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Dslr focus problem

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I have problem to reach focus with my dslr camera attach to the telescope.

The telescope is a Sw150 pds, and my camera is a canon 600d modded.

I can reach focus with my old dslr, canon 450d, but not with the 600d.

I have tried with a lower t-ring adapter,

And with extension tubes.

It feels like it need to further in, but it cant go more in.

I can get it to focus if i use a barlow lins with a extension tub attach.

Is it something i do wrong?

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Where was your focus position with the 450d?  Modding the camera might move the sensor slightly but unless you were pretty much at one end of the focuser's travel I wouldn't expect it to make that much difference (assuming you're using the same t-ring, etc).  How does the 600d focus with a canon lens?

Best thing I ever did with my 130pds is get a coma corrector which moved the focus position out.  Without I think I had about 9mm of inward travel on the focuser when in focus with my 550d.

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That sounds odd, I would have thought the spacing between sensor and the front face of the DSLR would be very similar for both models. Can you post an image? Has the scope been modded at all?



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Hi Hedlund

As Stefan said, unless the focuser was right at the end of it's travel with the 450D, you shouldn't have difficulty focusing the modded 600D.

The flange distance for all un-modded Canon DSLRs is 44mm.

The mod only adds about 0.25mm to that.


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On 16/02/2023 at 18:06, Hedlund said:

can reach focus with my old dslr, canon 450d, but not with the 600d


One idea...

Focus with your 450 (are you sure you still can?), lock the focuser and remove the camera from its adapter by depressing the bayonet release on the camera, so leaving the adapter in place.

Now simply fix the 600 to the same bayonet.

The flange to sensor distance difference between the unmodified 450 and the modified 600 is such that only a tiny tweak of the focus position be necessary to focus the latter. Any luck?


Edited by alacant
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Daylight focusing is an excellent idea, but do be sure to use quite a distant object. There is a big difference between "infinity" and "a few hundred meters away" for many scopes, and that might mask the problem you're having.

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I like to thank you all for the replys and help.
Sorry for the late update from me.

I found out what was wrong, it was the dslr (600d) itself the was broken.
Something has happend to the camera.
I thought it was working because i was testning it with a canon lens some days before, something must have happend after that, because now i cant focus with a canon lens.
And i borrowed a friends 600d, unmodded
Camera and that will focus.

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That is extremely odd as inside a DSLR there are no moving parts which contribute to focus management, it's all done via the lens/optics it's attached to.

Is anything amiss if you look at the sensor?

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Yeah i think so too.

Nothing i can see, but I hade the dslr standing on the desk a few days ago

And i have a 2,5 year old kid running around, so i suspect what can have happend 😅

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