Sometimes I get an idea in my head and just can’t get it out.
Modern digital cameras often have tiny sensors compared to 35mm film.
High-quality 1970s “prime” 35mm lenses had a reputation for being very sharp.
When one of those lenses is mounted on a small-sensor camera, the sensor covers only a tiny central region of the 35mm-sized image formed by the lens – essentially the sensor is cropping from the middle of the image, resulting in a telephoto effect.
This gives rise to the “crop factor” of small sensor cameras – at a given focal length, the field of view of the small sensor is much smaller (more “zoomed in”) than on the original 35mm film the lens was designed for.
What, I wondered, would images from a high-quality 1970s prime 35mm lens mounted on a modern small-sensor camera look like? Especially, could I get super-telephoto effects by mounting lenses that were considered long (telephoto) by 35mm standards, multiplied the “crop factor”?
I had to try it.
Above is a diagram showing the relative sizes of a 35mm film frame compared to the 1/2.3″ sensor in the Pentax Q.
The Q has the smallest sensor of any interchangeable lens camera I know of. While this may make it – ahem – less than ideal for general photography purposes (altho to be fair the latest versions of the Q have moved to a larger 1/1.7″ sensor, a huge improvement), that little 6.17 x 4.55 mm sensor does have an immense “crop factor” of 5.6x (comparing effective field of view at the same focal length – the number isn’t exact because the Q’s sensor has a 4:3 aspect ratio, while 35mm film is 3:2).
Off-topic, but other points in favor of the Q are the tiny flange focal distance of 9.2mm – it can mount just about any lens ever made – and Pentax’s excellent UI. I’m not sure there’s a mass market for a camera like this, but it sure can do some things that no other camera can.
So, while a “normal” 50mm lens on a 35mm camera has a 39.6 degree field of view (horizontal), the same lens on the Q sees only 7.1 degrees.
And – here’s the neat thing – a “telephoto” 200mm lens on a 35mm camera sees 10.3 degrees – but on the Q, only 1.8 degrees. That’s the equivalent of an immense 1120 mm lens in 35mm format. And a super-telephoto 500 mm lens sees just 0.71 degrees on the Q – equivalent to 2800 mm on 35mm.
So, I tried it. I got some Minolta MD/MC type prime (non-zoom) lenses on eBay, mainly because they have an excellent reputation and are a bit cheaper than other brands (because they don’t fit many modern cameras), and an adapter for the Q (also on eBay – remember I said the Q can mount almost anything?).
Here’s what I ended up with:
Left to right:
- Minolta 50mm f/1.7 MD Rokkor-X PF
- Minolta 135mm f/3.5 MD Celtic
- Minolta 200mm f/4.5 MC Tele-Rokkor PE
- Minolta 500mm f/8 RF Rokkor-X
From what I can tell online, these are all highly-regarded lenses. The “Celtic” line was Minolta’s cheaper brand, but it seems the economy came from using cheaper materials in the mount, etc. – supposedly it is optically identical the to more expensive “Rokkor” line. And of course, these are all primes – not zooms. Even today primes are generally sharper than zooms; this was even more true in the 1970s before improved manufacturing and computerized optical design.
In the second row you see the Pentax Q with a Tamron 3.5-8mm zoom f/1.8 lens in CS mount, via a “Hawk’s Factory” CS mount adapter (I told you the Q can mount most anything…), and the Minolta MD-to-Pentax Q adapter (just a hunk of metal – no glass).
Read the rest of this entry »