Hoods ‘n the boyz

Lens hoods – a good thing all round. There are those clever petal-shaped ones, square or rectangular ones to match the film format, the odd but sexy Leica ones with the cut-aways plus various rubber offerings. But what if you need one for a particular lens, perhaps only for a short time? How about making one?


We’re not talking 3d printing here. With a bit of calculation and the kind of drawing set you had at school, you can make a custom lens hood from black paper.

What you are going to make is a frustum, a cone with the top cut off. The narrow end of the frustum will fit over the front of your lens. The angle of the sides will match the angle of view of your lens. The depth of the hood will be what you want to make it, limited only by the size of your sheet of paper. There are some calculations involved, but I did this once in a spreadsheet so I only need to enter the key measurements to make a new hood.

The first key measurement is the diameter of the front of your lens. The lens hood will need to be a sliding fit over the lens. This measurement is not the filter thread size – measure the actual diameter of the lens.

Next is how deep you want the hood to be. This is handy if you are making a hood for a special situation, like using a long lens in strong side or frontal light.

Lastly, the difficult measurement: the lens’ angle of view. This can be difficult because it’s not just a function of the lens focal length: it’s the relationship between the focal length and the size of the film or sensor. This is why a 50mm lens is considered standard on 35mm film, but a 6×6 negative on 120 film uses a 75mm or 80mm lens.

What could be a right chore is made simple by looking-up your lens and film/sensor combination in previously published data. The BJP had a great article plus graphs in the 116th edition in 1976, but I bet you didn’t keep yours… There is also a useful calculator here.
I’ve got a 55mm lens for a 35mm camera. Looking-up the angle of view from the calculator I’ve linked above, the diagonal angle for a 35mm frame is 43 degrees. I use the diagonal angle because anything less than this is likely to vignette the corners. So this means my lens hood should be a cone with an angle of 43 degrees. I fancy making the lens hood 50mm deep – for no other reason than it feels like a useful compromise between no use and too big.

The last key measurement is the diameter of the lens; in this case 57mm.

So I want to do the trigonometry to calculate a frustum with a 57mm wide hole at the top, the sides sloping at an included angle of 43 degrees and with a vertical height of 50mm. The first time I did this I did all the calculations myself. Then I discovered a dedicated website with the sole intention of providing the calculations needed to effectively open-up a frustum and lay it out as a shape that can be drawn on paper. The formulae look difficult, but it’s simple to put them in a spreadsheet. If you provide cells to put the specific values into – lens diameter, angle of view, depth of hood – the same spreadsheet will give the drawing measurements for any hood that takes your fancy.

I made the calculations for my hood and got three key measurements: two radii needed to draw the pie-slice on the paper and an angle of arc for which I need to draw the curves. In the case of my special lens hood, I need to draw two arcs with radii 78 and 132mm and to draw the arcs with a sweep of 132 degrees.
Here’s a picture.

Hood 1

I used plain black art card. For the pictures I marked it out using a white pen, but for normal use I would use a pencil. I marked a tab at the end of the arc to give myself an overlap that I could hold down with tape. If I was going to use this hood a lot, I would use the tab and a slot to let me disassemble the hood when I wasn’t using it (or I would hold it together with masking tape, which peels off). I also left some extra material on the inside of the smaller radius. This is cut into a number of tabs that will go over the lens and hold the hood in position, particularly if you put a bit of tape on them.

Hood 2

It’s easy to find a protractor, but a large set of compasses is more difficult. I use a bit of card with holes for the tip of the pencil and a pin to pivot on.

Hood 3

Cut out and fitted it works just fine.

Hood 4

This is an excellent way to make a hood for short-term use or for a lens that you would not otherwise be able to fit. Unstick the masking tape and the hood can be stored flat.

There you go – something useful for a change in place of the usual grumbling.
If anyone wants to use my spreadsheet rather than do your own calculations, drop me a comment and I will post it somewhere accessible.

Classic lenses

Classic seems to mean ‘not made any more’. I used to be interested in classic motorcycles, but classic came to mean extinct rather than good and some complete dirtburgers were given a rebore and a coat of paint and became “classic”. Never mind that the refurb would have cost more than the bike was ever worth or that people who owned one at the time were only too happy to trade it for a Honda. And the result of all the effort is that the proud owner gets to take it to shows on a trailer and have people tell him that the shade of paint is wrong for that year.

I too rode a classic motorcycle, but it had raised compression, a twin-plug head and a chain oiler, and I rode it to work. Oh dear, I’m getting into reverse willy-waving again. Let’s get back to lenses.

