Modifying a Holga DSLR Lens to really be f/8
The Holga lens for DSLR is a small and lightweight 60mm fixed-aperture lens at a very inexpensive price (approximately $25 US). It's made of plastic and not intended to be a quality lens — and it isn't one — but it can be a lot of fun for goofing around with. It certainly makes the camera much less of a burden.
|The Holga HL-C lens for Canon DSLRs, mounted on a Digital Rebel XT (350D).|
Although Holga specifies that the lens is f/8, the current versions of the Holga DSLR lenses contain a couple of thin metal plates to produce a vignetting effect, and those plates reduce the aperture to approximately f/25. That's necessarily an estimate, because the vignetting produces widely varied exposure across the image.
Here's a comparison against a genuine Canon lens (the EF-S 17-85 IS USM). These are shots of an 18% gray card, taken under reasonably-controlled indoor lighting conditions — hence the long shutter speeds at a high ISO. The black strips on the sides are simply from what the gray card was placed on.
|Holga HL-C, 0.4 sec at ISO 1600.||Canon 17-85, f/25, 0.4 sec at ISO 1600.|
The Holga lens doesn't seem to have the slight greenish cast that I get from my 17-85.
The relatively tiny f/25 aperture obviously makes for a challenge in getting enough light — ISO 800 becomes pretty much the minimum for handheld use, even in broad daylight. It also introduces some diffraction and makes even the slightest bit of sensor dust stand out (unless it's in the dark corners). But most annoying to me was the almost impossibly-dark viewfinder — Live View users might not have so much problem with it.
NOTE: the test photos above, and the similar ones that follow, were made purely to compare exposure. I made no attempt to focus either lens, so do not attempt to judge sharpness from these photos. See the sample photos at the end of this article for an idea of what the modified lens produces.
Advantages of f/25: depth of field and depth of focus
Or course, a small aperture like f/25 increases depth of field. That's crucial because the focus range on the Holga lens is limited — it doesn't go all the way to infinity. Mine goes to about 25 feet (8 meters) maximum. At f/25, infinity is just within the classical depth of field on an APS-C camera.
The small aperture also increases depth of focus. The Holga lens is a single-element meniscus design, and any single-element lens will have significant longitudinal (axial) chromatic aberration (CA). Blues focus ahead of the greens which focus ahead of the reds. At f/25, the amount of image spread that occurs between the focus plane and the sensor is fairly small, so this isn't a big problem.
Sidebar: the lens on a Holga 120 camera
Amusingly, Holga also specifies this lens as being f/8 on the Holga 120 camera, with selectable f/11 for sunny daylight use. In fact, the lens on those cameras has an aperture plate that restricts it to about f/13, which brings infinity into the depth of field on the 6x6 film camera. On older Holga 120s, the sunny/cloudy selector had no effect; the aperture was f/13 in both settings. On recent Holga 120s (since 2010 or so), the sunny setting is about f/20. No unmodified Holga 120 has f/8 or f/11 apertures, regardless of the manufacturer's claims.
Overview of the modification to f/8
You can easily convert the lens to its designated f/8 aperture in just a few minutes. Bear in mind that you'll not only lose the vignetting, you'll be significantly sacrificing image sharpness beyond about 30 feet (10 meters). Given the lens's 60mm focal length, that means that you won't be able to fully capture objects larger than maybe 12 feet (4 meters) wide on an APS-C sensor without backing away into the Fuzzy Zone. You'll also need to be more careful with your manual focusing.
You'll also be increasing the longitudinal chromatic aberration, which is a type of CA that can't be corrected in software. Do take a look at the sample photos at the end of this article and see what you think.
But if you're ready to take the plunge, here are the illustrated instructions. The only tools needed are a Phillips screwdriver (#1 or so) and some improvised tools for pushing, scraping, and prying.
[These pictures were taken with my mobile phone, and I don't claim them to be great photography. They're intended to be practical.]
Step 1: separating the halves
The Holga lens consists of two pieces — the lens proper and the EOS-mount adapter — that screw together, with the screw threads also being the mechanism for adjusting focus. There is a stop-screw at the "close focus" end of the range. We're simply going to back that screw off and unscrew the two halves.
|Backing off the stop-screw. I recommend you not completely remove it.|
A #1 Phillips screwdriver is the tool of choice. I don't recommend that you completely remove this screw because the screw threads have a lubricant and you don't need the mess. Mine took about two full turns of the screwdriver before it was backed off enough, but I suspect that will vary a lot from lens to lens. You might want to keep track of how far you backed yours off, so you can tighten the screw the same amount when you're re-assembling.
Once you've gotten the stop-screw backed off enough, it's a trivial matter to unscrew the front and back halves. The lens threads have a lubricant, so you probably want to keep from getting the lubricant all over you, and keep crud from getting in the lubricant.
Step 2: removing the sieve plate
The sieve plate is the fairly large metal plate at the back of the EOS-mount adapter that has a central hole surrounded by a ring of other holes. This plate is used to simulate vignetting. It's held with a little rubber-cement or similar adhesive.
Push this plate out from what was the inside of the lens, using something reasonably large. You could use something smaller, or even pry the plate out, if you're not at all concerned with ever re-using the plate.
