Infinity question: I have a Nikon D 500 with the Nikkor 18 to 300 mm 3.5 to 5.6 Lens. My question is this I was always told and found it to be true that true infinity Very seldom...

dyximan

I have a Nikon D 500 with the Nikkor 18 to 300 mm 3.5 to 5.6 Lens. My question is this I was always told and found it to be true that true infinity Very seldom resides at the center of the infinity symbol on your lens. And that you should simply shoot something at infinity and see where it lands and Mark the lens. As I often want Infiniti when shooting long exposures of the Milky Way stars etc. My question is this, when I set the lens at 18 mm And shoot something anywhere from a half a mile to 3 miles away or more. It adjust to about 4 m and or 12 feet. Not until I open the lens to about 80 mm and above will it go to infinity slightly off center which is OK as that’s what I’m trying to identify. Could someone explain to me why it would not go to the same point When the Lance is set at 80 mm or less?

PHRubin Loc: Nashville TN USA

All I can say is I have noticed that on many zooms, as you adjust focal length, focusing changes. It is extremely difficult to make a constant focus zoom lens.

Nikonian72 Loc: Chico CA

Depth-of-Field is MUCH greater at 18-mm than at 300-mm, or even 80-mm.

For star photography, set lens to LONGEST length, aim at star cluster, and manually adjust focus using the camera LCD screen (Live View). You can also hit the magnification button (+) to increase image detail ON SCREEN to assist in precise focus. Mark your lens barrel, if you so desire.

Without changing focus, you can now re-set lens to widest coverage, which will retain established focus.

speters Loc: Grangeville/Idaho

PHRubin wrote:

All I can say is I have noticed that on many zooms, as you adjust focal length, focusing changes. It is extremely difficult to make a constant focus zoom lens.

I have several zoom lenses that are parfocal and they are truly my preferred lenses when it comes to zooms!

dyximan

Nikonian72 wrote:

Depth-of-Field is MUCH greater at 18-mm than at 300-mm, or even 80-mm.

For star photography, set lens to LONGEST length, aim at star cluster, and manually adjust focus using the camera LCD screen (Live View). You can also hit the magnification button (+) to increase image detail ON SCREEN to assist in precise focus. Mark your lens barrel, if you so desire.

Without changing focus, you can now re-set lens to widest coverage, which will retain established focus.

Thank you for that information

RWR Loc: La Mesa, CA

When the image is in focus on the focusing screen, it will be in focus at the focal plane.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

speters wrote:

I have several zoom lenses that are parfocal and they are truly my preferred lenses when it comes to zooms!

Which ones?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Nikonian72 wrote:

Depth-of-Field is MUCH greater at 18-mm than at 300-mm, or even 80-mm.

For star photography, set lens to LONGEST length, aim at star cluster, and manually adjust focus using the camera LCD screen (Live View). You can also hit the magnification button (+) to increase image detail ON SCREEN to assist in precise focus. Mark your lens barrel, if you so desire.

Without changing focus, you can now re-set lens to widest coverage, which will retain established focus.

I doubt that will work on most lenses.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

dyximan wrote:

I have a Nikon D 500 with the Nikkor 18 to 300 mm ... (show quote)

Many internal focus lenses, zooms included, change the focal length as you zoom. And most are varifocal, in order to keep weight, size, max aperture etc within reasonable limits. When I shoot stars, moon, etc - I will focus with my lens manually at the focal length I intend to use during the day and put a rubber band around the lens so I can keep infinity focus. It is nearly impossible to focus on stars at night. Focusing on the moon is even hard to do.

I wouldn't go by the lens markings. They are not accurate at all.

dyximan

Gene51 wrote:

Many internal focus lenses, zooms included, change... (show quote)

That is why I was focusing during the day to see what the lens set itself to when shooting at infinity, But I was curious as to why it did not go to the infinity mark until 80MM and above.

dyximan

I want to thank all of you for your responses, I will try the varies methods and see what turns out the best.

User ID

PHRubin wrote:

All I can say is I have noticed that on many
zooms, as you adjust focal length, focusing
changes. It is extremely difficult to make a
constant focus zoom lens.

Soooooo true. Thaz why cine grade, accurately
parfocal, zooms cost many thousand sheckels.

Some of my cameras have a special ability to
AF on a starfield to solve your problem. Mebbe
now that Nikon and Canon are moving beyond
the SLR they will acquire such an ability ? But,
at present your best bet is to lock down the FL
on your zoom and use the LV MF magnifier.

FWIW, some lenses have a band [line] next to
the inf'y mark to remind/warn that inf'y focus
may be anywhere along that band. Nice touch.

P.S.
I really looooove the thread title !

.

Dikdik Loc: Winnipeg, Canada

Lenses often have registration marks showing the range of the focus for different f-stops. I usually set the far registration mark at infinity so that everything from the near registration mark to infinity is in focus.

Dik

Architect1776 Loc: In my mind

dyximan wrote:

I have a Nikon D 500 with the Nikkor 18 to 300 mm ... (show quote)

Unless noted somewhere variable aperture lenses change focus all through the zoom range. With AF this is not a real issue as it would have been with MF.
So your infinity will likely vary as you zoom.
Not sure but you will need to verify and what you have done shows this.

mborn Loc: Massachusetts

dyximan wrote:

I have a Nikon D 500 with the Nikkor 18 to 300 mm ... (show quote)

with that lens, I would set it to 18 mm and f3.5 then focus at an object about 15-20 feet then turn all settings to manual and tape the lens in that position with gaffer tape you now will be at infinity for night sky photography