About Zoom lenses – Pt1.

Weighty Issues.

What lens should you use?  Its a common question and one that’s often seen on photography forums and often opens up a nightmare discussion.

Case in point is the current discussion in the Fuji X system forum at DPreview. Click this link to see the discussion. The forum post topic is the following question – “How do zoom shooters actually calculate their shots?”

The topic heading is in itself somewhat confusing and for many may be a little difficult to make sense of. Essentially what the member is asking is, how do you determine the depth of field based on the lens being used and distance from the subject. Right about now  many of you are no doubt going “WTF!!” Understandably so too.

The question is about how to balance those regions of the photograph to create the perception of depth in the image. What is going to be in focus in the foreground, mid ground & background areas.

For this exercise lets say we have a subject 3 meters from the camera. Then we have to decide what is to be in focus.  Obviously the subject needs to be in focus, but perhaps both the foreground and background should be somewhat out of focus. If  your lens has a native f ratio of 1.6 then you can have really well blurred background and foreground. If you select f4 then a little more of the foreground and background will be slightly more focused. If you then select f11 or f16 then everything in the image comes into sharp focus.

That’s why many photographers love to use fast Prime lenses that have typically f1.4 to f2.8 fixed focal ratios. Fixed aperture Prime lenses are without doubt some of the nicest lenses available when you are relatively close to your chosen subject, but they come with a few caveats. They are generally large lens in terms of size. Heavy or in some cases extremely heavy, bulky, and generally are extremely expensive. For most of us, trying to justify the purchase of fast prime lenses just isn’t in our budgetary constraints.

The size and weight issues continue when people consider buying premium grade telephotos lenses as well. Take for example a long time favorite the Canon 70-200mm f4 lens. At 979 grams in use plus the weight of a camera body, you have a  hefty piece of kit hanging around your neck. Consider that the Canon 600D is 575 grams the total weight of the EF 70-200 plus the 600d is just over 1.5kg or about 3.5 pounds.  Now add to this other equipment that you may have in your camera bag and all of a sudden those much touted fixed aperture primes are not so much fun to carry around.

Another fan favorite is the EF 85mm f 1.4 L IS USM lens. At 970 grams it too is a big piece of kit. So while these bulky, heavy expensive lenses are favored by pro photographers, and dare I say it – camera snobs, the reality is that for 99% of us these lenses are not something we are ever truly likely to own.

In the next section we will take a look at what is available that is lighter, less expensive and perhaps more versatile than the Pro class lenses, what some of the tradeoffs might be and how we can work around these perceived shortcomings.

Canon 600D Astrophotos & 18-135mm f3.5 -5.6 IS lens.

An extremely cold night under the stars with the Canon 18-135mm f3.5 -5.6 IS lens.

I shot the lens at 18 mm and at 135mm to get a feel for the ability of the lens. I found it to be reasonably well corrected with a certain amount of coma and chromatic aberration at the edges although to be fair not as much as I had anticipated.

As always with Canon DSLRs the 600D tends to be red heavy on the sensor. I have yet to determine why this is the case with these cameras as it makes post processing difficult. Ambient temperature was a balmy 2 degrees Celsius when I began the session and was subzero by the time I had finished.

The first image is a wide field view – shot at 18mm, ISO 3200 for 15 seconds. A stack of eight images.

The Coal Sack, Southern Cross and eta Carina region.

The second image is shot at 4 seconds at 135mm as is the third image. A stack of thirty three images.

Eta Carina Nebulae region.

The third image is of Messier objects M7 and M6. The larger of the two star cluster is M7 at center frame. Stack of twelve 4 second images.

Messiers 6 and 7.

Having a proper mount to sit the camera on would be a big benefit. The lens looks to be quite useful even if it isn’t an f2.8 lens. Currently I am considering getting an iOptron Sky Guider Pro and a suitable tripod to mount it on.

As always Happy Snappin’