New *istD Digital Body


Lurach

Link Posted 30/05/2003 - 15:00
Hi all,

I am looking forward to the arrival of the new *istD body. I was recently told that the new body will have no affect on the focal length of lenses i.e. where current digital SLR bodies increase the length of the lense attached.

Has anybody heard anything to confirm or deny this?
Lurach

MattMatic

Link Posted 30/05/2003 - 15:18
Lurach,

Hmmm....
The actual focal length itself cannot change, otherwise the images would be blurred

However, the effective focal length is 1.5x the lens. Hence, a lens marked as 200mm will behave as a 300mm.

In actual fact what is happening is the CCD area is smaller than the 35mm frame so you are getting a centred crop of what you would have on 35mm. This is perfectly in line with the competition, and personally I don't see this as a real disadvantage.

...that's one reason I invested in a 20-35mm It's very nice for my Z1, and will work well with the *istD when I can get my hands on one!

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

Lurach

Link Posted 30/05/2003 - 15:50
Many thanks for the information Matt.

Yes, I understand about the actual focal length, that would be a good trick!! I can see that the "extra" length will be handy at the telephoto end of the scale, but my main interest was what do I do at the "standard" end and you have answered that as well - buy a 20-35!!!

regards
Lurach

Lurach

Link Posted 30/05/2003 - 19:22
Hello Matt,

I'm back with another question. I thought I was happy with your answer regarding actual/effective focal lengths and then while munching on the dinner a thought struck me. It's common now on digital compacts and video to see "zoom rating" being quoted as 3x Optical / 10x Digital etc.

In the case of digital SLRs is the 1.5x alteration in the effective focal length a true optical view or is it a digital alteration? I am assuming (hoping??) it's optical but maybe I'm wrong

regards

MattMatic

Link Posted 30/05/2003 - 20:03
Lurach,

It's no digital trick
Think about it - 35mm has a frame size of 36mm x 24mm. Imagine the hole behind the shutter where the film sits. Now replace the film with a CCD (ie digital film). However, that CCD is quite a bit smaller than the whole 35mm frame. The ratio is the same (ie 3x2) but covers a "crop" of the whole 35mm frame.

What will happen is that your 50mm lens (in normal 35mm terms) will be focusing a 36mmx24mm image, but the sensor will be sited in the middle. As a consequence the image will appear as if it were taken with a longer focal length lens.

In a way this can be quite useful. Most lenses are sharper around the middle.

The end result should be fabulous anyway. If you get a chance to see any real Nikon D100 images, or Canon 10D or D60 images - I could live with them all However, having a neat Pentax that means I can carry digital and film with one set of lenses and flash equipment will be even better.

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)
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