Help please - Canon 50mm 1.8 ef lens won't reach infinity

[jdg600]

I've had a 50mm 1.8 lens on my eos 1100d for about a year now and I've never really had much luck with it for astro shots. Anyway this morning I had the wheeze of using my Rigel Quickfinder for setting the focus at infinity on my lenses. My idea was that as the quickfinder uses a lens to project a circle that is effectively infinitely far away I could focus on this circle with the camera and thus find the infinity focus point of my lenses. This seemed to work ok for my 18-55 kit lens but when I put the nifty-fifty on I found that it wont focus to infinity - it hits the focus-stop just as the ring is coming into focus.

Has anyone encountered this kind of problem before? Is it possible to adjust the focus-stop on the lens? I'd be very grateful for any ideas on this as I was hoping to use this lens with my new Vixen Polarie for some wide-field ap.

[RikM]

I haven't tried it, but I'm fairly sure it doesn't work like that. The red circles you see in the Rigel display are just scatter/reflection from the light hitting the plastic. They are not at infinity, you can just look through them.

I use the 50mm f/1.8 on a 1000D and focus either using live-view zoomed in on a bright star with a Y mask or via FWHM in APT software. It reaches focus just fine. Try it using live view zoom and manual focusing to check it before resorting to more drastic measures.

[jgs001]

When you did this test, did the lens barrel of the 50mm extend out of the body, or was it fully retracted ?

It sounds like the kit lens, was outside it's minimum focus distance, but the 50mm was not, and thus couldn't focus. The extension of the lens barrel will tell us which.

I use a similar method as Rik, but without the mark or using APT. At 50mm and shorter focal lengths, I find focusing by eye using liveview (when I'm wearing my glassees, I can't focus on the screen without them) more than sufficient. Alternatively, I use DSLR controller on my android devices to control the camera and lens focusing, and the larger 7" screen on my tablet is much easier to ensure decent focus on.

[hazegood]

as daft as it seems the Nifty fifty lens movement in auto focus mode, goes beyond focusing at infinity. reason being because the AF has to go beyond that and then back again to work,

If you have a bright light in view by that I mean 100 metres or more, then focus on that usuing AF mode,  then switch to manual focus, , don't touch the focus wheel,  some use a blob of blue tack or gaffa tape to lock it and you will not be far off,
 

Failing that, then use manual focus. on something bright a fair distance away,

If you wear glasses its worth adjusting the dioptre wheel  on the cameras view finder if possible so you can get focus without your glasses