Caution for the lubricant on the lens threads.
After removing the sieve plate, you probably should clean the remaining adhesive off of the back of the adapter. This is just a precaution to keep the adhesive from flaking off into your camera. Any adhesive that doesn't easily come off can be left alone.
|Pushing the sieve plate out the back of the EOS-mount adapter.|
Here's what my sieve plate looked like after I removed it, showing a bit of rubber cement that stuck to the plate.
|Removed sieve plate, with adhesive.|
If you were to stop at this point and reassemble the lens, you'd have opened it up one stop or so, to about f/18, and removed the vignetting:
|HL-C with no sieve plate, 1/5 sec at ISO 1600.||Canon 17-85, f/18, 1/5 sec at ISO 1600.|
Step 3: removing the aperture plate
The aperture plate is on the "inside" of the front half of the lens. There's no access to push this one out like we did with the sieve plate, so we'll have to resort to prying it out. I used an allen wrench.
|Prying the aperture plate out of the front of the lens. Here, an allen wrench is being used.|
There is no glue on this piece. It's purely press-fit, and it popped out without difficulty.
Step 4: reassembly
Screw the two lens halves back together. There are four sets of threads, and if you start from the wrong position you'll end up in the wrong position. Start with the stop-screw positioned between the "group" and "mountain" icons.
|Correct starting position for rethreading the lens onto the EOS-mount adapter. The stop-screw is between the "group" and "mountain" icons.|
When the lens is fully "tightened," it should be at the distant-focus setting — the mountain icon.
|Correct position when "tightened".||Wrong.|
Set the lens at a focus distance somewhere in the middle of the range, then turn the stop screw back in. Do not screw it all the way in. You're just placing it in the way of the front half. I turned mine in the two full turns that I'd backed it out.
Of course, you should have two pieces left over: the sieve plate and the aperture plate. Keep them or throw them away, as you wish.
|The removed sieve plate and aperture plate.|
The end result
The lens should now be at the claimed f/8, with no vignetting.
|Modified HL-C, 1/25 at ISO 1600.||Canon 17-85, f/8, 1/25 at ISO 1600.|
What about reinserting the sieve plate?
It's certainly possible to put the sieve plate back, or to not remove it in the first place, and remove only the aperture plate. However, there doesn't seem to be any real value to doing that. The resulting lens is approximately f/22 with no vignetting. If you want vignetting, you'll need to have both the sieve plate and the aperture plate in the lens, and you'll be stuck at f/25. Otherwise, you might as well remove both plates and get f/8.
I don't have any photos to demonstrate this. I didn't want to glue the sieve plate back in, and I didn't want to risk it scratching my reflex mirror if it fell out while I was snapping the test image. So you'll have to take my word for it, or else make the test yourself by removing the aperture plate first, reassembling the lens, and taking some test shots.
The following photos are full-size, straight-from-the-camera JPEGs.
|Model A pickup. At about 50' away, this was beyond the modified lens's depth of field.|
|I suspect a wino has used this bus-stop bench.|
|Oil pump in operation. This subject also was beyond the depth of field.|
Here's a look at how the major secondary lenses look with the modified Holga.
|Modified HL-C alone.||Modified HL-C with HW-05 wide-angle lens.|
|Modified HL-C with HT-25 tele lens.||Modified HL-C with FEL-HL fisheye lens.|
Here are some B&W conversions to illustrate the longitudinal chromatic aberration. The red channel is reasonably well-focused, considering that the truck is beyond the focus range of the lens to begin with. The green channel is focused ahead of the red channel, and the blue channel is focused well ahead of the green channel. As a result, the green channel is a bit blurry and the blue channel is rather unlike a tack.
|Straight desaturation.||Red channel.|
|Green channel.||Blue channel.|
Here's a comparison between my modified and unmodified lenses. These are two different lenses, and it's possible that some of the differences are due to variation between units rather than the modifications. The brick wall is about 10 to 11 feet (3.5 m or so) from the camera, and that's within the lens's range of focus.
|Modified HL-C. 1/50 at ISO 400.||Unmodified HL-C. 0.4 sec at ISO 400.|
|Modified HL-C. 1/500 at ISO 400.||Unmodified HL-C. 1/25 at ISO 400.|
I like the much brighter viewfinder, and the faster lens is easier to work with in conditions other than bright daylight. However, the limited focus range and longitudinal chromatic aberration are a problem, especially for distant objects. This modified lens really works best at short ranges — maybe 20 feet (7 m) or less — but that can sometimes be a challenge with its 60mm focal length. The modified lens likely comes into its own with the close-up and macro secondary lenses, as long as the longitudinal CA isn't a problem.
B&W photography won't be as sensitive to the longitudinal CA. You can select the sharpest channel — usually red for distant objects, blue for close ones, and green in-between.
A quirk of the modified Holga lens that I haven't noticed with my unmodified lens is blue shadows in bright daylight. For example, look at the grill of the white pickup on the left side of this picture. It's quite blue. Lots of blue on the billboard above that truck, too. But it's not that the lens can't render black: look at the black trim around the camper shell on the red truck at the right side. I'm guessing that this blue shadowing is caused by the longitudinal CA: the blue channel is rather blurry at a distance.
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