Time for a change

[Abitconfused]

Our digital cameras give us options for great accuracy in white balance, and at least a gauge for shutter speed and aperture but focus is in the dark ages. I want a focus range from 0 to 1000 that I can select. I need this for greater accuracy in astrophotography.

[george013]

Our digital cameras give us options for great accuracy in white balance, and at least a gauge for shutter speed and aperture but focus is in the dark ages. I want a focus range from 0 to 1000 that I can select. I need this for greater accuracy in astrophotography.

You mean a range from 0 to 1000 meter?? I don't understand your demand.

George

[Abitconfused]

0 being all the way in and 1000 being all the way out in manual mode.

[AG64]

Our digital cameras give us options for great accuracy in white balance, and at least a gauge for shutter speed and aperture but focus is in the dark ages. I want a focus range from 0 to 1000 that I can select. I need this for greater accuracy in astrophotography.

A flashlight on a distant rock or tree is my preferred method, but if your camera will allow you to zoom & focus in live view, pointing it at a bright star and adjusting it to a pinpoint works pretty effectively for me. Thankfully UWA lenses are pretty forgiving, even wide open.

[Tronhard]

I am a bit confused by your question. How will a scale of 0-1000 benefit you in manual mode. I assume you mean manual rather than auto-focus. What precisely are you trying to achieve?

[Abitconfused]

In the 0-1000 scheme, you can select any number between 0 and 1000 to obtain exactly the same focus from any point to any object.

[DanK]

Isn't that what the distance scale on the lens does, but in known metrics (meters, feet) rather than an unfamiliar one (how far away is 500 on your proposed scale)?

Lenses expand and contract with temperature changes, so anything on the scale (regardless of the metric) will be approximate. Modern lenses generally have a hard stop beyond what ends up being the infinity focus point under most conditions, which I think is for this reason, but someone can correct me.

On a wide angle lens, simply using the infinity point on the scale ought to be more than close enough, but using a magnified view in live view is what I would do. You could also take a test shot and magnify it to confirm.

[Polar01]

Ed have you looked at the SharpStar from Lonely Speck it maybe of some help. Including a link to the site:

https://www.lonelyspeck.com/sharpstar/

Cheers: Allan

[Shadowman]

Nice capture.

[Abitconfused]

The scale on a lens is not as easy to recall or describe as is a number. The idea is that you can return to the exact focus you used before. It really doesn't matter how any one person might use it, misuse it, forget about it, or stare at it in wonder. Our cameras are capable of providing more precise information than is presently provided. Information is power.

[Manfred M]

Of course, you can always get a non-autofocus lens. These have a non-adjustable hard stop for the "infinity" position that was set on an optical bench during lens assembly. That makes focusing on the stars quite easy.

[Tronhard]

A couple of point that I can't quite get:
1. the distance scale on a lens IS a number and it's absolute based on distance, not an abstract scale
2. Unless you have some kind of digital readout (like the Canon EF 70-300 F4-5.6 IS II USM) the information on the lens is going to be on a very small Vernier, so getting the ability to select the exact value again would be challenging.

Do you have an example of this somewhere?

I am struggling to think of a practical use or benefit for such a feature. To be able to reuse the exact focus one would have to have the exact same location for the camera and focal plane relative to the subject and point of focus. I have worked as a technical photographer and to be honest I never felt the need to know that, I re-focused as required.

For something to have a market a feature has to have a benefit, and right now what you are describing appears to me to be a feature looking for a benefit.

The scale on a lens is not as easy to recall or describe as is a number. The idea is that you can return to the exact focus you used before. It really doesn't matter how any one person might use it, misuse it, forget about it, or stare at it in wonder. Our cameras are capable of providing more precise information than is presently provided. Information is power.

[george013]

The scale on a lens is not as easy to recall or describe as is a number. The idea is that you can return to the exact focus you used before. It really doesn't matter how any one person might use it, misuse it, forget about it, or stare at it in wonder. Our cameras are capable of providing more precise information than is presently provided. Information is power.

Close to the fingers of the photographer you see " memory set". It seems you can set the focus info in memory and return the lens to exact the same focus distance to readjust it. This lens is about 7000 Euro. Ken Rockwell mentons a specific use for this somewhere in the middle http://www.kenrockwell.com/nikon/200400.htm. It's not astrophotography.

George

[Manfred M]

Close to the fingers of the photographer you see " memory set". It seems you can set the focus info in memory and return the lens to exact the same focus distance to readjust it. This lens is about 7000 Euro. Ken Rockwell mentons a specific use for this somewhere in the middle http://www.kenrockwell.com/nikon/200400.htm. It's not astrophotography.

George

I'm not sure why you are suggesting a long zoom (200-400mm) when Ed is shooting an ultra-wide angle lens (20mm according to the EXIF data).


Ed - what about a follow focus mechanism. These are commonly used for video work and give you a very high precision focus. The focus marks are can be marked on the follow focus barrel.

