Adapt to survive

Posted by @ 2:50 pm on Thursday 7th February, 2008.

When I was in engineering and fabrication, there was this principle of standardisation. It was brilliant - it meant that things would actually fit together, you know, things like nuts would fit onto bolts, hubs would fit into alloy wheels, coins would be accepted by vending machines. It's a principle that we all take for granted.

Well, I'm lost in a No-Man's land, surrounded by seemingly incompatible bits of camera and telescope. Sometimes things fit, sometimes they don't. Telescope bits are usually imperial (2" and 1.25" eyepieces, 8" mirrors etc. etc.) and cameras are metric. Wonderful.

So, in order to get these things to mate, we have to bring in a third class of component... the adapter (adaptor) widget. It's amazing just how many of these damned things can be needed, even to the point where an adapter needs another adapter in order to achieve a union. Here are some examples:

1. Prime Focus (just a camera body on a scope):

To fit a dSLR camera body (without lens) to a scope focuser needs a T-mount (item G) and either a telescope eyepiece-holder with a male T-thread (item A), or a T-threaded adapter that fits into the eyepiece holder. Simple, eh? Well, not so fast, boyo, let's look again. T-mounts are fun. One side fits directly onto the camera body, so you have to get the correct version for the camera that you intend to use (I needed the Nikon bayonet one for the D50). The other end of the T-mount has a 42mm female thread as standard across the range, and you woud be forgiven for thinking that, if you were so inclined, you could fit a 42mm filter/step-up/step-down ring, but you can't. You see, 42mm photographic filters and step-rings have a 1.00mm thread pitch, whereas T-mounts have a 0.75mm thread pitch. Brilliant. Anyway, then you might have a choice of eyepiece holder... if you've a dual-fit focuser, it'll accept either 2" or 1.25" fittings. I was lucky here - my scope came with a dual-fit focuser and a holder which has an integral male T-thread. Some don't.

2. Afocal (using the scope eyepiece and the camera lens):

To fit a dSLR camera and lens combo to a scope focuser needs similar jiggery-pokery. This usually entails using the filter thread of the lens as the attachment point, using a different type of adapter. Let's look at a few of the options that I have at my disposal:

First up: to connect the 18-55mm Nikon kit lens needs an adapter (item C) which clamps over the barrel of the 1.25" scope eyepiece (like item F) and which has a male 52mm thread on the end, this screws directly to the lens filter thread. Fairly simple, if you've got the adapter.

Second, let's ditch the 18-55mm lens and try the 70-300mm instead. That's got a 62mm thread, so another chunk of precision engineering (a 62-52mm step-down ring, item H) is required. And so on for each different lens thread... you get my drift?

Third, I've an Olympus non-dSLR digital camera (C730-UZ) which I want to try... that has an unthreaded lens that extends out of the camera body when in use, so fitment must be made to the body around the base of the lens housing, where there's a 45mm thread. This thread takes an extension adapter (Item I) which has the required 52mm thread at the end... confused yet?

Finally, I've a zoom-eyepiece (item E) on order, this can be used optically on the scope without any hassle, but fitting a camera to it will be interesting - I've no idea if the clamp-on 52mm adapter will fit, and rumour has it that it has a special thread hidden away under the rubber eye-cup, this special thread is purported to be an M54, but at present I don't know if it's a standard or a special pitch. No doubt I'll need yet another damned adapter to get it to hitch to the lens. Time will tell which one's required.

3. Eyepiece projection (with the scope eyepiece, without the camera lens)

Well, that's just a mash-up of bits of the previous two methods, it needs some sort of connection between the scope eyepiece and the T-mount. Another adapter, maybe? Surely not! Looks like it. I'll be leaving this method until I've got the hang of the others, I reckon.

Oh, I forgot to mention one thing... all of the methods that employ a telescope eyepiece require you to have yet another adapter (an eyepiece holder, like item B) to fit said eyepiece into the focuser on the scope.

Had enough yet? No? Well, I'll go on about filters.

I've already mentioned photographic filters (the screw-on type, not the drop-in type), they have metric threads so that they can be screwed directly onto the front of the camera lens. Now, let's consider astronomy filters. Imperial threads. To fit scope eyepieces. 2" or 1.25". Horses for courses, as they say. Now, that's not too much of a hardship, but it would be cool to be able to use an astro filter, such as the light-pollution reduction filter (item D), on the dSLR when out and about taking night-shots without the scope. Alas, there's not much chance of that happening, as 2"-to-52mm adapters are as rare as rocking-horse shit.

Not a clue what these bits look like? Well, here's a piccy to help you out. Of course, I've not pasted the images at a consistent scale... that would make things too easy.



It's all too much. I'm going for a lie down now. Later on, I'll post some pics of the things that can be constructed using these bits.

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2 Responses to “Adapt to survive”

  1. GeoffC says:

    Tell me about it!.
    When I was trying to fit an LPR filter to my C8 I thought it ought to fit, I didn't know about the imperial/metric differences - I literally took the skin off my hand in the attempt to screw it on.

  2. BG! says:

    [quote comment="1068"]Tell me about it!.
    When I was trying to fit an LPR filter to my C8 I thought it ought to fit, I didn't know about the imperial/metric differences - I literally took the skin off my hand in the attempt to screw it on.[/quote]
    Ouch! Rather you than me 🙂

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