|
Forum: Pentax Q
10-28-2012, 07:40 PM
|
| |
" I tried the Cosmicar 4.8mm f1.8 lens with a Voigtlander C mount to Q adapter. I could never get it in focus."
Do you still have the lens? If so mount it and then slowly unscrew the lens with the camera on and see if it focuses. If it doesn't your lens is too far forward. Did you take the back mount off the lens? It may have shims inside that you can remove to reduce the flange distance.
Otherwise your adapter may be too far forward.
I am using one of these:
Focus Infinity 16mm C Mount Movie Lens to Pentax Q Camera Adapter Free Shipping | eBay
And they seem to be slightly to close to the sensor which is why I am shimming.
Shawn
|
|
Forum: Pentax Q
10-28-2012, 05:57 PM
|
| |
It would be nice if Pentax built a real wide angle.
As far as the shimming on the 4.6 it turns out all that was needed was to loosen 3 allen screws to take the C to Q adapter apart, put three small squares of sticky note paper between the two sections of the C to Q adapter and then to put the two pieces together and tighten the 3 screws. Pretty easy. Most of the time I spent was when I was initially testing to lens and seeing if changing flange distance was improving the results or not.
Shawn
|
|
Forum: Pentax Q
10-28-2012, 04:56 PM
|
| |
" The images don't look bad, the colors are good and it's sharp in the center and soft on the outside in a good way,"
Some of that softness on the corners (the chairs shot esp.) is simply OOF due to the chair being inches away.
" but now having focus peaking, adjusting the focus for a fixed lens is probably very easy now."
Actually, focus peaking is basically useless on the 4.8mm or 6mm. Just about everything is in focus and the attempt at enhancement from the peaking actually makes it a little harder to gauge sharpness. When I was shimming the 4.8mm what worked best was comparing jpgs ( with different amounts of shimming) using the built in side by side comparison and zoom them both in. Now that I have that set there is no focusing on that lens at all. Just mount it and shoot.
The 6mm has adjustable focus, so you don't have to shim it unless you want infinity to match up. What is odd about that lens though is focus changes when you change aperture. If you have something in focus wide open and then stop it down a few stops what was in focus will no longer be and you have to readjust focus. I need to play with the flange distance and see if that alters that behavior.
Shawn
|
|
Forum: Pentax Q
10-28-2012, 04:30 PM
|
| |
" Not a fan of the C mount or D mount wides, I have a kern paillard 5.5mm D mount that has heavy vignetting"
I haven't tried a D mount that wide (I have a 13mm) but the 6mm and the 4.8mm Pentax C mounts don't vignette at all on the Q. I posted some sample shots of the 4.8mm in this thread:
https://www.pentaxforums.com/forums/pentax-q/172196-lets-share-shots-q-30.html#post2134234
Main trick with the 4.8mm is that it is fixed focus and I had to shim the C to Q mount adapter slightly which helped sharpen it up. I really like that lens on the Q.
I haven't had much of a chance to use the 6mm yet so I don't have any samples online yet.
Shawn
|
|
Forum: Pentax Q
10-28-2012, 02:14 PM
|
| |
"What I REALLY want is a 28mm (effective) prime... I'm more of a wide guy. 28 and 50 with an occasional 90 and even more occasional 21. "
Check out C and D mount lenses. I have a Pentax/Cosmicar 4.6mm f1.8 lens (effective 25mm) and just picked up a Pentax/Cosmicar 6mm f1.2 (effective 33mm) C mount lenses. The 6mm is soft at 1.2 but gets much sharper when stopped down.
For fast 25mm lenses there is a Petax/Cosmicar f1.4 that is pretty sharp at 1.4. I have a couple of Computars that are f1.3 but they are softer wide open and a Senko/Navitar f0.95.
Shawn
|
