test shot from my new 75mm Pentax 67 medium format lens (shot at f/11)

I find that most of my lenses are sharp around f/11 when shooting at 740nm. So that’s where I mostly shoot. It matters little to me if the exposures are longer. I always shoot IR with a tripod so I can take full advantage of the lens sharpness. If you’re interested in some light diffraction theory, there’s an interesting article I found discussing diffraction and photography. One last detail to consider. The onset of diffraction occurs earlier in crop sensor cameras vs. full size sensors. So if you’re shooting with a smaller sensor, you may need to open your aperture more than would be necessary on a larger sensor. Lots to keep in mind.

So what does this all mean? Well, if you typically shoot at large f/numbers, with a crop sensor camera and/or shoot IR photos, you can probably increase your image sharpness by opening the aperture slightly. Do your own tests on the lenses that you use most frequently. It’s important to know where your lenses perform best whether you shoot color or IR. Most importantly get out and shoot. It’s the only way to learn.

Short Sticks

Do you use a tripod? I do for almost every shot. The way I shoot IR necessitates the use of a tripod. Could I hand-hold my IR shots? Probably. But I love to shoot panoramas and in poor weather. I’m also a sort of a purist when it comes to getting the most out of the camera and lens. So I always use a tripod. This isn’t just another tripod tutorial. You can find enough of those on the web already. What I wanted to do here is share my struggles with finding the right tripod and how I solved the problem.

For those of you that follow my blog posts, you’re probably aware that I started my IR venture as a spin off of my astrophotography. The stability requirements for long exposure astro photos are much higher than that for photography. I realize that it’s not an apples-to-apples comparison as equipment for astrophotograpy is typically much heavier. But I guess my need for absolute stability rubbed off. When I started looking for a tripod for my IR photography, it should go without saying that my first requirement was a high degree of stability.

I shoot IR with a full frame DSLR and heavy lenses . I love the medium format lenses. Did I mention that they are heavy? Add any filters, lens converters, a battery grip and L-bracket and you’re into a fairly robust system. Even so, many of the lightest tripods will hold the weight of a camera and a lens in ideal conditions. I find however, that the load ratings of some units are a little misleading. Sure these ultralight sticks may hold the load. But I hate having to fiddle with the tripod and wait for everything to flex back to a stable position after making a ball head adjustment. So I knew I wanted a tripod that could also carry a decent load without flexing.

I also like to shoot down low. The desert has some interesting foreground elements. So I also wanted my tripod to be able to work well at low levels. Almost any tripod these days can splay the legs and get low. But this is where the strength of lighter tripods can be compromised. Splaying the legs can reduce the load capability and place additional demands on the materials. Adding to the list, I also wanted something that was fairly compact, for traveling. So with my laundry list in hand, I set off looking for the tripod that would fit my requirements. I never did find exactly what I wanted.

So after some thought, I decided I’d experiment by adapting a stock tripod to fit my needs. I’m fairly handy when it comes to machining, metalworking and the like. I felt confident that I’d be able to make the necessary modifications. I dug around the web until I found a possible candidate, an aluminum leg Benro A3580F. It met a couple of the initial requirements. It is stable and has a good load rating (about 6x my camera load) and was also fairly inexpensive.

I did a little reconnaissance to see if I was going to be able to work some magic on this tripod. It turned out to be a fairly simple design and I decided to proceed. I began by removing and disassembling the legs.

Once I had the legs completely apart, I proceeded by cutting off 5 inches off each segment of each leg. Cutting each leg segment the same amount kept the symmetry of the design. I then cleaned up the cuts and reassembled. Voila, a shortened tripod. There were some other details not mentioned. But in general, it was a fairly simple modification.

Here’s the finished product. It’s substantially shorter than stock. But it still maintains the same (or probably higher) load rating, especially when the legs are splayed.

Here’s a comparison with with one of my larger tripods. I still use the larger tripod for portraits and when I need additional reach. But for nearly all my IR photography, I take the little custom Benro.

Here’s an action shot with the shortie and my 5DII with a Pentax medium format 55mm lens. The set-up is really rigid and required a lot less fiddling when trying to set up a shot. There is almost none of the flex that appears with lighter tripods. It’s hard to describe the satisfaction, unless you’ve experienced such rigidity.

This thing is like a little tank. I call it my “tankpod”. It’s short, really stout and can travel almost everywhere. When I need more height, I can extend the leg segments and get up to about 45 inches (to the base where the ball head mounts). I usually use it with the segments retracted or only the first segment extended. When folded up, It travels well and fits in a carry-on bag. It’s not a Gitzo or RRS, so the build quality is not the same, but is still quite adequate for me.

The last time I presented my shortened tripod to a group of photographers I got a lot of eyebrow raises and eye rolls. It might not be the thing for you. But this modification turned out a tripod that suits my needs perfectly. It now goes with me everywhere I shoot. So if you’re handy and need something specific in a tripod, think about out what modifications might make it what you need. Happy shooting.

Medium Format Lenses on a DSLR

It’s no surprise that photography equipment is expensive. Think of the engineering and workmanship that goes into lenses and DSLR bodies. As with everything, there are always levels of expense. Lets examine lenses specifically. The professional-class lenses tend to have fewer issues. Yet, trade-off’s always exist with either professional or consumer glass. So we spend our time and money looking for the best equipment for our hobby or profession. Sometimes the limitation is money and sometimes it’s just the lack of that ideal piece that we need. For those willing to sacrifice some modern features there may be options to get top-quality glass at a fraction of the cost of similar modern equipment.