So – a classic lens is one that you can no longer buy new. I did ask and was firmly told that a classic lens is also a fixed focal length: zoom lenses are not classic. From what I can see, the most prized feature of a classic lens is the way it renders out of focus areas, particularly highlights. Remember the mirror lenses that were, for a while, the easiest way for mortals to afford a long lens? There were a load of 500mm f8 catadioptrics to choose from, but their distinguishing feature was the way they rendered out of focus highlights as circles. Pretty much a one-trick pony: once you had seen a picture full of bubbles you probably sold the lens and went back to refraction as your favoured method for bending light. And now people pay big wonga for Meyer Goerlitz lenses that have sufficient aberrations to recreate the effect. Want to do it for cheap? Try a longish lens with a clear filter and a disk of black paper or tape in the middle of the filter. If there wasn’t a Cokin filter that did this I’m sure I could sell you a bubble bokehlicious®️fuzzy duck filter.

A few minutes work with a marker pen and the first Fuzzy Duck filter leaves the production line

Ooh, bokeh balls, yum! The odd texture in them is due to the swirls of the marker pen

So ok, rings is a thing but not the only trick in town. The other things that classic lenses are supposed to be good for is micro-contrast, meaning low contrast as far as I can understand it, and not smoothing-out fine detail (which may be the same thing). But perhaps this only applies to CLASSIC lenses and not just any old bit of second-hand glass. From what I understand, older lenses suffered more with flare and reflections. This could mean that the overall contrast between highlights and shadows was reduced, so kept within the dynamic range of the film. If the lens was a good one and could resolve fine detail, this could be what people call microcontrast. As coatings got better I assume that the overall contrast rendered by the lens increased. It may well be that this exceeded the ability of film to capture it, and the abilities of earlier-generation digital sensors. Digital sensors now beat film on both dynamic range and sensitivity, so I would expect that a modern digital camera with a modern digital-designed lens will render both fine detail and a wide overall contrast. Stick this clever lens on a film camera and you might find it too contrasty. Stick an older film lens on a digital camera and you might find it reduces the overall contrast of the scene, so it needs less post-processing.

There are also some issues with putting older film lenses on digital sensors, in that a digital sensor prefers the light to arrive straight-on, where film doesn’t mind if the rays are oblique. This matters at the edge of the frame, and more in colour than black and white. So some film lenses on some digital cameras produce fuzzy edges or colour fringing.

The main idea seems to be though that older lenses contain magic. They don’t resolve every skin pore, the backgrounds are nicely smooth and not distracting, and the fall-off from sharp to out of focus looks nice. Sensors smaller than the original film size turn old lenses into longer focal lengths (narrower angle of view), so a fairly cheap 50mm film lens can become a very cheap wide-aperture portrait lens. This will throw the background out of focus and isolate the subject better than the zoom lens that came with the camera, and way cheaper than a sharp digital lens of the same size.

But watch what happens with mobile phones and how it will migrate to mainstream cameras. Before long you won’t need to buy a Planar or a Sonnar and deal with fungus or scratches; you will use the kit lens and dial-in your lens effect. The autofocus knows which parts of the image are sharp, so the in-camera computer can add your favourite aberrations back to the fuzzy bits. Pentax released a software developer’s toolkit for their K1 full-frame camera, so this might be where you see it first.

But this idea that old lenses were better than new lenses? Prove it. Technically better, in terms of resolving power, control of flare, sharpness across the image? I doubt it. A more pleasing rendering of the image due to design or manufacturing shortcomings? In the eye of the beholder, but apparently true if you have seen how the prices of some old lenses have risen. Come the revolution though, and I’m hoping the prices drop again as in-camera effects mean that everyone can have a Canon ‘dream‘ lens.

it’s already here.

Bodging lenses

Lenses are marvels of optical calculation and manufacturing craft. So why am I futzing around with old projector lenses and door viewers?

Part of is the joy of orneryness (easy for you to say): the pleasure in solving a problem by going against the grain and taking the less obvious path. Yes, I could spend the kids’ inheritance on eBay and buy a Meyer-Goerlitz lens with magical bubble bokeh. Or I could wrap an old slide projector lens in camping-mat foam and jam it up the middle of a set of extension tubes. There are some fantastic and rare macro lenses out there, but you could also pop an enlarger lens (which is usually well corrected for macro work) on some form of extension tube or bellows.

Something I have been looking at is the Petzval lens. I didn’t know they existed until Lomography started selling them. Nice results, even if you wouldn’t want to use it all the time. A lot of money to put out for something that would spend most of its time in the bag, though. Plus they don’t make them in either of the lens mounts I use. You can get old brass lenses that were made with the Petzval design on eBay, but they too have shot up in price. But the Petzval formula is pretty simple and some projector lenses use it. So I’ve been looking at old projector lenses but also thinking about building my own. There are places that sell lens elements in various types and strengths, so I’ve been tinkering with the maths to find a combination that works. By works, I mean can be far enough away from the film or image plane to allow for the depth of the camera body plus some means of focusing. This sets limits on the focal length of the lens, which in turns sets limits on how wide an aperture I could get.

