Showing posts with label pentax. Show all posts
Showing posts with label pentax. Show all posts

Sunday, November 21, 2010

SLR + InfraRed Filter

Eventually you will get bored of shooting landscapes and portraits until you can afford a lens upgrade, a trip to a remote place or find a new inspiration.

A very affordable ($10-$50) change of perspective  can solve your problem and get you inspired for weeks if you are up to the aesthetical challenge. An infrared filter allows into your camera's sensor only photons traveling with long wavelengths, mainly above 700nm. The most common and recommended filter is the R72, which filters light waves above 720nm. Infrared filters are known to add an eerie yet dreamy feel to your pictures as illustrated below (using R72). 







Infrared cameras are very sensitive to light, whereas more commercial SLRs need to be adjusted in order to see through the almost opaque infrared filters. Personally, I adjust the exposure to +4 EVs (about 16x slower shutter speed or faster lens) when using the filter and I use a white balance that is similar to that of indoor yellow light. State of art in lens production becomes a ball in the ISO's park with the inevitable noise for action shots or hand-held cameras (in contrast to using a tripod). I resort to ISO 1600 or 3200 when tripod-less.






With IR, any regular place can be turned into heaven with some skills and composition. Lamentably, the latter is not an easy game with a quasi-opaque filter. Therefore, you can either shoot blindly and then get feedback through the playback or you can compose without the IR and then attach it when done composing.






I hope you enjoyed this trip along with the slower photons. Bon voyage!

Saturday, November 20, 2010

ROKINON 500mm f/8 Mirror Lens Review

I must say that it is mostly thanks to this mirror lens I am about to review that this blog exists.

DESCRIPTION
ROKINON 500mm  f/8 MIRROR LENS
Purchased from overstock.com for $119
Came with T-mount for Pentax mount, x2 multiplier and 3 filters.
More details: http://www.overstock.com/Electronics/Rokinon-500mm-1000mm-Mirror-Lens-for-Nikon/3863117/product.html

USE
So far I have only used it for night sky photography and some telescopic silhouette patterns

PROS
Very compact and light 12.7 ounces and 3.4 in. L x 3 in.Diameter.

CONS
Terrible image quality (see images below)
Terrible light transmission at f/8 and f/16
Rough manual focus.

EXPERIMENT
Here I compare pictures of a full moon taken with the same pentax k-x body (at 12 MP) but with various lenses:
1. 70-300 mm zoom lens by Sigma at 300mm and f/5.8
2. 500 mm ROKINON mirror lens at f/8
3. 500 mm ROKINON mirror lens x 2 multiplier at f/8 theoretically























Click images to view in full resolution. Caveat, the images are cropped around the moon so expect the files to be bigger for the 500mm ones but is this extra tele worth the image quality?

OBSERVATION
I took more than 50 images to adjust to the right focal length but it seems that the image quality is independent. It is either T mount lenses in general, mirror lenses in general, ROKINON mirror lenses in particular or my ROKINON mirror lens specifically, but I doubt the latter. I wonder if any mirror lens owner can share his two cents worth conclusion to this confusion.