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DSLR focusing on telescope.

Dave Wall

By Dave Wall
in Getting Started With Imaging

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PhotoGav

PhotoGav

Posted
Posted

Absolutely - Bahtinov mask with liveview and then lock down the focus screw to hold.

One thing that I've been contemplating recently is how important is it to make sure that the scope is in a rough focus position before balancing the set-up? I noticed that on my frac, I have to rack the focus right in to put the scope back in its case and I was often balancing before racking out to the focus point. Anyway I make it procedure to rack out before balancing these days... Just some thoughts on another rainy day!

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lensman57

lensman57

Posted
Posted

How do you guys focus your DSLR's when they are attached to the scope. I have skywatcher 200p I had a quick go last night it seems very hard to do.

Hi,

You can try Bahtinov if you wish and that is more than good enough for observing, but the stars need to be measured for an accurate focus if you were imaging so I use the FWHM method which is available in software such  as APT. You'd be surprised at how much more accurate it can get. You do need to have a laptop and the sofware to do this ofcourse and steady hands. last night I was so cold for some reason that I just couldn't turn the focus knob hence the horribble focus I acheived for imaging.

Regards,

A.G

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ollypenrice

ollypenrice

Posted
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I get a good agreement between Bahtinov and FWHM on the smaller socpes but, on Yves' ODK14, FWHM is literally useless and leaps all over the place. There is also Bahtinov Grabber, a software written to analyse a Bahtinov pattern and refine your use of the mask. I haven't tried it. For a quick solution try a Y mask. Easy to make. Use a bright star at a similar elevation to your target.

Olly

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JamesF

JamesF

Posted
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A motorised focuser is a wonderful thing to have, but there are workable alternatives in the short term.  Some people have made a lever that attaches to the focuser wheel so you can move the focus just by gently pushing the lever up and down.  You can get far more control even with that relatively simple mod.

James

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LeeWilky

LeeWilky

Posted
Posted

Definately a Bhatinov but until then point your scope at a bright star or jupiter and switch to live view.  In live view zoom in as far as you can on the star or Jupiter and adjust focus in small amounts and wait for it to stop shaking then have a look.  Eventually you will get a pretty decent focus.  Snap a few shots off nd check them just to make sure.

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ollypenrice

ollypenrice

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That is just the coolest thing ever. :)

Heh heh, I know it's very Heath Robinson.  In fact it works pretty well.  A half turn of the home made knob equates to about the smallest focus movement that can be detected in FWHM so the reduction is about right. The other FSQ106 we use here has the standard Tak Microfocus. There isn't much to choose between them really.

Olly

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