My camera has a lens flange to focal plane distance of a gnat’s less than 46mm. So, without clever lens designs, the widest focal length I could use would be 46mm. At the long end I’m limited by the diameter of the lens elements I could find. It’s all very well building a 500mm lens, but not if it only works at f22. I might lose that swirly background I was working so hard to obtain. Besides, a long lens would turn into a ridiculous bazooka pipe. So I’m looking in the 80 to 150mm range. Focusing is not really a problem, as I have some magic focusing bellows left over from an earlier infatuation. On the other hand, life is short (and ars longa, even with support pants) so I will probably stick with bodging existing lenses.

Some years ago I was reading an article on Elliot Erwitt and his candid street photography. He was said to use an unusual lens combo: a longish manual lens mounted on a set of macro bellows. The lens was long enough to give a proper infinity focus and the bellows had a rack and pinion to focus. The bellows also meant that he could go from long shot to close-up without changing anything. So like photographers immemorial, I bought the kit to improve my pictures. This was when you could buy all sorts of accessories from Practika and Zenith at almost pocket-money prices.


Actually, it worked. With a 4″ enlarging lens on the front it really did cover a wide range at the expense of manual everything. So the bellows would be my focusing rack for further experiments. It didn’t work for slide projector lenses though. These were too wide to fit into the front of the bellows and the bellows wouldn’t shrink down enough to give an infinity focus. No problem, as bodging baffles brains. Along came a set of very cheap manual extension tubes from China. Then a layer of camping mat foam was wrapped around the lens using gaffer tape, until the lens was a snug fit inside the tubes. Then I had a lovely soft focus portrait lens that worked really well, as long as I didn’t point the camera downwards. The nice thing though is that it works for a whole range of projector lenses. If I need a longer flange distance I just add a couple more bits of extension tube.

proj 1

For anyone who is interested, the 150mm appears to have smooth bokeh while the 85mm looks like I could get some bubbly bokeh out of it.

Wide angles are a problem though. Proper wide angle lenses overcome the problem with the camera flange distance with clever optics. My 15mm lens can’t be 15mm away from the film or sensor due to the depth of the camera body and the need for a swinging mirror. The clever lens fairies in Japan made it work at a flange distance of around 46mm. But if I want to bodge something wide out of inappropriate parts that flange distance is the wasp at my picnic. And then I read an article on t’interweb… (which I have been searching for ever since). The idea is to use an extremely wide angle CCTV lens. Mount this on tome form of extension tube so that it would focus on a sensor, but leave the sensor as empty space. (OK, just mount the lens on a tube). Then mount this whole thing on the end of a reversed lens attached to a camera. The idea is that the virtual image focused by the CCTV lens is seen by the reversed (strong macro) lens and focused in turn onto a real sensor of film. And if I did the maths right, the macro lens would enlarge the virtual image from the CCTV lens to cover the camera sensor. Plus, a fisheye lens for a CCTV camera is not big bucks. Plus I could test this with my existing lenses before even buying a CCTV lens.

So I did the logical thing and experimented to see if it would work before I bought anything. Mount a lens in reverse on a camera and then hold another lens in front of it to see if I can focus any sort of image. All I got was a very good look at the dust on the second lens. I’m either missing something or the whole idea is daft. I do wish I could find the original article.

But in the meantime I have a couple of useful portrait lenses, a very close-focussing portrait lens and a huge glass condensing lens from an old overhead projector. I’ve been playing with the latter by taping it to the end of a cardboard tube. It’s got a focal length of around 330mm but I could shorten that by putting a magnifying lens between it and the camera.

I’ve also got a 9 diopter closeup lens that looks like it might be a doublet rather than a single element, so might be better quality. This particular one has a focal length of 115mm so fills-in the gap between my two projector lenses. The right size of step-up ring should mount this on my bellows. Or this might be the lens I use with the OHP lens to reduce the focal length. Decisions, decisions…

Go me! I’ve got more lenses than a Fleet Street pro (do they still exist?). There are people who pay good money for this sort of fuzziness.

Zoom zoom

Time was, that a zoom lens was what amateurs used. Real photographers use fixed lenses. A Real Photographer (RP) always had the right lens on the camera and a range of alternatives in their battered canvas shoulder bag. An RP could change a film under sniper fire and judge the right exposure by eye. And besides, all the magazines said that zooms were inferior. At the time they probably were, or perhaps the journalists had a heavy investment in fixed lenses and wished it so.

