not enough "in travel " to achieve focus?

[Pete Presland]

having waited ages to give the dslr a go in the 10" newt very disappointed to fall at the first hurdle,not enough inward focuser travel to achieve focus.

i think i know the answer to this question,but anyway is adding a Barlow the only way (other than moving the primary mirror) to resolve this problem?

thanks pete

[johnh]

You could also invest in a lower profile focuser - assuming you don't already have one. Altering collimation nuts to move primary forward will give you a few mm but thats all.

John.

[swag72]

Can you not use a 50mm extension piece from the scope to your camera?

[kookoo_gr]

if your 1.25'' eyepiece adapter of your focuser has threads from the outside and you can unscrew the the 1.25'' barrel then you can screw your camera directly to your focuser and have those precious mm for focusing

[brianb]

It's quite usual for Newtonian scopes designed for visual use to have insufficient "in travel" to get to prime focus with a SLR ... if they made them that way, the mirror would be considerably larger, collimation would be more awkward and you'd need an extension tube to focus with an eyepiece. Newtonians optimized for imaging are usually described as "astrographs".

If the amount that you are short of focus is only a few millimetres, you may be able to move the mirror up the tube a bit by loosening all the collimation adjustment bolts. You will certainly have to recollimate the primary afterwards and leaving the mirror in this position is likely to cause collimation errors after even gentle handling.

[davew]

I've got an Orion 250mm f4.8 and once I take the 1.25" adapter out I can attach via a T2 and reach focus. ( As Kookoo says )

Maybe the design has changed ?

One down side is that the focus tube intrudes on the light path.

Dave.

[black5f]

Hi. What make of DLSR? The flange to sensor distance varies, Canon EOS is quite short (and large diameter so you can use lots of different lenses via adapters. Nikon is one of the longest and wil not take many other lenses as you can't get to infinity. It's only 2.5 mm different, but one of the biggest short commings of the Nikon mount re asto stuff. Eyepiece projection? (Without spending huge quantities of money!) Is there something in the way that you could get a friendly friend with a lathe to turn off? Tom

[davew]

I feel that's a bit of a red herring. The flange to sensor of T2 is 55mm regardless.

There are specially made adapters that will give a shorter distance with Canons. You just have to find them.

Dave.

[Pete Presland]

the dslr is a canon eos rebel xt.the focuser is a crayford design, but not a low profile one.

i have been thinking about getting an apo for imaging and if i need to start spending serious cash on a low profile focuser i might go for the apo.

how would a 50mm extension piece from the scope to my camera help,is that the same principle as the barlow without doubling the mag.

[brianb]

how would a 50mm extension piece from the scope to my camera help

Awfully ... you actually want an extension with negative length, but these only seem to be available manufactured from solid unobtainium

[davew]

Ah. I have a R & P focuser on mine. It's no good but it does get to focus

Good luck,

Dave.

[Pete Presland]

Awfully ... you actually want an extension with negative length, but these only seem to be available manufactured from solid unobtainium

yea i did think of going to Pandora to get some but,some of the Na'vi are a bit funny with humans! especially since we knocked their tree over

[x6gas]

So can you not unscrew the EP holder from the focusser? That's what I do and it'e enough to get my Nikon D40 into focus. In fact, I leave the t-ring attached permanently and can then just unscrew the EP holder and attach the camera whenever I want to image...

...I just shouldn't have bothered buying a t-mount that I don't need!

[Pete Presland]

So can you not unscrew the EP holder from the focusser? That's what I do and it'e enough to get my Nikon D40 into focus. In fact, I leave the t-ring attached permanently and can then just unscrew the EP holder and attach the camera whenever I want to image...

...I just shouldn't have bothered buying a t-mount that I don't need!

thanks i will certainly look in to it,no pun intended