macro lens vs magnifying glass
 

Posted: Sun Jul 29, 2007 8:32 pm Post subject: macro lens vs magnifying glass

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I have been putting together my DIY box, and currently don't have a macro lens, but i've been using a magnifying glass.

Are the macro lenses and magnifying glasses basically the same thing? The problem I've been having is that i've been putting my camera in front of the box with the magnifying glass inside in front of the gg, but i'm just not getting close enough, the camera goes out of focus and i can't get a focused image on the gg.

I figured out that if I place my camera about 2 feet away from the ground glass, and put the magnifying glass in between, about one foot away from the gg, and 1foot away from the camera, this allows me to zoom all the way onto the image so the vignetting is gone, but it feels as if my image is slightly warped on the sides from the magnifying glass.

What do i do here?

The magnifying glass is not nearly powerful enough to serve as a macro, not to mention it's not an achromatic doublet which is why you're getting that distortion. You need to buy an actual macro lens. And don't skimp on it either; cheap macros will just make the image look bad.

If needed to get the macro lens within the next day or two (can't get it online, need to buy at an actual store where it is in stock) what type of stores should I be looking for, just general photography stores? video equipment stores? what places in specific would carry them?

I live in St. Catharines, Ontario, but I guess if I need to, i could drive to Toronto, Ontario or ideally Hamilton, Ontario, which is a bit closer.

Jay,

if your in canada, get in touch with dennis wood of cinevate, get his achromat lens instead of a macro. Macro lens will produce CA. dont waste your time in this route. An achromat is expensive. But will save you time in R & D. I ve been there. I started with a magnifying glass, then to close ups and macros. Finally got an achromat lens.


Ted

Ted, an achromat is a macro. In fact "achromat" is short for "achromatic doublet" where a plano-concave lens is optically glued to the double convex lens that is commonly referred to as a macro. This is done only to reduce chromatic aberration in the image.

Ben,
The macros i was referring to those single element close up filters which are cheap, such as those from cokin and asian. they sometimes come in packets of 3 pcs, +2 +4 up to + 10. The achromats i was referering to are the more expensive kind with coated dual elements intended to offset CA as youve mentioned.

Thanks for clarifying it.

Ted

i guess with these DOF kits, you have no choice but to zoom in farely far? I've gotten the zooming to work now with these new macro lenses, but you do have to zoom a ways, because the bright circle on the glass is so small.

This makes these DOF adapters so difficult to use handheld because every little movement it a big jitter on the recorded camera since it's zoomed in so far.... The other issue i'm having is that by the time i zoom in far enough to get rid of the darker outside, a good portion of the image is cropped off.

Like on my ground glass, have a bright circle in the middle, where the image is consistently bright in the shape of a circle, then this circle gradients out, and on the outsides, the image is also there, but much darker, so all this image get's wasted. Is this how it is supposed to be, or does the vignette go straight to black

ya this really isn't going to work, i'm losing way to much of my image, I can zoom in as far as I want, the image stays in focus, but in order to remove all the vignetting, i have to zoom in to the point that all i have are closeups, and I can' get any wide angle shots


the only thing I can think of is that my ground glass is on backwards. I ordered the DIY kit from Redrock, so i'm using their professional ground glass piece. if this was on backwards, would this cause what i am describing/see picture in previous post

currently, the ground glass is positioned so that shiny, smooth, un-etched side is the side my camera sees and records the image off of. The other side, which has the little texture pits on it, is the one facing the 35mm lens.

Your groundglass orientation is correct. What you need is a PCXL (plano-convex lens) to reduce vignetting. These are better used in pairs on both sides of the ground glass to cancel distortion. Also, wide angle lenses will exhibit vignetting no matter what you do.

I'd purhcase these PCXL lenses if i knew they'd fix my problem, but to me it just feels like another thing I need to buy for diy project, when I know in the end I'd end up buying a professional kit because I'll never quite get what I'm after with a home-made kit.

I think my issue isn't so much that there is vignetting, but that there is a hot-spot in the middle of the image, where it is much brighter, and then outside the hotspot, the rest of the image is shown, but darker, and therefore impossible to capture from the camera, because i can only adjust the exposure to fit the bright spot, or dark spot, but not both?


Is anyone familiar with this hot-spot I'm getting, surely the image your supposed to capture isn't this hot-spot only by zooming in, as so much of the image gets wasted because the rest of it would then be exluded, and its like turning a 50mm lens into a 120mm lens via cropping the image and then magnifying it.

Hotspot and vignetting are two names for the same thing.

You may feel like you're zooming in past the intended image, but you may not be. Check with a normal camera to see if the image you're getting when zooming in past the vignetting is the same with what you should be getting with the lens set on an actual camera.

Keep in the mind that a projected image from any lens will exhibit vignetting past the intended image plane area. The key is knowing how much image you should be getting with consistent luminosity. The culprit for unnaturally harsh vignetting is usually a focusing element that is too diffusive.

Sometimes the camera requires too high a macro power to focus on the intended image inside the vignetting, so us DIY'ers compensate by adding the PCXL pair that makes a larger area more consistent and able to be used for capture. Although this trade-off is that we are using the far edges of the lens that are significantly less sharp than the middle and that's where you get all the complaints these days about lack of edge-to-edge sharpness in even pro adapters.

I purchased a set of Double Convex lenses, and am currently using one between my 35mm lens and ground glass. It seemed to help a bit with vignetting, but still not greatly.

I find that if I take the lid off the back of my project box, so there is lots of light getting in, the vignetting is almost entirely gone, but as soon as I put the lid on, making the inside of the box completely dark, If i look at the image on my camera, there is a lot more vignetting again.

Why is this, and what can I do to fix it?

Double convex lenses may not do it for you especially if they are symmetrical (same curve on each side.)

The disappearance of the vignette is a mystery. All I can speculate is that the light is masking the vignette or something is happening with auto exposure levels in the camera if this function is switched on. The stray light would be additive to the darkened image so could be expected to restore the image in the darker falloff areas.

This might be something vaguely similar to the pre-fogging of film to enhance low-light images or an appliance which was apparently made by ARRI which added light into the image path for the same purpose.