Project:
Pentax 645 300 mm ED f/4 lens

Contents:

1. Overview
2. -

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

1: Overview

I have been very pleased with my medium format lens, a Pentax 6x7 165mm f/2.8. No vignetting to talk about even at f/2.8 but the color handling was far from perfect. A lens I have read about many years is the Pentax 645/67 300mm ED f/4, it use more advanced glasses of ED type and has a reputation to be very sharp, even at full opening. I have just bought one, a used Pentax 645, a smaller medium format compare to the earlier 6x7 I had. Now I have to take some test photos to see how good the quality is compared to my more modern designed Canon EOS 300 mm L f/4. The Canon lens is very sharp but have heavy vignetting problems, about half the signal is lost at the corners at full frame.

Have a look at my vignetting test:Analyze of lenes vignetting.

This is how the Pentax 645 300 mm ED lens looks, almost exactly the same size as my Canon 300 mm L lens. It looks to be in good condition too. They are hard to find in Sweden, more common in Japan, due the huge import cost it's not interesting to import it. You find them at eBay among other places.

There are lot of space where to place the two tube rings and a pulley for the focus motor. At rear the diameter is 75.5 mm and at the front 80.5 mm.

The infinity focus point looks to be far away from the true focus point for infinity, very good because then it's easier to handle it with a focus motor. The focus barrel rotates very smooth.

Photos with my earlier Pentax 6x7 165 f/2.8 lens.

I got both end caps included. The lens have 8 lens elements and of them are two of ED glass.

Have a look at the internal construction:

• https://www.pentaxforums.com/ forums/ 48-pentax-medium-format/ ... (Block diagram of every 645 series lens, Pentax forums)

The lens surfaces looks clean and they are in good condition. The filter diameter is 77 mm.

The rear end of the lens with its bayonet. The back focus distance is 70.87 mm compare to Canon EF's 44 mm. Some extra room for filter wheels, off-axis adapter etc.

Table of different lenses back focus:

• https://en.wikipedia.org/ wiki/ Flange focal distance (Flange focal distance, Wikipedia)

To do some test with my Canon full frame camera I bought this adapter, Pentax 645 lens to Canon EOS camera.

If I find that this lens is good for astrophoto I will later make a special adapter. A thinner adapter that let a filter wheel or something else be installed between the lens and the camera.

I got a message from Greg in Australia, he sent me this link: Greg's photo 1 and this link: Greg's photo 2. Maybe enough to explain why I bought this old ens.