11
votes
Accepted
What can cause double-vision effect in slightly out of focus areas?
A cheap filter (uncoated or poor coatings) can reflect some of the light which is always reflected off of the front element surfaces.
The primary reflection (blue in the drawing) will be stronger than ...
- 13.9k
8
votes
What lens do I need?
Lenses do not affect colour balance to any significant degree - they are designed to be as neutral as possible. If the colours are too warm, reduce the colour temperature in your camera (or in post-...
- 21.6k
7
votes
Accepted
How can I find a lens locking screw if I have lost the original one?
I managed to check it with a micrometer gauge and a thread comb.
The thread is metric, with nominal diameter 1.6 mm, and pitch 0.35.
After proper googling as @hobbs pointed out, I finally identified ...
- 111
6
votes
How can I find a lens locking screw if I have lost the original one?
You first need to know what the thread size is, which you could find from the manufacturer, or by using a thread gauge. I would be inclined to e-mail the manufacturer, asking for a replacement Iris ...
- 528
4
votes
Why do some lenses have a rounded front element?
The two basic shapes of lenses are convex (bulge outward) and concave (bulge inward). As light traverses a lens, the lens shape plus its hardness causes the light to change its travel direction (...
- 38.5k
4
votes
Accepted
Why do some lenses have a rounded front element?
It can see 180°.
To achieve that it has to be proud of the barrel.
All [or at least most] lenses have a convex front element - but they don't have a field of view so wide that their own barrel will be ...
- 23.1k
4
votes
What can cause double-vision effect in slightly out of focus areas?
The optical system consists of multiple surfaces of polished glass. Each will reflect away a small percentage of the light. Some of these reflections will hit other lens surfaces and reflect again. ...
- 38.5k
4
votes
Does the inverse square law apply to all lights, including light within a lens?
Light from a normal point source travels omnidirectionally, so a given number of photons(1) traveling outward from a light source must illuminate a larger sphere the further you get from the source.
...
- 3,181
4
votes
Accepted
Since we know that focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an F -stop of 16?
Because magnification (focal length and subject distance) affects the Depth of Field more than aperture does (approx twice as much generally).
Start with 50mm @ f/8 focused at 10 ft. If you halve the ...
- 13.9k
4
votes
Since we know that focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an F -stop of 16?
Focal length totally affects DOF. That's one of the reasons that older video camera footage and current-day cell phone video doesn't look "filmic". The sensor is tiny, so a short focal ...
- 141
3
votes
Accepted
How can a fixed-focus lens have a focus range of 0.5 meters to infinity?
Because the camera has a very small sensor (relative to full-frame) and thus a very large depth of field.
A 1/2.3" sensor is 6.17mm×4.55mm, giving a crop factor of 5.64 to full frame. With this, ...
- 21.6k
3
votes
Why do some lenses have a rounded front element?
The front element (or often, successive multiple elements) on fisheye and ultra-wide angle lenses are bulbous so that the lens "sees" a very wide angle of view in front of it.
Typical lens ...
- 32.1k
3
votes
Accepted
What causes photos from modern instant films cameras to look unique?
What causes the pictures produced by any chemical process to look unique?
The specific chemistry involved. Different chemical processes are more or less responsive to various wavelengths of light. One ...
- 174k
3
votes
Why is the focus distance for a mirror image further than the surface of the mirror itself?
Yes, you either get the lake (or mirror, with its beautiful carved wood frame !)) in focus, or the reflected clouds at infinity. If you want the ducks on the lake and the beautiful reflection of the ...
3
votes
Does the inverse square law apply to all lights, including light within a lens?
The law of the inverse square tells us that light intensity falls off 4x with each doubling of distance. In other words, if you are reading a book by the light of a single lightbulb 1 foot away from ...
- 38.5k
3
votes
Since we know that focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an F -stop of 16?
Circle of confusion is an absolute value. Circle of confusion can be drawn on the image itself. If you were to scale the image from 25mm lenses to match the image from 100mm you will find out that ...
- 4,637
3
votes
Since we know that focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an F -stop of 16?
In short: there are two reasons your expectations don't hold true:
In order for crop 'equivalence' to hold true, everything must scale with crop factor, including subject distance and subject size. ...
- 32.1k
2
votes
Understanding Entrance Pupil
Your statements 1-3 are correct... without an aperture diaphragm behind the objective the objective element's diameter is the entrance pupil.
The aperture diaphragm is then (potentially) an optical/...
- 13.9k
2
votes
Accepted
Understanding Entrance Pupil
Consider this simplified diagram.
Without a diaphragm all rays that hit the front lens are used:
With a diaphragm rays that went though the rim of the lens are stopped so the effective diameter of ...
- 20.2k
2
votes
How does an afocal lens produce an image on a screen?
Per the wikipedia article for an afocal system d=f1+f2, where d is the distance between the lenses, not the distance to the subject. Your equation then gives F as infinity, saying that you cannot ...
- 1,904
2
votes
Which is the cause of Barrel and Pincushion distortion?
"d" in the single lens formula stands for distance... i.e. magnification IS dependent on distance, axial or otherwise. A simple lens with uncorrected spherical aberrations will create an ...
- 13.9k
2
votes
Accepted
Which is the cause of Barrel and Pincushion distortion?
Look at it this way: Without any aperture in front of or behind the single element lens, both distortions make it through and are superimposed upon one another. That's a major part of why an ...
- 174k
2
votes
Accepted
Relationship between quad bayer sensor and the CMOS size
There is small mistake with the size of the Bayer matrix. It is 2x2 cells so you should divide each dimension by 2, not by 4.
P.S. for information Fujifilm X-Trans matrix is different, it is 3x3 so if ...
- 10.8k
2
votes
Could I have destroyed my Lumix GX80 by taking sun photos?
Not too likely. What makes you think your camera is damaged?
A sensor burned out should be quite easy to notice on recent pictures (assuming it works at all), and other damage (bent diaphragm) should ...
- 20.2k
2
votes
Accepted
Does image distance affect resolution?
There's a general answer to your question. But based on something specific you said, there's another answer based on a misunderstanding.
Specific issue: Mounting the lens too close to the image plane
...
- 32.1k
2
votes
Does the inverse square law apply to all lights, including light within a lens?
This answer is empirical. I will not try to make a mathematical one. This is only a series of statements.
In general, the inverse square law applies to a point light.
Every big diffusive light at ...
- 23.2k
1
vote
Which is the cause of Barrel and Pincushion distortion?
As you know, the camera lens projects an image of the outside world onto the surface of film / digital sensor. The size of the image of objects is intertwined with their actual size – their distance ...
- 38.5k
1
vote
How to calculate the required working distance for an object to fill the camera sensor?
This online field of view calculator will calculate the answer(s) you are looking for. I can't comment on the math involved, but the site does discuss approximations and lens types, too.
- 356
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