Infinity Focus on Manual

[Regulus]

I am wanting to buy some older manual focus lenses to use for Macro and astro-photography because there is more fine-focus control over the very limited travel of the focus ring on auto-focus lenses.
Q. Is there any problems with reaching infinity (or past infinity) focus when using an adapter like the Canon FD to EOS that u r aware of?
Pointless buying one if it wont reach focus.
Trevor

[speach]

you can't go past infinity

[raymo]

You can go past the infinity setting Simon. I suspect that that may have been what you did with your lunar pic. I used to use a couple of FD zoom lenses on my EOS 630 back in the days of film Trevor, and had no problem with focus. I don't understand however, what you mean by very limited travel of the focus ring on autofocus lenses. Manual focus lenses normally
have focus rings that are a bit tighter to turn, and consequently stay in
the selected position better.
raymo

[Regulus]

Raymo. What I meant was the travel on an auto lens is only a quarter of a turn because the motors r small. They have re-engineered the optics to reduce the distance.
A manual focus lens usually has a minimum of half a revolution and frequently more.
My old 300mm makes more than one revolution between closest focus and infinity.
The close up photography I do with my short zoom and standard is made harder by the short travel distance because a movement of 1/2mm will throw it well out. Just taking my fingers of the focus ring on auto focus lenses can ruin focus.

[Regulus]

Simon most lenses will be out of focus even on the most distant subject if u just set the lens to it's max setting (infinity). They focus past infinity.

[raymo]

I'm with you now Trevor; the smaller range of movement does indeed
make it more twitchy. I do however find that using a Bahtinov mask
makes it fairly easy to get spot on focus, even with the very loose focus
ring on auto focus lenses.
raymo

[doppler]

I purchased an adapter ring so I could use some old Ricoh lenses (pentax p/k mount I think) on my canon 1100d and they focus perfectly. The magnification is a bit higher than specified, ie 28mm is about 35mm but the 1100d is a crop sensor and the old lenses are made for 35mm film.
Rick

Here is a pic with the 28mm f2.8 tokina

[rmuhlack]

I believe that a Canon FD lens will not come to infinity focus on a Canon EOS without an adapter that includes a correcting lens [these correcting lenses are (apparently) of very low optical quality in most cases]. This is because EOS lenses have a backfocus of 44mm, whereas FD lenses only have a backfocus of 42mm. in otherwords, the FD lens is effectively too close to the camera sensor, preventing infinity focus.

Lenses which have a backfocus > 44mm can be used on an EOS camera, although you need to take the backfocus of any adapter into consideration as well. Manual focus Nikkor lenses can be used with a Canon EOS camera (I have several NIkkor lenses which I have used with my Canons); Pentax-K, Contax, Leica are also options. See here for a list of different lens mounts and their associated backfocus: http://en.wikipedia.org/wiki/Lens_mount

[speach]

Sorry you can I've just found this



CAMERA FOCUSING. Astrophotographers want their lenses focused at infinity, but newer autofocus lenses can go past infinity when focused by hand. To resolve this problem, set the lens at infinity during the day and then lock it there with one or two wraps of tape around the barrel. Use tape that won’t leave a residue (no duct tape). Manual focus lenses don’t have this problem, but some astrophotographers tape them anyway. It’s one less thing that can go wrong

[Regulus]

Thx Rick; that's a satisfying image and I look forward to achieving similar.
Raymo - Is a bahtinov mask design specific to the lens aperture/focal length, or will a standard type do. I noticed on a friends dob that by cutting 3 perfectly spaced circles in a cover that you could use that like a bahtinov mask to get focus.
Richard - thank you, that is very useful.
Thx Simon although I remember a few manual lenses that did go past infinity. My Kiron 80-200 did and others too. I workd in a specialist photography retail store and had the chance to try many, and various lenses. I was surprised and couldn't see the reason for it.
Trevor

[raymo]

Taping the lens in place doesn't guarantee accurate focus because it is almost impossible to hold it absolutely still whilst taping it, and also during an imaging session you can need to refocus to compensate for
expansion/contraction of the lens as the ambient temp changes.
Trevor, the three circle method is a variation on the Hartmann mask
which has two circles. They make the object look doubled or tripled, and
focus is achieved when the object appears single. The Bahtinov mask has
become more popular than the Hartmann because it is easier to judge
when lines cross each other, than when an object becomes single.
Bahtinov masks are simply scaled up or down in diameter to suit the
diam. of the scope or camera lens. My mask has sliding pegs that allow
it to be used with 6-7-8" scopes. You can get my size one for about $40
from Bintel. I imagine smaller ones would be a bit cheaper, and vice versa. Alternatively, you can make your own by downloading a template from the net. You could tape a lens whilst watching the mask effect
in Live View, to make sure you don't disturb focus while doing it, and do
the same again if you need to refocus during the session.
raymo

[raymo]

The reason for going past infinity setting is actually quite simple Trevor.
The manufacturer has to allow some leeway, because of expansion/contraction of the lens in different climates. If the lens limit
was set at an ambient of 20Degrees in the factory, it wouldn't reach infinity in very cold climates.
raymo

[rmuhlack]

My manual focus Nikkor ai lenses all have a hard stop at "infinity".

[rmuhlack]

Actually I think the main reason that autofocus lenses will focus beyond the infinity position is that during the autofocus process the camera needs to be able to automatically move the lens past the focus position (ie "out of focus" -> "focus" -> "out of focus again") in order to determine where the correct focus position actually is. It needs to be able to do this even when the subject is at a distance of "infinity", hence the focus barrel can be moved beyond the infinity position when focussed manually.

[Regulus]

Thx guys. I suspect both suggestions as to why are probably correct for Auto-focus while Raymo has hit the nail for the manual focus.
I'm off to make a bahtinov mask for my soon to arrive 6" Mak