And then computers happened. Or rather, Moore’s Law and whatever the equivalent is in manufacturing. (Foolish boy! Moore’s law is about manufacturing.) We are very good at learning how to make things better. Cars don’t rust like they used to and getting to 100,000 miles is not worth writing to the papers about. We no longer have to take engines apart to de-coke them or regrind the valves. So apply cheaper and more powerful computers to optical design and clever manufacturing to lens grinding and glass-making and we built a better zoom.

So zooms started to challenge the quality of fixed lenses. Remember of course that this mythical quality was measured by shooting resolution charts and not by the results people got using them. I reckon that people using zooms have always been happy with the results, or they wouldn’t shoot zooms.

And then along came the zoom compact and it sold by the squillion. I remember a TV ad that showed people photographing a group, perhaps at a wedding. The people using ‘ordinary’ point-and-shoots were sliding closer and further to the group to frame their shots. The smug one with the advertised camera used the in-built zoom lens to go from group to single portrait without having to move. Is this the camera that caused obesity? Anyway, we all bought 35mm compacts with zooms and a built-in flash. Although I bet almost all of the pictures were taken at one of the extreme ends of the zoom range.

Hot on the heels of the film compact came the digital one, and these all had zooms as standard. Then came the digital SLR with its standard zoom out of the box. Zoom became the default. I was at an event recently that had an official event photographer capturing the speakers for posterity. He had a pair of cameras, both fitted with zooms. Why not, when you can avoid even having to change lenses? He was shooting in the usual ill-lit theatre environment using a 70-210 zoom and no flash. And the shutter was going click rather than cliiiiiiiiiiiiiiick. So given you can push the ISO to the moon, why not use a zoom to get the framing rather than a wider fixed lens to grab the light?

In fact, the only reason I can see for people using a fixed lens at the moment is to get a special effect or to gain a wide aperture. Give it a year or so and the f1.4 zoom will be in the shops and we need never change lenses again. Although I suppose there will still be sports photographers or weird old codgers who mutter into their beards and smell of fixer. Or Leica users.

Sometimes you really need a wide aperture

I found an object of my youthful lust in a charity shop a few weeks back. A genuine Vivitar Series 1 70-210mm zoom. Filthy as hell, but £8. The joy of (some) old mechanical stuff though is that it was assembled by people, so it can be disassembled by people. You will know what I mean if you have ever tried to fix or replace a component in a smartphone. But the lens came apart in a logical order and cleaned up well. How well does it work? Not sure yet. I must say that I find myself using long lenses less often these days. I’m not a bird watcher and I don’t spectate at sport very often. So I find myself using lenses in the range covered by the zoom compacts of old: a bit wide to a bit long. My favourite zoom of all has the (35mm equivalent) range of 24-68mm and just lives on the camera. So yes, I probably didn’t need the Vivitar. But I can sit in a dark room with it, cackling and calling it precious. And that’s good too.

The serious question is that I am off on holiday next week. Do I take a bagful of fixed lenses or couple of zooms?


So I took the Vivitar 70-210 and a Pentax 24-50mm. I took a couple of shots on the long zoom and none at all on the wide. Part of it was the conditions – I spent a lot of time walking on beaches or sand dunes. I’ve got a rufty-tufty fixed lens camera that is sand and water proof and that got most of the action. I had no problem putting it down onto wet sand to take some very low-level shots or of using it in a storm of blown sand. I think the zoom lenses would have got a bit crunchy or the camera would have seized.

So it set me off to thinking again. I’ve got some compact cameras with built-in zooms. I don’t even think about it when I’m using them – it’s a very convenient way to get the framing quickly, particularly as they will also do macro. I have a digital SLR with two zooms that cover the range from wide to long. I’ve also got a lifetime’s worth of old fixed lenses that I have bought or been given over the years. And I’ve got some cameras that have fixed lenses. So the thinking has been reflection on how I actually use these things.

A Darth Vader memorial appears and you need to frame it? Time for a zoom.

On the digital stuff the zooms are autofocus and quick to zoom. So I just use them and don’t even think about it. The only problem with the film-camera zooms is their limited aperture, which can make focussing a bit iffy in poor light. The challenge to them though, is that I’m no longer a film-only photographer (but I am still a FUP duck). It used to be that if I wanted the benefits of carrying just the one lens, I had to fit something like a 35-70mm to my camera. I find that what has happened is that, if I want to use a zoom, I use a digital camera. The kinds of things I use a zoom for are the kinds of things that suit digital capture, with its low marginal cost, large capacity and opportunities to play around. And then the kinds of things I like using film for better suit the use of fixed lenses (or I can’t change the lens anyway). For film, part of the pleasure is the difficulty, or perhaps the right word is engagement.

Sometimes you can’t use your feet to zoom.

Until I started writing this and thinking about zooms, it had not occurred to me that I do this. So I wonder if I should flog all my film zooms on fleabay and settle down to being an old codger who smells of fixer? I could end up listening to the Classic Lenses Podcast.

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