Crop factor confusion

Hello,

After many false starts over the last couple of years, with something urgent always coming up before I took the plunge, it looks like I'm finally getting a camera this summer (and the K10D looks to be a bit of a silver lining to the whole business...).

I've also been pleasantly surprised to see that, instead of me going through all the crippling indecision and lack of sleep over what lens(es) to buy, Pentax don't seem to do duff lenses. And only offer ones you might actually find useful. And two from my wish list (the 35mm macro and the long zoom - weatherproofing being what led me here in the first place) haven't even been made yet. Bliss. And the posts on this forum have been a real help, BTW. Thanks.

There's just one thing keeping me up late, and it's a question about prime lenses. I understand that with digital sensors, the view you get is cropped by about a third, so you think of it as having a focal length about 1.5 times longer. But what about perspective? For example, is the perspective you get from e.g. the 77mm Limited (which I might just be able to afford) on a digital camera the same as you'd get from a full-frame film camera? It's just that 120-odd mm seems a little long for portraits.

I realise this isn't strictly a Pentax question (and I'm not strictly a Pentx user yet, either) but could anyone help?

Perspective is only affected by shooting distance, not by the lens in use.

It only appears that lenses affect perspective when you, for example, go close in with a wide angle lens to fill the frame with a subject. To fill the frame with the same subject and a telephoto you would obviously be much further away, hence the apparent perspective change is due not to the lens but the distance.

Try it and see. Photograph something with a telephoto and without moving take a second picture with a wide angle. Now blow up the centre of the wide angle shot to show the same image as the telephoto. The perspectiuve will be identical.

Thanks, and come the summer, that's exactly the kind of thing I hope to be trying out...

So if I did get this amazing 77mm lens, I'd always be further away from the subject with a digital camera than with a film one (for a given shot), and the perspective of the shot would indeed be quite a bit flatter? Sigh.

Which means that the question I should really have been asking was, is 120mm too long for doing portraits? Sorry to grind away here, but it's an expensive lens, and my pointing and shooting up to now has been mostly outdoor stuff.

I regularly used a 135mm lens on my Super A, I found it really good for more informal/candid shots of the kids as they were growing up.

That's splendid news, thanks very much. Just the kind of stuff my family are pestering me about. I think I'll probably give it a go, along with the weatherproof wide zoom.

Now if the pointing on the gable end can just hold out for another couple of years...

The 77mm is a superb portrait lens on digital. Quite superb.

G

I use my 90mm macro lens as a portrait lens too.

Isn't that a bad idea because it can be a little too sharp?

So far no complaints. I don't take a lot of portraits, and then mostly of my grandson, but I am happy with the results. And the victims of my efforts haven't complained yet, well Merlijn might to if he could speak, but nobody else has.....Maybe they are all just too polite

Now that's another good question. I've been thinking about getting the weatherproof (always weatherproof, if possible...) 35mm macro when it eventually arrives, and hoping it would double as a portrait lens.

Would that work? Or will old people shun me after seeing their portraits?

Sorry Gwyn, didn't get your reply before posting mine.

Sounds like I need to start a new piggy bank now, just to be redy when the time comes...

the 35 will behave like a 50mm on film, isn't that a little short for portraits?

I use my 35 zeiss flek for small groups occasionally, but for individual portraits I'd say it's a little on the wide side.

Portraits aren't really my thing though so many people here will have a better idea than me.

Macros do tend to be insanely sharp, see my thread from a month or two ago on hockey shots if you want a demo of what the Tamron 90 can do. They don't look that amazing until you realise that they are both cropped down from 10MP to less than 2.

A 50mm would make a nice portrait lens on digital, and they can be had for not much money.

Not saying don't get the 77mm...

Dan

[quote="alex_s"]A portrait is normally a picture of the head, or head and shoulders. 35mm is much too wide because, if you fill the frame, the perspective (even on a DSLR) will give an unnatural and usually unflattering result.

On a DSLR, 50mm should be considered a minimum for portraits. There isn't really an upper limit, though personally I would consider anything over 120mm to be impracticable because it places the subject so far away.

The 77mm is a superlative portrait lens because although it is as sharp as you could wish, it has a creamy quality that is flattering to the skin.

G

My sloppy use of language, sorry. I was thinking of full shots, groups, etc. A 35mm on digital is probably OK for that?

Yum. The subtlety of all this really intrigues and amazes... Now do you think the Pentax people sat down one day and decided "Let's design a lens that discerning photographers will one day describe as 'creamy'", or was it more a case of someone playing around with some glass and a loo roll, then suddenly going "Hey, that looks really creamy"? I'm in awe.