Here’s a Gerbera Daisy, shot with a medium format 55mm lens

As a photographer, I’m always looking for an edge, especially with my infrared images. As an engineer, I’m digging into the technical details of my photos & equipment. I always look for ways to improve my set-up. Many IR photographers have their cameras converted to dedicated IR use (with a fixed internal IR filter over the sensor). These converted IR cameras can be calibrated to autofocus in IR so they shoot just like a stock camera. The viewfinder can still be used for framing. However, for folks that use an external filter on full-spectrum cameras (like me) this is not an option. Longer wavelength filters block the viewfinder from transmitting visible light. So I always use the camera in live-view mode and use the LCD and a loupe to focus my lenses manually. Since the same sensor that records the photo is also producing the live-view image, framing and focus are easily managed. I always manually focus my IR images using this LCD technique. It gives me confidence that my images are, at least, focused.

In addition to photography, I have spent many years doing serious astrophotography. Several years back I had read about astrophotographers coupling medium format lenses to cooled CCD cameras. I wondered why these lenses so popular with astrophotographers. Beyond the obvious point of getting a wider view of the sky, a quick examination of the physical layout quickly made it clear. Medium format lenses are used primarily because of their longer flange-to-focal plane distance. On many Astro CCD set-ups filters, guides and other equipment can lie between the telescope and the camera. As an example, look at my wide-field (530mm) astrophotography set-up below. See all the equipment between the camera (box on the LHS) and the telescope? If you remove the telescope and replace it with a lens, this lens would require a fair distance between where it mounted to where it focuses.

Below is an example of how a dedicated medium format astro set-up is constructed. A custom machined the lens mount and motorized focus mounting bracket hold the medium format lens for coupling to the CCD. This assembly is then attached to an equatorial mount, in place of or in addition to a telescope.

(Image courtesy of Craig & Tammy Temple)

All the astrophotography work had me wondering how medium format lenses would work on a DSLR. They work very well. Some significant advantages exist when using medium format lenses on a DSLR. The largest advantage is cost. These lenses are seen as obsolete. So many of the older manual focus, medium format lenses are available quite reasonably. With a little research and patience, some excellent deals can be had. I use the Pentax 67 format, but many others should work equally as well.

Another advantage has to do with the film size of medium format cameras. Pentax 67 is a later version of the Pentax 6×7 format. This format came from the film size of 6 x 7cm. That’s a whopping 60 x 70mm. A standard DSLR full frame image format is 24 x 36mm. Medium format lenses will overfill a full frame sensor by a substantial amount. Why is that a big deal? Well, think about your lenses. Most of the bad things that happen to images occur on the fringes of the frame (chromatic aberration, coma, vignetting, etc). With a medium format lens, you’re shooting through the sweet spot. I was pleasantly surprised at the image quality of the vintage medium format lenses that I tried. I have some decent professional DSLR glass. But any of the medium format lenses that I’ve purchased give equal or better results. Here’s an example, a 2 frame panorama shot with a medium format 55mm prime lens.

This is a heavy snowfall in the desert of Far West Texas. In the distance are the Franklin Mountains that run through El Paso, Texas

Using a medium format lens has another advantage. If you understand how tilt-shift lenses work you may see where I’m going. With an OEM tilt/shift lens overfills the sensor. This allows the lens to be shifted and the image to still fall on the sensor. With a normal lens, the image will shift off the sensor or become heavily vignetted. For the price of one shifting adapter, you can shift any of your medium format lenses. If you read my blog last month you’ll know that I prefer to shoot panoramas with a shift lens. For fraction of what I paid for the spectacular Canon EF-24mm TS-E Tilt/Shift lens (also manual focus, by the way), I purchased an adapter and a small fleet of medium format prime lenses.

This is a 3 frame panorama of northern Norway, shot with my Canon 5DII, a 55mm Pentax 67 lens and a shift adapter (see below).

This is a Canon 5D Mk II coupled to a Pentax 67 55mm lens using a shift adapter.

A test shot using my 150mm Pentax 6×7 lens (my oldest medium format lens)

It’s not all roses, though. Most medium format lenses are huge. I mean huge, and they are heavy. They are generally much larger than their 35mm format counterparts. However, the size is what provides that impressive image circle.

A monster of a 55mm lens and probably one of the sharpest lenses I’ve ever used, in any format.

A disadvantage (for some folks) is that the older medium format lenses are all manual focus. So you have to be comfortable with shooting manual focus on an IR camera (and understand manual camera operation if you plan to do Pano’s). If you have an IR shooting style like mine, using a manual focus lens is inconsequential. I manually focus my AF lenses for IR anyway. You’ll also need to purchase an adapter (either fixed or shift) to interface to a DSLR. Finding the proper adapter for your camera and preferred lens brand may also be difficult. You also have to do your research to get the lenses that have the best image quality. Just like modern AF lenses, some were lemons and some were stars. I only pick medium format lenses that have the best reviews for image quality or sharpness. Finally, since many of these lenses are older you have to look out for dust, grease and fungus on the optics. I usually try to purchase the latest model of the particular focal length lens. So do your research, ask questions and shop carefully.

If you can get through all the details and decide to try shooting with medium format lenses, you’ll definitely have some seriously nice glass. You also get them for a fraction of what a similar modern lens might cost. Hopefully, my experience will shine a light on the pros and cons of using medium format lenses on a DSLR. If you’re up for a little challenge, give a medium format lens a try. You won’t be disappointed.

IR Fireworks

Medium Format Lenses – Part II

Diffraction and IR Photography

Short Sticks

Medium Format Lenses on a DSLR

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