Camera and Telescope Focal length Question

[medave]

So I connected my Pentax K-r to my telescope (came with barlow with T-Adapter). No problems so far, but I'm only testing. Done a couple of photos and Video of the moon. When I turn on my camera it comes up with 34 focal lengths to choose from, 8mm right up to 800mm. So since I have a Skymax 127 the focal Length is 1500mm (f/11.81).

Which leads me to my question:

1. What is the best focal to choose? (800 seems is the closest, but still far off 1500).

Thank You.

[Pig]

I would suggest a spot of  "trial and error"  and then judge the outcome to determine what bests suits your set up  

[Cornelius Varley]

Why do you need to select a focal length ? The information may be of some use when shooting terrestrially using older manual lenses that don't "talk" to the camera (for reference at a later date perhaps) but I don't think it will matter.

[Leveye]

I don't see where that would have any effect on your results with your set up but give it a test all the same. 

[jgs001]

That should make no difference to the image at all, I suspect the camera will embed that value into the EXIF data in the image... which really does make no difference... With Canon, the focal length in the EXIF is... hmm... I can't remember exactly, it's either blank or 0... 

[michaelmorris]

As long you are using the camera in manual exposure mode (much preferred option), it shouldn't make any difference what you select.

[medave]

Thank your for your responses, I always set to manual exposure mode. It is just something that comes up when the camera is switch on connected to the telescope (everytime). Got a decent video though of the moon and got a few family friends stunned at the detail. Which is great when some have never shown that great an interest. Power of Astronomy!