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Showing results for tags 'crayford'.
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Hi all gazers, i am having second thoughts about getting a crayford for my C9.25 (non HD) and that is because of the 0.63 Reducer / Flattener that i am imaging with. As camera i use the Nikon D7100. According to my calculations, and what i have read on internet, the optimal distance between the reducer and the chip is 105mm, the only focuser that allows for this distance (107-ish mm) is the feathertouch with the "shorty" sct-adapter witch is 56mm, my nikon T2-flange to the chip is 50mm. The Steeltrack and moonlite is far to long (93 and 91mm) But, according to some people, i can put my FR after the focuser with good performance, but how would that effect the reducing, and flattening? are there any out there who use crayfords and reducers on their SCT's with DSLR's? If nothing seems to work, i am getting the feathertouch microtouch replacement for the stock SCT-focuser. // Daniel
Okay folks, so, for a variety of reasons, including but not least an appalling sequence of poor weather since my last post on this particular topic, I have been unable to obtain an accurate measurement of the focal length off my 8” EdgeHD incorporating Baader SteelTrack Focuser and Click-lock Diagonal. I managed to remedy this situation over the weekend just past. Initial measurements based on adding the optical path of each of the components together, had the complete resulting optical path at about 2400mm, however this was not bourne out in practice. Using my 22mm T4 Nagler, at 2400mm focal length this should have given approx 45’ TFOV. Using M81 and M82 as a yardstick (approximate separation 36’), they should easily have been visible in the same field of view, however they were not. Extrapolating back from these values seems to be indicating a focal length somewhere between 3000 and 3225, which makes the revised speed of the system a whopping F15 to F16. This must be having a significant detrimental impact on the sub-aperture correction inherent in the Edge HD design, so I’m thinking of removing the Steeltrack from the system and replacing with a FeatherTouch or equivalent. This measurement is actually consistent with a drift measurement I made last year, (instructions courtesy of Don Pensack), but discarded due to it being so far removed from the expected result nearer 2400mm. But the proof as they say is in the pudding. So for those considering adding a Crayford to their EdgeHD, based on this experience I would say don’t. From feedback on this topic in CN, it is very possible that it is something to do with either the slightly faster primary/secondary combination in th EdgeHD and/or the sub-aperture correction in the baffle tube, possibly resulting in significant vignetting. (Thanks to Don Pensack and Edggie from CN, for their input). If you are interested in reading the CN thread discussing this you can find it here: https://www.cloudynights.com/topic/574002-calculating-effective-focal-length-of-an-edgehd/ Kind Regards Paul.
Folks just a short note to share a modification which some of you may find useful. The standard Crayford has fairly poor focus accuracy as we all know. But rather than chuck it and buy the twin speed version at about 150 quid... try this first. Simply double the gearing ratio by reducing the dimaeter of the spindle. I used a 2.5mm screwdriver and a ball of tape to give me a handle. The original spindle is abour 5mm So in stead of 3 full turns to rack end-to-end, you get amnost 6 full turns of the spindle. here is a fairly crude yet very effective implementation using a precision scredriver. this has greatly improved my focus accuracy! ...and as a bonus it can how hold my DSLR without applying the focus lock! Hope you like it and give it a go! Cheers Ray
Hi all, I've been thinking about a focuser upgrade for my 250PX for some time now, and recently spotted the above (link: http://www.tringastro.co.uk/skywatcher-dual-speed-low-profile-crayford-focuser-3948-p.asp ), which I like the look of. Opinions seem to vary, with some users reporting focusing issues and fitting problems. I know the focuser is claimed to suit DSLR users, the low profile nature allowing the camera to achieve focus, but is it also suitable for purely visual observing? Some users seem to be saying 'yes', by use of the inbuilt extending tube, whereas others suggest 'not'. If it is suitable for visual use, would I need anything else (eyepiece adaptor, for instance)? Anyone got any direct experience? Cheers, Kev
Hello, I am looking to upgrade the focuser of my SkyWatcher 80ED to resurrect it and use, along with an extension tube, for some night sky photography, if any body has a dual speed focuser for sale to fit my refractor I will be glad to evaluate offers. Has to be willing to ship to EU Thank uyou Giovanni
4 years after buying a Sky-Watcher dual speed Crayford focusser, I decided to fit it to my Evostar refractor tonight. I got a bit of a shock when the new focusser would not fit inside the Evostar white collar. I ended up sanding the white paint away from the inside of the collar with some wet & dry sand paper. It now fits like a glove but is this normal to have to do this?