Crop Factors?

[Nick Mercer]

I have been looking into the lenses for Epics and Scarlets. I've heard we will get a crop factor of x 2.47 with a S35 and x 3.56 with an FF35 lens. Does this mean anything more than my image will not be as wide as normal? Will I lose any quality? Will iris and focus work correctly? Have they even hinted at an adapter for this?

 

[Nathaniel Haban]

I have been looking into the lenses for Epics and Scarlets. I've heard we will get a crop factor of x 2.47 with a S35 and x 3.56 with an FF35 lens. Does this mean anything more than my image will not be as wide as normal? Will I lose any quality? Will iris and focus work correctly? Have they even hinted at an adapter for this?

Here is a link for a field of view calculator.
http://www.abelcine.com/fov/
Here will illustrate the difference between 2/3 and S35 and FF35. It does essentially mean that a lens will not be as wide as normal; in this, you're correct. Iris and focus will work the same. The image quality from a 2/3 will be the same as is you took a cropped image from the center of a FF35, meaning that you will see a slight drop in sharpness, and resolution. Redrocks makes an adapter that will allow FF35 lenses to be used on a 2/3 sensor but really, the price of the adapter is pretty cost-prohibitive. Then again, the best policy is going to be to wait until Scarlet is released to see what the specs -- whether 2/3rds or S35 -- before purchasing lenses.

 

[Jeff Kilgroe]

Crop factors have nothing to do with lenses, it's about the sensor (imager) size of the camera. What varies between lenses made for one imager format vs. another is the amount of coverage they provide. So a 50mm lens made to cover FF35 will most likely be physically larger than a 50mm lens designed to cover a 4/3rds sensor. The focal length is the same... If you put that FF35 50mm lens on the 4/3rds camera, you will get the same angle of view as you would with a 50mm lens that is intended for that 4/3rds camera. Or as Matthew Duclos likes to say, "A 50 is a 50 is a 50!".

Whether you put a S35 or FF35 lens on the camera doesn't matter, you are going to get the same Angle of View if both lenses have the same focal length. Based on the crop factors you have listed, you must be talking about Scarlet. Of course, all bets are off until November 3rd and the final specs come out. However, based on the currently known specs, we have a maximum image area of 3072x1620, which is 10.138mm wide -- that's 1.89:1 aspect if you're wondering. The maximum recordable 16:9 area is 2880x1620, which would be 9.504mm.

So, Scarlet at 1.89:1 or "3K full frame" would be a 3.55X crop factor from FF35 or a 2.46X crop from full-aperture Super35.

When you talk crop factors, they are relative to whichever format you're comparing. Those who are familiar with photography and lenses on FF35 will think that way. Several of the big camera and lens companies over the past few years have been pushing to use FF35 as the de-facto frame of reference. But those who shoot specific formats and are familiar with them will typically not try to confuse themselves with relational crop factors when choosing lenses. Someone who is accustomed to broadcast HD 2/3" cameras should have a good feel for which focal lengths produce which Angle of View they desire. Same with S35, APS-C, 4/3rds, etc..

When you get into the realm where people are primarily using cameras other than FF35 and you start throwing around crop factors, the ones who know what they're talking about will first ask you what the crop is relevant to. These days a lot of people assume FF35 due to its recent surge of popularity due to finally having full FF35mm DSLRs available at mainstream prices and due to all the DSLR video shooters.

You will find that with smaller formats, like 16mm, 2/3", 4/3rds, etc.. their primarily used focal lengths are shorter than the primary focal lengths for FF35 cameras. RED previously announced a set of "mini primes" for the interchangeable Scarlet-Cinema model camera. These ranged from a 6mm focal length at the wide end to a 50mm on the long end. Comparatively, this set would give the equivalent frame or Angle of View as you would get from a set of primes ranging from 15mm to 125mm on Super35 or APS-C / Nikon DX format sensors. Or the equivalent of 21mm to 180mm on FF35 cameras.

Iris and focus will work correctly if you use lenses made for larger formats. The lenses will just be physically larger and you will not have appropriate focal lengths for the smaller sensor. On a S35 camera, a 25mm lens is fairly wide. On a 2/3" Scarlet, 25mm becomes more telephoto because of the crop and would make a rather nice focal length for shooting portraits. So if you intend to use lenses from the SLR world, you will probably have a tough time finding focal lengths on the wide end of things. Or at least rectilinear lenses with the short focal lengths... Most lenses that are 10mm and wider for S35 (APS-C / DX) tend to be fisheye or have severe distortion. Image quality can become an issue or concern with lenses made for larger formats. They need to have a high enough MTF or ability to resolve the high pixel density of the Scarlet. Based on current specifications, the Scarlet's sensor is a bit over 300pixels/mm! Nearly double the pixel density of the Canon 1Ds III, which has a 21.1 megapixel FF35 imager with a density of 156 pixels/mm.

 

[Nick Mercer]

What is the biggest difference between the idea of red mini primes and the red pro primes we now know? I'm not asking for specs, just in general what would be the down side of using these smaller lenses.

 

[Jeff Kilgroe]

What is the biggest difference between the idea of red mini primes and the red pro primes we now know? I'm not asking for specs, just in general what would be the down side of using these smaller lenses.

No down-side, the mini-primes are just built for a different camera. They are super-tiny compared to the RPP's we all know. They are designed to cover the 2/3" Scarlet sensor and use a mini-PL mount. If you were to mount one on a RED One or Epic, it would not cover the sensor, you would see the image circle projected into the middle of what you record.

These mini-primes are all T1.5 and super sharp - optimized for the high resolution density of the smaller sensor. Actually the 50mm, as of the last time the specs were mentioned, was the only lens not T1.5. It was T2 or thereabouts. And it seems the primary reason for that has nothing to do with the focal length, but given the compact size of the lenses, and that it maintains the same external diameter as the others, there probably isn't enough room to make an aperture opening large enough to keep the T1.5. The lens would probably have to grow by 30% or so. Anyway, they looked like a great set of lenses.

 

[Nick Mercer]

Oh man. Now I either have to wait for RED to come up with a long focal length RMP or I just have to get the Scarlet-F. I just hate buying fixed lenses because of

1) Can't really upgrade except to a new camera
2) If you break the lens it will cost a lot to get a new lens for it and have it installed.

Seeing as the Scarlet's last publicly announced specs were including a 2/3 sensor, I think I will need the extra focal length for really nice shallow DoF.

Hopefully everything will change Nov. 3rd. :blush: