Infinity stop at the stars/DSO's.

[sconcemike]

I have a Nikon d3100 that I use with 3 lenses. My problem is focussing. My Samyang 14mm f2.8 will focus on the heavens if I turn the focus ring as far as possible. Great for sharp wide field. The kit 18-55mm is the same. However I have a Tamron 200mm that focusses beyond the stars and I can never tweak it except by pure luck. Does anyone have recommendations for a lens in that region (125-300mm?) where the infinity stop is at the stars? I also use a Star Adventurer for the longer exposures. Any thoughts greatly appreciated. Thanks.

[almcl]

Afraid I don't know enough about your particular camera, but for my Canon 200 mm lens I use a home made Bahtinov mask and live view or connect to a tablet or laptop and focus using that. 

The free version of APT (Astrophotography Tool) has some built in focusing aids, if that will work with a Nikon?

[PeterCPC]

Use Live view and a high ISO so that you can see stars and then adjust focus until star is as small as possible.

Peter

[sconcemike]

I've ordered a bahtinov mask for the lens thanks almcl. Dont know why I didnt think of that before as they can be useful for a telescope.

And thanks Peter for the advice, although I do try that each time - maybe my eyesight isn't quite good enough. Also the focus ring on the Tamron is not smooth so end up with a lot of movement.

 

[jiberjaber]

1 hour ago, sconcemike said:

I've ordered a bahtinov mask for the lens thanks almcl. Dont know why I didnt think of that before as they can be useful for a telescope.

And thanks Peter for the advice, although I do try that each time - maybe my eyesight isn't quite good enough. Also the focus ring on the Tamron is not smooth so end up with a lot of movement.

 

I'll be interested in your results, I tried making a mask for my lens and it's hard to get enough light in to see the focusing spikes in live view with teh ISO cranked all the way up (works in a photo though - but that's a lot harder to get the focus right using it that way)