First Forum Post ... Yashica 1000mm Mirror Lens

Hello from Peterborough UK ... My first forum post with a Q&D photo of a recently 'ebay acquired' Yashica 1000/11 mirror lens ... together with a smaller Yashica 500/8 reflex to show the size difference.



The 1000mm front lens plate and the turret filters looked very soiled in the ebay description ... much of which was caused by foam dust from disintegrating foam in the aged Yashica case. The UV filter and the front corrector plate cleaned up OK ... the revolving filters' rear glass surfaces are accessible through the rear lens mount. The other filters were / are soiled on both surfaces - so the whole filter turret needs removing for a thorough optical clean ... no hurry to do this as the coloured filters will not be used. I was hoping the filter turret wheel would pull out after removing the turret wheel exterior plate but no luck .. looks as if the actual lens mount needs removing to access the filter turret wheel's internal mount. Unfortunately the lens' primary mirror (i.e. the rear mirror) shows some silvering degradation on part of the perimeter ... thus looks ominous ... but the surface area affected is so small it has no effect at all on imaging. The photo shows a Telescope Services accessory lens hood / dew shield which wraps around the lens and is secured with Velcro tabs. Most mirror lenses have inadequate hoods; adding an accessory hood improves image contrast. I use several mirror lenses; they're so useful in cramped situations where there is little room to set up a long telephoto lens e.g. in town centres with busy pedestrian traffic. The Yashica 1000mm was acquired to specifically photograph Peregrine Falcons in residence on a local church steeple and tower. I’ve already tried an 800mm telephoto lens but its not quite long enough and it's physically too long to use on the relatively narrow pavement / sidewalk. As with all mirror lenses, the optics need to acclimate to ambient air temperature before imaging is optimised; this can take between 30 minutes to one hour depending on the primary mirror thickness/diameter. Many mirror lens reviews / lens tests make no mention of mirror lenses' "primary mirror" acclimation and their inadequate (too short) lens hoods … they're not on many reviewers’ radars. Hence otherwise quite good or excellent mirror lenses can receive poor reviews. Astronomers never expect their reflector telescopes to image optimally immediately after setting up ... especially if the 'scope has been stored indoors 'in the warm' before being set up outside on a cool or cold evening. Whilst 'in the warm', the primary mirror absorbs and stores heat'; when the used outside, the previously absorbed heat 'radiates' from the primary mirror ... creating 'thermals' ... which degrade the image. When temperature equilibrium is reached i.e. equal to the ambient air temperature, ’thermals’ cease and imaging is optimised. I'll post some actual 1000mm test images in due course.

BW

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