Long Perng 2" Adjustable Field Flattener for APO refractors

High-quality field corrector for astrophotography with adjustable operating distance - for all refractor telescopes with 2" focuser

With this field corrector, you can achieve a very good imaging quality with an outstanding star sharpness up to the corners. The focal length of the refractor is not changed.

Optimisation of the corrector to your telescope by shifting the connctor barrel

Every refractor needs its own operating distance which depends on the focal length of the telescope. Rule: The shorter the focal length of the refractor, the longer the operating distance from corrector to the chip. For obtaining best possible results up to the corners, many professionals recommend even adjusting the operating distance individually to the telescope, as it often depends on 1/2 millimetres.

That is not a problem if using the new Long Perng field flattener.

You can slide the camera barrel continously and thus, by taking test exposures, easily adjust the perfect distance for your telescope accurate to the millimetre. The scale provides good orientation.

A few hints for coarse adjustment of the distances:

Most astrophotographers work with DSLR cameras. The operating distance of an SLR with M48 ring is 55 mm.

Here are a few recommendations for coarse adjustment of the distances:

Focal length up from 1000 mm: 55 mm operating distance

Focal length 800-1000 mm: 58 mm operating distance

Focal length 600-800 mm: 60 mm operating distance

Focal length 480-600 mm: 65 mm operating distance

Focal length 400-480 mm: 70 mm operating distance

If you use these coarse presets, you will have to make only minimal adjustments for achieving perfect astrophotographic results with your refractor.

Question:
How do you have to measure the working distance?

Answer from Teleskop-Service:
The working distance is measured from the beginning of the connection thread on the housing of the corrector (see example picture):