Zoom Lens vs. Zoom IN on the Lens

K

Kholi

Section Moderator
Alright kiddies. With all of the adapter manufacturers popping out flip units we've all discovered that you can now zoom in further on the ground glass for a "pre-cropped" image. Consider that even at Academy frame you have the option of zooming in even further to turn your 50mm into an 85mm or so. And of course, zoom it out to "mimic" a wider lens. In truth you're not really mimicking, but doing the crop in camera which is much better than post.

Here's what I've calculated, roughly so, with my HVX200A and Ultimate:

A 35mm Lens @ 55.0mm is roughly equivalent to a 50mm Lens @ 25.0mm, perhaps a 60mm. That means you've turned your 35mm lens into a zoom lens that goes from 35-60. That's not an incredible range, but still, you've created a pseudo zoom lens from one lens, making it a 35-60mm. The trade-off is that the HVX lens, zooming in, becomes slower.

So if that same 35mm Lens is rated F1.4, then it's now something like an F1.4~3.4.

Great. Now the question is which scenario do you choose?


A) 35/1.4 Fixed Focal/Prime to enact as a 35-60mm Zoom lens in conjunction with your cameras widest frame to the longest or...

B) 35-70/2.8~3.4 Zoom lens?

Factors to Consider--

1. Fixed Focal Length may be sharper across the field than its equal in a zoom factor.
2. A Fast Fixed Focal Length may cost more or as much as a slower Zoom lens. In most cases a faster zoom lens will cost more than a fast prime of equal caliber.
3. The overall performance of the lens itself.
 
Its an interesting question, but You've left out the trickiest calculation, which is whether the resolution of the lens in the adapter is really as great when you are zoomed in on it.
Think about it - look at the glass size and the light gathering ability.

You are choosing between blowing up the image from the center say of a 35mm lens or using the full glass and image size of a 50mm lens. Plus you are blowing up the image on a piece of ground glass, so you are magnifying any grain or image degradation due to the fact that your image is being created on a GG. Something has to be missing in the former.

This is a question re: full frame vs Academy as well and a few years ago Brian at Redrock told me he thought that it was one advantage of still (full frame) vs Cine (academy ) lenses on an adapter. He said its similar to doing a blow up from a smaller negative, but I've never tested it or noticed it myself.

On an HVX it may make less difference because that camera may be the limiting factor. On an Ex-1 or an HDCAM it might be more noticeable. You also might not notice it unless the image is blown up on a bog monitor or screen.

Time to do some comparison tests with a chart Kholi?

Lenny Levy
 
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You're right! I did leave that out. What kind of resolution loss do you see through the zoom range when considering the camera lens itself. Add to that the Ground Glass equation (which I also forgot about) and grain size.

It really is time to do charts, man. They take SO long and I'd rather be out shooting but when it comes to deciding which of these paths will yield more efficient results it's gonna end up counting ye olde lines.

Do you have any theories on which might be the more efficient option in terms of overall image quality and light performance?

Note: I've had a blast reading reviews and looking at side-by-side comparisons between lenses from Photographers. The amount of edge softness present in even what we're considering the BEST glass is crazy. My favorite so far has been the 16-9.net comparison of the Zeiss Contax 21mm to the Nikon 17-35 and Canon 16-35L... the 21mm blows both clean out of the water in terms of overall sharpness. It's staggering.

That's honestly what began this in the first place. I got to thinking that you could spend X amount of dollars on this prime lens and have a sharp 21-40 or so, grab a hyper sharp 35 and have an extremely sharp 35 - 60 or so, grab an extremely sharp 50mm and have 50-85 or so and so forth. In effect, you could literally have about 4 extremely good lenses and be covered through the focal range.

But, you've got to consider a few other factors as well. ARG!
 
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Ive been zooming in on the GG to get a tighter shot ever since I got my SGpro, I thought you could do this with all adapters...?
 
If you zoom in on the HVX lens you risk the iris closing down to a smaller f/stop mid shot. That could be a problem.
 
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