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Astro Engineering M42 - T-Mount Camera Lens Adapter Mini Filter Holder

£27.00
AC631

Availability: Out of stock

Details

The Astro Engineering Camera lens adapter for CCD cameras and convenient inline 1.25” filter holder is a well made little gadget that allows M42 mount SLR lenses to be attached to T-threaded accessories, for example CCD imagers for astrophotography. (The male side being a T thread or M42x0.75mm pitch; the female side is standard M42 or M42x1mm pitch also known as the Pentax / Praktica screw thread).


As stated, the caddy also allows a standard 1.25" filter to be inserted between the lens and the CCD camera. The filter does not need to be into position, it simply drops in to the receiving slot (like a slice of bread in a toaster!) and is secured in place with a simple Velcro retainer that also acts as a light tight seal. To reverse the operation, a simple push on the steel plunger allows the filter to be easily popped back out. Very quick and very convenient.


Of course the filter caddy can be used with a range of other equipment besides CCD cameras and Camera lenses. The front female thread is M42x1mm (Pentax screw fit) a standard Pentax thread T ring can be employed to convert the front fitting to female T thread, thus allowing a much wider range of accessories to be used with the caddy (T mount prime focus cameras adaptors, eyepiece projection adaptors etc). Can be used with all 1.25” filters in standard threaded mounts.


To achieve focus at infinity when using camera lenses T thread extension tubes may be required see the range of Revelation M42 Spacer Extension Rings (FF269 5mm, FF270 10mm, FF271 20mm & FF272 30mm)


Fitting notes:


Most SLR & DSLR camera body lens flanges are around 45mm from the film plane. The AC631 is only 17mm thick so if your cameras flange to imaging chip distance is less than 28mm you will probably need an extension tube to place the lens further away from the chip to achieve focus at infinity. So achieve focus at infinity when using camera lenses T thread extension tubes may be required see the range of Revelation M42 Spacer Extension Rings (FF269 5mm, FF270 10mm, FF271 20mm & FF272 30mm)


Once again; what the world calls M42 (the Pentax standard thread) is a thread of 42mm external diameter with a 1mm thread pitch, normally written as ‘M42x1mm pitch’. The somewhat confusing standard T or T2 42mm thread is written ‘M42x0.75mm pitch’. The visible difference between these threads is simple enough; the Pentax M42 - at a straight 3 turns per 3 millimetres - is a coarser thread than the 42mm T thread at 4 turns per 3 millimetres.


The bodge fit? It’s worth noting that the moderately close thread specification between these standards allows a modicum of ‘bodge’ fitting both ways - but the level of fitness is far from symmetrical. A male M42 Pentax thread (limited to a few millimetres of total thread) will usually fit fairly fully into a female T thread whereas a male T thread only goes in about 1 to 1.5 turns into a female M42 Pentax thread. In the latter case – the male T thread into the female M42 Pentax thread – only lightweight equipment should be exposed to this level of fastening as the probability of total failure of the connection increases with both the payload weight and the wear level from the number of usage cycles (ie, the mechanical wear being confined to too few threads).


(Many thanks to, Robert Dalby for the detailed description used here)

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