Project:
Analyzes of vignetting from my
lenses and telescopes

Contents:

1. Introduction vignetting
2. Sigma 150 mm f/2.8 APO (f/4)
3. Pentax 67 165 mm f/2.8 (f/2.8)
4. Pentax 67 165 mm f/2.8 (f/4)
5. Canon 300 mm f/4 L (f/4)
6. Pentax 645 300 mm ED f/4 (f/4)
7. Pentax 500 mm f/4.5 (f/4.5)
8. TS130 2.5" x0.7 field flattener 684 mm f/5.3
9. TS130 3" x1.0 field flattener 910 mm f/7

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

6. Pentax 645 300 mm ED f/4 (f/4):

This Pentax 645 300 mm ED f/4 telephoto lens is something that I have looked for many years, now I have one. It has a good reputation to be sharp because of its ED lenses. I have also looked at astrophotos taken with a lens like this, looks very good. With it's big opening of f/4 I thought it will be a perfect lens to my astronomy hobby.

This was my first flat frame, didn't perform very well and did not correct the vignetting in the corners as it should do. In center the signal is about 66'000 and at the corners about 52'000. The signal drops 21 %.

Signal drop at corners relative center = 21 % or 0.17 EV (full frame sensor).

A later flat frame, this time I used the sky as reference with a white paper in front of the lens. From that I calculated a synthetic master flat. That is the method I use to create my master flat frames today. In center the signal is about 67'500 and at the corners about 47'500. The signal drops 39 %. Little bit high but still much less compare to my Canon 300 mm L lens.

Signal drop at corners relative center = 39 % or 0.7 EV (full frame sensor).

Information about the Pentax 645 300 mm ED f/4 lens:

• https://www.pentaxforums.com/ lensreviews/ SMC-Pentax-A-Star-645-300mm-F4-Lens.html

The result from this lens was as I expected very good, it cost just a fraction of the cost of my APO refractor. Have a look at one of the first photos with this lens, look at the stars at the corners, M101or nova V1405 Cas.