Unfortunately, modern lenses with internal focus motors have a very small focus throw, which makes precision focus impossible (hence my previous suggestion of an older manual focus lens plus the hard stop). For astrophotography you need to know where "infinity" is. as that is your subject distance. With a 20mm lens your depth of field is extremely wide, even when fairly wide open.

https://www.bhphotovideo.com/c/produ...ocus_Blue.html

[MrB]

I need this for greater accuracy in astrophotography.

If what you require is for astrophotography, would a number scale be necessary? I don't have the technical knowledge to know whether the following is possible, but the solution might be an electronic control of the lens that sets it accurately straight to its infinity position with a simple button press. Presumably any lens focused at infinity will have an infinite depth of field, so that everything in space will be in focus.

Cheers.
Philip

[george013]

I'm not sure why you are suggesting a long zoom (200-400mm) when Ed is shooting an ultra-wide angle lens (20mm according to the EXIF data).


Ed - what about a follow focus mechanism. These are commonly used for video work and give you a very high precision focus. The focus marks are can be marked on the follow focus barrel.

Unfortunately, modern lenses with internal focus motors have a very small focus throw, which makes precision focus impossible (hence my previous suggestion of an older manual focus lens plus the hard stop). For astrophotography you need to know where "infinity" is. as that is your subject distance. With a 20mm lens your depth of field is extremely wide, even when fairly wide open.

https://www.bhphotovideo.com/c/produ...ocus_Blue.html

I'm not suggesting anything. Just showing him the memory function on the lens. That's what he asked for.
Plus a remark I don't see the advantage for astrophotograpy.
I don't know what lenses have that function.

George

[Tronhard]

I am confused. Perhaps I am being incredibly thick here, but I fail to see the purpose in such a scale, and I have not seen a justification for it. Honestly I'm not trying to be difficult, pedantic or rude but the benefit of this still eludes me.

Point 1: The original question was "I want a focus range from 0 to 1000 that I can select. I need this for greater accuracy in astro-photography." WHY? Astronomical objects are a VERY long way away, so focusing on them will be very close to infinity. Is there a suggestion that somehow more precise measure is required considering: the objects are literally light years away, both they and we will be moving relative to each other and, unless you are using an astronomical telescope (which is not a normal lens)how is having a super-precise measure going to help?

If one accepts the fact that a perfect focus is a thin plane and all the rest is within a circle of confusion, then what is "in focus" depends on quite a few things. The f-stop - based on aperture and focal length for a start, which are likely to vary depending on the amount of light and the other variables such as shutter speed and ISO, and then there are the individual variations in optics of each lens. What is in focus may also change with ambient temperature around the equipment - if one is going to be that level of precision. While a lens+camera combination may be able to record a precise distance on a recordable scale, will that be true for another apparently identical lens and or camera? I'm not sure that conventional cameras are made to that level of tolerance. Finally the other variables will be the precision of how the image is displayed and one's own level of acuity.

Point 2: Quote "It really doesn't matter how any one person might use it, misuse it, forget about it, or stare at it in wonder. Our cameras are capable of providing more precise information than is presently provided." "Information is power." Not on its own it isn't. The original and more accurate quote is "knowledge is power" taken from the Latin and attributed to Fancis Bacon, although it is argued that a more accurate translation is "Wisdom is power" There is a big difference between a raw metric or DATA (which is what we are looking at) and something of value or power because it needs context and purpose. I refer you to the DIKW model Data - Information - Knowledge - Wisdom, where each step adds value to the material. see http://www.systems-thinking.org/dikw/dikw.htm for the gory details. If something has no perceived value, or it cannot be expressed (e.g. application and benefit) who is going to invest in it and who is going to use it?

As an example: Newton is famous for his observation and theory of gravitation attraction, made in a moment of brilliance. According to one of his biographers Newton took meteorological readings of temperature, humidity, wind speed etc. from his home throughout his adult life. That's a huge amount of data, for which, at the time of the biography in the 1970's, no-one had found any practical use or value.

[Stagecoach]

Ok, lets look at a practical scenario in astro photography.

Let's say a lens gives a digital readout from around 0 to 1000 (the figures simply represent the rotational position of the lens from min to max movement focus position).

I set my camera up on a tripod, use live view to determine 'best' focus on a star and at that time take a note of the digital reading, lets say 976.

I take some shots, bring the camera indoors (it gets damp here at night) and possibly move the focus barrel unintentionally.

Look at what I have taken and decide I want to use another ISO whatever.

Back outside, mount camera, adjust the lens focus back to 976 and shoot away, no need for timely live view (or other methods).

Is it worth it, well that depends on how often a scenario like this may happen and if you are going to trust the repeatability of this digital figure

[Tronhard]

To respond to Grahame's scenario. This is where the perception of accuracy by seeking a more precise measuring tool does not meet the constraints of practicality!

[Stagecoach]

To respond to Grahame's scenario. This is where the perception of accuracy by seeking a more precise measuring tool does not meet the constraints of practicality!

I can only think we have to assume the ease of "accuracy of positional repeatability" is the only advantage such an addition would give us

And then we could go on to hysteris, temp stability ........................