Sunday, 16 August 2009

tale of two teles


Comparing two 300mm bargain basement 300mm lenses on a micro 4/3rds camera (a Panasonic G1). Both cost around US$200 on ebay.

One of the really good things about 4/3rds sized sensors is how well they work with telephoto lenses, the x2 "focal length multiplier" making a 300mm lens have the feel of a 600mm lens on a full frame camera.

300mm telephoto lenses have been a popular choice for many photographers over the years as a good compromise between weight : telephoto reach : cost.

But for many wild life photographers (particularly small wildlife like birds) 300mm is not quite enough and 600mm is more like what people would like to use.

In the past (with 35mm film) that often meant the use of teleconverters, fitted behind the lens and extending the magnification.

This wasn't without penalty however and the extra optics soon made photographers aware of the limitations of their optics. When digital cameras started to appear in SLR bodies they came at first with smaller than 35mm sized sensors. This meant that the image was captured on a smaller area of recording surface resulting in talking about so called "crop sensors" or "focal length multipliers".

What ever you call it, it means that for digital camera users that if you are using APS or 4/3rds cameras that your telephoto is more telephoto than on a full frame and without the optical penalty of a teleconverter or the weight and cost of a longer lens.

Even better, the years of AutoFocus and SLR design changes have left the market with some really great high quality manual focus mechanical camera lenses at dirt cheap prices. Making it great for hobby people (like me) to get some excellent optics at bargain prices.

Two really great candidates are these, the FD 300mm f4 and the Olympus OM series f4.5

Better yet, these lenses work very very well on 4/3rds cameras (the EOS digital can't make use of the FD lens without optical based adaptors) and in my opinion better still on micro 4/3rds where stop down metering problems do not seem to exist and digital focus zooming makes accurate focus a simple thing.

I'm sure if you're interested in one of these lenses you've searched around on the net but haven't found much to help you in making any decision. Sure you can compare specs on both but having them both in your hands is quite different. Well, here I'll try to pass on what I found by taking the plunge and buying both.

Both come with nice lens based tripod mounts (takes the weight off your delicate G1 body as well as provides greater balance and stability on the tripod), and their weights are the same (within a few grams) and sat side by side you can see there is not a lot of difference between them, the OM lens seems more compact at first, but there is a difference.

The Canon lens employs Inner
ocus mechanism
, where only some internal lens elements move to change focus, the Olympus on the other hand uses a more simple design of focus by extension. This means that when you focus closely that the lens must get longer as the group of elements moves out. You can see the difference in the second image of the two lenses where the Olympus is now longer than the Canon.

Ok ... this may seem trivial but it has a few effects on both the lens physical operation and on the images.

The aspect of this is perhaps only obvious when you've seen it and if you understand macro photography (and have worked with larger format cameras too). You see, as you extend the lens you are of course moving it further away from the sensor (or film). This means that it becomes longer in focal length. So when focused at 4 meters from the camera the lenses each have different magnification. See below:

The FD:

The OM

Another issue is that because the extension of the lens puts a cantilever strain on the helical thread and focus becomes more 'stiff' as the lens extends further during focusing. If you support the front of the lens (of point it straight up) this reduced and makes it clear the physical benefits of the inner focus system.

Next is the tripod collar. I really like the FD lens tripod collar, it allows smooth and precise adjustment of camera alignment (vertical and horizontal) and is very nice on a mono-pod. The tension on the clamp is adjusted by rotating a knob on the side

and can be released by pulling it out popping open the clamp to allow you to quickly remove the lens from the tripod (if you decide to go hand held or pack it away leaving the clamp on the tripod.

in case you're wondering what the green thing is its a bit of plastic I jammed in there to prop open the clip for photography ;-)

the OM one however has a more simple clamp which even has a ratcheted connection (with a ball single bearing in the clamp). I found that this made adjustment of horizontal more tricky as you had a "click" either side of perfect ...

It also means that you can't quickly remove the lens from the clamp ... if you should want to do that.

Both lenses have an integral lens hood which slides forward to operate ... seems to work nicely in both cases, although I like that the Olympus one is held back by the lens cap. The Canon has the advantage of locking down when extended with a twist of the lens hood ... so even points distribution there.

Lastly an advantage (if you wish to call it that) on the OM lens is that the Depth of Field preview is a button on the lens. You can remove the "iris coupling pin" on the adaptor and have full aperture focus advantages and press the button on the lens to stop down just as you take.

This is not something you can do on any other lenses and is something which you can do on micro4/3rds but not all cameras.

Why? well I'm not entirely sure, but I think it has something to do with the metering from the focus screens and the type of focus screens.

I've tried using different apertures with my older EOS film camera found that it worked well but that it produced unreliable metering on my 10D.

I have also read of other 4/3rds users (not micro4/3rds) experience inaccurate metering on their cameras with stop down metering at smaller apertures (like below f5.6 or f8. So based on this I guess that those using 4/3rds in live view will not have this problem.

Since I use a micro4/3rds I don't even have to think about it.. I personally like the OM lens Depth of Field button as it makes manual focus in the EVF a peach and stopping down to 5.6 or 8 (giving better image quality) quick and easy.

That about sums up the physical differences between the two lenses that I can think of.

The optical differences are so minor as to be indistinguishable.

For example here are two samples. Both are taken from RAW and processed with DCRAW (-T option) then had some curves applied in an identical fashion.

Both are taken at the fullest opening of each lens.

hard so see much there despite the contrast with the background ... and

aside form some minor differences in focus if you can pick a major winner in the optical department then that's your call.

I hope this has been useful to ya' all

me? well I'm keeping both for now ... I like the FD to use more, but I can use the OM lens on my Canon EOS camera and I can't use the FD ...

1 comment:

gLOW-x said...

Very helpful !
Now I just need to buy one...or the other ;)
I'm glad the 300 FD seems to get less CA than 200/2.8.