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focus range with a 0.5 focal reducer?

PostPosted: Sun Oct 04, 2015 12:20 pm
by steve99
Hi, If I use a 0.5 focal reducer would that reduce the back focus on a telescope or extend it? Would I need an extension tube or would the range of focus be shorter?

Thanks in advance
Regards Steve

Re: focus range with a 0.5 focal reducer?

PostPosted: Sun Oct 04, 2015 8:49 pm
by martin_h
Usually shorter, the reducer usually has a critical back focus distance.

Re: focus range with a 0.5 focal reducer?

PostPosted: Wed Oct 07, 2015 6:24 am
by steve99
Thanks for the info. This probably explains why I can't get it to work with my telescope.

Steve

Re: focus range with a 0.5 focal reducer?

PostPosted: Wed Oct 07, 2015 8:25 am
by miked2111
Which focal reducer do you have ?
I have been using a .67 focal reducer on my set up, after reading the info about my reducer i found that i needed a critical back focus
of 100mm +or- 1mm. I then measured all the fixed parts ( any spacer, filter wheel, camera thread face to ccd face ect) add then all up which gave me the distance i needed to make up in extension tubes. I have now got it down to within .5mm :happydance2: . So have a look at the tec info for your focal reducer and it should give you this info about total back focus. Hope this helps.

Re: focus range with a 0.5 focal reducer?

PostPosted: Fri Oct 09, 2015 11:53 pm
by steve99
Hi, I'm about to try some astrophotography with a web cam if the weather permits and thought a focal reducer would be a good idea. I bought a cheap 0.5 one made by Revelation. When I try to use it with an eyepeice I can't get a focus. However I've only been aiming at moderately distant trees so far. The sky here is stedfastly cloudy. I can't find any technical information about the reducer on line. I must presume that the focal point of the telescope has changed so much that focus is not possible. I don't have any spacers etc and have a celestron 127mm maksutov cassagrain with a focal length of 1500mm.
Because it was so cheap it won't be a disaster if it won't work but getting it working would be nice.

Steve

Re: focus range with a 0.5 focal reducer?

PostPosted: Sun Oct 11, 2015 5:41 pm
by steve99
As it turns out the focal reducer works with my webcam but not with the eyepieces. All the websites I kooked at that sell this reducer say it works with 'standard eyepieces', but seemingly not mine. However now that I have found it works with the web cam I'm pleased that I didn't waste my money.

Steve

Re: focus range with a 0.5 focal reducer?

PostPosted: Tue Oct 13, 2015 1:47 pm
by Thom
I guess, it's not a problem wih your eyepieces, but with the backfocus of your MAK.