DSLR nosepieces

[lil_coz]

Hi all,

This is a really noob question, so apologies in advanced!

When it comes to t-thread nosepieces that go on a DSLR, is there any difference if you use a 1 1/4" or 2" nosepiece when it comes to light gathering? Or is there no difference at all because the image is still focused on the same chip?

Thanks

[Leveye]

I don't notice and vignetting or anything using the 2 different adaptors.  If you're going with prime focus, afocal or what not on the scope and what your imaging you will need certain adaptors to achieve certain things. I must use a coma corrector with my DSLR and Newt for DSO work and must use the 2" tube there.  For the CCD lunar/planetary at prime i adapt the tube to 1.25.  For projection and afocal i use a clamp that attaches to the 1.25 eyepiece extension. Be versatile have all the adaptors and you'll be ready for anything.

[jambouk]

This is assuming prime focus:

The limiting factors will be the light path from the scope, and the size of the sensor, and the distance between the two.

If you have  a narrow light path and a small sensor, then all the light may pass through a narrow 1.25" nosepiece.

If you have a wide light path and a massive DSLR (full frame) sensor, then the smaller nose piece may cut off some of the light and result in vignetting, hence a 2" might be better.

Vignetting is common anyway and may be unresolvable.

JD

[lil_coz]

OK, thanks for that. Now that raises the next question. What's prime focus, and a focal focus? :/

[jambouk]

Prime focus is when the nose piece of the camera is stuffed right up the focuser:

http://2.bp.blogspot.com/-fscdokeHW9U/UIRcIPP5YvI/AAAAAAAAAeM/5KKnUysmRbI/s640/4.jpg

With nothing between the light path thrown out of the naked telescope and the sensor of the DSLR (though people use barlows between and the like).

JD
 

[lil_coz]

Ah ok, in that case, all my DSO AP is done using prime focus with a 2" nosepiece.

The reason I'm asking is because my H-alpha, OIII and SII filters are 2", and my LRGB filters are 1 1/4". I'm just trying to figure out if I need to invest in 2" LRGB filters or if I can use my 1 1/4" nosepiece with the LRGB filters.

Thanks for the input guys

[jambouk]

You may get more vignetting when using the 1.25" nose piece, but if you heavily crop the final image, it may not be a problem. Like many things, it will be a case of trial and error.

JD

[lil_coz]

Sounds like 2" LRGB's it is! lol

Thanks again for the clear up!

[jambouk]

You could do some comparisons in day light at a distant object, to see how the vignetting compares between the two nose pieces.

JD
 

[lil_coz]

I'll give that a go and see what the difference is

[jambouk]

Post the two results so we can see and all learn

jD