MLAstro SHG Focusing Procedure

Summary

This instructional video explains how to calibrate and focus a spectrograph, specifically focusing on adjusting the camera and grating. It covers the procedure for achieving accurate infinity focus using a faraway object, then proceeds with the detailed steps for focusing the camera, adjusting the exposure, and fine-tuning the focus with a micrometer. The video also walks through mounting the SHG, adjusting the micrometer, and achieving clear, sharp focus on the slit and spectrum. Although the spectrograph comes pre-calibrated, this process is useful for those needing to perform calibration themselves.

Takeaways

• 😀 Pre-calibrated spectrometer can be adjusted if needed, including refocusing the lens or collimator.
• 😀 To calibrate, focus the camera lens on a far object at infinity for proper focus.
• 😀 The camera lens assembly can be adjusted by removing the collimator lens and refocusing the grating.
• 😀 The grating acts as a mirror to reflect incoming beams, aiding in proper calibration.
• 😀 Ensure that the camera is installed with the long edge facing the micrometer for proper orientation.
• 😀 To adjust the camera focus, use the micrometer to achieve an even and smooth focus.
• 😀 A distant object (at least 2 km away) is ideal to ensure the camera focuses at infinity.
• 😀 Fine adjustments can be made using the micrometer for both camera and slit focus.
• 😀 After focusing the camera at infinity, reattach the collimator lens and micrometer.
• 😀 When adjusting the slit focus, ensure the slit is clean and the spectral line is sharp for optimal calibration.
• 😀 The calibration process is optional if the spectrometer was pre-calibrated, but it is essential to follow these steps if re-calibration is needed.

Q & A

What is the first step in the calibration process for the spectrograph?

The first step is to focus the lens with the camera at infinity, which involves adjusting the camera's focus on a far-away object.

How can the lens assembly be refocused if it's not removable?

If the lens assembly cannot be removed, refocus is done by removing the collimator lens and adjusting the focus using the camera lens and a grating.

What is the role of the grating in the calibration process?

The grating acts as a mirror during calibration, reflecting the incoming beam from the camera to help with alignment.

Why is the camera oriented a certain way when installing it on the spectrograph?

The camera should be oriented with its long edge pointing towards the micrometer to ensure proper alignment, although perfect precision is not required initially.

What is the significance of choosing a far-away object for focusing the camera?

Choosing a far-away object, such as a building 2 km away, ensures that the camera focuses at infinity, preventing issues with near-focus adjustments and calibration errors.

What should be done if the focus on the camera is not fine enough?

If the focus is not fine enough, adjustments can be made using the micrometer to fine-tune the focus until it's as sharp as possible.

What happens after the camera focus is adjusted?

After the camera focus is adjusted, the collimator lens and micrometer are put back, and the slit is checked for focus.

How do you adjust the focus of the slit?

The slit focus is adjusted by using the micrometer to make fine adjustments to ensure a sharp and clear image of the slit.

What is the purpose of locking the grating in place during calibration?

Locking the grating ensures that it remains stationary while the micrometer is used to make precise micro-adjustments during the calibration process.

Is it necessary to recalibrate the spectrograph out of the box?

No, the spectrograph is pre-calibrated before shipping. However, if recalibration is needed in the future, the provided steps should be followed.