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Imaging with reflectors


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Hi all,

Apologies if this has been covered elsewhere.

I take it that the T ring set up connects a DSLR, minus it's lens assembly, to the 1.25 or 2 inch eyepiece end of a telescope.

What I fail to grasp is, using the above set up for a Newtonian reflector:

i. if there are no eyepieces in the system, is not the resultant image going to be really small (used for any telescope?)

ii. Is there not going to be a lot of dust/dew etc coated on the innards of the dslr, if it is directly connected without any barlows/eyepieces?

iii. where do you screw the filters?

Thanks in advance

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(i) What matters is arseconds per pixel, and this is determined by determined by the focal length of the scope and the pixel size of the DSLR - so you can have any size image you like, within reason!

(ii) Probably - I use a 2in adapter on the camera which takes a filter thread and leave a light pollution filter permanently attached. Having said that I ran without a filter for at least 6 months and had no problems with my Canon1000D (which self-cleans when you switch it off).

(iii) see above in my case


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when you connect a dslr or a ccd camera without a lens directly to the focuser of the telescope the telescope becomes the lens of the camera.

dust will go to the sensor of the camera even if you have the original lens on. but only if you are not careful. there are instructions at the camera manual how to clean a camera sensor. dew will form at a sensor if there is a lot of humidity in the atmosphere and low temperature at the site or at the camera body.

you conect the camera to the focuser with the help of a t-ring. this ring has threads to screw filters. alternatively you can use a filter wheel and place your filter there or filters that clip in front of the camera sensor and before the t-ring

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Yes and no.... thhe camera needs a T2 camera adaptor which gives you a T thread connection. Getting this to "talk" to the telescope focuser may require an additional 1.25" to T thread nosepiece which then sits with the camera in your focuser like an eyepiece.

i The focal length of the scope determines the plate scale and hence the size of the objects.

ii Yes there's a risk. You could fit a plain filter to give some protection

iii Usually the filters are screwed into the end of the nosepiece.

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