Lens not reaching infinity focus?

[meade expert]

Hi All

I purchased an m42 screw 200mm f2.8 and m42 to eos adapter to use in astrophotography.
AS can be seen from the attached photo I can't seem to reach focus.
I tried a 135mm m42 screw lens as well , same problem?
Using a 30D modded camera , tried it on a 40D unmodded , same problem?

Has anyone had this issue and solved it?
Is it the adapter thickness (one I have is the thinnest I could buy)

[tlgerdes]

Are you winding it out to infinity?

Most setups you back off slighty from infinity to find focus. Best is to check in daylight on a distant object IE +200m and check to see where you reach focus if you can, wind it all the way in and out.

Also try stopping the aperture down to increase your depth of field to see if that brings it to focus on land.

[Barrykgerdes]

Hi
I am no expert on camera lenses but a lens designed to fit a specific camera will have its infinity setting to place a correctly focusd object on the sensor plane.

If you adapt a foreign lens to the camera by means of a third party adaptor I would expect it to now have its infinity focal plane slightly in front of the sensor. This can often be compensated for by adjusting the lens focus past the infinity mark but it will will generally hit a stop that will stop infinity focus being reached in your camera.

I have been able to modify some lenses to reset the focus control to suit an adaptor but only some have sufficient range to do this.

Barry

[meade expert]

Do you have any instructions on how to mod the lens to go beyond infinity?

[Barrykgerdes]

No. It depends on how the focus mechanism works and how the focusing ring attaches to it. It is a specialist task sometimes requiring special tools.

Barry

[meade expert]

solved the problem..machined 0.1 mm off the flange surface... now the lenses can reach just past infinity focus !!

[Barrykgerdes]

Hi

Yes that is another option that I use.

Barry