Calibration Issue

[BowenZheng]

Hi there,

I've been having some calibration issue with the AC127-019-A achromat lens and the slit+50 mm achromat lens AC254-050-A. I feel confident about my calibration with the slit+50 mm achromat lens AC254-050-A, but combining it with AC127-019-A achromat lens is giving me an unfocused image (see "Calibration Issue") no matter how I adjust the distance between them.

I've followed the instruction (ie setting the gain to 0, adding a light source, increasing the exposure time slowly), but I'm getting a bad result. You can even see it impact the spectrum when I try adding in a diffraction grating and getting a spectrum of a red laser (see "Red_Laser_Spectrum).

Thank you,
Bowen

[Luc]

The slit image is of too low quality for any practical work -- clearly the sign that something is wrong.

Could you send a picture on how you adjust the position of the lenses? Preferably once they are at their aligned position.

As an order of magnitude, the focus range is on the order of 0.02 mm so you need to adjust the lenses within that range (ideally better).

[BowenZheng]

Hi Luc,

Here's an image of how I'm positioning the lens. Could you also clarify what you mean by adjusting the lenses? Is it just me moving it back and forth?

Thank you,
Bowen

[Luc]

Yes, adjusting means tuning the degrees of freedom until you get the best image. Here, thanks to the cage system bars, the only degree of freedom is moving the lens back and forth.

On the other hand, it looks like you've a missing lens in the setup :-/ you should have two lenses between the slit and the camera: one to create an image of the slit at infinity (collimation) and the other to create an image of the slit on the sensor.

While it's possible to use two achromats (I did it in the past), it's better to use an achromat for collimation and a machine vision lens for the camera. One other advantage of the machine vision lens is that you can use it as a semi-reference of infinity during alignment.