Nikon D7100 crop - Best lens for Landscape and Astro

[JessHens]

I currently shoot with a Nikon D7100 which obviously has a crop sensor. I have the two kit lenses with it:
15-55mm 1:3.5-5.6 GII DX VR
55-300mm 1:4.5-5.6 G ED DX VR

I'm looking for a lens for better f. so I can attempt some astro/night photography. What would you recommend that won't break the bank?
Thanks
Jess

[ameerat42]

I don't know of any particular lens, but I'm replying to add a requirement to your search:
- the lens should have GOOD performance at widest aperture, especially at the frame edges.

Now a question: Isn't your current 15/3.5 any good? I'm asking because I would have expected
it to be OK.

Edit: Some experiences...
1) Decades ago I had an f/1.7 tack sharp 50mm lens. I once "fancied" it was too slow for astro,
so I tried a friend's 50/1.2 with the aim of buying it. -- I gave it back post haste. It had the
worst coma and softness at f/1.2 and it would not go away until about f/4. At smaller apertures
was generally softer than my 50/1.7. It always took good astro shots anyway, so I wondered why
I had even bothered...

2) Now I have a 30/1.4. It's pretty sharp... - but not at f/1.4~3.5. I live with it because of its
performance from about f/4 on.

3) I have a f4.5-5.6 8-16mm that's sharp everywhere. It's glitch: being rectilinear, its image
projection stretches away from the centre of the field of view. An alternative projection is a
"fisheye" - which I leave to others

Moral: Are you sure yours isn't already suited?

[Glenda]

My husband uses a Tokina 11-16 f2.8 on his D7100 for astro with good results. Samyang lenses have an excellent reputation for astro but are only manual focus which is the reason I've always shied away from them. It wouldn't be such a problem for astro but for landscapes I no longer trust my eyes to be able to manually focus.

[arthurking83]

....

I'm looking for a lens for better f. so I can attempt some astro/night photography. What would you recommend that won't break the bank?
Thanks
Jess

You should define the bankers' limitations!
(note banker is usually the other half, but not always .. sometimes just plain old common sense too)

Anyhow: don't worry about the crop technicality, just look for lenses that will work.

*Samyang/Rokinon 14/2.8(manual version is cheap) .. ~ $600ish. AF version is much more exxy(think ~$1500 or so)
*Sigma have a nice sounding 20/1.4 .. I reckon would be awesome for astro/night stuff, but ~ $2K!!
(in saying that, if it weren't for lockdown and resulting lack of work, I'd have one already .. but has to wait for a lot longer yet again)
*Tokina 11-16/2.8 can be good.
*Nikon 10/2.8 fisheye (is Dx) ~$800
*Laowa 12/2.8 Zero D (manual focus) ~$1K

Q: do you want wide aperture or wide field of view(short focal length .. ultra wide angle) .. or both?

Reason for this Q, is specifically that you said you're after "better f.", and about the best F stop lens you can get on a Nikon F mount(easily!) is the 50mm f/1.2, but this is 50mm, and gives a narrow (75mm equiv) framing.
There isn't a big difference between f/3.5 and f/2.8, so the additional expense you're looking at may not be as a big a difference as you may think you will achieve. Hence why I mentioned the expensive Sigma 20mm f/1.4 lens too.

More importantly, define the(approximate) 'bank breaking' rules.
Another thing to note too, sometimes people want faster f stop simply to use wider open for lower ISO values during capture(static).
Some folks just want the brighter image through the view finder too tho, it's not the advantage you'd think it is tho.

An alternative to the lens search could be for a camera that allows higher ISO values using the same F numbers, that result in cleaner night images(eg. D7500), or the move up to full frame(Fx) camera(eg. D750 or D780).

There are multiple way to de-fur a feline .. as the saying is foretold.