The quality of the two are average and nothing exceptional but the controls are nice and easy to use and the all metal build makes it hard to ever buy a plastic lens again.
Firstly the Pentacon 1.8/50
It is a fun lens but would like more sharpness and less noise for a prime. Having to Manuel focus, set aperture, and set shutter speed is good and challenging but can get tedious. Not being able to focus further then around 4 meters because of the M42 to nikon mount moving the lens a tiny bit away from the sensor makes it a bit impractical but overall a great lens to have and good for a bit of fun.
Here are some test images:
This is what it looks like:
The problem I had with the pentacon was attaching it to my D90 as the pentacon has a depth of field preview button and has a little piece of metal that sticks out on the mount. So when I screwed it into my d90 it would hit something. I tried sticky taping it down but it popped back out after a while. If I screw the M42 to nikon mount in first when I attach it to the d90 I can't properly twist lock the mount in as the pentacon will twist and unscrew from the mount. Any solutions? Also found it annoying to have to push the depth of field button every time I changed the aperture from 1.8.
Helios 44-2 2/58
I prefer this lens over the Pentacon accept one advantage the Pentacon has is a min focus distance of 0.33 which is impressive. Haven't looked into the sharpness of the Helios yet but what I like about it is the helios effect. The bokeh has a swirly look and it's so different.
Here are some test images of my dog with it.
Went for a walk to pick up a M39 to nikon filter (for the Jupiter 8 ) from the post office. Was a bit of a trek for just a adapter and it was pouring rain but took some images on the way with the helios:
Both these lenses are manuel focus so soon I will be getting a Tenpa 1.36x eyepiece magnifier which should help significantly.
As fun and as different these lenses are I wouldn't see them as a replacement for AI-S Nikon lenses as they just aren't practical for general use but you have to remember how cheap they are and I was able to get the Praktica for around $15 and the Helios for $25. I have no regret in buying them and I am sure I will get great use out of them.
I also have a Voigtlander 58mm f1.4 lens coming and that will be my main nifty fifty (fiftyeight) I will use. It is a all metal build, made in japan, can meter with the any nikon camera (Nikon AI-S version) and only has manuel focus (I think it's great to only use mf). From all the reviews I have read it seems to be a great lens and a cheaper option for the Zeiss Planar T* 50mm f/1.4 ZF yet have similar image quality and construction. I have to thank aim54x for recommending it to me.
I broke down...and ordered the Voigtlander Nokton 58mm f/1.4 SL II.......now I really dont need a Helios 44-2/44-3
The images are so sharp I can't handle it. The focus ring is so smooth and the whole build quality is perfect. It works perfectly with my Nikon D90 as well. I will put test images up later but might start a new topic for it as it isn't related to M42 lenses. Also got some sunrise shots few days ago I might upload.
